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Dental Update – November 2003 5 1 1

Abstract: Dental articulators are instruments that reproduce jaw movements tovarying degrees of accuracy. This article aims to give an overview of the various types ofarticulator and describe their applications and limitations.

Dent Update 2003; 30: 511–515

Clinical Relevance: An understanding of the use of articulators is central to thesuccessful provision of indirect restorations.

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Alex Milosevic, PhD, BDS, FDS RCS, DRDRCS(Edin.), Consultant and Honorary SeniorLecturer in Restorative Dentistry, LiverpoolUniversity Dental Hospital, Pembroke Place,Liverpool L3 5PS.

rticulators can be classified as in Table 1. A further division relates to

whether or not the condyle is attached tothe upper arm of the articulator: if it is, thearticular is ARCON – anatomicallyarticulated condyle, e.g. Denar, Whipmix.When the condylar ball is on the lowerarm, the articulator is NON-ARCON (non-anatomically articulated condyle), e.g.Dentatus. The ARCON articulatorreproduces mandibular movement moreaccurately.

HINGE ARTICULATORThe hinge articulator is NOT anarticulator! At best it is a cast holder. Theonly movement is an inaccurate openingand closing. The shorter radius from thecentre of rotation to the lower incisors onthe hinge articulator, compared to thepatient, results in a more curved arc orpathway for the incisor. After the casts aremounted in ICP using an interocclusalrecord, the record is discarded and the

casts are closed through the thickness ofthe record. Because of the more curved(shorter) pathway taken by the incisors,these meet prematurely with a wedge-shaped space manifest between the teeth,the greatest gap occurring posteriorly(Figure 1). The consequent ‘high spot’ onthe restoration needs grinding down, moreso the further posterior the restoration.Thinner records are preferable.1 Providingthere are sufficient teeth to gain ICPmanually, it may be better not to take anyinterocclusal record but relate the casts byvisual and tactile methods.2 There is nopossibility of lateral or protrusivemovement on this ‘articulator’. Therefore,its applications are limited to themanufacture of a single crown in anotherwise fully dentate arch. It has noplace in diagnostic assessment. The riskof introducing interferences on anyrestoration can be reduced if the hinge isused in conjunction with a FunctionallyGenerated Pathway. The FGP is obtainedby asking the patient to carry outexcursions on soft wax held within acopper ring tightly placed on thepreparation (Figure 2). The cuspal pathscarved into the wax (-ve impression) arecopied in impression plaster (+ve cast)with inclusion of the adjacent occlusal

surfaces so that the FGP record can belocated on the working cast. Once thecrown is waxed up on the working die, theFGP record is fully seated on it and anyinterferences that show up on the wax canbe removed prior to casting.

PLANE LINE AND AVERAGEVALUEThe average value instrument tends to belarger than the plane line andconsequently better equipped toreproduce jaw movement. Botharticulators have limited lateral andprotrusive movement, usually set at 30o

for condylar guidance angle, 15o for

Occlusion: 3. Articulators andRelated Instruments

ALEX MILOSEVIC

A

Hinge

Plane line

Average value

Semi-adjustable (Arcon or Non-arcon)

Fully-adjustable

Fossa-moulded/stereographic

Table 1. Classification of dental articulators.

Figure 1. The shorter radius from the ‘articulator’centre of rotation to the incisor results in a morecurved arc of closure. Removal of a waxinterocclusal ICP record and closure through thethickness of wax leads to initial contact at theincisors and a wedge-shaped gap, widest posteriorly.

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incisal guidance and 110 mm for inter-condylar distance. For a couple ofposterior crowns or a short spanposterior bridge (max 3 units), an averagevalue can be used in preference to aplane line, although for complete dentureconstruction this distinction may be lessimportant. Some intra-oral adjustmentmay well be necessary, particularly RCP–

ICP and on lateral excursions. Forreplacement anterior teeth, the semi-adjustable articulator is the instrument ofchoice.

THE SEMI-ADJUSTABLEARTICULATORThese instruments are the workhorses formany restorative problems (Figures 3 and4). Although several differentmanufacturers make semi-adjustablearticulators (see Table 2), the principles ofrecord taking and programming aresimilar. They require a facebow to relatethe maxillary cast to the hinge axisaccurately, plus interocclusal records inprotrusion and left/right lateral excursionto programme condylar guidance angleand Bennett shift and/or angle,respectively. For all diagnosticprocedures (e.g. orthognathic treatmentplanning, occlusal analysis) an RCP(tooth apart) record is required, whereasfor restorative procedures either an RCPor ICP record is indicated. Once again,the latter can be dispensed with if asufficient number of teeth allow accuratevisual manipulation into ICP.

