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Articulators in OrthodonticsTheodore D. Freeland

This article discusses the subject of articulators in orthodontics. It is in 3

parts: the first deals with why articulators are used; the second deals with

techniques needed to use the instrumentation; and the third illustrates how

they are used in diagnosis. Using articulators, occlusal problems otherwise

hidden can be uncovered, especially the cases that involve the vertical

dimension. As with any diagnostic instrumentation, the practitioner has to

learn how to use the instrument and the limitations imposed by said

instrument. (Semin Orthod 2012;18:51-62.) © 2012 Elsevier Inc. All rights

reserved.

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T he use of articulators in orthodontics is acontroversial and debatable issue. This ar-

icle will focus on articulators as and when theyre used in orthodontics. In this discussion, thedvantages of articulators will be presented as aiagnostic tool (Fig. 1). This article is divided

nto 3 parts: the first part will explain why artic-lators are used; the second part will demon-trate the techniques needed to use the articu-ator system; and the third illustrates the uses inhe diagnostic techniques.

Why Articulators Are Used

The articulator and its jaw-recording system areoperator sensitive, as are the other diagnosticaids—cephalometrics, handheld models, andphotographs—that are used in diagnosis, treat-ment planning, and post-treatment analysis oforthodontic cases. The mounting of study mod-els on the articulator in the retruded condylaraxis is an operator-sensitive procedure requiringskill, practice, and the proper education. The

Director/Lecturer, Advanced Education in Orthodontic Group,Gaylord, MI; Adjunct Professor of Orthodontics, University of De-troit/Mercy Dental School, Detroit, MI; and Clinical Instructor,Department of Orthodontics, University of Pennsylvania, Philadel-phia, PA.

Address correspondence to Theodore D. Freeland, DDS, MS,801 East M-32 Gaylord, MI 49735. E-mails: tdfortho@freelandorthodontics.com or drfreeland@rothwilliams-aeo.com

© 2012 Elsevier Inc. All rights reserved.1073-8746/12/1801-0$30.00/0

doi:10.1053/j.sodo.2011.10.002

Seminars in Orthodontics, Vol 18, N

operator must be educated in its uses and tech-niques.

An articulator is a “diagnostic recording in-strument capable of receiving and registeringmaxillo-mandibular relations.”1 It is not capableof chewing like humans, but it can record andduplicate the border movements of the chewingcycle.2

The system can be useful to the clinician inuncovering occlusal problems,3 particularlyhose that occur in the vertical dimension,here the maximum intercuspation of teethauses a down and back distraction of theondyles. The articulator system can also mea-ure the coincidence or differences betweenhe maximum intercuspal (MI) position andhe patient’s seated condylar position.4,5 Pre-

and post-treatment evaluation with the articu-lator system can measure changes at the con-dylar level, providing a quantitative assessmentof the treatment outcome at the condylarlevel.

Orthodontists have often defined gnathol-ogy as “the science of how articulators chew.”6

Although this statement was made in jest, it isa correct description. The following statementby Stuart favors the above-stated opinion. “Anarticulator is first of all a diagnostic recordinginstrument capable of receiving and register-ing craniodental and maxilla-mandibular rela-tion, the three dimensions of oral organ, theaxes of mandibular rotations and the paths inwhich these axes travel in the various move-

ments of the mandible.” It was never intended

51o 1 (March), 2012: pp 51-62

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52 Freeland

to chew like the patient, as it does not have abrain.1 The practitioner has to have an under-tanding of the capabilities and limitations ofhe articulator system and also master theechnique of its use.

McCollum in 1926 coined the term gnathol-gy, which was defined as the study and treat-ent of the entire dentition as a functioning

nit. It stressed the creation of such an occlusionhat would be in harmony with other structuresf the stomatognathic system, including the tem-

Figure 1. Example of articulator system that can beprogrammed to the terminal hinge axis of the patient.(Color version of figure is available online.)

