GROWTH ROTATIONS

Growth rotationPresented byDr mohammed aslam2nd year pg studentDepartment of orthodontics 1

CONTENTSIntroduction.Principles of growth and development.Amount and timing of growth.Assessment of amount of growth.Growth of mandible.Mechanism of rotation.

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Growth rotations of mandible.Bjork.Direction of growth.Structural signs.According to Bjork.According to Petrovic.Results of implants studies.Type of rotations.Bjork and Skieller.Proffit. F.F. Schudy.Center of rotation of mandible- Isaacson.

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Growth rotations of maxilla.Tweeds facial growth trends.Rickets growth prediction.Compensatory growth.Clinical aspects.Conclusion.References.

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INTRODUCTIONGrowth and developmentFrequently heard together.Why both the terms?As growth is not merely a process of increase in size, rather is a progressive facial enlargement with differential growth processes in which the various parts develop earlier or later then other parts in different facial region, in a multitude directions and different rates.

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It is a gradual maturational process involving a complex of different but functionally interrelated organs and tissues.The growth process also involves a bewildering succession of regional changes of great proportions and it requires countless localized adjustments to achieve proper fitting and function among all the parts.

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PRINCIPLES OF GROWTH AND DEVELOPMENTBone grows by adding new bone on one side of bony cortex and taking it away from the other side, due to which bone drift occurs.The inner and outer surface of the bone are covered with mosaic type appearance of growth fields, which can be resorbtive or depository. If it is resorbtive on one side it will be depository on other.7

Bone has periosteal and endosteal layer if one is resorbtive then other will be depository.The control of growth is done by the soft tissue matrix present around the bone. The blueprint of the design construction and growth of the bone lies in the composite of muscles, tongue, lips, connective tissue, nerves, blood vessels, airways etc.8

The various sites of growth do not show a same rate of growth activity.Remodeling is a basic part of growth process.Growth process leads to primary or secondary displacement. 9

AMOUNT AND TIMING OF GROWTHThere are four growth spurts :On birth.1 yr. after birth.Pre pubertal growth spurt.6-7 yrs. in females.7-9 yrs. in males.Adolescent growth spurt.11-13 yrs. in females.14-16 yrs. in males.10

Prepuberal Growth Spurt

Occurs due to production of sex hormones from adrenal gland at the age of around 6 yrs. In the form of a weak androgen (Dihydroepiendosterone). This activation is therefore also referred to as adrenarche.In girls more amount of hormones are releases hence is more prominent than in boys.11

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Adolescent Growth SpurtInitiation occurs in the brain.

Hypothalamus releases releasing factor from neuroendocrine glands.Base of the hypothalamus near pituitaryVia cytoplasmic transportpituitaryVia capillariesAnt pituitary releases pituitary gonadotropinsStimulates endocrine cells in adrenal gland and sex glands to produce sex hormones

In malesIn testes Sertoli cells produce testosteroneLeydig cells produce estrogenIn adrenal cortex Male and female sex hormones are produced.

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In femalesIn ovariesEstrogen is produced initially and then progesterone.In adrenal cortex Male and female sex hormones are produced.

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sex hormones

blood streamdevelopment of secondarysexual characteristicsgrowth of genitalsGENERAL BODY GROWTHdecrease in lymphoid tissue

These sex hormones are released into the blood stream causing development of secondary sexual characteristics and accelerated growth of genitals. Also there is an increase in general body growth and decrease in lymphoid tissue.

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Timing of puberty makes a difference in ultimate body size. The earlier the puberty the smaller will be the body size.Height depends on endochondral bone formation. 16

These sex hormones are released into the blood stream causing development of secondary sexual characteristics and accelerated growth of genitals. Also there is an increase in general body growth and decrease in lymphoid tissue.

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sex hormones

sex hormonescartilage to growadolescent growth spurt

increase in skeletal maturationIncreases the rate at which cartilage is transformed into bone

Growth complete

This maturation occurs faster in females hence they have a shorter stature.

