Development of occlusion


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Development of occlusion

  1. 1. Index • Introduction • Periods of occlusal development  Neo-natal period.  Primary dentition period.  Mixed dentition period.  Permanent dentition period • References
  2. 2. Term occlusion is derived from the Latin word, “occlusio”; defined as the relationship between all the components of the masticatory system in normal function, dysfunction and parafunction. An ideal occlusion is the perfect interdigitation of the upper and lower teeth, which is a result of developmental process consisting of the three main events, jaw growth, tooth formation and eruption
  3. 3. Periods of tooth development Pre-dental Stage (0-6months) Deciduous dentition (6 months-6 years) Mixed dentition (6-12 years) Permanent dentition
  4. 4. Neonatal Period (lasts upto 6 months after birth)
  5. 5. Gum Pads• Alveolar processes at the time of birth- gum pads. • Pink in colour, firm and are covered by a dense layer of fibrous periosteum. •The gum pad soon gets segmented by a groove called transverse groove, & each segment is a developing tooth site. •The pads get divided into ‘labio-buccal’ & ‘lingual portion’, by a dental groove. • The groove between the canine and the 1st molar region is called the lateral sulcus, useful for judging the inter arch relationship at a very early stage.
  6. 6. Gum Pads contd… The upper gum pad is horse shoe shaped & shows: o Gingival groove: separates gum pad from the palate. o Dental groove: starts at the incisive papilla, extends backward to touch the gingival groove in the canine region & then moves laterally to end in the molar region. o Lateral sulcus.
  7. 7. Gum Pads contd… The lower gum pad is ‘U’ shaped and rectangular, characterized by: o Gingival groove: lingual extension of the gum pads. o Dental groove. o Lateral sulcus.
  8. 8. Relationship of Gum Pads o Anterior open bite is seen at rest with contact only at the molar region. o Complete overjet. o Class II pattern with maxillary gum pad being more prominent. o Mandible is distal to the maxilla of 2.7 mm- male and 2.5- female. ( Sillman JH 1938) oThe range of variation of this distal relationship is from 0 to 7 mm. . ( Sillman JH 1938)
  9. 9. Relationship of Gum Pads o Mandibular lateral sulci lies posterior to maxillary lateral sulci. o Mandibular functional movements are mainly vertical, and to a little extent antero-posterior. Lateral movements are absent.
  10. 10. A ‘precise bite’ or jaw relationship is not yet seen. Therefore, neonatal jaw relationship cannot be used as a diagnostic criterion for reliable prediction of subsequent occlusion in the primary dentition.
  11. 11. (From around the 6th month to 6 years)
  12. 12. Sequence of Eruption
  13. 13. Features Of Primary Dentition • Spacing- 2 types of dentition are seen: •A) Spaced dentition - usually seen in the deciduous dentition to accommodate the larger permanent teeth in the jaws. • More prominent in the anterior region, and are called ‘physiological spacing’ or ‘developmental spacing’. • Absence of spaces in the primary dentition is an indication that crowding of teeth may occur when the larger permanent teeth erupt.
  14. 14. Features Of Primary Dentition contd… • Most subhuman primates have it through out life and use it for interdigitation of the opposing canines. This space is used for early mesial shift. primate spaces’, ‘simian spaces’ or ‘anthropoid spaces’.
  15. 15. Features Of Primary Dentition contd… • Non- spaced dentition  Teeth are present without any spaces in between the teeth  Due to narrow dental arches or if teeth are wider than usual  Usually indicates in developing permanent dentition but it is not always the case
  16. 16. Features Of Primary Dentition contd… Shallow overjet & overbite. Initially a deep bite may occur due to the fact that the deciduous incisors are more upright than their successors. The lower incisal edges often contact the cingulum area of the maxillary incisors. This deep bite is later reduced by: oEruption of deciduous molars. oAttrition of incisors. oForward movement of the mandible due to growth.
  17. 17. Features Of Primary Dentition contd… Almost vertical inclination of anteriors.
  18. 18. Molar Relationship The molar relationship in the primary dentition can be classified into 3 types: oStraight/flush terminal plane. oMesial step. oDistal step.