Figure 2. (A) Condylar positioning indicator instrucrosshairs, and the centric occlusion (CO) bite (black

of figure is available online.)

oromandibular joint and periodontium, dur-ng maximum intercuspation and functional

ovements of the mandible, with the patientequiring the least amount of neuromusculardaptation.7

t. (B) The CR point (red dot) is registered at the) shows the condylar position change. (Color version

Figure 3. The CO bite is done with Moyco 10� wax(Moyco Industries, Inc, Philadelphia, PA). A singlesheet is fitted to the upper arch, and the patient thenbites hard. (Color version of figure is available on-line.)

mendot

53Articulators in Orthodontics

The first objective of a functional occlusion isto obtain a stable centric relation of the mandi-ble and have the teeth intercusp maximally atthis mandibular position. Centric relation willpermit seating of the condyles into the glenoidfossa at the most superior position, against theeminentia, and also centered in the transverseplane. In an ideal orthodontic finish, this shouldoccur when the upper and lower teeth areclosed in the MI position.8

The second objective of a good functionalocclusion is to have a harmonious glide path of

Figure 4. The 2-piece power bite is made from DelarBlue wax. First, a front piece is constructed at a verti-cal where the posterior teeth are at least 2 mm apart.Then, a soft posterior section is placed, and the pa-tient is instructed to bite half hard. (Color version offigure is available online.)

anterior teeth working against each other to

separate or disclude posterior teeth immedi-ately, but gently, as soon as the mandible movesout of centric closure. This anterior guidancemust be in harmony with the way in which themandible moves through its border excursions;thus, in a mutually protected occlusal scheme,the mandible can execute its total range or en-velop of motion without interference fromteeth. In turn, the teeth will direct and maintainthe centricity of the condyles in fossae duringclosure.

In diagnosis and treatment planning, toothposition and occlusion are evaluated in theintercuspal position, that is, unmounted hand-held casts and cephalograms in the position ofMI. These static characteristics are poor indict-ors of function. A functional and biologicalocclusion is a realistic goal for orthodontists.As the position of teeth is altered with orth-

Figure 5. The marking of the condylar location in CRand again in CO. (Color version of figure is available

online.)

figur

54 Freeland

odontic appliances, the patient’s MI adaptscontinuously, and the only reliable referencepoint is centric relation. Consideration for re-construction of effective dental occlusionshould include a minimal discrepancy be-tween centric relation and centric occlusion(CO), maintenance of the vertical dimension,a favorable direction of forces applied to theteeth, at rest and during function. Physiologi-cal approach, which is inclusive of the dynam-ics of growth, does not necessarily exclude themathematical gnathological approach. Thefact that gnathology provides a mechanism forevaluation of the occlusal constants helps theorthodontist to facilitate orthodontic treat-ment to individualized norms. Geometry andmathematics can only provide a template toapproximate nature. It certainly does not andcannot replace nature in form, function, oresthetics. It is necessary for evaluating what weare treating and approximately calculating ourtreatment goals. Although our treatment goalsshould not be mathematical, gnathology cer-tainly provides an alternative to better approx-

Figure 6. The distance between the markings that arover 1.5 mm vertically and/or horizontally indicates ddiscrepancy is significant clinically. (Color version of

imate nature. The goal of occlusal reconstruc-

tion in orthodontics should be to achieve astructural balance to facilitate physiologicaladaptation. Roth in 1981 and Cordray in 1996claimed that only by articulator mounting canthe true occlusion be investigated.9,10

The fully adjustable articulator system de-veloped by McCollum, Stuart, and Stallardgained usage in the restorative field, but itnever gained support in the orthodontic field,which is interesting because Stallard was anorthodontist.11

The use of cephalometrics, photography, lim-ited cone beam CT, and articulators are tech-nique sensitive. Orthodontists are required tolearn specific techniques for correct usage. Thefirst requirement for the use of articulators is totake and record 2 types of bite registrations. Oneis called the CO bite, and the other is the centricrelation bite. The first is where all the teeth aretouching, and the other records the best seatedcondylar position that can be obtained at thattime. Once these bites are recorded, the differ-ence in condylar position between CO and cen-tric relation can be measured in all 3 planes of

ated in CR and CO can be evaluated. Measurementced condyles. In the transverse dimension, a 0.5-mme is available online.)

e creispla

space for that patient. The normal range is 1.0

oo

is ava

55Articulators in Orthodontics

mm in the anterior–posterior and vertical di-mensions and 0.5 mm in the transverse direc-tion.12

The next area involved in the use of artic-ulator systems is the ability to receive and re-cord the patient’s true terminal hinge posi-tion.13 The estimated facebow is not accurateenough for purposes of diagnosis. The practi-tioner must obtain a terminal hinge positionfrom the patient and then record it so it can betransferred to the articulator. To gain such aposition, the use of splints may be needed.

