Endo Roots Pre-reading

recommended based on this ideal anatomy and the clinician works from “outside-in.” However, after restoration of a tooth, the occlusal anatomy may have no relevance to the position of the underlying pulp chamber (e.g. that of a porcelain-fused-to-gold crown). Using this artificial anatomy as a guide to where to begin accessing the tooth may lead to perforation in a lateral direction. In this study, the CEJ was the most consistent anatomic landmark observed. Regardless of how much clinical crown was lost or how extensive the crown restoration, the CEJ could always be observed. Given the observation that the CEJ is the most reliable guide for access, we encourage the clinician to ignore the clinical crown as a guide in directing access, and instead, recommend the use of the CEJ as the ultimate “Northstar” for locating the pulp chamber. Knowledge of the law of centrality will help prevent crown perforations in a lateral direction. Because the pulp chamber is always centrally located at the level of the CEJ, the operator can use the CEJ as a circular target regardless of how nonanatomic the clinical crown or restoration may be. Even if the crown sits at an obtuse angle to the root, the CEJ can still be a reliable landmark for locating the pulp chamber. The law of concentricity will help the clinician to extend his access properly. When the clinician observes a bulge of the CEJ to the mesiobuccal (Fig. 11), either visually or by probing, he will then know that the pulp chamber also will extend in that direction. If the tooth is narrow mesiodistally, then the clinician will know that the pulp chamber will be narrow mesiodistally (Fig. 12). This study has resulted in observations regarding the pulpchamber floor that have not been previously described. These observations were correlated to propose laws that can aid practitioners in determining the number and position of orifices of root canals of any tooth. Use of these laws takes the guesswork out of the task of finding canals. The only requirement for proper use is that the access to the chamber be completed so that the entire floor of the pulp chamber is visible without any overlying obstruction. The law of color change provides guidance to determine when the access is complete. Proper access is complete only when the entire pulp-chamber floor can be visualized. The operator knows that he has completed the access when he can delineate the junction of the pulp-chamber floor and the walls 360 degrees around the chamber floor (Fig. 13). Because a distinct light-dark junction is always present, if it is not seen in one portion of the chamber floor, the operator knows that additional overlying structure must be removed. This structure could be restorative material, reparative dentin, or even overlying pulp chamber roof. This interference with the complete visualization of the walls can be seen in Figs. 8 and 14. After this junction is clearly seen, all of the laws of symmetry and orifice location can be used to locate the exact position and number of orifices. The laws of symmetry can be invaluable in determining the exact position of canals and often indicate the presence of an additional unexpected canal. Look at the position of the orifices on the pulp chamber floor in [Fig. 15 (A and B)]. Knowledge of the laws of symmetry 1 and 2 immediately indicates the presence of a fourth canal. Indeed, it not only implies the presence of a fourth canal but exactly where it is located [Fig. 15 (C and D)]. The law of orifice locations 1 and 2 can be used to identify the number and position of the root-canal orifices of the tooth. Because all of the orifices can only be located along the floor-wall junction, black dots, indentations, or white dots that are observed anywhere else (e.g. the chamber walls or in the dark chamber floor) must be ignored to avoid possible perforation. The law of orifice location 2 can help to focus on the precise location of the orifices. The vertices or angles of the geometric shape of the dark chamber floor will specifically identify the position of the orifice. If the canal is calcified, then this position at the vertex will indicate with certainty FIG 6. (A) Cut specimenshowing the orifices located (OL) at the angles in the chamber floor and floor-wall junction (FWJ). (B) Diagram of mandibular molar showing orifice location at the angles of the chamber floor and floor-wall junction. 8 Krasner and Rankow Journal of Endodontics

where the operator should begin to penetrate with his bur to remove reparative dentin from the upper portion of the canal (Fig. 15A,E). The law of orifice locations 1 and 2, in conjunction with the law of color change, is often the only reliable indicator of the presence and location of second canals in mesiobuccal roots of maxillary molars [Fig. 16 (A and B)]. Look at the floor anatomy in Fig. 17A. Along the floor-wall junction, there is an angle in the floor geometry between the mesiobuccal and palatal orifices. The FIG 7. (A) Cut specimen showing the developmental root fusion lines (DRFL) and the floor-wall junction (FWJ). (B) Developmental root fusion lines of a mandibular molar. (C) Developmental root fusion lines of a maxillary molar. Vol. 30, No. 1, January 2004 Pulp–Chamber-floor Anatomy 9

laws of orifice locations 1 and 2 dictate the presence of a mesiopalatal orifice (Fig. 17B). This orifice can be any distance from either orifice but must be along this junction line. The laws of symmetry 1 and 2, color change, orifice locations 1 and 2 can be applied to any tooth. They are especially valuable when unexpected or unusual anatomy is present. Notice the diagrammatic representation of a chamber floor of a maxillary second premolar (Fig. 18A). Knowledge of the chamber-floor-anatomy laws immediately leads the observer to realize that there are three canals in this tooth (Fig. 18B). Another example of the value of chamber–floor-anatomy knowledge can be seen in Fig. 19A, which shows a mandibular molar that has been sectioned at the CEJ. Using the laws of chamber-floor anatomy, the observer is guided to realize that there are only two orifices in this tooth. Their positions are indicated in Fig. 19B. The relationships that we observed occurred with very high frequency. Over 95% of the specimens we observed demonstrated all of the laws. There were, however, exceptions. Mandibular second and third molars were especially deviant. Approximately 5% of these teeth most often showed a different anatomy. This anatomy has often been described in the literature and has been observed clinically as a C-shaped canal. Even in these teeth, however, the laws of color change and orifice location 1 apply. The laws of symmetry 1 and 2 and orifice locations 2 and 3, however, are not observed in them. The ramifications and use of these laws are far ranging and manifold. A specific technique has been developed using the laws to identify the number and position of root-canal orifices in teeth and especially those in heavily calcified pulp chambers. This technique will be discussed in a subsequent article. SUMMARY The cause of most endodontic failures is inadequate biomechanical instrumentation of the root-canal system. This can result from inadequate knowledge of root-canal anatomy. Because one can never know before treatment begins how many root canals are in a tooth, only a systematic knowledge of pulp–chamber-floor anatomy can provide greater certainty about the total number of root canals in a particular tooth. Knowing the average number of root canals in a tooth has limited clinical relevance to the specific tooth being treated. If one or more of the root canals remains undiscovered, failure potential increases. Therefore, the only way to provide the best environment for success is to establish the full extent of the root-canal system. This study showed that consistent patterns of anatomy of both the chamber and the pulp-chamber floor exist. These consistent patterns were analyzed and from them laws were proposed. These laws can be used to help practitioners identify the total number of canals in any tooth and their specific orifice location on the pulp-chamber floor. With the proposal of a systematic anatomic approach to pulp chamber and root–canal-orifice location, the practice of endodontics can now be based on fundamental surgical anatomic principles. As in other medical specialties, knowledge of basic concepts such as these laws is more important than the tools for measurement. With this anatomic basis, the use of supplementary instruments, such as microscopes, can now be rationally used, not as gimmicks, but as valuable tools for conducting treatment. Drs. Krasner and Rankow are professors, Temple University, School of Dentistry The authors thank all of our graduate students for their never-ending interest in this subject, Dr. Peter Friedman for editing help, and Mary Ferrell for inspiring us to complete this article. Address requests for reprints to Dr. Paul Krasner, 18 S. Roland Street, Pottstown, PA 19464. FIG 8. Cut specimen of a mandibular molar showing light colored reparative dentinonchamber floor. 10 Krasner and Rankow Journal of Endodontics

FIG 9. (A) Cut specimen of mandibular molar showing equidistance of orifices from mesiodistal line. (B) Mandibular molar showing equidistance of orifices from mesiodistal line. (C) Cut specimen of mandibular molar showing orifices perpendicular to mesiodistal line. (D) Mandibular molar showing orifices perpendicular to mesiodistal line. Vol. 30, No. 1, January 2004 Pulp–Chamber-floor Anatomy 11

FIG 10. (A) Cut specimen showing the laws of symmetry 1 and 2 and orifice locations 1, 2, and 3. (B) Laws of symmetry 1 and 2 and orifice locations 1, 2, and 3. FIG 11. Cut specimen showing CEJ bulge (CB) with concentric chamber wall. 12 Krasner and Rankow Journal of Endodontics

FIG 14. Cut specimenshows inadequate access. FIG 12. Cut specimen showing mesiodistally narrow pulp chamber in mesiodistally narrow clinical crown (cut at CEJ). FIG 13. Cut specimenshowing complete access, which allows visualizationof chamber floor meeting chamber walls 360 degrees. Vol. 30, No. 1, January 2004 Pulp–Chamber-floor Anatomy 13

FIG 15. (A) Cut specimen with pulp– chamber-floor anatomy that, through the laws of symmetry and orifice location, indicates the presence of a fourth canal. (B) Pulp– chamber-floor anatomy, which, through the laws of symmetry and orifice location, indicates the presence of a fourth canal. (C) Cut specimen of a mandibular molar that shows the presence and position of a fourth canal. (D) Mandibular molar that shows the presence and position of a fourth canal. (E) Cut specimen showing floor-wall junction (FWJ) and the lack of observation of distinct floor-wall junction (NFWJ). (F) Cut specimenshowing use of law of symmetry (arrows) to show where to beginto remove overlying roof or reparative dentin. 14 Krasner and Rankow Journal of Endodontics

FIG 16. (A) Cut specimenof maxillary molar that uses laws of orifice location to show potential sites of calcified canals (PCC) and orifice location(OL). (B) Maxillary molar that uses laws of orifice locationto show potential sites of calcified canals (PCC). FIG 17. (A) Cut specimenshowing positionof a mesiopalatal orifice (MPC) after the laws of orifice location. (B) Positionof a mesiopalatal orifice (MPC) after the laws of orifice location. Vol. 30, No. 1, January 2004 Pulp–Chamber-floor Anatomy 15

FIG 18. (A) Premolar access and pulp-chamber floor with an anatomy that, using the laws of symmetry and orifice location, shows the presence of a third canal. (B) Premolar access and pulp chamber that show the presence and position of a third canal. FIG 19. (A) Cut specimen of a mandibular molar that, using the laws of symmetry and orifice location, shows the presence of two orifices. (B) Mandibular molar that, using the laws of symmetry and orifice location, shows the presence of two orifices. 16 Krasner and Rankow Journal of Endodontics

Colleagues for Excellence Published for the Dental Professional Community by the American Association of Endodontists Spring 2010 Access Opening and Canal Location ENDODONTICS Cover artwork: Rusty Jones, MediVisuals, Inc.

he endodontic triad consisting of biomechanical preparation, microbial control and complete obturation of the canal space remains the basis of endodontic therapy.1 However, unless access to the canal orifices and the apical foramina are done properly, achieving the goals of the triad will be difficult and time consuming. The ultimate goal of endodontic treatment is to create an environment in which the body can heal itself. Adequate access is the key to achieving this and, therefore, the key to achieving endodontic success. The purpose of this newsletter is to help the practitioner develop an understanding of how to access the pulp chamber and find the orifices of the root canals. To do so, a systematic method for accessing the pulp complex and locating root canal orifices is presented. Basic Concepts The pulp complex should be conceptualized as a continuum beginning occlusally at the pulp horns and ending at the apical foramina.1 In order to remove pulp tissue entirely from the pulp complex, the coronal portion of the complex must be accessed in a manner that will permit pulp removal and facilitate the location and debridement of the root canals without compromising the strength of the coronal enamel and dentin. This process of cleaning and shaping the pulp complex can be broken down into four stages—pre-access analysis, removal of the pulp chamber roof, identification of the pulp chamber and floor root canal orifices, and instrumentation of the root canals. Pre-Access Analysis Removal of the pulp tissue begins with an analysis of the anatomy of the tooth being treated and the anatomy of the surrounding tissues. In order to remove the contents of the root canal system, the coronal portion of the system, the pulp chamber and the radicular pulp must be identified. According to Krasner and Rankow2 , the pulp chamber of every tooth is in the center of the tooth at the level of the cementoenamel junction; they described this as “The Law of Centrality.” The validity of this law can be seen in Figures 1a and 1b. The Law of Centrality can be used as a guide for the beginning of access. However, it is critical that the operator understand that the law is consistently true only at the level of the CEJ and unrelated to the occlusal anatomy.2 Since we know that the pulp chamber is always in the center of the tooth at the level of the CEJ, the initial penetrating bur should be directed towards the center of the CEJ. Therefore, in a counterintuitive method, access should be initiated by mentally ignoring the clinical or restored crown of the tooth and looking beyond the crown to the mentally imaged CEJ.2 As can be seen in Figure 2, prosthetic crowns can mislead a clinician because the crown’s anatomy is not always centered over the CEJ. Step 1 The first step in accessing any tooth begins with the physical identification of the shape and position of the CEJ. This can be accomplished by using a periodontal probe to explore the complete circumference of the CEJ in order to form a mental picture of its extent as shown in Figures 3a-d. Once the CEJ is visualized, a penetration point on the occlusal surface can be selected. On a restorative surface this point may be unrelated to the occlusal anatomy present. This can be seen in Figure 3e, on page 3, where the correct penetration point on the occlusal surface is indicated by the blue circle. This point has been determined by radiograophic examination, periodontal probing and the mental picture of the CEJ perimeter. ENDODONTICS: Colleagues for Excellence 2 T Fig. 1a. Cut specimens showing Law of Centrality. Fig. 1b. Fig. 2. Location of CEJ unrelated to oversized crown. Fig. 3a. Periodontal probing to locate the CEJ. Fig. 3b. Fig. 3c. Fig. 3d.