The sex hormones stimulates cartilage to grow faster causing adolescent growth spurt, at the same time they also cause a increase in skeletal maturation this is the rate at which cartilage is transformed into bone.

If the acceleration in maturation is faster then acceleration in growth it leads to cartilage getting used up faster then it is replaced, leading to growth completion.

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ASSESSMENT OF AMOUNT OF GROWTHVarious skeletal maturity indicators are

Hand wrist radiograph.Cervical vertebrae.Canine calcification.Corpus index.Hyoid bone position.Third molar level.Frontal sinus.Antigonial notch.

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GROWTH OF MANDIBLEMandible is basically composed of two structuresThe corpus The ramusCorpus of the mandible is a direct structural counterpart to the maxillary corpusRamus is related to the pharyngeal space and middle cranial fossa, with the function being to bridge the middle cranial fossa and place the corpus in proper relation with the cranial floor articulation on one side and maxillary corpus on other side.19

Ramus undergoes continuing remodeling as a part of its growth process and several basic functions are provided by these changesThe entire ramus gets progressively relocated posteriorly by combination of resorbtion and deposition.The ramus width increases to accommodate the increase in middle cranial fossa and the pharynx.

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The length of the ramus increases to accommodate the increased size of nasomaxillary complex and erupting teeth.Progressive remodeling changes occur in the ramus to place the mandibular corpus in proper relation with the maxillary corpus.

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These changes lead to change in orientation of the mandible leading to ROTATION OF THE MANDIBLE. (Rotation literally means to move round a axis or a centre.)Rotation can be Forward and upwardDownward and backward22

Since classic description of mandibular growth by John Hunter in 1771 there has been various studies and reports on it.He had applied anthropometry (aligned human skulls along symphyseal and lower border of mandible) to find out how mandible increased in size.

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He said mandible size increased by Apposition at posterior border, Increase at coronoid and condyloid process above the line of teeth The increase in height was mainly due to increase in alveolar bone.Later in 1955 Bjork coined the term growth rotations.

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25GROWTH ROTATIONS.

Bjork studyStarted his study in 1951Had a sample size of 100 children between the age group of 4 24 yrs.Used metal implants to find the sites of growth and resorption in individual jaws. Also examined individual variation in direction and intensity.Analyzed mechanics of changes in intermaxillary relations during growth.26

He disagreed with the concept that the given intermaxillary relation remained static through out life. Considerable variation in the development of facial form and intermaxillary relation was seen.

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Direction of GrowthMandible can have a forward direction of growth (good growing) or backward direction of growth (bad growing).Bjork gave seven structural signs to find the direction of mandibular growth.These signs are not clearly developed before puberty.

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Structural Signs Condylar inclination.Mandibular canal inclination.Lower border of mandible (Antigonial notch).Symphysis inclination.Interincisal inclination.Intermolar angle.Lower face height.29

CONDYLAR INCLINATIONForward or backward inclination of the condylar head is characteristic signIn forward growing mandible condyle is upright compared to a backward growing mandible in which it is inclined backwardIs difficult to identify on the lateral cephalogram.30

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MANDIBULAR CANALThe mandibular canal curvature remains the same throughout the life.In vertical growing mandible the curvature of the canal is more than that of the mandibular contour. Where as in case of horizontal growers the canal may be flat or may even be curved in opposite direction.

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Shape of the lower border of mandible.In vertical growers there is an increased deposition below the symphysis, anterior part of the mandible becomes thick along with this there is resorption at the angle producing a characteristic concavity.In horizontal growers the anterior rounding is absent so the concavity of the lower border is absent.

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INCLINATION OF THE SYMPHYSISIn horizontal growers chin swings forward to become prominent.In vertical growers symphysis is swung backward causing a receding chin.

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INTERINCISAL ANGLEInterincisal angle is almost constant showing that the lower incisors is related functionally to the upper incisorsIn vertical growers angle in lessIn horizontal growers there is an increased interincisal angle.

