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orm & malocclusion tendencies






nathic Surgery

ion for orthognathic surgery


mination of compensation or dysplastic development

INTRODUCTION In our life time, we have seen the faces of thousands of people , and each face is recognizable to us as distinct individual. No two faces are quite alike, even those of identical twins.

The coordination of the development of the upper and the lower jaws are far from perfect. This imperfection can be compensated by skeletal and dentoalveolar changes camouflaging the actual deviation. This mechanism first described by Bjork as the “dentoalveolar compensatory mechanism� and

“ Process or mechanism by which the

development of dental and alveolar arches are controlled so as to secure occlusion of the teeth and adaptation to the basal parts of the jaws.�

What is compensation ??? It is a constant ongoing process striving towards ultimate homeostasis during growth . When the growth process is complete a state of compromise equilibrium has been achieved .

Compensation can be more aptly called as

“ Developmental adjustments for working towards balance � .

If we have compensatory features , the built in tendencies are offset , to a greater or lesser extent . If it is less then complete malocclusion will be more fully expressed but less severe than the tendencies otherwise could produce.


Shape of the head There are two basic extremes in the shape of the head Dolichocephalic Brachycephalic The cephalic index is the ratio between overall head length & breadth: -Dolichocephalic = Upto 75.9% -Mesocephalic = 76 to 80.9% -Brachycephalic = Over 81%

Dolichocephalic head form

Brain is horizontally long and narrow

Cranial base is flat- flexure between the middle cranial floor & anterior cranial floor open . Occlusal plane is rotated downward.

mandibular retrusion, class II molar relation The resultant profile is retrognathic.


Brain is short, wide.

Basicranial floor is more upright and has a more closed flexure Decreased effective antero-posterior dimension of the middle cranial fossa Posterior placement of the maxilla Horizontal length of the nasomaxillary complex is short. Retrusion of nasomaxillary complex and more forward relative placement of mandible.

The resultant profile is prognathic Class III molar relationship


Growth of any given facial or cranial part relates specifically to other structural & geometric "counter parts" in the face & cranium. e.g maxillary arch is a counterpart of mandibular arch If part and counter part enlarge to same extent , balanced growth is produced.

COUNTERPART ANALYSIS In this method various facial and cranial parts are compared with each other. The individual is measured against himself,rather than compared with population standards and norms. Size and alignment of the bones are considered. Vertical and or horizontal size of one given part is compared with that of its specific counter parts. If they exactly match, or nearly so , a dimensional balance exist between them.

Three vertical architectural counterparts

1. Cranial floor ramus vertical.. 2. Posterior nasomaxilla.. 3. Anterior nasomaxilla..

If vertical dimensional imbalance occurs Downward occlusal rotation

Upward occlusal rotation

Open bite

Four horizontal architectural counter parts

4. Middle cranial fossa 5. Ramus 6. Maxilla 7. Mandibular corpus

Horizontal dimensional imbalance Maxillary protrusion

Dimensional compensationRamus Dimensional compensationCorpus

Factors responsible for dentoalveolar compensatory mechanism

1. Normal eruptive system 2. Soft tissue envelope 3. Influence on tooth exerted by neighboring teeth during growth

Dentoalveolar compensatory mechanism and malocclusion Two main types of malocclusion: •

Inter arch deviation - occlusion anomalies


Intra arch deviation - space anomalies

Three main situations where dentoalveolar compensation is impaired . 1. An





mechanism 2. In cases where functioning of dentoalveolar mechanism is incomplete 3. In cases where


some reason the compensatory

mechanism is inoperative


Horizontal dimension of the mandibular corpus short relative to its counter part

Mandibular retrusion, Anterior crowding . Need not be class II

Mandibular corpus is dimensionally longer relative to its counter part

Mandibular protrusion Class III molar relation depends on whether mandible is long mesial or distal to the I molar. Horizontally short maxillary arch has the effect

Horizontally long nasomaxillary complex

No effect on occlusion Individual can appear retrognathic – protrusive nature of upper part of face.

Horizontal dimension of the ramus is narrow relative to its counterpart-middle cranial fossa

Mandibular retrusive effect. This is one of basic skeletal cause that underlie a class II molar relationship

The effective horizontal dimension of the ramus is broad relative to middle cranial fossa

Mandibular protrusion. One of the reasons for class III molar relation

Vertically long nasomaxillary complex

Downward and backward rotation Mandibular retrusion

Vertically short nasomaxillary complex

Upward and forward rotation Mandibular protrusion

The Posterior Maxillary Plane The PM plane is a developmental interface between the vertical series of counterparts in front of, and behind it.

