Root Development PDF

Root Development Chider Chen, Ph.D. Assistant Professor Department of Oral & Maxillofacial Surgery [email protected] Agenda 1. Cervical loop 2. Root dentinogenesis and Hertwig’s epithelial root sheath 3. Cementogenesis 4. Root anomalies 5. Eruptive tooth movement Mature Tooth Tooth developmen...

Root Development Chider Chen, Ph.D. Assistant Professor Department of Oral & Maxillofacial Surgery [email protected] Agenda 1. Cervical loop 2. Root dentinogenesis and Hertwig’s epithelial root sheath 3. Cementogenesis 4. Root anomalies 5. Eruptive tooth movement Mature Tooth Tooth development Lamina Initiation Bud Stage Cap Stage Morphogenesis Bell Stage Cytodifferentiation How Does This All Happen? Eruption Matrix Apposition Cervical loop papilla Tooth root formation is initiated when the cervical loop of the enamel organ extends in the apical direction. Reduced enamel epithelium (REE) REE • Remnant of enamel organ. • Formed by all four layers of the enamel organ. • Combination of protective ameloblasts and papillary layer. • Covers unerupted crown. • REE will fuse with oral epithelium to form the junctional epithelium during tooth eruption. Reduced enamel epithelium (REE) Root Root dentinogenesis • REE grows in an apical direction at the cervical loop. • Becomes Hertwig’s epithelial root sheath (HERS). • Sheath formed by the joining of the IEE and OEE. • HERS induces DP outer cells to become root odontoblasts. Root dentinogenesis Root dentinogenesis • Root odontoblasts secrete circumpulpal predentin which soon mineralized. • HERS then detaches from root dentin and disintegrates- some remnants persist as epithelial rests of Malassez. • Roots are not complete until after the tooth has erupted and is in function. Root formation • REE → apical growth → Hertwig’s Epithelial Root Sheath (HERS). • Induction of DP cells to become root pre-odontoblasts, then odontoblasts. Induce dental papilla cells epith Hertwig’s epithelial root sheath if big, cannot have similar signal, uneven growth rate • Uniform growth of this sheath will result in the formation of a single rooted tooth. • Medial ingrowths or invaginations of this sheath will produce multi-rooted teeth. • The number of roots formed is determined by the number of medial ingrowths of the cervical loop. • Dentinogenesis: • REE → apical growth → Hertwig’s Epithelial Root Sheath (HERS). • Epithelial diaphragm • Inner layer → induction of root odontoblasts epithelium cell fusing together • Production of root mantle and circumpulpal dentin. for future root formation, how epithelial cells detach from dentin to form epithelial diaphragm, many roots in this tooth? if very small, incisor/canine, cervical root small and grows evenly to 1 root Formation of multiple roots Formation of Multiple Roots medial growth-->inroot epithelial diaphragm recieves signal, fuse together to become one tooth/root epithelial diaphragm important to determine # of roots • • • • Dentinogenesis: Occurs at slower rate than control dentin. Medial growth of epithelial diaphragm. Multiple root sheaths or tunnels Multiple root formation follows unequal proliferation of the epithelial diaphragm. Formation of multiple roots Root trunk Tongue-like extension • Differential growth of the epithelial diaphragm in the multirooted teeth causes the division of root trunk into 2 or 3 roots. • During the general growth of enamel organ, expansion of its cervical opening occurs in such a way that long tongue like extensions of the diaphragm develop. • Before division of the root trunk occurs, free ends of the epithelial tissues grow towards each other and fuse. • The single cervical opening is divided into 2 or 3 openings. Formation of multiple roots Epithelial diaphragm root #, driving force for pushing crown erupt, form multiple roots or single root, push the crown eruption from gingiva Disintegration of HERS after root dentin form, epithelial cell start to detach from root dentin Dental sac (follicle) Disintegration of HERS • Important to permit the invasion of dental sac cells. root dnetin formation, root cell start to detach, stimulate dental sac to come in, differentiate to cementoblasts de collagen, cementocyte-->mirrorize