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INTERMOLAR ANGLEIn case of forward rotation the molars get more upright increasing the intermolar and interpremolar anglewhile in case of backward rotation the molars become mesially tipped hence decreasing the intermolar and interpremolar angle

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LOWER FACE HEIGHTis increased in case of vertical growth pattern while is less in case of a horizontal growth pattern42

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According to Petrovic In orthognathic type of face the ramus and the body of the mandible are fully developed, and the width of the ascending ramus is equal to the height of the body of the mandible, including height of the alveolar process and the incisors. The condyle and coronoid process are almost in the same plane and symphysis is well developed.44

In case of a retrognathic mandible corpus is narrow in molar region. Symphysis is narrow and long, ramus is narrow and short and the gonial angle is obtuse and the coronoid process is relatively smaller than the condylar process..

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In prognathic type the corpus is well developed and wide in molar region. Symphysis is wider in sagital plane, ramus is wide and long and the gonial angle is acute or small.

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Results of the implants studiesIncrease in length of the mandible mainly due to deposition at the condyles.Anterior border of the symphysis is stable. Increased thickness of the chin was due to deposition at the posterior border and the increase in length was due to deposition at the lower border.The deposition at the lower border of the symphysis continues to the anterior border of mandible giving it the rounded appearance.47

Posterior border of the mandible shows resorption.Growth at the condyles is not in the direction of the ramus but slightly forward.Mandibular canal is not remodeled to the extent of the mandible. Trabaculae of the canal remains stable and the shape of the canal reflects the earlier shape of the mandible.48

The lower border of the developing tooth germ of lower molar is relatively stable till the root formation.Mandible can be considered as a unconstrained bone, it can change its inclination in several ways. One critical factor for this is the centre of rotation.

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According to the type of rotation and the centre of rotation the growth of the mandible can be divided intoForward rotationType IType IIType IIIBackward rotation (less common)Type IType II

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Forward rotation type ICentre of rotation is in the joint.Deep bite is seen.Decreased lower anterior facial height.Powerful musculature is usually seenMay lead to occlusal imbalance loss of teeth.

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Forward rotation type IICentre of rotation is at the incisal edges of the lower incisors.Increased posterior facial height normal lower anterior facial height.Posterior facial height can increase due toCaudally placed glenoid fossa because in increase in cranial flexure.Increased ramal height. As the mandible is held in its place by muscles and the ramal height increases there is swinging of mandible forward.

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Anterior facial height does not change asThe eruption of molars occurs in the pace with increased ramal height.Lower border of the mandible undergoes remodeling.Mandibular symphysis swings forward.

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Forward rotation type IIIIn cases of increased overjet the centre of rotation is displaced to the premolars.There is decreased lower facial height.Increased posterior facial height.Skeletal deep bite is seen.Mandibular symphysis swings forward.54

Rotation of the mandible effects the inclination of the teeth. The interincisal angle is almost constant (showing the lower incisors are functionally related to upper incisors). Hence their eruption is guided forward and there is increase in alveolar prognathisim.Rotation also influences the posterior teeth incase of forward rotation the posterior teeth become more upright, increasing the intermolar and interpremolar angles.

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Backward rotation type ICentre of rotation at the joint.Seen in cases ofBite is raised by orthodontic treatment increasing the lower anterior facial height.Growth of cranial base occurs such that the cranial base flexure flattens leading to the mandible being raised posteriorly.

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Backward rotation type IICentre of resistance is at the most distally occluding molar.Growth at the condyles is in the sagital direction.Mandible increases in length but is carried forward more due to its muscles and ligaments attachments.