The visualization of the ultimate outline of the pulp chamber can be aided by utilizing another law of pulp chamber anatomy, The Law of Concentricity.2 This law states that “the walls of the pulp chamber are concentric to the external outline of the tooth at the level of the CEJ.” The Law of Concentricity is illustrated in Figure 4. The Law of Concentricity will help the clinician to extend his access properly. If there is a bulge of the CEJ in any particular direction the pulp chamber also will extend in that direction. For example, if the tooth is narrow mesiodistally, then the clinician will know that the pulp chamber will be narrow mesiodistally, as shown in Figures 5a and 5b. Step 2 The second step is to determine the angulation of the tooth. This can be done by use of radiographs (Figure 6) and clinical observation. Cone beam tomography can aid in this determination in a faciolingual direction. Step 3 The third step, shown in Figure 7, is to measure, on the radiograph, the distance from the cusp tip to the furcation. Once the cusp tip-pulp floor distance (CPFD) has been determined, a bur can be set in the handpiece short of this length and, thereby, prevent perforation in the furcation. If the bur is directed towards the center of the CEJ, parallel to the long axis of the tooth and set short of the furcation, perforation of the chamber is unlikely.3 Step 4 Following the identification of the CEJ perimeter, the angulation of the long axis of the tooth and the CPFD, an initial occlusal penetration point can be selected. Thus, the entry point on the occlusal surface of the tooth is variable and will be completely dependent on all of these factors. All recommendations about beginning at a particular point on an occlusal surface such as a pit or fossa relationship can be misleading. In some bizarre circumstances, the access starting point can even be on a cusp. The underlying concept for this is: the internal anatomy of the pulp chamber dictates the ultimate outline form. This outline form may be triangular, trapezoidal or irregular. Technique of Access Step 1 Before beginning the mechanical portion of the access, all defective restorations and caries should be removed. Leaving leaky restorations or caries can permit bacterial contamination during and following treatment. Step 2 The shape and type of bur to be used is completely up to the clinician. A #4 carbide or round diamond or #557 taped fissure bur are commonly used. For prosthetic crowns, special metal cutting fissure burs are available. Whichever bur is selected should penetrate the occlusal surface at the point determined by the pre-access factors (CEJ perimeter, tooth angulation, CPFD). The bur should be advanced towards the center of the mentally imaged CEJ until a drop is felt or the head of the handpiece touches the cusp. However, a word of caution—a drop-off will only be felt when the pulp chamber is at least 2mm deep. When evaluating a tooth for treatment or referral, the pulp chamber roof to floor distance should influence this decision. Teeth that appear to have calcified pulp chambers, such as in Figure 8, should be considered for referral. ENDODONTICS: Colleagues for Excellence 3 Continued on p. 4 Fig. 3e. Location of initial penetration point based on the CEJ perimeter. Fig. 4. Fig. 5a. Cut specimens showing the Law of Concentricity. Fig. 5b. Fig. 6. Determining angulation with radiograph. Note mesial tipping of the maxillary second molar. Fig. 7. Measuring the occlusalfurcal distance. Fig. 8. Radiograph of calcified canals in a molar.

Step 3 The goal of every access is to remove the pulp chamber roof completely. 4 Until the roof is completely removed, a conscious effort should be made to avoid looking for orifices because there is a great danger of gouging either the floor or walls leading to a perforation. Orifices will be revealed once the roof has been removed and access is complete. This can be seen in “The Access Box: an Ah-Ha Phenomenon,”5 included in the online bonus materials. The two ways to unroof the chamber are to either place a straight bur and move it laterally while keeping it parallel to the long axis of the tooth, or place a round bur into the access engaging laterally under the remaining overhang and then withdrawing the bur occlusally, illustrated in Figure 9. The roof is continually shaved away until the access is complete. One of the most difficult steps during this process is determining when the access is complete. In order to know when an access is finished, the clinician needs to know another law, the Law of Color Change.2 This law states that the color of the pulp chamber is always darker than the surrounding walls. The Law of Color Change provides guidance to determine when the access is complete. Since the walls are lighter, there will be a junction at which the light walls meet the dark floor. This junction, the floor-wall junction shown in Figure 10, traverses the entire pulp chamber floor. An operator knows that the access is complete when he can see the floor-wall junction 360 degrees around the chamber floor as shown in Figure 11. Because a distinct light-dark junction is always present, if it is not seen in one portion of the chamber floor, the operator knows that additional overlying structure must be removed. This structure could be restorative material, reparative dentin or overlying pulp chamber roof. This interference with the complete visualization of the walls can be seen in Figure 12. The clear identification of the floor-wall junction is the single most important aspect of the accessing phase of endodontic treatment. If this can’t be achieved, the case should be strongly considered for referral. Figure 12 is an example of an incomplete access. Notice how you cannot see the floor meeting the walls 360 degrees around. Figure 13 illustrates a complete access. Notice how the walls can be seen meeting the floor around the entire perimeter of the pulp chamber. Orifice Location The number of root canal orifices in a particular tooth can never be known prior to the commencement of treatment. Although radiographs are helpful and can sometimes indicate the number of roots, and averages have been enumerated,6, 7, 8, 9 most of the time the number or position of the root canal orifices cannot be identified. So how does a clinician determine the exact number of orifices in a tooth without causing iatrogenic tooth destruction? The only effective and safe way is to visualize the full extent of the pulp chamber floor and use a variety of anatomic landmarks. In a previous article,2 it was demonstrated that a set of laws can be used to identify where orifices exist on the pulp chamber floor. These laws are: Law of Symmetry 1: Except for the maxillary molars, the orifices of the canals are equidistant from a line drawn in a mesial-distal direction through the center of the pulp chamber floor (Figure 14). Law of Symmetry 2: Except for the maxillary molars, the orifices of the canals lie on a line perpendicular to a line drawn in a mesial-distal direction through the center of the pulp chamber floor (Figure 15). ENDODONTICS: Colleagues for Excellence 4 Fig. 9a. Using different burs to unroof the pulp chamber. Fig. 9b. Fig. 9c. Fig. 10. Cut specimen showing floor-wall junction. Fig. 11. Cut specimen showing complete access. Fig. 12. An example of incomplete access. Fig. 13. An example of complete access. Fig. 14. A diagram of the Law of Symmetry 1. Fig. 15. A diagram of the Law of Symmetry 2.

Law of Color Change: The color of the pulp chamber floor is always darker than the walls (Figures 16a and 16b). Law of Orifice Location 1: The orifices of the root canals are always located at the junction of the walls and the floor (Figure 17). Law of Orifice Location 2: The orifices of the root canals are located at the vertices of the floor-wall junction (Figure 18). After the floor-wall junction is clearly seen, all of the Laws of Symmetry and Orifice Location can be used to identify the exact position and number of orifices. Look at the position of the orifices on the pulp chamber floor in Figure 19. Knowledge of the Laws of Symmetry 1 and 2 immediately indicates the presence of a fourth orifice. Indeed, it not only implies the presence of a fourth orifice but exactly where it is located. The Law of Orifice Locations 1 and 2 can be used to identify the number and position of the root canal orifices of the tooth. Because all of the orifices can only be located along the floor-wall junction, black dots, indentations or white dots that are observed anywhere else (e.g., the chamber walls or in the dark chamber floor) must be ignored to avoid possible perforation. The Law of Orifice Location 2 can help to focus on the precise location of the orifices. The vertices or angles of the geometric shape of the dark chamber floor will specifically identify the position of the orifice. If the canal is calcified, then this position at the vertex will indicate with certainty where the clinician should begin to penetrate with his bur to remove reparative dentin from the upper portion of the canal (Figure 20). The Law of Orifice Locations 1 and 2, in conjunction with the Law of Color Change, is often the only reliable indicator of the presence and location of second canals in mesiobuccal roots of maxillary molars (Figure 16). Look at the floor anatomy in Figure 16a. Along the floor-wall junction, there is an angle in the floor geometry between the mesiobuccal and palatal orifices. The Laws of Orifice Locations 1 and 2 dictate the presence of a mesiopalatal (MB2) orifice, seen in Figure 16b. This orifice, present in the overwhelming majority of maxillary molars,10 can be any distance from either orifice but must be along this junction line. The Laws of Symmetry 1 and 2 (except for the maxillary molars), Color Change, and Orifice Locations 1 and 2 can be applied to any tooth. They are especially valuable when unexpected or unusual anatomy is present. Notice the diagrammatic representation of a chamber floor of a maxillary second premolar in Figure 21a. Knowledge of the chamber-floor-anatomy laws immediately leads the observer to realize that there are three canals in this tooth (Figure 21b). Another example of the value of chamber floor anatomy knowledge can be seen in Figure 22a, which shows a mandibular molar that has been sectioned at the CEJ. Using the laws of chamber-floor anatomy, the observer is guided to realize that there are only two orifices in this tooth. Their positions are indicated in Figure 22b. The observer should be cautioned that the number of orifices does not necessarily correlate to the number of canals. Sometimes, more than one canal can be present in a single orifice. In spite of all of our best efforts, problems during treatment can occur. Following is a description of the most common problems that a practitioner might encounter and how to remedy them. ENDODONTICS: Colleagues for Excellence 5 Continued on p. 6 Fig. 16a. Fig. 16b. Examples of the Law of Color Change. Fig. 19. Orifice location using the Laws of Symmetry. Fig. 20. Cut specimen showing the vertices on the pulp chamber floor. Fig. 21a. Location of a third orifice on a maxillary premolar using the Laws of Floor Anatomy. Fig. 21b. Fig. 22a. Floor anatomy showing 2 orifices in a mandibular molar. Fig. 22b. Fig. 17. A diagram of the Law of Orifice Location 1. Fig. 18. A diagram of the Law of Orifice Location 2.

ENDODONTICS: Colleagues for Excellence 6 PROBLEM: Unable to observe the pulp chamber floor due to excessive bleeding Cause • This is usually caused by pulp tissue either in the chamber or in the canals Remedy • Enlarge the access by removing the pulp chamber roof without touching the chamber floor (Never touch the pulp chamber floor unless the floor-wall junction is fully seen) • Place hemostatic agents in the chamber • Use a barbed broach to remove the tissue PROBLEM: Unable to observe the pulp chamber floor due to inadequate removal of pulp chamber roof Cause • Improper selection of the initial access penetration point • Inability to see the floor-wall junction 360 degrees around Remedy • Return to previous bur (either round or tapered) and continue to shave back until the floor-wall junction is visualized PROBLEM: Unable to observe the pulp chamber floor due to restorative materials impinging onto the pulp chamber Cause • Inadequate removal of all restorative material before access has begun (in particular, Class V restoration may impinge onto the pulp chamber floor) Remedy • Remove all restorative material before beginning the access PROBLEM: Calcification/pulp stones Cause • Degenerating pulp Remedy • Following the complete removal of the pulp chamber roof and cessation of bleeding, a large smooth round bur (#6) can be used to smooth the pulp chamber floor to remove the calcification and delineate the floor-wall junction clearly PROBLEM: Unable to observe the pulp chamber floor due to inadequate light Cause • Access too small • Presence of crowns or restorative materials • Lack of smooth surfaces of walls or pulp chamber floor (usually caused by too small round burs) Remedy • Enlarge access until floor-wall junction can be seen • Remove restorative materials • Use accessory light (LED headlight or surgical operating microscope) when crown is present11 • Smooth all irregularities on walls and pulp chamber floor with round burs PROBLEM: Unable to observe the pulp chamber due to loss of orientation Cause • Using occlusal surface as reference point • Failure to observe tooth orientation such as rotated or tilted tooth • Losing sight of CEJ circumference • Improper angulation of initial access Remedy • Proper pre-access observation of tooth orientation • Proper mental imaging of the CEJ • Remove rubber dam during access to regain orientation • Appropriate angle of penetration of initial access bur Problem-Solving Flowchart

ENDODONTICS: Colleagues for Excellence 7 Continued on p. 8 Summary In order to increase the success rate of endodontically treated teeth, as much of the pulp complex should be removed as is possible. In order to accomplish this, all of the root canal orifices in a pulp chamber must be found. The only rational way to do this is by utilizing the laws of anatomy of the pulp chamber floor. The only way to utilize these laws is by having an access that permits the visualization of the pulp chamber walls meeting the floor 360 degrees around. This newsletter has demonstrated and provided solutions to all of the clinical conditions that may hinder this visualization. In addition, we have presented a problem-solving flowchart that addresses all of the common pitfalls during access and orifice location that may confront a general practitioner. PROBLEM: Floor perforation Cause • Premature attempt to identify orifices • Failing to measure occlusal-furcal distance • Improper identification of the floor-wall junction • Inadequate access Remedy • Remove entire pulp chamber roof before identifying orifice location • Observe floor-wall junction 360 degrees around • Set bur at length less than occluso-furcal distance • Direct accessing bur towards center of the CEJ perimeter PROBLEM: Lateral chamber wall perforation Cause • Failing to mentally image the CEJ • Improper angle of access entry • Using occlusal anatomy to begin access penetration Remedy • Remove entire pulp chamber roof before identifying orifice location • Observe floor-wall junction 360 degrees around • Direct accessing bur towards center of the CEJ perimeter • Choose initial penetrating access point based on CEJ imaged perimeter PROBLEM: Unable to identify all orifices Cause • Failure to establish a complete access • Lack of delineation of a distinct floor-wall junction • Presence of restorative materials • Presence of calcifications Remedy • Make sure a complete access is performed • Smooth the pulp chamber floor to remove calcifications and delineate floor-wall junction • Use laws of pulp chamber floor anatomy to identify the positions of orifices

ENDODONTICS: Colleagues for Excellence American Association of Endodontists 211 E. Chicago Ave., Suite 1100 Chicago, IL 60611-2691 [email protected] • www.aae.org The information in this newsletter is designed to aid dentists. Practitioners must use their best professional judgment, taking into account the needs of each individual patient when making diagnosis/treatment plans. The AAE neither expressly nor implicitly warrants against any negative results associated with the application of this information. If you would like more information, consult your endodontic colleague or contact the AAE. The AAE wishes to thank Drs. Paul Krasner, Henry J. Rankow and Edward S. Abrams for authoring this issue of the newsletter, as well as the following reviewers: Drs. James A. Abbott, Reid El-Attrache, Gerald N. Glickman, William T. Johnson and James F. Wolcott. References 1. Cohen S, Hargreaves K. Pathways of the Pulp 9th ed. Mosby, St. Louis, MO, 2006. 2. Krasner P, Rankow HJ. Anatomy of the pulp chamber floor. J Endodon 2004; 30(1):5. 3. Moreinis SA. Avoiding perforation during endodontic access, J Am Dent Assoc 1979; 98:707. 4. Weller RN, Hartwell G. The impact of improved access and searching techniques on detection of the mesiolingual canal in maxillary molars. J Endodon 1989; 15:82. 5. Rankow HJ, Krasner P. The Access Box: An Ah-Ha Phenomenon. J Endodon 1995; 21(4):212-214. 6. Hess W, Zurcher E. The Anatomy of Root Canals of the Teeth of the Permanent and Deciduous Dentitions. William Wood, New York, NY, 1925. 7. Nattress BR, Martin DM. Predictability of radiographic diagnosis of variations in root canal anatomy in mandibular incisor and premolar teeth, In Endod J 1991; 24(2):58. 8. Pineda F, Kuttler Y. Mesiodistal and buccolingual roentgenographic investigation of 7275 root canals. Oral Surg Oral Med Oral Pathol Oral Radio Endod 1972; 33:10. 9. Vertucci F. Root canal anatomy of the human permanent teeth. Oral Surg Oral Med Oral Pathol Oral Radio Endod 1984; 58:58. 10. Kulild JC, Peters DD. Incidence and configuration of canal systems in the mesiobuccal root of maxillary molar first and second molars. J Endodon 1990; 16(7):311-16. 11. Buhrley IJ, Barrows MJ, BeGole EA, Wenckus CS. Effect of magnification on locating the MB-2 canal in maxillary molars. J Endodon 2002; 28(4):324. Did you enjoy this issue of ENDODONTICS? Are there topics you would like ENDODONTICS to cover in the future? We want to hear from you! Send your comments and questions to the American Association of Endodontists at the address at left. AAE COLLEAGUES ONLINE Exclusive Bonus Materials This issue of the ENDODONTICS: Colleagues for Excellence newsletter is available online at www.aae.org/colleagues with the following exclusive bonus materials: • The Access Box: An Ah-Ha Phenomenon • Anatomy of the Pulp-Chamber Floor • “Ask the Author” Discussion Board for all of your questions and comments All back issues of this newsletter are also available for your ongoing reference online. Earn CE Online Earn CE credit for the ENDODONTICS: Colleagues for Excellence newsletter series via the AAE Live Learning Center at www.aae.org/livelearningcenter. New!

