GROWTH ROTATIONS
INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com www.indiandentalacademy.com
INTRODUCTION: The term growth rotation was introduced in 1955 by Bjork. He used it to describe a particular phenomenon, occurring during the growth of head. History: ď ś At the time when x-ray cephalometry was introduced research
was
concerned
primarily
with
AVERAGE
GROWTH CHANGES in the form of face and head. ď ś
These conventional x-ray measurement /tracings
showed comparatively small changes with age in the facial www.indiandentalacademy.com form and intermaxillary relationship.
A series of questions arose (i)
Is that intermaxillary relation static throughout the period of growth?
(ii) If the facial form remain static with age then is the treatment of malocclusion independent of age, sex or maturation rate? The answer was NO ď ś
It was at this time when longitudinal studies with cephalometry were conducted and the concept of INDIVIDUAL DIFFERENCES in the development of facial form and intermaxillary relations were recognized. www.indiandentalacademy.com
And it was Bjork who used metallic implants as markers in the jaws from which he located, 1. Sites of growth and resorption in the individual jaws and examined individual variation in direction & intensity of growth. 2. The mechanisms underlying changes in the intermaxillary relationship during growth. ď ś Until Bjork's studies, the extent to which both the maxilla and mandible rotate during growth was not appreciated. ď ś
ď ś Bjork identified stable points in the mandible and placed implants on those points. 1. The core of the mandible is the bone that surround the inferior alveolar nerve. 2. The rest of the mandible consists ofwww.indiandentalacademy.com several functional process.
He identified that the mandibular canal is not remodeled to the same extent as the outer surface of the jaw and the trabaculae related to canal (Core of the mandible) are therefore relatively stationary. Also the lower border of the developing molar tooth germ (before the roots begins to form) appears to be fairly stable point and serve as natural reference structure in the growth analysis of the mandible . In 1951, Bjork conducted a mixed longitudinal study by the use of these implants in about 100 children of each sex covering the age period from 4 to 24 years. By super imposing consecutive tracings, he concluded that rotation involved. 1. Marked resorption in the gonial region. 2. Apposition in the posterior and lower border of the www.indiandentalacademy.com symphysis.
The pattern of mandibular growth rotation is generally UPWARD & FORWARD curving growth whose degree of rotation is being masked by resorption on the lower aspect of the gonial angle and apposition below the symphysis.
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Thus these two factors the upward +forward growth rotations of 15 degrees to 2-4 degrees. With the conventional examination of the cephalametric radiograph (base of the mandible), TMJ was considered as the center of rotation of the mandible. Bjork with the implant method recognized various types of rotation with varying centres of rotation. BROADLY CLASSIFIED INTO FORWARD ROTATION
Type I
Type II
Type III
BACKWARD ROTATION
Type I
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Type II
FORWARD ROTATIONS COR
FACIAL HEIGHT Anterior
CAUSE
Posterior
Type I
Joint
Decrease AFH Deep bite
-
Type II
Inciscal edge of the lower anterior teeth
Normal AFH Marked increased PFH
(i). Lowering at middle cranial fossa, lowering the condylar fossa (ii). Vertical growth at the mandibular condyle
Type III
At the level of premolars
Decrease AFH Deep bite
In anamolous occlusion of anterior e.g. Increased overjet.
Increase PFH
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Occlusal imbalance due to loss of teeth / powerful musculature.
BACKWARD ROTATIONS Less frequent than forward rotations COR Type I
Type II
CAUSE
TMJ
Most distal occluding molars
FACIAL
1. Raising of bite by orthodontic means
Increased AFH
2. Flattening of cranial base 3. Oxycephaly
Decreased PFH Increased AFH
Growth in the saggital Basal open bite direction at the mandibular condyules
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Type II in both types of rotation is due to different condylar growth direction. FORWARD
BACKWARD
Vertical direction of condylar growth
Saggital direction of condylar growth
Lowering of mandible
Mandible grows in the direction of its length
This lowering of mandible in turn takes place as forward rotation due to the muscular and ligamentous attachments
Due to attachments of muscles and ligaments the mandible is rotated backwards
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TYPE - I
TYPE - II
TYPE - I
TYPE - III
TYPE - II
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Double Chin In Type II Backward rotation COR at the distal occluding molars Symphysis is swung backward Chin is drawn below the face Soft tissue do not follow the bony chin Characteristic double chin is formed Inclination of teeth: (Bjork & Skieller) (lower) ď ś The inclination of teeth, is also greatly influenced by rotation of the lower jaw. ď ś Incisors: Irrespective of jaw rotation the lower incisors are functionally related to the upper incisors & follow the upper www.indiandentalacademy.com incisors.