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Symphysis is swung backward, chin goes below the face. The soft tissues may not follow this leading to a double chin.Skeletal open bite is seen.Incompetent lips.Lower incisors retrocline and meet the upper incisors.Molars and premolars of mandible are inclined forward.58

BJORK AND SKIELLERDivided the mandibular rotations into three componentsTotal rotationMatrix rotationIntramatrix rotation

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Total Rotation

Is the rotation of the mandibular corpusIs measured as change in inclination of a reference line or a implant line in the mandibular corpus relative to the anterior cranial base,If line anteriorly rotate towards the face then is known as forward rotating and signated as -

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Matrix rotationWas called as apparent rotation by Lande.Is rotation of soft tissue matrix of the mandible relative to the cranial base.Is shown by a tangential mandibular line.It can rotate forward and backward in the same patient with condyles as the centre of rotation and is described by the term pendulum movement.

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Intramatrix rotationIs the difference between total rotation and the matrix rotation.It is an expression of remodeling of the lower border of the mandible.It is found out by the change in inclination of an implant line or reference line in the mandibular corpus to the tangential mandibular line.

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Rotation of the corpus relative to the tangential line such that it faces front is called as forward rotation.Centre of rotation is somewhere in corpus and depends on rotation of corpus, growth rotation of the maxilla and occlusion of the teeth.

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Bjork and Skieller said that three changes occur in Intramatrix rotationThe mandible wiggles in in its matrixThis wiggling is associated with the corpus and is caused by growing condyle.The rotation results from or compensates for genetically predetermined program.

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PROFFITRotation occurring in the core of the jaw were called as INTERNAL ROTATION. Hence is the rotation which is visualized by the implant line. (This is the rotation in the mandibular core proper or total rotation according to Bjork)

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Rotation caused by the surface changes and the alteration in the rate of tooth eruption is called as EXTERNAL ROTATION. (this is the remodeling that is occurring of the mandible or intramatrix rotation according to Bjork)

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Rotation occurring due to rotation around the condyle is called as TOTAL ROTATION. (This is the rotation of the mandible that is occurring arounda the condyles or matrix rotation according to Bjork)

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BJORK SOLOW AND HOUSTONPROFITTRotation of mandibular core relative to cranial baseTotal rotationTrue rotationInternal rotationMandibular plane relative to cranial baseMatrix rotationApparent rotationTotal rotationMandibular plane relative to core of the mandibleIntra matrix rotationAngular remodelling of lower borderExternal rotation

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F.F. SCHUDYRotation of the mandible is a result of in-harmony between vertical growth, antero-posterior growth and horizontal growth.Clockwise rotation is a result of increased vertical growth causing a decrease in bite.Counter-clockwise rotation is a result of decreased vertical growth causing a deep bite.

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Growth increments causing downward movement of chin is called as vertical growth, while growth increments causing forward movement of chin are called as horizontal growth.If growth at the condyles is more than molar eruption it causes horizontal growth deepening the bite.If growth at the condyles is less then molar eruption is leads to vertical growth and a decreased bite.

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There are four vertical growth elements which increase the facial height, these are:-Anterior growth of nasion.Corpus of maxilla getting palatal plane down.Eruption of maxillary molars.Eruption of mandibular molars.74

The migration of glenoid fossa is cancelled by growth of condyles.Clockwise rotation is when there is an increased growth at the condyles than the vertical growth of the mandible. It can increase ANB angle and can correct deep bite if present.Counterclockwise rotation is when there is decreased condylar growth then the vertical growth.

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CENTER OF ROTATIONIsaacson has devised a method for determining the centre of rotation of the mandible.

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STEPS IN FINDING CENTRE OF ROTATION OF MANDIBLEOn pre-observation tracing reference points are selected in the region of the symphysis and the mandibular foramen.

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The post observation tracing is super-imposed on the previous tracing on the mandibular canal, third molar follicle and symphysis internal border. The two reference points are transferred to this tracing.The areas where the tracing do not coincide shows the areas of external remodeling and tooth movement.

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A reference line is arbitrarily drawn in the anterior cranial fossa region.

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The two tracings are superimposed on the anterior cranial structures. Lines are drawn connecting the two pre and post reference points.

