Growth rotations

CONTENTS

1. INTRODUCTION

2. IMPLANT RADIOGRAPHY

3. MANDIBULAR GROWTH ROTATIONS

4. MAXILLARY GROWTH ROTATION

5. JAW ROTATIONS AND TOOTH ERUPTION

6. MUTUAL RELATIONSHIP OF ROTATING JAW BASES

7. ROLE OF GROWTH ROTATIO1NS IN ORTHODONTIC TREATMENT PLAN

8. CONCLUSION

9. BIBILOGRAPHY

1SEMINAR ON GROWTH ROTATIONS1

INTRODUCTIONThe phrase growth rotation was introduced in 1955 by Bjork, who used it to describe a particular phenomenon occurring during the growth of the head. The technique whereby metal implants are inserted in bone has been used in animals for more than a century, but the application of the method in craniometrics studies of growth in man is of a more recent date. Professor Bjork is considered the father of implant radiography. Cephalometric implant radiography has revolutionized the growth studies in the field of orthodontics. Of all the pattern of growth, growth rotations assume an important role in orthodontics because of its major impact on treatment strategies. The rotation of maxillary and mandibular jaw bases is a major factor in etiological assessment, determining the nature of anomaly, the prognostic evaluation, determining the possible forms of treatment in choosing the principles of treatment and also in assessing the stability of treatment results. Certain rotational patterns of jaw bases can be manipulated quite effectively by means of functional and orthopaedic devices. Extreme rotations are very difficult to treat and surgical correction has to be performed at a later stage.

IMPLANT RADIOGRAPHY4

The first implant radiographic study was initiated in the 2year 1951 by Bjork. The implant radiography, metallic implants have been inserted in the jaws to serve a fixed reference points. By means of the implant method, it is possible to locate sites of growth and resorption in the

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individual jaws and to examine individual variations in direction and intensity.

Technique for implant radiography

Rotation of jaw bases was estimated using implant radiography only. In this procedure, inert metal pins are placed in the mandible and maxilla. Tantalum inert pins which are 1.5cm long and have 0.5mm diameter are used. Osseo integrated implants have serve as reference points and serial cephalometric radiographs are taken repeatedly over a period of time and compared.

Site of implants

Mandible :

Symphysis in the midline below roots.Right side body of mandible one below first premolar second below first molar.Outer surface of ramus on the right side in level with occlusal plane3

Maxilla :


Inferior to anterior nasal spine.Bilaterally in the zygomatic process.Hard palate behind canines, front of first molar in the junction between alveolar process and palate

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MANDIBULAR GROWTH ROTATIONS1,2,3,5,10

Mandibular rotations assume an important role in orthodontic treatment planning because mandibular growth rotations are more common than maxillary rotations. It drastically affects facial morphology, and treatment planning and treatment outcome. Implants were placed on the indicated site of mandible. By superimposing two consecutive tracings of child mandible registered on implants. Bjork

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found that the image of the older mandible had appeared to have rotated slightly forward during the intervening period.

BJORKS CLASSIFICATION 5,4

In the year 1969, Bjork has classified ro5tation of mandible into forward and backward rotations.

Forward rotation has three types


Type A – in this type there is forward rotation about centres in the joints which give rise to deep bite, in which the lower dental arch is pressed into the upper, resulting in underdevelopment of the anterior facial height. The cause may be occlusal imbalance due to loss of teeth or powerful muscular pressure.

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Type B – forward growth rotation of mandible about a centre located at the incisal edges of the lower anterior teeth due to combination of marked development of posterior face height and normal increase in anterior height. The posterior part of the mandible then rotates away from the maxilla.


Type C – the anomalous occlusion of the anterior teeth, the forward rotations of the mandible with growth changes its character. In case of large maxillary overjet or mandibular overjet, the centre of rotation no longer lies at the incisors but is displaced backward in the dental arc7h, to the level of premolars. In this type of rotation, the anterior


facial height becomes underdeveloped when the posterior face height

increases.

In the growth rotation type 2 and 3 the mandibular sym8physis swings forward to a marked degree and thechin becomes prominent. The inclination of the teeth is also greatly influenced by the rotation of the jaw. The interincisal angle undergoes a smaller change than the rotation of the jaw. The incisors in their eruption are guided forward and there is an increase in the alveolar prognathism right down to apical zone. This is contrary to the impression given by the jaw profile. Rotation, also displaces the path of eruption of all the teeth in the mesial direction, thereby tending to create crowding in the anterior segment through what may be referred to as packing. The rotation also effects the position of the lower posterior teeth in relation to the upper teeth. Forward growth rotation thus causes the lower posterior teeth to be more uprightthan the usual in relation to upper posterior


9teeth, with an increase in what may be called interpremolar and intermolar angles.

