DENTOALVEOLAR COMPENSATION INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com
orm & malocclusion tendencies
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 â€œdentoalveolar compensatory mechanismâ€? and www.indiandentalacademy.com
â€œ 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.â€?
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
â€œ Developmental adjustments for working towards balance â€? . www.indiandentalacademy.com
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.
HEAD FORM & MALOCCLUSION TENDENCIES
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% www.indiandentalacademy.com
Dolichocephalic head form
Brain is horizontally long and narrow www.indiandentalacademy.com
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.
BRACHYCEPHALIC HEAD FORM
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. www.indiandentalacademy.com
Three vertical architectural counterparts
1. Cranial floor ramus vertical.. 2. Posterior nasomaxilla.. 3. Anterior nasomaxilla.. www.indiandentalacademy.com
If vertical dimensional imbalance occurs Downward occlusal rotation
Upward occlusal rotation
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 www.indiandentalacademy.com
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: â€˘
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 www.indiandentalacademy.com
DIMENSIONAL AND ALIGNMENT PATTERN COMBINATIONS
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 samewww.indiandentalacademy.com effect
Horizontally long nasomaxillary complex
No effect on occlusion Individual can appear retrognathic â€“ 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 www.indiandentalacademy.com
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 www.indiandentalacademy.com
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.. www.indiandentalacademy.com
Upper teeth drift inferiorly till they contact the antagonist. Occlusal plane is a straight line , inclined downward. www.indiandentalacademy.com
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. www.indiandentalacademy.com
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. â€˘ 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.
â€˘ In cases of skeletal class III. The upper incisors are proclined and the lower incisors are retroclined to maintain normal overjet.
(Hiroyaki ishikava et.al) www.indiandentalacademy.com
Compensation for variation in vertical jaw relationship. â€˘ 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.
â€˘ 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. â€˘
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. â€˘
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
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. www.indiandentalacademy.com
( BELL AND PROFIT ) 1 ) When segments in
gross occlusa1 interferences
gross malrelation of
teeth to their supporting
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.
NEED FOR PRESURGICAL
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. www.indiandentalacademy.com
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. www.indiandentalacademy.com
measured between the mandibular plane (Go-Gh) and the mandibular occlusal plane (mean 20 +\-
measurement are increased in a patient
increased vertical jaw relations; favourable dentoalveolar compensation is indicated. On www.indiandentalacademy.com
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 et.al
www.indiandentalacademy.com Leader in continuing dental education