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Perpendicular bisector of these two lines are made. The intersection of these two perpendicular bisector gives us the center of rotation of the mandible.81

GROWTH ROTATION OF MAXILLA

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Growth of maxilla occurs by two waysPassive displacement- in primary dentition periodActive growth is by surface remodeling

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The maxilla can be divided intoIts functional processAlveolar processParts of bone surrounding the air passageCore of its bone

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Implants placed on maxillary alveolar process show that the core of the maxilla undergoes a small and variable degree of rotation- forward and backward INTERNAL ROTATIONTOTAL ROTATION, MATRIX ROTATION not possible in a maxilla (condyle).

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Varying degree of resorption on nasal side and deposition on palatal side, also varying amount of eruption of incisors and molars lead to EXTERNAL ROTATION, INTRAMATRIX ROTATION (lower border).

In most individuals the external and internal rotations cancel each other.86

MECHANISM OF ROTATIONS87

Mechanism of rotationsDisplacement type.Remodeling type.

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Displacement type of rotationMandible rotates on the condylar pivot.The primary reason for this is to adjust to the vertical size of midface and alignment of middle cranial fossaRotates forward to meet short mid face or closed bicranial flexure. Rotates backward to meet vertically increased mid face or open bicranial flexure.89

Remodeling typeOccurs at angle between corpus and ramusOccurs due to resorbtive and depository changes occurring at this junction.It basically leads toMore upright ramus alignment relative to corpus accommodating a vertically lengthened mid face.

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TWEEDS GROWTH TRENDS91

Two cephalograms are taken at a gap of 12-18 months.They are then superimposed on S-N keeping S as the reference point.Three types of growth was seen.Tweed classified it into Type ASubdivisionType BType C92

Type AMiddle and lower third grew forward and downward The ANB value remained constant.If the ANB value does not exceed 4.5o and case is having a molar relation of Class I then is type AIf molar relation is of Class II and ANB is more then 4.5o then is called as Type A subdivision.

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Type BThere is an change in ANB reading in Pre and Post radiographs.The growth trend is in downward and forward direction with middle face growing more rapidly then the lower face.In cases of ANB of less then 4o the prognosis is fair while in cases with a increased ANB of 7o or beyond the prognosis is poor.

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Type CIn case the lower face is growing downward and forward more rapidly then the middle face.The ANB decreases.The mandibular incisors usually get tipped lingually and get crowded or the max incisors get tipped labially.95

RICKETTS GROWTH PREDICTION96

Ricketts Growth PredictionAccording to Ricketts a normal human mandible grows by superior-anterior (vertical) apposition at the ramus on a curve or a arc which is a segment formed from a circle.Then radius of the circle is described by using the distance from the mental protuberance to a point at forking of the stress lines at the terminus of oblique ridge on the medial side of the ramus.

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On basis of studies a primary method of growth prediction was devised. A line was plotted through the long axis of the condyles extending it through the line making the lower border of the mandible.Keeping these lines as reference line a bending of the mandibular form was studied.

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Later use of mandibular plane as the reference plane was refuted as its lower border showed resorbtion.Also the ramus as reference area was disapproved as it also showed remodeling as shown by Enlows studies.99

So new reference points were taken

Xi pointCentre of the ramusContacts the mandibular canal

Suprapogonion (Po, Pm)Bone crest on the superior aspect of the compact bone and anterior contour of the symphysis.Was taken as was located at the stress centre (ricketts), is the site of reversal lines (Enlow), and is a stable unchanging point as seen by implant studies (Bjork)100

DcPoint at the bisection of the condyle neck as high as visible in the cephalogram below the fossa.

Now by joining Dc to Xi and Xi to Po a repeatable condyle and corpus axis could be made. And by studying the changes in the mandible in relation to these axis the growth could be predicted.101

By studying the mandibular growth on these axis it was found that the bending of the mandible occurred in an orderly fashion, with greater the magnitude of growth greater was the bending.Now the next task was to make a arc to predict this growth.

