The Dentition

1. The Dentition

2. Why Study Teeth? • Very resistant to decay and often outlast bone • More resistant to chemical destruction from taphonomic processes (diagenesis) • Have genetic and functional characteristics to study • Help assess sex, age, health, diet, and genetics • Can be directly observed without radiographs

3. 4 types of teeth • Incisors (8)- designed for cutting • Canines (4)- pointed for tearing and incising • Premolars (8)- broad chewing surface for grinding, to reduce food for digestion • Molars (12)- same function as premolars, crushing and grinding food • Agenesis of 3rd molar is common • Genetically unstable tooth

4. Dentition • Incisor • Canine • Premolar • Molar

5. Dentition

6. Dental Direction and Terminology • Mesial—toward anterior midline of mouth • Distal—away from anterior midline of mouth • Occlusal—chewing surface of teeth • Labial—surface of tooth toward the lips • Buccal—surface of tooth toward the cheek • Lingual—surface of tooth toward the tongue

7. Adult & Subadult Dentition • Adult mouth usually has 32 teeth • Dental formula: 2123 2123

8. Adult & Subadult Dentition • Sub-adult mouth has 20 teeth • Dental formula: 2102 2102

9. Teeth • Deciduous (primary, milk) teeth are systematically shed and replaced by permanent (secondary, adult) teeth. • Teeth are first formed within the jaw and then they erupt through the gum line • Tooth buds or germs develop within the jaw in hollows of alveolar bone called crypts

10. Tooth Formation

11. Dental Development

12. Structure of Teeth (Enamel) • Structurally, the tooth is composed of enamel, dentin, and cementum. • Enamel caps the crown and is the hardest substance found in the body. • No cells penetrate the enamel, it is not considered a living tissue. • Heavily mineralized & acellular (96% mineral) • Hydroxyapatite is primary component • Enamel is brittle (dentin adds support)

13. Dentition CEJ • Enamel (crown) • Ameloblasts • Amelogenesis • Cementum (root) • Dentin • Odontoblasts • Odontogenesis • Pulp cavity • CEJ = Cemento-enamel junction / Cervico-enamel junction

14. Structure of Teeth (Dentin) • Dentino-enamel junction (interface between enamel & dentin)

15. Structure of Teeth (Cementum)

16. Tooth Numbering System: Adults • Dental arcade • Dental numbering system (1-32) • Begin at Right 3rd Maxillary Molar (#1) • End at Left 3rd Maxillary Molar (#16) • Begin again at Left 3rd Mandibular Molar (#17) • End at Right 3rd Mandibular Molar (#32)

17. Tooth Numbering System: Nonadults • Dental arcade • Dental numbering system (a-t) • Begin at Right 2nd Maxillary Molar (#a) • End at Left 2nd Maxillary Molar (#j) • Begin again at Left 2nd Mandibular Molar (#k) • End at Right 2nd Mandibular Molar (#t)

18. Tooth Abbreviation System Permanent dental arcade • Maxillary • Incisors (I1, I2) • Canines (C1) • Premolars (P3, P4) • Molars (M1, M2, M3) • Mandibular • Incisors (I1, I2) • Canines (C1) • Premolars (P3, P4) • Molars (M1, M2, M3) Deciduous dental arcade • Maxillary • Incisors (i1, i2) • Canines (c1) • Molars (m1, m2) • Mandibular • Incisors (i1,i2) • Canines (c1) • Molars (m1, m2)

19. Age Estimation • Age estimations for sub-adults based on tooth eruptions (crown to root) are most accurate because if the high correlation with chronological age

20. The Dentition

21. The Dentition Maxilla Mandible

22. Steps for Identifying Teeth • What tooth class does it belong? (incisor, canine, premolar, molar)

23. Steps for Identifying Teeth • What tooth class does it belong? (incisor, canine, premolar, molar) • Is it a permanent or deciduous tooth?

24. Steps for Identifying Teeth • What tooth class does it belong? (incisor, canine, premolar, molar) • Is it a permanent or deciduous tooth? • Is it an upper (maxillary) or lower (mandibular) tooth?

