Possibilities and Limitations of Variables and Analyses
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Orthodontic Cephalometry
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Wehrbein H, Bauer W, Schneider B, Diedrich P
Siersbaek-Nielsen S, Solow B (1982) lntra- and (1990) Experimented korperliche Zahnbewegung
interexaminer variability in head posture recorded durch den knochernen Nasenboden - eine
by dental auxiliaries. Am ] Orthod 82:50-7. Pilotstudie. Fortschr Kieferorthop 51:271-6.
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102
Possibilities and Limitations of Variables and Analyses
Foodside DG, Linder-Aronson S, Lundstrom A,
[McWilliam J (1991) Mandibular and maxillary
growth after changed mode of breathing. Am J
■OrtbodDentofacial Orthop 100:1-18.
Young TM, Smith RJ (1993) Effects of orthodontics
on the facial profile: A comparison of changes
during nonextraction and four premolar extraction
treatment. Am ] Orthod Dentofacial Orthop
:452-8.
Zimmer M, Miethke RR (1989) Fernrontgen-
seitenbildanalyse der Abteilung fur Kieferorthopadie
und Kinderzahnheilkunde der Polikliniken Nord der
Freien Universitat Berlin. Prakt Kieferorthop
3:33-48.
CHAPTER 4
Cephalometric Methods for Assessment of
Dentofacial Changes
htnir E Bishara and Atbanasios E Athanasiou
INTRODUCTION the infant face is transformed into that of the adult
face by increases in size, by changes in proportion,
(During the last hundred years, orthodontics has pro and by adjustment in position. Today, Hellman's
cessed from being a simplistic treatment modality statement is universally accepted.
(for aligning teeth to a science of therapeutic inter- Cephalometry has significantly increased our
'ventioii in the complexities of the cranial, facial, and understanding of normal facial growth as well as the
(dental structures. The study of the morphological outcome of orthodontic treatment, particularly
relationships of the various parts of the face has alsothrough the use of cephalometric superimpositions.
[developed from its early period of craniometry - an A cephalometric superimposition is an analysis of
janthropologic three-dimensional method of mea lateral cephalograms of the same patient taken at dif
suring the skull and head - to roentgenographic ferent times. These superimpositions are used to
I cephalometry - a two-dimensional radiographic evaluate a patient's growth pattern between different
study of the skull. More recently, attempts have been ages and to evaluate changes in the dentoalveolar and
| made to digitize the investigative methods used and basal relationships after a course of orthodontic or
reconstruct three-dimensional images of the head surgical treatment. However, if such superimpositions
and face through the use of computers and serial are to be meaningful, the appropriate procedures
jtomograms (Marsh and Vannier, 1990). must be exxecuted in a technically accurate and bio
[ In 1931, Broadbent in the USA and Hofrath in logically sound manner. Furthermore, such cephalo
Germany introduced the technique of radiograph- metric procedures and evaluations should be
tic cephalometry. Since then, clinicians and research considered in the light of:
ers have adopted and routinely used this valuable • rhe pretreatment objectives;
| tool on orthodontic patients in order to analyse • the orthodontic treatment modalities used; and
j underlying dentofacial relationships. In addition, • the long-term follow-up of the treatment results
I cephalometrics is used to gain a better understand- during the retention and post-retention periods.
[ing of the facial changes that accompany growth
[ and/or orthodontic treatment.
Since the early application of cephalometry for METHODS OF ASSESSING DENTO
studying dentofacial growth, there have been dis FACIAL CHANGES
agreements about how and when the dimensions of
die face change. Brodie (1941) and Broadbent When evaluating the dentofacial changes that occur
i (1941) felt that dentofacial growth patterns are as a result of growth or treatment, orthodontists are
established at a very early age and thereafter are interested in observing specific areas of alterations
[subject to proportional changes. Downs (1948) and (Kristensen, 1989). As a result, cephalometric super-
Ricketts (1975) pointed out that several angles and impositions involve the evaluation of:
(dimensions change with age but in an orderly and • changes in the overall face;
[progressive manner. However, the view that there • changes in the maxilla and its dentition;
lire no differential growth rates in the face was not • changes in the mandible and its dentition;
shared by everyone. The concept that had been • amount and direction of condylar growth; and
expressed earlier by Hellman (1935) suggested that • mandibular rotation.
105
\
Orthodontic Cephalometry
An early method used to determine the changes placement of metallic implants in the maxilla and
that occur in the dentofacial complex was the com mandible for subsequent use as stable structures has
parison of linear and angular measurements from been advocated by researchers (Bjork, 1968) (4.1).
consecutive cephalograms. The major disadvantage For fairly obvious reasons, it is n o t recommended
of this method is that it does not accurately portray that such implants be used routinely as a means of
the actual changes in the dentofacial structures; determining the changes t h a t occur as a result of
rather it reflects the relative changes between specific growth and treatment. However, information
cephalometric landmarks located on the radi- gathered from earlier implant studies (Bjork, \%3)
ographic profiles of various bones. As an example, as well as studies on human autopsy materials
the angle SNA not only represents the changes at (Melsen, 1974; Melsen and Melsen, 1982) are useful
point A, but also the spatial changes that occur at in identifying which areas are relatively stable (i.e.
sella and at nasion. Of course, if numerous angles, areas where the changes are of relatively small mag
lines, and ratios are measured and calculated, an nitude). O n the other h a n d , cephalometric super-
understanding of the changes in the facial structures impositions performed on patients w h o have
is conceptually possible. Such a process, however, is completed their g r o w t h are likely to be more
time consuming and clinically impractical. accurate.
The use of serial superimpositions from cephalo In addition to quantitative information, cephalo
grams that have been taken at different times is one metric superimpositions can provide important
method for accurately determining the relative qualitative information. However, for these judge
changes in the face. For a meaningful interpretation ments to be useful, they have t o be obtained from
of these superimpositions, they have to be registered consecutive cephalograms taken under identical
on stable reference areas. Unfortunately, areas in the conditions of magnification, head position, and
craniofacial complex that do not change during the radiological exposure; furthermore, the tracing of
period of growth cannot be easily identified. The the superimpositions must be accurate. According
4.1 The p l a c e m e n t o f m e t a l l i c implants in the maxilla and
mandible has been used t o create stable structures. (A) Implants
are inserted in four regions of the mandible: one in the midline of
the symphysis, t w o under the first o r second premolar or first
molar on the right side, one on the external aspect of the right
ramus, and one under the second premolar on the left side. (BJ
Implants are inserted in four zones in the maxilla: before eruption
of the permanent incisors, one on each side of the hard palate,
behind the deciduous canines, after eruption of the permanent
incisors, one o n each side of the median suture, under the anterior
nasal spine, and t w o o n each side in the zygomatk process of the
maxilla. (After Bjork, 1968; reprinted with permission.)
106
Ceph lometric Methods for Assessment of Dentofacial Changes
toBroadbent et al (1975), when tracing serial films, EVALUATION OF THE OVERALL
one may start with the youngest pair and follow the CHANGES IN THE FACE
child rovvards maturity, or start at the most mature
stage and work backwards. Either method allows BACKGROUND
the examiner to observe gradual morphological
changes. The benefits of sequential progression or Cranial structures have traditionally been used for
regression are forfeited if the cases are not traced in these superimpositions based on the fact that both
order. the neurocranium and its related cranial base
achieve most of their growth potential at a relatively
It is of great importance that exactly the same early age. At birth, the intersphenoidal and intereth-
structures and their corresponding radiographic moidal synchondroses are closed. By six or seven
shadows be traced in the consecutive cephalograms years of age, the only synchondrosis remaining open
that are to be evaluated. One of the prerequisites of is the spheno-occipital synchondrosis. As a result,
tracing is ro locate precisely the outlines of the there is relatively little anteroposterior change in the
relevant structures and to eliminate the confusing, ethmoidal portion of the anterior cranial base
unusable details. (Knott, 1971). From this age onwards, any changes
that occur on the bone surfaces are due to remodel
Colour coding f o r t r a c i n g ling. Therefore, this part of the cranial base is con
sidered to be relatively stable.
border to facilitate identification of consecutive
cephalograms the following colour code has been SUPERIMPOSITION METHODS
suggested by the American Board of Orthodontists
11990): Broadbent triangle
i •pretreatment - black;
f progress- blue; The Broadbent triangle (Na-S-Bo) and its registra
j 'end of treatment - red; tion point R were among the first structures used for
j ' retention - green. superimpositions to determine overall changes. With
this method, the two tracings are oriented so that
the R points are registered and the Bolton planes
(Bo-Na) are parallel (Broadbent, 1931) (4.2).
Sella-nasion line
Another method of superimposition orients the two
tracings on the Sella-nasion line with registration at
sella (American Board of Orthodontics, 1990) (4.3).
This method provides a composite view of the
amount of growth change during the period
between the two films; it is reasonably accurate as
long as the growth change at nasion follows the
linear extention of the original sella-nasion line.
42 Use of the Broadbenc triangle (N-S-Bo) and its registration The major disadvantage of these methods of
pontR (arrow) for superimposition to determine overall changes. superimposition is that they incorporate areas of the
tai this method, the two tracings are oriented with the R points cranial base that continue to change during most of
ngistered and the Bolton planes (Bo-N) parallel. (After Broadbent the growing years. Growth at the spheno-occipital
synchodrosis (Khott, 1971) as well as bone remod
1975: reprinted with permission.) eling at Nasion and Sella are responsible for these
changes. Nasion is displaced forward during remod-
107
Orthodontic Cephalometry
eling but with no consistent superioinferior direc growth. According to Coben (1986), the relation
tion. Most of the changes in the position of nasion ships among the position of the head in normal
are due to the enlargement of the frontal sinus, and posture, the visual axis of the eyes, and the anterior
consequently the upward or downward migration cranial base do not change. As a result, serial
of the frontonasal suture would result in superim- tracings should be registered at basion and oriented
position errors (Nelson, 1960; Knott, 1971). Sella with the S-N planes parallel. The line from basion
turcica also undergoes eccentric remodelling during drawn parallel to the original Frankfort horizontal,
adolescence and beyond, and this results in signifi or the mean Frankfort horizontal of the several radi
cant changes in the configuration of the fossa ographs, establishes the constant SN-FH relation
(Melsen, 1974). As a result, the position of the ship and the Basion Horizontal plane of the series.
midpoint of the sella turcica (point sella) moves Each subsequent co-ordinate tracing film may be
either downwards and backwards or straight down superimposed by simply aligning the co-ordinate
wards. Similarly, Bolton point is frequently obscured grids that have been especially designed for this
by the mastoid process in the teenage years purpose (Coben 1979) (4.4).
(Broadbentetal, 1975).
Basion-Nasion plane
Basion Horizontal The use of Basion-Nasion plane as an area of reg
Cohen (195J, 1986) presented the Basion istration for overall evaluation of the dentofacial
Horizontal concept. The Basion Horizontal is a changes has been suggested by Ricketts et al (1979).
plane constructed at the level of the anterior border According to Ricketts, if the superimposition area
of the foramen magnum parallel to Frankfort hor is the Ba-Na line with registration at CC point (the
izontal. With this method, basion is used as the point where the basion-nasion plane and the facial
point of reference for the analysis of craniofacial axis intersect), it is possible to evaluate changes in
4.3 Orientation of three subsequent tracings on the sella-nasion 4.4 According t o the Basion Horizontal concept, serial tracing!
line and with registration at sella. This example corresponds t o the should be registered a t basion and o r i e n t e d w i t h S-N planes
pretreatment (black), end of treatment (red), and retention (green) parallel. T h e line f r o m basion d r a w n parallel t o the original
phases of orthodontic therapy. F r a n k f o r t h o r i z o n t a l o r the mean F r a n k f o r t horizontal of the
several radiographs establishes the constant S N - F H relationship
and the Basion Horizontal plane of the series. Each of the two
subsequent co-ordinates o n the tracing may be superimposed ty
m e r e l y aligning the specially designed c o o r d i n a t e grids. This
example c o r r e s p o n d s t o the p r e t r e a t m e n t (black) and end of
treatment (red) phases of an orthodontic patient.
