GROWTH ROTATION
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CONTENTS • • • •
• • • • • •
INTRODUCTION REVIEW OF LITERATURE FACIAL ROTATIONS MANDIBULAR ROTATIONS ROTATION OF MANDIBLE DURING GROWTH PREDICTION OF MANDIBULAR GROWTH ROTATION PRINCIPLE OF ARCIAL GROWTH OF MANDIBLE MAXILLARY ROTATIONS MUTUAL ROTATION OF BOTH JAWS COMPARISON OF SHORTFACE AND LONGFACE CLINICAL IMPLICATIONS OF JAW ROTATIONS CONCLUSION BIBILOGRAPHY www.indiandentalacademy.com
INTRODUCTION
An intensive study of the growth of the human head will inevitably lead to the realization that it involves the most complicated anatomical complex in all creation.The inter relationships are infinite and the cause and effect of these relationship almost cannot be estimated.
The phrase growth rotation was introduced in 1955 by Bjork. In reporting a case states the lowering of the mandible during growth was “considerably greater posteriorly than anteriorly, Bjork drew attention to what he called the mandibular rotation”.
This was based on the fact that Bjork metallic implants, had given him precise markers from which he could infer the sites and amount of growth and resorption in a given mandible. www.indiandentalacademy.com
INTRODUCTION
By superimposing two consecutive tracings of the childs mandible registered on the implants, the image of the older mandible appeared to have rotated during the intervening period relative to its original shape.
Orthodontic and orthopedic treatment can change the facial growth direction, various terms have been used to describe how orthodontic and orthopedic treatment affects the growth.
These include stimulation, inhibition, retardation, redirection, correction and guidance. The use of such terminology indicates that growth manipulation is possible.
Hence a thorough knowledge regarding the craniofacial morphogenesis and mutual jaw relationship and rotational patterns is essential for diagnosis, treatment planning and www.indiandentalacademy.com correction of the malocclusion.
REVIEW OF LITERATURE • Lande in 1952 - Pointed that lower border of mandible on average becomes less steeply inclined with growth. • Bjork in 1955 –Drew attention to mandibular growth rotation as a feature of normal facial growth,& he done metallic implant study & demonstrated the much greater underlying mandibular rotation that was masked by periosteal remodelling at the lower border. • F. F. Schudy in 1965 – studied growth changes which produce rotation of the mandible and depending on the vertical growth and horizontal growth (condylar growth) he classified rotation in to clockwise rotation and counterclockwise rotation. •Bjork in 1969- Discussed different direction of rotation of the mandibular implant line & the relation of these to mandibular form. •Odegard in 1970 –Discribed as a rotation, the change in orientation that occur b/w the implant line & the lower border of the mandible. •Bjork & Skieller in 1972 –Demonstrated that dentoalveolar adaptation in response to mandibular growth rotation could result in occlusal change such as late lower incisor crowding. www.indiandentalacademy.com
REVIEW OF LITERATURE • Lavergne & Gasson in 1977 - Discribed “positional rotation” change in the orientation of the mandible relative to the cranial base, & “morphogenetic rotations” change in the shape of the mandible. • Bjork & Skieller in 1983 – Rotation of invarient structure in the mandible ( implant /natural reference structure) relative to the cranial base was termed “total rotation”. Rotation of the lower border of the mandible relative to the cranial base was “matrix rotation” and change in the orientation of implant line in the mandible relative to the lower border was “intramatrix rotation”. • Dibbets in 1985 – Introdused the term “ counter balancing rotation ‘ for what is essentially “intramatrix rotation” with the implication that the changes discribed by this term represent adjustments of the contribution of condylar growth to overall growth in the length of the mandible. • Rune et al in 1987 – reviewed the terms introdused by Bjork & Skeiller in 1983 & remarked that in the context of intramatrix rotation Bjork & Skeiller’s interpritation of the findings seems to have no relation to the general concepts of craniofacial bone growth. www.indiandentalacademy.com
FACIAL ROTATIONS • The expansion of the frontal and particularly, the temporal lobes of the cerebrum relates to a rotation of the orbits towards the midline. The eyes come closer together. • Two separate axes of orbital rotation are thus associated with the massive expansion of the cerebrum. One displaces the orbits vertically, and the other carries them horizontally in medial directions into a binocular position.
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• The enlarged human cerebrum also causes a downward rotational displacement of the olfactory bulbs. In all other mammals, they are nearly upright or obliquely aligned, depending on the size and configaration of the frontal lobes. • In man , the bulbs have been rotated into horizontal positions by the cerebrum. This is a significant factor in the basic design of the human face.
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•
The plane of the nasomaxillary region is thereby approximately perpendicular to the plane of the olfactory bulbs. This is a major anatomic and functional relationship involved in the basic plan of the face in any mammal. • As the bulbs become rotated progressively from a vertical position to a horizontal one because of increase in brain size or because of its shape (1,2,3), the whole face is similarly rotated from a horizontal to a vertical plane(1a,2a,3a). Or stated another way,the face is rotated down by the expanded anterior cranial floor as it rotates downward as result of the enlargement of the frontal lobes.
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• The maxilla of most mammals has a triangular configuration. In man, it is uniquely rectangular. This is caused by a rotation of the occlusion into a horizontal plane to adapt to the vertical rotation of the whole midface.
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• The occlusal plane in most mammals, including man, is approximately parallel to the Frankfort plane ( a plane from the top of the auditory meatus to the inferior rim of the orbit).This aligns the jaws in a functional position relative to the visual, olfactory, and hearing senses. • In the human maxilla, the design change that allows for this resulted in the creation of a new arch positioning facial region, the suborbital compartment. Most of this expanded area is occupied by the maxillary sinus.
