Therapeutic Class III molarocclusion

Camille PHILIP-ALLIEZ, Michel LE GALL,

Danielle DEROZE, Jean-Daniel ORTHLIEB,

Pierre CANAL

ABSTRACT

The objective of this work is to study the static and dynamic occlusion ofdentitions in a Class III molar relationship to determine what might be theindications for treatment that would leave buccal segments in this position, andto evaluate the occlusal adaptions that would be needed to make it functionallyacceptable.

KEYWORDS

Occlusion

Class III

Occlusal equilibration.

Address for correspondence:

C. PHILIP-ALLIEZ,Assistant hospitalier universitaire,faculte d’odontologied’Aix-Marseille II,27, boulevard Jean-Moulin,13355 Marseille cedex 5.cvlphilip@free.fr

DOI: 10.1051/odfen/2009407 J Dentofacial Anom Orthod 2009;12:169-181� RODF / EDP Sciences

169

Article available at http://www.jdao-journal.org or http://dx.doi.org/10.1051/odfen/2009407

1 - INTRODUCTION

A primary therapeutic objective oforthodontic treatment is to obtain aClass I canine and molar relationshipand to provide functional anteriorguidance.

In some specific cases, orthodon-tists have concluded that a ‘‘therapeu-tic’’ Class II molar relationship,associated with a Class I caninerelation and harmony with well equili-brated incisal segments is acceptableso long as the upper molars arepositioned in a manner different fromthose in a Class I relationship. This"therapeutic" Class II relationship hasbeen considered suitable because, asa part of a well equilibrated dentition itis deemed not to be traumatogenic.

We are suggesting the hypothesisthat orthodontists should considerbestowing the same acceptable sta-tus on a ‘‘therapeutic’’ Class III rela-tionship. We shall attempt to validate

this hypothesis and we shall try toestablish the criteria for the rareindications for treatment that wouldresult in such a termination.

We shall also endeavor to deter-mine what type of static and dynamicocclusions should be present whenfirst molars are left in a therapeuticClass III relationship.

However, it should be clear that aClass III molar relationship, even whenassociated with a Class I canineposition and well functioning incisorsblocks, should not be considered initself an orthodontic objective but,instead, an occlusal compromise.

In addition, as we shall postulatelater in this paper, it is possible to askthe question whether a finished resultin therapeutic Class III, despite thereservations we might have about it,can be considered a "lesser evil" insome situations.

2 - INDICATIONS

In cases of congenitally absent lowersecond premolars, well formed andcomplete maxillary arch, and a flatprofile, a treatment plan calling for nocompensating maxillary extractionsand mandibular space closure by me-sial movement of the buccal segmentsmight be appropriate especially whereeconomic considerations are a factor.

Similar treatment plans may beappropriate for cases of excess mesialpositioning of lower molars wheremoving them distally might poseserious technique problems or risk

causing an unacceptable increase invertical dimension.

Similar considerations may apply incases of mild skeletal Class III with nodento-alveolar compensation thatshows a mandibular arch with anteriorcrowding while the teeth in maxillaryarch are perfectly aligned. By extractingtwo lower premolars or one lowerincisor the orthodontist can resolvethe problem of the crowding of themandibular anteriors and their relation-ship to their maxillary antagonists with-out making any demands on the

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satisfactory upper arch. The alternativeprocedure of extracting the uppersecond premolars to mesialize the firstmolars and obtain a Class I molarrelationship would risk ‘‘dishing in’’the face.

A similar problem can arise in ClassII skeletal cases when retracting themandibular incisors to obtain sufficientoverjet to accommodate surgical ad-vancement of the mandible requiresthe extraction of two lower premolars.Traditional treatment plans would callfor compensatory maxillary extrac-

tions in order to achieve a Class Imolar relationship even if the upperarch is well aligned. Are such extrac-tions always necessary?

If the end-of-treatment Class IIIdentition can be well enough equili-brated to eliminate all occlusal trauma,can we consider it to be ‘‘therapeutic’’provided that the canines are in Class Iand the incisors are in good function?We believe that indications for such asolution exist even though they arerare.