the cementum, mirrorize, no cell inside the ntCementogenesis cementum, detach epithelial cells to differentiate cementoblast, collagne fiber, al mineralized tissue, no more cementoids • After first root dentin is deposited, the cervical portion of Herwig’s root sheath breaks down. • This new dentin comes in contact with dental sac ectomesenchymal cells that have migrated from the dental sac. • This contact and signals from the odontoblasts induces the dental sac ectomesenchymal cells to differentiate into cementoblasts, which then produce cementum. dental folllicle cell simulate dental sac cell to cementoblast to secrete cementoid, collagen fiber w/ protein, mirrorize tissue to Cementogenesis • Dental sac cells migrate in and contact new root dentin surface. • Induction of dental sac cells to differentiate into cementoblasts. • Cementoblasts secrete organic matrix – cementoid – on new dentin surface. • Cementoid mineralizes into cementum. • In the apical 1⁄2 to 2/3 of the root, cementoblasts become entrapped in lacunae as cementocytes. Cementogenesis • Acellular extrinsic fiber cementum: • Primary cementum • HERS disintegrates • Source of cementoblasts: • Dental sac ectomesenchyme cells induced by local factors. • Epithelial-mesenchymal transformation of HERS cells. • Collagen fibril deposition and intermingling with mantle dentin fibrils. • Mineralizes internal to external. • Slow development during eruption → cells remain on surface. • No cementoid periodontial ligament from dental sac cells Periodontal ligament • Dental sac ectomesenchyme cells differentiate into fibroblasts. • Fibroblasts secrete collagen fibers. • Collagen fibers become anchored in cementum as it is deposited by cementoblasts. after root dentin forms, form new dentin, permit area of newly formed dentin with dental sac cells, drive dental sac cells into cementoblast, which produce cementoid no cells in cementum, just collagen and dentin, no more cementoid after cells a while, periodontal ligament Fate of HERS dental sac cells-->fibroblasts->ECM, collagen fibers • Epithelial Rests of Malassez: • Remnant of HERS that have detached from the root surface. • Network of epithelial cells that remain within the PDL. • Can become tumor-forming cells within the PDL. • Most will degenerate and disappear, while a few may calcify and become ‘cementicles’. may maintain balance of root, stimulate new dentin formation, no evidence why they still remain, can be a tumor or smth some epithelial cells remain Epithelial rests Root anomalies anamolies of root formation, exposed root dentin-->enamel pearlers- • Anomalies are resulted from a disturbance in Hertwig’s epithelial root sheath. • Exposed root dentin. • Enamel pearls. • Accessory root canals. Formation of exposed root dentin some epithelial cells form new dentin, cannot form cementum because no space to contact dental sac scells, exposed root dentinn, no compaction w/ cementum, causing it to be exposed to damage Formation of enamel pearls attach to area, epthelial cell differentiate to ameloblast, enamel pearl @ root area, normal root formation epithelial root cell-->ameloblast-->enamel pearl Formation of accessory root canals epithelial cells, if they detach too quick, before root dentin and odontoblasts form, will get accessory root canal, usually good structur,e as it links to surounding soft and hard tissue, but when doing root canal, hard to remove eopithelial cell_.odontoblast formation, detach too fast, become accessory root canal root dentin-->epithelium cell in growth, dental papila cell-->odontoblast-->root dentin formation, if detach too quick, create a space to form structure called accessory root canal root formation driving force 4 layer of cells fuse to become reduced dental epithelium cell to stimualte information cerival loop-->root sheath epithelia-->l 4 layers root formation involves both epithelial and mesencyme cells root sheathe-->odontoblast mesenchyme: dentalpapilla and follicle root formation STIMULATES< not makes enamel -->root and bone formation epithelial diagragm grows form epithelial cell--.root sheath-->epithelial diaphragm, fuses with apcical root -->go into bone area, and fuse with