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Point Pm, Xi, Dc were used to depict the mandibular core, and the prediction of the mandibular size and shape at five years interval was done.The current arcial prediction of ricketts was reached in three steps

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A arc was made passing through these three points. But it was found that the increase in size could be produced but not increase in curvature. The Pm point was taken as constant.A second arc was made using tip of coronoid process, anterior border of ramus at the deepest point R1 and Pm. Using this was found that the mandible would bend too much.

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So it was thought that the actual arc must lie in between these two.So a point in between Xi and R1 was selected.A arc was made with a radius from this point to Pm.Was found that it still causes increased bending of the mandible, also the mandible kept increasing in size causing a spiral shaped arc.105

A mandible 850 yrs old was taken. In it the stress lines were visible.The stress lines were seen to converge at the tubercle menti, from there they swung downward then upward and backward and outward through the oblique ridge.In the medial aspect a Y shaped bony prominence was seen at the superior aspect of the mylohyoid ridge, also above this point a small nutritive canal was seen,106

Experimentally two points were foundPt. Eva just over the forking of the stress linesIs made by bisecting Xi to R3 point and make a line Pt. Mu

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XiR3RREVAPmTRMu

Now the arc that the mandible will follow to grow is found out, next part was to find the amount of growth that will take place.It was found that the mandible increased by 2.5mm per year.Coronoid process shows an increment of 0.8mm per year.

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COMPENSATORY GROWTH110

Involves morphogenetic changes (resorption and deposition) among various regional parts as each grow in close relation.

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Commonly seen is case of vertically long naso-maxilary complex.

Mandible rotates forward and downward

Retruded mandibleAnd Class IIWidening of the ramusVertically long nasomaxillary complex

Mandibular comes forward and Class I results

CLINICAL ASPECTS113

MUTUAL RELATIONSHIP BETWEEN ROTATING JAW BASESRotation of mandible decides the vertical proportions of the face.Horizontal growers have a Short lower anterior facial height.Predisposed to having a deep bite.Opposite of above for the vertical growers.

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According to Lavergne and Gasson the mutual rotation of the upper and lower jaw can be of following 4 typesConvergent rotation.Severe deep bite.Difficult to treat with a functional therapy.Divergent jaw bases.Severe open bite.In severe cases orthognathic surgery is required.

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Cranial rotation of both the bases.Horizontal growth pattern.Maxillary cranial rotation compensates for the mandibular rotation.Normal overbite.Caudal rotation of both bases.Vertical growth pattern.Maxillary caudal rotation compensates for the mandibular rotation.Normal overbite.116

CLINICAL ASPECTSGrowth rotation of mandible influence the amount the teeth can erupt.Also it influences the direction of eruption and ultimate position of teeth.Eruption of maxillary teeth is in a downward and forward direction.Forward rotation of maxilla causes incisors to tip forward.Backward rotation of maxilla causes incisors to tip palatally.

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Eruption of mandibular teeth is in a upward and forward direction.Forward rotation of mandible causes incisors to tip lingually.Backward rotation of maxilla causes incisors to tip labially.Normal internal rotation rotates mandible forward uprighting the incisors and allowing the molars to mesialize.

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Normally the forward rotation of the maxilla is less then that of mandible causing the mandibular arch length to decrease.Therefore in brachyfacial individuals the mandibular incisors tend to retrocline more, decreasing the arch length leading to crowding.119

In dolicofacial individuals there is usually a anterior open bite, unless the incisors over erupt, also the incisors tend to flare out.In case of vertical growers the ANB, or the Class II does not improve, but the correction and retention of the deep bite is facilitated, visa-versa for horizontal growers.

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In case of vertical growers the occlusal forces on the molars are less hence is more easy to loose anchorage, while in horizontal growers it is difficult to loose anchorage.Functional appliances lead to opening of mandibular plane angle hence are contraindicated in cases of vertical growers.