3 - CONTRA-INDICATIONS

Contra-indications for orthodontictreatment leaving molars in Class IIIrelationship are essentially those of aClass III skeletal type that requiresurgical intervention. In these cases,where there is often a problemof vertical dimension, the skeletaldiscrepancy is so great that no den-to-alveolar compensation can be ac-complished. Most often surgery inboth jaws is required.

And if the lower third molars arecongenitally absent, there is added

reason to presume that a final ‘‘ther-apeutic’’ Class III molar relationshipwould be imprudent.

In cases of congenital absence oflower second premolars, closing thespaces by a planned mesial move-ment of the molar teeth is a temptingprospect, but orthodontists must eval-uate the risk of its adversely affectingthe appearance of patients with flat orconcave profiles when the inevitablereciprocal distal movement of theincisal block occurs.

4 - CURRENT CONCEPTS OF OCCLUSION

Clark and Evans1 reviewed theliterature searching for criteria thatcould define ideal functional occlusion,but were unable to find any clear andwell accepted benchmarks, writing,‘‘no pertinent definition of the idealocclusion can be established in aconclusive fashion.’’ At best, theydiscerned a convergence of ideas of

authors about competing principles forthe achievement of good occlusion:

– both left and right segments of theupper and lower arches should be incontact in centric relation.

– there should be less than 1 mmdifference between centric relationand maximum intercuspation.

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– contacts in lateral excursion shouldoccur only on the working side, eitherbetween canines, in canine protectedocclusion, or between two pairs of

laterally adjacent teeth in the buccalsegments, in group function, with nocontact on the non-working side.

5 - CRITERIA FOR FINE DETAILING OF OCCLUSION

5 - 1 - In Angle Class I normalocclusion

Because of the nature of the inter-cuspation between the two arches,the teeth of the lower arch are a half-cusp in advance of the upper teeth, allteeth occluding with two antagonistsexcept for the mandibular centralincisors and the maxillary third molars(fig.1 and 2).

5 - 2 - In therapeuticClass III molar occlusion

The over-all decrease in the numberof contact points between the twoarches and their less favorable ar-

rangement weakens the stability of atherapeutic Class III occlusion. In it theClass I canine relationship is pre-served but the Class III molar position-ing promotes a tooth on tooth inter-arch relationship for the maxillarysecond premolars and the mandibularfirst molars (fig. 3 and 4).

5 - 2 - 1 - In the maxilla

• Static occlusion

The palatal cusp of the maxillarysecond premolar should, in occlusion,lie in the central fossa of the mandibularfirst molar. But the mesio-palatalcusp of the first maxillary molar, inocclusion, can scarcely fit in the mesialfossa of the second mandibular molar.

Figure 1Occlusion 1 tooth with 2 teeth: mandibular workingcusps. After Orthlieb3.

Figure 2Occlusion 1 tooth with 2 teeth: maxillary working cuspsAfter Orthlieb3.

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• Dynamic occlusion

– On the working side in lateralexcursion: The mesio-palatal cusp ofthe maxillary first molar tends to beblocked by the mesio-buccal cusp ofthe second mandibular molar.

– On the non-working side in lateralexcursion:

The mesio-palatal cusp of the firstmaxillary molars buts up against themesiolingual cusp of the second man-dibular molar.

5 - 2 - 2 - In the mandible

• Static occlusionThe buccal cusp of the second

mandibular premolar makes contactwith the embrasure between maxillarycanine and first premolar. This posi-

tioning presents no problems whenthe teeth of the two arches are inocclusion or are functioning.

The mesio-buccal cusp of the man-dibular first molar lodges in the oppos-ing upper embrasure between thesecond maxillary premolar and themaxillary first molar.•Dynamic occlusion

– On the working side in lateralexcursion:

In lateral movements, the distalpalatal surface of the palatal cusp ofthe upper second premolar makes ahard contact with the mesio-buccalcusp of the lower second premolar.