  19. 19. Flush Terminal Plane • If the distal surface of maxillary and mandibular deciduous second molars are in the same vertical plane; then it is called a flush terminal plane • Normal molar relationship in the primary dentition, because the mesiodistal width of the mandibular molar is greater than the mesiodistal width of the maxillary molar.
  20. 20. Mesial Step Distal surface of mandibular deciduous second molar is mesial to the distal surface of maxillary deciduous second molar.
  21. 21. Distal Step Distal surface of mandibular second deciduous molar is more distal to the distal surface of the maxillary second deciduous molar
  22. 22. Canine relationship • Relationship of maxillary & mandibular deciduous caninnes is one of the most stable in primary dentition • Classified as:  Class 1  Class 2  Class 3 Class 1 Class 2
  23. 23. Mixed Dentition Period (Around 6 years- 12 years) The mixed dentition period can be divided into three phases: o First transitional period. o Inter-transitional period. o Second transitional period.
  24. 24. First Transitional Period
  25. 25. Eruption of 1st Permanent Molar The location & relation of the 1st permanent molar depends much upon the distal surface of the upper & lower 2nd deciduous molar.
  26. 26. Transition to Class I Molar Relation
  27. 27. Early Shift • Early shift occurs during the early mixed dentition period. • Since this occurs early in the mixed dentition, it is called early shift.
  28. 28. Late Shift This occurs in the late mixed dentition period and is thus called late shift.
  29. 29. Leeway Space of Nance • Described by Nance in 1947 Maxilla: 0.9 mm/segment = 1.8 mm. Mandible: 1.7 mm/segment = 3.4mm.
  30. 30. • Although the deciduous posterior segment of teeth is larger than the permanent segment, converse is true of the anterior segments • Nance did not consider large difference in mesiodistal size between the deciduous incisor teeth & their permanent successors– arch needs to be looked in its totality • Maxillary incisors, as a group in one quadrant– 3.2to 3.5 mm larger • Mandibular incisors, as a group in one quadrant – 2.4 to 2.5 mm larger • The latter figures balance out or cancel the 1.7 mm of so called leeway space
  31. 31. Secondary spacing • Term was coined by Baume • Observed in closed primary dentition • Secondary spacing can also occur during the eruption of permanent central incisors
  32. 32. Distal Step When the deciduous second molars are in a distal step, the permanent first molar will erupt into a class II relation. This molar configuration is not self correcting and will cause a class II malocclusion despite Leeway space and differential growth.
  33. 33. Mesial Step Primary second molars in mesial step relationship lead to a class I molar relation in mixed dentition. This may remain or progress to a half or full cusp class III with continued mandibular growth.
  34. 34. Influence of terminal plane on the position of 1st permanent molar Distal Step – 23.3% incidence, abnormal, Class II- 38.6% Straight terminal plane – 49.2% incidence, Class I or II Mesial Step - <2mm 26.7%, class I 58.9% >2mm 0.8%. Class III- 2.5%
  35. 35. Exchange of Incisors
  36. 36. Transition of Incisors The incisal liability is over come by the following factors: Interdental physiological spacing in the primary incisor region. (4 mm in maxillary arch & 3 mm in mandibular arch)
  37. 37. Transition of Incisors contd… Increase in inter-canine arch width: Significant amount of growth occurs with the eruption of incisors and canines.
  38. 38. Transition of Incisors contd… Increase in anterior length of the dental arches: Permanent incisors erupt labial to the primary incisors to obtain an added space of around 2-3 mm.
  39. 39. Transition of Incisors contd… Change in inclination of permanent incisors: Primary teeth are upright but permanent teeth incline to the labial surface, thus decreasing the inter-incisal angle from about 150 degrees in the deciduous dentition to 123 degrees in the permanent dentition. This increases the arch parameter.
  40. 40. Inter-Transitional Period
  41. 41. Inter-Transitional Period contd… •Root formation of emerged incisors, and molars continues, along with concomitant increase in alveolar process height. •Resorption of roots of deciduous canines and molars.
