Artículo referente ala ATM

1. Condylar position assessed by magnetic
resonance imaging after various bite
position registrations
Sanjivan Kandasamy,a
Rudolf Boeddinghaus,b
and Estie Krugerc
Nedlands and Subiaco, Western Australia, Australia, and St Louis, Mo
Introduction: In this study, we evaluated the reliability and validity of 3 bite registrations in relation to condylar
position in the glenoid fossae using magnetic resonance imaging in a symptom-free population. Methods: Nine-
teen subjects, 14 men and 5 women (ages, 20-39 years) without temporomandibular disorders were examined.
Three bite registrations were taken and evaluated on each subject: centric occlusion, centric relation, and Roth
power centric relation. The differences in condyle position among the 3 bite registrations were determined for the
left and right condyles: centric occlusion-centric relation, centric occlusion-Roth power centric relation, and
centric relation-Roth power centric relation for each plane of space. Results: The results indicated that (1) all
measurements collected had large standard deviations and ranges with no statistical significance, and (2) of
the 19 subjects and 38 condyles assessed, 33 condyles (87%) were concentric in an anteroposterior plane.
In the transverse anatomic plane, all condyles were concentric. Conclusions: The clinical concept of positioning
the condyles in specific positions in the fossae with various bite registrations as a preventive measure for tempo-
romandibular disorders and as a diagnosis and treatment planning tool is not supported by this study. (Am J
Orthod Dentofacial Orthop 2013;144:512-7)
T
he relationship among condylar position, occlu-
sion, and temporomandibular disorders (TMD)
has been the subject of much debate in dentistry
for more than a century. A significant part of the debate
involves establishing coincidence between a specific
definition of centric relation and centric occlusion. It is
believed by many gnathologists and the like that failure
to achieve this position will predispose patients to devel-
oping TMD in the future.1
Despite the lack of data available to support this
assertion, many dentists continue to persist in marrying
a particular definition of centric relation with centric oc-
clusion as a main goal of treatment. With the current
emphasis in dentistry on evidence-based decision-mak-
ing, the routine establishment of centric occlusion with
centric relation in all patients is subject to question.
Centric relation is defined as a position of the con-
dyles in the glenoid fossae, irrespective of the occlusion
or tooth contact. Centric occlusion is an interocclusal
dental position of the maxillary teeth relative to the
mandibular teeth. Over the past half century, the defini-
tion of centric relation has evolved from a posterior po-
sition of the condyle in relation to the glenoid fossa to a
posterosuperior position to eventually an anterior and
superior position.2-6
Before 1968, centric relation was
considered to be a retruded (posterior) condylar
position. The latest edition of the Glossary of
Prosthodontic Terms defines centric relation as “a
maxillomandibular relationship in which the condyles
articulate with the thinnest avascular portion of their
respective disks with the complex in the anterosuperior
position against the slopes of the articular eminences.”6
Contemporary orthodontic gnathologists believe in
attaining an anterosuperior condyle position at the
a
Clinical associate professor, Department of Orthodontics, School of Dentistry,
University of Western Australia, Nedlands, Western Australia, Australia; adjunct
assistant professor, Center for Advanced Dental Education, Saint Louis Univer-
sity, St Louis, Mo.
b
Clinical senior lecturer, School of Surgery, University of Western Australia, Ned-
lands; and Perth Radiological Clinic, Subiaco, Western Australia, Australia.
c
Associate professor, Dental Public Health, Faculty of Medicine, Dentistry and
Health Sciences, University of Western Australia, Nedlands, Western Australia,
Australia.
All authors have completed and submitted the ICMJE Form for Disclosure of Po-
tential Conflicts of Interest, and none were reported.
Funded by the Australian Society of Orthodontists Foundation for Research and
Education.
Reprint requests to: Sanjivan Kandasamy, Department of Orthodontics, School of
Dentistry, University of Western Australia, 17 Monash Ave, Nedlands, 6009, WA,
Australia; e-mail, sanj@kandasamy.com.au.
Submitted, May 2013; revised and accepted, June 2013.