– In lateral movements on the non-working side, the distal surface of themesio-buccal cusp of the lower first

Figure 3Horizontal view of teeth left half arches intherapeutic Class III molar occlusion. AfterOrthlieb3.

Figure 4Occlusal contacts in therapeutic Class IIImolar relationship. After Orthlieb3.

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molar will encounter the internalmesial surface of the buccal cusp ofthe upper second premolar.

– In protrusive movement.The details of an adjustment of a

Class III occlusion do not interferewith protrusive movements. The teethroutinely come out of occlusal contact,in part as a result of the orthodontist’sregulating the components of tooth totooth articulation: orientation of the

occlusal plane, the curve of Spee,cusp height, and incisal slope toharmonize its function with condylarslope.

To assure all these aspects ofcorrect function are in place, ortho-dontists must finish treatment with anocclusal equilibration that will stabilizea therapeutic Class III molar relation-ship.

6 - OCCLUSAL EQUILIBRATION

6 - 1 - In the area of the maxillaryfirst molar

The orthodontist should deepen thecentral fossa of the upper first molar.(fig. 5) and re-shape the enamel bridge(fig. 6) so that the mesio-buccal cuspof the lower second molar can adaptitself. It is advisable to apply buccalroot torque to the upper first molars tocompensate for the decrease in man-dibular width and thereby eliminateocclusal interferences (fig. 7).

By slightly rotating the upper firstmolars mesially, orthodontists canimprove their occlusion with the lowersecond molars. So, as in regular ClassII therapy, they should not use brack-ets with toe-in incorporated in them.In order to determine how muchmolars that vary in size from patientto patient should be rotated, it isadvisable to mount models on anarticulator.

6 - 2 - In the area of the maxillarysecond premolar

Orthodontists should incorporatebuccal root torque into their appli-ances in order to facilitate properocclusion of the palatal cusp of theupper second premolar with the cen-tral fossa of the mandibular first molar(fig. 7).

The disparity between bucco-lingualwidths of the maxillary second pre-molar and the mandibular first molar,which occlude with each other, re-mains the most important problemposed by establishment of a thera-peutic Class III occlusion. To compen-sate fo r th is d i f fe rence , theorthodontist can deepen the buccalgroove of the lower first molar (fig. 9)so it will be better adapted to receivethe buccal cusp of the upper secondpremolar.

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Figure 5Central fossa of the firstmaxillary molar. AfgerCretot2.

Figure 6Enamel bridge of the firstmaxillary molar. AfterCretot2.

Figure 7Buccal root torque applied tofirst maxillary molar. AfterCretot2.

Figure 8Rotational force to applyto first maxillary molar.After Cretot2.

Figure 9Buccal view of 36: buccal groove. AfterCretot2.

Figure 10Lingual crown torque to be applied toupper second premolar. After Cretot2.

Figure 11Central fossa of the mandibular first molar(in red) and stabilizing stops (in blue). AfterCretot2.

Figure 12Mesial facet of the mandibular second molar(in red) and the toe-in force to be applied to it(in blue). After Cretot2.

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6 - 3 - In the area of themandibular first molar

The orthodontist can deepen thesmall central fossa of the mandibularfirst molar (fig. 11) with a cylindricaldiamond bur and create stops byplacing composites on the mesio anddisto-lingual cusps of that tooth inorder to stabilize its occlusion withthe maxillary second premolar.

6 - 4 - In the area of themandibular second molar

The orthodontist should deepen themesial fossa of the mandibular secondmolar so that the large mesio-palatalcusp of the maxillary first molar willfind enough room for proper engage-ment in occlusion (fig. 12).

It is advisable to apply toe-in force tothe lower second molars to improvetheir occlusion with the upper firstmolars (fig. 12).

