Theories and mechanism of eruption of primary and

THEORIES OF ERUPTION
ERUPTION SEQUENCE
PHYSIOLOGY OF TOOTH ERUPTION
CELLULAR BASIS
MOLECULAR BASIS
PRODUCTION OF OSTEOCLAST
ANOMOLIES OF TOOTH ERUPTION

1. THEORIES AND MECHANISM OF ERUPTION OF PRIMARY AND PERMANENT DENTITION 1

2. CONTENTS INTRODUCTION THEORIES OF ERUPTION ERUPTION SEQUENCE PHYSIOLOGY OF TOOTH ERUPTION CELLULAR BASIS MOLECULAR BASIS PRODUCTION OF OSTEOCLAST ANOMOLIES OF TOOTH ERUPTION CONCLUSION 2

3. INTRODUCTION The timely initiation and eruption of teeth into the oral cavity is very important for healthy dentition . It is the process by which tooth moves within the jaw bone, comes into the oral cavity and comes up to the occlusal contact and maintains its clinical position.   3

4. Human tooth eruption is a unique developmental process. Eruption Erumpere Latin word 4

5. Human beings are Diphyodont 5 MONOPHYODONT

6. THEORIES OF TOOTH ERUPTION Bone remodeling Root formation theory Vascular hydrostatic pressure Periodontal ligament traction Dental follicle 6

7. The growth pattern of maxilla and mandible moves teeth by selective deposition and resorption of bone. 7 BONE REMODELLING THEORY Results in eruption

8. According to root growth theory Cushion hammock ligament The cushion hammock ligament straddles the base of the socket from one bony wall to the other like a sling. Function : provides a strong base for the growing root to grow against. But the cushion hammock ligament is a pulp- delinating membrane that runs across the apex of the tooth and has no bony insertion. 8 ROOT FORMATION

9. But if occlusal movement is prevented, resorption of bone occurs at the base of the socket. This illustrates that if root formation is to result in eruptive force, the apical growth of root needs to be translated to occlusal movement and requires a fixed base. There is no fixed base because pressure on bony base result in resorption. Root formation may be a necessary pre-requisite for eruption Manson JD et al, 1967 9

10. VASCULAR PRESSURE Rich vascular supply between the teeth and bony structures Increased pressure by vessels Vascular supply generate an erupting force 10 Facilitate eruption

11. PERIODONTAL LIGAMENT TRACTION Formation and renewal of PDL fibres has been considered a factor in tooth eruption because of the traction power that fibroblasts have. This force is transmitted from the extracellular compartment to collagen fibres, which is aligned in an appropriate inclination to bring about tooth movement . 11

12. Impacted teeth with well developed PDL fibres does not erupt . Rootless teeth also erupt . Gowgiel , 1961 12

13. ROLE OF DENTAL FOLLICLE Cahill and Marks (1980) Demonstrated a study to show the importance of dental follicle in eruption. Removal of dental follicle from premolar prior to eruption prevented unerupted tooth from erupting 13 In 1984 Keeping the dental follicle intact, they removed the tooth bud and inserted artificial replica of tooth Resulted in eruption of artificial tooth Cahill and Marks ( 1984)

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15. ERUPTION SEQUENCE 15

16. PHYSIOLOGY OF TOOTH MOVEMENT 16

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18. PRE-ERUPTIVE MOVEMENT Made by deciduous and permanent tooth germ within the tissues of the jaw before they begin to erup t. 18

19. Permanent anterior tooth germ develop lingual to the primary anterior teeth and later primary teeth erupt, the permanent crowns lie at  apical 3 rd of primary tooth. Premolar tooth germs lie between the divergent roots of deciduous molars 19

20. The permanent molars which have no deciduous predecessors also exhibit movement 20

21. Histological features Remodelling of bony wall of crypt by selective deposition and resorption of bone by osteoblast and osteoclast. Normal skeletal morphogenesis is involved in determining tooth position. 21

22. ERUPTIVE MOVEMENT Root starts to form and ends when the tooth reaches the occlusal plane PDL fibres start to develop Remodeling of PDL fibres to accommodate the eruptive tooth movement Intraosseous and Supraosseous movement 22

23. The tissue in front of the erupting primary tooth is different from that of the permanent tooth. A strand of fibrous tissue, known as Gubernacular cord forms a pathway in advance of developing permanent teeth. During eruptive phase the crown breaks the double layer epithelium, overlying it and enters the oral cavity. This causes the tissue around it to form junctional epithelium and gingiva 23

24. Gubernacular canal and cord play a role in the guiding the course of tooth eruption 24

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26. As the tooth erupts , space is created underneath the tooth to accommodate the root Fibroblast around the tooth apex form collagen and attach to the newly formed cementum Bony trabecular fill the space underneath in the pattern of ladder which gets denser as the tooth erupts Once tooth reaches the functional occlusion the PDL fibres attach to the cementum and adjacent bone . 26

27. HISTOLOGY Degeneration of connective tissue overlying the erupting tooth. Macrophages destroy cells and fibres by secreting hydrolytic enzymes. The connective tissue overlying the successional tooth that connects with the lamina propria of the oral mucosa by means of a strand of fibrous connective tissue that contains remnants of dental l amina. 27