0889-5406/$36.00
Copyright Ó 2013 by the American Association of Orthodontists.
http://dx.doi.org/10.1016/j.ajodo.2013.06.014
512
ORIGINAL ARTICLE

2. same time the teeth are in centric occlusion (centric rela-
tion equals centric occlusion); however, there is little or
no scientific evidence to support this view.7
Dentists who
believe in establishing a coincidence of a specific defini-
tion of centric relation with centric occlusion
unnecessarily subject their patients to procedures that
might include orthodontics and irreversible bite-
altering procedures, leading to significant financial
and biological costs to their patients. In fact, the evi-
dence supports the contrary notion. According to Alex-
ander et al,8
magnetic resonance imaging (MRI) data
of the temporomandibular joint showed that condyles
are not located in the assumed positions as advocated
by certain centric bite registrations such as retruded
centric relation and leaf-gauge generated centric rela-
tion registrations. Centric bite registrations attempting
to locate retruded (posterosuperior) centric relation
and contemporary anterosuperior centric relation do
not correspond to the condyle positions of people
without TMD. The location of the condyles in the gle-
noid fossa, irrespective of position, has not been demon-
strated to be consequential to the presence or absence of
TMD symptoms.9-12
The Roth power centric relation is perhaps the most
commonly used contemporary gnathologic record aimed
at attaining an anterosuperior centric relation position.
To date, MRI has not verified the actual anatomic posi-
tion of the condyles when this bite registration is taken.
The condylar positions in centric occlusion and Roth
power centric relation have only been studied on articu-
lators with mandibular or condylar position indicators.
The validity of this approach has been questioned and
is not supported by MRI data, presumably the most ac-
curate ionizing radiation-free means of assessing 3-
dimensional condyle-disc-fossa relationships.13
In this
study, condylar position was assessed using MRI after
the use of 3 common bite registrations: centric occlu-
sion, retruded centric relation, and the so-called Roth
power centric relation.14-16
MATERIAL AND METHODS
Ethics approval for this study was obtained from the
Human Research Ethics Committee at the University of
Western Australia. Guided by a power analysis, a sample
of 19 subjects was studied.
The subjects were 14 men and 5 women (ages, 20-39
years) who met the following criteria: (1) permanent
dentition, (2) no congenital craniofacial anomaly or syn-
drome, (3) no skeletal asymmetry or premature tooth
contacts leading to any functional mandibular displace-
ments, (4) no history of trauma to the face or jaws, (5)
positive overjet and overbite, (6) no TMD signs or symp-
toms (all subjects underwent a TMD examination based
on the Research Diagnostic Criteria for TMD; although
clicking without other symptoms does not indicate pa-
thosis or dysfunction, subjects with clicking were
excluded from the study17
), and (8) completed an MRI
safety screening check.
Each participant was also informed of the risk of
finding any incidental pathology after the MRI scan,
but no significant incidental pathology was found.
To standardize the bite registration technique, all
records were taken by the same investigator (S.K.). Three
bite positions were assessed. The first was centric occlu-
sion, with the subject biting together in maximum inter-
cuspation.
The remaining 2 bite registrations were taken in wax
(blue wax; Delar, Lake Oswego, Ore).
Retruded centric relation was taken by applying
distal pressure to the chin and taking a wax record at
the first point of light occlusal contact. All subjects ex-
hibited a discrepancy between centric relation and
centric occlusion. By taking a record at the first point
of light occlusal contact, we were able to establish a
reference point to base our repeated measurements.
This proved to be a highly reproducible registration
technique in this study.
Roth power centric relation was taken with a 2-
piece wax registration consisting of anterior and poste-
rior sections.14-16
The anterior section was first
constructed at a vertical where the posterior teeth are
at least 2 mm apart. This piece of wax was chilled
and allowed to harden. This wax was then placed
back into the mouth, a softened posterior section was
placed, and the patient was instructed to bite. The
mandibular anterior teeth were guided into the
hardened anterior section of wax without a slide into
the indentations. As the patient closed into the
hardened anterior section, he or she was instructed to
“close firmly and hold.” The posterior section was
chilled with air. When the posterior section had
hardened sufficiently to prevent distortion, both wax
sections were removed and chilled.