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MANDIBULAR ROTATIONS
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THE ROTATION OF MANDIBLE DURING GROWTH • In 1951 Bjork conducted a mixed longitudinal study by the use of metallic implants of about 100 children of each sex covering the age period from 4 to 24 years by means of the implant method, he located sites of growth and resorption in the individual jaws and examined individual variations in direction and intensity. • By super imposing consecutive tracings, he concluded that, rotation involved marked resorption in the lower border of the mandible in the gonial region which masked the underlying mandibular rotation.
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Until longitudinal studies of growth using metalic implants were carried out in 1960, by Bjork and coworkers in Copenhagen, the extent to which both maxilla and mandible rotate during growth was not appreciated. •
• The reason is that the rotation that occurs in the core of each jaw called internal rotation ,tend to be masked by surface changes and alteration in the rate of tooth eruption. The surface changes produce external rotation . It is easier to visualize the internal and external rotation of the jaws by considering the mandible first. The core of the mandible is the bone that surrounds the inferior alveolar nerve the rest of the mandible consist of its several functional processes. •
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Bjork and Skieller distinguished two contribution to internal rotation (which they called total rotation) of the mandible: 1) matrix rotation or rotation around the condyle. fig(A) 2) intramatrix rotation, or rotation centered within the body of the mandible. fig(B) • When the implant line or reference line rotates forward relative to the S-N line during growth the rotation is designated as and negative (more growth posteriorly) and positive (more growth anteriorly) if it is rotated backward.
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Internal rotation of mandible ranging up to 10-15 degrees. •
• For an average individual with normal vertical facial proportion, there is about a -15 degree (forward) internal rotation from age 4 to adult life. • Of this, about 25% results from matrix rotation (A) and 75% results from intramatrix rotation(B). www.indiandentalacademy.com
During the time that the core of the mandible rotates forward an average of 15 degrees, the mandibular plane angle, representing the orientation of the jaw to an outside observer, decrease only 2- 4 degrees on an average. •
• The reason that the internal rotation is not expressed in jaw orientation because suraface changes (external rotation) tend to compensate. • This means that the posterior part of the lower border of the mandible must be an area of resorption ,while anterior aspect of lower border is unchanged or undergoes slight apposition. www.indiandentalacademy.com
• On an average, there is about 15 degrees of
internal rotation, forward rotation. • 11 to 12 degrees of external , backward rotation producing the 3- 4 degree decrease in mandibular plane angle observed in the average individual during childhood and adolescence .
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According to Bjork (1969) – Based on the center of rotation he classified rotation as forward rotation and backward rotation. FORWARD ROTATION: When posterior growth is greater than anterior. This may occur in the following 3 Types. TYPE I (Forward Rotation): • There is a forward rotation about centers in the joints. The lower dental arch is pressed into the upper, resulting in deep bite as well as under development of the anterior face height. • The cause may be occlusal imbalance due to loss of teeth or powerful muscular pressure. www.indiandentalacademy.com
TYPE II: Forward rotation of the mandible about a center located at the incise edges of the lower anterior teeth. • This is due to the combination of marked development of the posterior face height and normal increase in anterior face height. • The posterior part of the mandible then rotated away from the maxilla.
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The increase in posterior face height has 2 components: (1)
One is lowering of the middle cranial fossa in relation to the anterior one as the cranial base bends, the condylar fossa then being lowered.
(2)
Second is the increase in the height of the ramus due to vertical direction growth at the condyles, the mandible is lowered more than it is carried forward.
•
Because of the muscular and ligamentous attachments carry it forward in relation to the maxilla with the center at the incisal edges of the lower incisors.
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TYPE III FORWARD ROTATION : This occurs in anomalous occlusion of the anterior teeth where there is a large overjet. • The center of rotation no longer lies at the incisors but is displaced backward to the level of the premolars. • In this case, the dental arches are pressed into each other and a basal deep bite develops and the anterior face height becomes underdeveloped.
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BACKWARD ROTATION:- Less frequent than forward. TYPE I BACKWARD ROTATION: - Centre of rotation lies in the TMJ This occurs when : (a) The bite is raised by orthodontic means. (b) In the case of flattening of the cranial base. Where the middle cranial fossa is raised in relation to the anterior, which also raises the mandible . c) In case where there is incomplete development in height of the middle cranial fossa. • This underdevalopment of the posterior face height leads to a backward rotation of mandible, with over devalopment of the anterior face height and this results in increase in anterior face height and possibly open bite. The mandible is normal. www.indiandentalacademy.com
TYPE II BACKWARD ROTATION: • Centre of rotation is situated at the most distal occluding molars, This occurs in connection with growth in the saggital direction at the 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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Shudy described rotation as: 1) Clockwise rotation: ( as viewed from the patients right side) This is a result of excessive vertical growth as it relates to horizontal growth, and tends to cause a reduction in the vertical overbite. The point of rotation is at the condyles. fig showes :Growth study from 6 to10 years the chin grew downward and forward and the mandibular plane moved downward in parallel manner. At age 10 the condyles almost completely ceased growing. Then chin movied downward and backward, mandibular plane became 7degree steeper. The post. Growth analysis showed that the condyles grew 4mm while vertical growth in the molar area was 10.5mm . The mandibular 1st molars moved backward about 3mm; thus it would have been impossible to have corrected a class II condition www.indiandentalacademy.com under these circumstances.
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2) Counter Clockwise rotation -Is result of a deficiency in vertical growth as related to horizontal growth and tends to cause an increase of the vertical overbites. ď Ź
Fig .Showing the growth of female, age 11 to 14 years , here condyles grew out of proportion to vertical molar growth. This resulted in a 4 degree rotation and marked forward swing of the mandible ,a 2mm increase in vertical overbite. Extremes of this condition cause closed bites.