Forward rotation Dentoalvealar proclination of lower anteriors Mesial path of eruption leading to crowding (packing) Backward rotation Dentoalvealar retroclination of lower anteriors Crowding. Lower posterior teeth Forward :
Upright
(than normal) lower posteriors in
relation to the upper posteriors. Increase in interpremolar and intermolar angles www.indiandentalacademy.com
and the vice versa for backward rotations.
Bjork also named 7 structural signs of extreme growth rotations. He also stated these signs will help in a clinical aspect to detect extreme types of mandibular rotation, occurring during growth. 1. Inclination of the condylar head. 2. Curvature of the mandibular canal. 3. Shape of the lower border of the mandible 4. Inclination of the symphysis. 5. Inter Incisal Angle. 6. Inter premolar, Inter molar Angle. 7. Anterior lower Facial height. ď ś All these signs will not be found in an individual www.indiandentalacademy.com
ď ś These signs are not clearly developed before puberty
Schudy’s concept of Mandibular notion The rotation of the mandible result from inharmony between vertical growth and anteroposterior or horizontal growth of the mandible. He dealt with growth increments which cause positional changes of the chin. To those increments which cause the chin to move vertically he applied the term -VERTICAL GROWTH To the one increment (condyle) which causes the chin to move forward he applied - HORIZONTAL GROWTH He named the condyle as horizontal element and listed out three vertical elements 1. growth at nasion & corpus of the maxilla. 2. growth of the maxillary posterior alveolar process 3. growth at the mandibular posterior alveolar process www.indiandentalacademy.com causing the molar teeth to move occlusally. ,
If the condylar growth is greater than the vertical growth in the molar area, the mandible rotates COUNTER CLOCKWISE resulting in horizontal change of the chin and less increase in facial height Extreme of this condition cause CLOSED BITES . causes increase in facial angle and flattening of MANDIBULAR PLANE. Conversely if vertical growth in the molar region is greater than that at the condyles, the mandible rotates CLOCKWISE resulting in more Anterior facial height. Extremes of this condition cause OPEN BITESÂ : with steepening of mandibular plane. ď ś The horizontal condylar growth is pitted against the combined vertical elements of growth . The final vector of growth of the chin is a resultant of the struggle between www.indiandentalacademy.com horizontal growth and vertical growth.
When the growth at the condyle equals the growth of the vertical elements, the net result is usually downward and forward.
In clockwise rotation the point of rotation being the condyles.
In counter clockwise rotation the point of rotation is the most distal mandibular molar in occlusal contact. He called the ratio between horizontal and vertical growth increments as POSTERIOR GROWTH ANALYSIS. It is this ratio depicting the relationship of vertical & horizontal increments one to another that controls the forward growth and rotation of the mandible. www.indiandentalacademy.com
ENLOW’S CONCEPT OF MANDIBULAR ROTATION: 1. Displacement type 2. Remodeling type Displacement type Rotational positioning of the entire mandible. Caused by changes in the placement of the functional contacts with both the cranial floor and the maxilla. The dimensions & angular positions of the cranial floor and maxilla directly affect the consequent rotational position of the mandible. If cranial base angle is open downward and backward DISPLACEMENT rotation of the mandible and converse occurs if the angle is closed. If Nasomaxillary and dental complex is vertically long downward and backward DISPLACEMENT rotation of the mandible, and www.indiandentalacademy.com converse occurs if nasomaxillary complex is vertically short.
Remodeling type There are two reasons why a mandible undergoes the remodeling type of rotation. 1. To produce a more upright ramous alignment relative to the corpus. This accommodates the continued vertical growth of ethmomaxillary region and the eruption of permanent dentition. 2. To provide ramus-corpus angular adjustments to accommodate the effect of the whole mandible displacement rotations. e.g., : of the displacement rotation causes more upward & forward alignment of the mandible as a whole then the remodeling rotation, partially or completely offsets this by www.indiandentalacademy.com opening the ramus-corpus angle.