108
Cephalometric Methods for Assessment of Dentofacial Changes
facial axis (BA-CC-GN), in the direction of chin REFERENCE STRUCTURES FOR OVERALL
>wth, and in the upper molar position (4.5). FACE SUPERIMPOSITIONS
Melsen (1974), on the other hand, has observed
it the position of Basion is influenced by the Nelson's (1960) cephalometric study and Melsen's
lodeling processes o n the surface of the clivus (1974) histological investigation identified various
id on the anterior border of the foramen magnum, bony surfaces in the anterior cranial base that are
well as by displacement of the occipital bone. suitable for accurate superimpositions. These
^placement of the occipital bone is associated with surfaces undergo relatively minimal alterations
growth in the spheno-occipital synchondrosis. during the growth period and have been called
Isen's histological investigation revealed appo- stable structures or reference structures. They
>n on the anterior border of the foramen include (4.6):
ignum, with simultaneous resorption on the inner • the anterior wall of sella turcica;
rface of the basilar part of the occipital bone and • the contour of the cribiform plate of the ethmoid
tsition on its outer surface. bone (lamina cribrosa);
• details in the trabecular system in the ethmoid cells;
Because nasion, sella, and basion move during • the median border of the orbital roof; and
rowth, the methods of overall super imposition on • the plane of the sphenoid bone (planum sphe-
S-Na or Ba-Na lines have a low degree of validity,
although they have high degree of reproducibility noidale).
(Kristensen, 1989). (See chapter 5 for a discussion For registration purposes, Nelson (1960) recom
of validity and reproducibility of methods.) mended the use of the midpoint between the right
and left shadows of the anterior curvatures of the
great wings of the sphenoid bone where they intere-
sect the planum.
15 For superimpositions, Ricketts used the BA-NA line with 4.6 Bony surfaces in the anterior cranial base that are suitable for
jnpscration at CC point (point where the BA-NA plane and the accurate superimposition. These surfaces undergo relatively
fid axis intersect). Changes in the facial axis (BA-CC-GN), in minimum alterations during growth and are called stable structures
I (he direction of the chin point and in the upper molar position, can or reference structures. They include:
Kt evaluated. (After Ricketts et al, 1979; r e p r i n t e d w i t h 1 the anterior wall of sella turcica
■mission.) 2 the contour of the cribriform plate of the ethmoid cells (lamina
cribrosa)
3 details in the trabecular system in the ethmoid cells
4 the median border of the orbital roof
5 the plane of the sphenoid bone (planum sphenoidale).
109
Orthodontic Qephalometry
STEP-BY-STEP EVALUATION OF WHAT CAN WE LEARN FROM
THE OVERALL FACE OVERALL SUPERIMPOSITIONS?
The approach for the overall superimposition on Cranial base superimpositions provide an overall
stable cranial structures includes the following steps assessment of the growth and treatment changes of
(4.7): the facial structures, including the amount and
1. Place tracing paper on the first cephalogram and direction of maxillary and mandibular growth or
displacement, changes in maxillary-mandibular
stabilize it with tape. Use black tracing pencil to relationships, and the relative changes in the soft
complete the tracing, which should include as tissue integument (specifically the nose, lips, and
many of the above-mentioned stable structures as chin). In addition, cranial base superimpositions
possible. provide information on the overall displacement of
2. Trace the second cephalogram with either a blue the teeth. As mentioned before, this technique will
or red tracing pencil, depending on whether it is not identify specific sites of growth, but it will
a progress or post-treatment record. provide a quantitative directional appraisal of the
3. Superimpose the second tracing on the first one, translatory changes that have occurred in the
again using as many as possible of the stable various facial structures.
structures of the cranial base that have been
clearly identified from both cephalograms. ASSESSMENT OF CHANGES IN
Register on the midpoint between the right and TEETH POSITION
left shadows of the greater wing of the sphenoid
as they intersect the planum sphenoidale. It needs to be realized that the cranial base super-
Stabilize the tracing with tape. impositions do not provide for an assessment of the
changes in the position of the teeth within the
This method of overall superimposition presents a maxilla or mandible. In order to obtain this infor
high degree of validity and a medium to high degree mation, maxillary and mandibular superimpositions
of reprod ucibility. are required.
110
Cepbalometric Methods for Assessment of Dentofacial Changes
11 53
-52
' Jilm
4H|
■P ^WB
m■
a
^ ^ jfl
^Iftb— ""^^^H
4.7 A step-by-step approach for the overall superimposition on stable cranial
structures. (A) Pretreatment cephalogram; (B) Pretreatment tracing on cephalo-
gram; (C) Pretreatment tracing; (D) Progress cephalogram; (E) Progress tracing on
cephalogram; (F) Progress tracing; (G) Superimposition of pretreatment and
progress tracings.
E.H.
Pre-Trealmeni
Progress
111
Orthodontic Cephalometry
MAXILLARY SUPERIMPOSITIONS 3. Superimposition along the palatal plane regis
tered at the pterygomaxillary fissure (Moore,
Background 1959) (4.10).
The purpose of maxillary superimpositions is to
evaluate the movement of the maxillary teeth in 4. Superimposition on the outline of the infratem-
relation to the basal parts of the maxilla. A number poral fossa and the posterior portion of the hard
of methods for superimposing the maxillary struc palate (Riedel, 1974) (4.11).
tures have been suggested, including the following:
1. Superimposition along the palatal plane regis 5. Superimposition registering the maxilla on the
common Ptm co-ordinate, maintaining the Basion
tered at anterior nasal spine (ANS) (Broadbent, Horizontal relationship (Coben, 1986) (4.12).
1937; Moore, 1959; Salzmann, 1960; Ricketts,
1960, 1972,1981; McNamara, 1981) (4.8). 6. Superimposition on the best fit of the internal
2. Superimposition on the nasal floors with the films palatal structures (McNamara, 1981) (4.13).
registered at the anterior surface of the maxilla
(Downs, 1948; Brodie, 1949) (4.9). 7. Superimposition on metallic implants (Bjork and
Skieller, 1976a, b) (4.14).
8. The structural superimposition on the anterior
surface of the zygomatic process of the maxilla
(Bjork and Skieller, 1976a, b; Luder, 1981) (4.15).
4.8 Maxillary superimposition along the palatal plane registered at 4 . 9 Superimposition on the nasal f l o o r s w i t h the traci
ANS. registered at the anterior surface of the maxilla.
4.10 Maxillary superimposition along the palatal plane registered 4.1 I Maxillary superimposition registered on the outline of the
at the pterygomaxillary fissure. infratemporal fossa and the posterior p o r t i o n of the hard palate.
112
Cephalometric Methods for Assessment of Dentofacial Changes
4.13 Maxillary superimposition on the best fit of the internal
palatal structures. (After McNamara, 1981; reprinted with per
mission.)
412 Superimposition registering the maxilla on the c o m m o n Ptm
pordinate and maintaining the Basion Horizontal relationship.
k illustrates the maxillary contribution t o midface depth and the
■rizontal and vertical changes of the palate and the maxillary
■notion relative to both Ptm and the foramen magnum plane of
orientation (Basion Horizontal).
NSLg 3 —i
NSLA
■ .*
^
rrr■ \ P
. \Ji -
II ^
vy
■ \f .
/
4.15 The structural superimposition on the anterior surface of
the zygomatic process of the maxilla.
14 Maxillary superimposition o n metallic implants. G r o w t h of
maxilla and the dental arch is analysed by means of implants.
BterBjork, 1968; reprinted with permission.)
113
Orthodontic Cephalometry
The various methods of maxillary superimpositions basal part of the bone. However, this method of
that use either the palatal plane between the anterior maxillary superimposition is characterized by a low
nasal spine and the posterior nasal spine (ANS-PNS degree of validity and only a medium degree of
line) or the best fit on the maxilla are compromised reproducibility (Kristensen, 1989).
by the remodelling of the palatal shelves. It has been
shown that the hard palate undergoes continuous On the other hand, Bjork and Skieller (1977b),
resorption on its nasal surface and apposition on the using implants, suggested the use of a structural
oral side, making most of these methods of super- method of superimposition in order to evaluate
impositions unsatisfactory/ (Bjork and Skieller, maxillary growth and treatment changes (4.15),
1977a, b) (4.16). Furthermore, registration on either With this approach, the tracings are superimposed
ANS or PNS should be avoided, since both these on the anterior contour of the zygomatic process of
structures are known to undergo significant antero- the maxilla, which shows relative stability after the
posterior remodelling (Bjork and Skieller, 1977a). age of eight. The second film is oriented so that the
resorptive lowering of the nasal floor is equal to the
The best fit method provides a higher degree of apposition at the orbital floor.
validity than the ANS-PNS line, since the palatal
structures used for superimposition incorporate the Nielsen (1989) examined the validity and relia
bility of the structural method of superimposition
4 . 1 6 Mean growth changes from four years until adult age in nine
boys, measured f r o m the lateral implants. (After Bjork and Skieller,
1977a; reprinted with permission.)
Su - sutural lowering of the maxilla
O - apposition at the floor o f the o r b i t
A - appositional increase in height of the alveolar process
Re - resorptive lowering of the nasal floor
C - apposition at the infra zygomatic crest
114
Cepbalometric Methods for Assessment of Dentofacial Changes
and compared it to the implant and best fit methods. between the structural and the implant methods in
Hie best fit superimposition w a s made as the the vertical plane. In the horizontal direction,
optimal fit of the hard palate with the nasal floors however, the structural method on average demon
aligned and registered at ANS. The various super- strated a posterior displacement of the reference
impositions were constructed from tracings points by an average of 0.5 mm.
obtained from cephalograms taken on 18 subjects As a result, it has been concluded that the struc
at 10 and 14 years of age. Nielsen found that the tural method for superimposing head films is a valid
best fit method significantly underestimates the and reliable method for determining maxillary
vertical displacement of both the skeletal and dental growth and treatment changes (Nielsen, 1989). The
landmarks as a result of the remodelling of the major disadvantage of using the structural method
maxilla (4.17, 4.18). The study further demon is that the zygomatic process of the maxilla is char
strated that, with both the implant method and the acterized by double structures, which makes it dif
structural method, ANS showed twice as much ficult to identify accurately and hence to trace the
vertical displacement as PNS. On the other hand, no construction line. As a result, this method has a low
statistically significant differences were found degree of reproducibility.
IMPLANT-BEST FIT DIFFERENCES (TIMEPOINT II) STRUCTURAL-BEST FIT DIFFERENCES {TIMEPOINT
PNS PNS
1.39 ANS
t 0.94
initial * Initial
Best Fit
0 - — ™ implant n Best Fit
I Structural
4.17 Mean and standard deviations of differences in displacement 4.18 Mean and standard deviations of differences in displacement
ofikeletal and dental landmarks between the implant and the best of skeletal and dental landmarks between structural and best fit
It super-impositions during a four-year p e r i o d ( N = I 8 ) . ( A f t e r superim positions during a four-year period ( N = I 8 ) . (After Nielsen,
tfelsen, 1989; reprinted with permission.) 1989; reprinted with permission.)
115
Orthodontic Qephalometry
WHERE TO SUPERIMPOSE IN THE The structural method of maxillary superimposi
MAXILLA? tions has a medium t o high degree of validity and
low degree of reproducibility (Kristensen, 1989).
