Occlusion for the class III jaw relations patient

Occlusion Wilbur

for the class III jaw relations

0. Jensen,

patient

D.D.S.*

University of Southern California, School of Dentistry, Los Angeles,Calif. The class III jaw relations patient possesses challenging changes in occlusal patterns. The interocclusal distance, evelope of motion, chewing stroke, toothto-tooth relations, and the determinants of occlusion vary from the criteria established for the class I or class II occlusions. The lack of anterior guidance and the added width and length of the mandible have a significant effect on occlusal morphology. Several stable forms of occlusal relationships can be found at one time in the same dentition. The occlusal morphology is dictated by the condylar movements and mandibular size. The balancing cusps must provide the proprioceptive guidance for the chewing cycle. One half to 1 mm, rest interocclusal distance is adequate to allow the teeth to separate in speech and function. (J PROSTHETDENT

1990;64:566-8.)

T

he patient exhibiting a mandibular macrognathic jaw relationship possesseschallenging changes in occlusal patterns from the criteria established for patients with class I jaw re1ationship.l The large size of the mandible creates a unique occlusal design. The interocclusal distance, envelope of motion, chewing stroke, tooth-to-tooth relations and the determinants of occlusion vary from the criteria outlined for class I or class II occlusions. The lack of anterior guidance has a significant effect on the occlusal scheme as does condylar function in conjunction with the articular eminence and the disparity in jaw size relative to cusp height, tooth placement, and chewing cycle.2

CENTRIC OCCLUSION (MAXIMUM INTERCUSPAL POSITION) Centric occlusal contacts do not follow a definite pattern in the macrognathic patient. Each patient has a different pattern of centric occlusal contacts depending upon the relative size of the mandible. In most cases,both the anterior teeth and posterior teeth display simultaneous centric contacts. The posterior contacts can vary greatly from a cusp-fossa relationship to a cusp tip-to-cusp tip and, in some cases, a complete crossbite. All of these tooth relationships may be present in the same dentition, providing a unique contact pattern. Tooth-to-tooth closure patterns vary according to the size of the mandible. The mandibular first molar may occlude with the maxillary second and first premolars. Mandibular length can also produce an anterior crossbite relationship where the maxillary anterior teeth are overlapped by the mandibular anterior teeth.

WORKING-SIDE

MOVEMENT

The incisor teeth in an end-to-end, or beyond, relationship are almost free of working contacts. If any occur, they

*AssociateClinical Professor,Continuing Education. 10/l/20625

are seen at the beginning of the stroke and are of short duration. This anterior relationship provides no discluding abilities for the canines or anterior teeth. The articular eminence, jaw size, and the posterior teeth become the guiding factors. The major working contacts are found on the posterior teeth. They occur in variable patterns and are difficult to describe in terms of the usual occlusal philosophies. With the lack of anterior guidance, this occlusion is a type of group function that has no discluding ability from the canines or incisors. It is, therefore, a component of bilateral balanced occlusion. Definite working facets are observed and can be measured.3 The class III patient has a more limited functional range than the class I or class II patient, but a range of function does exist and must be allowed for when contemplating restorative dentistry or equilibration.

BALANCING-SIDE

MOVEMENT

The posterior teeth show balancing wear facets, particularly on the second and third molars. Because of the longer arch, the balancing contacts increase in duration and intensity the more posterior the tooth. Each of the posterior quadrants show balancing contacts. The lack of guidance generally provided by the anterior teeth leaves the remainder of the determinants of occlusion to be provided by the temporomandibular joints, relative jaw size, and tooth-to-tooth relationships. This combination of joint guidance with no canine or anterior disocclusion, and resulting flatter curve of Spee, does not provide the ability for group function disocclusion, and dictates a functional balancing-side contact during lateral movement. The occlusal contacts start at centric closure and remain heavy during the entire balancing movement. This movement differs from the balance of the class II relationship in that it appears to be more intense, broader, and rides higher on the balancing cusp. A naturally developed balanced occlusion is observed

NOVEMBER

1960

VOLUME

04

NUMBER

6

C!LASS

III

JAW

RELATIONS

I-Amm

-I

\ 20f

\

irh

CLASS

I

mm

CLASS

III

Fig. 1. I, Hinge axis; II, terminal hinge opening; III, maximum opening; h, habitual opening; x, physiologic rest postion; p, maximum protrusion.

often in the macrognathic mandible. Balancing contacts are physiologic for this jaw relationship and should not be disturbed during equilibration or restoration of occlusion. Arbitrary removal of balancing contacts to fit a formula often causes discomfort, rotational pressures, and increased stress on the periodontal apparatus.