DISPLACEMENT TYPE
REMODELLING TYPE
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On contrast a downward and backward wholemandible displacement can be offset by closing the ramuscorpus angle by remodeling rotation. ď ś It is necessarily a function of the ramus, rather than the corpus to provide the basic remodeling changes leading to a more open/more closed ramus-corpus angle. ď ś The same combinations of resorption and deposition in the various parts of the ramus that bring about relocation of the ramus in posterior direction also serve to remodel and www.indiandentalacademy.com adjust the RAMUS CORPUS ANGLE.
As growith proceeds, the utilization of these ramus growth changes to alter ramus corpus alignment decreases and finally ceases. Another remodelling mechanism takes over. • Condyle previously growing in a more vertical direction now begins to grow anteriorly as well. • This anterior condylar growth is complemented by bone deposition superiorly on the anterior border of the ramus. • Resorption continues inferiorly on the anterior border to provide space for molars. • A converse combination of remodelling takes place on the posterior border.www.indiandentalacademy.com
ď ś BJORK AND SKIELLER subsequently focused attention on different patterns that emerged when different registrations for superimposition were used. ď ś
These various patterns can be expressed in a rotational terminology. The rotation of mandibular corpus
I. Total rotation:
(implant line) relative to the anterior cranial base. Solow an Houston
-
True rotation
Proffit
-
Internal rotation.
II. Matrix rotation: Rotation of soft-tissue matrix of the mandible (Tangential mandibular line) relative to the cranial base.
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Center - condyles
II. Solow an Houston Proffit
-
Apparent rotation
-
Total rotations.
III. Intramatrix rotation: The difference between the total rotation and the matrix rotation. The change in inclination of an implant or reference line in the corpus relative to the tangential mandibular line. It is an expression of the remodeling at the lower border of the mandible. center – corpus. III. Solow an Houston PROFIT
-
Angular remodelling
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-
External rotations
MATRIX AND INTRAMATRIX ROTATIONS
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PROFFIT : Total Rotation
= Internal rotation
External rotation
BJORK
= Total rotation
Intramatrix rotation
: Matrix Rotation
SOLOW : Apparent Rotation
= True Angular rotation Remodelling For an average individual with normal vertical facial proportions there is about -15 of Internal Rotation (Total, True) from 4 years – Adults life and 11-12° of external rotation.
(- sign = forward rotation). X= 150 -(11-12)0 X= 30 - 40
15° – External, Intramatrix, Angular remodelling.
3° – 4° - Total, Matrix, www.indiandentalacademy.com Apparent.
The different interpretations of the intra matrix rotation were given by : 1.Lavergne and Gasson - He defined rotations as a.Morphogenetic - Concerning the shape of the mandible similar to intramatrix rotation. b. Positional – Dealing with the position of the mandible. They used a line joining condylon and pogonion to super impose cephalogram and determine the angle between the 2 implant lines. They concluded that Anterior rotation of the mandible is associated with a vertical or even anterior condylar growth direction and a marked closure of the gonial angle and these minimize the effects of condylar growth. They postulated that intramatrix rotation is essentially a compensating mechanism which is capable of reducing or enlarging the mandibular length by opening or closing the www.indiandentalacademy.com gonial angle.
2. Dibbets - He gave a third interpretation which is based on two hypothetical divergent patterns of growth. a. A circular growth pattern resulting in only intra matrix rotation and no enlargement of the mandible. b. A linear growth pattern characterized by absence of intramatrix rotation but with mandibular enlargement. He showed that the external configuration of the mandible need not change its form or position within the head to allow intramatrix rotation and any resorption or deposition only serves to maintain the original contours. He also stated that every millimeter of condylar growth along the pogonion condylon diagonal would enlarge the mandible by 1mm. This is compensated by remodelling at the lower border. This mechanism is termed as the counterbalancing rotation. Thus counterbalancing rotation is a mechanism that (i) Neutralizes effect of www.indiandentalacademy.com growth of the condylar cartilage.
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Rotation of Maxilla : Core of the maxilla Functional process
-
above the alveolar process. alveolar process, bones surrounding air passages.