Two methods for superimposing the maxillary struc
tures are recommended - the structural method and Modified best fit method of superimposing the
a modified best fit method. maxillary structures
If the details of the zygomatic process of the maxilla
The structural method of superimposing the are not clearly identifiable, a modified best fit
maxillary structures method is recommended. The superimpositions are
The use of the structural method is recommended if made on the nasal and palatal surfaces of the hard
the details of the zygomatic process of the maxilla palate in an area that is not significantly influenced
are clearly identifiable in both cephalograms. The by incisor tooth movement. The approach for max
approach for maxillary superimpositions on stable illary superimpositions by means of the best fit
structures includes the following steps (4.19): method include the following steps (4.20):
1. Place a cellophane tracing paper on each cephalo- 1. Trace t h e maxillary structures, including the
gram. Trace the anterior contour of the zygomatic outline of the palate, the first permanent molars,
process and construct a line that is tangential to the entrance of the incisal canal (when it can be
it. When two contours are present, bisect them to visualized), and the most labially positioned
trace the midline between them. central incisor on the t w o consecutive cephalo
2. On each cephalogram, trace the contour of the grams, using the appropriate colours.
palate, the maxillary first molar, the most labially 2. Place t h e second tracing over the first one and
positioned central incisor, the zygomatic process, adjust it to have the following structures arranged
the floor of the orbit, N - S line, and the con in a best fit alignment:
struction line (which is a line tangential to the • the contour of the oral part of the palate;
anterior contour of the zygomatic process). The • the contour of the nasal floor; and
tracing from the first cephalogram is drawn in • the entrance of the incisal canal.
black and the tracing from the second tracing in
blue or red depending on whether it is a progress Stabilize the two cephalograms together by means
or post-treatment record. of a tape.
3. The two tracings should be superimposed on each
other on the construction line to determine the As stated earlier, when using the best fit method,
amount of apposition at the floor of the orbit. it needs to be remembered that the downward
Move the superimpositions so that the amount of remodelling of the nasal floor should be accounted
resorption at the nasal floor is equal to the appo for from the overall superimpositions on the cranial
sition at the floor of the orbit. Stabilize the base. Furthermore, the molar eruptions are under
tracings together with a tape. estimated by 3 0 % and the incisor eruptions are
4. The amount of maxillary rotation can be esti underestimated by 5 0 % .
mated from the two N - S lines. The angle formed
between the lines expresses the rotation of the The best fit method has a low degree of validity
maxilla. For instance, if the two lines cross ante and a medium degree of reproducibility (Kristensen,
riorly then the rotation has taken place in an 1989).
anterior direction.
I 16
Cephalometric Methods for Assessment of Dentofacial Changes
G.R. 4.19 A step-by-step approach for maxillary superimpositions on
Pre-Trcatment stable structures. (A) Pretreatment cephalogram (maxillary area);
Pose-Treatment (B) Pretreatment maxillary tracing on cephalogram; (C)
Pretreatment maxillary tracing; (D) Post-treatment maxillary
cephalogram; (E) Post-treatment maxillary tracing on cephalogram;
(F) Post-treatment maxillary tracing; (G) Superimposition o n stable
structures of pretreatment and post-treatment maxillary tracings.
117
Orthodontic Cephalometry
B
4.20 A step-by-step approach for a modified best fit
method of maxillary superimposition. (A) Pretreatment
cephalogram (maxillary area); (B) Pretreatment
maxillary tracing on cephalogram; (C) Pretreatment
maxillary tracing; (D) Progress maxillary cephalogram;
(E) Progress maxillary t r a c i n g on cephalogram; (F)
Progress maxillary tracing; (G) Best fit superimposition
of pretreatment and progress maxillary tracings.
118
Cephalometric Methods for Assessment of Dentofacial Changes
MANDIBULAR SUPERIMPOSITIONS Stable structures for superimposition on the
mandible
Background From their implant studies, Bjork (1963,1969) and
the purpose of mandibular superimpositions is to Bjork and Skieller (1983) have indicated that the fol
evaluate the movement of the mandibular teeth in lowing structures are relatively stable and could be
Relation to the basal parts of the mandible. A used for superimposition purposes (4.21):
wumber of areas have been suggested for superim- 1. The anterior contour of the chin (area 1).
Ipositions (Salzmann, 1972), including: 2. The inner contour of the cortical plates at the
• the lower border of the mandible; inferior border of the symphysis and any distinct
I a tangent to the lower border of the mandible; trabecular structure in the lower part of the sym
and physis (area 2),
• the constructed mandibular plane between 3. Posteriorly, the contours of the mandibular canal
Menton and Gonion. (area 3) and on the lower contour of a mineral
ized molar germ (area 4). The latter structure can
)wever, these methods are not very accurate in only be used from the time of initial mineraliza
escribing the changes within the mandible itself, tion of the crown until the beginning of root for
mse of the significant remodelling that occurs at mation. Before and after these two stages of
mandibular border (Bjork, 1963). development, it was observed that the tooth germ
Superimposition on the mandibular plane is a significantly changes its position (Bjork and
I method of low degree of validity, but of high degree Skieller, 1983).
|of reproducibility (Kristensen, 1989).
4.21 The structures in the niandibular corpus used for mandi
bular superimpositions. (After Bjork, 1969; reprinted with per
mission.)
119
Orthodontic Cepbalometry
Step-by-step approach for mandibular to the stable structures listed earlier, and it therefore
superimpositions exhibits great variation. This remodelling is char
The recommended approach for mandibular super- acterized by apposition in the anterior part and
impositions by using stable structures includes the some resorption in the posterior part, i.e. the gonion
following steps (4.22): area (Bjork, 1969).
1. On each of the two cephalograms, trace the fol
Evaluation of amount and direction of
lowing structures using the appropriate colours: condylar growth and evaluation of mandibular
• the symphysis with the inner cortical bone; rotation
• the inferior and posterior contour of the Condylar growth can be evaluated from the
mandible; mandibular tracing if the head of the condyle can be
• the point Articulare; clearly identified. Since the condyles are difficult to
• the anterior contour of the ramus; identify on a lateral cephalogram taken in centric
• the mandibular canal; occlusion, a supplementary lateral cephalogram,
• third molar tooth buds before root formation; taken with the mouth maximally open, can provide
• the most labially positioned lower incisor; and the best imaging of the condylar head. In order to
• the first molars. avoid exposing the patient to extra radiation, point
2. If the four stable structures described earlier are Articulare can be used as a substitute for this eval
all clearly identifiable on the cephalogram, they uation^ Changes at Articulare will reflect approxi
should all be used for superimposition purposes. mate changes of the condylar area and provide some
However, in some patients the third molars are information concerning the amount and direction
congenitally missing, while in others tooth devel of condylar growth. The recommended approach
opment might not yet have shown crown miner for assessing true mandibular rotation includes the
alization or the roots may have already started following steps (4.23):
forming. In these cases, the third molar tooth 1. On each of the two cephalograms trace the fol
germ is not a useful structure for superimposition
purposes. Similarly, the outline of the mandibu lowing structures using the appropriate colours:
lar canal is often difficult to identify in consecu • the symphysis with cortical bone;
tive lateral cephalograms. A further problem is • the inferior and posterior contour of the
that the shadows of the right and left sides can mandible;
overlap, further confusing the picture. As a result, • the point Articulare;
the only surfaces that can be reliably and consis • the anterior contour of the ramus;
tently used for the purpose of superimposition are • the mandibular canal;
the inner cortical structure of the inferior border • third molar tooth buds before root formation;
of the symphysis and the anterior contour of the • the most labially positioned lower incisor;
chin. • the first molars; and
3. Place the last cephalogram on the first one and • the N-S line.
adjust it in relation to the stable structures of the 2. If the four stable structures described earlier are
mandible. Then stabilize the two cephalograms all clearly identifiable on the cephalogram, they
together with tape. should all be used for superimposition purposes.
3. Place the last cephalogram on the first one and
The method of using stable structures for mandibu adjust it in relation to the stable structures of the
lar superimpositions is characterized by medium to mandible. Then stabilize the two cephalograms
high degree of validity and medium to high degree together by means of a tape. The true mandibu
of reproducibility (Kristensen, 1989). lar rotation can be evaluated by the changes in
the N - S lines between the two consecutive
When the stable structures that are intended to mandibular tracings. The angle expresses the
be used for superimposition are not easily identifi amount of mandibular rotation. For instance, if
able, the lower border of the mandible can be used they cross anteriorly, the mandible has rotated
for orientation purposes. However, it needs to be anteriorly.
realized that the lower border of the mandible
undergoes significant remodelling when compared
120
Cepbalometric Methods for Assessment of Dentofacial Changes
fvy A.D.
Progress
V
\
\3 |flK1/
V
i 11
A.D. 4.22 A scep-by-step approach for mandibular superimposicions on stable structures:
P re-Treatment (A) Pretreatment cephalogram (mandibular area); (B) Pretreatment mandibular tracing
Progress on cephalogram; (C) Pretreatment mandibular tracing; (D) Progress mandibular
cephalogram; (E) Progress mandibular tracing on cephalogram; (F) Progress mandibular
tracing; (G) Structural superimposition of pretreatment and progress mandibular
tracings.
121
Orthodontic Cephalometry
■i -
r..*. C.R.
3 h o TrrulBCnt —
- ^H
W' -'ijMisM ^BjkfW?
^B
£j* A
w ~^B jj
^MH r ■
tf ^ h i ^ i
I I■A^. • JK V
£■ f^~>A * V
C.R.
jiSil—
4.23 A step-by-step approach for determining mandibular rotations. (A) Pretreatment
C.R. cephalogram; (B) Pretreatment tracing o n cephalogram including mandibular area and N-S
line (NSL1); (C) Pretreatment tracing including mandibular area and N - S line (NSL1); (D)
Pr» ICMtSMt - P o s t - t r e a t m e n t c e p h a l o g r a m ; (E) P o s t - t r e a t m e n t t r a c i n g o n cephalogram including
Pom trc.Kwot
mandibular area and N-S line (NSL2); (F) Post-treatment tracing including mandibular area
and N - S line (NSL2); (G) Structural superimposition o f pretreatment and post-treatment
Mi
mandibular tracings. T h e true mandibular rotation can, thus, be evaluated by the changes
in t h e N - S lines between the t w o consecutive mandibular tracings. The angle expresses
the amount o f mandibular r o t a t i o n . If they cross anteriorly, the mandible has rotated |
anteriorly.
122
r \c Methods for Assessment of Dentofacial Changes
CONCLUSION
Bjork A, Skieller V (1976) Postnatal growth and
I In this chapter an attempt has been made to present development of the maxillary complex. In:
| the scientific basis on which accurate superimposi- McNamara JA Jr (ed) Factors Affecting the Growth
jfions can be made. If the tracings are not accurate of the Midface. Monograph No. 6. (University of
and the superimpositions and registrations are not Michigan: Ann Arbor) 61-99.
made on radiographic structures that have been
proved to be relatively stable and reliable, the super- Bjork A, Skieller V (1977a) Growth of the maxilla
impositions can be manipulated to show anything in three dimensions as revealed radiographically by
the operator wants to show.
the implant method. Br J Orthod 4:53-64.
Short of using metallic implants, superimposi
tions performed using the suggested approaches rep Bjork A, Skieller V (1977b) Roentgencephalometric
resent the best available methods for interpreting the growth analysis of the maxilla. Trans Eur Orthod
changes in the dentofacial complex that have Soc 7:209-33.
mccurred as a result of growth or treatment.
To perform an accurate superimposition, one has Bjork A, Skieller V (1983) Superimposition of
to have an excellent knowledge of the anatomy of profile radiographs by the structural method. In:
the dentofacial and cranial structures as well as of Normal and Abnormal Growth of the Mandible.
die radiographic interpretation of these structures. Eur J Orthod 5:40-6.
This is essential, since the radiograph is a two-
Mimensional image of three-dimensional structures, Broadbent BH (1931) A new X-ray technique and
(and the view it provides in profile. Without such its application to Orthodontia. Angle Orthod
Knowledge and understanding, radiographic inter 1:45-66.
pretations become a guessing game rather than the
pence that cephalometrics is supposed to be. Broadbent BH (1937) Bolton standards and tech
[Furthermore, the scientific knowledge should be nique in orthodontic practice. Angle Orthod
[supplemented by the manual skills needed to draw 7:209-33.
pe structures that have been identified accurately.
Broadbent BH (1941) Ontogenic development of
occlusion. Angle Orthod 1 1 : 2 2 3 ^ 1 .
REFERENCES
Broadbent BH Sr, Broadbent BH Jr, Golden WH
[American Board of Orthodontics (1990). Exami- (1975) Bolton Standards of Dentofacial
mtkm Information Manual. (American Board of Developmental Growth. (CV Mosby: St Louis.)