The average position of the hinge axisfor placement of the condylar points ofthe facebow is 13 mm anterior to thetragus on the trago-canthal line. In-built

compensation allows other systems touse an earbow placed into the externalauditory meatus, which is arguably moreuser-friendly. The true position of theterminal hinge axis can only bedetermined dynamically using a kinematicbow which is attached to mandibularteeth. Pure rotation of the side armpointers indicates the place to mark theskin for placement of the separatemaxillary bow and thus accurately relatethe maxillary cast to the hinge axis on thearticulator. Facebows correctly positionthe maxillary cast spatially in 3-D by wayof the third reference point (usually theorbital pointer) and thus give thetechnician an aesthetic perspective.

The ability to adjust condylar guidanceFigure 2. (a) Functionally generated path in soft wax retained within copper ring on prepared 6/(46). (b) Plaster positive of FGP held in silicone putty (another case). (c) FGP placed on waxed upcrown. (d) Single waxed up crown on hinge ‘articulator’ with harmonious occlusal anatomy.

a b

Figure 3. (a) Dentatus semi-adjustablearticulator. (b) Dentatus with facebowattached to condylar ball (Non-arcon) andrelated to orbital pointer.

Figure 4. Denar MKII semi-adjustable.

a

b

Figure 5. The effect of varying inter-condylardistance (ICD) on cuspal paths. Red lineindicates true path with ICD of 110 mm. If ICD isgreater (blue path) or less than (green path)true ICD, paths followed by the teeth on thearticulator will differ.

Figure 6. Illustration of both the horizontal andvertical centres of rotation and the radius to acusp tip.

c d

>ICD

<ICD

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Figure 7. (a and b) Techniques to check reproducibility ofintra-oral records. These show the Lauritzen split cast withtwo different RCP records for the same patient. The gap in(b) alerts the dentist to a discrepancy during record taking.It’s best to take at least three records in each position.

a b

Figure 8. Another technique to check RCPrecord accuracy or consistency. The DenarVericheck or Centricheck uses a special upperarm with flags and pointers. Note the siliconebuccal index record and the custom-madeacrylic incisal guidance table.

angle and Bennett shift will facilitateocclusal harmony of restorations withinany given stomato-gnathic system. Ifincisal guidance is unknown, i.e. in caseswith an old partial denture replacing allfour upper incisors or four poorlycontoured pontics on an upper six-unitbridge, then incisal guidance can becustomized in acrylic and then adjusted onthe incisal guidance table of the articulator.

Some instruments allow limitedadjustment of the inter-condylar distance.The horizontal path taken by a molar cuspacross the opposing tooth with either agreater or lesser inter-condylar width onthe articulator is illustrated in Figures 5and 6. For clarity, this illustration does notconsider the effect of Bennett shift. Somesemi-adjustable articulators facilitate thewaxing-in of RCP-ICP movement, freedomin centric.

Despite these added features, mostinterocclusal records taken in wax areprone to distortion.3 On withdrawal fromthe mouth, great care is needed to avoidbending the heels of the record inwards.Closure into wax with muscle force riskstooth and/or mandibular displacement/flexion4,5 which can be avoided by usingbuccal indices taken whilst the patient

holds the appropriate position andsilicone is injected around the teeth (seeprevious paper on the RCP record). Noneof the current techniques or materials isideal (see Table 3), although certain waxesdistort less (Moyco Beauty Pink suppliedby Procare). Finally, the paths takenbetween two points are linear on the semi-adjustable articulator but curved in thehuman condyle. Pathways on fossa-moulded and fully adjustable instrumentsare curved and thus more accuratelyreproduced. Dynamic methods rather thanstatic wax records are utilized by somesemi-adjustable articulators, such as theGerber. In this instrument, condylarguidance angle is gained using a kinematicbow and the gothic arch tracing relates thecasts in RCP. Techniques to check theaccuracy of an RCP record are shown inFigures 7 and 8.

FULLY ADJUSTABLEARTICULATORSAs the name implies, these instrumentsprovide more adjustments and greateraccuracy, particularly in respect ofchanges in vertical dimension, bordermovements, Bennett shift and Bennett

ARCONDenar MKII (Water Pik Inc. supplier Prestige Dental)KaVo EWL (KaVo, POB 1320, Leutkirch, D-88293, Germany)SAM (Prazisionstechnik, Munich, D-8000, Germany)Whip Mix 3040 (Whip Mix Corp. POB 17183, Louisville, Kentucky, USA)

NON-ARCONDentatus ARL/ARH (Dentatus Int. AB, Hagersten, Sweden, 126-53)Gerber (Condylator, Zurich 8028, Switzerland)Hanau (Teledyne Hanau, Buffalo, NY, USA)

Table 2. Types of semi-adjustable articulator.

l Does not displace teeth duringintercuspation.

l Little or no dimensional change on setting.

l Accurate reproduction of occlusal/incisalsurfaces.

l Remains rigid after setting.

l Offers minimal resistance during closurein order to reduce mandibular flexion ordisplacement.

