Primary Dentition and Tooth Development

Exam 4

1. Primary Dentition & Tooth Development Chapter 13 & 14

2. Primary Dentition- Review Chapter 13

3. Objectives At the completion of this chapter, you will be able to Identify name, number, and eruption dates of primary teeth Describe function of primary teeth Compare primary teeth to permanent teeth

4. Primary Teeth Names/Numbers Twenty primary teeth Ten maxillary and ten mandibular 5 primary teeth in each quadrant Each quadrant has central incisor, lateral incisor, canine, first molar, and second molar No premolars in primary dentition Also referred to as deciduous teeth, baby teeth, milk teeth, or first teeth NOT temporary teeth

5. Primary Teeth Names/ Numbers (cont’d.)

6. Eruption/Exfoliation Period of eruption for primary teeth is between 6 months and 2½–3 years All primary teeth usually emerged and aligned by age 3 Spacing between the teeth referred to as primate spacing Exfoliation begins at age 6 S equence is same as eruption sequence of permanent dentition Mandibular centrals are usually first to exfoliate

7. Comparison With Permanent Teeth Primary anterior teeth and secondary molars resemble their permanent counterparts Primary teeth have more pronounced cervical ridge Roots of posterior teeth are more flared (divergent) Allowing growth of the permanent teeth forming beneath them Cervix appears to be more constricted than permanent teeth Primary crowns have less enamel than permanent teeth, and pulp horns extend more occlusally Pulp is closer to the surface of primary crowns making it necessary to reduce excessive friction when polishing.

8. Maxillary Incisors Maxillary Central Incisors: E, F Maxillary Lateral Incisors: D, G Labial crown of incisor is smooth with a straight incisal edge No mamelons Crown is wide with a cingulum and marginal ridges on lingual

9. Maxillary Incisors (cont’d.)

10. Maxillary Canines C, H Broad cervical ridge on canine causes cervix to appear constricted Short, pointed cusp with long, slender root

11. Maxillary First Molar B, I Number of cusps varies from 2 to 4 No dividing groove on buccal surface Three roots on all maxillary molars Occlusal surface has central fossa and mesial triangular fossa connected by central groove

12. Maxillary Second Molar A, J Anatomy is same as permanent maxillary first molar Two buccal cusps divided by buccal groove Two lingual cusps with a cusp of Carabelli on mesiolingual Three roots Two buccal, one lingual

13. Maxillary First and Second Molars

14. Mandibular Incisors Mandibular Central Incisors: O, P First tooth to exfoliate Mandibular Lateral Incisors: N, Q Both labial and lingual surfaces are smooth Slight cingulum marginal ridges on lingual

15. Mandibular Canines M, R Buccal surface has pronounced cervical ridge Lingual surface has cingulum and lingual ridges

16. Mandibular First Molar L, S No definite anatomy, like maxillary first molar Only primary tooth not anatomically identical to any permanent tooth Usually two buccal cusps divided by depression (rather than a groove) and two lingual cusps Two long, slender roots are divergent Occlusal surface has central groove crossed by buccal/lingual grooves

17. Mandibular Second Molar K, T Identical anatomy and groove pattern to permanent mandibular first molar Grooves divide three buccal cusps and two lingual cusps Two long, thin, divergent roots Can be twice as long as crown

18. Mandibular First and Second Molars

19. Importance of Primary Teeth Both form and function of primary dentition is important Each primary tooth has same function as permanent tooth that follows Maintains a solid position for permanent tooth replacement Damage to primary teeth could cause problems with permanent dentition When both deciduous and permanent teeth are present in the oral cavity its called mixed dentition.

20. Summary Primary dentition 10 maxillary and 10 mandibular teeth A-T for universal system No primary premolars Eruption is completed between 2½ and 3 years Primary tooth resembles permanent version but smaller Posterior teeth have flared roots to fit permanent teeth developing below

21. Tooth Development Chapter 14

22. General Information Development of a human begins with an embryo, which has three layers Ectoderm forms lining of oral cavity As well as outer covering of the body Mesoderm forms the skeletal/muscular systems, cementum , dentin, and pulp Endoderm forms the lining of internal organs

23. General Information During the third week of fetal life, when the embryo is only 3mm ling, the face begins its development. At one end of the embryo there is an invagination of the ectoderm forming the stomodeum , or primitive mouth, which becomes oral and nasal cavities. The primitive mouth is lined with ectoderm and becomes the oral epithelium. Beneath this is the mesenchyme, developed from mesoderm, which becomes the underlying connective tissue. Between the fifth and sixth week in utero, the first signs of tooth development is evident. Teeth are formed from the ectoderm and mesoderm in a complex histologic process simplified into the following pattern.