28. STAGES OF TOOTH ERUPTION 28

29. POST ERUPTIVE TOOTH MOVEMENTS Movements made by tooth once it has reached its functional position in occlusal plane . 29

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31. CELLULAR BASIS OF ERUPTION Prior to onset of eruption Influx of mononuclear cells into coronal portion of dental follicle Increase in the number of osteoclast in the coronal third of alveolar crypts Resorb bone in the eruptive pathway 31

32. Morphologically, dental follicle is interposed between the alveolar bone and the tooth . An ideal location to regulate cellular events of eruption . As the dental follicle delivers resorptive cells to the alveolar bone, it is also in a position to receive signals from the tooth. 32 Wise et al, 1998

33. MOLECULAR BASIS OF ERUPTION Tooth eruption appears to be a programmed event in which a given tooth erupts at its appointed time. The molecules that initiate eruption their localization their regulation of the cellular events o f eruption All must fit within the context that each tooth erupts independently .   33

34. The eruption molecules and their genes are localized primarly in the dental follicles or stellate reticulum . Dental follicles produce majority of the potential eruption molecules. The remaining molecules reside in the stellate reticulum and adjacent dental follicle . Interlukein -1 reside in the dental follicle D-95 reside in the stellate reticulum 34

35. Molecules required for eruption began with isolation of: EGF(Cohen1962) TGF α (Tam 1985) Colony stimulating factor 1 TGF α and EGF share the same receptor for their action and have the same result on eruption. 35

36. In mice devoid of TGF α gene the teeth still erupted on time suggesting that EGF alone can initiate incisor eruption.(Mann et al;1999) Unerupted teeth is seen in osteoporitic mice lacking CSF-1 CSF-1 TRAP- positive monuclear cells osteoclast 36

37. Comparing EGF and CSF-1 it was found that EGF accelerated incisor eruption but not the molar eruption and CSF-1 caused the opposite . ( C ielinski et al,1995) 37 c- fos NFkB1 & NFkB2 ODF Interluekin-1a Other molecules that help in eruption Kong et al,1999

38. Tooth eruption fails in the absence of parathyroid hormone related protein( PTHrP ) 38 Failure of osteoclastic bone resorption on the coronal tooth surface to form an eruption pathway Nakchibandhi et al,2000

39. PRODUCTION OF OSTEOCLAST IN TOOTH ERUPTION Signaling cascade initiate the influx of mononuclear cells into dental follicle. CSF-1 AND MCP-1 Prime candidates for recruiting osteoclastic precursor cells Act as chemokines 39

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41. Current concept of osteoclast formation shows two major molecules: RANKL OPG RANKL IS EXPRESSED IN THE DENTAL FOLLICLE BUT ITS EXPRESSION IS REDUCED BY CSF-1 OR PTHrP SYNTHESIZED IN THE DENTAL FOLLICLE OR STELLATE RETICULUM Wise et al, 1999 41

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43. OPG is expressed in the dental follicle but the expression is reduced by CSF-1 or PTHrP synthesized in the dental follicle. 43 Presence of osteoblast is required for activation of osteoclast via the RANKL/OPG pathway.

44. ANOMALIES OF TOOTH ERUPTION MISSING TEETH DISTRUBANCE OF ERUPTION ECTOPIC ERUPTION LOCAL ERUPTION DEVIATION DENTAL PAPPILAE DESTROYED AS A RESULT OF INFECTION PREMATURE ERUPTION DELAYED ERUPTION 44

45. MISSING TEETH Hypodontia Oligodontia Anodontia missing teeth as a result of their failure of development multiple (usually more than six) teeth are missing total lack of teeth of one on both dentitions In the primary dentition, missing teeth occur more commonly in the maxilla and typically the maxillary lateral incisor is the tooth involved.   Missing permanent teeth are seen in 30–50% of patients who have missing primary teeth 45

46. ETIOLOGY Low birth weight Increased maternal age Rubella Thalidomide embryopathies Multiple missing teeth, as well as teeth with small crowns, may be seen in: Ectodermal dysplasia Ellis–van creveld syndrome Down syndrome (trisomy 21) 46

47. PREMATURE AND DELAYED ERUPTION HERIDITARY FACTORS POOR NUTRITION HYPOTHYROIDISM 47 HYPERTHYROIDISM

48. inadequate breastfeeding low supplementation from infant formula . 48

49. Maxillary canines Etiology – genetic factors Small jaws Early tooth extraction Retained primary tooth 49 ECTOPIC ERUPTION Peck et al, 1994

50. Eruption restrored by barely removing the tooth 50 IMPACTION

51. Pathologies of jaw Supernumerary teeth Hyper IgE syndrome Primary or secondary retention of permanent molars 51 LOCAL ERUPTON DEVIATION

52. Cementum fused to alveolar bone - ANKYLOSIS 52 ANKYLOSED TOOTH- WHY IT DOES NOT ERUPT ??? Ankylosed teeth different from impacted teeth Eruption potential is destroyed Bone grows by surface deposition Biderman et al,AJO 1962

53. CONCLUSION Human tooth eruption is a unique developmental process in the organism. T he scientific literature in the field is extremely sparse and studies are still being conducted. 53