PROTRUSIVE

MOVEMENT

It is generally taught that class III patients do not function in the protrusive range. Protrusive movement may not involve the front teeth, and the patient may incise on an open and close movement. In addition, incising may occur on a chewing or grinding stroke. Protrusive faceting is observed on the posterior teeth in almost all class III patients. The wear facets are not long but are present, with the molar teeth showing the most distinct facets. Mandibular macrognathic patients have a short protrusive stroke, and occlusion is improved if incorporated into posterior restorations and appliances.

THE

JOURNAL

OF

PROSTEETIC

DENTISTRY

ENVELOPE

OF MOTION

The envelope of motion, as established by Posselt,4 is different from the class I jaw or class II jaw relationships (Fig. 1).The protrusive movement is smaller; the maximum opening is greater because of the length of the mandible; the arc of hinge opening is greater because of the jaw size; the interocclusal rest space is less. A slide from centric relation to maximum intercuspal position is variable. The envelope of motion includes a smaller protrusive movement, longer maximal opening, and reduced interocclusal rest dimension.

VERTICAL

DIMENSION

When the anterior teeth are in an end-to-end occlusion, the mandible is not required to move forward for speech or to incise. The condyles, therefore, have limited movement down the eminence during function, and little space is needed to clear occlusal contacts. Vertical clearance of 0.5 to 1 mm is adequate interocclusal rest space in macro-

567

JENSEN

gnathic jaw relations, compared with the 2.5 mm in the class I, and the 3 to 5 mm in the class II relationships.

OCCLUSALMORPHOLOGYOFTHE POSTERIOR TEETH The added width and length of the mandible and the lack of anterior guidance from the anterior teeth have a significant effect on occlusal morphology: 1. Centric closure and lateral movements or “orbiting” movements become dominant movements in establishing occlusion. 2. Orbiting movements determine balancing cusp height, fossa width, and escape groove location. 3. The tooth-to-tooth contact in centric closure is forward from the normal pattern and varies with jaw size. 4. Arc of movement is longer and the escape grooves are located farther mesially on the mandibular teeth. 5. There is no limiting action from the anterior determinants. Jaw movements should be accurately recorded and reproduced in the restored occlusal scheme. 6. The balanced occlusion is shallower and has longer balancing contacts on the molars. It is a definite balanced occlusion. Balance should be used to provide the necessary guidance in crossbite occlusions.

SUMMARY A class III mandible exhibits stable forms of occlusal relationships. Cusp-fossa, cusp-marginal ridge, cusp tipto-cusp tip, and crossbite tooth relations may all be found

568

at one time in the same dentition. Each can be stable or corrected to a stable occlusion. The lack of anterior guidance creates major changes. No protection is given by the anterior teeth to the posterior occlusion. The occlusal morphology is dictated by the condylar movements and mandibular size. Accurate interarch recordings are important to reproduce the extent of the condylar movement. Balanced occlusion is dictated by lack of function of anterior determinants. Balancing cusps must provide the proprioceptive guidance for the chewing cycle and crossarch balance for patient comfort. One half to 1 mm interocclusal rest distance is adequate to allow the teeth to separate in speech and chewing. The macrognathic occlusion may be a stable and comfortable occlusion. I acknowledgethe valuable assistanceand recommendationsof Dr. R. Bruce Coye.

REFERENCES 1. Huffman RW, Regonos JW. Principles of occlusion-laboratory and teaching manual. London, Ohio: H&R Press, 1973. 2. Ingraham R. Physiology of occlusion. Los Angeles: University of Southern California, 1972. 3. Waliszewski KJ. A study and classification of centric and eccentric tooth contacts in patients with Angles’ class II and class III molar relationships. M.S. thesis. Milwaukee, Wis: Marquette University, 1974. 4. Posselt U. Physiology of occlusion. Philadelphia: FA Davis Co, 1962. Reprint requests to: DR. WILBUR 0. JENSEN 1441 AVXADO AVE., STE. 508 NEWPORT BEACH, CA 92660

NOVEMBER

1990

VOLUME

84

NUMBER

5