See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/351934789 Access Cavity Preparations: Classification and Literature Review of Traditional and Minimally Invasive Endodontic Access Cavity Designs Article  in  Journal of Endodontics · May 2021 DOI: 10.1016/j.joen.2021.05.007 CITATIONS 26 READS 6,376 7 authors, including: Some of the authors of this publication are also working on these related projects: Electricity theft protection system View project Modulating Therapeutic Properties of Oral Tissue-Derived Mesenchymal Stem Cell View project Juzer Shabbir Liaquat College of Medicine and Dentistry 18 PUBLICATIONS   195 CITATIONS    SEE PROFILE Tazeen Zehra Liaquat College of Medicine and Dentistry 9 PUBLICATIONS   57 CITATIONS    SEE PROFILE Arshad Hasan Dow University of Health Sciences 43 PUBLICATIONS   184 CITATIONS    SEE PROFILE Lucila Piasecki University at Buffalo, The State University of New York 53 PUBLICATIONS   833 CITATIONS    SEE PROFILE All content following this page was uploaded by Lucila Piasecki on 28 June 2021. The user has requested enhancement of the downloaded file.

REVIEW ARTICLE Access Cavity Preparations: Classification and Literature Review of Traditional and Minimally Invasive Endodontic Access Cavity Designs ABSTRACT Introduction: Several endodontic access cavity designs have been proposed in the past decade to access the root canal space in a minimally invasive manner. The rationale for this approach was derived from the assumption that preserving more tooth structure during access preparation will improve the tooth’s resistance to fracture and its long-term survivability. However, is this assumption valid? Also, can this approach compromise other treatment-related aspects? Methods: We conducted a literature review using 4 online databases and classified the access cavity designs presented in each article according to our proposed classification. Results: Through the literature search, we identified 49 articles that evaluated the effect of the access cavity design on 11 different treatment parameters. The majority of the studies failed to demonstrate clear benefits of the minimally invasive access designs, whereas others raised concerns regarding the ability to adequately disinfect, fill, and restore teeth with a minimally invasive access cavity design. Conclusion: Minimally invasive access cavity designs present more risk than benefit on the outcome of endodontic treatment. Clinicians should reconsider the application of a minimally invasive access cavity for routine endodontics and cautiously apply it in selected cases when the proper armamentarium is available. (J Endod 2021;-:1–16.) KEY WORDS Access cavity preparations; conservative access cavity; computer-aided access cavity; guided access cavity; minimally invasive access cavity An endodontic access cavity (EAC) is the first step in nonsurgical endodontic treatment. The objectives of an access preparation have been established for several decades, which are to remove any caries, deroof the pulp chamber, locate all of the canal orifices, and establish straight-line access to the canals while also conserving the remaining tooth structure.1 Currently, the use of minimally invasive treatments is adopted in the medical and dental fields given the technological advancement in applied sciences, magnification, and imaging techniques. For instance, the dental operating microscope has enhanced visibility and allowed the endodontic treatment to be more conservative and predictable.2 Similarly, cone-beam computed tomographic (CBCT) imaging has increased the detection of extra canals and complex anatomic variations.3 The improvement in the quality and properties of endodontic files has also allowed them to bear substantial stresses without separation or deviation from the original canal anatomy.4 Moreover, irrigation activation has enabled the debridement and disinfection of unreachable areas of the root canal system without the need for excessive enlargement of the root canal space.5 With all these advancements, is it now possible to perform an effective endodontic treatment through conservative endodontic access? Minimally invasive access cavity preparations have been proposed in endodontics with the aim of preserving the pericervical dentin. Because the pericervical dentin functions as a stress distributor, preserving it may potentially improve the resistance to fracture.6 This approach was proposed by Clark and Khademi6 based on the assumption that the removal of dental hard tissues such as the pericervical dentin, the oblique ridges, and thinning the marginal ridges for clinical convenience can potentially SIGNIFICANCE There is a lack of evidence that minimally invasive access cavity designs will improve the fracture resistance of root canal–treated teeth. They also present potential risks during endodontic treatment. From the *Department of Operative Dentistry and Endodontics, Liaquat College of Medicine and Dentistry, Karachi, Pakistan; † Department of Operative Dentistry and Endodontics, Dow Dental College, Dow University of Health Sciences, Karachi, Pakistan; and ‡ Department of Periodontics and Endodontics, School of Dental Medicine, University at Buffalo, Buffalo, New York Address requests for reprints to Dr Adham A. Azim, Advanced Specialty Program in Endodontics, School of Dental Medicine, University at Buffalo, 240 Squire Hall, Buffalo, NY 14214. E-mail address: [email protected] 0099-2399/$ - see front matter Published by Elsevier Inc. on behalf of American Association of Endodontists. https://doi.org/10.1016/ j.joen.2021.05.007 Juzer Shabbir, MDS, BDS,* Tazeen Zehra, FCPS, BDS,* Naheed Najmi, MCPS, BDS,* Arshad Hasan, FCPS, BDS,† Madiha Naz, BDS,* Lucila Piasecki, DDS, PhD,‡ and Adham A. Azim, BDS‡ JOE
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increase the chances of tooth fracture.7 Although traditional access preparations have consistently achieved the required goals, concerns were raised on their effect on tooth survivability and resistance to fracture. On the other hand, minimally invasive access preparations in their attempt to preserve the tooth structure may potentially compromise 1 or more of the access preparation goals. Clinicians should strive to minimize the amount of tooth structure lost during access preparation. However, it is essential to critically evaluate the pros and cons of minimally invasive approaches before full embracement. In this literature overview, we describe and classify the various access designs proposed in the endodontic literature, compare the findings, and present the potential limitations of the existing published data. CLASSIFICATION AND DESCRIPTION OF EAC DESIGNS There is a wide variety of minimally invasive and novel access designs that have been recently mentioned in the endodontic literature.8 The objective of most of these types of cavity designs is the preservation of the tooth structure. However, there is a discrepancy in their titles, definitions, and dimensions. Thus, we find it essential to group the various access cavity designs that have been proposed in the literature to facilitate easier identification and standardization for future research in this field (Fig. 1). The EAC in anterior teeth is usually designed from the palatal/lingual (lingual access cavity) side for esthetic purposes. It also represents the shortest path to the pulp chamber.9 The access would extend from just coronal to the cingulum to within 2 mm of the incisal edge to remove the entire pulp chamber cervicoincisally and mesiodistally.10 These types of access cavities can either be ovoid (in canines) or triangular (in incisors) in shape. However, it was reported that through this design, straight-line access could only be achieved in 10% of the maxillary central incisors and 0.8% of the maxillary lateral incisors and was unachievable in mandibular incisors.11–13 This is because the long axis of the crown and root are not parallel in anterior teeth. The “incisal access cavity” (IAC), or “incisally shifted access cavity,” has been proposed as an alternative access location for anterior teeth.13,14 It starts from the center of the incisal edge toward the lingual/palatal surface and extends buccolingually and mesiodistally to include the entire pulp chamber.15 The facial access cavity is another access cavity design for anterior teeth in which access is gained just occlusal to the midfacial point and extends until the entire chamber is deroofed.14 It is often considered when the lingual or incisal approaches are not feasible or when a significant amount of tooth structure is already compromised on the facial side.14 The lingual, facial, or incisal approaches can all be designed conservatively without any extensions, and thus part of the pulp chamber roof will be preserved (Fig. 2). In posterior teeth, traditional access cavity (TAC) preparation includes complete deroofing of the pulpal chamber and achieving straight-line access to the first curvature or the apical part of the canal.1 Other access cavity designs have been proposed in posterior teeth to be minimally invasive by being conservative or ultraconservative. The conservative access cavity (CAC) represents a contracted form of conventional cavities. It starts from the central fossa and extends just as necessary to detect the canal orifices with small files. In this cavity design, the pericervical dentin and part of the pulp chamber roof are preserved.16 The CAC can either be divergent or convergent based on the orientation of the walls. It can also follow the outlines of the orifices like a splat.16 Ultraconservative access cavities aim to conserve as much tooth structure as possible at the expense of visibility and convenience and preserve a significant amount of the pulp chamber roof and the pericervical dentin. They generally can be divided into 2 types. For the ninja access (NA), also known as “point access,” access is gained through the central fossa or deepest part of the occlusal surface and advanced apically with a minimal increase in dimension.17,18 Through this small hole, all the canals should be accessed. The truss access, or “orifice-directed access,” is another ultraconservative cavity design in which the access targets only the canal orifices, and the dentinal bridge between the mesial and distal canals (in mandibular molars) or the buccal and palatal canals (in maxillary molars) is preserved.19,20 This design can be modified further to access each canal through a separate hole. However, the truss access is not standardized and has been presented in the endodontic literature with different sizes.21–24 It has also been suggested that the design of the truss access is dependent on the size of the pulp chamber and the taper of the rotary instruments.15,21,25 (Fig. 3). Computer-assisted access cavity (CAAC) preparations, as the name suggests, include the use of software and 3-dimensional imaging to assist in establishing a predictable path to the root canal space while conserving the tooth structure. This approach was imported from implant dentistry, and it is considered a form of minimally invasive access. It can be classified into 2 types. The first is the guided access cavity (GAC), which uses intraoral scanners and CBCT imaging to create a custom-made stent that guides the access drill to the desired location. This type of cavity is conservative, purpose based, and not operator dependent (Fig. 4). A few limitations of the GAC include longer treatment planning, delayed treatment, the requirement of a straight path to the apex or until the canal is located, poor accessibility in posterior teeth, and overheating while drilling.26 Moreover, the accuracy in locating the canals can be affected by artifacts generated while acquiring the CBCT scan. The other computer-assisted design is referred to as dynamic-navigated access. It is a freehand approach that uses a dynamic navigation interface aided by passive optical technology, CBCT imaging, and software to guide the drilling procedure in real time. Although this approach may not require a significant amount of planning compared with the GAC, it is a costly device with multiple intraoral attachments that are required to be in place before initiating treatment.26 CAACs have been recently introduced in the field of endodontics through a few in vitro studies and case reports as a proof of concept.27–29 They appear to be promising, particularly in the management of calcified structures. Review of the Literature Search Methodology A MEDLINE literature search was performed via PubMed, Scopus, Web of Science, and ScienceDirect to identify articles published on access cavity preparation with no date restrictions until October 29, 2020. In PubMed, the following combinations of key words (All fields) were used to identify the articles: (1) ((access cavity) AND (design)) AND (types), (2) (access cavity) AND (conservative), (3) ((Traditional) OR (Conventional)) AND (Access cavity), (4) ((Incisor) OR (Incisal)) AND (access cavity), and (5) (Guided) AND (access cavity). Additionally, the following key words (All fields) were used separately: (1) Endodontic access cavities, (2) Truss access, (3) Contracted access cavity, (4) Anterior teeth access cavity, and (5) Ultraconservative access cavity. The same key words were used to search articles in Scopus (TITLE-ABS-KEY), Web of Science (TOPIC), and ScienceDirect (ALL FIELDS, Research articles). To be included in the review, the articles had to meet the following criteria: 1. Articles in English 2. Full text available 2 Shabbir et al. JOE
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3. A clear definition and description of the access cavity design 4. The presence of a description and illustrative images for any of the CAC designs presented 5. Experimental studies that included at least 2 types of access cavities First, the title and abstracts of all the articles were read independently by 3 reviewers (J.S., T.Z., and M.N.) for preliminary exclusion of unrelated articles. The remaining articles were then reviewed for inclusion by reading the full-text articles. Duplicate articles and articles not related to comparisons of access designs were eliminated by the second set of reviewers (A.H. and N.N.). The access designs presented in each study were evaluated and assigned to 1 of the access designs mentioned in Figure 1. In case of disagreement on inclusion or the access cavity design appraised, a discussion was held with an independent reviewer (A.A.A.) who made the final decision. After reviewing the full text of all the relevant articles, the selected articles were then categorized based on the following methodologies: 1. Remaining tooth structure 2. Stress distribution 3. Resistance to fracture 4. Ability to locate the canal 5. Remaining pulp tissue and hard tissue debris 6. Uninstrumented areas 7. Canal transportation and centering ability 8. Operation time 9. Obturation and restoration quality 10. Retreatment 11. Internal bleaching RESULTS OF THE REVIEW A total of 6510 articles were identified from the initial search. After preliminary exclusion and manual elimination of duplicate entries, a total of 139 articles related to EACs were included for full-text review. Of these articles, 49 articles met the inclusion criteria and were qualitatively analyzed. The articles reviewed are presented in Tables 1–4, respectively. Remaining Tooth Structure The amount of remaining tooth structure was evaluated in 14 studies (Table 1). Ten studies evaluated only the amount of tooth structure removed from the crown portion (until the cementoenamel junction).7,15,26,30–36 Three studies evaluated the amount of dentin removed from the canal during instrumentation (root portion only).20,37,38 Only 1 study evaluated the total amount of tooth structure lost in the crown and root portion simultaneously.39 There was a unanimous agreement among the studies that more tooth structure is lost from the crown with the TAC compared with any of the conservative approaches, and there was no difference between the various EACs in regard to dentin volume removed in the root canal space. Stress Distribution Seven studies evaluated the amount of stress distribution (Table 1) through finite element analysis (FEA). Five studies concluded that TACs consistently showed more stresses generated, particularly at the cervical area.16,25,40–42 On the other hand, 2 studies showed opposite results. Guler43 showed that stress values were lower with the TAC compared with the NA.7 Saber et al7 also showed that the size of the EAC was inversely proportional to the cervical stresses generated, with more apical transmission of stresses as the size of the access cavity becomes larger. Resistance to Fracture A total of 24 studies compared various access cavity designs in regard to fracture resistance (Table 1). All studies evaluating fracture resistance in anterior teeth (5 studies)36,37,44–46 showed no difference between the different EAC designs and fracture resistance. FIGURE 1 – A diagram showing the different types of standard and minimally invasive access cavity preparations in anterior and posterior teeth. JOE
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However, there were discrepancies in the results among posterior teeth. Eleven studies showed no difference between the different EAC designs,17,20–24,38,39,47–49 and 9 studies showed a decreased fracture resistance with TACs compared with other conservative designs,16,18,35,36,40,42,50–52 most of which were FEA studies. Ability to Locate the Canal We found 3 studies that assessed the relationship of computer-guided access cavity approaches with canal orifice location FIGURE 3 – A micro–computed tomographic illustration of a mandibular first molar showing traditional, conservative, and ultraconservative access cavity preparations. The access is presented from the occlusal and buccal views. The green area represents the tooth structure removed during access preparation. FIGURE 2 – A micro–computed tomographic illustration of a maxillary central incisor showing lingual, incisal, and facial access cavity preparations in standard and conservative manner. The access is presented from the sagittal, coronal, and axial views. The green area represents the tooth structure removed during access preparation. 4 Shabbir et al. JOE
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(Table 2). Two studies 26,32 suggested there was no difference between the different approaches, and 1 favored the guided approach with simultaneous conservation of dental hard tissue.36 When nonguided approaches were compared, 3 studies were identified, with only 1 showing the superiority of TACs compared with CACs. The NA was evaluated in only 1 study and showed more difficulty in detecting the second mesiobuccal canal compared with CACs and TACs.53 Microbial Reduction Only 3 studies were found that investigated the impact of the EAC designs on bacteria reduction inside the root canal space. In posterior teeth (2 studies),20,54 there appears to be no difference between TACs and minimally invasive access cavities in regard to microbial reduction (Table 2). On the other hand, in anterior teeth (1 study), the minimally invasive access yielded more bacteria-positive samples and a higher bacteria count compared with the TAC.55 Remaining Pulp Tissue and Hard Tissue Debris Three studies17,37,49 evaluated the amount of hard tissue debris inside the root canal space, all of which showed no significant difference between TACs and any of the minimally invasive approaches (Table 2). Only 1 study evaluated the amount of remaining pulp tissue in the root canal space and the pulp chamber after TACs and truss access. Their results showed that truss access yielded more remaining pulp tissue in the pulp chamber but not in the root canal space or the isthmus area. Uninstrumented Areas Ten studies were identified that addressed the amount of untouched/uninstrumented areas within the root canal space (Table 3). In anterior teeth (4 studies),10,36,37,55 only 1 study comparing the TAC and IAC showed that the IAC had the highest proportion of instrumented root canal surface and the TAC had the worst.10 However, the study used ink to compare the touched/untouched surfaces, and there was no standardization in terms of canal volume before instrumentation. In studies using micro–computed tomographic imaging for assessment (3 studies),36,37,55 no difference was found between the LAC and conservative access preparations regardless of their position (incisal or lingual). In posterior teeth (7 studies), there was disagreement among the studies, with 4 studies showing no difference17,21,38,49 and the other 3 favoring TACs in addressing more canal walls.20,36,39 Canal Transportation and Centering Ability Eight studies were identified that evaluated canal transportation and centering ability (Table 3). Only 2 studies evaluated these parameters in anterior teeth. When the IAC-C was compared with LAC, no differences were found in regard to transportation and centering ability.37 However, transportation was significantly less in the regular IAC compared with LAC.57 In posterior teeth (6 studies), 2 studies49,58 showed that the CAC increased the chance of canal transportation, and 3 studies showed no difference between the TAC and minimally invasive designs.20,38,59 One study compared the TAC and the GAC.39 Their results showed no difference when single-rooted premolars were compared, but in 2-rooted premolars, the deviation of the central point after instrumentation for the TAC was significantly smaller. Time for Access Preparation and Instrumentation Overall, 8 studies evaluated the treatment time (Table 3). When CAAC techniques were evaluated (3 studies), all the studies were associated with a decreased treatment time to locate the canals compared with freehand approaches in anterior26,32,34 and posterior FIGURE 4 – An illustration of GAC preparation performed on a maxillary central incisor and a mandibular first molar. The green area represents the tooth structure removed during access preparation. JOE
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TABLE 1 - A Summary of In Vitro Studies Evaluating Remaining the Tooth Structure, Stress Distribution, and Fracture Resistance of Traditional and Minimally Invasive Access Cavity Designs Author and year EAC design Tooth type Position Main outcome Remaining coronal tooth structure Isufi et al, 202033 TAC vs CAC vs NA Maxillary and mandibular molars and premolars Posterior Dentinoenamel removal was ,6% in the NA group, up to 15% in the CAC group, and .15% in the TAC group. Saber et al, 20207 TAC vs CAC vs truss Mandibular molars Posterior CAC and truss preserved a significant amount of tooth structure. Loureiro et al, 202030 LAC vs GAC TAC vs GAC Mandibular incisors and maxillary molars Anterior and posterior Increased preservation of tooth structure in GAC in maxillary molars No difference in tissue removal between the groups in incisors Lin et al, 202031 TAC vs CAC vs NA Maxillary and mandibular molars Posterior TAC had the greatest tooth substance loss at the cervical area followed by CAC and NA. Jain et al, 202032 IAC vs DNA Maxillary and mandibular central incisors Anterior Significant conservation of tooth structure in the DNA group compared with IAC Xia et al, 202039 TAC vs GAC Maxillary and mandibular first premolars (single rooted and 2 rooted) Posterior GAC resulted in increased tooth structure conservation in 2-rooted first premolars. Dianat et al, 202026 LAC vs DNA Single-rooted teeth Anterior and posterior Significantly increased tooth conservation in the DNA group Connert et al, 201934 LAC vs GAC Incisors Anterior Less substance loss in GAC compared with LAC Makati et al, 201835 TAC vs CAC Mandibular molars Posterior The remaining dentin thickness was less in TAC than CAC. CAC was more conservative at the PCD. Varghese et al, 201612 LAC vs IAC Mandibular anterior Anterior Significant loss of tooth structure was observed in the LAC group at all the surfaces compared with IAC in which only mesial, lingual, and distal surfaces had significant loss of tooth structure. In IAC, less loss of dentin at peri-cervical region was observed Krishan et al, 201436 LAC vs LAC-C TAC – CAC Incisors Premolars and molars Anterior and posterior Significantly less removal of dentin was observed in CAC compared with LAC/ TAC in incisors, premolars, and molars. Dentin removed from the canal only Barbosa et al, 202020 TAC vs CAC vs Truss Mandibular molars Posterior No difference in the amount of dentin removed from the canal Augusto et al, 202038 NA vs TAC Mandibular molars Posterior No difference in the amount of dentin removed from the canal Xia et al, 202039 TAC vs GAC Maxillary and mandibular first premolars (single rooted and 2 rooted) Posterior No difference in the amount of dentin removed from the canal (continued on next page) 6 Shabbir et al. JOE
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TABLE 1 - Continued Author and year EAC design Tooth type Position Main outcome Rover et al, 202037 LAC vs IAC-C Mandibular incisors Anterior No difference in the amount of dentin removed from the canal Stress distribution Saber et al, 20207 TAC vs CAC vs truss Mandibular molars Posterior The size of the EAC was inversely proportional to cervical stress. As the size increased, the stresses were transmitted more apically. Wang et al, 202040 TAC vs NA Maxillary first molars Posterior NA reduced tensile stress and failure chance of dentin. Guler, 202043 TAC vs NA Maxillary molars Posterior Stress values were lower in TAC compared to NA Zhang et al, 201916 TAC vs CAC vs NA Maxillary molar Posterior Larger stress concentration areas were found in cervical region in TAC and the CAC as compared to NA Allen et al, 201842 TAC vs NA Mandibular molar Posterior TAC access had higher stress values Jiang et al, 201841 TAC vs extended TAC vs CAC Maxillary molars Posterior Stress concentration on PCD was directly proportional to the size of the EACs. No difference in the distribution of stress on occlusal surfaces between the EACs Yuan et al, 201625 TAC vs CAC Mandibular molars Posterior CAC resulted in lesser stress at crown and cervical area as compared to TAC Fracture resistance Maske et al, 202047 TAC vs NA Mandibular molars Posterior No difference in fracture resistance Barbosa et al, 202020 TAC vs CAC vs truss Mandibular molars Posterior No difference in fracture resistance Rover et al, 202037 LAC vs IAC-C Mandibular incisors Anterior No difference in fracture resistance Augusto et al, 202038 TAC vs NA Mandibular molars Posterior No difference in load to fracture Wang et al, 202040 TAC vs NA Maxillary first molars Posterior CAC reduced the failure chances of dentin Saberi et al, 202050 TAC vs truss Mandibular molars Posterior Minimum fracture strength was observed in TAC with thermocycling. Truss had better fracture strength under thermal stresses. Silva et al, 202017 TAC vs NA Maxillary premolars Posterior No difference in mean load to induce fracture. Xia et al, 202039 TAC vs GAC Maxillary and mandibular first premolars (single rooted and 2 rooted). Posterior No difference in mean load to fracture. Marinescu et al, 202051 TAC vs CAC vs NA Maxillary and mandibular molars Posterior CAC and NA had increased fracture resistance compared to TAC. Abou-Elnaga et al, 201952 TAC vs truss Mandibular molars Posterior Truss improved the fracture resistance of teeth with MOD cavities. Zhang et al, 201916 TAC vs CAC vs NA Maxillary molar Posterior (continued on next page) JOE
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teeth.26 All the other studies (5 studies)17,38,59–61 consistently showed that minimally invasive approaches took a longer time to perform the root canal in initial treatments or retreatments. Obturation and Restoration Quality Overall, 5 studies assessed the impact of different EACs on the presence of voids in the root canal filling (4 studies)17,20,37,39 and the coronal restoration (1 study)2 (Table 4). In posterior teeth, the size of the access did not appear to affect the presence of voids in the root canal filling (3 studies)17,20,39 In anterior teeth (1 study),37 more voids were noted when the minimally invasive access was used. As far as coronal restoration is concerned, 1 study directly evaluated the voids in the postendodontic composite restoration and found more voids associated with the NA compared with the TAC. Two other studies showed more remaining gutta-percha in the pulp chamber with minimally invasive approaches, which can indirectly affect the quality of the coronal restoration. Retreatment Two studies evaluated the effect of the EAC design on retreatment procedures60,61 (Table 4). The results showed more guttapercha remaining with minimally invasive approaches and a longer time to remove gutta-percha from the canal. One study suggested that the type of rotary files used with TABLE 1 - Continued Author and year EAC design Tooth type Position Main outcome The NA increased the ultimate loads that caused crack initiation of dentin compared with TAC and CAC. D’amico et al, 201944 LAC vs FAC vs LAC-C Mandibular incisors Anterior No difference in fracture strength between the groups Allen et al, 201842 TAC vs NA Mandibular molar Posterior TAC access had greater chances of tooth fracture. Sabeti et al, 201848 TAC vs CAC Maxillary molars Posterior No significant difference in fracture resistance Corsentino et al, 201823 TAC vs CAC vs truss Mandibular molars Posterior No significant difference in fracture strength Makati et al, 201835 TAC vs CAC Mandibular molars Posterior Significantly less load was required to induce fracture in TAC compared with CAC. Ozy € urek et al, 2018 € 22 TAC vs Truss Mandibular molars Posterior No significant difference in fracture strength between the groups with class II cavities Rover et al, 201749 TAC vs CAC Maxillary molars Posterior No difference in fracture resistance Plotino et al, 201718 TAC vs CAC vs NA Maxillary and mandibular premolars and molars Posterior The mean load required for fracture was significantly higher in the CAC and NA groups compared with TAC in all types of teeth tested. No difference in fracture strength between CAC and NA Chlup et al, 201724 TAC vs NA Maxillary and mandibular premolars Posterior No difference in fracture load Moore et al, 201621 TAC vs NA Maxillary molars Posterior No difference in the mean load to fracture between the groups Ozkurt-Kayahan and € Kayahan, 201645 LAC vs FAC Maxillary incisors Anterior No difference in fracture resistance between the groups Krishan et al, 201436 LAC vs LAC-C TAC vs CAC Incisors Premolars and molars Anterior and posterior CAC increased the fracture resistance in mandibular molars and premolars but not in anteriors. Nissan et al, 200746 LAC vs FAC Maxillary central and lateral incisors Anterior No difference in failure load values CAC, conservative access cavity; DNA, dynamic-navigated access; EAC, endodontic access cavity; FAC, facial access cavity; LAC, lingual access cavity; LAC-C, lingual access cavitycontracted; MOD, mesial occlusal distal; NA, ninja access; PCD, per-cervical dentin; TAC, traditional access cavity. 8 Shabbir et al. JOE
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minimally invasive designs can play a role in reducing the amount of remaining guttapercha in the canal.61 Internal Bleaching Only 1 study evaluated the effect of the EAC on internal bleaching and showed that lightness values were only reestablished with bleaching in the TAC group compared with the CAC groups 62 (Table 4). DISCUSSION Recently, a few authors attempted to summarize and analyze the various access preparations used in endodontic treatment.8,63 However, a few access designs were not mentioned, and many of those proposed categorically belong to the same design. To enable clinicians to understand the core differences between the various designs, herein we presented a concise classification to standardize the endodontic access preparation terms and definitions presented in the endodontic literature. In this literature review, we presented the outcome of 49 studies evaluating 11 different parameters in regard to the access preparation size and location. We also reviewed every access described and assigned it 1 of the designs proposed in our classification. It was noted that different terms were used for the same access designs, which can be challenging to TABLE 2 - A Summary of In Vitro Studies Evaluating the Ability to Locate Canals, Reduce the Microbial Load, and Remove the Remaining Pulp Tissue and Hard Tissue Debris When Accessing the Tooth Using Traditional and Minimally Invasive Cavity Designs Author and year Access cavities designs Teeth type Position Outcome Canal location Mendes et al, 202056 TAC vs NA Mandibular first molar Posterior No significant difference in the detection of the middle mesial canal between the groups Jain et al, 202032 IAC vs DNA Maxillary and mandibular central incisors Anterior Increased (but insignificant) precision in the DNA group for locating calcified canals Dianat et al, 202026 LAC/TAC vs DNA Single-rooted teeth Anterior and posterior No significant difference in the number of unsuccessful attempts to locate calcified canals Connert et al, 201934 LAC vs GAC Incisors Anterior Increased canal location in GAC compared with LAC Success was not dependent on the operator’s experience Saygili et al, 201853 TAC vs CAC vs NA Maxillary first molars Posterior CAC and TAC had significantly more MB2 detection compared with NA Rover et al, 201749 TAC vs CAC Maxillary Molars Posterior Increased canal detection in the TAC group with and without magnification No difference between the groups in canal detection under microscope when ultrasonic troughing was used Microbial reduction Barbosa et al, 202020 TAC vs CAC vs truss Mandibular molars Posterior No difference between the different access cavity designs Tufenkçi, 2020 € 54 TAC vs CAC Mandibular First molars Posterior No difference between the different access cavity designs Vieira et al, 202055 LAC vs IAC-C Mandibular incisors Anterior Higher bacteria-positive culture was found in IAC-C compared with LAC after root canal preparation. Higher reduction of bacterial count in the LAC group compared with IAC-C Remaining pulp tissue and hard tissue debris Silva et al, 202017 TAC vs NA Maxillary premolars Posterior NA had significantly more hard tissue debris accumulation compared with TAC. Rover et al, 202037 LAC vs IAC-C Mandibular incisors Anterior No difference in accumulated hard tissue debris Neelakantan et al, 201819 TAC vs truss Mandibular Molars Posterior The remaining pulpal tissue in the pulp chamber was significantly more in truss compared with TAC. No significant difference in residual pulpal tissue in root canals and in the isthmuses Rover et al, 201749 TAC vs CAC Maxillary molars Posterior No significant difference in the accumulated hard tissue debris CAC, conservative access cavity; DNA, dynamic-navigated access; EAC, endodontic access cavity; GAC, guided access cavity; IAC, incisal access cavity; LAC, lingual access cavity; LAC-C, lingual access cavity-contracted; MOD, mesial occlusal distal; MB2, second mesiobuccal canal; NA, ninja access; PCD, per-cervical dentin; TAC, traditional access cavity. JOE
