Page 1


INDIAN DENTAL ACADEMY Leader in continuing dental education

CONTENTS          

Introduction Implants What is rotation Different terminologies Cause of rotation Face types Tooth eruption Prediction of growth rotation Clinical implications conclusion

Introduction The introduction of cephalometric radiography in 1930’s initiated new trends in orthodontics It became a widely used tool in orthodontic diagnosis and treatment planning.

It facilitated the longitudinal study of craniofacial growth by the method of superimposition of radiographs on specific landmarks.  Various angular and linear measurements were used to determine & predict the pattern of growth, and  forward downward growth concept of the face was accepted. 

ď °

But growth in the craniofacial region is not that simple or straight forward.

ď °

The concept of growth rotation helps us to understand this complex process in a better way. With the use of metallic implants inserted in bone, the understanding of vertical jaw relation along with sagittal jaw relation was made easier .

ď °


ď °

ď °

The technique where metal implants are inserted in bone, has been used in animals for more than a century but the application of the method in growth studies of human is of more recent date. This method of study is used extensively by Bjork and coworkers at Royal Dental College copenhagen Denmark. These implants were made up of Tantalum, an inert material . This method is useful, as bone does not grow interstitially and therefore once placed inside the bone, the implants are stable.

The sites where implants are placed are-

Maxilla 1. Hard

palate behind the deciduous canines (Prior to eruption of maxillary permanent incisors) 2. Below the anterior nasal spine (after eruption of maxillary incisors) 3. Two implants on either side of the zygomatic process of maxilla 4. Border between hard plate and alveolar process medial to the first molars

  

Mandible 1. Anterior aspect of symphysis, in the midline below the root tips 2. Two pins on the right side of the mandibular body, one pin under the 1st premolar and other below the 2nd premolar or first molar 3. One pin on the external aspect of the right ramus in level with the occlusal surface of molars.

Rotations 

The phrase “growth rotation” was introduced in 1955 by Bjork who used it to describe a particular phenomena occurring during the growth of head. reporting a case in which lowering of the mandible during growth was different dorsally than frontally

    

What is Rotation? It is the angular movement of one rigid body relative to another. 1. a wheel may rotate with reference to its supporting framework. 2. A tooth may rotate as it is moved through its supporting bone. the displacement that satisfy, the concept of “Rigid body model” should be termed rotations.

  

Terminologies . . Angular Change: When a single body changes in form due to surface accretion and removal there may be changes in orientation between reference lines within that body, these changes are angular changes not the rotations as in true sense. . Forward rotation given by Bjork ( counter clockwise rotation with the patients right in front) . This is the rotation of the mandible in a direction when posterior growth of mandible is more than anterior growth

. Backward rotation ( or clockwise with patients right in front)  When anterior growth is more than posterior growth.  . Negative Rotation-By convention all forward rotation are given a negative sign.  . Positive Rotation- All backward rotations are given a positive sign. 

ď °

concept of forward and backward rotation.

ď °

This was given by Bjork and Skeiller based on their longitudinal implant studies.

FORWARD ROTATION Forward rotation can occur in 3 ways.  Type I- Forward rotation about the centre in the joints which gives rise to deep bite.  Results in the reduced anterior facial height. 

ď ° Type

II- Forward growth rotation of the mandible about a centre located at the incisal edges of the anterior teeth. This is due to the combination of marked development of posterior face height and normal increase in anterior height

•Type III- This is the forward rotation of the mandible with centre at the level of premolars. So this is a combination of decreased anterior facial height and increased posterior facial height.

So in forward rotation the mandible symphysis swings into a more forward direction & this is the one of the reasons for the chin formation characteristic of man

Backward Rotation It can occur in 2 ways. Type I-In this the centre of rotation lies in the temporomandibular joints. Results in an increased anterior facial height

Type II – Rotation occurs about at the most distal occluding molars. This is a combination of increased anterior facial height and decreased posterior facial height.

ď °

The concept of rotation was originated in relation to mandible and then was studied for maxilla also.

Maxillary Rotations Rotation of maxilla during normal growth was not suspected until the implant study of Bjork & coworkers.

There seems to be an almost parallel lowering of nasal floor( was shown by Brodie in 1941)

Why is it so? It is because of the reasons that whatever rotation that takes place in maxilla [ Whether it is backward or forward] is masked by the process of remodeling.

So, when metallic implants were placed above the maxillary process usually rotation in a forward direction were observed but in some cases backward rotation was also seen. But the angle between the s-n plane and nasal floor didn’t show much variation this is because of the compensatory remodeling that took place on the nasal floor.