.Orthodontics: St Louis.)
Brodie AG (1941) On the growth pattern of the
Bjork A (1963) Variations in the growth pattern of human head from the third month to the eighth year
[the human mandible: Longitudinal radiographic of life. Am J Anat 68:209-62.
study by the implant method. / Dent Res
12:400-11. Brodie AG (1949) Cephalometric roentgenology:
history, technics and uses. J Oral Surg 7:185-98.
Bjork A (1968) The use of metallic implants in the
■Study of facial growth in children. Am J Phys Coben SE (1955) The integration of facial skeletal
mbropol 29:243-54. variants. Am) Orthod 41:407-34.
Bjork A (1969) Prediction of mandibular growth Coben SE (1961) Growth concepts. Angle Orthod
fetation. Am J Orthod 55:585-99. 31:194-201.
123
Orthodontic Cephdlometry
Coben SE (1979) Basion Horizontal coordinate Melsen B, Melsen F (1982) The postnatal develop
tracing films./ C/m Orthod 13:598-605. ment of the palatomaxillary region studied on
human autopsy material. Am] Orthod 82:329-42.
Coben SE (1986) Basion Horizontal: An integrat
ed Concept of Craniofacial Growth and Moore AW (1959) Observations on facial growth
Cephalometric Analysis. (Computer Cephalometric and its clinical significance. Am J Orthod
Associated: Jenkintown, Pennsylvania.) 45:399-423.
Downs WB (1948) Variations in facial relations: Nelson T O (1960) Analysis of facial growth utiliz
their significance in treatment and prognosis. Am ing elements of the cranial base as registrations. Am
J Orthod 34:812-40. J Orthod 46:379.
Downs WB (1952) Cephalometrics in case analysis Nielsen IL (1989) Maxillary superimposition: A
and diagnosis. Am} Orthod 38:162-82. comparison of three methods for cephalometric
evaluations of growth and treatment change. Am]
Hellman M (1935) The face in its developmental Orthod Dentofac Orthop 95:422-31.
career. Dental Cosmos 77:685-99.
Hofrath H (1931) Die Bedeutung der Rontgenfern Ricketts RM (I960) The influence of orthodontic
und Abstandandsaufname fur die Diagnostic der treatment on facial growth and development. Angle
Kieferanomalien. Fortschr Ortodont 1:232-57. Orthod 30:103-32.
Knott VB (1971) Changes in cranial base measures Ricketts RM (1972) An overview of computerized
of human males and females from age 6 years to cephalometrics. Am] Orthod61:1-28.
early adulthood growth. Growth 35:145-58.
Ricketts RM (1975) New perspectives on orienta
Kristensen B (1989) Cephalometric Superim- tion and their benefits of clinical orthodontics - Part
position: Growth and Treatment Evaluation. (The 1. Angle Orthod 45:238-48.
Royal Dental College: Aarhus.)
Ricketts RM (1981) Perspectives in the clinical
Luder HU (1981) Effects of activator treatment - application of cephalometrics. Angle Orthod
evidence for the occurrence of two different types of 51:115-50.
reaction. EurJ Orthod 3:205-22.
Ricketts RM, Bench RW, Gugino CF, HilgersJJ,
Marsh JL, Vannier MW (1990) Three-dimensional Schulhof RJ (1979) Bioprogressive Therapy. (Rocky
imaging from CT scans for evaluation of patients Mountain Orthodontics: Denver, Colorado.)
with craniofacial anomalies. In: Strieker M, Van Der
Meulen J, Mazzola RR (eds) Craniofacial Riedel RA (1974) A postretention evaluation. Angle
Malformations. (Edinburgh: Churchill Livingstone) Orthod 44:194-212.
367-73.
Salzmann JA (1960) The research workshop on
McNamara JA Jr (1981) Influence of respiratory cephalometrics. Am ] Orthod 46:834-47.
pattern on craniofacial development. Angle Orthod
51:269-300. Salzmann JA (1972) Orthodontics in Daily Practice.
(JB Lippincott: Philadelphia.)
Melsen B (1974) The cranial base. Acta Odont
Scand 32(suppl 62).
124
CHAPTER 5
Sources of Error in Lateral Cepbalometty
Vincenzo Macri and Athanasios E Athanasiou
NTRODUCTION clusion has to be drawn from cephalometric data, it
is equally important to consider both the validity
According to Moyers et al (1988), cephalometrics is and the reproducibility of the method used.
aradiographic technique for abstracting the human
head into a geometric scheme. Cephalometric radi
ography may be used: VALIDITY
• for gross inspection;
P to describe morphology and growth; Validity, or accuracy, is the extent to which - in the
|* to diagnose anomalies; absence of measurement error - the value obtained
• to forecast future relationships; represents the object of interest (Houston, 1983).
• to plan treatment; and Both what is being measured and the method of
• to evaluate treatment results. measurement have to be taken into account. Some
cephalometric landmarks and planes do not agree
Gross inspection does not require identification, with the anatomical structures they are meant to
tracing, or measurement of the various dentoskele- represent because they have been chosen for con
ialand soft tissue relationships, since it consists of venience of identification rather than on grounds of
a visual examination of the X-ray image only. All anatomic validity. Variations in skeletal structure
the other functions listed above are principally con can affect the identification of these landmarks, and
cerned with the identification of specific landmarks their inconsistency as reference points during
and with the calculation of the various angular and growth or treatment can be misleading.
linear variables that are described by means of these
landmarks. The last three functions require more
complex mathematical and statistical calculations REPRODUCIBILITY
orspecific reference planes for superimposition tech
niques. Reproducibility, or precision, is the closeness of suc
All these procedures are potentially affected by cessive measurements of the same object (Houston,
several sources of error whose influence can vary to 1983). If a certain measurement is persistently over
agreat extent. Unfortunately, many of these sources estimated or under-estimated, a systematic error or
of error are inter-related in such a way that a clear- bias is introduced. If no systematic error is present,
cut distinction cannot be easily made. However, in the cluster of observations will be randomly dis
| this chapter such a separation has been attempted tributed around the true value to express the
with the aim of better presenting the sources of error random error (McWilliams, 1983).
iincephalometry.
The term reliability is used as a synonym for
Since cephalometry deals with geometric con- reproducibility, but it is sometimes also used in a
jstructions and calculations, it presupposes the accep- broader sense that encompasses both validity and
jtance of some conventions related to the type of reproducibility (Houston, 1983).
analysis chosen. Subsequently, if any consistent con
125
Orthodontic Cephalometry
ERRORS OF CEPHALOMETRIC focus-film distance of more than 280 cm does not
MEASUREMENTS significantly alter the magnitude of the projection
error (Carlsson, 1967; Ahlqvist et al, 1986, 1988).
Cephalometric measurements on radiographic The use of angular rather than linear measurements
images are subject to errors that may be caused by: is a consistent way to eliminate the impact of mag-
• radiographic projection errors; r> nification (Adams, 1940), since angular measures
• errors within the measuring system; and remain constant regardless of the enlargement
• errors in landmark identification. factor.
RADIOGRAPHIC PROJECTION ERRORS Distortion
Distortion occurs because of different magnifica
During the recording procedure, the object as tions between different planes. Although most of the
landmarks used for cephalometric analysis are
imaged on a conventional radiographic film is sub located in the midsagittal plane, some landmarks
and many structures that are useful for superim
jected to magnification and distortion. posing radiographs are affected by distortion, owing
to their location in a different depth of field. In rhis
■ instance, both linear and angular measurements will
be variously affected.
Magnification
Magnification occurs because the X-ray beams are Linear distances will be foreshortened, an effect
not parallel with all the points in the object to be that can be compensated for if the relative lateral
examined. The magnitude of enlargement is related displacement of the landmarks and their distance
to the distances between the focus, the object, and from the midsagittal plane are known. A combina
the film (Adams, 1940; Brodie, 1949; Hixon, 1960; tion of information from lateral and frontal films
Bjork and Solow, 1962; Salzmann, 1964). The use has been proposed (Broadbcnt, 1931; Savaraetal,
of long focus-object and short object-film distances 1966), but only a few landmarks can be located on
has been recommended in order to minimize such both projections.
projection errors (Franklin, 1952; Nawrath, 1961;
van Aken, 1963) (5.1, 5.2). However, although rel
atively long focus-film distances are favourable, a
5.1 Effect of focus-film distance on radio-
graphic magnification. (After Franklin, 1951
reprinted with permission.)
V AMooe y
2h *"CDC
7 /■¥ y. /*Aa#'S/(0 0/j roe T/OM
*8
'S 3S X J*f
126
r Sources of Error in Lateral Cephalotnetry
Projected angular measurements (e.g. the gonial It is convenient, therefore, to average and trace
ein a lateral headplate) are distorted according as a single image those structures whose images are
rto the laws of perspective (Slagsvold and Pedersen, doubled and exhibit an apparent asymmetry (e.g.
1977). Furthermore, landmarks and structures not the mandibular ramus and corpus, the pterygoid
situated in the midsagittal plane are usually bilat space, and the orbits). However, this type of tracing
eral, thus giving a dual image on the radiograph. is inadequate to describe a head that is truly asym
The problem of locating bilateral structures sub metrical (Grayson et al, 1984). In addition, in cases
jected to distortion can t o some extent be compen- of mild asymmetry it is difficult, using a lateral
sated for by recording the midpoints between these cephalogram, to differentiate between geometric dis
structures. %\atera\ structures m the symmetric Yicad" tortion and true subject asymmetry (Cook, 1980).
do not superimpose in a lateral cephalogram. The Misalignment or tilting of the cephalometric com
fan of the X-ray beam expands as it passes through ponents (e.g. the focal spot), the cephalostat, and
the head, causing a divergence between the images the film with respect to each other, as well as rota
of all bilateral structures except those along the tions of the patient's head in any plane of space, will
central beam. introduce another factor of distortion (5.3).
5.2 Effect of object-film distances on
radiographic magnification and sharpness.
(After Franklin, 1952; reprinted with per
mission.)
u&oeaAf'c raojicrtoM or e+stcr * wo** *M*C ruajecTfo" or OMJtcr *r
SMf.
•^cMt'Sto &MTA**C*Z 0SOM SM.A*.
/.AM*** nA>mmtftCAr>o*/ or is****
5.3 Directions of possible misalignments
of the patient's head. (After Ahlqvist et al,
1986; reprinted with permission.)
127
Orthodontic Cepkatometry
Malposition of the patient in the cephalostat ERRORS W I T H I N THE MEASURING
produces an asymmetric distortion for both linear SYSTEM
and angular measurements on lateral cephalograms
(Baumrind and Frantz, 1971b) (5.4). By using a In conventional cephalometry, the development of
mathejmatic model, however, Ahlqvist et al (1983, computerized equipment for electronic sampling of
1986) demonstrated that minor malpositions in the landmarks has greatly speeded up data collection
cephalometric devices are of little importance for the and processing a n d has reduced the potential for
total projection error. The same model was applied human measuring errors. The first computerized
to determine linear and angular distortion due to measuring devices were electromechanical and had
incorrect patient positioning (Ahlqvist et al, 1988). built-in sources for parallax and mechanical errors
The resulting projection error seemed in no instance (Butcher a n d Stephens, 1 9 8 1 ; Cohen and Linney,
to be of major concern, as angle distortion never 1984).
exceeded ± 0.5° for rotations of the head up to ± 5°.
