Articulators in orthodontics an evidencebased

SPECIAL ARTICLE
Articulators in orthodontics: An evidence-
based perspective
Donald J. Rinchusea
and Sanjivan Kandasamyb
Pittsburgh, Pa, and Perth, Australia
W
hether to mount cases on an articulator has
been a heated debate in orthodontics for at
least 3 decades.1-36
Articulators can be use-
ful for gross ﬁxed and removable prosthodontics and
orthognathic surgical procedures to at least maintain a
certain vertical dimension while preclinical laboratory
procedures are performed on dental casts.25
However,
their validity in orthodontics is equivocal. A recent
survey of randomly selected subscribers of the Journal
of Clinical Orthodontics in 2001 showed that about
21% of the respondents routinely mounted models,
44% mounted models occasionally, and 35% never
mounted models. The differing opinions ranged from
those who mounted models for gnathologic or temporo-
mandibular disorder (TMD) considerations to those
who believed that there was no rationale for mount-
ing.37
The evidence-based paradigm has 3 hierarchical
model levels.38,39
Model level #3, a systematic review
of literature involving a meta-analysis, is the highest
level.38
With this in mind, there is no systematic review
(evidence-based model #3) of mounting in orthodon-
tics, and it does not appear that there will be one soon.
Therefore, the decision to mount should be based on an
evaluation of the best available research data in which
the data from sample studies (evidence-based model
#2) are considered superior to case studies, anecdotal
reports, and clinicians’ personal clinical experiences
(evidence-based model #1).38
When logical and prac-
tical considerations are added to the evaluation of the
scientiﬁc data, we argue against the need to mount in
orthodontics. Hence, this article is a position statement
supported by evidence-based model #2, and argues that
the use of articulators in orthodontics is an unnecessary
diagnostic procedure. We consider both sides of the
issue of mounting.
THE VIEW IN FAVOR OF MOUNTING
Supporting a gnathologic view of occlusion and
condyle position, Dr Ron Roth in the early 1970s
advocated that orthodontists should perform pretreat-
ment diagnostic articulator mounting.1
Roth1-5
believed
that pretreatment articulated centric-relation (CR)
mounted models would best aid the orthodontist in
identifying the so-called “Sunday bite” and the minutia
of occlusal and condyle disharmonies. During this era,
CR was considered a posterior-superior (retruded) con-
dyle position (condyle relationship to glenoid fossa).
Roth rationalized that, since prosthodontists, restorative
dentists, and oral surgeons (when performing orthog-
nathic surgery) use articulators for preclinical proce-
dures, so should orthodontists. He further argued that
orthodontists are just as much (or more) involved in
altering occlusion (static and functional) as other dental
professionals, particularly prosthodontists, who use ar-
ticulators.1,2,5
Today’s gnathologically oriented orthodontists ad-
vocate the use of a fully adjustable articulator in which
dental casts are mounted in anterior-superior CR. A major
goal of orthodontic treatment is to establish coincidence of
maximum intercuspation (MI)-CR (when the condyles
are at the same time seated in anterior-superior CR).9,40
They argue that MI-CR slides (discrepancies) are dis-
cernable only with articulator-mounted casts and not
with hand-held models. They further advocate the need
for pretreatment CR-MI converted cephalograms and
the placement of gnathological, hinge-axis positioners
immediately after orthodontic appliances are re-
moved.16
Gnathologically oriented orthodontic practi-
tioners also believe that the tolerance for MI-CR
discrepancies is 1.5 mm in the horizontal and vertical
planes and 0.5 mm in the transverse plane (average of
Utt et al,13
2.0 mm horizontal and vertical, 0.5 mm
transverse; and Crawford,11
1.0 mm horizontal and
vertical, 0.5 mm transverse).11,16,18,41,42
The gnatholo-
gists also favor “canine protected occlusion” as the
preferred lateral functional occlusion type and anterior
a
Clinical professor, Department of Orthodontics and Dentofacial Orthopedics,
University of Pittsburgh School of Dental Medicine; private practice, Greens-
burg, Pa.
b
Research fellow, Department of Orthodontics, Oral Health Centre, University
of Western Australia, Perth.
Reprint requests to: Dr Donald J. Rinchuse, 510 Pellis Rd, Greensburg, PA
15601; e-mail, bracebrothers@aol.com.
Submitted, December 2004; revised and accepted, March 2005.