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• Growth at the mandibular condyle only produces a forward component of the chin, not a downward, nor a downward and forward component. It is only when vertical increments of facial growth begin assert their influence on condylar growth through occlusal contact that a downward and forward direction of the chin is produced.
Thus the final vector of growth of the chin is a resultant of the struggle between the horizontal growth and vertical www.indiandentalacademy.com growth, in other words, b/w condylar growth and
Then what are these vertical “elements� of growth which produce an increase in facial height??? 1. Anterior-posterior growth at nasion. 2. growth in the corpus of the maxilla which produces as increase in the distance from nasion to the anterior nasal spine and causes the maxillary molars and posterior nasal spine to move away from the sella -nasion plane. 3. Growth at the maxillar posterior alveolar processes causing the molar teeth to move away from the palatal plane. 4. Growth at the mandiular posterior alveolar processes causing the molar teeth to move occlusally. www.indiandentalacademy.com
•When Pog-nasion grow forward at an equal rate, increment A =sum of increments I,II,III& IV, In other words the condyles must equal the antero-posterior growth at nasion,plus the vertcal growth of the corpus of the maxilla,plus the vertical growth of the maxillary alveolar process,plus the vertical growth of the mandibular alveolar process. • When growth at A exceeds I,II,III,&IV, the mandibular plane becomes flatter & Pog moves forward more than nasion. • When growth of the sum of I,II,III,&IV exceeds A, Pog will move backward with relation to nasion & mandibular plane will become steeper. • When growth at A equals the sum of I,II,III, & IV, the mandibular plane moves down in a parallel manner. www.indiandentalacademy.com
Three cephalogrms were taken 1) in centric occlusion with denture in place.2)in a position of overclosure with denture removed and 3)with a block of wax b/w dentures. • As the molar height increases the chin swings downward &backward, the mandibular plane becomes steeper,the gonial angle moves posteriorly and the facial angle decreases. • Thus,by varying the molar height we were able to change the facial angle, i.e molar height not only controls the vertical position of the chin, but also anteroposterior position.
• These principles have a very definite application to the treatment of class II malocclusion. Too much vertical growth of the molar teeth would prevent the forward positioning of the chin and thereby render class www.indiandentalacademy.com II correction very difficult.
• What is the clinical application?
All investigation are agreed that orthodontic treatment does not stimulate growth at the mandibular condyles.If this is true we have only the vertical increments that we may possibly change to serve our purposes. i.e. if we can inhibit vertical growth it will have the same effect as stimulating growth at the condyles. If vertical growth is deficient we try to stimulate it, & if vertical growth is excessive we try to inhibite it.
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THE BEHAVIOUR OF THE OCCLUSAL PLANE DURING MANDIBULAR ROTATION
The inclination of occlusal plane seemes to reflect natures attempt to compensate for inharmonies of growth. The vertical growth of the anterior alveolar processes seems to try to compensate for the inharmonies b/w posterior alveolar growth www.indiandentalacademy.com and ramus growth. •
• In a study of 62 untreated & 50 treated cases by Creekmore – Compared forward movement of the chin. • The untreated group had an average SN-MP angle of 34 degrees and treated 31.5 degrees. • The untreted group Pog moved forward an average of 3.48mm, while in treated group this reding was 2.49mm. • This showes that treatment retards the forward positioning of the chin. The cause of this difference was a difference in the amount of vertical devalopment of the molar area. • A number of investigators have found that there is little or no difference b/w mandibular length in class I & class II malocclusions. www.indiandentalacademy.com
• In a comparison of retrognthia and prognathia Bjork states that, “ a comparison b/w the two extreme percentiles indicate that mean length of the lower jaw is practically the same in both”. • Maj & Luzi in discussing class II, div I malocclusion states “in most instances, the component parts (maxilla & mandible) are normal by themselves but their association results in a disharmony”. • Thus, it can be said that most class II cases have had average horizontal growth. Their principal shortcoming is that they have had too much vertical growth. •The vertical component of growth limits the horizontal component. This in turn prevents the forward movement of the chin. www.indiandentalacademy.com
Dr.Tom Creekmore & Schudy designed a high pull face bow for extraoral anchorage. Elastic traction is then applied in an upward & back ward direction for inhibiting the downward growth of the maxillary alveolar process & possibly the body of the maxiila. This type of traction is used primarily on open bite cases & individules with high SN-MP angles. • When vertical growth is deficient, resulting in a deep overbite, we try to stimulate the vertical growth of the alveolar processes with class II elastics and / or the conventional face bow headgear with cervical traction.
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Subsequently Bjork and skieller showed that different patterns emerged when different registration for super imposition were used i.e., a striking contrast in the mandibular position was seen when superimposed on the cranial base and superimposed on metallic implants. They classified rotation in to 1) Total rotation 2) matrix rotation 3) intramatrix rotation
1.
1) TOTAL ROTATION: The rotation of the mndibular corpus measured as a change in inclination of an implant line in the mandibular corpus relative to the anterior cranial base (Bjork and skieller)
2.
Solow and Huston called this the “True rotation” and
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2) MATRIX ROTATION: Bjork and skieller - Defined it “as a rotation of the soft tissue matrix of the mandible relative to the cranial base”. The soft tissue matrix is the tangential mandibular line. It has its center at the condyles. •Solow and Houston called this “apparent rotation” and •Proffit called this “total rotation”. • Lavergne & Gasson called it as Positional rotation.