Backward rotation of the mandible is less frequent than the forward rotation. Two types have been recognized.

Type A – herethe centre of the backward rotation lies in the TMJ. This is case when the bite is raised by orthodontic means, by a change in the intercuspation or by a bite raising aplliance, and results in an increase in anterior face height.

Type B – backward rotation occurs about a centre situated at the most distal occluding molars. This occurs in connection with growth in the saggital direction at the mandibular condyles. As the mandible grows in the direction of its length, it is carried forward more than it is lowered in the face, and because of its attachment to muscles and ligaments it is rotated backward

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BJORK AND SKEILLER’S METHOD2,3,4,8

Bjork and skeillerin the year 1972 subsequently together carried out extensive implant studies and introduced various terminologies to understand the rotational pattern of mandible.T10hey divided the rotation into three components

Matrix rotation : this is the rotation of the soft tissue matrix of the mandible relative to the cranial base. The soft tissue matrix is defined by the tangential mandibular line. The matrix rotation has its centre at the condyles

Intramatrixrotation: the difference between the total rotation and the matrix rotation is an expression of the remodelling at the lower border of the mandible.itis identified by the change in inclination of an implant reference line in the mandibular corpus relative to tangential mandibular line. The intramatrix rotation has its centre somewhere in corpus.

Total rotation : therotation of the mandibular corpus meas11ured as a change in inclination of an implant line in the mandibular corpus relative to the anterior cranial base.

12Bjork also makes a clear distinction between what he terms matrix rotation and intramatrix rotation. Matrix rotation often goes in the form of a pendulum movement with the rotation point in the condyle.Intramatrix rotation is the rotation of the mandibular corpus inner half of its matrix within the mandibular corpus and not in the condyle. It is imporatant to note that skeiller, Bjork et al showthat

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total so called rotation is made up of sum of both matrix and intramatrix rotation.According to ENLOW anatomic function of the mandibular ramus, in addition to providing insertion for masticatory muscles is to properly position the lower dental arch in occlusion with upper. It is primarily remodelling of the ramus not the corpus, that is responsible and it is a combination of remodelling fields that carries out the remodelling rotation of the ramus. As the growth change proceeds, the entire mandible can also become rotated more downward and backward or upward and forward. This is a displacement rotation of the mandible as a whole as its ramus simultaneously rotates to a usually more closed position by anadjustive remodelling rotation.13

SCHUDY’S CONCEPT6,4

Schudy in 1965 considers the rotation of the mandible is the result of disharmony between vertical growth and anteroposterior or horizontal growth of jaws.

Schudys concept of growth rotations14

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The clockwise rotation:

Clockwise rotation of the mandible is a result of more posterior vertical growth than the condylar growth, the point of rotation being the condyles. If the vertical growth in molar region is greater than that at the condyles, the mandible rotates clockwise resulting in more anterior facial height and less horizontal change of the chin. Extreme of this condition causes open bite.

Counterclockwise rotation:

It ia a result of more condylar growth than combined vertical growth. 15This type of rotation is nearly always accompanied by a forward movement of pogonion and an increase in the facial angle. The point of rotation is the most distal mandibular molar in occlusal contact. This flattening of the mandibular plane tends to increase the vertical overbite and render vertical overbite correction and retention more difficult.The size of the gonionnagle has an important influence upon the number of degrees of resultant counterclockwise rotation. The smaller the gonion angle, the greater is rotation which is produced for each millimetre of forward movement of pogonion. When this angle is extremely small, it results in extreme flattening of the mandibular angle together growth of pogonion.

DIBBETS CONCEPT9


Dibbets re-examined the concept of intramatrix rotation as defined by Bjork and skeiller in 1983. Lavergne and Gasson on the other hand , contended that the rotation affected the ramus and the gonial angle and consequently the length of the condylion – pogoniondiagnol. An alternative interpretation of the mandibular rotation was presented by dibbets in order to overcome the controversies of intramatrix rotation. Dibbets hypothetically constructed two possible divergent patterns of16 mandibular growth.

1. Circular growth pattern : which postulates condylar growth as a segment of a circle with its centre at the chin. The whole mandible would then rotate around itself within its periosteal countours, resulting in intramatrix rotation without enlargement of mandible.

2. Linear growth pattern : without any intramatrix rotation and maximum enlargement of the mandible

This mechanism for selective enlargement of the mandible in response to condylar growth increments may be termed counterbalancing rotation. An operational definition is presented as follows: counterbalancing rotation pertains to circular condylar growth, accompanied by selective coordinated remodeling, which does not contribute to the incremental growth of the mandible.