Am J Orthod Dentofacial Orthop 2006;129:299-308
0889-5406/$32.00
Copyright © 2006 by the American Association of Orthodontists.
doi:10.1016/j.ajodo.2005.03.019
299

guidance when the mandible is protruded. Furthermore,
Chiappone6
and Roth1
recommended the use of panto-
graph tracings with articulators. Factors such as inter-
condylar distance, angle of the eminentia, the amount
and quality of the Bennett side shift, and the direction
of the rotating condyle in a vertical plane are presumed
to play roles in attaining their treatment objectives,1,6
even though these factors seem to have limited, if any,
relationships and applicability with the articulator.
Also, McLaughlin43
adds the following list of addi-
tional benefits of mounting: discern vertical MI-CR
discrepancies such as “molar fulcruming,” show cants
to the occlusal plane, uncover functional side shifts of
the mandible, perhaps show premature anterior contacts
with a lack of posterior contacts, and might show
unilateral prematurities with lack of contact on the
opposing side.
In addition to the foregoing, the Roth view also
maintains that patients need to be deprogrammed from
their preexisting occlusions before obtaining CR
records even when they do not have TMD.2-4,9
He
believed this can be achieved only with a repositioning
splint for at least 3 months.9
Roth1-5
conjectured that
the stability of the orthodontic treatment result is
jeopardized when CR is recorded in any other way.
Wood et al7
suggested that it might be impractical to
place every patient in a CR splint and instead advocated
using Roth’s 2-piece power CR registration before
treatment because it “seats the condyles better than
other techniques that do not use a hard anterior stop.”
Conversely, nongnathologic orthodontists tend to
use hand-held models and noninstrument-oriented CR
techniques. Treatment goals are more general and
include the attainment of the best occlusal relationship
within the framework of favorable dentofacial esthet-
ics, function, and stability. Nongnathologic orthodon-
tists assert that there is a tolerance for MI-CR slides up
to perhaps 2-4 mm in the horizontal plane with little or
no attention to the relevance of the vertical and trans-
verse dimensions.25,26,29,33,36
In support of the gnathologic view and the use of
articulators, there are several anecdotal reports of ortho-
dontic patients’ treatments that have allegedly gone
wrong because they were not initially diagnosed via an
articulator mounting. An example of this is the case
report by Derakhshan and Sadowsky.8
Their article is
an afterthought reflection about the orthodontic treat-
ment of a 41-year-old woman who they initially be-
lieved had a very slight Angle Class II Division 1
malocclusion. After several months in orthodontic
treatment, they observed a significant increase in over-
jet, anterior bite opening, increased anterior face height,
and excessive lip strain. The patient eventually had to
have adjunctive orthognathic surgery. The authors la-
mented that they had not performed a pretreatment
mounting, which might have aided in the diagnosis of
the hidden dental/skeletal problem.
Logically, one would think that the change in
definition and the movement of CR from a posterior-
superior to an anterior-superior position would have
eliminated or reduced the magnitude of centric slides
and possibly the importance of mounting.29
To a
degree, this has proven to be true. Furthermore, only
minor differences for MI-CR discrepancies have been
found between gnathologically treated and nongnatho-
logically treated orthodontic cases as determined via
articulator mountings and only for the vertical (not
horizontal or transverse) dimension. The MI-CR differ-
ence is only about 1 mm (discussed further in next
paragraph).38
Nonetheless, gnathologists argue that
consideration and measurements of minor MI-CR
slides (discrepancies) are still valid and can be diag-
nosed only by articulator mountings.1-21,40
Using a Roth power centric bite registration and
articulator-mounted models, Utt et al13
found centric
occlusion (CO) condyles (via student articulating mod-
ule articulator with mandibular position indicator) lo-
cated on average 0.53 mm posterior and 0.72 mm
inferior to the anterior-superior CR. There was, how-
ever, much individual variation, with 39% of the CO
condyles positioned anteroinferiorly from anterior-su-
perior CR.13
Recent studies comparing gnathological
(Panadent articulator with condylar-position indicator and
Roth principles) with nongnathologic finished ortho-
dontic cases have generally found articulator-recorded
MI-CR differences of 1 mm greater in the vertical plane
in nongnathologically treated patients (1.41 mm for the
nongnathologically treated v 0.41 mm for the gnatho-
logically treated; difference of 1 mm).18
Based on the
results of Utt et al13
and Crawford,11
orthodontic
gnathologists claim that anterior-superior CR slides
average 0.6 to 0.7 mm horizontally, 0.7 to 0.8 mm
vertically, and 0.27 to 0.3 mm transversely.40
Klar et
al41
found a small but statistically significant (perhaps
not clinically significant) change in the before and after
MI-CR recordings of 200 consecutively treated orthodon-
tic patients for whom gnathologic principles were used:
horizontally, 0.81 to 0.53 mm (difference of 0.28 mm);
vertically, 0.99 to 0.60 mm (difference of 0.39 mm);
transversely, 0.44 to 0.25 mm (difference of 0.20 mm).