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3) INTRAMATRIX ROTATION:According to Bjork and skieller- It is the change in inclination of a reference line/ implant line in the mandibular corpus relative to the tangential mandibular line. The center of rotation lies in the corpus. (Fig B) • • • •
Solow and Houstion called this Angular remodeling of the lower border. Proffit called it External rotation. Lavergne & Gasson called it as Morphogenetic rotation. Dibbets called it as Counterbalancing rotation
Fig (A):matrix rotation Fig (B):intramatrix rotation
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THREE DIFFERENT INTERPRETATION OF INTRAMATRIX ROTATION 1)
1) According to Bjork and skieller:- They speculated that the intramatrix rotation reflected in the rotation of the mandibular corpus relative to the lower border is a result of genetically determined condylar growth and that the center of rotation lies in the corpus and not in the condyles.
According to them mandibular growth rotation may be found to be closely associated with both the direction and the amount of growth at the condyles First , mandible “wiggles” or move from side to side with in its matrix. Second, this “wiggling” is associated predominantly with the corpus but it is caused by the growing condyle. Third, rotation results from,or compensates for, a genetically determined program. This last conclusion, in particular, makes rotation an attractive item in growth prediction. www.indiandentalacademy.com
2) Lavergne and Gasson defined rotation as: a) Morphogenetic- Concerning the shape of the mandible. Similar to intramatrix rotation. b) Positional- Dealing with the position of the mandible with in the head. Similar to matrix rotation
They used a line joining condylon and pogonion to superimpose cephalogram and the angle between the 2 implant lines is determined & this corresponds to the degree of “ morphogenetic rotation”. The fact that fixed points, represented by the implants, are measured in relation to a line that represents the contours of the mandible brings Lavergen & Gasson’s scheme of “morphogenetic rotation” into focus with Bjork’s definition of “intramatrix rotation”. www.indiandentalacademy.com
• Lavergne & gasson 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 mandibular 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 gonial angle.
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• The Size of the gonial angle has an important influence upon the degree of anterior rotation. The smaller the gonial angle, the greater rotation is produced for each mm of forward movement of the pogonion. • An obtuse gonial angle compensate for a short ramus and corpus i.e. the gonial angle helps to compensate for length.
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3) Dibbets: (AJO-DO,1985-Jun)
Gave a third interpretation which is based on two hypothetical divergent patterns of growth.
a) One pattern 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 contours,resulting in “intramtrix rotation” with out enlargment of the mandible. b) The other pattern is a linear growth curve of the condyle, without any “intramatrix rotation”and maximum enlargement of the mandible.
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Two methods of superimposing the mandible: Fig (A) :tracing, at different ages, of the same mandible registered upon natural reference structures “Bjork approach�. (inner cortical structure of the symphysis, tip of the chin, & mandibular canal) . Note the curved condylar growth direction and extensive resorption of the inferior border Fig (B): same mandible as in (A), superimposed upon the traditional Hunterian conception of posterior ramal deposition &anterior ramal resorption www.indiandentalacademy.com
Schematic illustration of intramatrx rotation : fig (A), two mandibles superimposed on their external contours. Note divergence of the implant lines indicative of “intramatrix rotation” not reflected in dimensional change or alteration of mandibular contours. fig (B), the same two mandibles superimposed on the implant markers. There is lack of concordance of mandibular contours, indicating extensive remodeling during development. • The figure is constructed in a such a manner that the center of rotation is on the chin,this indicates condyle growes on a circular arc (C-C’) with the radius of fixed length, running from the center at the chin to the condyle. It is noted that the form of the mandible has not changed in fig (A). • He showed that external configuration of the mandible need not change its form or position within the head to allow intra matrix rotation and any www.indiandentalacademy.com resorption or deposition only serves to maintain the original contours.
According Dibbets growth of the condyle has at least 2 effects: 1) Intramatrix rotation 2) Enlargement So linear growth pattern due to growth of the condyle, It follows that every millimeter of condylar growth along the pogonion- condylon diagonal would enlarge the mandible by 1 mm. in the event that the direction of the condylar growth follows a pattern that enlarge the mandible maximally, then it would follow that the hardly any “itramatrix rotation� will occur. All growth increments will be expressed in dimensional gain.
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•
This is compensated by remodeling at the lower border. This mechanism is termed as the “counterbalancing rotation”. (Dibbet’s)
•
Thus counterbalancing rotation is mechanisum “relates to circular condylar growth,accompained by selective co-ordinated remodeling, which does not contribute to the incremental growth of the mandible”
i)
It neutralizes effect of growth of the condylar cartilage.
ii) Result in selective enlargement of the mandible. www.indiandentalacademy.com
Enlow categorised rotations as: a) Displacement type b) Remodeling type a) Displacement type - Involves the rotational positioning of the entire mandible. This is caused by changes in the placement of junctional contacts with cranial floor and the maxilla i.e., the dimensions and angular positions of these separate parts directly affect the rotational position of the mandible. b) Remodeling
type : This utilizes depository and resorptive growth processes and produces angular and dimensional changes in the ramus and corpus of an individual mandible i.e., rotations in these parts occur in relation to one another. www.indiandentalacademy.com
a) Displacement rotation: (for exp) i) If the cranial base angle is open, the effect can be a downward and backward displacement rotation of the mandible. • If the cranial base angle is closed converse effect is seen.
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ii) If the nasomaxillary complex is vertically long, a down word and backward displacement rotations of the whole mandible results. A vertically-short nasomaxillary complex has a converse effect. Vertically long nasomaxillary complex
Vertically short nasomaxillary complex
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b) Remodeling rotation- there are 2 reasons why a mandible undergoes the remodeling type of rotation. 1. The first is to prodce a more upright ramus alignment relative to the corpus. This is necessary to accomodate the continued vertical growth of the naso-maxillary region and the eruption of the permanent dentition. 2. The seconds reason is to provide ramus corpus angular adjustments to accomodate the effects of the whole mandibular displacement rotation i.e., if the whole mandible is aligned in an upward and forward manner, an upward inclined mandibular corpus and occlusal plane would result. This can be offset by an opening of ramus-corpus angular relationship and similarly a downward inclined mandibular corpus can be offset by a closing of ramus- corpus angle. www.indiandentalacademy.com
• Most
of the remodeling changes in the ramus corpus angular relationship are carried out by the ramus. However bone deposition on the inferior bordor may occur which rotates the mandibular plane inferiorly . • A mandible characterically has a more prominent antegonial notch, if the gonial angle opened. Fig (a) • A mandible has a less prominent antegonial notch (fig (b) if the gonial angle becomes closed.