  42. 42. Second Transitional Period
  43. 43. Ugly Duckling Stage (Broadbent’s phenomenon) Around the age of 8 - 9 years, a midline diastema is commonly seen in the upper arch, which is usually misinterpreted by the parents as a malocclusion. Its typical features are: oFlaring of the lateral incisors. oMaxillary midline diastema. Crowns of canines on young jaws impinge on developing lateral incisor roots, thus driving the roots medially and causing the crowns to flare laterally. o The roots of the central incisors are also forced together, thus causing a maxillary midline diastema.
  44. 44. Ugly Duckling Stage contd…
  45. 45. Ugly Duckling Stage contd… With the eruption of the canines, the impingement from the roots shift incisally thus driving the incisor crowns medially, resulting in closure of the diastema as well as the correction of the flared lateral incisors.
  46. 46. Ugly Duckling Stage contd… Hence this unaesthetic metamorphosis, eventually leads to an aesthetic result.
  47. 47. Sequence of Eruption The canines in the upper arch erupt only after the premolars have replaced the deciduous molars, whereas the canine erupt before the premolars in the lower arch.
  48. 48. Second Transitional Period contd…
  49. 49. Second Transitional Period contd… Eruption of permanent second molars • Before emergence- second molars, oriented in a mesial & lingual direction • Teeth- formed palatally, guided into occlusion by Cone Funnel mechanism , upper palatal cusps (cone) slides into the lower occlusal fossa (funnel) • Arch length is reduced by mesial eruptive forces • Thereby, crowding if present is accentuated
  50. 50. The Permanent Dentition Calcification begins at birth with the calcification of the cusps of the first permanent molar and extends as late as the 25th year of life. Complete calcification of incisor crowns take place by 4 – 5 years and of the other permanent teeth by 6 – 8 years except for third molars.
  51. 51. The Permanent Dentition contd… The permanent incisors develop lingual to the deciduous incisors and move labially as they erupt. The premolars develop below the diverging roots of the deciduous molars.
  52. 52. The Permanent Dentition contd… At approximately 13 years of age all permanent teeth except third molars are fully erupted.
  53. 53. Features of Permanent Dentition Vertical overbite of about one third the clinical crown height of the mandibular central incisors. Overjet and over bite decreases throughout the second decade of life due to greater forward growth of the mandible.
  54. 54. Andrews keys to normal occlusion • Key I – Molar relationship MB cusp of the max 1st molar falls into the mesiobuccal groove of the mand 1st molar and that the distal surface of the DB cusp of the upper first permanent molar should make contact and occlude with mesial surface of the MB cusp of the lower second molar.
  55. 55. Andrews keys to normal occlusion Key II Crown angulation (Tip) • The angulation of the facial axis of every clinical crown should be positive • The gingival portion of the long axis of the all crowns must be distal than the incisal portion.
  56. 56. Andrews keys to normal occlusion Key III Crown inclination • In upper incisors, the gingival portion of the crown’s labial surface is lingual to the incisal portion. • In all other crowns, including lower incisors, the gingival portion of the labial or buccal surface is labial or buccal to the incisal or occlusal portion.
  57. 57. Andrews keys to normal occlusion Key IV – Rotations • The fourth key to normal occlusion is that the teeth should be free of undesirable rotations.
  58. 58. Andrews keys to normal occlusion Key V – Tight contacts • contact points should be tight (no spaces). • In absence of abnormalities such as genuine tooth size discrepancies, contact point should be tight.
  59. 59. Andrews keys to normal occlusion Key VI – Occlusal plane or curve of spee • The curve of Spee should have no more than a slight arch. • Intercuspation of teeth is best when the plane of occlusion is relatively flat. • A deep curve of spee results in a more contained area for the upper teeth, making normal occlusion impossible.
  60. 60. Andrews keys to normal occlusion Key VII – Correct tooth size or the bolton’s ratio • Bennett and McLaughlin in 1993 gave seventh key to normal occlusion. i.e. the upper and lower tooth size should be correct.
  61. 61. REFERENCES • Shobha tandon • Nikhil marwah • Basavaraj subhashchandra phulari • S.I .Bhalajhi