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TABLE 3 - A Summary of In Vitro Studies Evaluating the Uninstrumented Canal Areas, Transportation and Centering Ability of Instruments, and the Time for Access Preparation and Instrumentation When Traditional and Minimally Invasive Cavity Designs Were Implemented Author and year Access cavities designs Teeth type Position Outcome Uninstrumented/untouched areas Rover et al, 202037 LAC vs IAC-C Mandibular incisors Anterior No significant difference between the 2 EACs Vieira et al, 202055 LAC vs IAC-C Mandibular incisors Anterior No significant difference between the 2 EACs Augusto et al, 202038 TAC vs NA Mandibular molars Posterior No significant difference between the 2 EACs Silva et al, 202017 TAC vs NA Maxillary premolars Posterior No significant difference between the 2 EACs Barbosa et al, 202020 TAC vs CAC vs truss Mandibular molars Posterior Significantly decreased the percentage of unprepared root canal surface in TAC compared with CAC and truss Xia et al, 202039 TAC vs GAC Maxillary and mandibular first premolars (singleand 2-rooted premolars) Posterior The untouched canal wall was significantly lower in the TAC in single-rooted premolars. Rover et al, 201749 TAC vs CAC Maxillary molars Posterior No significant difference Moore et al, 201621 TAC vs CAC Maxillary molars Posterior No significant difference between the 2 EACs Krishan et al, 201436 LAC vs LAC-C TAC vs CAC Incisors Premolars and molars Anterior and posterior No significant difference between the different EAC in anterior teeth More untouched canal surface in the distal canals of molars with CAC Mannan et al, 200110 LAC vs LAC-modified vs IAC Maxillary incisors and canines Anterior IAC had the highest proportion of instrumented root canal surface and LAC had the worst Transportation and canal centering ability Barbosa et al, 202020 TAC vs CAC vs truss Mandibular molars Posterior No significant difference in transportation or canal centering ability Rover et al, 202037 LAC vs IAC-C Mandibular incisors Anterior No significant difference in transportation or canal centering ability Augusto et al, 202038 TAC vs NA Mandibular molars Posterior No significant difference in transportation or canal centering ability Xia et al, 202039 TAC vs GAC Maxillary and mandibular first premolars (singleand 2-rooted premolars) Posterior GAC resulted in significantly increased transportation in 2-rooted first premolars and no difference in single-rooted first premolars. Marchesan et al, 201859 TAC vs NA Mandibular molars Posterior No significant difference in changes within the primary canal curvature parameters between the EACs Alovisi et al, 201858 TAC vs CAC Mandibular molars Posterior Better preservation of original canal anatomy (centering ability) and less apical transportation in TAC compared with CAC Yahata et al, 201757 LAC vs IAC Maxillary central incisors Anterior Transportation was significantly less in IAC compared with LAC. (continued on next page) 10 Shabbir et al. JOE
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follow by clinicians. In this review, we also excluded any study that did not present clear images and definitions to their access designs to avoid misunderstanding of the proposed design and its extensions. Although the primary purpose of minimally invasive preparations is to improve the fracture resistance, this hypothesis was not accepted in any of the studies evaluating anterior teeth despite preserving more tooth structure. However, in posterior teeth, there were discrepancies in the results between the different studies. The differences may stem from the following: (1) the variation in the definition and extension of the various access cavity designs, (2) the lack of proper sample distribution and standardization between the different access groups, (3) the type of study (in vitro vs FEA), and (4) the presence/absence of coronal restoration before conducting the fracture tests. There was inconsistency noted in the cavity design illustrations and images presented in some of the reviewed articles regarding the TAC designs. For example, the illustrations of TACs in mandibular molars presented by Plotino et al18 and Allen et al42 appear to be larger than those by Corsentino et al.23 This may explain why the formers showed a reduced load to fracture based on the access cavity design, whereas the latter did not. Generally, access designs using freehand approaches, whether traditional or minimally invasive, cannot be standardized because of anatomic variations between teeth as well as variation among operators. To provide proper comparison between the different access groups, teeth should be TABLE 3 - Continued Author and year Access cavities designs Teeth type Position Outcome IAC is beneficial in maintaining apical configuration. Rover et al, 201749 TAC vs CAC Maxillary molars Posterior Canal transportation was significantly higher in the CAC group in the palatal canal. Canal preparation was more centralized in the TAC group in the palatal and distobuccal canal in the CAC group. Time for access preparation and instrumentation Augusto et al, 202038 TAC vs NA Mandibular molars Posterior Time required to prepare root canals was significantly lower in TAC compared with NA. Dianat et al, 202026 LAC/TAC vs DNA Single-rooted teeth Anterior and posterior The mean time required for locating calcified canals was significantly less in the DNA group. Jain et al, 202032 IAC vs DNA Maxillary and mandibular central incisors Anterior DNA was significantly less time-consuming in preparing the endodontic access cavity. Silva et al, 202017 TAC vs NA Maxillary premolars posterior No difference in time required to access and prepare the root canals. However, NA required more time for filling and cleaning the chamber. Connert et al, 201934 TAC vs GAC Incisors Anterior Lesser treatment time required for GAC Marchesan et al, 201859 TAC vs NA Mandibular molars Posterior Treatment time was significantly longer for NA compared with TAC. Fatima et al, 201860 TAC vs CAC Mandibular premolars Posterior TAC required less time for the removal of obturating material compared with CAC. Niemi et al, 201661 TAC vs NA First and second mandibular premolars Posterior Significantly more time was required for retreatment in the NA group. CAC, conservative access cavity; DNA, dynamic-navigated access; EAC, endodontic access cavity; GAC, guided access cavity; IAC, incisal access cavity; IAC-C, incisal access cavitycontracted; LAC, lingual access cavity; LAC-C, lingual access cavity-contracted; NA, ninja access; TAC, traditional access cavity. JOE
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matched regarding tooth size and dentin volume using micro–computed tomographic imaging. This methodology has been implemented in most of the studies investigating canal geometry.4,64 However, it was not implemented in any of the studies that showed improved resistance to fracture with minimally invasive designs18,35,50–52 These studies used either CBCT imaging or occlusal measurements to standardize their samples, which may not be as accurate. Although FEA studies are able to overcome this limitation, those studies still showed contradicting results. This may stem from the parameters provided in the FEA models. For example, Allen et al42 did not have periodontal ligament and bone modeled in their FEA, which would affect the results. The other studies supporting increased stresses at the per-cervical dentin showed minimal differences between the load to failure among the various EAC designs. These differences were as low as 3.6 N in enamel and 140 N in dentin,16 which questions how much these differences may be of clinical relevance. Finally, the absence of a coronal restoration can skew the results of fracture resistance tests. Krishan et al36 were among the first to show that the mean load to fracture was significantly higher in conservative compared with traditional access in anteriors, premolars, and molars. However, there was no coronal restoration in place when the fracture resistance tests were conducted, which does not resemble a realistic clinical scenario. When the same research group later repeated the work on maxillary molars after the placement of a composite restoration in the access cavity, no significant difference was noted in the resistance to fracture between the CAC and TAC.21 The fracture resistance of posterior teeth appears to be primarily affected by the presence or absence of the marginal ridge. In a well-designed in vitro study, Corsentino et al23 showed that losing 1 or more of the marginal TABLE 4 - A Summary of In Vitro Studies Evaluating Voids in the Obturation and Restoration Material as Well as the Ability to Retreat and Bleach Teeth Through Traditional and Minimally Invasive Cavity Designs Author and year EAC Tooth type Tooth position Outcome Voids in obturation and coronal restoration Barbosa et al, 202020 TAC vs CAC vs truss Mandibular molars Posterior No difference in presence of voids in root filling Decreased volume of remaining endodontic filling material within the access cavity in TAC groups compared with CAC and truss Rover et al, 202037 LAC vs IAC-C Mandibular incisors Anterior IAC-C had more voids in root canal fillings. No difference in remaining remnants of filling material between the EACs Silva et al, 202017 TAC vs NA Maxillary premolars Posterior No difference in terms of voids in the root fillings NA had more remaining root filling material in the pulp chamber compared with TAC Silva et al, 20202 TAC vs NA Maxillary premolars Posterior Significantly more voids were found in the postendodontic composite restoration in the NA group compared with TAC. Xia et al, 202039 TAC vs GAC Maxillary and mandibular first premolars (single rooted and 2 rooted) Posterior No difference in terms of voids in root fillings Retreatment Fatima et al, 201860 TAC vs CAC Mandibular premolars Posterior More remaining obturating material in canals in CAC Niemi et al, 201661 TAC vs NA First and second mandibular premolars Posterior NA with combination of instrumentation with Vortex Blue (DentsplySirona, YorkPennsylvania) had significantly higher remaining obturating material in root canals compared with other groups. NA with combination of instrumentation with TRUShape (DentsplySirona, YorkPennsylvania) had the highest efficacy in removing obturating material from single-rooted oval canals as compared with other groups. Internal bleaching Marchesan et al, 201862 LAC vs IAC-C Maxillary incisors Anterior Statistically similar bleaching in both groups Lightness values were only reestablished with bleaching in the LAC group. The acceptable threshold for bleaching was affected when done through IAC-C compared with LAC. CAC, conservative access cavity; EAC, endodontic access cavity; GAC, guided access cavity; IAC-C, incisal access cavity-contracted; LAC, lingual access cavity; NA, ninja access; TAC, traditional access cavity. 12 Shabbir et al. JOE
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ridges was the only factor affecting the fracture resistance of mandibular molars regardless of the size of the access cavity (TAC, CAC, or TA). Interestingly, similar findings were concluded by Reeh et al65 almost 30 years earlier regarding the significant reduction in tooth stiffness of teeth after losing 1 or 2 marginal ridges. As far as the impact of the access cavity design on the fracture resistance, the available evidence does not appear to support the assumption that minimally invasive designs will improve the fracture resistance of anterior or posterior teeth. It should be noted that there is an inherent limitation in most fracture resistance studies because the load applied is static, single load to failure. This constitutes a test with less external validity compared with cyclic loading that is more representative of masticatory forces.66 The healing of apical periodontitis relies primarily on adequate chemomechanical disinfection of the root canal space, which is entirely performed through the access cavity. Failing to adequately disinfect or remove the remaining pulp tissue may have negative consequences on the treatment outcome.67 Although only a few studies evaluated these parameters, there appear to be some concerns about the irrigation efficacy, canal debridement, and remaining pulp tissue material in the pulp chambers of teeth with minimally invasive designs. Minimally invasive access cavities usually provide a curved path for the endodontic instruments to enter the canal and reach the apical area rather than the straight-line access achieved with traditional approaches. Thus, it can potentially give rise to more canal transportation and iatrogenic errors.19,36,58 However, this was only observed in a few studies, possibly due to the improved metallurgy and heat treatment of the recent endodontic file system, which increased their flexibility and centering abilities.4,68 Treatment time is another important factor that has an effect on the operator and the patient as well. Freehand minimally invasive designs required consistently longer preparation and/ or treatment time. This can be expected because the visibility and accessibility have been compromised. When CAAC preparations were used, opposite results were achieved. It provided a high level of accuracy, precision, and faster canal location. However, all studies using computer-assisted designs were primarily focused on narrow/calcified canals. These results may be different when assessing these designs in noncalcified canals or nonobstructed pulp chambers. The quality of endodontic treatment and the quality of the coronal restoration both play an important role in the success of endodontic treatment.69 The presence of voids in either may jeopardize the coronal seal and affect the long-term success.70,71 In posterior teeth, the size of the access did not appear to affect the presence of voids in the root canal filling.17,20 However, in anterior teeth, more voids were noted when the minimally invasive access was used. This can be attributed to the anatomy and obturation techniques used in these studies. All studies evaluating the quality of obturation in posterior teeth used a singlecone obturation technique, which can be performed through minimally invasive designs.8,20 Also, posterior teeth generally have a smaller canal space compared with anterior teeth, and thus the single-cone technique can be an appropriate obturation approach. On the other hand, anterior teeth have larger canal anatomy and may require more than 1 cone to adequately fill the root canal space. The use of the warm vertical technique will require the insertion of pluggers and proper visibility to pack the gutta-percha apically, which may not be feasible through the minimally invasive access. As far as voids in the coronal restoration, only 1 study was identified showing significantly more voids in the composite restoration when the NA was used.2 Posterior teeth were also associated with more root canal filling in the pulp chamber, which can potentially affect the coronal seal.20 As far as obturation and restoration, minimally invasive designs may limit adequate root canal obturation when certain techniques are used. It can also potentially compromise the quality of the coronal restoration. Remanent pulpal tissue as well as root canal filling material within the pulp chamber roof need to be removed to avoid tooth discoloration.72 Accordingly, for an internal bleaching procedure to be effective, complete deroofing of the pulp chamber is essential. This cannot be achieved with a minimally invasive access design in anterior teeth. Marchesan et al62 found that minimally invasive cavities may affect the lightness values achieved with internal bleaching, and the best results were observed with the traditional lingual access. Therefore, in the esthetic zone, when internal bleaching is desired, the LAC should be considered. Based on this review and the limitation of the published data, we can conclude that minimal benefits have been demonstrated with a minimally invasive approach that is primarily focused on preserving more tooth structure from the crown portion and potentially minimizing stresses at the per-cervical dentin. However, this did not translate to consistently improving the resistance to fracture of root canal–treated teeth. There are also concerns associated with minimally invasive techniques in regard to disinfection, procedural errors, tooth discoloration, and extended operation time. Studies that defend minimally invasive access cavity designs as a resource to minimize dental fractures must be reanalyzed under other methodological parameters that mimic masticatory forces to provide external validity to this approach. On the other hand, the CAAC appears to be of value when attempting to manage calcified canals without compromising the tooth structure. However, more studies are needed to evaluate the remaining pulp tissue and the level of bacteria reduction that can be achieved with the CAAC. ACKNOWLEDGMENTS The authors deny any conflicts of interest related to this study. REFERENCES 1. Gutmann J, Fan B. Tooth morphology, isolation, and access. In: Hargreaves KM, Berman LH, Rotstein I, editors. Cohen’s Pathways of the Pulp. 11th ed. St Louis, MO: Elsevier; 2016. p. 142–4. 2. Silva E, Oliveira VB, Silva AA, et al. Effect of access cavity design on gaps and void formation in resin composite restorations following root canal treatment on extracted teeth. Int Endod J 2020;53:1540–8. 3. Manigandan K, Ravishankar P, Sridevi K, et al. Impact of dental operating microscope, selective dentin removal and cone beam computed tomography on detection of second mesiobuccal canal in maxillary molars: a clinical study. Indian J Dent Res 2020;31:526–30. JOE
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4. Webber M, Piasecki L, Jussiani EI, et al. Higher speed and no glide path: a new protocol to increase the efficiency of XP Shaper in curved canals-an in vitro study. J Endod 2020;46:103–9. 5. Azim AA, Aksel H, Zhuang T, et al. Efficacy of 4 irrigation protocols in killing bacteria colonized in dentinal tubules examined by a novel confocal laser scanning microscope analysis. J Endod 2016;42:928–34. 6. Clark D, Khademi J. Modern molar endodontic access and directed dentin conservation. Dent Clin North Am 2010;54:249–73. 7. Saber SM, Hayaty DM, Nawar NN, Kim H-C. The effect of access cavity designs and sizes of root canal preparations on the biomechanical behavior of an endodontically treated mandibular first molar: a finite element analysis. J Endod 2020;46:1675–81. 8. Silva E, Pinto KP, Ferreira CM, et al. Current status on minimal access cavity preparations: a critical analysis and a proposal for a universal nomenclature. Int Endod J 2020;53:1618–35. 9. Watson A. Pulp space anatomy and access cavities. In: Chong BS, editor. Harry’s Endodontics in Clinical Practice. St Louis, MO: Elsevier; 2009. p. 35–53. 10. Mannan G, Smallwood ER, Gulabivala K. Effect of access cavity location and design on degree and distribution of instrumented root canal surface in maxillary anterior teeth. Int Endod J 2001;34:176–83. 11. LaTurno SA, Zillich RM. Straight-line endodontic access to anterior teeth. Oral Surg Oral Med Oral Pathol 1985;59:418–9. 12. Zillich RM, Jerome JK. Endodontic access to maxillary lateral incisors. Oral Surg Oral Med Oral Pathol 1981;52:443–5. 13. Mauger MJ, Waite RM, Alexander JB, Schindler WG. Ideal endodontic access in mandibular incisors. J Endod 1999;25:206–7. 14. Madjar D, Kusner W, Shifman A. The labial endodontic access: a rational treatment approach in anterior teeth. J Prosthet Dent 1989;61:317–20. 15. Varghese VS, George JV, Mathew S, et al. Cone beam computed tomographic evaluation of two access cavity designs and instrumentation on the thickness of peri-cervical dentin in mandibular anterior teeth. J Conserv Dent 2016;19:450–4. 16. Zhang Y, Liu Y, She Y, et al. The effect of endodontic access cavities on fracture resistance of first maxillary molar using the extended finite element method. J Endod 2019;45:316–21. 17. Silva AA, Belladonna FG, Rover G, et al. Does ultraconservative access affect the efficacy of root canal treatment and the fracture resistance of two-rooted maxillary premolars? Int Endod J 2020;53:265–75. 18. Plotino G, Grande NM, Isufi A, et al. Fracture strength of endodontically treated teeth with different access cavity designs. J Endod 2017;43:995–1000. 19. Neelakantan P, Khan K, Hei Ng GP, et al. Does the orifice-directed dentin conservation access design debride pulp chamber and mesial root canal systems of mandibular molars similar to a traditional access design? J Endod 2018;44:274–9. 20. Barbosa AF, Silva E, Coelho BP, et al. The influence of endodontic access cavity design on the efficacy of canal instrumentation, microbial reduction, root canal filling and fracture resistance in mandibular molars. Int Endod J 2020;53:1666–79. 21. Moore B, Verdelis K, Kishen A, et al. Impacts of contracted endodontic cavities on instrumentation efficacy and biomechanical responses in maxillary molars. J Endod 2016;42:1779–83. 22. Ozyurek T, Ulker O, Demiryurek EO, Yilmaz F. The effects of endodontic access cavity preparation design on the fracture strength of endodontically treated teeth: traditional versus conservative preparation. J Endod 2018;44:800–5. 23. Corsentino G, Pedulla E, Castelli L, et al. Influence of access cavity preparation and remaining tooth substance on fracture strength of endodontically treated Teeth. J Endod 2018;44:1416– 21. 24. Chlup Z, Zi  zka R, Kania J, Pribyl M. Fracture behaviour of teeth with conventional and miniinvasive access cavity designs. J Eur Ceram Soc 2017;37:4423–9. 25. Yuan K, Niu C, Xie Q, et al. Comparative evaluation of the impact of minimally invasive preparation vs. conventional straight-line preparation on tooth biomechanics: a finite element analysis. Eur J Oral Sci 2016;124:591–6. 26. Dianat O, Nosrat A, Tordik PA, et al. Accuracy and efficiency of a dynamic navigation system for locating calcified canals. J Endod 2020;46:1719–25. 14 Shabbir et al. JOE
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27. Lara-Mendes ST, Barbosa CF, Santa-Rosa CC, Machado VC. Guided endodontic access in maxillary molars using cone-beam computed tomography and computer-aided design/ computer-aided manufacturing system: a case report. J Endod 2018;44:875–9. 28. Lara-Mendes ST, Camila de Freitas MB, Machado VC, Santa-Rosa CC. A new approach for minimally invasive access to severely calcified anterior teeth using the guided endodontics technique. J Endod 2018;44:1578–82. 29. Nahmias Y. Dynamic endodontic navigation: a case report. Oral Health 2019;109:45–56. 30. Loureiro MA, Elias MR, Capeletti LR, et al. Guided endodontics: volume of dental tissue removed by guided access cavity preparation-an ex vivo study. J Endod 2020;46:1907–12. 31. Lin CY, Lin D, He WH. Impacts of 3 different endodontic access cavity designs on dentin removal and point of entry in 3-dimensional digital models. J Endod 2020;46:524–30. 32. Jain SD, Saunders MW, Carrico CK, et al. Dynamically navigated versus freehand access cavity preparation: a comparative study on substance loss using simulated calcified canals. J Endod 2020;46:1745–51. 33. Isufi A, Plotino G, Grande NM, et al. Standardization of endodontic access cavities based on 3- dimensional quantitative analysis of dentin and enamel removed. J Endod 2020;46:1495–500. 34. Connert T, Krug R, Eggmann F, et al. Guided endodontics versus conventional access cavity preparation: a comparative study on substance loss using 3-dimensional-printed teeth. J Endod 2019;45:327–31. 35. Makati D, Shah NC, Brave D, et al. Evaluation of remaining dentin thickness and fracture resistance of conventional and conservative access and biomechanical preparation in molars using cone-beam computed tomography: an in vitro study. J Conserv Dent 2018;21:324–7. 36. Krishan R, Paque F, Ossareh A, et al. Impacts of conservative endodontic cavity on root canal instrumentation efficacy and resistance to fracture assessed in incisors, premolars, and molars. J Endod 2014;40:1160–6. 37. Rover G, de Lima CO, Belladonna FG, et al. Influence of minimally invasive endodontic access cavities on root canal shaping and filling ability, pulp chamber cleaning and fracture resistance of extracted human mandibular incisors. Int Endod J 2020;53:1530–9. 38. Augusto CM, Barbosa AF, Guimaraes CC, et al. A laboratory study of the impact of ultraconservative access cavities and minimal root canal tapers on the ability to shape canals in extracted mandibular molars and their fracture resistance. Int Endod J 2020;53:1516–29. 39. Xia J, Wang W, Li Z, et al. Impacts of contracted endodontic cavities compared to traditional endodontic cavities in premolars. BMC Oral Health 2020;20:250. 40. Wang Q, Liu Y, Wang Z, et al. Effect of access cavities and canal enlargement on biomechanics of endodontically treated teeth: a finite element analysis. J Endod 2020;46:1501–7. 41. Jiang Q, Huang Y, Tu X, et al. Biomechanical properties of first maxillary molars with different endodontic cavities: a finite element analysis. J Endod 2018;44:1283–8. 42. Allen C, Meyer CA, Yoo E, et al. Stress distribution in a tooth treated through minimally invasive access compared to one treated through traditional access: a finite element analysis study. J Conserv Dent 2018;21:505–9. 43. Guler MS. Effect of access cavity designs on stress distribution. Emerg Mater Res 2020;9:220–5. 44. D’amico YC, da Silva Neto UX, Westphalen VP, et al. Fracture strength of teeth with access cavity preparation with operating microscope or on buccal surfaces. Braz Dent Sci 2019;22:88–93. 45. Ozkurt-Kayahan Z, Kayahan MB. Fracture resistance of prepared maxillary incisor teeth after € different endodontic access cavity location. Biomed Res 2016:27. 46. Nissan J, Zukerman O, Rosenfelder S, et al. Effect of endodontic access type on the resistance to fracture of maxillary incisors. Quintessence Int 2007;38:e364–7. 47. Maske A, Weschenfelder VM, Soares Grecca Vilella F, et al. Influence of access cavity design on fracture strength of endodontically treated lower molars. Aust Endod J 2020;47:5–10. 48. Sabeti M, Kazem M, Dianat O, et al. Impact of access cavity design and root canal taper on fracture resistance of endodontically treated teeth: an ex vivo investigation. J Endod 2018;44:1402–6. 49. Rover G, Belladonna FG, Bortoluzzi EA, et al. Influence of access cavity design on root canal detection, instrumentation efficacy, and fracture resistance assessed in maxillary molars. J Endod 2017;43:1657–62. JOE
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50. Saberi EA, Pirhaji A, Zabetiyan F. Effects of endodontic access cavity design and thermocycling on fracture strength of endodontically Treated Teeth. Clin Cosmet Investig Dent 2020;12:149– 56. 51. Marinescu A-G, Cîrligeriu L-E, Boscornea-Pușcu SA, et al. Fracture strength evalaution of teeth with different designs of endodontic access cavities. Rom J Oral Rehabil 2020;12:76–84. 52. Abou-Elnaga MY, Alkhawas MA, Kim HC, Refai AS. Effect of truss access and artificial truss restoration on the fracture resistance of endodontically treated mandibular first molars. J Endod 2019;45:813–7. 53. Saygili G, Uysal B, Omar B, et al. Evaluation of relationship between endodontic access cavity types and secondary mesiobuccal canal detection. BMC Oral Health 2018;18:121. 54. Tufenkci P, Yilmaz K. The effects of different endodontic access cavity design and using XP-endo Finisher on the reduction of Enterococcus faecalis in the root canal system. J Endod 2020;46:419–24. 55. Vieira GC, Perez AR, Alves FR, et al. Impact of contracted endodontic cavities on root canal disinfection and shaping. J Endod 2020;46:655–61. 56. Mendes EB, Soares AJ, Martins JN, et al. Influence of access cavity design and use of operating microscope and ultrasonic troughing to detect middle mesial canals in extracted mandibular first molars. Int Endod J 2020;53:1430–7. 57. Yahata Y, Masuda Y, Komabayashi T. Comparison of apical centring ability between incisalshifted access and traditional lingual access for maxillary anterior teeth. Aust Endod J 2017;43:123–8. 58. Alovisi M, Pasqualini D, Musso E, et al. Influence of contracted endodontic access on root canal geometry: an in vitro study. J Endod 2018;44:614–20. 59. Marchesan MA, Lloyd A, Clement DJ, et al. Impacts of contracted endodontic cavities on primary root canal curvature parameters in mandibular molars. J Endod 2018;44:1558–62. 60. Fatima K, Nair R, Khasnis S, et al. Efficacy of rotary and reciprocating single-file systems on different access outlines for gutta-percha removal in retreatment: an in vitro study. J Conserv Dent 2018;21:354–8. 61. Niemi TK, Marchesan MA, Lloyd A, Seltzer RJ. Effect of instrument design and access outlines on the removal of root canal obturation materials in oval-shaped canals. J Endod 2016;42:1550–4. 62. Marchesan MA, James CM, Lloyd A, et al. Effect of access design on intracoronal bleaching of endodontically treated teeth: an ex vivo study. J Esthet Restor Dent 2018;30:E61–7. 63. Maqbool M, Noorani TY, Asif JA, et al. Controversies in endodontic access cavity design: a literature review. Dental Update 2020;47:747–54. 64. Azim AA, Piasecki L, da Silva Neto UX, et al. A novel adaptive core rotary instrument: microcomputed tomographic analysis of its shaping abilities. J Endod 2017;43:1532–8. 65. Reeh ES, Messer HH, Douglas WH. Reduction in tooth stiffness as a result of endodontic and restorative procedures. J Endod 1989;15:512–6. 66. Ordinola-Zapata R, Fok A. Research that matters: debunking the myth of the “fracture resistance” of root filled teeth. Int Endod J 2021:297–300. 67. Nair PN. On the causes of persistent apical periodontitis: a review. Int Endod J 2006;39:249–81. 68. Vorster M, van der Vyver PJ, Paleker F. Canal transportation and centering ability of WaveOne Gold in combination with and without different glide path techniques. J Endod 2018;44:1430–5. 69. Gillen BM, Looney SW, Gu LS, et al. Impact of the quality of coronal restoration versus the quality of root canal fillings on success of root canal treatment: a systematic review and meta-analysis. J Endod 2011;37:895–902. 70. Azim AA, Griggs JA, Huang GT. The Tennessee study: factors affecting treatment outcome and healing time following nonsurgical root canal treatment. Int Endod J 2016;49:6–16. 71. Chugal NM, Clive JM, Spangberg LS. Endodontic infection: some biologic and treatment factors associated with outcome. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2003;96:81–90. 72. Davis MC, Walton RE, Rivera EM. Sealer distribution in coronal dentin. J Endod 2002;28:464–6. 16 Shabbir et al. JOE
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Fracture Strength of Endodontically Treated Teeth with Different Access Cavity Designs Gianluca Plotino, DDS, PhD,* Nicola Maria Grande, DDS, PhD,† Almira Isufi, DDS, PhD, MSc,* Pietro Ioppolo, DpHS,‡ Eugenio Pedulla, DDS, PhD,
§ Rossella Bedini, DSc, PhD,‡ Gianluca Gambarini, MD, DDS,* and Luca Testarelli, DDS, PhD* Abstract Introduction: The purpose of this study was to compare in vitro the fracture strength of root-filled and restored teeth with traditional endodontic cavity (TEC), conservative endodontic cavity (CEC), or ultraconservative ‘‘ninja’’ endodontic cavity (NEC) access. Methods: Extracted human intact maxillary and mandibular premolars and molars were selected and assigned to control (intact teeth), TEC, CEC, or NEC groups (n = 10/group/type). Teeth in the TEC group were prepared following the principles of traditional endodontic cavities. Minimal CECs and NECs were plotted on conebeam computed tomographic images. Then, teeth were endodontically treated and restored. The 160 specimens were then loaded to fracture in a mechanical material testing machine (LR30 K; Lloyd Instruments Ltd, Fareham, UK). The maximum load at fracture and fracture pattern (restorable or unrestorable) were recorded. Fracture loads were compared statistically, and the data were examined with analysis of variance and the Student-Newman-Keuls test for multiple comparisons. Results: The mean load at fracture for TEC was significantly lower than the one for the CEC, NEC, and control groups for all types of teeth (P < .05), whereas no difference was observed among CEC, NEC, and intact teeth (P > .05). Unrestorable fractures were significantly more frequent in the TEC, CEC, and NEC groups than in the control group in each tooth type (P < .05). Conclusions: Teeth with TEC access showed lower fracture strength than the ones prepared with CEC or NEC. Ultraconservative ‘‘ninja’’ endodontic cavity access did not increase the fracture strength of teeth compared with the ones prepared with CEC. Intact teeth showed more restorable fractures than all the prepared ones. (J Endod 2017;43:995–1000) Key Words Conservative access cavity, endodontic access cavity, fracture resistance, ‘‘ninja’’ cavity, traditional endodontic cavity One of the most important steps for successful endodontic treatment is access cavity preparation. The traditional endodontic cavity (TEC) design for different tooth types has remained unchanged for decades, and only minor modifications have been done(1). However, the removal of tooth structure needed for access cavity preparation may undermine the strength of the tooth to fracture under functional loads (2, 3). Extraction is the most frequent consequence of fracture of endodontically treated teeth (4–6). Extended preparation of endodontic access cavities critically reduces the amount of sound dentin (7–10) and increases the deformability of the tooth (8), compromising the strength to fracture of endodontically treated teeth (7). Recently, conservative endodontic cavity (CEC) preparation (11, 12)to minimize tooth structure removal and preserve some of the chamber roof and pericervical dentin was reported in the literature. This sound dentin preservation could be achieved with the help of cone-beam computed tomographic (CBCT) imaging to identify all the canals (13, 14). This could improve the fracture strength of endodontically treated teeth (11). Following this concept, an extreme conservative approach has recently been proposed, which is conventionally known as ‘‘ninja.’’ This technique may improve the fracture strength of endodontically treated teeth (15). To date, there are no studies comparing CEC access cavity preparation with ultraconservative ‘‘ninja’’ endodontic cavity (NEC) access. Therefore, the purpose of this study was to investigate the fracture strength of endodontically treated teeth with a TEC, CEC, or NEC access cavity. Materials and Methods Specimen Selection and Preparation After ethics approval, 160 recently extracted intact human maxillary and mandibular molars and premolars from a white population with completely formed apices were used. The exclusion criteria for the tested teeth were the presence of caries, previous restoration, and visible fracture lines or cracks. After a debridement with hand scaling instruments and cleansing with a rubber cup and pumice, the teeth were stored in individually numbered containers with 0.1% thymol solution at 4
C until used and during all the time between the different phases of the experiment in order to prevent their dehydration. From the *Department of Endodontics, La Sapienza University of Rome, Rome, Italy; † Catholic University of Sacred Heart, Rome, Italy; ‡ Technologies and Health Department, Istituto Superiore di Sanit
a, Rome, Italy; and § Department of General Surgery and Surgical-Medical Specialties, University of Catania, Catania, Italy. Address requests for reprints to Dr Eugenio Pedull
a, Via Cervignano, 29, 95129, Catania, Sicily, Italy. E-mail address: [email protected] 0099-2399/$ - see front matter Copyright ª 2017 American Association of Endodontists. http://dx.doi.org/10.1016/j.joen.2017.01.022 Significance CEC and NEC access was proposed to reduce fracture risk of endodontically treated teeth. Teeth with CEC and NEC showed similar fracture strength, which was higher than that of teeth with traditional endodontic access. Basic Research—Technology JOE — Volume 43, Number 6, June 2017 Fracture Strength of Endodontically Treated Teeth 995

