articuladores e ortodontia

SPECIAL ARTICLE

Articulators in orthodontics: An evidence-based perspectiveDonald J. Rinchusea and Sanjivan Kandasamyb

Pittsburgh, Pa, and Perth, Australia

Whether to mount cases on an articulator hasbeen a heated debate in orthodontics for atleast 3 decades.1-36 Articulators can be use-

ful for gross fixed and removable prosthodontics andorthognathic surgical procedures to at least maintain acertain vertical dimension while preclinical laboratoryprocedures are performed on dental casts.25 However,their validity in orthodontics is equivocal. A recentsurvey of randomly selected subscribers of the Journalof Clinical Orthodontics in 2001 showed that about21% of the respondents routinely mounted models,44% mounted models occasionally, and 35% nevermounted models. The differing opinions ranged fromthose who mounted models for gnathologic or temporo-mandibular disorder (TMD) considerations to thosewho believed that there was no rationale for mount-ing.37

The evidence-based paradigm has 3 hierarchicalmodel levels.38,39 Model level #3, a systematic reviewof literature involving a meta-analysis, is the highestlevel.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 anevaluation of the best available research data in whichthe data from sample studies (evidence-based model#2) are considered superior to case studies, anecdotalreports, and clinicians’ personal clinical experiences(evidence-based model #1).38 When logical and prac-tical considerations are added to the evaluation of thescientific data, we argue against the need to mount inorthodontics. Hence, this article is a position statementsupported by evidence-based model #2, and argues thatthe use of articulators in orthodontics is an unnecessaryaClinical professor, Department of Orthodontics and Dentofacial Orthopedics,University of Pittsburgh School of Dental Medicine; private practice, Greens-burg, Pa.bResearch fellow, Department of Orthodontics, Oral Health Centre, Universityof Western Australia, Perth.Reprint requests to: Dr Donald J. Rinchuse, 510 Pellis Rd, Greensburg, PA15601; e-mail, [email protected], December 2004; revised and accepted, March 2005.Am J Orthod Dentofacial Orthop 2006;129:299-3080889-5406/$32.00Copyright © 2006 by the American Association of Orthodontists.
doi:10.1016/j.ajodo.2005.03.019
diagnostic procedure. We consider both sides of theissue of mounting.

THE VIEW IN FAVOR OF MOUNTING

Supporting a gnathologic view of occlusion andcondyle position, Dr Ron Roth in the early 1970sadvocated that orthodontists should perform pretreat-ment diagnostic articulator mounting.1 Roth1-5 believedthat pretreatment articulated centric-relation (CR)mounted models would best aid the orthodontist inidentifying the so-called “Sunday bite” and the minutiaof 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, restorativedentists, and oral surgeons (when performing orthog-nathic surgery) use articulators for preclinical proce-dures, so should orthodontists. He further argued thatorthodontists are just as much (or more) involved inaltering occlusion (static and functional) as other dentalprofessionals, particularly prosthodontists, who use ar-ticulators.1,2,5

Today’s gnathologically oriented orthodontists ad-vocate the use of a fully adjustable articulator in whichdental casts are mounted in anterior-superior CR. A majorgoal of orthodontic treatment is to establish coincidence ofmaximum intercuspation (MI)-CR (when the condylesare 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 notwith hand-held models. They further advocate the needfor pretreatment CR-MI converted cephalograms andthe placement of gnathological, hinge-axis positionersimmediately after orthodontic appliances are re-moved.16 Gnathologically oriented orthodontic practi-tioners also believe that the tolerance for MI-CRdiscrepancies is 1.5 mm in the horizontal and verticalplanes and 0.5 mm in the transverse plane (average ofUtt et al,13 2.0 mm horizontal and vertical, 0.5 mmtransverse; and Crawford,11 1.0 mm horizontal andvertical, 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
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300 Rinchuse and Kandasamy

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 amountand quality of the Bennett side shift, and the directionof the rotating condyle in a vertical plane are presumedto 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-CRdiscrepancies such as “molar fulcruming,” show cantsto the occlusal plane, uncover functional side shifts ofthe mandible, perhaps show premature anterior contactswith a lack of posterior contacts, and might showunilateral prematurities with lack of contact on theopposing side.