Once the hard wax bite registrations were obtained,
they were used to position the subjects' mandibles in
the various occlusal positions as the MRI data were ob-
tained. Originally, acrylic records of the bite positions
were fabricated after the articulation of plaster, with
the assumption that they would be more accurate. We
found, however, that these acrylic records distorted
significantly during the fabrication process and provided
an inaccurate reflection of the bite records. Since the
changes in the bite positions were small, this would
have significantly affected the results. We then decided
to use the hard wax records, which were stable and
more accurate.
Kandasamy, Boeddinghaus, and Kruger 513
American Journal of Orthodontics and Dentofacial Orthopedics October 2013 Vol 144 Issue 4

3. MRI scans of each subject were acquired as the sub-
jects occluded at each of the 3 bite relationships. All
scans were performed on the same MRI scanner (1.5 T,
Signa Excite; General Electric, Fairfield, Conn). Scans
were performed with dedicated phased array surface
temporomandibular joint coils. An initial low-resolution
T1-weighted (repetition time [TR]: 340 ms; echo time
[TE], 8 ms) axial localizing scan was followed by a
high-resolution T2-weighted (TR 2800 ms, TE 72 ms)
sagittal oblique scan acquired perpendicular to the
long axis of each condyle (Fig 1). The MRI scans were in-
terpreted by a head and neck radiologist (R.B.) with 8
years of experience reading MRIs of the temporoman-
dibular joint. He was blinded as to which bite registration
he was assessing in each subject, and the order of scan-
ning was randomized by the MRI technician. On each
side and in each position, measurements of the antero-
posterior and superoinferior positions of the condyle
with respect to the temporal bone were measured using
the following standard cortical bony landmarks: for the
anteroposterior position, the anterior margin of the
condyle and the summit of the articular eminence; for
the superoinferior position, the highest point of the
condyle and the deepest concavity of the glenoid fossa
(Fig 2).
From the sagittal and transverse anatomic plane MRI
views, the radiologist evaluated the concentricity of the
left and right condyles in the glenoid fossa in the centric
occlusion position. This was done by dividing the
condyle into thirds and determining which third was
within the central point of the glenoid fossa.
Guided by a power analysis, the 19 subjects were
studied to produce 80% power to detect mean differ-
ences of at least 1 mm at the 0.05% level of signifi-
cance.
To assess the variability and reproducibility associ-
ated with taking the centric occlusion, centric relation,
and Roth power centric relation bite registrations, 3
sets of each were recorded on 3 separate occasions on
2 subjects. These readings were analyzed by a 1-way
repeated-measures analysis of variance (ANOVA), which
showed no significant (P0.05) difference between the
repeated positions, an indication that this method of
determining centric occlusion, centric relation, and
Roth power centric relation is reliable.
One observer (the radiologist, R.B.) made all mea-
surements, 3 times on 2 randomly chosen subjects
with a 1-week interval between measurements. Intra-
class correlation coefficients (ICC) were used to deter-
mine the intraobserver reliability, and 95% prediction
limits for the errors in measurement are provided. A
mean ICC of 0.992 was determined, with an upper limit
of 0.995 and a lower limit of 0.985.
Statistical analysis
For both the left and right condyles, the differences in
condyle position among the 3 bite registrations were
determined: centric occlusion-centric relation, centric
occlusion-Roth power centric relation, and centric
relation-Roth power centric relation for each plane of
space. The data were analyzed by 1-way ANOVA and
by randomized block 1-way ANOVA with Tukey
follow-ups.
RESULTS
For both the left and right condyles, the differences
in condyle position between the different bite registra-
tions were determined as follows: centric occlusion-
centric relation, centric occlusion-Roth power centric
Fig 1. Axial low-resolution T1-weighted planning scan
(A), showing the plane for planning the oblique sagittal
scans (white lines) perpendicular to the long axis of
each condyle (C). Note that there is frequently some
asymmetry of the axes of the condyles, as in this
case. The resultant high-resolution T2-weighted sagittal
oblique image (B), showing the articular disc (between
arrows), the mandibular condyle (C), and the articular
eminence (AE) of the temporal bone.