7 - CRITIQUES

In orthodontic cases treated to afinal therapeutic Class III molar rela-tionship, the lower third molars shouldhave a morphology that allows themto articulate well with the uppersecond molars. But the question iscan one type of molar become anacceptable substitute for another?Lower third molars are often smallerthan second molars and are extremelyvariable in size and shape. Unfortu-nately, at the beginning of treatmentthese teeth are usually nothing morethan buds, incompletely calcified, andlocated deep in the body of themandible. So orthodontists can evalu-ate them only through radiographsthat frequently give an inaccuratepicture of these incompletely formedand unerupted teeth, especially if theyare malpositioned. This uncertaintymay be greatly reduced in the future

thanks to the introduction of newX-Ray techniques such as NewTom3G and Cone Beam CT.

Another issue is that a therapeuticClass III relationship puts the survivalof the upper third molars at risk. In thatocclusion the only possible occlusalcontact that can be envisioned forthem is between their mesial marginand the disto-lingual cusps of thelower third molars.

Comparably, the same observationcan be made about the lower thirdmolars in cases of therapeutic Class IImolar relationships.

Orthodontists must consider thepossibility that the congenital absenceof lower third molars may constitute acontra-indication for a treatment planthat proposes a finished result in atherapeutic Class III relationship.

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8 - CLINICAL CASE

The lower second premolars of thispatient, a 13 year-old girl (fig. 13 to 16)were congenitally absent. The treat-ment plan called for the extraction of

the lower second temporary molarsfollowed by the mesializing of thelower first molars (fig. 17 to 20).

Figures 13 a to cClinical exam, before treatment.

Figures 14 a to cIntra-oral photographs, before treatment.

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Figures 16 a and bSupplementary examination, before treatment.

Figures 15 a to eSupplementary examination, before treatment.

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Figures 18 a to cIntra-oral photographs, after treatment.

Figures 17 a to cClinical exam, after treatment.

Figures 19 a and bSupplementary examination, after treatment.

Cas des Dr Bachet, Dameron et Le Gall.

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9 - CONCLUSION

Orthodontists should not reject outof hand a treatment plan that willresult in a "therapeutic Class III molarrelationship" despite the problems thatwe have indicated can accompany itbecause it is an acceptable and,perhaps, preferable solution in certainspecific cases.

They should not consider it an easyway out because its proper executionrequires very precise adjustments topalliate the natural imperfections thatare inherent in it.

Talked about for years but veryrarely actually studied, this type ofocclusion can be acceptable if thepractitioner finishes treatment with a"good" occlusal equilibration. When-ever orthodontists conclude that this

therapeutic route might be best for apatient, they should always include aset-up as a part of their diagnosticprocedures because it is the only waythey can accurately predict the finalocclusal result.

If they can put their patient’s teethin a Class III molar relationship that isnon-traumatic they can consider it tobe a "therapeutic occlusion" providedthat the canines are in Class I and theupper and lower incisors function wellwith each other.

They should also attempt to evalu-ate the long-term stability of such aresult, even if, at this time, not enoughevidence is available to provide ananswer to this question.

Figures 20 a and bSupplementary examination, before treatment.

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REFERENCES

1. Clark JR., Evans RD. Functional occlusion. I. A review. J Orthod 2001;28(1):76-81.2. Cretot M. L’arcade dentaire humaine. Paris: Editions CdP, 1983.3 Orthlieb J.D. Occlusion et dysfonction: le paradoxe de l’orthopedie-dento-faciale

(Rapport) 1998;69(1).

Michel LE GALL, Maitre de conferences des Universites, chef de service, faculted’odontologie d’Aix- Marseille II, 27, boulevard Jean-Moulin, 13355 Marseille cedex5, France.

Danielle DEROZE, Maitre de conferences des Universites, faculte d’odontologied’Aix-Marseille II, 27, boulevard Jean-Moulin, 13355 Marseille cedex 5, France.

Jean-Daniel ORTHLIEB, Professeur des Universites, Faculte d’odontologie d’Aix-Marseille II, 27, boulevard Jean-Moulin, 13355 Marseille cedex 5, France.

Pierre CANAL, Professeur des Universites, Faculte d’odontologie de Montpellier,545, avenue du Professeur Jean-Louis Viala, 34000 Montpellier, France.

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