PROFFITS DESCRIPTION ON ROTATION 1

Profit carried different terminologies to explain growth rotation of mandible, namely internal rotation, external rotation and total rotation. The core of the mandible that surrounds the inferior alveolar nerve. The rest of the mandible consists of its several functional


processes. These are the alveolar process, muscular process and the condylar process. If implants are placed in areas of stable bone away from the functional processes it can be observed in most individuals, the core of the mandible rotates during growth in a way that wou17ld tent to decrease the mandibular plane angle.

Internal rotation :

It is the rotation that occurs in the core of the18 jaw. The internal rotation is marked by surface changes and alterations in the rate of eruption of teeth. There are two contributions to internal rotations, namely MATRIX ROTATION (A) and INTRAMATRIX ROTATION (B). Matrix rotation occurs around the condyle while Intramatrix rotation is centred within the body of mandible.


External rotation :

It is the result of surface changes. These surface changes include resorption in the posterior part of the lower border of the mandible,

while the anterior aspect of the lower border is unchanged or undergoes slight apposition. The external compensation in an19 average growing adult is about 11 to 12 degree.

In short face type there is excessive forward rotation of mandible due to increase in internal rotation and decrease in external rotation. A high angle case shows backward rotation due to lack of normalinternal rotation

MAXILLARY GROWTH ROTATIONS1,10


It is less easy to divide the maxilla into core of bone and a series of functional processes. The alveolar process is certainly a functional process, but there are no areas of muscle attachment analogous to those of the mandible. If implants are placed above the maxillary alveolar process, one can observe the core of the maxilla that undergoes a small and a variable degree of rotation. Bjork and Skeiller in 1972 studied rotational growth of maxilla with thehelp of implants. Indicated sites of implants were placed. The lateral implant placed on the anterior and posterior countours of zygomatic process seems to give best results when compared to other sites. Seri20al superimposition of the lateral cephalogram at these revealed varying degree of rotation of the jaw bases. Based on these studies Bjork and skeiller introduced terminologies to describe maxillary growth rotations.

Internal rotation :This internal rotation is analogous to the rotation within the body of the mandible. It occurs in the core of the maxilla. It is also called intramatrix rotation

External rotation :At the sametime that internal rotation of the maxilla is occurring, there also are varying degree of remodelling of the palate. Similar variations in the amount of eruptions of incisors and molar occurs. These changes amount to an external rotation. The external rotation is opposite in direction and equal in magnitude to the internal rotation, so that the two rotations cancel and the net change in jaw orientation is zero.Depending upon the different degree s of combination of internal and external rotations, Bjork and skeiller observed two types of rotational growth. The terminologies they used are forward and backward rotations

Forward growth rotation : this condition occurs either due to excessive internal rotation or lack of normal compensatory external rotation or both. The maxilla is inclined upward and forward i.e 20SEMINAR ON GROWTH ROTATIONS 17

anterior end is tipped up. This is called ante inclination coined by Schwarz. He also named this condition as pseudotrusio21n. This actually aggrevates maxillary protrusion, tends to tip the incisorsforward increasing their prominence. The extent of forward tipping in relation to anterior cranial base is given in degrees by Schwarz. It is defined as the angle between the Pn-perpendicular and the palatal plane (j angle). The normal angulation is 85 degrees but in ante inclination it is greter than 85 degrees.

Backward rotation : it is exactly opposite to that of forward rotation where there downward and backward tipping of the anterior end of the palatal plane and the maxillary base. This is otherwise called retroinclination a term coined by Schwarz. In this type the jaw bases are translated posteriorly and the upper incisors appear to tip lingually. The angle between palatal plane and the anterior cranial base is lesser than the normalvalue. It is less than 85 degree.


JAW ROTATION AND TOOTH ERUPTION 1,8

Growth of the mandible away from the maxilla creates a space into22 which teeth erupt. The rotational pattern of jaw growth obviously influences the magnitude of tooth eruption, direction of eruption and the ultimate anterioposterior position of the incisor teeth. The path of eruption of the maxillary teeth in downward and somewhat forward. In normal growth the maxilla usually rotates a few degree forward but frequently rotates slightly backward. Forward rotation would tend to tip the incisors forward, increasing their prominence while backward rotation directs the anterior teeth more posteriorly than would have been the case without rotation, relatively uprighting them and decreasing their prominence. The eruption path of the mandibular teeth is upward and somewhat forward. The normal internal rotation of the mandibular caries the jaw upward infront. This rotation alters the eruption path of the incisors tending to direct them more posteriorly. Because the internal jaw rotation tends to upright the incisors, the molars migrate further mesially during growth than do the incisors and this migration is reflected in the decrease in arch length. Since the forward internal rotation of the mandible is greater than that of the maxilla it is not surprising that the normal decrease in mandibular arch length is somewhat greater than the decrease in maxillary arch length. Implant studies that revealed the internal jaw rotation also confirmed that changes in the anteroposterior position of the incisors teeth are a major influence on arch length changes. When excessive rotation occurs in short face type of development, the incisors tend to be carried into an overlapping position even if they erupt very little, thus the tendency for deep bite malocclusion in short face individuals. The rotation also progressively uprights the incisors, displacing them lingually and causing a tendency towards crowding.


