Growth rotations /certified fixed orthodontic courses by Indian dental academy


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  • Growth rotations /certified fixed orthodontic courses by Indian dental academy

    1. 1. GROWTH ROTATIONS INDIAN DENTAL ACADEMY Leader in continuing dental education
    2. 2. Introduction Traditional view : mandible grows in a downward and forward direction via posterior growth and anterior displacement. Rotation: Bjork ( 1955) Since then , the concept has been an issue of debate!! Rotational aspect greatly influences therapeutic result of orthodontic treatment.
    3. 3. General concepts of craniofacial bone growth      Articular growth Remodelling growth Increased volume of craniofacial cavities surrounding bones displaced differential articular bone growth occurs. Overall change in shape and size due to both articular & remodelling growth 3 Dimensions: Rotation + Translation Assessed by superimpositions. 
    4. 4. Bjork’s studies on growth rotation   Mixed longitudinal study begun in 1951 at Dept of Orthodontics, Royal Dental College, Copenhagen. Sample: 100 persons of each sex. Age range 4-24 years. Normal Healthy children with & without malocclusion, & also children with pathologic conditions.
    5. 5. Mandibular Growth pattern:  Condylar growth  increased length of mandible.  Ant. Aspect of chin : stable Thickening of symphysis: lower border and posterior surface.  Ant part of lower border of mand : periosteal apposition.  Below Angle: resorption
    6. 6.  Apposition + Resorption  individual shaping of lower border, which characterizes the type of growth.  Mand. Canal curvature: reflects earlier shape of mandible  Lower border of developing molar tooth germ: relatively stationary till root formation begins. Can act as natural reference structure for growth analysis.
    7. 7.
    8. 8. Two types of rotation   ( I)FORWARD ROTATION Type I : - Center in the joint. - lower dental arch pressed into upper; underdeveloped ant. face height. - Cause: occlusal imbalance due to loss of teeth or powerful muscular pressure.
    9. 9.    Type II: Center at incisal edges of lower anteriors. Cause: combination of marked development of the posterior face height, and normal increase in the anterior height
    10. 10.     Vertical direction of condylar growth  mandible lowered more than it is carried forward. Muscular & Ligamentous attachments  forward rotation with center at incisal edges. Eruption of molars keeps pace with rotation. Resorption below gonial angle  remodelling.
    11. 11.     Type III: In Case of large maxillary overjet or mandibular overjet, CRot no longer at incisors, but displaced backward to premolar region. Ant. Face height underdeveloped, posterior face height increases. Basal deep bite
    12. 12.  In Growth Rotations of Type II and III, symphysis swings forward to a marked degree and chin becomes prominent.
    13. 13.     (II) BACKWARD ROTATION Type I: CRot lies in TMJ Eg.: when bite is raised by orthodontic means, change in intercuspation or bite raising appliance.
    14. 14.   Increase in Ant. Face height. May occur in connection with growth of cranial base: Flattening of cranial base  Middle cranial fossa raised in relation to anterior one  Incomplete development in height of MCF --- mandible raised
    15. 15.     Type II: Center at most distal occluding molars. Growth in sagittal direction at mand. condyle; curves increasingly backward As the mandible grows in the direction of its length, it is carried forward more than it is lowered, and because of muscular and ligament attachments, it rotates backward.
    16. 16.  Symphysis swung backward, chin drawn back below face. Soft- tissues may not follow  doublechin  Basal open bite can develop, with lip strain.
    17. 17. BJORK’S 7 STRUCTURAL SIGNS OF GROWTH ROTATION    Help to detect extreme patterns of rotation during growth. Not all signs are present in 1 individual; greater the no., more reliable the prediction. Not so clearly developed before puberty.
    18. 18. 1) Inclination of condylar head: forward  forward rotation backward  backward rotation 2) Curving of Mand. Canal: forward rotators  curve greater than that of contour backward rotators  canal straight or curved in opp. direction. 3) Shape of lower border: forward rotators  apposition below symphysis produces anterior rounding & thick cortical layer, while resorption at angle produces typical concavity. backward rotators ant. rounding absent, cortical layer thin, lower contour at jaw angle convex.
    19. 19. 4) Inclination of symphysis: forward rotators  symphysis swung forward, prominent chin. backward rotatots  symphysis swung back, receding chin. 5) Inter-incisal angle: increased in forward rotation. decreased in backward rotation. 6) Inter-molar angle: increases in forward rotation ( lower posteriors upright) decreases in backward rotation ( lower posteriors mesially inclined) 7) Anterior lower face height: decreased in forward rotation. increased in backward rotation.