In addition to the foregoing, the Roth view alsomaintains that patients need to be deprogrammed fromtheir preexisting occlusions before obtaining CRrecords even when they do not have TMD.2-4,9 Hebelieved this can be achieved only with a repositioningsplint for at least 3 months.9 Roth1-5 conjectured thatthe stability of the orthodontic treatment result isjeopardized when CR is recorded in any other way.Wood et al7 suggested that it might be impractical toplace every patient in a CR splint and instead advocatedusing Roth’s 2-piece power CR registration beforetreatment because it “seats the condyles better thanother techniques that do not use a hard anterior stop.”

Conversely, nongnathologic orthodontists tend touse hand-held models and noninstrument-oriented CRtechniques. Treatment goals are more general andinclude the attainment of the best occlusal relationshipwithin the framework of favorable dentofacial esthet-ics, function, and stability. Nongnathologic orthodon-tists assert that there is a tolerance for MI-CR slides upto perhaps 2-4 mm in the horizontal plane with little orno 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 ofarticulators, there are several anecdotal reports of ortho-dontic patients’ treatments that have allegedly gonewrong because they were not initially diagnosed via anarticulator mounting. An example of this is the casereport by Derakhshan and Sadowsky.8 Their article isan 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 1malocclusion. After several months in orthodontictreatment, 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 pretreatmentmounting, which might have aided in the diagnosis ofthe hidden dental/skeletal problem.

Logically, one would think that the change indefinition and the movement of CR from a posterior-superior to an anterior-superior position would haveeliminated or reduced the magnitude of centric slidesand possibly the importance of mounting.29 To adegree, this has proven to be true. Furthermore, onlyminor differences for MI-CR discrepancies have beenfound between gnathologically treated and nongnatho-logically treated orthodontic cases as determined viaarticulator mountings and only for the vertical (nothorizontal or transverse) dimension. The MI-CR differ-ence is only about 1 mm (discussed further in nextparagraph).38 Nonetheless, gnathologists argue thatconsideration and measurements of minor MI-CRslides (discrepancies) are still valid and can be diag-nosed only by articulator mountings.1-21,40

Using a Roth power centric bite registration andarticulator-mounted models, Utt et al13 found centricocclusion (CO) condyles (via student articulating mod-ule articulator with mandibular position indicator) lo-cated on average 0.53 mm posterior and 0.72 mminferior to the anterior-superior CR. There was, how-ever, much individual variation, with 39% of the COcondyles positioned anteroinferiorly from anterior-su-perior CR.13 Recent studies comparing gnathological(Panadent articulator with condylar-position indicator andRoth principles) with nongnathologic finished ortho-dontic cases have generally found articulator-recordedMI-CR differences of 1 mm greater in the vertical planein nongnathologically treated patients (1.41 mm for thenongnathologically treated v 0.41 mm for the gnatho-logically treated; difference of 1 mm).18 Based on theresults of Utt et al13 and Crawford,11 orthodonticgnathologists claim that anterior-superior CR slidesaverage 0.6 to 0.7 mm horizontally, 0.7 to 0.8 mmvertically, and 0.27 to 0.3 mm transversely.40 Klar etal41 found a small but statistically significant (perhapsnot clinically significant) change in the before and afterMI-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 involveswhether some or all orthodontic cases need to bemounted. Some gnathologists believe that only certainones need mounting: patients requiring orthognathicsurgery, TMD patients, most adult patients, those with
many missing permanent teeth, those with functional

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crossbites and midline discrepancies, and those withdeviations on opening/closing. The most logical re-sponse to this subissue was addressed by Roth advocateCordray,9 who believes that all cases need to bemounted. He based his thinking on the notion that nopractitioner can determine beforehand which patientsare 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-typearticulators. Alpern and Alpern44 stated:

All of the existing jaw replicators or articulators(except the POLY) currently used today are based onknowledge 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 humanjaw movements required to build dental appliances.

POLY advocate Leever45 claimed:

The polycentric hinge joint occlusal system . . . pro-vides the freedom of opportunity to . . . reproduceindividualized jaw movement and associated toothrelationships. The condyle/fossa relationships . . . arejuxtaposed 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 ofeach condyle, and programming this information into afully adjustable polycentric hinge joint articulator.Nuelle46 proposed that, if 1 condyle imaged fromsubmentovertex is cocked and at a higher angle than theopposite condyle, the condyle with the higher anglewill move faster than the opposite condyle with a lowerintercondylar angle. Nuelle and Alpern47 asserted thatthis type of condyle variation and others can beincorporated into the POLY.