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ENLOWS CONCEPT Maxillary Rotations

Displacement Remodeling

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DisplacementPrimary displacement occurs-antroinferior direction.Sutures are tension adapted-cannot grow by pushing-apart.Stimulus for sutural remodeling is due to the displacement.

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Secondary displacement124

Drift of the teeth125As the maxilla and mandible enlarge, dentition drifts-horizontally and vertically.

The whole tooth and its socket move.

Nasal and palatal remodeling126

The balance between greater and lesser amounts of remodeling in the posterior & anterior parts of the maxilla is the response to clockwise/ counterclockwise rotatory displacement of middle cranial fossa.Compensatory remodeling rotation of the nasomaxillary complex-sustains its proper position relative to the neutral orbital axis.Remodeling also occurs as bones assume new positions with expansion of the soft tissue matrix.

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BJORKS CONCEPTLongitudinal study done by implant method. Lateral implants:4yrs of age -inserted laterally in the zygomatic process of the maxilla (2 on each side).

-increase in distance between the implants on the frontal film - increase in the width in the median suture at the level of the 1st molars.

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Anterior implants:10-11yrs of age -inserted below the anterior nasal spine.

-one on each side of the median suture at level with the apices of the central incisors.

- increased distance bw the implants measured on frontal film - growth in the width in the median suture at the level of the incisors. 129

Implant line-

-Tip of 1 anterior implant to midpoint of 2 lateral implants.

-Change in the inclination of implant line to the S-N line-vertical rotation of maxilla in relation to cranial base.

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MAXILLARY GROWTH-LATERAL IMPLANTS [4YRS]Height -growth at frontal and zygomatic process.

-apposition at lower alveolar process and eruption of teeth.

-apposition at floor of the orbit.

-nasal floor lowered down.

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Lateral implants-vertical component calculated at right angles to S-N.

Sutural lowering -11.2mmApposition at the floor of the orbit-6.4mm.

Lowering of nasal floor-4.6mm

Appositional growth in height of alveolar process-14.6.mm132

Width -growth in the median suture. -appositional remodeling in the outer aspects. -Enlow-widening of hard palate mainly result of remodeling. -Persson, Melsen-growth in median suture upto adolescence.

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Implants study show -median suture growth-6.7mm

-outer aspect of maxilla-9.5mm

-growth in the median suture follow the same curve as their growth in body height.

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Growth of maxilla in 3-d - anterior and lateral implants(10-11 yrs)Length- -sutural growth towards palatine bone by apposition on tuberosities.

-anterior surface was thought to be resorptive; unchanged when studied using implants.

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Sagittal growth studied in relation to infrazygomatic crest.

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ROTATIONSTransverse plane

Vertical plane.

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Joining anterior and lateral implants on each side a triangle is constructed with sides of constant length.

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Lateral implants increased 3mm against 0.9mm of the anterior implants.

Thus, the lateral implants separate more.

This reduces length of maxilla in mid sagittal plane.

The distance between 1st molars increases more than canines

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VERTICAL ROTATIONSSuperimposition shows parallel lowering of nasal floor.140

Implant studies- -maxilla undergoes vertical rotation.

-inclination of anterior cranial base to nasal floor is maintained by compensatory remodeling.

-forward rotation-anterior resorption & deposition posteriorly.

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Backward rotation--Rotates down anteriorly.

-posterior resorption more than anterior.

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CONCLUSIONThe ability of an orthodontist to predict future mandibular growth would greatly aid in the diagnosis and treatment planning. Better therapeutic decisions could be made regarding timing and length of the treatment, appliance selection, extraction pattern and possible need for surgery. 143

referencesEssentials of facial growth-D.H.EnlowContemporary orthodontics-W.R.ProffitHandbook of orthodontics-R.E.MoyersDentofacial orthopaedics with functional appliance-M Graber,Thomas Rakosi,G.PetrovicPrediction of mandibular growth rotation-A.Bjork,Am J Orthod june 1969;585-599144