In cases of forward rotation; as the anterior part of palate was tipped upward resorption took place on the anterior aspect of nasal floor and deposition on the posterior aspect.

In cases of backward rotation of maxilla, there is pronounced resorption posteriorly

The mean of forward rotation of 21 cases was -2.5 degrees.

Rotation of maxilla Normal inclination = 850  Ante inclination >850  Retro inclination <850  Inclination angle records rotation of maxilla to the anterior cranial base i.e. to the SN line as described by A.M. Schwarz 

Maxillary anteinclination with reduced overbite

Maxillary retroclination with increased overbite

ď ° ď °

ď °

Transverse mutual rotation of two maxillae: Since right and left maxillae are two separate bones, joined along the median suture, there is an anterior and a lateral implant in each maxilla, so that distance between these implants is constant throughout growth. In the transverse plane, a triangle is constructed with sides of constant length. It was seen that the increase in width from age 10 - 11yrs in 9 cases, measured between lateral implants was 3 times as great as that between anterior implants. From this it is inferred that

1. Lateral implants separate more than anterior during growth indicating that the two maxillae rotate in relation to each other in transverse plane.

2. The length of maxilla is reduced in mid saggital plane, due to this transverse rotation. Lateral segments of dental arch also separate more posteriorly than anteriorly due to transverse rotation of the two maxillae. Hence distance between molars increases more than canines. Also the length of dental arch becomes reduced in mid-sagital plane.

Mandibular Rotations as given by different authors

Bjork /Skeiller They used 3 terms to describe mandibular rotation

Total – Matrix – Intramatrix 1. Total Rotation – The rotation of the mandibular corpus measured as a change in inclination of an implant line in the mandibular corpus relative to anterior cranial base.

2. Matrix Rotation â&#x20AC;&#x201C; This is the rotation of tangential manibular line with respect to cranial base Matrix Rotation has its centre at the condyles

3. Intramatarix Rotation : The difference between total and matrix rotation and it is an expression of the remodeling at the lower border of the mandible It is identified by the change in inclination of an implant or reference line in the manibular body relative to the tangential mandibular line This rotation has its centre somewhere in body of the mandible

According to Bjork and skeiller the position of centre of rotation of “total rotation” is dependent on the other two centres of rotation. (Bjork & skiller case reports AJO Oct 72) material – 21 subjects 9 girls 12 boys

Method – Metallic implants were inserted in both jaws except for in 2 cases where no implant was present in maxilla.  The study was limited to 6 year period around puberty  Lateral cephs for all 3 periods were taken 

Result Mean forward rotation of the mandible for the whole series was â&#x20AC;&#x201C; 6 degrees. For the maxilla the mean for the forward rotations was -2.5 degrees . Rotations were more than twice as great for the mandible as for the maxilla

As observed in conventional cephalometry ie. Between NS line and mandibular line the forward rotation was –3.4 degrees.  It is evident that about half the rotation was masked by remodeling.  Remodeling at the lower border of the mandible was 2.6 degrees on an average. . 

•Inclination of the ramus in relation to nasion – sella line, unlike that of the body of the mandible was on an average practically unchanged over the period. Mean change was -1 degree. •This constancy in the ramus inclination is because of remodeling of the ramus in order to maintain its functional relation to the neck muscles and the spinal column.

In maxilla It was found that remodeling of the nasal floor varied in the cases according to the difference in direction of rotation of maxilla. So, we see that inclination of the nasal floor showed greater stability, irrespective of the direction and magnitude of the rotation of the maxilla .

. Causes as mentioned by Bjork & skeiller were 1. Condylar growth  2. Development of cranial base  3. Instability of incisal occlusion  4. Lip and tongue dysfunction  5. Interaction of jaw and neck musculature. 

Importance of condylar growth

forward path â&#x20AC;&#x201C; forward rotation backward path â&#x20AC;&#x201C; backward rotation.

Solow â&#x20AC;&#x201C; Houston Solow & Houston in EJO 1988 proposed their own terminology True rotation of the mandible term was introduced by Solow Siersback- Nielsen (1986) This is the rotation of the mandibular body as represented by implants or stable trabecular reference structures, relative to anterior cranial base. This is similar as total rotation of Bjork and Skeiller

Apparent Rotation of the mandible Angular change in the orientation of mandibular line relative to the cranial base . Lande(1952) observed that the lower border of the mandible becomes less steeply inclined with growth. The observation made by him was the same as Solow Houstonâ&#x20AC;&#x2122;s Apparent rotation and also similar to Bjork & Skeillerâ&#x20AC;&#x2122;s Matrix rotation.