A subissue of the mounting debate involves
whether some or all orthodontic cases need to be
mounted. Some gnathologists believe that only certain
ones need mounting: patients requiring orthognathic
surgery, TMD patients, most adult patients, those with
many missing permanent teeth, those with functional
American Journal of Orthodontics and Dentofacial Orthopedics
February 2006
300 Rinchuse and Kandasamy

crossbites and midline discrepancies, and those with
deviations on opening/closing. The most logical re-
sponse to this subissue was addressed by Roth advocate
Cordray,9
who believes that all cases need to be
mounted. He based his thinking on the notion that no
practitioner can determine beforehand which patients
are really, or will turn out to be, the troubling ones;
therefore all need mounting.
THE POLYCENTRIC HINGE JOINT ARTICULATOR
Advocates of the polycentric hinge articulator
(POLY) believe this instrument resolves some limita-
tions of the hinge-axis based conventional arcon-type
articulators. Alpern and Alpern44
stated:
All of the existing jaw replicators or articulators
(except the POLY) currently used today are based on
knowledge and technology more than a century old.
They are primitive replications of the human TMJ.
. . . Being single centric hinge joint mechanisms,
they could not possibly reproduce all of the human
jaw movements required to build dental appliances.
POLY advocate Leever45
claimed:
The polycentric hinge joint occlusal system . . . pro-
vides the freedom of opportunity to . . . reproduce
individualized jaw movement and associated tooth
relationships. The condyle/fossa relationships . . . are
juxtaposed to reproduce the bilateral, asymmetric con-
dyle/fossa relationships of the human skull complex.
The use of the POLY involves taking a submento-
vertex radiograph, measuring the angle and distance of
each condyle, and programming this information into a
fully adjustable polycentric hinge joint articulator.
Nuelle46
proposed that, if 1 condyle imaged from
submentovertex is cocked and at a higher angle than the
opposite condyle, the condyle with the higher angle
will move faster than the opposite condyle with a lower
intercondylar angle. Nuelle and Alpern47
asserted that
this type of condyle variation and others can be
incorporated into the POLY.
UNDERSTANDING THE ISSUES RELATED TO
MOUNTING
For the pro-mount viewpoint to have credibility and
merit, its arguments must be both logical and evidence-
based. The “mounters” must provide support for the
following:
In light of the modern view of occlusion and
condylar position and their minimal impact on temporo-
mandibular disease, gnathologically oriented ortho-
dontists must provide evidence for the need to analyze
and evaluate orthodontic patients’ occlusions and con-
dylar positions in a microscopic v macroscopic manner.
They must provide evidence that the use of mounted
models affects in some appreciable way how orthodon-
tic patients are diagnosed and treated and that all of this
has something to do with their stomatognathic health.
Next, there must be proof for the basic tenets of the
gnathology/mounting philosophy, such as a true (phys-
iologic) verifiable terminal hinge axis and CR position.
In this regard, there must be a consensus as to what
constitutes CR (definition).
They must also substantiate that the current static
bite registrations used to program the articulator are
valid—ie, have something to do with jaw function and
temporomandibular joint (TMJ) health—and locate
condyles in a seated anterior-superior CR position. If
so, they must provide evidence that the articulator and
mounting protocol can accurately receive and duplicate
the recorded jaw positions and movements.
