1. UNIVERSITATEA DE STAT DE MEDICIN I FARMACIE NICOLAE TESTEMIANU DEVELOPMENT OF THEDECIDIUOUS &PERMANENT TEETHCATEDRA HISTOLOGIE, CITOLOGIE I EMBRIOLOGIE

2. TOOTH STRUCTURECROWN(anatomical& clinical)NECKROOT 3. Hard tissues of the tooth: ENAMEL DENTIN CEMENTUMSoft tissue of the tooth:DENTAL PULP(crown pulp & rootcanal) 4. Tooth development begins from the 6th week of theintrauterine development2 embryonic origins:I. Ectoderm - oral epithelium - enamelII. Ectomesenchyme (neural crests) dentin, cement, dental pulp,periodontal ligament 5. 2 main processes in the toothdevelopment Crown formation Root formation (is usually completedapproximately 2 -3 years after the tootherupts) 6. FUNCTIONAL STAGES OF TOOTH DEVELOPMENT Initiation Proliferation Morpho-differentiation andHisto-differentiation Apposition Root development 7. MORPHOLOGICAL STAGESOF TOOTH DEVELOPMENT Bud stage Cap stage Bell stage (early & late) Early & late crown Early root formation 8. Correlation of morphological stages of tooth development and functional features Morphological stage Main functional activityDental laminaInitiation of tooth germBud stageProliferation (cell division)Cap stageProliferation Beginning of histo-differentiationBell stage Prominent histo-differentiation Morpho-differentiationEarly crown stageApposition (formation of dentin & enamel)Late crown stage Continued apposition of dentin & enamel including enamel maturationEarly root stage Formation of radicular dentin & cementum 9. BUD stage CAP stage LATE CROWN stageBELL stage 10. Tooth development The first recognizable sign of toothdevelopment in humans occurs during the5-6th week of intrauterine life. At this time is characteristic the appearanceof vestibular & dental laminae as a result ofproliferation of oral epithelium. 11. PRIMITIVE EPITHELIAL BAND1 2Is subdivided into: 1. VESTIBULAR LAMINA2. DENTAL LAMINA 12. VESTIBULAR LAMINA It is an ectodermal epithelial extension from thelining of the oral cavity that proliferates into theunderlying ectomesenchyme of the maxilla andthe mandible lateral to the dental lamina. Thecentral cells of this lamina disintegrate to formthe sulcus which is the space between themaxilla and the mandible on one side and thelips and the cheeks on the other side. 13. DENTAL LAMINA it is derived from the ectodermal epitheliallining of the oral cavity. These epithelialcells form a sheet-like structure that extendsinto specific areas of the ectomesenchymaltissues within the alveolar processes of themaxilla and mandible. These areas are partsof the developing dental arch regions whereteeth form and eventually erupt. 14. 12 15. THE MAXILLARY AND MANDIBULAR DENTAL LAMINAE 16. THE INITIATION. BUD STAGEEpithelial cells are inductors in the tooth developmentEpithelial cells produce growth factors (TGF1, BMP2, IGF),that transmit the role of inductor through the basementmembrane to ectomesenchyme 17. The progressive proliferation of the dental lamina into theectomesenchyme results in the formation of a DENTAL BUDat the distal end of the dental lamina. 18. DENTAL BUD is a future ENAMEL ORGAN 19. DENTAL BUD The dental bud looks like a round mass ofproliferating epithelial cells and it issurrounded by condensation ofectomesenchymal tissues which form thedental papilla and dental sac. 20. BUD stage 21. DENTAL BUD 22. DENTAL BUDDental bud - is the future enamel organEctomesenchyme of this region is the futuredental papillaEctomesenchyme of this region is the future dental sac 23. Cap stage The dental bud differentiates into a cap-shapedenamel organ. The epithelial dental organ looks like a head capwith a round convex side and a straight orslightly concave one. During the cap stage are formed the dentalpapilla & dental sac. 24. PROLIFERATION. CAP stage- enamel organ- dental papilla- dental sacare differentiated at this stage 25. ENAMEL ORGAN 1 2Enamel organ consists of:31. Outer enamel epithelium2. Stellate reticulum3. Inner enamel epithelium 26. ENAMEL KNOT appearsasa densely packedaccumulation of cells projecting from theinner enamel epithelium into the dentalpapilla. 27. ENAMEL KNOT 28. ENAMEL KNOT 29. ENAMEL CORD A linear group of cells collectively termedthe enamel cord traverses the stellatereticulum. It is a temporary structure withno known function. 30. ENAMEL CORD 31. Enamel niche Successional lamina 32. Dental papilla & dental sac The concentration of ectomesenchyme,which is in part enveloped by theinvaginated inner enamel epithelium, isnamed the dental papilla. The dental sac is a concentration ofectomesenchyme that encircles the enamelorgan and the dental papilla. 