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• Effect of whole mandible rotations and ramus-to-corpus rotations are opposite. when the entire mandible is aligned downward, a mandibular retrusive effect is prodused, but when just the corpus is aligned downward, a mandibular protrusive effect results. An upward whole mandible alignment is mandibular protrusive, and an upward alignment of the corpus only is mandibular retrusive.
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TERMINOLOGIES & SUMMARY OF GROWTH ROTATION CONDITION
BJORK
SCHUDY
ANTERIOR GROWTH GREATER THAN POSTERIOR GROWTH
BACK WARD ROTATION
CLOCKWISE ROTATION
POSTERIOR GROWTH GREATER THAN ANTERIOR GROWTH
FORWARD ROTATION
COUNTER CLOCKWISE ROTATION
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Bjork & Condition Skieller Rotation of mandibular core relative to cranial base
Total rotation
Rotation of mandibular Plane relative to cranial base
Matrix rotation
Rotation of Mandibular plane relative to core of mandible
Intra matrix rotation
Solow, Houston
True rotation
Apparent rotation
Proffit
Lavergne, Gasson
Enlow
Dibbets
Internal rotation
Total rotation
Positional rotation
Angular External MorphogRemodrotation enetic eling Rotation Of lower www.indiandentalacademy.com border
Displacement rotation
Remodelling Rotation
Counter Balancing rotation
PREDICTION OF MANDIBULAR GROWTH ROTATION
If an attempt is made to assess the growth trend at an early age , this information can be used in designing the treatment or evaluating the problems that may arise before growth is completed.
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 rediograph.
In an attempt to analyse the possibility of predicting growth of single facial dimension, Bjork and Palling correlated liner and angular measurements at pubertal age with residual growth of these dimension up to adulthood. These correlations were however www.indiandentalacademy.com found to be low.
• Hixson 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. Several authors adopted this method. However, this estimate would fit an average but not an extreme growth pattern, where prediction from a clinical point is more important. • Levergne tried to individualize the prediction by a subdivision according to 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 Bjorn-Jorgensen.
A growth analysis consists of essentially 3 items:
1) Assessment of the development in shape of the face which ,in the first place, implies changes in the intermaxillary relationship. 2) Assessment of whether the intensity of the facial growth is high or low. 3) Evaluation of the individual rate of maturation. This is important in establishing whether puberty has been reached and when the growth may be expected to be completed. www.indiandentalacademy.com
According to Bjork In the assessment of shape there are three methods. 1) Longitudinal method 2) Metric method 3) Structural method I) longitudinal method: which is commonly used, consists of following the course of development in annual celphalometric films. It is for the subjects displaying the most pronounced changes is facial forms that the diagnoisis of growth pattern is important. www.indiandentalacademy.com
Limitation of longitiudinal method are: 1. Pattern of growth is not constant and the pattern recorded at a juvenile age may be changed by adolescence. 2. It permits the observation of changes in the sagittal jaw relation with growth, and those changes occurring in the vertical jaw relation are masked due to remodeling of lower border of the mandible. Changes in the vertical positions of the jaws 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. www.indiandentalacademy.com
• For clinical purposes, the 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 them with reference to these structures, one may estimate the growth pattern of the mandible by reading the angle between the nasion sells lines for the two ages. •
Longitudunal method of analysis of mandibular growth rotation from the angle b/w the N-S lines,at two stages (A&B) after superimposition of the mandibles on natural reference structures. (1)Tip of the chin (2) Inner cortical structure at the inferior border of the symphysis. (3) lower contour of a molar germ. (4) from the time mineralization of the crown is visible untile the roots begin to form. www.indiandentalacademy.com
II) METRIC METHOD: • Aims at a prediction of facial development on the basis of facial morphology, determined metrically from a single x- ray 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. • The changes in shape of the face during adolescence, expressed in terms of anglular measurements, were also weakly correlated with the shape of the face at 12 years, which is the age at which treatment is instituted or planned. www.indiandentalacademy.com
III) 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 remodeling in particular type of mandibular rotation.
•
A prediction of the subsequent course is then made on the assumption that the trend will continue. www.indiandentalacademy.com
STRUCTURAL SIGNS OF GROWTH ROTATION: • There are seven signs and not all of them will be found in a particular individual, but the greater the number, the more reliable the prediction will be. They are 1. 2. 3. 4. 5. 6. 7.
Inclination of the condylar head Curvature of the mandibular canal Shape of lower border of mandible Inciination of the symphsis Inter molar angle Inter incisal angle Anterior lower face height. www.indiandentalacademy.com
1) A
forward or backward inclination of the condylar head is a characteristic sign of forward or backward rotation FORWARD ROTATION
BACKWARD ROTATION
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2) Curvature of the mandibular canal: In the vertical of condylar growth, the curvature of the canal tends to be greater than that of the mandibular contour (b) whereas in the sagittal type curvature of the canal is smaller than the mandibular counter (a).