514 Kandasamy, Boeddinghaus, and Kruger
October 2013 Vol 144 Issue 4 American Journal of Orthodontics and Dentofacial Orthopedics

4. relation, and centric relation-Roth power centric rela-
tion for each plane. The results are presented in the
Table.
All measurements collected had no statistical signif-
icance given the large associated standard deviations
and ranges. Interestingly, asymmetric and opposite
changes were noted between the left and right condyles
between the bite registrations. Qualitatively, the only
measurement with the only noticeable and similar sym-
metric difference at both condyles was the difference be-
tween centric occlusion and Roth power centric relation
bite registrations. Although it was statistically not signif-
icant, both condyles were located more superiorly in the
Roth power centric relation bite registrations by 0.28
mm on average.
Of the 19 subjects and the 38 condyles assessed, 33
condyles (87%) were concentric in an anteroposterior
plane. The remaining 5 were positioned posteriorly.
No pair of condyles had been positioned posteriorly.
In the transverse anatomic plane, all condyles were
concentric.
DISCUSSION
Based on our findings, the differences between the 3
bite positions were small and, more importantly, highly
variable. Since 87% and 100% of the condyles were
concentric in the glenoid fossa in centric occlusion in
the anteroposterior and transverse planes, respectively,
we can safely infer that any significant positioning
that would occur from the centric relation and the
Roth power bite registrations would be detectable. If
the condyles were not concentric in centric occlusion,
this would lead to much ambiguity in terms of condylar
positioning that would occur with the bite registrations.
Our findings show that the posterior condylar posi-
tioning and the anterosuperior condylar positioning
associated with centric relation and Roth power centric
relation bite registrations, respectively, do not occur.
Variability in the findings between the bite registrations
appear to reflect the lack of accuracy and predictability
in these bite registration processes, especially in terms
of determining and positioning the condyles in certain
locations of the glenoid fossae. Based on the findings
that we are not positioning the condyles in specific po-
sitions in the fossae with various bite registrations, the
clinical significance followed by the routine practice of
condylar positioning must be questioned. Hence, previ-
ous studies reporting any changes as a result of these
centric relation bite registrations14,15,18-21
and studies
using these centric relation bite registrations to assess
and report any differences between nongnathologically
treated and gnathologically treated orthodontic
patients would appear to be invalid.22-24
The variability in the findings might be related to the
asymmetry in the long axes of each pair of condyles in
each subject. This is a normal finding,25
and this asymme-
try prevents each pair of condyles from functioning like a
hinge axis as originally proposed by the flawed terminal
hinge axis theory of Posselt.26
The presence of 2 asym-
metrically angulated condylar long axes would naturally
lead to condyles translating and rotating simultaneously
as soon as mandibular opening and closing is initiated.27
The Roth power bite registration is taken when there
is at least 2 mm of separation at the posterior teeth. This
bite registration is then transferred onto an articulator,
with its known inaccuracies, to facilitate mounting of
the upper and lower study casts.28,29
After removal of
the bite registration after the mounting, the upper and
lower casts close down to occlude, reducing the
vertical dimension. Since the condyles rotate and
Fig 2. Reference points for measurement: this is a
sagittal oblique scan from the center of the condyle. The
anteroposterior measurement (A, thick white line) is
made from the anterior cortical margin of the condyle to
the summit of the articular eminence. The superoinferior
measurement (B, thick white line) is made from the high-
est point of the condyle to the highest point (deepest con-
cavity) of the glenoid fossa.
Kandasamy, Boeddinghaus, and Kruger 515
American Journal of Orthodontics and Dentofacial Orthopedics October 2013 Vol 144 Issue 4

5. translate on mandibular opening and closing, this
further reduces the validity of determining or
establishing any position of the condyles in the
glenoid fossae from centric relation to centric
occlusion. Furthermore, if the Roth power bite
registration is taken when there is at least 2 mm of
separation at the posterior teeth, then this is the
position of the condyles at that particular vertical
dimension. This would lead to the assumption that
every patient's vertical dimension is planned to be
opened to at least 2 mm during orthodontic treatment
to establish this particular Roth power centric relation.