33. CAP stage7 dental papilla8 dental sac 34. HISTO-DIFFERENTIATION & MORPHO-DIFFERNTIATION. BELL stage 35. ENAMEL ORGAN (bell stage)Consists of 4 epithelia:1. Outer enamel epithelium2. Stellate epithelium3. Stratum intermedium4. Inner enamel epithelium1. 2.3. 4. 36. Stratum intermedium The layer adjacent to the inner enamelepithelium is the stratum intermedium,and will become important in transportingnutrients to the future ameloblasts. 37. ENAMEL ORGAN 2.3.1. 4. 38. Preameloblasts initiate the differentiationof odontoblasts which arise from cells inthe dental papilla. The odontoblasts arecalled preodontoblasts before they beginthe production of dentin. 39. INNER ENAMEL EPITHELIUMPREAMELOBLASTSODONTOBLASTSInitiate the differentiation of 40. PREDENTINFormation of the PREDENTIN DENTIN initiate theformation of the ENAMEL 41. REGRESSING OF THE DENTAL LAMINAAn invasion of mesenchymal tissue corresponds with the disruptionof the dental lamina 42. REGRESSING OF THE DENTAL LAMINAEpithelial pearl formations are evident in the regressing dentallamina. 43. DENTAL PULP Successional lamina 44. DENTAL GERM OF THE PERMANENT TOOTH 45. LATE BELL stageIs characterized of:-Appearance ofdentin-Appearance ofenamel-Transformation ofthe dental papillainto DENTALPULP-Morphologicalchanges appear inthe dental sac 46. APPOSITION. LATE CROWN stage Deposition of the dentin & enamel occurs by appositionwith alternation of active & resting states 47. PREDENTIN ENAMELDENTIN 48. APPOSITION, LATE CROWN stagePOINT OF MATURATIONPOINT OF MATURATION is the place at which for the firsttime appear dentin & enamel. 49. STELLATE EPITHELIUM INVOLUTION 50. Outer enamel epithelium, intermedium epithelium & stellateepithelium become thinner and together form STRATIFIEDEPITHELIUM 51. REDUCED ENAMEL EPITHELIUM Takes part in the crown modeling Induces the dentinogenesis of the crown &root Assists in enamel formation & in theformation of dentin-gum connection Isolates the enamel from the connectivetissue of the dental sac Takes part in the tooth eruption 52. REDUCED ENAMEL EPITHELIUM (A)Consists of: stratified epithelium & resting ameloblastsB ameloblasts, C - capillary 53. ROOT FORMATION Begins after complete formation of thetooth crown & continues after the eruption. Key elements, that take part in the rootformation, are:1. Cervical loop that is transformed into EPITHELIAL ROOT SHEATH OF HERTWIG , that differentiates into EPITHELIAL DIAPHRAGM2. Dental sac 54. CERVICAL LOOPThe layer of low columnarcells of the inner enamelepithelium is continuous withthe layer of cuboidal cells thatform the outer enamelepithelium at the structuretermed the cervical loop. 55. EPITHELIAL ROOT SHEATH OF HERTWIG 56. EPITHELIAL ROOT SHEATH OF HERTWIG 57. ROOT FORMATION After complete formation of the crown of thetooth, the root begins to form. An extension ofthe enamel organ, called the epithelial rootsheath of Hertwig, continues to grow apically.The epithelial root sheath induces thedifferentiation of odontoblasts which form rootdentin. The apical most portion of the rootsheath turns inward toward the radicular pulpcavity (that portion of the pulp cavity insidethe root) and is called the epithelialdiaphragm. 58. EPITHELIAL ROOT SHEATH OF HERTWIG & EPITHELIAL DIAPHRAGMEPITHELIAL ROOT SHEATHOF HERTWIG EPITHELIAL DIAPHRAGM 59. EPITHELIAL DIAPHRAGM 60. EPITHELIAL DIAPHRAGM 61. EPITHELIAL DIAPHRAGM DENTAL PULPEPITHELIALDIAPHRAGMAPICAL FORAMEN 62. Hertwigs root sheath determines thenumber, size and shape of roots andis presumably the inductor of dentinformation in the developing root. 63. THE EPITHELIAL ROOT SHEATH OF HERTWIG The epithelial root sheath is made up of innerand outer enamel epithelial layers without theother two interposing layers. Following theinduction of odontoblast and dentin formation,the epithelial root sheath disintegrates formingepithelial rests, small groups of epithelial cellsthat can remain around the root. 64. Tooth eruption is defined as Themovement of a tooth from its site of development within the alveolar process to its functional position in oral cavity, 65. Stage of tooth eruption Pre-eruptive Eruptive (intraosseous& extraosseous) Post-eruptive 66. Factors consideration in tooth eruption development ofperiodontium, root, pulp,alveolar bone events during eruption eruptive pathway: gubernacular canal 67. Gubernacular canalGubernacular cordEruptive Pathway 68. FORCES of Tooth Eruption Root Formation Pressure ( Pulp andHydrostatic ) Periodontal Ligament Bone Remodeling 69. ERUPTION intraosseous stage 70. ERUPTION extraosseous stage