Forty maxillary first molars with 3 separate roots, 40 mandibular first molars with 2 separate roots, 40 maxillary first premolars with 2 separate roots, and 40 mandibular first single-rooted premolars were selected based on similar dimensions. The anatomic crown height was measured from the occlusal surface to the cementoenamel junction on all 4 sides of the teeth; buccolingual and mesiodistal (MD) dimensions were measured at the occlusal surface. Tooth measurements were taken with a digital caliper (Digimatic 500; Mitutoyo, Kanagawa, Japan). Specimens were subsequently assigned to 4 groups (n = 10) for each tooth type. Therefore, the following homogenous groups were created based on the averages of tooth dimensions in order to minimize the influence of size and shape variations on the results: 1. Group A: the control group, which included teeth that were left intact 2. Group B: the TEC group 3. Group C: the CEC group 4. Group D: the NEC group TEC, CEC, and NEC cavity accesses of all teeth were drilled with size 856 diamond burs (Komet Italia srl, Milan, Italy) mounted on a highspeed handpiece with water cooling (16). Teeth in the TEC, CEC, and NEC groups were mounted in a custom-made device (17) and imaged with a CBCT scanner (Kodak 9000 3D; Carestream Health, Inc, Marnela-Vallee, France) with a spatial resolution of 200 mm; the scans were used to plan TEC, CEC, and NEC outlines. Teeth in the TEC group Figure 1. (A–D) Sketches with an (A–C) occlusal view and a (D) sagittal view of access cavity designs of a first mandibular molar. (A–D) A traditional access cavity (black line dashed), (A, C, and D) conservative access cavity (green), and (B–D) ultraconservative ‘‘ninja’’ access cavity (red). Comparison of the 3 access cavity designs in the (C) occlusal and (D) sagittal view, respectively. The sagittal view shown as a conservative access cavity maintains a robust amount of pericervical dentin. B, buccal; D, distal; L, lingual; M, mesial. Figure 2. (A–F) CBCT 3-dimensional reconstructions and segmentations of lower molars prepared with different access cavity designs in (A–C) the sagittal view and (D–F) the axial view at the occlusal surface. (A and D) A traditional access cavity (purple), (B and E) conservative access cavity (green), and (C and F) ultraconservative ‘‘ninja’’ access cavity (red) are segmented on CBCT reconstructions. Basic Research—Technology 996 Plotino et al. JOE — Volume 43, Number 6, June 2017