We must ask then ourselves, “What happens if further
bite opening or closing occurs during treatment?”
It would appear from the data that if we cannot accu-
rately predict and position condyles in certain locations
in the fossae, then the original position of the condyles
in centric occlusion is a reasonable physiologic guide
on which to base treatment. These findings appear to
support the logical and more compelling notion that
any procedure that deviates or positions the condyles
away from a position they naturally occupy is not only
unphysiologic but perhaps also potentially harmful to
the patient in the long term.
When centric relation bite registration procedures are
carried out in children, it appears that little consideration
is given to any growth-related changes during treatment
in terms of trying to establish and then maintaining this
particular centric relation. Not only are there cranial
base, maxillary, and mandibular growth changes, but
also condylar growth changes and glenoid fossae remodel-
ing.30
This would mean that centric relation bite registra-
tions need to be taken regularly during treatment to
accommodate any growth-related changes; this is not
done. This further reduces the validity of establishing any
particular centric relation before, during, and after ortho-
dontic treatment.
Because the practice of positioning condyles in spe-
cific positions in the fossae routinely to mitigate or pre-
vent TMD has been followed for the last several decades,
it would appear that condyles might have been placed
unpredictably in the glenoid fossae, while clinicians
have assumed otherwise.31-35
According to our
findings, any observed reduction in TMD after
treatment involving condylar positioning with different
bite registrations would most likely be related to
observer bias, the biopsychosocial medical model, the
cyclical nature of TMD, and the placebo effect, rather
than to some specific positioning of the condyles in
the fossae that was actually random.36,37
Because of
the small and unpredictable nature of condylar
positioning associated with centric relation and Roth
power bite registrations, advocating this modality
routinely in clinical practice as a prophylactic measure
for TMD is invalid and unjustified.
According to our findings and the available evidence-
based literature, treatment philosophies based on clin-
ical assumptions purporting an improved long-term
functional superiority of one centric relation to another
is unsupported and clinically insignificant.
CONCLUSIONS
Our data fail to support the claim that certain bite
registrations can accurately and predictably position
condyles into specific locations in the glenoid fossae.
These findings question the physiologic and clinical rele-
vance of certain treatment philosophies that aim to
orthodontically establish occlusions around a particular
centric relation position.
Table. Means, ranges, and standard deviations (mm) for the left and right condyles of the differences in condyle po-
sition between the bite registrations for each plane
Plane Reference Side Mean (SD) Minimum Maximum
Anteroposterior CO-CR Right 0.16 (0.90) À1.20 2.90
Left À0.16 (0.58) À1.00 1.20
CO-Roth CR Right À0.03 (0.78) À1.20 1.30
Left À0.14 (0.80) À1.50 1.70
CR-Roth CR Right 0.19 (0.89) À2.40 0.90
Left 0.01 (0.57) À0.90 1.30
Superoinferior CO-CR Right 0.26 (0.43) À0.70 1.30
Left À0.04 (0.43) À0.80 0.60
CO-Roth CR Right 0.21 (0.53) À0.70 1.40
Left 0.36 (0.43) À0.90 0.80
CR-Roth CR Right À0.06 (0.43) À0.90 0.80
Left 0.07 (0.28) À0.60 0.50
CO, Centric occlusion; CR, centric relation.
516 Kandasamy, Boeddinghaus, and Kruger
October 2013 Vol 144 Issue 4 American Journal of Orthodontics and Dentofacial Orthopedics

6. ACKNOWLEDGMENTS
We thank the Perth Radiological Clinic for subsidiz-
ing the costs of the MRI scans, Jodie Panagopoulos at
Perth Radiological Clinic, Dr Kandasamy's clinical staff
for their involvement, and Marc Tennant for facilitating
the ethics approval of this study.
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