THE VIEW AGAINST MOUNTING
The compelling evidence of today, and the historic,
evidence-based data of some 30 years, makes one
question some of the past gnathological thinking and
ideas about the rationale for mounting.25,27,28,30,31,48
Denotatively, the findings in the 1960s that centric
slides caused TMD were based on faulty information
from descriptive studies that lacked control or compar-
ison groups. When comparison groups that used TMD-
asymptomatic subjects were added to the studies’
designs, the same centric slides were also observed in
the TMD-asymptomatic group. Hence, many studies of
the 1960s had high diagnostic sensitivity but poor
diagnostic specificity, leading to false-positive TMD
diagnoses.49
Furthermore, intraoral telemetry studies of
the 1960s (in which miniature radio implants were
placed in fixed prosthesis of subjects and radio frequen-
cies monitored outside the mouth) found that, even
though entire dentitions were reconstructed into
retruded, posterior-superior CR, subjects continued to
use and function in CO.50-53
Parenthetically, Mc-
Namara et al,26
in a recent summary article, found TMJ
arthropathies associated with centric slides greater than
4 mm. However, they contended that the slides were
probably the result of the TMD rather than the cause.26
There is the suggestion that the routine mounting of
orthodontic patients’ casts allows for a detailed analysis
of the occlusion.1-21,40-42
However, the roles of occlu-
sion and condyle position have been demonstrated to be
less important than once thought.23,25-29,48,49,54-66
In
addition, it has been demonstrated that there is poor
diagnostic sensitivity and specificity of occlusal factors
related to TMD.25,26,48,49,54-57
Furthermore, the centric-
ity of the condyles in the glenoid fossa involves a
range, and eccentricity does not necessarily indicate
Volume 129, Number 2
Rinchuse and Kandasamy 301

TMD.49,56-59,61-65
Therefore, the analysis of articulated
casts will not be diagnostic of TMD per se.49
And,
if TMD is a collection of disorders with many sub-
classes23,56,57
with a multifactorial etiology (it previ-
ously was viewed as a single disorder—TMJ pain-
dysfunction syndrome or myofascial pain dysfunction,
with a single etiology, ie, occlusion or stress) and
occlusion is only a very small piece of the puzzle, then
the need to record, measure, and focus on the details of
occlusion and condyle position does not make sense.
The rationale for the need and use of a sophisticated
instrument (and the articulator is not one) to analyze
and evaluate occlusion and condyle position would be
illogical.
Another antithetical point to the mounting position
is the evidence-based data that supports the view that
orthodontics does not cause TMD.22-29,34-36,61-65
The
gnathologists of the 1970s taught that, because ortho-
dontists ignore functional occlusion (including centric
slides) and treat only to a static, morphologic, ideal
occlusion, their patients would develop occlusal dishar-
monies or displaced condyles that would predispose to
TMD. Parenthetically, orthodontic gnathologists of that
era recommended treating patients to a fallacious
retruded CR position (posterior-superior). The ortho-
dontic gnathologist now accepts the current anterior-
superior definition of CR. If the gnathologically ori-
ented orthodontists’ views were correct, orthodontic
patients treated with hand-held models should have
different types of functional occlusion and condyle
positions and consequently increased TMD than similar
untreated comparison groups. However, the evidence-
based literature supports the contrary position: func-
tional occlusions, condyle positions, and level of TMD
are no different in orthodontically treated than un-
treated comparison groups.22-29,34-36,61-66
Johnston29
offered a critique of orthodontic gna-
thology and the false notions related to retruded CR:
I know of no convincing evidence that condyles of
the patients with intact dentitions “should” be placed
in centric relation or that once having been placed
there, the resulting improvement on nature will be
stable. . . . Instead of demanding a rational theoret-
ical basis and convincing proof, we took ‘how to’
courses and bought big articulators. . . . [I]t could be
argued that the progressive modification in the defi-
nition of centric relation has done more to eliminate
centric slides than 20 years of grudging acquiescence
to the precepts of gnathology.
One of the more-often cited reasons for mounting is
to identify the patient who has a dual bite. It is argued
that this might preclude an accurate diagnosis of the
patient’s skeletal pattern and dental classification.9
However, once a dual bite has been identified clinically,
how does the mounting of casts allow for a more
accurate treatment plan? Isn’t obtaining the correct bite
the critical factor?
CR RECORDS: RELIABILITY?
Orthodontic gnathologists argue that the assessment
of 3-dimensional condylar position is not possible with
2-dimensional radiography. They contend that the
power centric bite registration with articulator mount-
ings is the best and only way to evaluate CR.9,11-21
This
notion of the gnathologists appears to ignore the known
superiority of TMJ magnetic resonance imaging
(MRI).30
Admittedly, gnathological records such as the
Roth power centric bite registration and the articulator
mounting instrumentation appear to be reliable (repeat-
ability and consistency of the records/techniques) at
least under controlled laboratory conditions.16,42
How-
ever, in 1 study, standard deviations were found for
gnathologic MI-CR records as high as 0.16 mm in the
horizontal and vertical planes and 0.13 mm in the
transverse plane, and “play” error was calculated as
0.01 to 0.05 mm.16
Furthermore, the extent of error in
the gnathologic approach has not been fully investi-
gated. Orthodontic gnathologists Lavine et al16
stated,
after conducting their study dealing with the reliability
of the articulator condylar-position indicator (Pana-
dent): “The exact sources of error, material or human,
were not assessed; however, a trend of increased
variability was noted as the complexity and number of
the steps and materials increased.” Also, there might be
potential errors from using average values in the
articulator setup and an instrument that has the maxil-
lary component moving rather than the mandible as
does the human jaw.67-70
And, because there are only
very small differences between gnathologic and nong-
nathologic MI-CR records, even a small error calcu-
lated against any of the study findings would further
reduce the significance of gnathologic data.