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a) Horizontal growth
b) Vertical growth
3) Shape of the lower border of the mandible-
In forward growth rotation there is apposition below the symphysis and anterior part of the mandible producing anterior rounding , while resorption at the angle produces a concavity. (a)
In back ward growth rotation the anterior rounding is absent resulting in a linear shape of anterior lower border and the contour at the jaw angle is convex. (b)
a) Forward rotation b) Backward rotation
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a. 4) Inclination of the symphysis• This is measured as the angle between the tangent to the anterior surface of the mandible and the anterior cranial base. This is an important feature in mandibular growth prediction because this surface is free from remodeling. In forward growth rotation ( fig. a & b) characterized by retroclination of the syphysis, irrespective of small (a) or great(b) mandibular inclination. In backward growth rotation (c) characterized by proclination of the symphysis & great inclination of the mandible, (d) pathologic www.indiandentalacademy.com form.
5) Inter molar angle • The inter molar angle tends to increase in forward
rotation of the mandible and decrease when the rotation is directed backward.
Change in molar inclination a)Forward rotation b)Backward rotation www.indiandentalacademy.com
6) Inter incisal angle: In backward rotation the inter incisal angle is redused (b), where as in forward rotation it is increased (a). •
b) Backward rotation www.indiandentalacademy.com a) Forward rotation
7) Anterior lower face height: • In forward growth rotation there is deep overbite and reduced lower face height. • In backward rotation there is increased lower face height and open bite. a) Forward growth rotation of the mandible with normal incisal occlusion b) Forward rotation with deep over bite & redused LAFH c) Backward rotation with increased LAFH www.indiandentalacademy.com
PRINCIPLE OF ARCIAL GROWTH OF THE MANDIBLE (Robert M. Ricketts 1972)
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PRINCIPLE OF ARCIAL GROWTH OF THE MANDIBLE (Robert M. Ricketts 1972)
•The essence of this principle is as follows, a normal human mandible grows by superior-anterior (vertical) apposition at the ramus on a curve or arc, which is a segment formed from a circle. • The radius of this circle is determined by using the distance from supra pogonial ( Pm) to a point at the forking of the stress lines at the terminus of the oblique ridge on the medial side of the ramus. www.indiandentalacademy.com
Intially to locate the arc of the mandibular growth a stable landmark is selected in the center of the mandibular ramus and this is obtained by bisecting the height of the ramus and the mid point termed xi point. •
• This mid point is selected because as Bjork reported earlier there is remodeling changes observed on the surface of the mandible and he also reported that supra pogonial area (Pm) was stable. www.indiandentalacademy.com
• By selecting these landmarks first curve tested was one from Pm, xi, and Dc point (bisecting the condyle) by extending this arc the size increase was produced but not enough bending is resulted. • He was satisfied with the landmark Pm as it is reliable reference and retained it for further study.
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• The second arc was explored by using the tip of the coronoid process (CR), the anterior border of the ramus at its deepest curve (R1) and the same Pm point.
• The extension of this curve exhibited the segment of a circle too small in radius and resulted in excessive bending of the mandible when the same gradient of growth was employed for a projection. www.indiandentalacademy.com
It was obvious that the characteristics of typical growth had been bracketed by the two arcs produced. One straightening the mandible too much and the other bending. A true arc of growth therefore must be some where in the mandible between the condyloid and the coronoid process and between the ramal center and anterior border of ramus. •
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• They construoted an experimental arc bisecting the two previously arcs. By establishing a halfway point between xi and R1 points and using the distance from this point to Pm as a radius of a circle an arc could be produced. • The use of this arc still bent the mandible a fraction too much. In addition, a radius selected from this point would increase with size of the mandible and a progressive increase or a changing arc or ultimate spiral shape would result.
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• On examining the weathered mandible state of disintegration of 850 years old mandible they traced the interprismatic substance of the external cortical bone. And therefore clearly showed stress lines in the outer and inner plate.
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• Close examination confirmed the covergence of stress lines at the protuberance menti. The stress lines seemed to swing downward and then upward and backward and outward through the external obligue ridge. • From this ridge on the exernal table at the base of cornoid process the stress lines are divided at the base of the coronoid process. • An irregular gnarled area was located at this area on the lateral surface as the strees seemed to divide forward or backward in respect to coronoid and condyloid demands.
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• Even in the medial aspect greater bifurcating of stress lines observed followed the mylohyoid ridge upward into a thick mass to terminate at a ‘y’ shaped bony prominence. • This was almost the center of anterior superior quadrant of the ramus they even observed a small apparently nutritive foramena immediately superior to this area on the medial aspect. It was hypothesized that these might be trophic for a possibly an important growth area.
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• Experimentally, two new points (Eva and true radius (TR)) were located geometrically, point Eva is also a biologic point as it is located over the point of forking of the stress lines in the ramus. • When the size increase of the mandible as determined in the computer study was incrementally added to the arc at the sigmoid notch, It was found that the predicted mandible was almost absolutely correct in size and form when compared with final composite. • The method as devised proved extremely accurate in fifty treated cases which were predicted and compared for period of as long as fourteen years.
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Having the arc as a tool for prediction is satisfactory, the next problem lay in the amount of growth to forecast on the arc. The yearly increase from the combined studies was found to be almost precisely 2.5 mm. Cutoffs for growth were determined to the 14.5 years for females and age 19 years for males. •
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•Further studies consistent with the gonion behaviour and found that the gonial angle drifted posteriorly on the arch almost exactly one half or 50% of the total increase in mandibular growth on the arc.
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• The final consideration is need to complete forecasting of the mandibular form this is a critical point because it helps to determine the space available for the developing mandibular third molar at the anterior border of the ramus. • For this determination the ramus reference (RR) point was reemployed. As the time 1 tracing is compared with forecast being constructed. It is assumed that stable bone is located in this area. • Thus with normal anatomical contouring the coronoid process is connected to RR point. Which tends to determine ramal width, Slightly below this point, The external oblique ridge will show apposition of almost 0.4. mm per year.