were prepared following the principles of TECs as previously reported (1, 18). In the CEC group, premolars were accessed 1 mm buccal to the central fossa, and cavities extended apically, maintaining part of the chamber roof and lingual shelf. Molars were accessed at the mesial quarter of the central fossa, and cavities extended apically and distally while maintaining part of the chamber roof. Mesiodistal, buccolingual, and circumferential pericervical dentin removal was minimized to ensure the maintenance of the part of the chamber roof compatible with the localization of all root canal orifices from the same visual angulation (11, 12, 19). This was caused by the shape of preparation; the occlusal enamel was only beveled at 45
(12). The extension was not balanced equally between the buccal and palatal orifices but rather slightly favored the buccal orifice (11). In the NEC group, premolar and molar teeth were accessed in the same way as the teeth in the CEC group, but the chamber roof was maintained as much as possible. The access ‘‘ninja’’ outline was derived from the oblique projection toward the central fossa of the root canal orifices on the occlusal plane. By doing this, localization of all the root canal orifices was possible even from different visual angulations because the endodontic access was parallel with the enamel cut at 90
or more to the occlusal table (12, 15) (Fig. 1A–D). The extension was equally balanced between the buccal and lingual/palatal orifices. Then, teeth in the TEC, CEC, and NEC groups were scanned again using CBCT imaging as described earlier. Digital Imaging and Communications in Medicine data were moved to the MeVisLab image processing and visualization platform (MeVis Research, Bremen, Germany) to perform 3-dimensional surface rendering of the teeth and segmentation of the TEC, CEC, or NEC access (Fig. 2A–F). The percentage of volume of coronal enamel and dentin removed by TEC, CEC, and NEC access cavities and the total enamel and dentin crown volume for each type of tooth were calculated. Endodontic Treatment Root canals were negotiated with size 10 K-type files (Flexofile; Dentsply Maillefer, Ballaigues, Switzerland) to the major apical foramen, and canals were instrumented to length with Mtwo nickeltitanium rotary instruments (Sweden & Martina, Padova, Italy), with a 16-mm working part, up to the #25 tip size and 0.06 taper file. During endodontic treatment, 5.25% sodium hypochlorite (Niclor 5; Ogna, Muggi
o, Italy) for irrigation was intermittently deposited using ProRinse side-vented 30-G needles (Dentsply Tulsa Dental Specialties, Tulsa, OK), and after instrumentation, the root canals were irrigated with 17% EDTA solution. The canals were dried with paper points and filled with gutta-percha (single-cone size 25, 0.06 taper) and a resin-based endodontic sealer (AH Plus; Dentsply De Trey, Konstanz, Germany). Afterward, the teeth were subjected to postoperative radiographs and CBCT imaging to evaluate the endodontic treatment. Figure 3. (A–D) Representative pictures of fractured molars for different groups. (A) Intact teeth had more restorable fractures than teeth prepared with (B) TEC, (C) CEC, and (D) ultraconservative NEC, which had unrestorable fractures often. Basic Research—Technology JOE — Volume 43, Number 6, June 2017 Fracture Strength of Endodontically Treated Teeth 997