CR RECORDS: VALIDITY?
CR recordings assume that it is possible to precisely
locate particular positions of the condyles. For exam-
ple, a 2-piece bite registration technique by Roth called
the power centric bite registration presumably seats the
condyles in an anterior-superior CR position, ie, “con-
dyles centered transversely and seated against the
articular disk at the posterior slope of the articular
eminences without dental interferences.”13
However,
Roth and other authors1-5,9,11,13,14,16,18-21
did not fur-
nish any evidence (MRI preferred) that subjects’ con-
dyles were actually in the positions that they described.
February 2006

The validity of mounted dental casts very much de-
pends on the reliability and validity of the patient’s bite
registrations.30,31
Therefore, although the Roth bite
registration might be reliable, is it valid? Does the
technique actually “capture” condyles in anterior-supe-
rior CR? Does this have any relationship to human jaw
function and stomatognathic health?
Interestingly, recent MRI data have indicated that
condyles are not located where clinicians think they
will be as a result of certain bite registrations.30
Therefore, the validity of the Roth centric bite registra-
tion has been questioned.25,29,30
A study by Alexander
et al30
compared and evaluated the MRI condyle
positions of 28 TMD-asymptomatic men in regard to 3
different occlusal and jaw bite registrations. The CO
(maximum intercuspation) bite-generated condyles
were considered the ideal condyle position because
they naturally existed in the 28 TMD-asymptomatic
subjects. The CO condyles were compared with bite
registered retruded condyles (RE) and anterior-superior
(CR) condyles. Interestingly, the CO-generated con-
dyles were shown to be distinct and positioned inferior
and anterior to the retruded (RE) and CR condyles.
Furthermore, the CO-generated condyles were not co-
incident with CR (anterior-superior) condyles. And it
was not possible to discriminate between the positions
in retruded (RE) and CR condyles. Alexander et al30
concluded that the clinical concept of treating to CR as
a preventive measure to improve disk-to-condyle rela-
tionships was unsupported.
Furthermore, Roth propagated the notion that the
power centric bite registration is physiologic and un-
manipulated based on his claim that it is “muscle
dictated.”1,9,13,17
However, the converse is probably
true; the power centric record is operator manipulated
and unphysiologic.25
Parenthetically, manipulated cen-
tric records (doctor manipulates subject’s mandible)
have been demonstrated to be more reliable than
unmanipulated centric records, but they are less phys-
iologic.25
Nuelle and Alpern47
reflected on the absur-
dity of gnathologic bite registrations:
Gnathologists . . . believe that the dentist can be
properly trained to manipulate, romance, dual wax
bite take, or other techniques which supposedly
permit the dentist or orthodontist to take control of all
the neuromuscular inputs to the patient and position
the mandible with the condyles positioned up and
forward against the eminence. . . . [N]o dentist or
orthodontist is knowledgeable enough to know the
proper three-dimensional position for two asymmetri-
cally angulated condyles, irregularly and individually
suspended in a polycentric hinged joint . . . Doctor se-
lected TMJ positioning at the dental chair is a blind
procedure.
An additional point somewhat related to bite regis-
tration is that the occlusal records used in mounting are
static and not dynamic. Patients or subjects are not
asked to chew food, swallow, or exercise any parafunc-
tion movement. Perhaps the way a patient or subject
uses his or her occlusion is far more important than the
occlusal morphology. Furthermore, the chewing-pat-
tern shape varies from subject to subject. Some people
possess a more vertical chewing pattern, and others
have a more horizontal pattern; this appears to be
independent of the occlusal scheme.25
A more erudite
explanation is that the chewing-pattern shape is sex-
specific, and there are more than half a dozen different
chewing patterns directly related to craniofacial mor-
phology.60
How then does the orthodontic gnathologist
justify articulator mountings that come from static and
not dynamic occlusal registrations? Even if the patient
was asked to perform any of these movements, how is
this incorporated into the articulator mounting?
Next, in the gnathologic approach, bite registrations
and mounted casts are taken just short of tooth contact.
