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TOOTH ERUPTION DentEazy GENERAL MECHANISM OF TOOTH ERUPTION 1. Move from bony crypt 2. Through alveolar bone 3. Break epithelial integrity 4. Eruption into oral cavity DENTAL FOLLICLE • Made up of loose connective tissue sac • Regulates alveolar bone activity • Initiation of root formation stimulates dental follicle by recruiting multiple growth/transcription factors/hormones needed for osteoclastogenesis (alveolar bone resorption) & osteogenesis (bone deposition) WHAT IS REQUIRED FOR TOOTH ERUPTION? (2 marks) • Development of tooth support tissues • Dento-gingival junction INTRA-OSSEOUS ERUPTION 1. Spatially restricted removal of bone on coronal side of tooth creating eruption pathway 2. Tooth moves occlusally 3. Bone positioning in apical follicle, translocating tooth 4. Bone deposited in bucco-lingual aspect forming dental alveolar process SUPRA-OSSEOUS ERUPTION • Night • Drift continues through life via remodelling of PDL EPITHELIAL PLUG • Connective tissue complex • Reduced enamel epithelium in dental follicle + oral epithelium • Formed as tooth pierces oral mucosa • Transforms into squamous mucosal cells MUCOSAL PENETRATION • Coronal aspect reaches mucosa and formation of epithelial plug JUNCTIONAL EPITHELIUM • Central cells of epithelial degenerate so tooth erupts with no bleeding WHAT LOCAL FACTORS AFFECT THE SPEED OF ERUPTION? (5 marks) • Crowding • Disturbed bone modelling • Obstacles (supernumerary/cysts) • Trauma • Early loss of deciduous teeth GUBERNACULAR CANAL • Chord in canal has remnants of dental lamina & connective tissue • Between permanent tooth germ and apex of deciduous tooth • Lingual side of deciduous • Provides directional eruption pathway • Eruption widens canal by osteoclasts GUBERNACULAR CORD • Remaining epithelium cells and fibres connecting to permanent tooth development PERMANENT TOOTH ERUPTION 1. Shedding - deciduous roots resorbed 2. Directional pull for teeth to erupt apically 3. Gubernacular canal (directional pathway) 4. Canal widened by bone resorption during eruption PERMANENT INCISOR ERUPTION • Permanent incisor or canine developed lingually • Deciduous root resorption of lingual surface • Dental pulp intact • Tooth eruption lingually PERMANENT MOLAR ERUPTION 1. Root resorption & pulp degradation 2. Bone formation 3. Bone resorption STAGES OF TOOTH ERUPTION 1. Pre-eruption 2. Eruption 3. Post eruption PRE-ERUPTIVE STAGE • After crown formation • Dental follicle surrounded by bony crypt, between alveolar bone of socket and enamel organ of unerupted teeth • Deciduous & permanent tooth germs within tissues of jaw • Total bodily movement of tooth germ • In intraosseous locations - bony remodelling of crypt wall • Well-regulated signalling events between dental follicle and stellate reticulum • Permanent tooth on lingual side of deciduous, share bony crypt in early stages then develop own and gubernacular canal ERUPTIVE STAGE • Tooth approaches oral cavity - overlying bone resorbed • Intraosseous stage: in bony crypt • Extraosseous stage: out bony crypt (faster) • Collagen degraded, oral epithelium + reduced enamel epithelium cells in overlying soft tissues • Epithelium degenerates from centre as tooth tip emerges forming junctional epithelium POST ERUPTIVE STAGE • Tooth reaches functional position • Accommodates growing jaws - bone remodelling of tooth socket • Compensates for occlusal wear - axial movement • Continued cementum formation at root apical site • Accommodates interproximal - mesial drift TOOTH SHEDDING (EXFOLIATION) 1. Reduced enamel epithelium 2. Fusion of oral epithelium + REE 3. Epithelium degenerated 4. Forming junction of epithelium NAME CELLULAR OR MOLECULAR FACTORS AFFECTING TOOTH ERUPTION (6 marks) • Colony-stimulating factor 1 (CSF-1) • Colony-stimulating factor 1 receptor (CSF-1R) • Macrophage colony-stimulating factor (M-CSF) • Receptor activator of nuclear factor kappa-B (RANK) • Receptor activator of nuclear factor kappa-B ligand (RANKL) • Osteoprotegerin (OPG) OSTEOCLASTS • Bone resorption • Multinuclear cells • Derived from bone marrow monocytes • TRAP+ and H⁺ secretion • Proteolytic enzyme secretion • Active site = ruffled edge • Enzymes produced by osteoclasts break down collagen fibres OSTEOCLAST FORMATION 1. Osteoclasts differentiate from monocytes 2. Monocytes receive signal produced by macrophages or osteoblasts, producing M-CSF 3. Become matured macrophage/osteoclast precursor producing RANK on cell surface 4. Fuse with RANKL on osteoblasts to become osteoclast THEORIES FOR MECHANISM OF TOOTH ERUPTION • Root Formation - growing root accommodated by occlusal movement • Bone remodelling - deposition/resorption of bone around teeth • Periodontal ligament remodelling - functions of PDL cells/fibres in controlling eruption • Dental follicles - periodontal fibroblast contraction & vascular/tissue hydrostatic pressure ROOT FORMATION For Against Extending length of root may Tooth eruption continues serve eruptive force without root formation Removal of HERS didn't stop root formation Teeth erupted greater than their root extension BONE REMODELLING For Against Maxilla & mandible move teeth into position Base of crypt continues being resorbed via remodelling Gubernacular canals widen by osteoclast Without follicular tissue, bone deposition on crypt floor can't result in tooth eruption Bone deposition on crypt floor can lead to eruption PDL REMODELLING For Against Tooth eruption after root resection or Eruption without well-developed PDL transection Lathyrogen selectively disrupts collagen crosslinking without slowing eruption PERIODONTAL FIBROBLAST CONTRACTION For Against Migration along with eruption Periodontal fibroblast ER has no migratory or contractility molecules Cyclophosphamide suppressed eruption No microfilament bundle Myofibroblast generated contraction and tension VASCULAR/TISSUE HYDROSTATIC PRESSURE For: • Tooth moves with artery pulse • Blood pressure influences eruption • Hypotensive drug increased capillary and periodontal tissue hydrostatic pressure resulting in eruption