This key plane retains these basic relationships throughout the growth process.

Neutral Occlusal Axis (N.O.A.):-

In a well balanced face both functional occlusal plane and N.O.A. will be coinciding.

The alignment of parts are in neutral position. Occlusal plane is perpendicular to PM plane and parallel to neutral orbital axis

COMPENSATORY MECHANISM During the development and establishment of the occlusion, ongoing and intensive adjustment occurs involving dentoalveolar remodeling . The effect of dentoalveolar compensatory mechanism on dimension of the dental arches ,the inclination of the teeth and occlusal relationships has been well documented

Compensation by ramus in dolicocephalic pattern

Nasomaxillary complex lengthened vertically

Mid facial growth has exceeded the growth of ramus and middle cranial fossa complex Downward backward alignment of the whole mandible to accommodate the longer nasomaxillary complex..

Upper teeth drift inferiorly till they contact the antagonist. Occlusal plane is a straight line , inclined downward.

Dentoalveolar curve (Curve of spee)

Upper teeth drift down . The upper anterior drift only to the level of the premolar. Anterior mandibular teeth drift superiorly till they contact the upper. Occlusal plane is curved.

ANTERIOR CROWDING Teeth have very little capacity to remodel after they are formed fully. Only a limited extent of root resorption, deposition of cementum , crown wear are possible in this regard. This means that adaptive adjustment for a tooth must be carried out by the displacement process .

While extensive resorptive & depository remodeling is a basic growth function for the housing alveolar bone, it is not a factor for the tooth itself . Thus anterior crowding is , in effect, a compensatory means by which the teeth are housed beyond the limit provideded by the alveolar bone .

Compensation for variation in the sagittal jaw relationship. • In cases of skeletal class II. To compensate for the large sagittal discrepancy in jaw relationship the upper incisor are retroclined and lower incisor are proclined to maintain normal overjet.

• In cases of skeletal class III. The upper incisors are proclined and the lower incisors are retroclined to maintain normal overjet.

(Hiroyaki ishikava

Compensation for variation in vertical jaw relationship. • In cases of skeletal open bite, To maintain the normal overbite, the posterior dentoalveolar segment intrudes. The anterior dentoalveolar segment extrudes or both can happen.

• In a case of skeletal deep bite The posteriors can extrude or the anteriors can intrude to maintain a normal overbite.

Compensation for variations in transverse jaw relationship. •

A discrepancy between a narrow maxillary base and a

wide mandibular base is compensated by buccal tilting of upper teeth and lingual tilting of lower teeth. •

Discrepancy between wide maxillary base and narrow

mandibular base is compensated by lingual tilting of upper teeth and by buccal tilting of lower teeth.

In ideal situations, this compensation masks discrepancies in all three planes of space. The dentoalveolar changes may however also be unfavourable or dysplastic and contribute to an occlusal problem more severe than that caused by actual


discrepancy .

Orthognathic Surgery:-

Every patient who goes for a surgical line of treatment should be put on an orthodontic appliance to carry out the presurgical decompensation. Here upper and lower arches are separately aligned but no attempt is made to correct the bite by orthodontic means as bite will be corrected by surgical repositioning of the jaw to get a near occlusal fit as possible.





( BELL AND PROFIT ) 1 ) When segments in









a satisfactory


because of

gross occlusa1 interferences


gross malrelation of

teeth to their supporting

bone .

2 ) When postsurgical orthodontic work would necessitate tooth

What is decompensation? In many cases of severe jaw imbalances and the resulting malocclusion, the teeth are inclined in such a manner as to partially offset the discrepancies.

Pre surgical orthodontics should be aimed at removing this natural compensation or to decompensate.



1. To position the teeth in an ideal axial inclination with respect to the jaws. 2. To optimize the magnitude of surgical advancement or repositioning. 3. For better esthetics , stability and function. 4. If malpositioned anterior teeth are not corrected , they may hinder the repositioning of jaws at the time of surgery.

Determination of compensation or dysplastic development

IN THE MAXILLA, the "maxillary zone" measured as the angle between the palatal plane (ANS-PNS) and the maxillary occlusal plane ( mean 10 +\- 3 ), describes the extent of compensatory or dysplastic development.







measured between the mandibular plane (Go-Gh) and the mandibular occlusal plane (mean 20 +\-





compensation. If






measurement are increased in a patient


increased vertical jaw relations; favourable dentoalveolar compensation is indicated. On

Dentoalveolar compensation in negative over jet cases were statistically confirmed for both incisor inclination and occlusal plane angulation. However the compensatory effects were weaker than with positive overjet cases. Hiroyaki ishikava Leader in continuing dental education

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