This is what we see when superimposing cephalograms conventionally . This apparent rotation is the result of true mandibular rotation and remodeling at the lower border .

Angular remodeling of the mandibular border Angular change in the mandibular line when the mandible is registered on implants or stable natural structures This is a measure of amount of remodelling at the mandibular border

• This angular remodeling amounts to about 50 percent of the true mandibular rotation. • when we see for the posterior border of the mandible, Bjork & skeiller (1972) showed that average angular remodeling (5degree) was almost as large as the average true rotation (-6degree) over the 6yr period. • So the efficiency of the counter remodelling process was around 80 percent. • The apparent rotation of ramus line was only – 1 degree.

ď °

The same terminology can be applied to remodeling of hard palate. When maxilla rotates forward, counter remodeling of nasal and palatal surfaces take place and apparent rotation of palatal plane is much less then the true rotation of maxilla.

Profitt Internal rotation -rotation of mandibular core relative to cranial base implant.  Total Rotation – Rotation of mandibular plane relative to cranial base.  External Rotation – Rotation of mandibular plane. 


Resorption on nasal floor and deposition on palatal side plus eruption of teeth corresponds to external rotation of maxilla.

In total external and internal rotations cancel each other leading to zero effect or minimal forward rotation of maxilla.

. Lavergne and Gasson (1976) They defined rotation as Positional and

Morphogentic Positional rotation deals with the position of the mandible within the head. Morphogenetic rotation concerns with shape of the mandible. They postulated that this is a compensating mechanism which is capable of enlarging or reducing mandibular length as measured along the condylion pogonion diagonal.

. Enlow Displacement  Remodelling  a) involves rotational positioning of jaws in vertical and horizontal or antero – posterior direction.  b) Remodelling – involves resorptive and despository growth process resulting in angular as well as dimensional change. 

. Dibbets Dibbets in his article puzzle of growth rotation ( Am J Orthod 1985) coined the term counter balancing Rotation counter balancing rotation pertains to circular condylar growth, accompanied by selective coordinated remodeling which does not contribute to the incremental growth of the mandible. ď °

Dibbets made a hypothetical construction of the two possible divergent patterns of mandibular growth A circular growth pattern, resulting only in intramatrix rotation and marked by the absence of actual enlargement of mandible. A linear condylar growth pattern characterized by the absence of intramatrix rotation but evidencing mandibular enlargement

This counter balancing rotation is a mechanism that  1. neutralizes growth  2. Results in selective enlargement of the mandible 

Mutual rotation of the jaws  

Rotation of the jaws are a major contributing factor in deciding the vertical proportions of face. . convergent rotation of jaws creates a severly deep overbite which is difficult to manage using functional methods. Divergent rotation of the jaw bases-- this can cause marked open bite.

. Cranial rotation â&#x20AC;&#x201C; In this there is relatively harmonious rotation of both jaws in an upward and forward direction. ď ° Caudal rotation In relatively harmonious manner the downward and backward maxillary rotation offsets what could be an open bite created by downward and backward mandibular rotation.

CAUSE OF ROTATION Houston Concept – EJO 1988  According to him mandibular growth rotation is merely a reflection of an imbalance of growth in anterior and posterior facial heights. Posterior facial height  This is measured between the cranial base and mandibular implant line .  It is the sum of the Vertical components of –  The descent of the middle cranial fossa  growth of the mandibular condyle 

Anterior facial height Schudy (1965)  Growth in anterior facial height is caused by growth at maxillary sutures and at the alveolar process together with eruption of teeth  But these all are secondary 

ď °

ď °

Growth in the anterior facial height can be understood only by examining the wider context of the skeleton, muscles and fascia of neck and head Brodie (1950) stated that posture of the head depends on the muscles of the neck and muscles of mastication . Supra and infra hyoid muscles act as link in a chain joining the cranium ,mandible, hyoid done and shoulder girdle.

ď °

Bench (1963) examined growth of the upper cervical vertebrae and related this to descent of the hyoid bone and chin, relative to the Frankfort plane.

Solow and Krieborg (1977) suggested that cranio cervical angulation might influence facial growth direction through the mechanism of soft tissue stretch ď ° Solow (1966) have found correlation between facial height and stature in cross section studies. ď °

According to Houston growth in cervical column is the primary factor determining growth in anterior face height. ď ° Acts through differential growth in muscles and fascia that are attached to the mandible and to the cranium above and to the hyoid bone and shoulder girdle below. ď °

ď °

ď °

In the normally growing child, the head is carried upwards relative to the shoulder girdle due to growth of cervical vertebrae. Decent of hyoid bone and mandibular symphysis relative to the cranial base is largely the result of the differential growth and strength of the musculature, fascia and other soft tissues that pass between the cranium, mandible , hyoid bone and shoulder girdle. Thus growth in anterior facial height is paced.