dental papilla, epithelial attachment Human root development tip of root: apical papilla, part of dental papilla, structured didferently from proliferating cell, Pulp Pulp Roots R Proliferating cells Roots Proliferating cell Epithelial rests Epithelial root sheath Apical papilla Epithelial diaphragm Apical papilla Apical papilla trauma on tooth, root canal, fill w/ material and seal up the tooth, after 3 months, look to see root is still growing, when tooth is broken, still growing, even whe nremoved pulp and sill have apical pailla, there's still root formation= msesenchyme tissue for root formation Function of human root apical papilla Sonoyama et al JOE 2008 Function of minipig root apical papilla cut apical papilla on just one root, allow the others to grow, extract, look, after removing the pailla, starts growing even after pulp area, tissue different funcon Eruptive tooth movement Reduced enamel epithelium produces and releases enzymes that degrade the tissues between REE and oral epithelium allow for fusion of gingiva, reduced epithelial laer fuse with oral epithelium/ gingiva , release enzymes to digest epithelial layer to prepare for eruption Eruptive tooth movement Reduced enamel epithelium fuses with oral epithelium Eruptive tooth movement Breakdown of oral epithelium fuse together, Eruptive tooth movement epithelial junction , after emergent from gingiva, speed increase further than initia lcstep • The initial emergence of the tooth in the oral cavity. • Formation of the initial junctional epithelium. crown formation, epithelial redued, root continue formng, driving force to erupt, help gngiva to erupt, coming and growing , afer tooth erupt, the roots are still developing, root process formation and crown eruption Eruptive tooth movement • • • • • • Alveolar process continues to develop. PDL fibers develop. Tissues between reduced enamel epithelium and oral epithelium degenerates. Reduced enamel epithelium and oral epithelium fuse. Enzymes break down fused epithelia → tunnel for eruption of crown Following initial emergence of a tooth in oral cavity, its eruption speeds up (at maximum rate) until it reaches the occlusal plane. Eruptive tooth movement no blood formation • Dentogingival junction forms initially from REE. • No hemorrhage, since the REE and oral epithelium have no blood vessels in them . • The root formation of a tooth is not complete after the tooth has been in function: • Deciduous teeth: 1-1.5 years. • Permanent teeth: 2-3 years. erupt the tooth, when root formation, bone socket for rootformation, after root formation, cetai nstage, will fill in to push the tooth for eruption, dynamic process where root forms and resolv bonee, then bonepushes to cause eruption Eruptive tooth movement • Roots grow apically → bony fundus resorbs. • During eruption, bony trabeculae fill in resorbed fundus → “bone ladder”. small pieces of small bone =trabeceluae Fundic area (Bottom of the alveolar socket) Take home message 1. Tooth root formation is initiated when the cervical loop of the enamel organ extends in the apical direction. 2. Reduced enamel epithelium (REE) is the remnant of enamel organ and covers unerupted crown. 3. Reduced enamel epithelium grows in an apical direction at the cervical loop and becomes Hertwig’s epithelial root sheath (HERS). 4. HERS induces dental papilla outer cells to become root odontoblasts. 5. HERS then detaches from root dentin and disintegrates- some remnants persist as epithelial rests of Malassez. 6. Medial ingrowths or invaginations of this sheath will produce multi-rooted teeth. 7. Dental sac (follicle) contributes to cementum, periodontal ligament, and avelolar bone development. Take home message 8. Root anomalies are resulted from a disturbance in Hertwig’s epithelial root sheath. 9. Three major anomalies are exposed root dentin, enamel pearls, and accessory root canals. 10. Dentogingival junction forms initially from REE. 11. No hemorrhage, since the REE and oral epithelium have no blood vessels in them. 12. During eruption, bony trabeculae fill in resorbed fundus → “bone ladder”. Chider Chen, Ph.D. Assistant Professor Department of Oral & Maxillofacial Surgery [email protected]