Larger rotations of the head are unlikely, as they N o w d a y s , the general diffusion of digitizers and
would be obvious to the examiner (Spolyar, 1987). recording tablets has virtually eliminated these
problems. The accuracy of the digitizer determines
In several clinical studies in which errors between the m i n i m u m measuring e r r o r possible with this
single tracings from duplicate radiographs were system. The errors related t o the recording proce
compared to errors arising from double tracings of dure have t w o c o m p o n e n t s : the precision with
single radiographs, the differences found were small which a marked point on the film or tracing can be
(Bjork, 1947; Solow, 1966; Mitgaard et al, 1974; identified by the cross-hair of the recording device,
H o u s t o n et al, 1986). Therefore, if proper care in and the errors of the digitizing system (Eriksen and
obtaining radiographic records is taken, the errors Solow, 1991). An accuracy of 0.1 mm is desirable,
introduced during this phase can be regarded as neg without any distortion over the surface of the digi
ligible for routine clinical purposes. In order to tizer (Houston, 1979).
control errors during radiographic projection, the
relationships among the X-ray target, the head Although errors of digitizers have been consid
holder, and the film must be fixed (Coben, 1979). ered to be small, it has been shown that digitizers
The metal markers in the ear-rods must be aligned, may suffer from varying degrees of scaling errors
and it is good practice to include a metal scale of and fields of non-linearity (McWilliams, 1980;
known length at the midsagittal plane to provide Kriksen a n d Solow, 1991). Eriksen and Solow
permanent evidence of the enlargement of each radi (1991) have described specific procedures for testing
ograph (Houston, 1983). For special research appli and correcting the digitizers before any routine use
cations, projection errors can be also reduced by a in cephalometric research. Errors of scaling can be
combination of stereo head films and the use of corrected by setting switches in the control unit of
osseous implants (Rune et al, 1977). the digitizer or by scaling the incoming x—y co-ordi
nates by a software programme. Non-linearities can
be corrected by including the DXji and DYji
5.4 The effect of head rotation on the
value of an angle assumed to be measured
in the midsagittal plane. The angle
forehead-nose-chin appears progressively
more obtuse as the head rotates from the
true midsagittal plane. In addition, the
more acute the true angle is, the greater
the distortion will be. (After Baumrind and
Frantz. 1971b; reprinted with permission.)
128
Sources of Error in Lateral Cephatometry
latriccs in the digitizing programme and adjusting tracing of an indistinct structure might help in the
le recorded co-ordinates by the weighted mean of identification of a related landmark (e.g. tracing an
che DXji and DYji values of the four points that incisor's root might help in the identification of the
.'limit the square in which the recorded point is landmark incisor apex).
situated. Finally, weighting should depend on the
location of the recorded point within the square. There is no doubt that electronic plotting devices,
If these requirements are met, measurements per which make repetitive measurements faster and less
formed by digitizer arejnore reliable than those tedious and which introduce facilities like error
obtained with any manual device, owing to the checking routines, can greatly reduce the random
superior accuracy of the digitizer (Richardson, cephalornetric errors.
1981). Moreover, the use of a digitizer allows direct
registration of landmarks on the cephalogram, thus ERRORS IN LANDMARK IDENTIFICATION
eliminating the need for tracing procedures.
Whether this has removed a possible source of error Landmark identification errors are considered the
is still a matter of debate. major source of cephalornetric error (Bjork, 1947;
Hixon, 1956; Savara, 1966; Richardson, 1966,
Richardson (1981) and Cohen (1984) claimed 1981; Carlsson, 1967; Baumrind and Frantz, 1971a;
lat direct observation on untraced lateral head- Sekiguchi and Savara et al, 1972; Gravely and
iates resulted in an increased reliability in Benzies, 1974; Mitgaard et al, 1974; Cohen, 1984).
landmark location, though the differences compared Many factors are involved in this uncertainty. These
paper tracings were not big and represented only factors include:
small part of the total error in landmark location. • the quality of the radiographic image;
)th authors traced only the landmarks and not the • the precision of landmark definition and the
latomic outlines. When these were traced
louston, 1982), the tracings sometimes showed a reproducibility of landmark location; and
lightly higher reproducibility, possibly because the • the operator and the registration procedure.
t)A'4*
**4*
Effect of focal spot size on radiographic sharpness. A ' and B' represent areas of radiographic penumbra with
sequent loss of sharpness. (After Franklin, 1952; reprinted with permission.)
129
Orthodontic Cephalometry
Quality of the radiographic image the film-cassette system and the kV-level used. High
In principle, the quality of a radiograph is expressed kV values tend to level out any differences in radi
in terms of sharpness - blur and contrast - and noise ation absorption, thus reducing the difference in
(Rossmann, 1969; McWilliams and Welander, 1978; grey levels between various tissues. Noise refers to
Hurst et al, 1979; Broch et al, 1981; Kathopoulis, all factors that disturb the signal in a radiograph.
1989). It may be related to:
Sharpness is the subjective perception of the dis • the radiographic complexity of the region (i.e. the
tinctness of the boundaries of a structure; it is radiographic superimposition of anatomical
related to blur and contrast. structures situated in different depth planes) - this
is known as noise of pattern, structure, or
Blur is the distance of the optical density change anatomy; or
between the boundaries of a structure and its sur
roundings (Haus, 1985). It results from three • receptor mottle - this is known as quantum noise.
factors, namely geometric unsharpness, receptor It depends on the sensibility and the number of
unsharpness, and motion unsharpness. radio-sensitive grains present in the film.
Geometric unsharpness is directly related to the
size of the focal spot (5.5) and to the focus-film In principle, structured noise can be reduced by the
distance. Receptor unsharpness depends on the use of cephalometric laminography (Ricketts, 1959),
physical properties of the film and the intensifying but in conventional cephalometry it is unavoidable.
screen. Combinations of fast films and rare earth These types of errors can be minimized by films
intensifying screens are used to reduce the radiation of high quality (Houston, 1983).
exposure, but produce images with poorer defini In recent years, the application of digital tech
tion. It is still a matter of controversy whether the nology to conventional radiography has changed the
loss of sharpness from this source results in signifi parameters of image quality by making it possible
cant differences in the reproducibility of landmark to process the image in order to enhance sharpness
identification (McWilliams and Welander, 1978; and contrast and to reduce noise. It has been argued
Stirrups, 1987). that the main advantage of digital processing may
Movement of the object, the tube, or the film be a reduction in radiation dose due to lower
during exposure results in image blur. By increasing exposure times (Wenzel, 1988). Furthermore, the
the current, it is possible to reduce the exposure contrast and density of a single underexposed image
time, thus reducing the effect of movement. Blur can be adjusted for several diagnostic tasks, thus
from scattered radiation can be reduced using a grid reducing the number of examinations. Jager et al
at the image receptor end. In clinical orthodontic (1989b) presented digital images in which resolu
practice, however, the major parameters that influ tion and the discrimination of anatomical structures
ence the sharpness of cephalograms are the focus- were improved after digital filtering. This improve
to-film distance (geometric unsharpness) and the ment was claimed to be particularly appreciable for
voltage capacity (kV) of the cephalometric equip underexposed radiographs.
ment (motion unsharpness).
Contrast is the magnitude of the optical density Precision of landmark definition and
differences between a structure and its surroundings. reproducibility of landmark location
It plays an important role in radiographic image A clear, unambiguous definition of the landmarks
quality. Increased contrast enhances the subjective chosen is of the utmost importance for cephalo
perception of sharpness, but excessive contrast leads metric reliability. Definitions such as 'the most
to loss of details, owing to blackening of regions of prominent' or 'the uppermost' should always be
low absorption and reverbering of regions of high accompanied by the reference plane that they are
absorption. The contrast is determined by: related to. If the conditions required to record some
• the tissue being examined; landmarks - e . g . Mips in repose', 'centric occlusion',
• the receptor; and or 'head posture' - are ambiguous or neglected, an
• the level of kV used. invalidation of the measurement involved can occur
(Wisth and Boe, 1975; Spolyar, 1987). As it has been
In clinical practice, the most important parameters pointed out by several investigators (Richardson,
influencing the contrast of cephalometric films are 1966; Baumrind and Frant?., 1971a; Broch et al,
130
Sources of Error in Lateral Cephalometry
[1981; Stabrun and Danielsen, 1982; Cohen, 1984; imposed structure. This may cause, for example, dif
I Miethke, 1989), some cephalometric landmarks can ficulty in accurately locating the cusps of posterior
I be located with more precision than others. teeth or the lower incisor apex (Miethke, 1989).
Geometrically constructed landmarks and land- Furthermore, the distribution of errors for many
marks identified as points of change between con landmarks is systematic and follows a typical
vexity and concavity often prove to be very pattern, some landmarks being more reliable in
unreliable. The radiographic complexity of the either the vertical or horizontal plane, depending on
'region also plays an important role, making some the topographic orientation of the anatomic struc
landmarks more difficult to identify. For these tures along which their identification is assessed
reasons, the validity of the use of some cephalo (Baumrind and Frantz, 1971a). The validity of indi
metric landmarks has often been questioned vidual landmarks will also depend on the use the
(Moorrees, 1953; Graber, 1954; Salzmann, 1964; orthodontist is making of them (e.g. some land
marks are designed to assess angular measurements,
Richardson, 1966; Broch et al, 1981). Miethke others to assess linear measurements).
! (1989) found that the landmarks that can be local
ized most exactly are incision superior incisal and Baumrind and Frantz (1971b) pointed out that
incision inferior incisal, with a value of the mean x the impact that errors in landmark location have on
and y standard deviations as polar co-ordinates of angular and linear cephalometric measurements is
0.26 mm and 0.28 mm respectively. A value of up a function of three variables:
to 2.0 mm was observed in the majority of the 33 1. The absolute magnitude of the error in landmark
landmarks in this study, which were, on this basis, location.
considered to be of acceptable reproducibility. 2. The relative magnitude or the linear distance
About 25% of the reference points showed a vari between the landmarks considered for that
ation amounting to more than 2.0 mm (Table 5.1). angular or linear measurement.
Anatomical porion and cephalometric landmarks on 3. The direction from which the line connecting the
the condvle cannot be located accurately and con- landmarks intercepts their envelope of error.
sistently on lateral cephalograms taken in the closed-
mouth position (Adenwalla et al, 1988). The envelope is the pattern of the total error distri
Landmarks located on structures that lie within bution. Since cephalometric landmarks have a non-
the confines of the skull have a greater likelihood of circular envelope of error, the average error
being confounded by noise from adjacent or super- introduced in linear measurements will be greater if
Table 5. \ Value of vector V (the expression of the mean x and y
standard deviations as polar co-ordinates) in mm for all assessed
cephalometric landmarks as expression of the precision in
localization. A smaller value for vector V corresponds to greater
precision in definition of the landmark (Miethke. 1989).
131
Orthodontic Cephalometry
the line segment connecting them to another point location were generally the same. An exception were
intersects the wider part of the envelope. For measures of face height, which were more reliable
example, a greater error is expected when point A for hard tissues. When analysing cephalometric
is used to assess the inclination of the maxillary data, errors in landmark location for points or lines
plane rather than to assess the maxillary prog- common to more measurements can generate mis
nathism, as the direction of the former line is hori leading topographic correlations, which may
zontal to and thus intersects the envelope of error in obscure or exaggerate a true biologic correlation
its broader side (5.6). Therefore, the various (Bjork and Solow, 1962; Solow, 1966; Houston,
cephalometric measurements used have different 1983) (5.7).
reliability since their landmarks, angular measure
ments, or linear measurements are influenced by Errors in landmark identification can be reduced
errors of different origin and whose magnitude if measurements are replicated and their values
greatly varies. averaged. Consecutive evaluation of one cephalo-
gram at random showed that the localization of a
When the reliability of cephalometric soft tissue landmark is more exact the second time than at the
measurements was studied by analysing compara first judgement (Miethke, 1989). The more the
ble hard and soft tissue measures (Wisth and Boe, replications, the smaller the impact of random error
1975), it was found that the errors of landmark on the total error becomes. There is, however, a
.t 5.6 Effect of a non-circular envelope of landmark error on the
i c o m p u t a t i o n of values o f a r e p r e s e n t a t i t i v e m e a s u r e . The
i scattergram of e r r o r for 100 estimates of nasion is shown, with
boxes indicating zones I, 2, and 3 standard deviations of the
i estimating e r r o r in the x and y directions taken separately. It may
i be observed that the errors are greater in the vertical direction
i than in the horizontal d i r e c t i o n . For this reason, other factors
I being equal, a greater e r r o r will be introduced in the computation
/ of the angle sella-nasion-pogonion by the line segment from sella
Ii (A) than by the line segment from pogonion (B). (After Baumrind
and Frantz, 1971a; reprinted with permission.)
