Development of occlusion

Orthodontics

1. Development of Occlusion

2. Index Introduction Periods of occlusal development Neo-natal period. Primary dentition period. Mixed dentition period. Permanent dentition period References

3. Introduction 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

4. Periods of tooth development

5. Neonatal Period (lasts upto 6 months after birth)

6. 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 1 st molar region is called the lateral sulcus , useful for judging the inter arch relationship at a very early stage.

7. Gum Pads contd … The upper gum pad is horse shoe shaped & shows: Gingival groove: separates gum pad from the palate. 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 . Lateral sulcus .

8. Gum Pads contd … The lower gum pad is ‘U’ shaped and rectangular, characterized by: Gingival groove: lingual extension of the gum pads. Dental groove. Lateral sulcus .

9. Relationship of Gum Pads Anterior open bite is seen at rest with contact only at the molar region. Complete overjet . Class II pattern with maxillary gum pad being more prominent. Mandible is distal to the maxilla of 2.7 mm- male and 2.5- female. ( Sillman JH 1938) The range of variation of this distal relationship is from 0 to 7 mm . . ( Sillman JH 1938)

10. Relationship of Gum Pads Mandibular lateral sulci lies posterior to maxillary lateral sulci . Mandibular functional movements are mainly vertical, and to a little extent antero -posterior. Lateral movements are absent.

11. Neonatal Jaw Relationship 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.

12. Primary Dentition Period (From around the 6 th month to 6 years)

13. Sequence of Eruption

14. 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.

15. 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’.

16. 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

17. 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: Eruption of deciduous molars. Attrition of incisors. Forward movement of the mandible due to growth.

18. Features Of Primary Dentition contd … Almost vertical inclination of anteriors .

19. Molar Relationship The molar relationship in the primary dentition can be classified into 3 types: Straight/flush terminal plane. Mesial step. Distal step.

20. 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.

21. Mesial Step Distal surface of mandibular deciduous second molar is mesial to the distal surface of maxillary deciduous second molar.

22. Distal Step Distal surface of mandibular second deciduous molar is more distal to the distal surface of the maxillary second deciduous molar

23. 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

24. Mixed Dentition Period

25. Mixed Dentition Period (Around 6 years- 12 years) The mixed dentition period can be divided into three phases: First transitional period. Inter-transitional period. Second transitional period.

26. First Transitional Period

27. Eruption of 1 st Permanent Molar The location & relation of the 1 st permanent molar depends much upon the distal surface of the upper & lower 2 nd deciduous molar.

28. Transition to Class I Molar Relation The shift in lower molar from a flush terminal plane to a class I relation can occur in two ways: Early shift. Late shift.

29. Early Shift Early shift occurs during the early mixed dentition period. Since this occurs early in the mixed dentition, it is called early shift.

30. Late Shift This occurs in the late mixed dentition period and is thus called late shift .

31. Leeway Space of Nance Described by Nance in 1947 Maxilla: 0.9 mm/segment = 1.8 mm. Mandible: 1.7 mm/segment = 3.4mm.

32. 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

33. Secondary spacing Term was coined by Baume Observed in closed primary dentition Secondary spacing can also occur during the eruption of permanent central incisors

34. 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.

35. 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 .

36. Influence of terminal plane on the position of 1 st 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%

37. Exchange of Incisors During the first transitional period the deciduous incisors are replaced by the permanent incisors. The mandibular central incisors are usually the first to erupt. The permanent incisors are considerably larger than the deciduous teeth they replace. This difference between the amount of space needed for the accomodation of the incisors and the amount of space available for this, is called ‘ Incisal liability ’. The incisal liability is roughly about 7.6 mm in the maxillary arch & about 6 mm in the mandibular arch (Wayne).

38. 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)

39. Transition of Incisors contd … Increase in inter-canine arch width: Significant amount of growth occurs with the eruption of incisors and canines.

40. 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.

41. 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.

42. Inter-Transitional Period This is a stable phase where little changes take place in the dentition. The teeth present are the permanent incisors and first molar along with the deciduous canines and molars. This phase prepares for the second transitional phase. Some of the features of this stage are: Any asymmetry in emergence and corresponding differences in height levels or crown lengths between the right and left side teeth are made up.

43. 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.

44. Second Transitional Period The second transitional period is characterized by the replacement of the deciduous molars and canines by the premolars and permanent canines respectively. At around 10 years of age the deciduous canines shed, but just before the shedding there is a transient or self correcting malocclusion seen in the maxillary incisor region between the age of 8 – 9 years.

45. 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: Flaring of the lateral incisors. Maxillary 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. The roots of the central incisors are also forced together, thus causing a maxillary midline diastema .

46. Ugly Duckling Stage contd …

47. 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.

48. Ugly Duckling Stage contd … Hence this unaesthetic metamorphosis, eventually leads to an aesthetic result.

49. 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.

50. Second Transitional Period contd … Favorable occlusion in this area is largely dependent on: Favorable eruption sequence. Satisfactory tooth size to available space ratio. Attainment of normal molar relation with minimum diminution of space available for the bicuspids.

51. 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

52. The Permanent Dentition Period

53. The Permanent Dentition Calcification begins at birth with the calcification of the cusps of the first permanent molar and extends as late as the 25 th 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.

54. 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 .

55. The Permanent Dentition contd … At approximately 13 years of age all permanent teeth except third molars are fully erupted .

56. 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.

57. Andrews keys to normal occlusion Key I – Molar relationship MB cusp of the max 1 st 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 .

58. 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.

59. 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.

60. Andrews keys to normal occlusion Key IV – Rotations The fourth key to normal occlusion is that the teeth should be free of undesirable rotations.

61. 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.

62. 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.

63. 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.

64. REFERENCES Shobha tandon Nikhil marwah Basavaraj subhashchandra phulari S.I . Bhalajhi

65. Thank You.