Teeth Restoration The enamel and dentin of the access cavity were cleaned and etched with 37% phosphoric acid for 30 and 15 seconds, respectively; rinsed for 30 seconds with a water/air spray; and gently air dried to avoid desiccation. A light-polymerizing primer bond adhesive (XP Bond; DentsplyInternational, York, PA) was applied, gently air thinned, and exposed to light-emitting diode polymerization for 30 seconds. At the end, the access cavities were restored with direct composite restorations (CeramX mono, Dentsply International). Fracture Test The 120 teeth in the TEC, CEC, and NEC groups and the 40 teeth ( n = 10/type) kept intact were mounted on brass rings with the roots embedded in self-curing resin (SR Ivolen; Ivoclar Vivadent, Schaan, Lichtenstein) up to 2 mm apical to the cementoenamel junction as reported in a previous study(19). The 160 tooth specimens were placed in a custom-made water bath and mounted in a mechanical material testing machine (LR30 K; Lloyd Instruments Ltd, Fareham, UK) (19). The teeth were loaded at their central fossa at a 30
angle from the long axis of the tooth. The continuous compressive force at a crosshead speed of 0.5 mm/min was applied using a 6-mm-diameter ball-ended steel compressive head. The loads at which the teeth were fractured, indicated by the software of the load testing machine, were recorded in newtons. The fractured specimens were examined under a stereomicroscope (SZR- 10; Optika, Bergamo, Italy) to determine the fracture levels. Fracture patterns were classified as ‘‘restorable’’ when the failures were above the level of bone simulation (site of fracture above the acrylic resin) and ‘‘unrestorable’’ when the failures were extending below the level of bone simulation (site of fracture below the acrylic resin) (20) (Fig. 3A –D). Statistical Analysis The data were first verified with the Kolmogorov-Smirnov test for normal distribution and the Levene test for homogeneity of variances. Thus, they were statistically evaluated using analysis of variance and the Student-Newman-Keuls test for multiple comparisons (Prism 5.0; GraphPad Software Inc, La Jolla, CA), with the significance level established at 5% (P < .05). Results The mean of the buccolingual and mesiodistal dimensions at the occlusal surface and the anatomic crown height of the tested teeth are presented in Table 1. No significant differences were found when comparing all teeth dimensions in the control and test groups for each type of tooth (P > .05). Table 2 shows the mean volume percentages of the coronal enamel and dentin removed by different access cavity designs in each tooth type. The mean load at fracture for teeth in the TEC group was significantly lower than the intact, CEC, and NEC groups (P < .05), whereas no difference was observed among the control, CEC, and NEC groups (P > .05) in all types of teeth (Table 3). Intact premolars had mostly cuspal chipping, whereas those with TEC, CEC, and NEC consistently had wall fractures extending below the cementoenamel junction. Molars in all the groups had mesiodistal fractures with a varying apical extent. The restorable fractures were significantly higher than the unrestorable ones in the intact teeth (P < .05), whereas the number of unrestorable fractures was higher than the restorable ones in the TEC, CEC, and NEC groups in every type of tooth (P< .05). No difference in the number of restorable or unrestorable fractures was observed for the TEC, CEC, and NEC groups in every type of tooth (P > .05). TABLE 1. Mean and (Standard Deviation) of the Mesiodistal (MD) and Buccolingual (BL) Dimensions and the Anatomic Crown Height (Measured at the 4 Sides of the Tooth) of the Tested Teeth in Each Group Groups Control TEC CEC NEC Tooth type (n = 10) Occlusal surface Anatomic crown height Occlusal surface Anatomic crown height Occlusal surface Anatomic crown height Occlusal surface Anatomic crown height MD BL MD BL MD BL MD BL Upper Premolars 8.1a (1.0) 7.8a (1.6) 5.2 (0.7)b 8.0a (0.8) 8.1a (0.7) 5.3 (0.7)b 7.9a (0.3) 8.0a (0.5) 5.0 (0.8)b 7.9a (0.9) 8.2a (0.9) 5.3 (0.3)b Lower Premolars 7.4a (1.2) 7.6a (0.9) 4.5 (0.4)b 7.2a (1.3) 7.8a (0.9) 4.9 (0.3)b 7.3a (0.5) 7.9a (0.8) 5.1 (0.4)b 7.5a (1.4) 7.8a (0.9) 4.7 (0.5)b Upper molars 9.7a (0.6) 9.4a (0.7) 5.4 (0.1)b 9.7a (0.5) 9.6a (0.9) 5.3 (0.2)b 9.9a (0.3) 9.5a (0.9) 5.6 (0.5)b 9.8a (0.7) 9.5a (1.0) 5.3 (0.3)b Lower molars 10.7a (1.2) 10.3a (0.6) 5.8 (0.4)b 10.6a (1.3) 10.2a (0.9) 5.7 (0.5)b 10.7a (1.0) 10.2a (0.5) 5.6 (0.4)b 10.5a (0.9) 10.1a (0.8) 5.7 (0.6)b CEC, conservative endodontic cavity; NEC, ‘‘ninja’’ endodontic cavity; TEC, traditional endodontic cavity. Similar lowercase letters in the same row indicate no statistically significant differences (P > .05). Basic Research —Technology 998 Plotino et al. JOE — Volume 43, Number 6, June 2017