•<
■
A J'
Lm
i
•1 •
•
ID
5 . 7 Topographic c o r r e l a t i o n can arise
through random errors in the location of a
p o i n t o r line c o m m o n t o both
m e a s u r e m e n t s . For e x a m p l e , in (a), if
repeated measurements are made of A and
B, the dividing line between them varying at
r a n d o m , t h e r e w i l l be a negative
correlation between their lenghts. In (b).
t w o angular measures share a common line
and random e r r o r s in its orientation will
lead t o a negative c o r r e l a t i o n between
t h e m . O t h e r p o s i t i v e and negative
topographic correlations can arise in this
manner. (After H o u s t o n , 1983; reprinted
with permission.)
132
Sources of Error in Lateral Cepbalometry
practical limit to repeated assessment of cephalo- Another kind of bias can be introduced because
grams, especially for clinical routine. Even for the of subconscious expectations of the operator when
purpose of scientific research, if cross-sectional or assessing the outcome of the scientific research (i.e.
serial measurements from two groups must be the outcome of different treatment results).
compared, duplicate measurements are sufficient Randomization of record measurements or double
(Miethke, 1989). More replications should instead blind experimental designs can be used for reducing
be performed for the evaluation of individual such bias.
changes (Baumrind and Frantz, 1971b; Gravely and
Benzies, 1974; Houston, 1983). When serial records are being analysed, it has
been suggested that all the records of one patient
For specific landmarks, the application of alter should be traced on the same occasion (Houston,
native techniques of radiological registrations can 1983). This minimizes the error variance within
minimize errors in landmark identification. For individual observers, although it increases the risk
■example, if the mandibular condyle is to be used as of bias. Since serial tracing must maintain precise
an important landmark in cephalometric studies, an common landmarks in regions without change
open-mouth cephalogram should be taken. during treatment or growth, landmark location in
Subsequent superimposition on the respective such regions can be identified in one of the cephalo-
! cephalogram in the centric occlusion position can grams and transferred to the other cephalograms of
provide the most accurate and reliable measurement the patient by use of templates of the corresponding
(Adenwalla et al, 1988). Also, if porion is defined structure (e.g. incisal edges of maxillary and
as a machine point rather than an anatomical point, mandibular incisors) (Gjorup and Athanasiou,
higher reliability should be anticipated (Baumrind 1991).
and Frantz, 1971a).
After collection, cephalometric measurements
The operator and t h e registration procedure should be checked for wild values (Houston, 1983).
These values can be expressions of normal variation,
Several studies have pointed out that operator's but sometimes can be attributed to incorrect identi
alertness and training and his or her working fication of a landmark or misreading of an instru
conditions affect the magnitude of the ment.
cephalometric error (Kvam and Krogstad, 1972;
ERRORS IN GROWTH PREDICTION
I Gravely and Benzies, 1974; Houston, 1983). These AND SUPERIMPOSITION
parameters influence landmark identification in a TECHNIQUES
fashion directly related to the difficulty of
identifying each individual landmark. In Growth prediction has been attempted by several
cephalometric studies, the error level, specific to the methods. Growth prediction is quite difficult for a
operator, has to be established, if any meaningful number of reasons (Ari-Viro and Wisth, 1983).
conclusion is to be drawn from the data presented. Among these factors are:
The most important contributions to improve • the wide range of morphological differences;
ment in landmark identification are experience and • the varying rates and directions during the
calibration (Houston, 1983). In studies that
compare two groups of radiographs, the operator growth period;
can introduce different types of systematic error (or • the varying influence of modifying environmen
bias) depending on the design of the study. One type
of operator bias is the operator's variability, which tal factors;
involves both inter-observer variability (the dis • the variation in the timing of the different areas
agreement among observers for theIdentification of
a particular landmark) and intra-observer variabil of active growth; and
ity (the disagreement within the same observer over • the lack of correlation between the size of the
a period of time owing to changes in his or her iden
tification procedure). A good method to reduce this facial structures at an early age and the ultimate
error consists of calibration and periodical recali- adult size.
bration tests to establish specific confidence limits
of reproducibility for each observer (Houston, 1983; Rakosi (1982) has given some good examples of the
Houston etal, 1986). sources of error in growth prediction, including:
• variable growth rate in regional growth sites;
133
Orthodontic Cephalotnetry
• growth pattern not being fully taken into lar and maxillary growth rotations (Bjork and
account; and Skieller, 1972; Skieller et al, 1984). However, a
clinical test t o determine the effectiveness of a
• the relationship of form and function. number of experienced clinicians at predicting
mandibular rotations showed that, independently
Variable g r o w t h r a t e in regional g r o w t h sites of the prediction method used, no judge performed
The mean annual rate of increase in the base of the significantly better than chance (Baumrind et al,
maxilla between the ages of eight and 14 is approx 1984). The method of structural growth prediction
imately 0.8 m m , c o m p a r e d to 1.9 m m in the introduced by Bjork (1963) has been investigated in
mandibular base. During the same period, the another study that used two sets of lateral cephalo-
growth ratio of the S-N length to the mandibular grams of 42 children, taken four years apart before
base ranges from 1:1.35 to 1:1.65 and that of S-Ar and after the pubertal growth period (Ari-Viro and
to A r - G o is approximately 1:1.3. Wisth, 1983). There was no absolute correlation
between the scores for the different criteria and
Growth pattern not being fully taken into mandibular growth rotation during the four years
account of observation.
Many methods do not include consideration of the
growth pattern, and patients are assessed only in According to the authors, this does not mean that
relation to a population mean. Usually growth rates the method is useless, but in cases showing relatively
vary quite considerably for different growth types. small rotational changes the method does not work
Generally speaking, horizontal growth changes are well. In this investigation, n o study of the structur
more predictable than vertical changes. al characteristics was performed in cases showing
extreme anterior or posterior growth rotation.
T h e relationship of form and function Therefore, the main error in growth prediction pro
The inter-relationship of form and function is not cedures is the lack of validity of any method until
taken into consideration. For example, soft tissue now proposed, when it comes to prediction of the
influences in a patient with m a n d i b u l a r retrog- individual. In the light of these results, it is even
nathism can alter a tendency for compensatory pro- doubtful if cephalometric films contain enough
clination of the lower incisors to a dysplastic information about future growth to ever be of pre
retroclination (Melsen and Athanasiou, 1987). dictive value.
The simplest method of prediction assumes that LONGITUDINAL CRANIOFACIAL
growth will take place as a linear expansion along ANALYSIS
the long axis of the structures being examined and
that its a m o u n t is quantified as averaged growth Longitudinal craniofacial analysis is based on super-
increments added progressively through time imposition procedures that vary according to struc
(Johnston, 1975; Popovich and Thompson, 1977). tures used as references within the skull. A number
The major limitation of this method is that individ of methods for growth analysis have been devel
ual variability is not taken into account (Greenberg oped, based on axiomatic rules for superimposition
and Johnston, 1975; Schulhof and Bagha, 1975). on selected reference points and lines, including
cranial base superimposition on N-S, N-Ba,
Individualized prediction has been attempted by Ptm-vertical, basion-horizontal, Bolton-nasion line,
analysing the existing facial pattern. However, the maxillary superimposition on P N S - A N S , and
relationship of existing facial dimensions and of mandibular superimposition on mandibular plane,
previous growth changes to future growth has not XI point, and symphysis (Broadbent et al, 1975;
been found to be of predictive value (Bjork and Ricketts et al, 1979; Bjork and Skieller, 1983;
Palling, 1955; Harvold, 1963; Hixon, 1972) with Baumrind et al, 1983; Coben, 1986; Movers et al,
some exceptions in children with extreme skeletal 1988).
patterns (Schulhof et al, 1977; Nanda, 1988).
Any variation due to remodelling processes that
Prediction of growth direction, particularly for have affected the reference structures can dramati
m a n d i b u l a r r o t a t i o n , has also been attempted in cally change the outcome of the superimposition
implant studies analysing certain structural features and lead to erroneous conclusions about the vectors
(Bjork, 1968), and a qualitative relationship has
been described between these features and mandibu
134
Sources of Error in Lateral Cephalometry
of growth. Therefore, it is important to choose struc ing pin holes, the blink method, or the subtraction
tures subjected to as little remodelling change as technique. When tested, however, all these methods
possible in order to ensure the validity of the meth showed an appreciable error and none of them was
od. In the absence of implants to be used as refer significantly more accurate than the others
ences, some structures of the cranial base have been (Houston and Lee, 1985).
found to be stable through time (Melsen, 1974) (5,8).
A study by Fisker (1979) evaluated the repro
The reproducibility of the superimposition along ducibility of superimpositions on different cranial
the chosen reference structures is another source of structures. Superimposition on structures in the
error (5.9). The precision of tracing superimposi- cranial base proved to have the greatest repro
rions for different reference planes and lines has ducibility. Least reliable was the superimposition on
been found to be very unsatisfactory (Baumrind et zygomatic process. An increase in the interval
al, 1976); precision depends also on the amount of between the recording of the head films in the same
time between the films to be superimposed series appeared to lead to an increase in the error of
(Pancherz and Hansen, 1984). the method when orientating on the zygomatic
process, the palatal structures and the mandible. The
Regardless of the reference planes used, several expediency of using repeated separate measurements
techniques have been claimed to improve the repro of the same dimension on the cephalograms was
ducibility of superimposition, such as best fit direct also concluded by the same investigation.
supermimposition, tracing superimposition, punch-
//?c _rrr^^ 1
s
^ -j"1
$
-A**
vt '^c
v\ i
I \ :<=r— 1: /
;
j
Jl ^* ^w A*"
* ^L
t*|
'•'
I '** v * *■ 1
»* J * II
5.8 Diagrammatic representation of g r o w t h remodelling in the *f * '
cranial base. The variation in the age at which g r o w t h ceases in the ft
different segments is not indicated. (After Melsen. 1974; reprinted *■* f rr *■*
with permission.)
5.9 Errors in superimposition that are due either t o displacement
and remodelling or t o poor reproducibility of the reference points
o r structures may give a false impression of facial g r o w t h . A small
rotation at sella can produce an evident displacement at Menton.
(After Houston and Lee. 1985; reprinted with permission.)
135
Orthodontic Cephalometry
CONCLUSION REFERENCES
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137
Orthodontic Cephalometry
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Sources of Error in Lateral Cephalometry
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13V
Orthodontic Cephalometry
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140
CHAPTER 6
Posteroanterior (Frontal) Cepbalometry
Atbanasios E Athanasiou and Aart JW Van der Meij
INTRODUCTION TECHNICAL ASPECTS
Malocclusions and dentofacial deformities consti CEPHALOMETRIC SET-UP
tute three-dimensional conditions or pathologies.