UNDERSTANDING THE ISSUES RELATED TOMOUNTING

For the pro-mount viewpoint to have credibility andmerit, its arguments must be both logical and evidence-based. The “mounters” must provide support for thefollowing:

In light of the modern view of occlusion andcondylar position and their minimal impact on temporo-mandibular disease, gnathologically oriented ortho-dontists must provide evidence for the need to analyzeand evaluate orthodontic patients’ occlusions and con-
dylar positions in a microscopic v macroscopic manner.
They must provide evidence that the use of mountedmodels affects in some appreciable way how orthodon-tic patients are diagnosed and treated and that all of thishas something to do with their stomatognathic health.

Next, there must be proof for the basic tenets of thegnathology/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 whatconstitutes CR (definition).

They must also substantiate that the current staticbite registrations used to program the articulator arevalid—ie, have something to do with jaw function andtemporomandibular joint (TMJ) health—and locatecondyles in a seated anterior-superior CR position. Ifso, they must provide evidence that the articulator andmounting protocol can accurately receive and duplicatethe 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 onequestion some of the past gnathological thinking andideas about the rationale for mounting.25,27,28,30,31,48

Denotatively, the findings in the 1960s that centricslides caused TMD were based on faulty informationfrom 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 inthe TMD-asymptomatic group. Hence, many studies ofthe 1960s had high diagnostic sensitivity but poordiagnostic specificity, leading to false-positive TMDdiagnoses.49 Furthermore, intraoral telemetry studies ofthe 1960s (in which miniature radio implants wereplaced in fixed prosthesis of subjects and radio frequen-cies monitored outside the mouth) found that, eventhough entire dentitions were reconstructed intoretruded, posterior-superior CR, subjects continued touse and function in CO.50-53 Parenthetically, Mc-Namara et al,26 in a recent summary article, found TMJarthropathies associated with centric slides greater than4 mm. However, they contended that the slides wereprobably the result of the TMD rather than the cause.26

There is the suggestion that the routine mounting oforthodontic patients’ casts allows for a detailed analysisof the occlusion.1-21,40-42 However, the roles of occlu-sion and condyle position have been demonstrated to beless important than once thought.23,25-29,48,49,54-66 Inaddition, it has been demonstrated that there is poordiagnostic sensitivity and specificity of occlusal factorsrelated 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



TMD.49,56-59,61-65 Therefore, the analysis of articulatedcasts 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) andocclusion is only a very small piece of the puzzle, thenthe need to record, measure, and focus on the details ofocclusion and condyle position does not make sense.The rationale for the need and use of a sophisticatedinstrument (and the articulator is not one) to analyzeand evaluate occlusion and condyle position would beillogical.

Another antithetical point to the mounting positionis the evidence-based data that supports the view thatorthodontics does not cause TMD.22-29,34-36,61-65 Thegnathologists of the 1970s taught that, because ortho-dontists ignore functional occlusion (including centricslides) and treat only to a static, morphologic, idealocclusion, their patients would develop occlusal dishar-monies or displaced condyles that would predispose toTMD. Parenthetically, orthodontic gnathologists of thatera recommended treating patients to a fallaciousretruded 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, orthodonticpatients treated with hand-held models should havedifferent types of functional occlusion and condylepositions and consequently increased TMD than similaruntreated comparison groups. However, the evidence-based literature supports the contrary position: func-tional occlusions, condyle positions, and level of TMDare 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 ofthe patients with intact dentitions “should” be placedin centric relation or that once having been placedthere, the resulting improvement on nature will bestable. . . . Instead of demanding a rational theoret-ical basis and convincing proof, we took ‘how to’courses and bought big articulators. . . . [I]t could beargued that the progressive modification in the defi-nition of centric relation has done more to eliminatecentric slides than 20 years of grudging acquiescenceto the precepts of gnathology.

One of the more-often cited reasons for mounting isto 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 moreaccurate treatment plan? Isn’t obtaining the correct bitethe critical factor?

CR RECORDS: RELIABILITY?