25. Steps for Identifying Teeth • What tooth class does it belong? (incisor, canine, premolar, molar) • Is it a permanent or deciduous tooth? • Is it an upper (maxillary) or lower (mandibular) tooth? • What position does the tooth belong within a given tooth class? • (White 3rd Edition Appendix 2: Decision Tree)

27. Deciduous Teeth • Tooth formation begins ~14-16 weeks in utero

28. Deciduous Teeth • Tooth formation begins ~14-16 weeks in utero • Not visible at birth, i1 erupts ~6 mos

29. Deciduous Teeth • Tooth formation begins ~14-16 weeks in utero • Not visible at birth, i1 erupts ~6 mos • Erupted by 2-3 years of age

30. Deciduous Teeth • Tooth formation begins ~14-16 weeks in utero • Not visible at birth, i1 erupts ~6 mos • Erupted by 2-3 years of age • Smaller than permanent teeth

31. Deciduous Teeth • Roots (shorter); often partly resorbed • Much more splayed in molars

32. Deciduous Teeth • Roots (shorter); often partly resorbed • Much more splayed in molars • Cusp features less well-defined (bulbous cusp)

33. Deciduous Teeth • Roots (shorter); often partly resorbed • Much more splayed in molars • Cusp features less well-defined (bulbous cusp) • Often yellow due to thin enamel and thin cementum layer

34. Mandibular Molars Maxillary Molars Incisors Canines

35. Incisors

36. Incisors (General) • 8 total- 4 central / 4 lateral • Crown—spatulate (flat, blade-like) • Rectangular/square dentine patch exposure • Single-rooted

37. Incisors (Upper vs. Lower) • Upper—wider crowns; pronounced cingulum; root round in cross-section • Central: • Largest crown, straight apex (others incline distally); square mesial edge • Lateral: distal edge is more rounded than central; may have a pit at base of cingulum

38. Incisors (Upper vs. Lower) • Lower—narrower crowns; usually lack cingulum; root narrows mesiodistally; root oval in cross-section; groove on distal surface • Central • smallest crown; square mesial edge • Lateral—distal edge is more rounded than central

39. Rounded root Cingulum Pit at base of cingulum Root narrows mesiodistally Right Incisor

40. Canines

41. Canines (General) • “Eye teeth”- 4 total • Single root (oval in cross-section) • Conical (tusk-like) pointed cusp • Diamond-shaped dentine exposure patch

42. Canines (General) • Longest tooth in the mouth • Largest root in relation to crown surface • Confusion: caniform incisors or incisiform canines

43. Canines (Upper vs. Lower) • Upper: crown wider and larger w/ cingulum • Mesial aspect more inferior than distal aspect • Sharp, single-cusp • More lingual relief • More lingual wear • Lower: crown narrower & no cingulum • Mesial aspect more superior than distal aspect • Blunt, single-cusp • Less lingual relief • More labial wear

44. Root tilts distally Distal groove Mesial edge of crown more inferior Mesial edge of crown more superior Root tilts distally Right Canine

45. Premolars

46. Premolars (General) • “Bicuspids” – 8 total (4 upper / 4 lower) • P3 & P4 • Short, rounded crown • Usually 2 cusps on crown • Single-rooted lower & bi-rooted upper • Confusion: caniform premolars vs. premolariform canines

47. Premolars (Upper vs. Lower) • Upper: • Nearly equal size cusps and 2 fused roots • Buccal slightly more pronounced • Pronounced occlusal groove (mesiodistally) • Bi-rooted • Crown oval in cross-section

48. Premolars (Upper vs. Lower) • Upper: • Nearly equal size cusps and 2 fused roots • Buccal slightly more pronounced • Pronounced occlusal groove (mesiodistally) • Bi-rooted • Crown oval in cross-section • Lower: • Much larger buccal cusp than lingual cusp • Crown round in cross-section • Pronounced mesial & distal pits • Single-rooted • Single root and curved root tip (distally)

49. Root tilts distally ~Equal cusp size Root tilts distally Unequal cusp size Right Premolars

50. Molars