24. Growth and Development Formation of teeth Progression begins during fifth or sixth week in utero Process continues until 10 maxillary and 10 mandibular teeth are formed Permanent teeth begin forming around fourth or fifth month of fetal life but do not calcify until birth Proper diet during tooth formation is crucial for long-term health

25. Growth and Development

26. Initiation: Bud Stage First stage of odontogenesis or origin of tooth, is referred to as bud stage During this stage, tooth begins formation from dental lamina referred to as initiation Dental lamina is growth from oral epithelium that gives rise to tooth buds 10 growths on each arch later become primary teeth Permanent teeth develop similarly

27. Proliferation: Cap Stage Bud of tooth grows and changes shape during cap stage Organ is indented on lower side and appears much like a cap, hence name Primary embryonic ectoderm layer develops into the oral epithelium Epithelium matures into the enamel of the tooth

28. Proliferation: Cap Stage Primary embryonic mesoderm layer develops into connective tissue during Proliferation when the cells multiply Histodifferentiation when the cells develop into different tissues Morphodifferentiation , when the cells begin to outline the future shape of the developing organ

29. Morpho / Histodifferentiation : Bell Stage Further specialization of cells takes place in the bell stage Inner epithelium of enamel organ become ameloblasts , enamel-forming cells Dental papilla peripheral cells become odontoblasts , dentin-forming Dental sac form c ementoblasts , cementum-forming cells Enclosed area of tissue that later matures into the dentin and pulp of the tooth.

30. Apposition-Maturation State Odontogenesis reaches completion in this stage Tissues of enamel, dentin, and cementum formed in layers and fused together Calcium and other minerals are deposited in formed teeth in this stage. Process is called calcification and is last developmental state prior to eruption The final stage is attrition , the wearing away of the incisal or occlusal surfaces

31. Apposition-Maturation State The root of the tooth does not develop fully prior to eruption. The phase when the tooth passes through the bone and the oral mucosa and into its place in the oral cavity. Twenty of the permanent teeth are located below and distal to the primary teeth. Which ones aren’t? As permanent teeth erupt, they apply pressure to the apices of the roots of the primary teeth. During this force, osteoclasts, bone resorbsion cells, dissolve the rooth of the primary tooth. This Resorption first takes place at the apex and continues up toward the crown When very little root structure is left, the tooth loosens because of lack of support… and? Children often assist the final stages of loosening the tooth by moving it back and forth until they break the attaching fibers.

32. Eruption Eruption is the movement of the tooth from its position within the jaw to its position in the oral cavity The process is divided into active and passive eruption

33. Eruption and Importance of Primaries Primary teeth occupy and maintain space in the dental arches for permanent teeth and act as guides during the eruption process. If the primary teeth are removed early, the spaces may be diminished, causing crowding when the permanent teeth erupt.

34. Active Eruption Process where crown moves from within jaw into oral cavity Continues until tooth meets its antagonist in opposite jaw 1½ to 3 years for completion of deciduous root 3 years for completion of the permanent root The entire process of permanent tooth development, from initiation to completion, takes about 10 years .

35. Passive Eruption Increase in length of clinical crown caused by gingival recession is referred to as passive eruption F actors such as wear from use or trauma can cause peridontial attrition/ breakdown E xposure of cementum Wearing of the enamel Gingival recession

36. Developmental Anomalies Disturbances in development stage of teeth and bones can cause abnormalities Can be hereditary or nutritional factors Excessive fluoride Disturbances during the formation of the tooth can cause faulty enamel An extra tooth forms called a supernumerary tooth

37. Summary Tooth development begins between 5-6 week in utero and continues until entire tooth is formed 2–3 years for primary teeth 9–10 years for permanent teeth Once tooth is formed, it cannot repair itself Proper diet during tooth formation and preventive care after eruption is critical