Orthodontic gnathologists argue that the assessmentof 3-dimensional condylar position is not possible with2-dimensional radiography. They contend that thepower centric bite registration with articulator mount-ings is the best and only way to evaluate CR.9,11-21 Thisnotion of the gnathologists appears to ignore the knownsuperiority of TMJ magnetic resonance imaging(MRI).30 Admittedly, gnathological records such as theRoth power centric bite registration and the articulatormounting instrumentation appear to be reliable (repeat-ability and consistency of the records/techniques) atleast under controlled laboratory conditions.16,42 How-ever, in 1 study, standard deviations were found forgnathologic MI-CR records as high as 0.16 mm in thehorizontal and vertical planes and 0.13 mm in thetransverse plane, and “play” error was calculated as0.01 to 0.05 mm.16 Furthermore, the extent of error inthe gnathologic approach has not been fully investi-gated. Orthodontic gnathologists Lavine et al16 stated,after conducting their study dealing with the reliabilityof the articulator condylar-position indicator (Pana-dent): “The exact sources of error, material or human,were not assessed; however, a trend of increasedvariability was noted as the complexity and number ofthe steps and materials increased.” Also, there might bepotential errors from using average values in thearticulator setup and an instrument that has the maxil-lary component moving rather than the mandible asdoes the human jaw.67-70 And, because there are onlyvery small differences between gnathologic and nong-nathologic MI-CR records, even a small error calcu-lated against any of the study findings would furtherreduce the significance of gnathologic data.

CR RECORDS: VALIDITY?

CR recordings assume that it is possible to preciselylocate particular positions of the condyles. For exam-ple, a 2-piece bite registration technique by Roth calledthe power centric bite registration presumably seats thecondyles in an anterior-superior CR position, ie, “con-dyles centered transversely and seated against thearticular disk at the posterior slope of the articulareminences 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.



The validity of mounted dental casts very much de-pends on the reliability and validity of the patient’s biteregistrations.30,31 Therefore, although the Roth biteregistration might be reliable, is it valid? Does thetechnique actually “capture” condyles in anterior-supe-rior CR? Does this have any relationship to human jawfunction and stomatognathic health?

Interestingly, recent MRI data have indicated thatcondyles are not located where clinicians think theywill 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 Alexanderet al30 compared and evaluated the MRI condylepositions of 28 TMD-asymptomatic men in regard to 3different occlusal and jaw bite registrations. The CO(maximum intercuspation) bite-generated condyleswere considered the ideal condyle position becausethey naturally existed in the 28 TMD-asymptomaticsubjects. The CO condyles were compared with biteregistered retruded condyles (RE) and anterior-superior(CR) condyles. Interestingly, the CO-generated con-dyles were shown to be distinct and positioned inferiorand anterior to the retruded (RE) and CR condyles.Furthermore, the CO-generated condyles were not co-incident with CR (anterior-superior) condyles. And itwas not possible to discriminate between the positionsin retruded (RE) and CR condyles. Alexander et al30

concluded that the clinical concept of treating to CR asa preventive measure to improve disk-to-condyle rela-tionships was unsupported.

Furthermore, Roth propagated the notion that thepower centric bite registration is physiologic and un-manipulated based on his claim that it is “muscledictated.”1,9,13,17 However, the converse is probablytrue; the power centric record is operator manipulatedand unphysiologic.25 Parenthetically, manipulated cen-tric records (doctor manipulates subject’s mandible)have been demonstrated to be more reliable thanunmanipulated 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 beproperly trained to manipulate, romance, dual waxbite take, or other techniques which supposedlypermit the dentist or orthodontist to take control of allthe neuromuscular inputs to the patient and positionthe mandible with the condyles positioned up andforward against the eminence. . . . [N]o dentist ororthodontist is knowledgeable enough to know theproper 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 blindprocedure.

An additional point somewhat related to bite regis-tration is that the occlusal records used in mounting arestatic and not dynamic. Patients or subjects are notasked to chew food, swallow, or exercise any parafunc-tion movement. Perhaps the way a patient or subjectuses his or her occlusion is far more important than theocclusal morphology. Furthermore, the chewing-pat-tern shape varies from subject to subject. Some peoplepossess a more vertical chewing pattern, and othershave a more horizontal pattern; this appears to beindependent of the occlusal scheme.25 A more eruditeexplanation is that the chewing-pattern shape is sex-specific, and there are more than half a dozen differentchewing patterns directly related to craniofacial mor-phology.60 How then does the orthodontic gnathologistjustify articulator mountings that come from static andnot dynamic occlusal registrations? Even if the patientwas asked to perform any of these movements, how isthis incorporated into the articulator mounting?