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MAXILLARY ROTATIONS
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Maxillary rotation • It is less easy to divide the maxilla into a core of bone and a series of functional processes. • The alveolar process is certainly a functional process in the classic sense. If implants are placed above the maxillary alveolar process, core of the maxilla undergoes a small and variable degree of rotation, forward or backward . • This internal rotation is analogous to the intramatrix rotation of the mandible. Matrix rotation is not possible for maxilla.
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At the same time that the internal rotation of maxilla is occurring, there are also varying degrees of resorption on the nasal side and apposition of bone on the palatal side in the anterior and posterior parts of the palate. •
• Similar variations in the amount of eruption of the incisors and molars occur.These changes amount, to an external rotation. • External rotations 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. www.indiandentalacademy.com
• Until longitudinal studies of growth using mettalic implants in the jaws were carried out in the 1960 by Bjork and co-workers in Copenhagen the extent to which the maxilla and mandible rotate during growth was not appreciated. In fact rotation of maxilla during normal growth had not been suspected. • However now we are aware that the maxilla does Indeed show rotations during growth and this rotation may be divided. 1. Vertical rotation of the Maxilla 2. Transverse mutual rotation of the two maxilla
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Vertical rotation of the Maxilla 1. Super imposition of the longitudinal profile radiographs on the sella- nasion line show generally an almost parallel lowering of the nasal floor as described the Brodie in 1941. which led to the view that during growth the maxilla is lowered without rotation in the vertical plane. 2. However implants Studies by Bjork and skieller (1972) have shown that the downward and forward displacement of the maxilla during growth is associated with a varying degree of vertical rotation which is most cases is directed forward. Despite the vertical rotation of the maxilla, the inclination of the nasal floor, the palate as well as well as the orbital floor to the anterior cranial base is maintained by differential resorption and deposition. www.indiandentalacademy.com
Vertical rotation of maxilla
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• Generally inclination of the maxillary base stable and no growth dependent changes are seen, environmental influences such as neuromuscular dysfunction, occlusal forces, gravity and nasorespiratory malfunction can modify this inclination as upward & forward tipping of the anterior part of the maxilla seen in confined mouth breathes. • A downward and backward tipping of the anterior part of the maxillary base is seen as a natural compensation in patients with vertically growing faces.
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Transverse mutual rotation of the two maxilla:• The right and left maxilla are 2 separate bones joined along the medial suture and Bjork in his experiment placed an anterior & lateral implant in each maxilla so that the distance between each implant is constant throughout growth. • He found that the increase in width from the age of 1011 years in the nine case measured between the lateral implants was an average 3 1/2 times as great as that between the anterior implants.(3.0mm against 0.9mm). That the lateral implants separated more than the anterior during growth indicate that the two maxilla rotate in relation to each other in the transverse plane. www.indiandentalacademy.com
As a result of the mutual transverse rotation : • The lateral segments of the dental arch separate more posteriorly. • The distance between the first molars increases more than the distance between the canines
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MUTUAL ROTATION OF UPPER AND LOWER JAW BASES
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MUTUAL ROTATION OF U/L JAW BASES: • Rotations of the mandible can be decisive in establishing the vertical proportions of the face. In a horizontal rotation the anterior face profile is short whereas in a vertically rotating mandibular pattern it is long. A horizontal rotation means that there is a predisposition towards a deep overbite. •An excessively vertical rotation means a tendency toward an open bite the inclination of the maxillary base is also important to the occlusal relationship. The resultant dentoalveolar malocclusion depends on the combination of these rotations we can differentiate the following type of rotations as shown by Lavergne and Gasson.
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1) Convergent rotation of jaw bases: This creates a severely deep overbite.
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2) Divergent rotation of the jaw bases: This can cause marked open bite problems. In severe cases orthognathic surgery is required for the correction.
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3) Cranial rotation of both jaw bases: In this there is horizontal growth pattern & there is a relatively harmonious rotation of both jaws in an upward and forward direction. The upward and forward rotation of the maxilla compensates for the upward and forward mandibular rotation, offsetting what could be a deep bite.
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4) Caudal or downward and backward rotation of the both bases: In relatively harmonious manner the downward and backward maxillary rotation offsets what could be an open bite created by the downward and backward mandibular rotation.
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COMPARISON OF SHORT FACE SYNDROME AND LONG FACE SYNDROME www.indiandentalacademy.com
1) Short face syndrome • They are characterized by short anterior lower face height with excessive forward rotation of the mandible during growth resulting from both an increases in the normal internal rotation and decrease in external compensation. This results in: Nearly horizontal palatal plane Mandibular morphology of the “ square jawâ€? type Low mandiular plane angle Square gonial angle Deep bite Crowded incisors
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Long face syndrome This is characterized by increased anterior and total face height and results primarily from a lack of the normal forward internal rotation or even a backward internal rotation. The internal rotation in turn is primarily matrix rotation not intramatrix rotation. 2)
This results in: • Palatal plane rotates down posteriorly. • Mandible shows an opposite backward rotation. • Increase in mandibular plane angle. • Associated with open bites . www.indiandentalacademy.com
CLASSIFICATION OF SHORT FACE SYNDROME & LONG FACE SYNDROME • Based on the parameters like ramus length, the SN to MP angle, and posterior vertical maxillary dentoalveolar height the short face syndrome group is divided into two sub types. SUBTYPE I: It is characterised by a long ramus and extremely low SN-MP angle and slightly redused posterior maxillary dentoalveolar height. SUBTYPE II: A short ramus and a vertical maxillary deficiency were the dominant findings, while the SN-MP angle was only slightly redused. These persons manifest extreme reduction of lower anterior face height. www.indiandentalacademy.com
The long face syndrome group can be sub divided in to Two sub types: SUBTYPE I: Is characterised by a long ramus, increased occlusal plane to palatal plane angle, an increased SN to MP angle, and excessive lower anterior facial height. These persons manifest the most typical clinical characteristics of the the long face syndrome and have excessively long face. SUBTYPE II: However, extreme backward and downward rotation of the mandible combined with a short or extremely short ramus, is associated with an increase in LAFH. The increase in posterior maxillary height was not striking in this subtype.