Figure 7. (A) The axiopath tracing is used to calculahinge axis, performing the eminence tracing, and deis placed on the data sheet. (Color version of figure

Splints are used to eliminate neuromuscular c

reflexes until a stable, comfortable, repeatablejaw position has been achieved.14

Once the patient’s joint data are recorded,the instrument can be set to duplicate theborder movements of this functional pat-tern.15,16 The maxillary cast can be properlypositioned in the instrument using the hingeaxis transfer method. Then, the Roth powercentric bite technique is used to mount thelower model to the articulator.17,18 An analysis

f the patient’s occlusion can then be carriedut. By using the 5-part centric test and a split

e angle of the eminence. (B) Locating the terminalining the amount of the side shift. This informationilable online.)

te thterm

ast mounting, the centric relation position of

56 Freeland

the condyles can be verified.19-21 If the modelssplit cast check at 5 different verticals, one canbe sure of having recorded the correct termi-nal hinge axis position of the condyles. Thediagnostic phase of using the articulator sys-tem begins after this procedure.

The condylar positioning indicator (CPI) in-strument (Fig. 2) permits the calculation of theamount of condylar distraction. Diagnosis of thevertical dimension discrepancies is possible withthis system, which cannot be done with hand-held models.

Because the models are mounted on the ar-ticulator using the terminal hinge axis, a splitcast analysis can be done to determine whetherthe malocclusion is in a vertical, horizontal, ortransverse direction. This information becomes

Figure 8. Transferring the terminal hinge axis to the

Figure 9. Performing the terminal hinge axis transfer

figure is available online.)

important for deciding the treatment mechanicsfor that particular orthodontic problem.

Other diagnostic uses of the articulator sys-tem can be the creation of diagnostic setups.This may include an orthodontic, surgical, re-storative, or any combination setup. This al-lows the practitioner, before treatment, to de-termine the post-treatment relationship of theocclusion and the temporomandibular joints.In this manner, the roles of the restorativedentist, surgeon, periodontist, and orthodon-tist in the patient’s treatment can be deter-mined pretreatment. It is beyond the scope ofthis article to discuss how all these techniquescan be accomplished. Photographs of the tech-nique will be used to illustrate the basic infor-mation.

nt’s face. (Color version of figure is available online.)

the mounting of the maxillary cast. (Color version of

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for

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57Articulators in Orthodontics

The Techniques Needed to Use theArticulator System

The second part of this article will deal withthe techniques needed to accurately use artic-ulators. The first technique involves the CO ormaximum intercusptation bite (Fig. 3).

After the CO bite is finished, the Rothpower centric bite is used to seat the condyles.The technique involves creating a hard ante-rior stop and then using a soft piece of bluewax in the posterior. This allows the masse-teric sling to seat the condyles up and forward.Only Delar Blue wax (Delar Corp, Lake Os-wego, OR) is used for this bite (Fig. 4). TheCPI test is done by comparing the CO bite(black dot) and CR bite (red dot). The instru-ment used to make this comparison is called acondylar position indicator (CPI) instrument.It consists of upper and lower articulatorpieces. The upper member has the fossa boxes

Figure 10. Placing the terminal hinge axis transfer onhe mounting stand and mounting the maxillary cast.Color version of figure is available online.)

replaced with moveable tables, and the lower

member has a pin placed in the middle of thecondylar sphere. Graph paper is then placedon the tables, and when the CR bite is placedin the instrument, the point is located on thegraph paper in red. Once CR is measured,then black articulating paper is used to markCO. The CO bite is placed between the teeth,and the condylar position is marked in black.The difference between the CR and CO mark-ings can now be calculated (Figs. 5 and 6).

The amount of discrepancy between CR andCO determines the change in the bite duringtreatment.

The technique used to mount the uppermodel is called a terminal hinge axis facebowtransfer. The use of palpation, arbitrary mea-surements, or an estimated facebow transfer isnot accurate. These methods can result in alarge error in the articulator mounting of themaxillary and mandibular casts.13

The recording of the terminal hinge axis lo-cation, the eminence tracing, and the amount ofside shift are used to position the cast correctlyand program the articulator to duplicate thepatient’s border movements (Figs. 7-9).

The terminal hinge axis facebow is now at-tached to the hinge axis mounting stand, andthe maxillary cast is mounted to the upper mem-ber of the articulator (Fig. 10).

Figure 11. Mounting of the mandibular model usingthe Roth power centric bite. (Color version of figure

is available online.)

58 Freeland

Once the maxillary model is mounted, thelower model is positioned using the Roth PowerCentric. The mandibular model is then attachedto the articulator (Fig. 11).

When the models are correctly placed in thearticulator, the diagnostic techniques using thearticulator system can be performed by the or-thodontist.

