Development of occlusion

The presentation features the developmental stages of occlusal development sequentially.

1. Dept. of pedodontics Govt. College of Dentisry , indore SUBMITTED BY: PALLAVI TRIPATHI ARVIND UIKEY BDS FINAL YEAR Development of Occlusion

2. Index Introduction Evolution Periods of occlusal development Neo-natal period. Primary dentition period. Mixed dentition period. Permanent dentition period Conclusion 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. Evolution To develop a functional occlusion it became necessary for the teeth and bones to develop synchronously. Over a period of time there was loss or fusion of cranial and facial bones, the number of bones have reduced and the dental formula has also undergone changes

5. Periods of Occlusal Development Occlusal development can be divided into the following development periods: Neo-natal period. Primary dentition period. Mixed dentition period. Permanent dentition period.

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

7. 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 Gum Pads

8. 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

9. 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

10. 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.

11. Status of Dentition at Birth

12. Natal,Neonatal & Pre-erupted Teeth Natal Teeth (Present at Birth) Neonatal Teeth (Erupted during the 1 st month) Pre-erupted (Erupting during the 2 nd & 3 rd month) Clinical Significance Difficulty to mother during breast feeding Remove only if they are superneumeraries or if they are loose enough that there is danger of exfoliation

13. One week old boy with two neonatal teeth

14. Primary Dentition Stage (From around the 6 th month to 6 years)

15. Sequence of Eruption A B D C E

16. Primary (upper) First evidence of calcification (Weeks in utero) Crown completed (months) Eruption (months) Root completed (years) Central 14 (13-16) 1 1/2 10 1 1/2 Lateral 16 2 1/2 11 2 Canine 17 9 19 3 1/4 1 st molar 15 1/2 6 16 2 1/2 2 nd molar 19 11 29 3 Chronology of Primary Dentition

17. Primary (Lower First evidence of calcification (Weeks in utero) Crown completed (months) Eruption (months) Root completed (years) Central 14 (13-16) 2 1/2 8(6-10) 1 1/2 Lateral 16 3 13( 10-16) 1 1/2 Canine 17 9 20(17-23) 3 1/4 1 st molar 15 1/2 5 1/2 16( 14-18) 2 1/4 2 nd molar 18 10 27 3

18. Some of the characteristic clinical features of deciduous dentition are: Both the dental arches are half round in shape or ovoid. Almost no curve of Spee is present. Shallow cuspal interdigitation. Slight overjet. Deep bite. Vertical inclination of the incisors. Spaced dentition. Different maxillo-mandibular relations like flush, mesial & distal terminal planes. 18

19. 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.

20. FIRST TRANSITIONAL PERIOD The first transitional period is characterized by the emergence of the first permanent molars and the exchange of deciduous incisors with the permanent incisors. Emergence of first permanent molars The mandibular first molar is the first permanent tooth to erupt at around 6 years of age. The location and relationship of the first permanent molars depends much upon the distal surface relationship between the upper and the lower second deciduous molars. 20

21. The mesio-distal relation between the distal surfaces of the upper and lower second deciduous molars can be of 3 types: Flush terminal plane Mesial step terminal plane Distal step terminal plane . 21

22. A. Flush terminal plane, B. Distal step terminal plane, C. mesial terminal plane

23. 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 accommodation 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.

24. 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)

25. Increase in inter-canine arch width: Significant amount of growth occurs with the eruption of incisors and canines.

26. 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.

27. 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 151 degrees in the deciduous dentition to 124 degrees in the permanent dentition. This increases the arch perimeter.

28. Inter-transitional Period In this period the maxillary and mandibular arches consist of sets of deciduous and permanent teeth. Between the permanent incisors and the first permanent molars are the deciduous molars and canines. This phase during the mixed dentition period is relatively stable and no change occurs. 28

29. Fig: OPG of mixed dentition 29

30. Second Transitional Period The second transitional period is characterized by the replacement of the deciduous molars and canines by the premolars and permanent cuspids respectively. The combined mesio-distal width of the permanent canines and premolars is usually less than that of the deciduous canines and molars. The surplus space is called leeway space of Nance. 30

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. Ugly DUCKLING STAGE Sometimes a transient self-correcting malocclusion is seen in the maxillary incisor region between 8 to 9 years of age. This is a particular situation seen during the eruption of the permanent canines. As the developing permanent canines erupt they displace the roots of the lateral incisors mesially. This results in transmitting the force on to the roots of the central incisors, which also get displaced mesially. A resultant distal divergence of the crowns of the two central incisors causes a midline spacing. This situation has been described by Broadbent as the ugly duckling stage. This condition usually corrects by itself when the canines erupt and the pressure is transferred from the roots to the coronal area of the incisors. 32

33. 33

34. PERMANENT DENTITION PERIOD Permanent dentition forms within the jaws soon after birth, except for the cusps of the first permanent molars, which form before birth. Permanent incisors develop lingual or palatal to the deciduous incisors and move labially as they erupt. Premolars develop below the diverging roots of the deciduous molars. 34

35. 35

36. Chronology of human primary teeth 36

37. Permanent (Upper) First evidence of calcification ( weeks in utero) Crown completed (months) Eruption ( months) Root completed (years) Central 3-4 mo 4-5 yr 7-8 yr 10 Lateral 10-12 mo 4-5 yr 8-9 yr 11 Canine 4-5 mo 6-7 yr 11-12 yr 13-15 1 st premolar 1 1/2 -1 3/4 yr 5-6 yr 10-11 yr 12-13 2 nd premolar 2-2 1/4 yr 6-7 yr 10-12 yr 12-14 1 st molar At birth 2 1/3 -3 yr 6-7 yr 9-10 2 nd molar 2 1/3 -3 yr 7-8 yr 12-13 yr 14-16 3 rd molar 7-9 yr 12-16 yr 17-21 yr 18-25 Chronology of Permanent Dentition

38. Eruption sequence The frequently seen sequences in the maxillary arch (permanent): 6-1-2-4-3-5-7 or 6-1-2-3-4-5-7 The frequently seen sequences in the mandibular arch (permanent): 6-1-2-3-4-5-7 or 6-1-2-4-3-5-7 39

39. The Permanent Dentition The permanent incisors develop lingual to the deciduous incisors and move labially as they erupt.

40. The Permanent Dentition The premolars develop below the diverging roots of the deciduous molars .

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

42. 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.

43. CONCLUSION In its simplest of definition, occlusion is the way the maxillary and mandibular teeth articulate, but in reality dental occlusion is a much more complex relationship, because it not only involves the study of the teeth, but also their morphology and angulations, the muscles of mastication, the skeletal structures, the temporomandibular joint, and the functional jaw movements. In addition to this, it also involves the relationship of the teeth in centric occlusion, in centric relation, and even during function, and because all this, requires neuromuscular coordination, occlusion should also involve an understanding of the neuromuscular systems, it is the responsibility of we ‘ pedodontists ’ to have an adequate knowledge on these subjects, to help us differentiate abnormal from normal, before initiating therapy.

44. references Orthodontics The Art and Science by S. I. Bhalajhi Textbook of Pediatric Dentistry by Nikhil Marwah Textbook of Pedodontics by Shobha Tandon 45

45. Thank You.