Table 3. Ideal requirements of a material usedfor inter-occlusal records.

angle. Examples of fully adjustablearticulators are:

l Denar D5A (see Figure 9) andl Stuart.

These articulators requirepantographic tracings to set theadjustments. Upper and lower bows areattached to the teeth via clutches andseparated by an intra-oral central bearingpoint. Styli record the paths on tracingtables after which the bows are locked,dismantled from the clutches and re-assembled on the articulator. Apart fromrecording mandibular border movementsaccurately, the pantograph has also beenapplied as a diagnostic and prognostictool in the management of TMJdysfunction. The PantographicReproducibility Index (PRI) wasdeveloped to confirm dysfunction and tomonitor progress of treatment.6 However,technique sensitivity, equipment expenseand the time involved in clutchconstruction, recording and programminghave deterred many dentists frominvesting in such instrumentation.

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Moreover, for most restorative treatment,the semi-adjustable articulator shouldprove perfectly acceptable. Recentdevelopment of an electronic jaw-trackingdevice significantly reduces chairsidetime (Figure 10). The system facilitatesdetermination of condylar guidance angleand Bennett shift by having ‘flags’ akinto recording tables over each TMJ, with astylus or sensor on a mandibular bowattached to the teeth via a clutch. Themovements are digitized by the table/stylus assembly and subsequentlyshown on a LCD or printed as apermanent record for the patient’s file.

STEREOGRAPHIC ORFOSSA-MOULDEDStereographic techniques simplifyarticulator programming by dispensingwith the pantograph and using intra-oralclutches with studs which mould softacrylic during border movements. These

dynamically carved, intra-oral 3D recordsare then transferred to the articulatedcasts (Figure 11). Cold cure acrylic isplaced in special fossa inserts andarticulator excursions are guided by theintra-oral engravings. Whilst thearticulator arm is moved, the condylarhead on the instrument carves the acrylicresin in the fossa insert, thus generatingpermanent condylar moulds thatincorporate condylar inclination, Bennettshift and angle at the correct inter-condylar width. Other devices utilize pre-moulded plastic fossa analogues withfixed Bennett angle and various Bennettshifts. Condylar Guidance angle can bevaried either by orienting the analogue orsome analogues also have pre-setcondylar inclines.

Such instruments include:

l TMJ Stereographic system;l Denar Combi and Anamark;l Panadent Corp. USA.

CONCLUSIONOcclusion is not an inherentlycomplicated subject. Understandingocclusion is not easy becauseexplanation of condylar and mandibularmovement is difficult. This has more todo with the author or teacher trying toget a message across to his/heraudience. Hopefully, readers will havetheir appetites whetted for furtherstudy.

REFERENCES

1. Adrien P, Schouver J. Methods for minimising theerrors in mandibular model mounting on anarticulator. J Oral Rehabil 1997; 24: 929–935.

2. Walls AWG, Wassell RW, Steele JG. A comparisonof two methods for locating the intercuspalposition (ICP) whilst mounting casts on anarticulator. J Oral Rehabil 1991; 18: 43–48.

3. Mullick SC, Stackhouse JA, Vincent GR. A studyof interocclusal record materials. J Prosthet Dent1981; 46: 304–307.

4. Teo CS, Wise MD. Comparison of retruded axisarticular mountings with and without appliedmuscular force. J Oral Rehabil 1981; 8: 363–376.

5. Omar R, Wise MD. Mandibular flexure associatedwith muscle force applied in the retruded axisposition. J Oral Rehabil 1981; 8: 209–221.

6. Shields JM, Clayton JA, Sindledecker LD. Usingpantographic tracings to detect TMJ and muscledysfunction. J Prosthet Dent 1978; 39: 80–87.

FURTHER READING

Klineberg I. Occlusion: Principles and Assessment, 1st ed.Oxford: Wright, 1991.

Warren K, Capp NJ. Occlusal accuracy in restorativedentistry: the role of the clinician in controllingclinical and laboratory procedures. QuintessenceInt 1991; 22: 695–702.

Winstanley RB. A retrospective analysis of thetreatment of occlusal disharmony by selectivegrinding. J Oral Rehabil 1986; 13: 169–181.

Wise MD. A Clinical Guide to Occlusion, 1st ed. BDJPublications, 2002.

Figure 11. Upper intra-oral clutch for dynamicstereographic reproduction of mandibularmovement. Note: the three acrylic engravingswith a gothic arch trace.

Figure 9. (a and b) The Denar D5A fully-adjustable articulator and close-up view of thecomplex condylar assembly.

a b

Figure 10. (a) Denar Cadiax facebow inposition via mandibular clutch. (b) Close-upof electronic digitizing table/sensor assembly.(c) Monitor showing left and right condylarpath during protrusion.

a b

c