Internal rotation: The cove of the maxilla undergoes a small and variable degree of rotation forward or backward. At the same time resorption of bone on the nasal side and apposition of bone on the palatal side in the anterior and posterior part of palate occurs. Eruption of molars and incisors occurs. The above two factors account for the external rotation. For most patients the external rotation is opposite in direction and equal in magnitude to Internal rotation. The two rotations thus cancel each other and the net change in jaw orientation (palatal plane) is zero. Variation from this average pattern is common and result in www.indiandentalacademy.com moderate variation in Jaw orientation.
ROTATION OF MAXILLA
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PREDICTION OF MANDIBULAR GROWTH ROTATION If an attempt is made to assess the growth trend at an early stage, this information can be used in designing the treatment of evaluating the problems that may arise before growth is complete. In spite of several attempts in recent years, there is still doubt as to the extent to which growth of the face as a whole can be predicted from a single profile radiograph. In an attempt to analyse the possibility of predicting growth of single facial dimension, Bjork and palling correlated linear and angular measurements at pubertal age with residual growth of these dimensions up to adulthood. www.indiandentalacademy.com
correlations were however found to be low.
These
Hixon suggested that the best estimate of an adult facial dimension for a given child is to use the dimension presented by the child and add to that the remaining average growth for the group. This method was adopted by several authors. However, this estimate would fit an average but not an extreme growth pattern, where prediction from a clinical point is more important. Lavergne tried to individualize the prediction by a subdivision according to the morphogenetic types. Ricketts arcial method of long range growth prediction uses geometric procedures to gain information about the growth pattern of the mandible. A computerized system for short range facial growth prediction and treatment simulation, based on longitudinal observations of individual growth rate and direction has been www.indiandentalacademy.com developed by Bjork-Jorgensen.
A growth analysis consists of essentially 3 items 1.
assessment of the development in shape of the face.
2. assessment of whether the intensity of the facial growth is high or low. 3.
evaluation of the individual rate of maturation.
In the assessment of shape there are three methods. I. Longitudinal method – Consists of following the course of development in annual cephalometric films. It is for the subjects displaying the most pronounced changes in facial forms that the diagnosis of growth pattern is important.
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Limitation 1. Pattern of growth is not constant and may be changed later. 2. Permits observation of changes in the saggital jaw relation with growth and those occurring in the vertical jaw relation are masked. Changes in the vertical positions of the jaw in the form of rotation appear to be smaller when assessed with conventional longitudinal X-ray films by using the base of the mandible as the reference than when assessed with the help of implants. Analysis of vertical development of the face may done using natural reference structures in the mandible by superimposing two radiographs taken at different ages and orienting reference to these structures, one may estimate the growth pattern of the mandible by reading the angle www.indiandentalacademy.com between the Nasion sells lines for the two ages.
II. METRIC METHOD Aims at a prediction of facial development on the basis of facial morphology, determined metrically from a single Xray film. However, prediction of development from size and shape at childhood is not very accurate. The growth in length of the mandible during adolescence could not be judged from its size before puberty and also the changes in shape of the face during adolescence, expressed in terms of angular measurements also weekly correlated with the shape of the face at 12 years which is the age at which treatment is instituted. II. STRUCTURAL METHOD Is based on information concerning the remodelling process of the mandible during growth, gained from the implant studies. The principle is to recognize specific structural features that develop as a result of remodelling in a particular type of mandibular rotation. A prediction of the subsequent course is then made on the assumption that the www.indiandentalacademy.com trend will continue.
Gonial Angle and mandibular rotation
The size of Gonion angle influence the number of degree of counter clockwise rotation of mandible.
The smaller the gonion angle, the greater the rotation is produced for each mm of forward movement of pogonion
Facial divergence and mandibular rotation
The degree of facial divergence (SN – MP) has a significant bearing on mandibular rotation.
Larger SN-MP angle, the more the mandible tends to become steeper and the chin moves more backward.
The smaller the angle, the greater the tendency of the mandible to become www.indiandentalacademy.com flat and the chin to grow forward.
REVIEW OF LITERATURE 1. Schudy study : Growth was studied on 62 patients. 29 – 11 – 14 years 33 – 8 – 11 years Treated cases 50 – 11 – 14 years Aim of the study – To determine the cause of mandibular rotation. Measuring vertical growth in the first molar teeth and www.indiandentalacademy.com relating this growth to that at the mandibular condyles.