Next, in the gnathologic approach, bite registrationsand mounted casts are taken just short of tooth contact.Cordray9 addresses the reasoning for this:

The mandibular cast must be mounted at a point onthe seated condylar axis before first tooth contactoccurs, using an interocclusal record to relate it to themaxillary cast. This is necessary to prevent a centricprematurity from deflecting the mandible upon clo-sure, which in turn allows for diagnosis of theproblems.

Although the rationale for taking the bite registra-tion and mounting short of occlusal contact is clear, isit valid? The fact remains that the articulator (verticalstop pin) must eventually be released so that the teeth(or perhaps a single tooth) finally drop into contact(occlusion). Does gravity ultimately determine the finalseating of the casts after all the trouble and effort ofmounting?

Curiously, the mounting advocates believe that themounting process and instrumentation are accurate(valid) without verification. Cordray9 wrote, “Whenthese records are properly transferred to an articulator,the relationships between the teeth and jaws can bestudied accurately.” However, the validity of the artic-ulator and the methods used in mounting are dubious.Alpern and Alpern44 stated, “Nearly all existing singlecentric hinge joint articulators produce only two pathsof straight-line movement, whereas the patient has aninfinite number of unique multiple paths of movementas teeth function.”

Finally, the anatomy of the articulator does not



mimic human form. The articulator condyle does notlook like an actual condyle. The articulator does notaccount for differences in the size, shape, and orienta-tion of condyles between the right and left sides or forright-and-left asymmetries in ramus height. Articula-tors do not legitimately account for differences in theangle of the slope of the articular eminence. And thearticulator does not have TMJ discs and capsules,ligaments, muscles, blood vessels, or nerves of thehuman stomatognathic system.

ABILITY OF ARTICULATORS TO SIMULATE JAWMOVEMENTS?

The most important argument against mounting isthat the articulator is based on the faulty 1952 conceptof Posselt.71 Posselt assumed that, in the initial phase ofjaw opening, the condyles only rotate and do nottranslate—ie, terminal hinge axis. There is, however, aninstantaneous center of rotation (translation) supportedby Luce in 1889 and later by Bennett in 1908, cited inLindauer et al.31 That is, the mandible initially under-goes both rotation and translation around an axis, whichcontinues as the jaw opens. Support for this notioncomes from the study of Lindauer et al,31 who studiedcondylar movements and centers of rotation during jawopening in 8 normal (no TMD) subjects with theDolphin Sonic Digitizing System. They found that allsubjects demonstrated both rotation and translationduring initial jaw opening, and none had a center ofrotation at the condylar head. Their findings supportedthe theory of a constantly moving, instantaneous centerof jaw rotation (translation) during opening that isdifferent in every person. The arcon hinge-type articu-lator does not incorporate initial translatory movementof the condyles during opening. The authors con-cluded that the use of articulators to simulate “jawmovements to identify occlusal interferences cannotbe expected to replicate the patient’s mandibularmovements precisely.”31 They further stated, “Theuncertainty of predicting mandibular rotation for agiven patient should be considered when planningsurgical treatment and fabrication of orthodontic appli-ances.”31

Nuelle and Alpern47 believed that the polycentrichinge articulator “can reproduce the patient’s individualchewing stroke” and avoid the problems of the arconhinge-type articulators. Arguably, they believe that thePOLY can incorporate initial translation not possiblewith hinge axis articulators. Parenthetically, Nuelle andAlpern47 recommended using a full-arch splint “for aperiod of time to eliminate all muscle splinting and/or
joint inflammation,” and then the “patient’s joints will
consistently demonstrate where their natural centric islocated.”

IS THERE AN OUTCOME BENEFIT?