Cordray9
addresses the reasoning for this:
The mandibular cast must be mounted at a point on
the seated condylar axis before first tooth contact
occurs, using an interocclusal record to relate it to the
maxillary cast. This is necessary to prevent a centric
prematurity from deflecting the mandible upon clo-
sure, which in turn allows for diagnosis of the
problems.
Although the rationale for taking the bite registra-
tion and mounting short of occlusal contact is clear, is
it valid? The fact remains that the articulator (vertical
stop pin) must eventually be released so that the teeth
(or perhaps a single tooth) finally drop into contact
(occlusion). Does gravity ultimately determine the final
seating of the casts after all the trouble and effort of
mounting?
Curiously, the mounting advocates believe that the
mounting process and instrumentation are accurate
(valid) without verification. Cordray9
wrote, “When
these records are properly transferred to an articulator,
the relationships between the teeth and jaws can be
studied accurately.” However, the validity of the artic-
ulator and the methods used in mounting are dubious.
Alpern and Alpern44
stated, “Nearly all existing single
centric hinge joint articulators produce only two paths
of straight-line movement, whereas the patient has an
infinite number of unique multiple paths of movement
as teeth function.”
Finally, the anatomy of the articulator does not

mimic human form. The articulator condyle does not
look like an actual condyle. The articulator does not
account for differences in the size, shape, and orienta-
tion of condyles between the right and left sides or for
right-and-left asymmetries in ramus height. Articula-
tors do not legitimately account for differences in the
angle of the slope of the articular eminence. And the
articulator does not have TMJ discs and capsules,
ligaments, muscles, blood vessels, or nerves of the
human stomatognathic system.
ABILITY OF ARTICULATORS TO SIMULATE JAW
MOVEMENTS?
The most important argument against mounting is
that the articulator is based on the faulty 1952 concept
of Posselt.71
Posselt assumed that, in the initial phase of
jaw opening, the condyles only rotate and do not
translate—ie, terminal hinge axis. There is, however, an
instantaneous center of rotation (translation) supported
by Luce in 1889 and later by Bennett in 1908, cited in
Lindauer et al.31
That is, the mandible initially under-
goes both rotation and translation around an axis, which
continues as the jaw opens. Support for this notion
comes from the study of Lindauer et al,31
who studied
condylar movements and centers of rotation during jaw
opening in 8 normal (no TMD) subjects with the
Dolphin Sonic Digitizing System. They found that all
subjects demonstrated both rotation and translation
during initial jaw opening, and none had a center of
rotation at the condylar head. Their findings supported
the theory of a constantly moving, instantaneous center
of jaw rotation (translation) during opening that is
different in every person. The arcon hinge-type articu-
lator does not incorporate initial translatory movement
of the condyles during opening. The authors con-
cluded that the use of articulators to simulate “jaw
movements to identify occlusal interferences cannot
be expected to replicate the patient’s mandibular
movements precisely.”31
They further stated, “The
uncertainty of predicting mandibular rotation for a
given patient should be considered when planning
surgical treatment and fabrication of orthodontic appli-
ances.”31
Nuelle and Alpern47
believed that the polycentric
hinge articulator “can reproduce the patient’s individual
chewing stroke” and avoid the problems of the arcon
hinge-type articulators. Arguably, they believe that the
POLY can incorporate initial translation not possible
with hinge axis articulators. Parenthetically, Nuelle and
Alpern47
recommended using a full-arch splint “for a
period of time to eliminate all muscle splinting and/or
joint inflammation,” and then the “patient’s joints will
consistently demonstrate where their natural centric is
located.”
IS THERE AN OUTCOME BENEFIT?
An important question that can be asked of the
orthodontic gnathologist is: how does the mounting of
dental casts affect orthodontic diagnosis and treatment
planning and lead to improvements in orthodontic
treatment outcomes—ie, occlusion and TMJ health?
Just because an additional step is incorporated into the
diagnostic protocol does not mean it is efficacious.
Ellis and Benson32
recently assessed whether articula-
tor-mounted casts in CR compared with intercuspal
position (CO) hand-held casts made a difference in
orthodontic treatment planning. They concluded that
mounting the study models of 20 orthodontic patients
did not meaningfully affect the treatment planning
decisions of 10 orthodontists in the United Kingdom
compared with hand-articulated casts.32
Last, mounting patient casts on an articulator fur-
nish no biologic information about apparent health or
disease. Diseases of the TMJ such as disc displacement
and osteoarthrosis are diagnosed via TMJ imaging
(MRI) and clinical examination, not by using articula-
tors.