Discussion One of the most important causes of fractures in root-filled teeth is the loss of tooth structure. The preparation of the endodontic access cavity following the TEC principals was reported as the second largest cause of loss of tooth structure (20). Thus, a proper and reduced endodontic access design could improve the prognosis for an endodontically treated tooth (21). Recently, CEC and NEC were proposed to reduce the fracture risk in endodontically treated teeth (15, 19). However, clinically, these approaches can mainly be performed on intact teeth that are going to be treated endodontically. This clinical scenario does not seem to occur frequently, representing only 8% of the cases treated by the authors in the last 5 years (G. Plotino et al, unpublished data, 2016). Until now, in the literature, the fracture strength of teeth with CEC and NEC access was investigated in a few studies (19, 22) and no studies, respectively. For this reason, the fracture strength of endodontically treated teeth with TEC, CEC, or NEC access cavity was tested in the present study. The use of mature, intact maxillary and mandibular molars and premolars was a priority to avoid the effects of different amounts of tooth structure loss (22). Anterior teeth were not tested in this investigation because no differences between TEC and CEC fracture strength in these teeth were reported (19). Although premolars and molars are subjected to a different occlusal force in the clinical situation (23), in this study the same loading force was applied to standardize the procedure (19). Fracture resistance was assessed with a mechanical testing machine as in other studies (19, 24–26). A 30
inclination angle was used because teeth are most vulnerable to fracture when eccentric forces are applied (27), reaching the failure point at lower loads when compared with the axial fracture loads of other studies (28, 29). However, loading to fracture methodology used for in vitro analyses does not accurately reflect intraoral conditions in which failures occur primarily because of fatigue. In the same way, axial cyclically fatigued tests may not reflect complete root strain patterns for the complex chewing process (22). Access cavities were restored with bonded resin composite to simulate clinical procedures and facilitate loading tests(22). Restoration of endodontic access cavities may restore the fracture strength of teeth up to 72% of that of intact teeth (22, 30). The same expert operator performed all specimen preparation procedures in order to avoid different results caused by different operator skills. In this study, the TEC group presented lower fracture strength than the control, CEC, and NEC groups. These results are in agreement with a previous study in which the teeth were tested without any restoration, which is different from clinical practice (19). The results of the present study are in agreement and corroborate reports that showed improved fracture strength of teeth because of dentin preservation obtained by cavity size reduction (9, 31, 32). In addition, no difference in the fracture strength was observed among the CEC, NEC, or control groups in all tested teeth. These results, relative to CEC, are in agreement with a previous study (19). Despite the fact that our results related to NEC cannot be directly compared with previous reports, it is not surprising that teeth in the NEC group showed no difference in fracture strength compared with the control and CEC groups because of the minimally invasive access cavity designs of NEC. However, in a recent study, the CEC cavity did not increase the fracture strength of restored maxillary molars in comparison with ones prepared with TEC, suggesting no apparent benefit of CEC in this regard (22). This contrasting finding is probably because of the differences in the methodology of that study including the type of teeth considered (only maxillary molars were reported to be subjected to fracture more than mandibular ones [33]); the techniques and materials used for endodontic and restoring procedures; and the method used to assess the fracture strength (teeth were cyclically fatigued and subsequently loaded to failure [22]). Although CEC improved fracture strength more than TEC, it could increase the risks of inefficient canal instrumentation and the occurrence of procedural errors as previously reported (19). However, a recent study showed that CECs in maxillary molars did not appear to impact instrumentation efficacy (22). No studies have investigated the quality of endodontic procedures using NEC. In addition, the ideal access cavity would allow complete removal of pulp tissue, debris, and necrotic materials. However, the smaller the access cavity, the higher the risk of bacterial contaminations and the possibility of missing some root canal orifices (22, 34). The results of the present study showed a higher number of restorable fracture patterns in intact teeth than in the ones prepared with TEC, CEC, or NEC. These findings are in agreement with a previous report (35). Furthermore, the majority of the teeth prepared with TEC, CEC, or NEC showed unrestorable fracture patterns with no significant difference among the different access cavity designs. TABLE 3. Load at Fracture (Mean  Standard Deviation) and Type of Fracture, ‘‘Restorable’’ (R) or ‘‘Unrestorable’’ (U), for Intact Teeth (Control) or Traditional, Conservative, or ‘‘Ninja’’ Access Assessed after the Static Test Using a Mechanical Material Testing Machine Tooth type (n = 10) Load at fracture (N) Type of fracture Control TEC CEC NEC Control TEC CEC NEC RURURURU Upper premolars 913 (188)a 498 (250)b 821 (324)a 805 (204)a 7a 3b 2b 8a 3b 7a 3b 7a Lower premolars 1006 (313)a 704 (310)b 929 (384)a 945 (267)a 7a 3b 3b 7a 2b 8a 3b 7a Upper molars 1172 (598)a 810 (425)b 1143 (506)a 1170 (432)a 8a 2b 3b 7a 3b 7a 3b 7a Lower molars 1572 (639)a 923 (393)b 1401 (495)a 1459 (278)a 7a 3b 2b 8a 2b 8a 3b 7a CEC, conservative endodontic cavity; NEC, ‘‘ninja’’ endodontic cavity; TEC, traditional endodontic cavity. Similar lowercase letters in the same row indicate no statistically significant differences (P > .05). TABLE 2. The Volume Percentage (Mean and Standard Deviation) of the Coronal Enamel and Dentin Removed in Teeth with Different Access Cavity Designs Including Traditional, Conservative, and ‘‘Ninja’’ Access Tooth type (n = 10) Coronal dentin and enamel volume removed (% of total crown volume) TEC CEC NEC Upper premolars 22.15 (3.71)a 13.43 (3.12)b 5.13 (0.76)c Lower premolars 23.89 (3.04)a 15.17 (3.67)b 6.07 (0.54)c Upper molars 19.27 (3.82)a 11.03 (2.81)b 5.92 (0.75)c Lower molars 16.48 (3.47)a 7.31 (3.33)b 4.81 (0.82)c CEC, conservative endodontic cavity; NEC, ‘‘ninja’’ endodontic cavity; TEC, traditional endodontic cavity. Similar lowercase letters in the same row indicate no statistically significant differences (P > .05). Basic Research—Technology JOE — Volume 43, Number 6, June 2017 Fracture Strength of Endodontically Treated Teeth 999

Within the limitations of this study, it can be concluded that conservative endodontic access cavities such as CEC and NEC increased the fracture strength of teeth compared with those with TEC. The ultraconservative NEC access did not improve the fracture strength of teeth with CEC access. Moreover, restored CEC and NEC did not reduce the fracture strength, but they did influence the fracture pattern of intact teeth. Further clinical studies are necessary to determine the efficacy of instrumentation, difficulties during endodontic procedures and longterm prognosis of endodontically treated maxillary and mandibular molars and premolars with CEC or NEC. Acknowledgments The authors thank Giusy La Rosa from the University of Catania for the support in the sketches of teeth with CEC and NEC accesses. The authors deny any conflict of interests related to this study. References 1. Ingle JI. Endodontic cavity preparation. In: Ingle J, Tamber J, eds. Endodontics, 3rd ed. Philadelphia: Lea & Febiger; 1985:102–67. 2. Kishen A. Mechanisms and risk factors for fracture predilection in endodontically treated teeth. Endod Topics 2006;13:57–83. 3. Tang W, Wu Y, Smales RJ. Identifying and reducing risks for potential fractures in endodontically treated teeth. J Endod 2010;36:609–17. 4. Vire DE. Failure of endodontically treated teeth: classification and evaluation. J Endod 1991;17:338–42. 5. Tzimpoulas NE, Alisafis MG, Tzanetakis GN, et al. A prospective study of the extraction and retention incidence of endodontically treated teeth with uncertain prognosis after endodontic referral. J Endod 2012;38:1326–9. 6. Tour
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e F, Ganahl D, Peters OA. Effects of root canal preparation on apical geometry assessed by micro- computed tomography. J Endod 2009;35:1056–9. 18. Patel S, Rhodes J. A practical guide to endodontic access cavity preparation in molar teeth. Br Dent J 2007;203:133–40. 19. Krishan R, Paque F, Ossareh A, et al. Impacts of conservative endodontic cavity on root canal instrumentation efficacy and resistance to fracture assessed in incisors, premolars, and molars. J Endod 2014;40:1160–6. 20. Rezaei Dastjerdi M, Amirian Chaijan K, Tavanafar S. Fracture resistance of upper central incisors restored with different posts and cores. Restor Dent Endod 2015; 40:229–35. 21. Ikram OH, Patel S, Sauro S, et al. Micro-computed tomography of tooth tissue volume changes following endodontic procedures and post space preparation. Int Endod J 2009;42:1071–6. 22. Moore B, Verdelis K, Kishen A, et al. Impacts of contracted endodontic cavities on instrumentation efficacy and biomechanical responses in maxillary molars. J Endod 2016;42:1779–83. 23. Ogawa T, Suzuki T, Oishi N, et al. Tactile sensation and occlusal loading condition of mandibular premolars and molars. Odontology 2011;99:193–6. 24. Luthria A, Srirekha A, Hegde J, et al. The reinforcement effect of polyethylene fibre and composite impregnated glass fibre on fracture resistance of endodontically treated teeth: an in vitro study. JConserv Dent 2012;15:372–6. 25. Pradeep P, Kumar VS, Bantwal SR, Gulati GS. Fracture strength of endodontically treated premolars: an in-vitro evaluation. J Int Oral Health 2013;5:9–17. 26. Cobankara FK, Unlu N, Cetin AR, Ozkan HB. The effect of different restoration techniques on the fracture resistance of endodontically-treated molars. Oper Dent 2008;33:526–33. 27. ElAyouti A, Serry MI, Geis-Gerstorfer J, et al. Influence of cusp coverage on the fracture resistance of premolars with endodontic access cavities. Int Endod J 2011;44:543–9. 28. de Freitas CR, Miranda MI, de Andrade MF, et al. Resistance to maxillary premolar fractures after restoration of class II preparations with resin composite or ceromer. Quintessence Int 2002;33:589–94. 29. Ortega VL, Pegoraro LF, Conti PC, et al. Evaluation of fracture resistance of endodontically treated maxillary premolars, restored with ceromer or heat-pressed ceramic inlays and fixed with dual-resin cements. J Oral Rehabil 2004;31:393–7. 30. Hamouda IM, Shehata SH. Fracture resistance of posterior teeth restored with modern restorative materials. J Biomed Res 2011;25:418–24. 31. Assif D, Nissan J, Gafni Y, et al. Assessment of the resistance to fracture of endodontically treated molars restored with amalgam. J Prosthet Dent 2003;89:462–5. 32. Al-Omiri MK, Al-Wahadni AM. An ex vivo study of the effects of retained coronal dentine on the strength of teeth restored with composite core and different post and core systems. Int Endod J 2006;39:890–9. 33. Zadik Y, Sandler V, Bechor R,, et al. Analysis of factors related to extraction of endodontically treated teeth. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2008;106:31–5. 34. Caicedo R, Clarck S, Rozo L, et al. Guidelines for access cavity preparation in endodontics. Available at: http://www.devosendo.nl/uploads/pdf/116_Guidelines% 20for%20access%20cavity.pdf. Accessed September 18, 2016. 35. Hansen EK, Asmussen E. Cusp fracture of endodontically treated posterior teeth restored with amalgam: teeth restored in Denmark before 1975 versus after 1979. Acta Odontol Scand 1993;51:73–7. Basic Research—Technology 1000 Plotino et al. JOE — Volume 43, Number 6, June 2017

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