Although all orthodontic patients deserve an In order to produce a posteroanterior cephalogram,
equally comprehensive three-dimensional diagnos the same equipment that is used for lateral cephalo
tic examination, assessment of posteroanterior and metric projections, as described in chapter 1, is
basilar cephalometric views are of particular impor utilized. The basic apparatus consists of a head-
tance in cases of dentoalveolar and facial asymme holder or cephalostat, an X-ray source, and a
tries, dental and skeletal crossbites, and functional cassette holder containing the film.
mandibular displacements. The transverse dimen
sion of a patient who seeks orthodontic treatment Different ways of producing cephalograms by
requires a diagnostic protocol that includes sys means of different set-ups and patient positioning
tematic evaluation of: in the cephalostat have been described and are still
• the soft tissues, by means of clinical examination used. In all instances, the patient is in an upright
position, either standing or sitting, and is facing the
and photography; film, because this provides the best quality rendi
• the dentofacial skeleton, by means of pos tion of the facial structures that are of primary
interest in orthodontics.
teroanterior cephalograms and submental vertex
X-rays; and In all techniques, it is of paramount importance
• the dentition, by means of dental casts, occluso- that the connection between the X-ray source and
grams and sometimes occlusal X-rays. the cassette holder containing the film is rigid, in
order to maintain a constant relationship of the X-
Since facial asymmetries and crossbites are very ray beam perpendicular to the surface of the
often associated with dysfunction of the stomatog- cassette (Manson-Hing, 1985).
nathic system, an important component of the dif
ferential diagnosis should be the assessment of The initial unit described by Broadbent (1931)
functional and structural status of the patient by consisted of a set-up in which two X-ray sources
means of history, clinical and instrumental func with two cassettes were simultaneously used, so
tional evaluation, occlusal splints, imaging of the that lateral and frontal cephalograms were taken at
tempromandibular joint, and laboratory tests the same time. In this technique, the patient was
(Athanasiou, 1993). placed with the Frankfort horizontal plane parallel
to the floor. The X-ray source exposing the cassette
Since the advent of cephalometric radiography, for the posteroanterior cephalogram was 5 feet
orthodontists have focused on the lateral cephalo (152.4 cm) away from the earpost axis, behind the
grams as their primary source of skeletal and den patient, and the central X-ray beam passed at the
toalveolar data; however, posteroanterior level of the Frankfort horizontal plane and at a 90°
cephalometric projections and relevant analyses angle to the beam of the lateral cephalogram.
constitute an important adjunct for qualitative and
quantitative evaluation of the dentofacial region.
141
Orthodontic Cephalometry
Although precise three-dimensional evaluations N a t u r a l head position
are possible using this technique, it has now been Natural head position is a standardized orientation
almost abandoned since it requires a rather large of the head, which is readily assumed by focusing
equipment with two X-ray sources. on a distant point at eye level (Moorrees, 1985).
Modern equipment uses one X-ray source. Reproducibility of natural head position, assessed
Therefore, following lateral cephalometric regis as the error of a single observation, has been found
tration, the patient must be repositioned if a pos- to be close to 2°, which supports its use in
teroanterior cephalogram has to be produced. A cephalometry (Lundstrom and Lundstrom, 1992).
rj headholder or^ephalostat that can_be rotated 90°
The natural head position cephalometric regis
is used, so that the central X-ray beam penetrates tration has been described in detail in other chapters
the skull of the patient in a posteroanterior direc of this book. If a posteroanterior registration is
tion and bisects the transmeatal axis perpendicu taken in the natural head position, the ear-rods are
larly. The standard distance from X-ray source to placed directly in front of the tragus so that they
patient is 5 feet (152.4 cm). For the posteroanteri lightly contact the skin, thus establishing bilateral
or projection the distance is measured to the earpost head support in the transverse plane (6.2). The radi-
axis. ographic image of ;i metallic chain, hanging on one
side of the film cassette, defines the true vertical
Fixed head position plane on the radiograph.
In the most commonly used technique, the patient In using the natural head position for pos
is fixed in the headholder with the use of two ear- teroanterior cephalometric registrations, some prac
rods, and the patient's head rests on the uppermost tical problems are encountered. The patient's head
side of the rods, which are inserted into the ear is facing the cassette, which makes it difficult for
holes (6.1). Care must be taken that the Frankfort the patient to look into a mirror to register natural
horizontal relationship of the head with the floor is head position (Solow and Tallgren, 1971).
not altered during this procedure. This reproduc Furthermore, space problems in some X-ray equip
tion of the head position in the cephalostat is crucial ment make it impossible to place a nosepiece in
because, when the head is tilted, all vertical dimen front of nasion, lightly touching the skin, as is some
sions measured change. Maintaining the identical times done to establish support in the vertical plane
horizontal orientation from lateral to posteroan (Viazis, 1991).
terior projections is critical when comparative
measures are made from one to the other (Movers
etal, 1988).
6.1 Fixed head position - the patient is 6.2. Natural head position - the ear-rods
fixed in a headholder with the use of the are placed directly in front of the tragus,
two ear-rods and the head rests on the lightly touching the skin, thus establishing
uppermost side of the rods, which are bilateral head support in the transverse
inserted into the ear holes. (Photo: Lars plane. (Photo: Lars Kruse)
Kruse)
142
Posteroanterior (Frontal) Cephalometry
Other techniques o f head positioning ANATOMY
According to Chierici (1981), the patient's head
should be positioned with the tip of the nose and Many anatomical structures located in the anterior,
forehead lightly touching the cassette holder (6.3). middle, and posterior areas of the skull are usually
The author claims that this technique enables better projected in a posteroanterior cephalogram. The
evaluation of patients with craniofacial anomalies anatomical structures of the skull seen from the
that require special attention to the upper face. front are shown in 6.5, and those seen from behind
Faber (1985) has suggested that, in cases of sus are shown in 6.6.
pected significant mandibular displacement, the
posteroanterior cephalogram should be taken with
the mouth of the patient slightly opened (6.4). In R A D I O G R A P H I C A N A T O M Y
this way a differential diagnosis between function
al mandibular displacement and dentoskeletal facial The various structures of the skull that can be seen
asymmetry can be made. in a posteroanterior cephalogram are shown in 6.7
and 6.8. In these two figures, an excellent visual
Exposure conditions and considerations ization of the structures that can be traced has been
Film exposure depends on several factors, includ achieved by wiring the two skulls with fine lead fuse
ing the speed of the film, the speed of the screens, wire. The structures have been labelled alphabeti
the tube-to-film distance, the size of the patient's cally (Broadbent et al, 1975).
head, the milliamperage and kilovoltage used in
generating the X-ray beam, and the film exposure
time (Manson-Hing, 1985). More exposure is nec
essary for posteroanterior cephalograms than for
lateral views (Enlow, 1982).
\
M\
: ! Tracing of a posteroanterior cephalogram taken w i t h the 6.4 Head positioning in cases of significant mandibular
[dent's head positioned w i t h the tip of the nose arid forehead displacement - the cephalogram is taken with the mouth of the
tehtly touching t h e c a s s e t t e h o l d e r . ( A f t e r C h i e r i c i , 1 9 8 1 ; patient slightly opened. (After Faber, 1985; reprinted with
(printed with permission.) permission.)
143
Orthodontic Cephalometry
6.6 The skull seen from behind presents the following anatomical
structures. (After McMinn etal, 1981; reprinted with permission.)
6.5 The skull seen from the front presents the following 1 Sagittal suture
anatomical structures. (After McMinn et al, 1981; reprinted with 2 Parietal foramen
permission.) 3 Lambda
4 Lambdoid suture
1 Frontal bone 18 Anterior nasal spine 5 Parietal bone
2 Glabella 19 Nasal septum 6 Parietal tuberosity
3 Nasion 20 Inferior nasal concha 7 Temporal bone
4 Superciliary arch 21 Mastoid process 8 Mastoid process
5 Frontal notch 22 Zygomaticomaxillary 9 Squamous part of occipital bone
6 Supraorbital foramen 10 External occipital protuberance (inion)
7 Lesser wing of sphenoid suture 11 Supreme nuchal line
23 Infraorbital margin 12 Superior nuchal line
bone 24 Marginal tubercle 13 Inferior nuchal line
8 Superior orbital fissure 25 Frontozygomatic suture 14 Body of the mandible
9 Greater wing of sphenoid 26 Supraorbital margin 15 Angle of the mandible
27 Orbital part of frontal bone 16 Ramus of the mandible
bone 28 Optic canal 17 Occipitomastoid suture
10 Zygomatic bone 29 Posterior lacrimal crest 18 Parietcmastoid suture
11 Inferior orbital fissure 30 Fossa for lacrimal sac
12 Infraorbital foramen 31 Anterior lacrimal crest
13 Maxilla 32 Frontal process of maxilla
14 Mandibular ramus 33 Nasal bone
15 Body of the mandible 34 Frontonasal suture
16 Mental foramen o f the 35 Frontomaxillary suture
mandible
17 Mental protuberance of the
mandible
144
Posteroanterior (Frontal) Cephalometry
6.7 and 6.8 Posteroanterior cephalogram of a skull, wired, and L - Zygomatic arch to key ridge; inferior surfaces of malar bone,
alphabetically labelled in order t o describe structures that can be maxilla, and key ridge
traced. The following structures are identified. (After Broadbent M - Mastoid process
etal. 1975; reprinted w i t h permission.) N - Occipital bone: inferior surface of jugular process, condyles,
A-Crista galli and anterior margin of foramen magnum
8-Nasofrontal suture: external surface O - Occipital bone: posterior border of foramen magnum and
C - Orbital roof: most superior area of inferior surface of orbital most inferior area of lateral part
plate of frontal bone P - Occipital bone: superior surface of area of greatest depth in
D - Orbit: superior border (frontal bone); lateral border posterior fossa (fossa of cerebellum)
(zygoma); inferior border (zygoma and maxillary bones) Q - Occipital bone: cross-section of border of foramen posterior
E- Lesser wing of sphenoid bone: anterior clinoid process to left occipital condyle
F - Planum of sphenoid bone: across planum and down through R - Posterior nasal aperture (choana): vomer. sphenoid, and
optic foramen palatine bones; medial pterygoid plate of sphenoid; and horizontal
G - Petrous portion of temporal bone: superior surface part of palatine bone
H - Greater wing of sphenoid bone: temporal surface and S - Sphenoid bone (cross-section): floor of pituitary fossa through
infratemporal crest foramen lacerum across inferior surface of body of sphenoid bone
I - Maxilla: infratemporal surface d o w n t o and including alveolar between vomer bone and basilar part of occipital bone
process in molar area T A n t e r i o r nasal aperture: nasal bone and maxilla
J - Lateral ptcrygoid plate and greater wing of sphenoid bone; U - Mandible, condyle, neck, lateral border of ramus, and inferior
infratemporal fossa and crest border of body of mandible
K-Zygomatic arch; superior surface of the zygomatic process of V — Coronoid process and mandibular notch
temporal and malar bones and cross-section of zygomatic process W - Ramus: medial surface of posterior part of ramus
of temporal bone at greatest bizygomatic w i d t h
145
.
Orthodontic Cepbalometry
Tracing suggestions patient (i.e. the patient's right should be on the
Before tracing the various skeletal and dental struc examiner's left). The tracing should include most of
tures of a posteroanterior cephalogram, the exami the important structures of the upper, middle, and
ner must ensure that the head position and the lower anterior face as well as of the posterior face.
intermaxillary occlusal relationships that appear in By including relevant structures, which will be pre
the X-ray do not differ significantly from those sented in this chapter, the tracing should allow the
identified during the clinical or photographic eval overall qualitative assessment of the morphology,
uation of the patient or those found in the analysis size, and harmony of the skull.
of dental casts. Any significant deviation between
them may be due to registration errors in one or During the tracing of the posteroanterior cephalo
more of these diagnostic modalities. gram, it is essential to bear in mind where the struc
tures have been identified in the current lateral
Another important step before tracing commences cephalogram of the same patient. In this way, a
is to examine the posteroanterior cephalogram in more meaningful assessment of the information
order to exclude the possibility of pathology of the gathered from both the posteroanterior and the
hard and soft tissues involved (see Chapter 8). lateral X-rays can be achieved. A method for accu
rately relating the lateral to the posteroanterior
The tracing of the posteroanterior cephalogram cephalogram by using the Bolton Orientator has been
should be carried out by placing the cephalogram developed and described by Broadbent et al (1975).
in front of the examiner as if he were looking at the
6.9 Structures that should be included in the
tracing of a posteroanterior cephalogram. The
numbers in the diagram refer to the descrip
tions in the text.
146
Posteroanterior (Frontal) Cephalometry
The tracing of the posteroanterior cephalogram cephalogram, it can nevertheless provide useful
may begin with the midline structures seen in the information and complement our diagnostic tools.
lateral cephalogram and should include the occip Some of the functions of the posteroanterior
ital, parietal, frontal, and nasal bones, the maxilla, cephalometry extend beyond the traditional appli
the sphenoid bone, and the symphysis of the cations of determining breadth and symmetry.
mandible (Broadbenr et al, 1975).