An important question that can be asked of theorthodontic gnathologist is: how does the mounting ofdental casts affect orthodontic diagnosis and treatmentplanning and lead to improvements in orthodontictreatment outcomes—ie, occlusion and TMJ health?Just because an additional step is incorporated into thediagnostic protocol does not mean it is efficacious.Ellis and Benson32 recently assessed whether articula-tor-mounted casts in CR compared with intercuspalposition (CO) hand-held casts made a difference inorthodontic treatment planning. They concluded thatmounting the study models of 20 orthodontic patientsdid not meaningfully affect the treatment planningdecisions of 10 orthodontists in the United Kingdomcompared with hand-articulated casts.32

Last, mounting patient casts on an articulator fur-nish no biologic information about apparent health ordisease. Diseases of the TMJ such as disc displacementand osteoarthrosis are diagnosed via TMJ imaging(MRI) and clinical examination, not by using articula-tors.

PRACTICAL CONSIDERATIONS

Interestingly, many who support the mountingviewpoint use gnathologic positioners to finish theirtreatments. However, the objections for the use ofarticulators we offer are multiplied when using agnathologic positioner. Alpern and Alpern44 discussedthe further problem of opening the pin on hinge-typearticulators when constructing splints or performingclinical laboratory procedures for dental restorations.They stated:

Existing knowledge clearly states that you cannotopen the front pin or post on any single centric hingejoint articulators. If you do, the resultant dentalrestoration 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 todetail an orthodontic case over 2 years and then finishwith an absolutely inaccurate appliance such as agnathologic positioner.

Furthermore, how does the use of an articulatorfactor in the settling of the occlusion after orthodonticappliances are removed? Surely, when the gnathologistperforms a pretreatment diagnostic mounting, he or sheassumes that this process will have an ultimate impacton establishing the final occlusion (assuming a final
occlusion is ever established). Would it not be defeat-



ing to learn that, after all the effort involved withmounting and the attention paid to the details ofocclusion and condyle position, the final occlusion isoften arbitrarily determined by nature? The patient’sown adaptation (settling) overrides the immediate pos-torthodontic occlusion.

Several additional points can be made that arecritical 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 Ifthis is true, the gnathologist would have to periodicallyremount and reevaluate growing children’s cases. Howmany gnathologists consider this?

Additionally, in modern health care when costcontainment is a critical element, a question can beasked: what is the added cost to mount versus not tomount? The gnathologists ardently argue that there isno more added cost to mount than that of obtaininghand-held models. However, no matter how passion-ately they argue, the fact remains that there are greatercosts if one considers factors such as staff training anduse, additional laboratory time, and the storage ofarticulator records. Furthermore, if e-models take holdand the orthodontic office of the future becomes moredigital and paperless, how do the articulator and itsrecords factor into this new paradigm?

RECENT STUDIES SUPPORTING MOUNTINGQUESTIONED

Several recent studies presumably support themounting viewpoint.7,8,11-18,40-42 Even though there isno perfect study, the studies supporting mounting areflawed and reflect more general problems about articu-lators. Rinchuse25 reviewed 1 of these articles13 andclearly pointed out many shortcomings beyond those oftypical published studies. Some of the general short-comings of the articles are:

● The studies were descriptive rather than experimentalor observational and did not address cause and effect.

● No comparison group was used, or, when a compar-ison group was present, the selection process wasbiased.

● The findings had nothing to do with the health ordisease of subjects’ TMJs. The studies, for the mostpart, did not relate millimeter differences in articu-lator recordings to TMD or stomatognathic health. Ifdifferences exist between articulated condyles ofsubjects, so what?

● The basic premise was faulty in that the findingsgenerally 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 reportof the exact error involved in the bite registrationsand mounting procedures are problematic.

● The studies did not validate the power centric biteregistration and demonstrated that this registrationactually seats human condyles in the predicted fossaposition of anterior-superior CR.

The study by Crawford11 was perplexing. Its pur-pose was to determine whether there is a relationshipbetween occlusion-dictated Panadent articulator condy-lar position axis and signs and symptoms of TMD. Thatis, do subjects having mutually protected occlusionswith MI and CR relatively coincident have fewer signsand symptoms of TMD than subjects without thesetypes of occlusion and condyle position?73 The findingspurport that a relationship exists between occlusion-dictated condylar position and TMD symptomatology.However, the study has many limitations, the mostapparent of which is the sample. Thirty subjects with agnathologic, ideal occlusions, in which CR was coin-cident with CO (intercuspal position, MI), were com-pared with 30 subjects randomly selected from thegeneral population. Curiously, the so-called “ideal sam-ple” was selected from a population that had undergonefull-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 generalpopulation, making the acquisition of an adequatesample of ideal occlusions by random selection imprac-tical.” Crawford11 wrote:

This was a sample of convenience, and it was highlyselected. The contributing clinicians chose subjectsaccording to their own concept of ideal, and thenumber selected was determined by the availabilityand 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 standardis it considered the ideal for which patient treatmentshould be directed toward? Perhaps the author unknow-ingly acknowledged the shortcoming concerning thevalidity of the study before the data were even col-lected. There was also an age difference between the 2samples. The average age for the restored, ideal samplewas 50.8 years; that of the comparison group was 38.4years. Age is a factor in TMD26,30,54,55,57 (TMD in-creases with age but decreases after age 50).73 Thereare 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 aboutthe study’s premise? It seems illogical that they did notknow the TMD status of these subjects a priori. Theexaminers used in the study were not blinded and knewwhich patients had full-mouth reconstructions andwhich did not.73 Furthermore, the number of subjects ineach of the 2 groups (30 subjects) was inadequatebecause of the many uncontrolled confounding factors.Several additional points: the untreated subjects werenot deprogrammed, the palpation recording was notstandardized, the Helkimo index was modified to makethe data “work,” the Helkimo index is not specific forTMD, possibly only happy patients were recalled, theanamnestic results are questionable because subjects’abilities to recall information 10 years later are tenu-ous,73 and an impossible finding of a superior positionof the condylar-postion indicator was excused as an“artifact.”

DEPROGRAMMING SPLINTS

The use of deprogramming splints has become anintegral part of the gnathological view on the proposition of mounting. The evidence for using depro-grammers is equivocal, with no true physiologicbasis. Several essays have described techniques fordeprogramming or discussed the benefits of depro-gramming before performing a centric bite registra-tion.74-85 Several studies have shown a possible benefitof deprogramming,86,87 although most have not.88-90

All studies used deprogrammers for relatively shorttime 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) in40 subjects. Minor differences were noted in articulatorcondyle position indicator centric recording before andafter using the deprogrammer for 6 hours. The mostprevalent type of centric slide resulted on average in aposterior and inferior distraction of the articulatorcondyles from MI-CR of 0.37 mm horizontally and0.57 mm vertically. Conversely, Kulbersh et al18 foundno difference in MI-CR measurements between 34postorthodontic subjects who wore gnathologic full-coverage splints for 3 weeks (24 hours per day) and 14postorthodontic subjects who did not wear splints.

CONCLUSIONS

Science and the practice of orthodontics are notmutually exclusive, as the orthodontic gnathologistsseem to believe. One would think that a considerationof the modern knowledge that occlusion and condyleposition have minimal or no influence on TMD would
have quieted the debate on the use of articulators in
orthodontics. Also, the evidence that orthodontics doesnot cause TMD should have been detrimental to themounting argument. In addition, the credibility of theorthodontic gnathologists should certainly have beenshattered by their claim of mounting cases to a pastincorrect retruded CR position that they do not accepttoday.

Although there is no evidence-based systematicreview (evidence-based Model 3)38,39 about mounting,enough evidence clearly argues against orthodonticpatient mounting. A critical review of the availableliterature and a logical consideration of the notionsabout mounting in orthodontics make the pro positiondifficult.

● The articulator can never simulate human mandibu-lar movement and is based on the faulty theory of theterminal hinge-axis.

● There is no evidence that orthodontic treatmentresults (outcomes) are better when articulators areused in terms of improved patient TMD status andstomatognathic health.

● No scientific evidence suggests that the use ofarticulators will influence orthodontic diagnoses inany meaningful way.

● Although the polycentric hinge articulator is possiblybetter than the hinge axis arcon articulator, it is by nomeans ideal.

● CR records have only been demonstrated to bereliable under controlled laboratory conditions.

● The errors involved in taking the bite registrationsand the mounting procedures reduce the significanceof the gnathologic findings.

● Bite registrations used in the mounting process arestatic records and do not encompass any meaningfulmovement of the human mandible.

● The internal validity of the Roth power centric biteregistration has not been established. Roth did notdemonstrate where patients’ condyles are positionedas a result of the power centric bite registration; heassumed they are in an anterior-superior seatedposition, but he gave no documentation.

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