The CPI instrument has the ability to measurethe difference between CO and CR at the con-dylar level. This information can be used todetermine whether the condyle is seated before

Figure 12. The centric bite (red dot) is always locatedat the center; if not, then a mounting error has beencommitted. The CO bite (black dot) is located eitherdown and forward (A) or down and back (B). If theCO mark is down and forward, it is a Class II horizon-tal problem. If the black dot is down and back, itindicates a Class II vertical problem. (Color version offigure is available online.)

starting the orthodontic treatment(Fig. 12).

The comparison of the pretreatment CPIreadings and post-treatment CPI readings candetermine whether the orthodontic treatmentwas successful at the condylar level. The successof orthodontic treatment can thus be objectivelymeasured (Fig. 13).

The next diagnostic technique is the occlusalvertical analysis. Because the case is mountedusing the terminal hinge axis, changes in verticaldimension can be performed by removing theposterior teeth and autorotating the mandibularmember closed. Observation of the overbite andoverjet can help differentiate between a verticaland a horizontal problem of the malocclusion(Fig. 14).

Once the case is mounted on the articulatorand the instrument is programmed to the pa-tient’s condylar movements, the occlusal char-acteristics can be assessed. The working, bal-ancing, and protrusive excursion can beviewed for any lateral movement interfer-ences. Without the articulator mounting andthe patient’s recorded joint data, the interfer-ences in lateral movements cannot be as-sessed. When trying to assess this informationintraorally, the neuromuscular avoidance pat-tern will prevent any direct observation (Fig.15).

When the patient’s models are mounted on afully adjustable articulator, using the true hingeaxis, accurate treatment setups can be pre-formed. The teeth and jaws can be set to func-tion with the patient’s functioning axis, thusgiving an accurate pretreatment picture of howthe case will respond to the chosen treatmentplan. This can be done for orthodontics, restor-ative dentistry, orthognathic surgery, and anycombination (Fig. 16).

Conclusions

Without the use of the articulator, there is avolume of information that is left out, resultingin diagnostic and treatment planning errors inorthodontic cases. The 3-dimensional thinkinginduced by the use of articulators includes theteeth, jaws, and joints, permitting the orthodon-tist to create optimum function in the mastica-tory complex. Gnathologic practice includes thevertical dimension for the diagnosis and treat-ment planning process, resulting in the elimina-

tion of posterior premature occlusal contacts.

59Articulators in Orthodontics

Figure 13. The post-treatment comparison of occlusal correction at the condylar level is shown. (A) Pretreat-

ment CPI readings. (B) Post-treatment readings. (Color version of figure is available online.)

60 Freeland

The vertical dimension of the occlusion will berevealed by instituting articulators, terminalhinge axis, and axiopath tracings that can thenbe adequately dealt with in the mechanics. Ap-plying gnathologic principles to the field of or-thodontics, through the use of articulators alongwith photographs, cone beam computed tomog-

Figure 14. The case has been mounted using the patieand the articulator rotated closed. If a normal OB anproblem is diagnosed. (Color version of figure is avai

Figure 15. The occlusal analysis is done first in protruthe example given, the occlusal interferences that exis

(Color version of figure is available online.)

raphy, and surface-mapping imaging, helps thepractitioner to treat to a fully functioninggnathic system.

This comprehensive approach to orthodonticdiagnosis, treatment planning, and re-evaluationis appropriate for complex orthodontic prob-lems that require surgical, prosthodontic, or

terminal hinge axis, so the back teeth can be removedoccur, then a vertical problem and not a horizontalonline.)

then in right working, and lastly in left working. Fromhis post-treatment orthodontic case can be visualized.

nt’sd OJlable

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61Articulators in Orthodontics

periodontic interdisciplinary management. Be-cause we do not have a way to predict the hostadaptive processes, all the tools available must beused to evaluate and treat.

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Figure 16. The use of the different setups in a case,The pretreatment and post-treatment images show pplinary treatment for the benefit of the patient. (A)setup, (D) restorative setup, (E) pretreatment mountin(H) facial photo. (Color version of figure is available

G Publishing, 2005

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thop 107:278-308, 1995

62 Freeland

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11. Stallard H: Dental articulation as an orthodontic aim.JADA D Cosmos 24:348-376, 1937

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13. Freeland DF, Kulbersh T, Kaczynski R, et al: Comparisonof maxillary cast positions mounted from a true hingekinematic facebow versus an arbitrary facebow in threeplanes of space [master’s thesis]. The University of De-troit/Mercy Orthodontic Department. RWISO 2, 2010,

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