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CLINICAL IMPLICATIONS OF GROWTH ROTATIONS
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CLINICAL IMPLICATIONS OF GROWTH ROTATIONS • Vertical malocclusion often receives less consideration than sagittal. No doubt, this is due in some measure to difficulty in detecting their relation to facial growth types. • More extreme the rotation of the mandible during growth , the greater the clinical problems that it presents. It is important to predict such rotations at an early stage, regardless of whether or not malocclusions have developed. • Extreme rotation, whether forward or backward greatly influences the paths of eruption of the teeth. This has a bearing on the orthodontic tooth movement and account must be taken in planning treatment. www.indiandentalacademy.com
• The path of eruption of the mandibular teeth is upward and some what forward. The normal internal rotation of the mandible carries the jaw upward in front. • This rotation alters the eruption path of 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 is reflected in the decrease in arch length that normally occurs.
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• Since the forward internal rotation of the mandible is greater than that of the maxilla, normal decrease in mandibular arch length is somewhat greater than the decrease in maxillary arch length.
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• Individuals of short face type have excessive forward rotation of the mandible during growth, resulting from both an increase in normal internal rotation and a decrease in external compensation. The result is a horizontal palatal plane and a low mandibular plane angle. A deep bite malocclusion and crowded incisors are also often seen.
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• In long face individuals, the palatal plane rotates down posteriorly. The mandible shows a backward rotation with an increase in mandibular plane angle. This type of rotation is associated with anterior open bite malocclusion and anterior face height increases.
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•Posterior rotations are induced by orthodontic treatment and this is usually associated with the use of class II clastics, anchore bends and bite plane. However these are transient. •In the child growth in lower anterior face height is accelerated during treatment of this type but will subsequently lag while posterior face height catches up thus there may be no long term effects on the position of the mandible relative to the cranial base. In adults or in children where the treatment induced increase in anterior face height exceeds that which would normally have occurred with growth, there will often be a gradual anterior rotation associated with intrusion of the teeth under the influence of occlusal forces. www.indiandentalacademy.com •
However in some cases, where anterior face height is increased by treatment the position of the mandible relative to the cranial base will change permanently because of adaptation in the cranio cervical musculature and fascia and probably head posture. This occurs more commonly in cases that already have a tendency to posterior mandibular growth rotation. •
• When facial morphology indicates that vertical growth has been excessive or that condylar growth has been deficient we try to inhibit the downward growth of the maxillary molars we could use a face bow with a high pull head gear.
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• When it has been determined that vertical growth is deficient, resulting in deep overbite, we try to stimulate the vertical growth of the alveolar process with class II elastics and/or the conventional face bow with cervical traction. • Clockwise rotations of the mandible would not help reduce the ANB angle and would not aid in correction class II molar relation. • However it would tent to help correct the vertical overbite, while on the other hand counter clockwise rotations is nearly always accompanied by forward movement of the pogonion, a flattending of the mandibular plane which tends to increase the vertical overbite and renders vertical overbite correction and retention more difficult. www.indiandentalacademy.com
CONCLUSION • We orthodontist are interested in facial growth and development basically because growth can be altered for the need of application of therapy. Therefore we should predict future growth changes that occur. There by avoid making undesirable changes and can alter undesireble growth pattern. • The rotation of the mandible during growth appears to be a complex phenomenon showing annual variataions in direction & intensity. Such rotation is not only dependent on mandibular factors, but also is strongly related to the intensity of growth of both jaws. • Clinician should confine his effort to correct the abnormal growth pattern during the process of correcting the malocclusion for better prognosis. www.indiandentalacademy.com
BIBILOGRAPHY 1) F.F. Schudy: The rotation of the mandible resulting from growth: its implications in orthodontic treatment. Angle orthodontics,1965- vol.35, No.1, 36-50. 2) Bjork. A : Prediction of mandibular growth rotation Am.Journ of orthodontics 1969-55: 585-599. 3) Robert M.Ricketts: A Principle of Arcial Growth of mandible;1972;42;4;368-386 4) Jean Lavergne, Nicole Gasson: A metal implant study of mandibular rotation: Angle Ortho-1976-46;146-150
5) Bjork.A.,Skieller: Prediction of mandibular growth rotation evaluated from a longitiudinal implant sample:AJO-DO;1984-Nov-359-370 6) Sheldon Baumrind: prediction of mandibular rotation:an empirical test of clinician performance: AJO-DO ,1984-NOV-371-385. www.indiandentalacademy.com
BIBILOGRAPHY 7) J.M.H.Dibbets : The puzzle of growth rotation – AJO-DO1985JUN-473-480 8) Beni Solow & william j. Houston :Mandibular rotations: concept and terminology- EJO-1988 (10) 177-179. 9) Surender K. Nanda : growth patterns in subjects with long and short faces, AJO-DO-1990;98;247-58 10) W.J.B. Houston et al – A Textbook of Orthodontics, 2nd edn 11) Donald.H.Enlow:Facial growth. 3rd Edn., W.B. Saunders Co., 12) Willliam R.Proffit; contemporary orthodontics; 3rd edn www.indiandentalacademy.com
BIBILOGRPHY 13) Thomas. Rakosi et al:Orthodontic diagnosis: colour atlas and manual 14) T.M. Grebar & Swain : text book of Orthodontics current principals and tecq ,1st edn. 15) Thomas. Rakosi : text book of cephalometric radiography
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