PRACTICAL CONSIDERATIONS
Interestingly, many who support the mounting
viewpoint use gnathologic positioners to finish their
treatments. However, the objections for the use of
articulators we offer are multiplied when using a
gnathologic positioner. Alpern and Alpern44
discussed
the further problem of opening the pin on hinge-type
articulators when constructing splints or performing
clinical laboratory procedures for dental restorations.
They stated:
Existing knowledge clearly states that you cannot
open the front pin or post on any single centric hinge
joint articulators. If you do, the resultant dental
restoration will not fit, with the posterior teeth touch-
ing first and an anterior open bite resulting.
It seems ridiculous to go through all the effort to
detail an orthodontic case over 2 years and then finish
with an absolutely inaccurate appliance such as a
gnathologic positioner.
Furthermore, how does the use of an articulator
factor in the settling of the occlusion after orthodontic
appliances are removed? Surely, when the gnathologist
performs a pretreatment diagnostic mounting, he or she
assumes that this process will have an ultimate impact
on establishing the final occlusion (assuming a final
occlusion is ever established). Would it not be defeat-
February 2006

ing to learn that, after all the effort involved with
mounting and the attention paid to the details of
occlusion and condyle position, the final occlusion is
often arbitrarily determined by nature? The patient’s
own adaptation (settling) overrides the immediate pos-
torthodontic occlusion.
Several additional points can be made that are
critical to the debate on mounting in orthodontics. First,
there is evidence that the glenoid fossa/condyle com-
plex changes position in children due to growth.72
If
this is true, the gnathologist would have to periodically
remount and reevaluate growing children’s cases. How
many gnathologists consider this?
Additionally, in modern health care when cost
containment is a critical element, a question can be
asked: what is the added cost to mount versus not to
mount? The gnathologists ardently argue that there is
no more added cost to mount than that of obtaining
hand-held models. However, no matter how passion-
ately they argue, the fact remains that there are greater
costs if one considers factors such as staff training and
use, additional laboratory time, and the storage of
articulator records. Furthermore, if e-models take hold
and the orthodontic office of the future becomes more
digital and paperless, how do the articulator and its
records factor into this new paradigm?
RECENT STUDIES SUPPORTING MOUNTING
QUESTIONED
Several recent studies presumably support the
mounting viewpoint.7,8,11-18,40-42
Even though there is
no perfect study, the studies supporting mounting are
flawed and reflect more general problems about articu-
lators. Rinchuse25
reviewed 1 of these articles13
and
clearly pointed out many shortcomings beyond those of
typical published studies. Some of the general short-
comings of the articles are:
● The studies were descriptive rather than experimental
or observational and did not address cause and effect.
● No comparison group was used, or, when a compar-
ison group was present, the selection process was
biased.
● The findings had nothing to do with the health or
disease of subjects’ TMJs. The studies, for the most
part, did not relate millimeter differences in articu-
lator recordings to TMD or stomatognathic health. If
differences exist between articulated condyles of
subjects, so what?
● The basic premise was faulty in that the findings
generally demonstrated normal variability of condyle
position from subject to subject. Slight millimeter
and fraction of millimeter differences between sub-
jects in the studies might not be clinically significant.
● The use of average condylar readings and no report
of the exact error involved in the bite registrations
and mounting procedures are problematic.
● The studies did not validate the power centric bite
registration and demonstrated that this registration
actually seats human condyles in the predicted fossa
position of anterior-superior CR.
The study by Crawford11
was perplexing. Its pur-
pose was to determine whether there is a relationship
between occlusion-dictated Panadent articulator condy-
lar position axis and signs and symptoms of TMD. That
is, do subjects having mutually protected occlusions
with MI and CR relatively coincident have fewer signs
and symptoms of TMD than subjects without these
types of occlusion and condyle position?73
The findings
purport that a relationship exists between occlusion-
dictated condylar position and TMD symptomatology.
However, the study has many limitations, the most
apparent of which is the sample. Thirty subjects with a
gnathologic, ideal occlusions, in which CR was coin-
cident with CO (intercuspal position, MI), were com-
pared with 30 subjects randomly selected from the
general population. Curiously, the so-called “ideal sam-
ple” was selected from a population that had undergone
full-mouth reconstruction with gnathologic principles.
The author11
claims that he used a selected sample
“because the incidence of adult occlusion with CR coin-
cident with CO (ICP; MI) is very low in the general
population, making the acquisition of an adequate
sample of ideal occlusions by random selection imprac-
tical.” Crawford11
wrote:
This was a sample of convenience, and it was highly
selected. The contributing clinicians chose subjects
according to their own concept of ideal, and the
number selected was determined by the availability
and willingness of the subjects to participate.