Gross inspection
Furthermore, the authors of this chapter suggest Gross inspection of a posteroanterior cephalogram
that the following structures should be included in can provide useful information concerning overall
the tracing of the posteroanterior cephalogram. The morphology, shape, and size of the skull, bone
numbers refer to the diagram of 6.9. Other struc density, suture morphology, and possible premature
tures may be added, depending on the needs of the synostosis. Furthermore, it can contribute to the
examiner. detection of pathology of the hard and soft tissues
(see 6.10).
1. External peripheral cranial bone surfaces.
2. Mastoid processes. Description and comparison
3. Occipital condyles. Description of the skull by means of a posteroan
4. Nasal septum, crista gaHi, and floor of the terior cephalogram can be accomplished by com
parison with other patients or with existing
nose. appropriate norms (Solow, 1966; Wei, 1970;
5. Orbital outline and inferior surface of the Ricketts et al, 1972; Broadbent et al, 1975;
Ingerslev and Solow, 1975; Svanholt and Solow,
orbital plate of the frontal bone. 1977; Costaras et al, 1982; Droschl, 1984; xMoyers
6. Oblique line formed by the external surface of et al, 1988; Athanasiou et al, 1991; Athanasiou et
al, 1992).
the greater wing of the sphenoid bone in the
area of the temporal fossa. Diagnosis
7. Superior surface of the petrous portion of the Meaningful diagnostic information can be collect
temporal bone. ed from posteroanterior cephalograms by several
8. Lateral surface of the frontosphenoid process reliable methods and analyses. The diagnostic
of the zygoma and the zygomatic arch, includ purpose of the posteroanterior cephalogram is to
ing the key ridge. analyse the nature and origin of the problem, thus
9. Cross-section of the zygomatic arch. providing the possibility of quantification and clas
10. Infratemporal surface of the maxilla in the sification.
area of the tuberositv.
11. Body and rami, coronoid processes, and
condyles of the mandible, when visible.
12. As many dental units as possible.
POSTEROANTERIOR Treatment planning
CEPHALOMETRIC LANDMARKS Some of the diagnostic information that can be
gathered from a posteroanterior cephalogram after
Several cephalometric analyses have been proposed appropriate elaboration and analysis should be
since posteroanterior cephalometry was introduced. valuable enough to be used to produce a compre
These analyses use various landmarks. An attempt hensive and precise treatment plan with regard to
for <m almost all-inclusive presentation of these the specific orthodontic, orthopaedic, or surgical
landmarks, together with their description, has been treatment goals for the individual patient.
made in 6.10.
Growth assessment and evaluation of
PURPOSES O F P O S T E R O A N T E R I O R treatment results
CEPHALOMETRY Growth assessment by means of posteroanterior
cephalometry is difficult but it is possible. The main
Although superimposition of several structures problems are related to the absence of well-defined,
makes interpretation of a posteroanterior cephalo stable (or relatively stable) structures for the super-
gram more difficult than interpretation of a lateral imposition of the subsequent cephalometric tracings,
and to the difficulties in obtaining consecutive
147
Orthodontic Cephalometry
6.10 Definitions of posteroanterior cephalometric landmarks. The landmarks are presented with their most usual names.
ag - antegonion - the highest point in the antegonia/ notch (left and right)
ans — anterior nasal spine
cd - condylar - the most superior point of the condylar head (left and right)
cor - coronoid — the most superior point of the coronoid process (left and right)
i i f - incision inferior frontale - the midpoint between the mandibular central incisors at the level of the incisal edges
isf - incision superior frontale - the midpoint between the maxillary central incisors at the level of the incisal edges
Ipa - lateral piriform aperture - the most lateral aspect of the piriform aperture (left and right)
lo - latero-orbitale - the intersection of the lateral orbital contour with the innominate line (left and right)
m - mandibular midpoint - located by projecting the mental spine o n the lower mandibular border, perpendicular t o the line ag-ag
Im - mandibular molar - the most prominent lateral point on the buccal surface of the second deciduous o r first permanent mandibular
molar (left and right)
ma - mastoid - the lowest point of the mastoid process (left and right)
mx - maxillare - the intersection o f the lateral contour o f the maxillary alveolar process and the l o w e r c o n t o u r o f the maxillozygomatic
process of the maxilla (left and right)
um - maxillary molar - the most prominent lateral point on the buccal surface of the second deciduous o r first permanent maxillary
molar (left and right)
m o - medio-orbitale - the point o n the medial orbital margin that is closest t o the median plane (left and right)
mf - mental foramen - the centre of the mental foramen (left and right)
om - orbital midpoint - the projection on the line lo-lo of the top of the nasal septum at the base of the crista galli
za - point zygomatic arch - point at the most lateral border of the centre of the zygomatic arch (left and right)
tns - t o p nasal septum - the highest point on the superior aspect of the nasal septum
mzmf - zygomatic ofrontal medial suture point-in - point at the medial margin of the zygomaticofrontal suture (left and right)
Izmf - zygomaticofrontal lateral suture point-out - point at the lateral margin of the zygomaticofrontal suture (left and right)
148
Posteroanterior (Frontal) Cepbalometry
cephalograms in a standardized manner with regard left-sided and right-sided as well as upper and lower
to head posture and skull enlargement. face, can be examined concerning their vertical
dimension, position and proportionality. The
In patients who are not growing, evaluation of analysis proposed by Grummons and Kappeyne van
treatment results can be accomplished by superim de Coppello (1987) contains quantitative assess
posing the tracings of the subsequent posteroante ment of vertical dimensions and proportions.
rior cephalograms on the external peripheral cranial Vertical asymmetry can be observed readily in a
bone outline or on any of the reference horizontal posteroanterior cephalogram by connecting bilat
planes whose structures have not been influenced eral structures or landmarks, by drawing the trans
by the specific treatment. The cephalograms should verse planes, and by observing their relative
betaken at different time intervals in a standard orientation (Sollar, 1947; Proffit, 1991).
ized manner with regard to head posture and mag
nification. Since the primary indication for obtaining a pos
teroanterior cephalomctric film is the presence of
Assessment of growth and treatment results can facial asymmetry (Proffit, 1991), many analyses
be done without superimposing the different contain variables and measurements of the trans
cephalograms or tracings. Critical interpretation of verse dimension. After establishing the midsaggital
the characteristics and relationships of the various plane, linear measurements, angular measurements,
craniofacial structures, or comparison of the and proportional measurements can be made in
various measurements, can provide significant order to evaluate the severity and degree of asym
information concerning changes that took place metry or transverse deficiency (Ricketts et al, 1972;
during the period of observation. Svanholt and Solow, 1977; Moyers et al, 1988;
Athanasiou et al, 1992). Relating the midline land
POSTEROANTERIOR marks to the midsagittal plane will provide a qual
CEPHALOMETRIC ANALYSES itative evaluation to help clarify the source of the
asymmetry. Vertical planes constructed through the
AIMS AND MEANS angles of the mandible and the outer borders of the
zygomatic arch can also highlight asymmetry in the
Most of the posteroanterior cephalomctric analyses position of these structures (Proffit, 1991).
described in the literature are quantitative, and they
evaluate the craniofacial skeleton by means of Landmarks and variables that can be identified
linear absolute measurements of: on coronal planes of different depths in the same
• width or height (Solow, 1966; Ricketts et al, posteroanterior cephalogram can provide useful in
formation concerning the vertical, transverse, and
1972; Ingerslev and Solow, 1975; Movers et al, sagittal dimensions of the craniofacial skeleton. The
1988; Nakasima and Ichinose, 1984; Grummons multiplane analysis developed by Grayson et al
and Kappeyne van de Coppello, 1987; (1983) is the best and most complete method in this
Athanasiou et al, 1992); category.
• angles (Ricketts et al, 1972; Svanholt and Solow,
1977; Droschl, 1984; Grummons and Kappeyne LIMITATIONS
vande Coppello, 1987; Athanasiou et al, 1992);
• ratios (Costaras et al, 1982; Grummons and Measurements on posteroanterior cephalograms,
Kappeyne van de Coppello, 1987; Athanasiou et like those on lateral cephalograms, are subject to
al, 1992); and errors that may be related to the X-ray projection,
• volumetric comparison (Grummons and the measuring system, or the identification of land
Kappeyne van de Coppello, 1987). marks.
The different structures of the craniofacial complex It is possible to produce linear measurements on
can also be analysed using qualitative methods the posteroanterior cephalometric film, but precise
(Sollar, 1947; Grayson et al, 1983; Proffit, 1991). measurements of details are likely to be misleading.
There is a chance that the apparent distance will be
A posteroanterior cephalogram can be analysed affected by a tilt of the head in the headholder, as
so that the vertical, transverse, and sagittal dimen this is more difficult to control in posteroanterior
sions can be evaluated. Different structures, both than in lateral cephalograms (Proffit, 1991). For the
149
Orthodontic Cephalometry
same technical reason, angular measurements can METHODS OF ANALYSES
also be influenced in an uncontrolled manner.
Ricketts analysis
Cephalometric variables that describe width are This analysis incorporates the following measure
least affected by postural alterations of the head ments (6.11) whose clinical norms are presented in
during registrations. According to an earlier inves Table 6.1 (Ricketts et al, 1972).
tigation concerning the geometric changes on the • nasal cavity width - measured from NC to NC
posteroanterior headfilm in the various head posi
tions, a change of ± 10° of up—down movement or (widest points in nasal capsule). In clinical diag
right-left rotation is less than the method error and nosis this measurement is used in combination
is, therefore, a negligible factor in breadth mea with the palatal plane;
surements (Ishiguro et al, 1976). • mandibular width - measured from Ag to Ag (at
trihedral eminence above notch);
The use of ratios in a posteroanterior cephalo • maxillary width - two frontal lines, left and
metric investigation is advantageous. This is because right, are constructed from the medial margins
the results can be used for comparison with other of the zygomaticofrontal sutures to Ag points,
persons or groups whose radiographs have been and the maxillarv width is evaluated on left and
taken with uncontrolled or unknown enlargement right sides separately by relating J point or point
of the different structures of the skull on the X-ray jugale (defined as the crossing of the outline of
film (Athanasiou et al, 1992). However, diagnos the tuberosity with that of the jugal process) to
tic interpretation of ratios for clinical applications these lines. In this way the maxillary width is
in individual cases is difficult and often unclear. evaluated in relation to the mandible;
• symmetry - a midsagittal plane is constructed by
dropping a line through the top of the nasal
septum or crista galli, perpendicular to the line
Table 6.1. Clinical norms for the Rickett's posteroanterior 6.1 I Variables used in the posteroanterior analysis of Ricketts et
cephalometric analysis (Ricketts et al, 1972). al (1972).
150
Posteroanterior (Frontal) Cepbalometry
connecting the centres of the zygomatic arches. Svanholt and Solow analysis
Asymmetry is evaluated by relating point ANS
and pogonion to this midsagittal plane; This method aims to analyse one aspect of trans
• intermolar width - measured from the buccal verse craniofacial development, namely the rela
surface of the first permanent molars transversely; tionships between the midlines of the jaws and the
dental arches (Svanholt and Solow, 1977). This
• intercuspid width - the width between the tips of analysis incorporates variables that have been
designed to be zero in the symmetrical subject (6,12,
the lower cuspids; 6.13).
• denture symmetry - the midpoints of the upper • transverse maxillary position - mx-om/ORP;
• transverse mandibular position - m-om/ORP;
and lower central incisor roots are related to the • transverse jaw relationship - CPL/MXP;
midsagittal plane; • upper incisal position - isf-mx/MXP;
• lower incisal position — iif-m/MLP;
• upper to lower molar relation - the differences • upper incisal compensation - isf-mx/m;
in width between the upper and lower molars.
The measurement is made at the most prominent
buccal contour of each tooth.
6.12 Reference points and lines used in the posteroanterior
cephalometric analysis suggested by Svanholt and Solow (1977).
(After Svanholt and Solow. 1977; reprinted with permission.)
6.13 Angles used in the posteroanterior
cephalometric analysis suggested by
Svanholt and Solow (1977). (After
Svanholt and Solow, 1977; reprinted with
permission.)
15!
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