In the long face pattern, on the other hand, an anterior openbit23e will develop as anterior face height increases unless the incisors erupt for an extreme distance. The rotation of the jaws also carries the incisorforward, creatind dental protrusion.

MUTUAL RELATIONSHIP OF ROTATING JAW BASES 10

When Bjork introduced the concept of rotation to orthodontics after using metallic implants, the concept was widely extended and misused. In an attempt to clarify this situation a classification was proposed whereby a clear cut distinction between morphogenetic and positional rotations were presented. Morphogenetic rotation of the mandible concerns with the shape of the mandible itself, while the positional rotation deals with the position of the mandible. Four types of mutual rotation of jaw bases were proposed by Lavergne and Gasson after extensive implant studies in 1982. This is important clinically because dentoalveolar malocclusion depend24 on the combination of these rotations.


1. Convergent rotation of jaw bases : this rotation results with closing of maxilla mandibular plane angles creating a severe true deep bite that is difficult to manage. Both maxilla and mandible converge towards each other.

2. Divergent rotation of jaw bases : the maxilla and mandible move away or diverge from each other. This rotation leads to the opening of the basal angle and can result in open bite. Ex25treme cases require surgical correction.


3. Cranial rotation of maxilla and mandible : both maxilla and mandible rotates upwards and forwards.this horizontal growth pattern occurs in a relatively harmonious manner wherein rotation of maxilla occurs upwards and forwards and compensates for cranially rotating mandible.

4. Caudal rotation of maxilla and mandible : both maxilla nad mandible rotates downward and backward s26imilar to cranial rotation wherein the downward and backward maxillary rotation causes open bite.


ROLE OF GROWTH ROTATIONS IN ORTHODONTIC TREATMENT PLANMandibular rotation is a major factor in the development of malocclusion. Posterior rotation is frequently seen with retrognathia, anterior rotation with prognathia. Skeletal open bite is concomitant with posterior rotation, skeletal deep bite with forward rotation. The variations in direction of growth giving rise to the above rotations are not only a factor in development of malocclusions, but also play an important role in the treatment planning. With forward rotation, treatment of class III and deep bite is difficult, with the backward rotation that of class II and open bite. It is therefore important to determine the growth type before orthodontic treatment is initi27ated.


CONCLUSION Growth rotations play a major role in orthodontic treatment planning and outcome. Though various diagnostic methods were evolved to predict growth rotations, none seems to be fulfilling and newer diagnostic methods have to be used in future. Better therapeutic decisions should be made regarding timing and length of treatment, appliance selection, extraction patter and possible need for surgery

BIBILOGRAPHY :1. CONTEMPORARY ORTHODONTICS – PROFFIT W R 5th EDITION

2. HAND BOOK OF ORTHODONTICS – ROBERT E MOYERS

3. ESSENTIALS OF FACIAL GROWTH – ENLOW D. H

4. TEXT BOOK OF CRANIOFACIAL GROWTH – SRIDHAR PREMKUMAR

5. Bjork A. Prediction of mandibular growth rotation AJO-DO 1969;55:585- 599

6. F Schudy. The rotation of the mandibleresulting from growth: its implications in orthodontic treatment. Angle orthod 1965;1:36-50

7. Julian von Bremen, Hans Pancherz. Association between bjork’s structural signs of mandibular growth rotation and skeletofacial morphology. Angle orthod 2005;75:506-509

8. A Bjork, V Skeiller. Facial development and tooth eruption. An implant study at the age of puberty AJO DO 1972;62(4):339-83

9. Dibbets JMH. Puzzle of growth rotation, AJO-DO 1985;473-80

10. ORTHODONTIC DIAGNOSIS – THOMAS RAKOSI, IRMTRUD JONAS, THOMAS M. GRABER

11. AN ATLAS AND MANUAL OF C28EPHALOMETRIC RADIOGRAPHY – THOMAS RAKOSI


Science

Growth rotations