Results : Untreated
Treated
Effective condyle growth
7.2 mm
6.7mm
Vertical growth
6.3mm
7.1mm
73% of vertical growth in the Untreated group (4.6mm) was in the maxilla and 27% in the mandible. Treated 68% maxilla, 32% mandible. Thus he concluded that MAXILLA is responsible for about 70% of total vertical growth and has an important effect on the ‘tilt’ of thewww.indiandentalacademy.com mandible.
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2. Alf Tor Karlsen -1997 Angle orthodontist. Study : Aim : - Association between vertical craniofacial growth and mandibular growth rotation. Study group – Two groups (i) Low MP-SN angle (ii) High MP-SN angle Nature - Longitudinal study from 6 – 15 years of age Results : • Increased posterior Positively correlated with lower facial height FORWARD MATRIX ROTATION Increase in ramus height Irrespective of MPA / age 2. Increase in LAFH Weakly correlated with mandibular rotation. (?) Strongly and positively www.indiandentalacademy.com correlated with increased in corpus length
Over development of LAFH in high angle cases occurred because the steep mandibular plane directed corpus growth more downward. 3. 1995 A.O The same author did a longitudinal study with boys having low and high MP-SN angles. Aim :- Compare the two groups with regard to dimensional changes and mandibular growth rotation. Result : - Significant correlations were almost exclusively noted between dimensional change and total rotation and dimensional change andwww.indiandentalacademy.com matrix rotation.
4. 1984 – Nov- Bjork and Skieller A.J.O. Aim – To estimate the possibility of predicting the direction and amount of growth rotation of the mandible on the basis of morphologic criteria observed on a single profile radiograph at pubertal age. Forty four morphologic variables were employed and four among them gave the best prognostic estimate (86%) of mandibular growth rotation in the sample. 1.Mandibular inclination a. Proportion between posterior and AFH (Index – I) b. Lower Gonial angle (GOL) www.indiandentalacademy.com
c. Lower border inclination (NSL – ML1)
2. Inter molar angle (MOLs – MOLi) 3. Shape of lower border (ML1 – ML2) 4. Inclination of symphysis (CTL – NSL). 5. AJO Dec – 1998 In response to Bjork & Skieller’s article (1984 AJO) Laurel R. Leslie Published a article assessing the reliability of their method of predicting growth rotation using the four variables. They concluded that only 9% of the variability in mandibular growth rotation could be accounted for using the four variables in combination in contrast to 83% given by Bjork. Thus he stated that the method does not permit clinically www.indiandentalacademy.com useful predictions of future mandibular growth rotation.
Clinical Implications 1. Downward alignment
of the whole mandible at the
condylar pivot has a mandibular retrusive effect. Only Corpus mandibular protrusive effect. Upward alignment of the whole mandible Mandibular protrusive effect Only corpus Mandibular retrusive. 2. The more extreme the rotation of the mandible during growth, the greater the clinical problems that is presents. Extreme rotation greatly influence the path of eruption of the teeth, magnitude of tooth eruption, anteroposterior position of incisor teeth. Path of eruption of max teeth www.indiandentalacademy.com Downward and somewhat forward
In normal growth, maxilla usually rotates a few degrees forward. It may be normal but usually the maxilla rotates slightly backward. Forward Rotation of maxilla Tends to tip the incisors forward and increase their prominence. Backward Rotation of maxilla Directs the anterior teeth more posteriorly relatively up righting them and decreasing their prominence. During adolescence about half the total maxillary teeth movement is due to rotation of maxilla (Teeth moved along www.indiandentalacademy.com with the jaw - Translocation).
Mandible Path of eruption of mandibular
-
Upward and forward
-
Lingual positioning of mandibular incisors relative to mandible.
Teeth Forward rotation of growth
Lingual positioning of mandibular incisors Molars migrate further mesially during growth than the incisors Decrease in the arch length The forward rotation progressively uprights the www.indiandentalacademy.com incisors, causing a tendency toward crowding.