Rotation--- Any discrepancy in the relative growth of the anterior and posterior face heights will be manifested as true rotation of mandible. ď ° According to Ballard growth of the alveolar process and eruption of the teeth adapt to the growth in height of the intermaxillary spaces so that in most cases normal occlusion is established ď °

In cases- anterior face height is greatly increased.inadequate vertical dentoalveolar compensation skeletal anterior open bite.

Solow and Tallgren (1976) found that posture of head in relation to the cervical column was related to craniofacial morphology. Where the head was tilted back, the face was retrognathic and the mandible plane angle as well as the total and anterior face height was large

Solow Kreiborg (1977) ď ° Factors effecting the adequacy of nasal airway can result in a posterior tilt of the head, and these factors are-: 1 Nasal obstruction due to adenoids( Linder Aronson 1979) 2 Experimental nasal obstruction( Vig et al 1980) 3 Allergic rhinitis( Wenzel etal 1983) ď °

According to Schudy ď °

ď °

ď °

He postulated that growth rotation of the mandible results from an inharmony between vertical growth and anteroposterior or horizontal growth. Clockwise rotation (as from patients right) is a result of excessive vertical growth as it relates to horizontal growth and causes reduction of overbite. Counter clockwise rotation is a result of deficiency in vertical growth as relates to horizontal growth and causes deep bite.

 

What is vertical and horizontal growth ? Increments of growth which cause the chin to move vertically are called vertical growth. Increments which cause the chin to move forward i e condylar growth are termed – horizontal growth.

ď °

Condylar growth is pitted against combined vertical elements of growth and the final position of chin will be resultant of the horizontal and vertical growth.

ď °

What are these vertical elements ?

1) Growth of nasion and in the corpus of the maxilla which produces an increase in the distance from nasion to anterior nasal spine and cause the maxillary molars and posterior nasal spine to more away from the sella-nasion plane. 2) Growth of maxillary posterior alveolar processes causing the molar teeth to move away from the palatal plane. 3) Growth at the mandibular posterior alveolar process causing the molar teeth to move occlusally.

   

Clockwise Rotation Result of more posterior vertical growth than condylar growth, Centre of rotation is at condyles. Pogonion cannot keep pace with the forward growth of the upper face and mandibular plane becomes steeper.

 

Counter clockwise Rotation- is a result of more condylar growth than combined vertical growth . There is forward movement of pogonion and an increase in overbite. Flattening of mandible plane renders vertical overbite correction and retention more difficult. The ratio between horizontal and vertical growth increment is called the posterior growth


The size of the gonion angle has an important influence upon the number of degrees of resultant counter clockwise rotation.

The smaller the gonion angle the greater rotation is produced for each millimeter of forward movement of pogonion.

The degree of facial divergence ie SN –MP has an effect on rotation. The longer the SN-MP angle more the mandible tends to become steeper and more the chin moves backward Smaller the angle mandible becomes flatter and chin grows forward.


  1. 2.

Why do we need to study face types? Because certain types of facial morphology are identified with specific type of malocclusion Schudy selected angle SN-MP for identifying face types He classified face type as Hyper divergent Hypodiverent

Schendel described hyper divergent as long face syndrome and hypo divergent as short face syndrome

Long face Horizontal facial planes tend to be steeper Tendency for open bite Associated with backward rotational growth

Short face Less steeper

Obtuse gonial angle Palatal plane tipped down posteriorly

Small gonial angle Flatter palatal plane

  

 

For deep bite Associated with forward rotational growth

â&#x20AC;˘ Nanda in his study (AJO 1990) â&#x20AC;˘ 32 subjects were selected with extremes of facial heights and various relationships between horizontal planes was given.

. Inclination of palatal plane is significantly different between two extreme type of faces ď ° Mandibular plane, Occlusal plane and gonial angle steadily decreased in both open and deep bite cases. ď °

ď °

Interaction between Jaw Rotation and Tooth eruption

ď °

It is essential to take into consideration that the rotation of the jaws during growth exerts an influence on the path of eruption of the teeth and hence on the occlusion .