If the author recognizes that CR coincident with CO
(ICP; MI) is so rare in nature, then by whose standard
is it considered the ideal for which patient treatment
should be directed toward? Perhaps the author unknow-
ingly acknowledged the shortcoming concerning the
validity of the study before the data were even col-
lected. There was also an age difference between the 2
samples. The average age for the restored, ideal sample
was 50.8 years; that of the comparison group was 38.4
years. Age is a factor in TMD26,30,54,55,57
(TMD in-
creases with age but decreases after age 50).73
There
are also other biases dealing with how the restored
“ideal” sample was selected. How much did the clini-

cians who furnished subjects for the study know about
the study’s premise? It seems illogical that they did not
know the TMD status of these subjects a priori. The
examiners used in the study were not blinded and knew
which patients had full-mouth reconstructions and
which did not.73
Furthermore, the number of subjects in
each of the 2 groups (30 subjects) was inadequate
because of the many uncontrolled confounding factors.
Several additional points: the untreated subjects were
not deprogrammed, the palpation recording was not
standardized, the Helkimo index was modified to make
the data “work,” the Helkimo index is not specific for
TMD, possibly only happy patients were recalled, the
anamnestic results are questionable because subjects’
abilities to recall information 10 years later are tenu-
ous,73
and an impossible finding of a superior position
of the condylar-postion indicator was excused as an
“artifact.”
DEPROGRAMMING SPLINTS
The use of deprogramming splints has become an
integral part of the gnathological view on the pro
position of mounting. The evidence for using depro-
grammers is equivocal, with no true physiologic
basis. Several essays have described techniques for
deprogramming or discussed the benefits of depro-
gramming before performing a centric bite registra-
tion.74-85
Several studies have shown a possible benefit
of deprogramming,86,87
although most have not.88-90
All studies used deprogrammers for relatively short
time periods.86-90
The study of Karl and Foley87
involved the place-
ment of a Lucia-type anterior deprogramming jig (an-
terior tooth contact without posterior tooth contact) in
40 subjects. Minor differences were noted in articulator
condyle position indicator centric recording before and
after using the deprogrammer for 6 hours. The most
prevalent type of centric slide resulted on average in a
posterior and inferior distraction of the articulator
condyles from MI-CR of 0.37 mm horizontally and
0.57 mm vertically. Conversely, Kulbersh et al18
found
no difference in MI-CR measurements between 34
postorthodontic subjects who wore gnathologic full-
coverage splints for 3 weeks (24 hours per day) and 14
postorthodontic subjects who did not wear splints.
CONCLUSIONS
Science and the practice of orthodontics are not
mutually exclusive, as the orthodontic gnathologists
seem to believe. One would think that a consideration
of the modern knowledge that occlusion and condyle
position have minimal or no influence on TMD would
have quieted the debate on the use of articulators in
orthodontics. Also, the evidence that orthodontics does
not cause TMD should have been detrimental to the
mounting argument. In addition, the credibility of the
orthodontic gnathologists should certainly have been
shattered by their claim of mounting cases to a past
incorrect retruded CR position that they do not accept
today.
Although there is no evidence-based systematic
review (evidence-based Model 3)38,39
about mounting,
enough evidence clearly argues against orthodontic
patient mounting. A critical review of the available
literature and a logical consideration of the notions
about mounting in orthodontics make the pro position
difficult.
● The articulator can never simulate human mandibu-
lar movement and is based on the faulty theory of the
terminal hinge-axis.
● There is no evidence that orthodontic treatment
results (outcomes) are better when articulators are
used in terms of improved patient TMD status and
stomatognathic health.
● No scientific evidence suggests that the use of
articulators will influence orthodontic diagnoses in
any meaningful way.
● Although the polycentric hinge articulator is possibly
better than the hinge axis arcon articulator, it is by no
means ideal.
● CR records have only been demonstrated to be
reliable under controlled laboratory conditions.
● The errors involved in taking the bite registrations
and the mounting procedures reduce the significance
of the gnathologic findings.
● Bite registrations used in the mounting process are
static records and do not encompass any meaningful
movement of the human mandible.
● The internal validity of the Roth power centric bite
registration has not been established. Roth did not
demonstrate where patients’ condyles are positioned
as a result of the power centric bite registration; he
assumed they are in an anterior-superior seated
position, but he gave no documentation.
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February 2006

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