LINGUALLY PLACED INCISORS
MESIAL MOLAR MIGRATION
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ď ś Incase of pronounced forward rotation, there is a major risk of deep bite developing. ď ś
In the case of backward rotation, opening of the bite is
difficult to prevent during treatment so in the case of extreme forward rotation a stabilizing appliance like bite plane is introduced before puberty and continued until growth completion. ď ś According to Bjork, it is advisable to delay orthodontic extractions until beginning of pubertal growth spurt. www.indiandentalacademy.com
2. Facial patterns : SHORT FACE PATTERN Excessive forward rotation of mandible during growth. Short Anterior LFH
Horizontal palatal Deep bite and plane crowding
Square jaw (Mandible)
Square gonial angle
Excessive forward rotation may be due to (i)
Increase in internal mandibular rotation
(ii) Decrease in external rotation www.indiandentalacademy.com
Low MPA
LONG FACE PATTERN (INCREASED LAFH) Backward rotation of mandible Anterior open Increase MPA bite
Palatal plane rotates down posteriorly
Mandibular deficiency
Mandibular backward rotation result primarily from
Lack of normal internal rotation
Or even backward internal rotation
The internal rotation is primarily matrix rotation (Corcondyle) and not intramatrix rotation. Backward rotation of mandible also occur in patients www.indiandentalacademy.com with abnormalities or pathologic changes in TMJ
3. According to schudy : Clockwise rotation of mandible (effect upon treatment) Would not help reduce ANB angle Not aid in correction of class – II molar relation. Would tend to help connect the vertical overbite of incisors and maintain it. Counter clockwise rotation Tends to increase the vertical overbite (deep bite) and renders vertical overbite correction and retention more difficult. According to schudy the condylar growth versus vertical growth determines the mandibular rotation. Orthodontic treatment does not stimulate growth at the condyles. It is only the vertical increments that we may www.indiandentalacademy.com possibly alter with orthodontic treatment.
Inhibition of growth of vertical increments will have the same effect as stimulating growth at the condyle. So if vertical growth is deficient we try to stimulate it. (Cervical pull head gear, class II elastics). If vertical growth is excessive we try to inhibit it (Inhibit downward growth of maxillary molar – high pull head gear). 4. It is also important to identify the relationship between jaw base rotations and occlusal findings (e.g., Inclination of upper anteriors and lower anteriors and over bite) and accordingly plan the treatment, especially if the patient is in growth phase.
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6. Combinations of maxillary and mandibular rotation and its clinical implications (Lavergne and Gasson 1982). The combinations are very important for occlusal relationship. Convergent rotation of jaws during growth. A deep bite which is very difficult to correct even by functional methods. Divergent rotation skeletal open bite often results. Severe cases require orthognathic surgery. Rotation in the same direction : The occlusal relationship is maintained normally in most situations (e.g., deep bite avoided in cranially www.indiandentalacademy.com
directed rotation of both jaws).
COMBINATIONS OF ROTATIONS OF JAW BASES www.indiandentalacademy.com
7. Upward and forward tipping of anterior maxilla is often observed in confirmed mouth breathers. 8. Mandibular rotation is caused by both growth dependent and functional influences only functional influences can be altered therapeutically while growth can only be guided so the rotation of mandible can be only moderately influenced therapeutically. Generally the inclination of maxillary base is stable and no growth dependent influences seen, thus the inclination can be influenced by both fixed orthopedic and www.indiandentalacademy.com functional therapeutic techniques.
CONCLUSION Though different authors give different mechanisms and terminologies for Growth rotations, the jaw should rotate either forward or backward.
It is upto the
orthodontists to identify the rotation early and its clinical presentation and apply it in treatment, so that treatment can be started at the earliest.
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REFERENCES 1. Contemporary Orthodontics
-
Proffit
2. Handbook of Facial Growth
-
Enlow
3. Orthodontic Diagnosis
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Rakosi
4. Dento facial orthopeadics with functional appliances Petrovic 5. Prediction of Mandibular growth rotation - Bjork (1969 June AJO) 6. The rotation of the mandible resulting from growth : Its implications in Orthodontic treatment - F.F. Schudy (1965 Angle Orthodontist 7. The puzzle of growth rotation June 1995)
J.M.H. Dibbets (AJO
8. Mandibular rotation and enlargement – J.M.H. Dibbets (AJO June 1990) 9. Bjork (1972) AJO
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