1. Eruption of lower molars was greater than that of the incisors. 2. Eruption of upper molars was greater than that of the incisors. 3. Lower incisor were inclined backward in relation to NS line, but only to the extent of two thirds of the mandibular rotation, and thus were tipped forward on the mandibular base. 4. upper incisors proclined in relation to the NS line but followed maxilla in its forward rotation.

 

5.Molars followed mandible in its rotation.  6. Intermolar angle remained unchanged  7. Lower incisors compensated by forward tipping.  8. Lower molars had a compensatory forward tipping on the jaw base 

Backward Rotation of the face  Centre of rotation at molars  1. Incisors erupted further than molars  2. Incisors tipped backward 

ď °

ď °

ď °

Path of eruption of the maxillary teeth is downward. When maxilla rotates forward this will tip incisors forward but backward rotation directs anterior teeth posteriorly. The molars migrate further mesially during growth than incisors so, there is decrease in arch length. As forward rotation of mandible is greater than maxilla, there is more decrease in mandibular arch length. places greater importance on lingual movement of the incisors as for the cause of decrease in arch length


BACKWARD rotation of maxilla


ď °

FORWARD rotation of mandible

Open Bite 


 

FORWARD rotation of Maxilla backward rotation of Mandible

GROWTH PREDICTION Methods of growth prediction  1.Longtudinal  2.Metric  3.Structural . 

 

 

Longitudinal Method It is commonly used and consists of following the course of development in annual X-Ray cephalometric films. Limitation 1. The pattern of growth is not constant and the pattern recorded at a juvenile age may well have changed by adoloscence. 2. Particular limitation of this method is that it permits the observation of changes in the sagittal jaw relation but those occuring the vertical direction are masked. This method can be made more useful by superimposition on natural reference structures

 

Metric Method Aims at a Prediction of facial development on the basis of facial morphology, determined metrically from a single X-Ray film. But there is only weak correlation between the dimensions of face at the age of 12 years and the residual growth ( as was shown by Bjork by his study on Swedish boys in 1954.) So, we can say that length of the mandible during adoloscence can’t be judged from it size before puberty.

Structural Method ď ° This is based on information concerning the remodeling processes of the mandible during growth, gained from implant studies ď °


Bjork in 1969 gave 7 structural signs to predict future growth rotation. 1. Inclination of condylar head 2. Curvature of mandibular canal 3. Shape of Lower border of Mandible 4. Inclination of symphysis 5. Interincisal Angle 6. Inter premolar or intermolar angles 7. Anterior Lower facial Height

Leslie et al ( 1998 AJO) Reviewed this method       

Obtained result that – Out of the four individual independent variable ie i) Mandibular inclination ii) Intermolar angle iii) Shape of the lower border of the mandible iv) Inclination of symphysis Minimal ability of any of the four individual independent variables to predict mandibular growth rotation. Highest predictive value was of intermolar angle.

Brema and Pancherz (angle 2005)  Again reviewed Bjork’s method and found that  symphysial inclination is a reliable sign.  Lower border is less reliable  And also found that hypodivergent patterns can be easily recognised . 

Clinical Implications 1. It has been agreed that orthodontic treatment does not stimulate growth at mandibular condyles. So, we have got only vertical increments that can be possibly changed to serve our purpose. inhibiting vertical growth is equivalent to stimulating condylar growth eg- high pull head gear , face bow.

. •2. When we see deep bite cases because of deficient vertical growth,. we should stimulate vertical growth of alveolar process with class II elastics and /or conventional face bow head gear with cervical traction. •.

•3 Predominance of vertical growth of the face facilitates correction and retention of vertical overbite.

ď °

4 Too much vertical growth of the molar teeth would prevent forward positioning of the chin and render class II correction very difficult

ď °

5 Forward rotation pattern renders vertical overbite correction and retention difficult.

ď °

6 When at the completion of orthodontic treatment mandibular plane is increased, most commonly it will return to normal , as condyles will grow and horizontal growth will compensate

. ď °

7. Posterior rotations induced by orthodontic treatment, ie by the use of class II elastics, anchorage bends and anterior bite planes are often transient as posterior facial height will catch up.


The ability of an orthodontist to understand and predict future mandibular growth rotation would greatly aid in diagnosis and treatment planning

Better therapeutic decisions could be made regarding timing and length of treatment, appliance selection ,extraction pattern and possible need for surgery

. 

Treatment planning can be customized with the possibility of optimal results in a shorter period of time.

Thank you Leader in continuing dental education

Growth rotations 2/ dental implant courses by Indian dental academy  

The Indian Dental Academy is the Leader in continuing dental education , training dentists in all aspects of dentistry and offering a wide r...