    20. 20. Structural signs of mandibular growth rotation demonstrated in two craniums-one with basal deep-bite and one with basal open-bite.
    21. 21.  Skieller, Bjork & Linde Hansen (AJO 1984): - 21 individuals from original implant study. -44 morphologic variables evaluated. - 4 variables gave best prognostic estimate (86%) of mand. growth rotation: 1) Mandibular inclination, represented by 3 alternatives: (a) Index 1 ( proportion between PFH & AFH) (b) Lower gonial angle. (c) Inclination of lower border (NL – ML1) 2) Intermolar angle 3) Shape of lower border 4) Inclination of symphysis.
    22. 22.   Limitations: represented cases with extreme growth patterns. Leslie et al (AJO 1998) : not clinically useful to predict mandibular rotation in a general population.
    23. 23. COMPONENTS OF ROTATION  Bjork & Skieller ( EJO 1983): emergence of different patterns when different registrations for superimposition were used. Superimposition on cranial base Superimposition on metallic implants Superimposition on metallic implants Striking contrast
    24. 24.  1) Divided the phenomenon of rotation into 3 components: TOTAL ROTATION - Rotation of the mand corpus measured as a change in inclination of implant line relative to the anterior cranial base. - largely determined by amount & direction of growth in the condyles.
    25. 25. 2) MATRIX ROTATION: -Rotation of the soft tissue matrix of the mandible relative to cranial base ( soft tissue matrix defined by tangential mandibular line). - center at condyles. - articular growth + remodelling.
    26. 26. 3) INTRAMATRIX ROTATION : Change in the inclination of an impalnt line or reference line in the corpus relative to the tangential mandibular line. Difference between the total rotation and the matrix rotation; expression of remodelling at the lower border
    27. 27.     Center somewhere in the corpus. Independent rotation of the corpus within the outer contour of the mandible. Concept based upon local behaviour of sites of deposition & resorption. According to Rune et al (EJO 1987), the defining of various centers of rotation for bone contours affected by remodelling is inappropriate, as only displacements that satisfy the concept of rigid body model can be accounted for, and not those due to remodelling.
    28. 28. Schudy’s studies ( Fred Schudy, Angle 1965)     Clockwise & counterclockwise rotation Hypo- & hyper-divergence. Final vector of growth of the chin is a resultant of the struggle between horizontal growth ( growth at condyles) & vertical growth (vertical growth of molars) Resultant  downward, forward direction.
    29. 29.   A > I + II + III + IV  -Hypodivergent facial pattern. - Mand plane becomes flatter. - Pogonion moves forward more than Nasion. A < I + II + III + IV -Hyperdivergent pattern - mand. Plane becomes steeper - Pogonion moves back.
    30. 30.    “ It is not the growth pattern of the mandible per se which primarily determines its posture, but instead the vertical growth if the maxilla”. Clockwise rotation ( viewed from right): more posterior vertical growth than condylar growth, point of rotation being the condyles. ( Bjork’s Backward Rotation) Counterclockwise rotation : more condylar growth than combined vertical growth, point of rotation is most distal molar in oclusal contact. ( Bjork’s Forward Rotation)
    31. 31.
    32. 32.
    33. 33. Lavergne & Gasson: Metal implant study of mandibular rotation ( Angle 1976) Defined rotation as positional & morphogenetic.  Morphogenetic : concerns the shape of the mandible itself The angle between 2 implant lines when 2 cephs are superimposed on a line through Condylion & Pogonion.  Similar to Bjork’s concept of intramatrix rotation. 
    34. 34.  Positional rotation : Deals with position of mandible within the head. Degree of rotation Difference in rate of growth between jaws
    35. 35.  Unlike Bjork & Skieller, they do not consider the key factor in intramatrix rotation to be found in corpus; they locate the effective mechanism in the ramus and its forward or backward growth, thereby shortening or elongating the effective length of the mandible.  Opening/ closing of gonial angle  minimizes manxillary-mandibular sagittal discrepancy.
    36. 36. Dibbets’s concept of counterbalancing rotation ( AJO 1985, AJO 1990)  1) Based on 2 diverging patterns of mandibular growth: A circular growth pattern, resulting only in intramatrix rotation, & marked by absence of actual mandibular enlargement. ( condylar growth as the segment of a circle with its center at the chin).
    37. 37. 2) Linear growth curve of the condyle along Pogonion-Condylion diagonal, resulting in maximum enlargement, without any “intramatrix” rotation.  Most children fall between these 2 postulated extreme patterns.
    38. 38.   The dimension pogonion to articulare represents mandibular size. Mandibular growth is determined by subtracting Pg-Ar1 from Pg-Ar2. Condylar growth is represented by the dimension Ar1 to Ar2. Counterbalancing proportion = Growth of Ar to Pg X 100% Condylar incremental growth
    39. 39.   Should approximate 100% in congruous mandibular growth. (In reality  50-97%) “Thus, counterbalancing rotation pertains to circular condylar growth, accompanied by selective coordinated remodelling, which does not contribute to the incremental growth of the mandible”.
    40. 40. Solow & Houston’s terminology ( EJO 1988)   ROTATION: only displacements that satisfy the concept of rigid body model. ANGULAR CHANGE: change in form due to surface accretion and removal, causing change in orientation between reference lines within that body.
    41. 41.  1) 2) 3) 3 changes with respect to growth rotation of mandible: True rotation of mandible: Rotation of Mand. body relative to anterior cranial base. ( Total Rotation) Apparent rotation of mandible: Angular change of mandibular line relative to anterior cranial base. True Rotation + Remodelling. ( Matrix rotation) Angular remodelling of lower border: Angular change of mand. line when mandible is registered on implants or stable trabecular structures. ( Intramatrix rotation)
    42. 42. Proffit’s terminology & comparison with other authors Condition Bjork Schudy Post. Growth> Anterior Forward Rotation Counter Ant Growth Backward > Posterior clockwise (Viewed from right) Clockwise
    43. 43. Bjork Rotation of mand core relative to cranial base Rotation of mand plane relative to cranial base Rotation of mand plane relative to core of mandible Solow, Houston Proffit Total Rotation True rotation Internal Rotation Matrix rotation Apparent rotation Total rotation Intramatrix rotation Angular remodelling of lower border External rotation
    44. 44. GROWTH ROTATION OF MAXILLA      Small & variable degree of rotation. Forward  more usual pattern. Analogous to intramatrix rotation of mandible. Varying degrees of resorption on nasal side & apposition on palatal side. Similar variations in the amount of eruption of the molars & incosors occur. These changes amount to external rotation. Mostly, external = internal rotation, Net =0
    45. 45. INTERACTION BETWEEN JAW ROTATION & TOOTH ERUPTION  Rotation magnitude tooth eruption direction Translocation within jaw + True eruption  Movement of teeth relative to cranial base
    46. 46.    Maxillary teeth : path of eruption is downward, somewhat forward. Forward rotation of maxilla  tends to tip incisors forward, increasing their prominence. Backward rotation  relatively uprights the ant teeth, decreases their prominence.
    47. 47.     Mandibular teeth: eruption path upward & somewhat forward. Forward rotation uprights incisors Molars migrate furthur mesially than do incisors decreased mand arch length  crowding tendency. Incisors carried into overlapping position, hence deep bite. Lower Posterior teeth upright, hence increased intermolar angle. Backward rotation Ant open bite as AFH increases. Incisors carried forward, creating dental protrusion. Reduced intermolar angle. Brin et al ( AJO 1982) no significant correlations between molar occlusion & growth rotation.
    48. 48. References 1) 2) 3) 4) Bjork A. Prediction of mandibular growth rotation. Am J Orthod 1969;55:585-599. Skieller V, Bjork A, Linde-Hansen T. Prediction of mandibular growth rotation evaluated from a longitudinal implant study. Am J Orthod 1984;86:359-370. Leslie et al. Prediction of mandibular growth rotation: assessment of the Skieller, Bjork & Linde-Hansen method. Am J Orthod Dentofacial Orthop 1998;114:659-67. Schudy F.The rotation of the mandible resulting from growth: its implications in treatment. Angle Ortho 1965;35:36-50.
    49. 49. 5) Diabbets. Mandibular rotation & enlargement. Am J Orthod Dentofacial Orthop 1990;98:29-32. 6)Dibbets. The puzzle of growth rotation. Am J Orthod 1985;87:473-480. 7)Solow & Houston. Mandible rotations: concepts & terminology. EJO 1988;10:177-179. 8)Brine et al. Molar occlusion & mandible rotation: a longitudinal study. Am J Orthod 1982;81:397-403. 9) Lavergne & Gasson. Metal implant study on mandibular rotation. Angle ORthod 1976;46:144150. 10) Rune et al. Growth Rotation– A puzzle? EJO 1987;9:237-239.
    50. 50. Thank you Leader in continuing dental education