2024 - 101 Test Revision.pdf

REVISION 2024 DEOH 101 Stages in tooth development (based on the appearance of the developing structure)  Initiation (Dental lamina)  Bud stage (A)  Cap stage (B)  Bell stage (C)  Early Bell stage  Late Bell stage  Appositional stage (D & E)  Crown formation (F)...

REVISION 2024 DEOH 101 Stages in tooth development (based on the appearance of the developing structure)  Initiation (Dental lamina)  Bud stage (A)  Cap stage (B)  Bell stage (C)  Early Bell stage  Late Bell stage  Appositional stage (D & E)  Crown formation (F)  Root formation & Eruption (G)  Maturation stage  Function (H)  Initiation Stage 1. Cells of oral epithelium near the future dental arches proliferate & form a thick band Ref. Fehrenbach & Popowics Horse-shoe (“U”) shaped → primary epithelial bands (odontogenic epithelium) 4. Basement membrane (acellular) 2. Induction process (cellular interactions) separates these two 3. Ectomesenchyme condensation under the ectodermal oral epithelium (Odontogenic Cells) 3 2. Bud Stage Formation of localised thickening (placodes) Extensive proliferation → buds Sites corresponding to future deciduous teeth Condensation of ectomesenchyme Basement membrane remains between bud & ectomesenchyme Future maxillary & mandibular arches have 10 buds each Patterning of dentition – determination of specific tooth type & their correct position in jaws 4 3. Cap Stage Proliferation continues with unequal growth 1 Marks the onset of differentiation 2 3 At the end of the cap stage, tooth germ is formed Ten (10) tooth germs in each dental arch – primary dentition Tooth germ has 3 components 1. Enamel organ - Ectodermal cells in the tooth bud Form → Enamel 2. Dental papilla - Condensed ectomesenchyme within the concavity Form → Pulp/Dentine complex (dental pulp & dentine) 3. Dental follicle / dental sac - Remaining ectomesenchyme surrounding the enamel organ Basement membrane Form → Dento-alveolar articulation (cementum, periodontal separates enamel organ from ligament & alveolar bone) Dental papilla & dental sac 4. Bell Stage Four different types of cells develop in enamel organ Layers in enamel organ 1.Outer enamel epithelium (OEE) Cuboidal or flattened cells on the outer surface protective barrier to the enamel organ 1.Stellate reticulum (SR) Star-shaped cells in many layers support the future production of enamel 1.Stratum intermedium (SI) Dental papilla – undergo Compressed layer of flat/cuboidal cells adjacent to differentiation IEE support future production of enamel Two types of cell layers Outer cells →differentiate into 2.Inner enamel epithelium (IEE)– low Columnar odontoblasts dentine-secreting cells cells lining the concave surface - will differentiate Central cells → become primordium of pulp 6 into Ameloblasts enamel-secreting cells  Vascular supply  Clusters of blood vessels proliferate around the dental follicle Nerve Supply  Form rich plexus around the tooth germ  Pulpal innervation – at the time of dentinogenesis  No nerve in the enamel organ Ref. Fehrenbach & Popowics, p. 60 7  Late Bell Stage  Dental Lamina Fragments & separate the developing bud from the oral epithelium  Fragmented epithelial cells degenerate  Some may persist as epithelial pearls  Eruption cysts  Odontomes  Supernumerary teeth  Tooth crown assumes final shape  IEE completes its folding & completes the mapping of future crown  Cervical loop – the region where inner & outer enamel epithelia meet at the rim of the enamel organ 8 5. Apposition (secretory) stage 1. Inner enamel epithelial cells→ Preameloblsts 2. Induce outer cells of the dental papilla to become odontoblasts 3. Apposition of dentine matrix 4. Basement membrane disintegrates 5. contact between newly formed dentine with Preameloblasts → ameloblasts 6. Enamel Matrix formation 7. Mineralisation: 1. Ameloblasts secrete an organic cuticle; developmental/primary cuticle 2. Cells of enamel organ flatten and fuse to form Reduced Enamel Epithelium (REE)  Mantle dentine – first Ameloblasts begin amelogenesis layer of dentine which supports overlying (apposition of enamel matrix enamel layer from the Tomes’ process an angled part of each ameloblast ) Predentine – newly formed dentine – not fully mineralised – next With a newly formed enamel to pulp chamber matrix in contact with predentine, mineralisation of the disintegrated basement membrane occurs, forming DEJ Both ameloblasts and odontoblasts retreat away from DEJ while forming enamel & dentine, respectively 10 Crown Maturation ….. With the completion of matrix deposition phase: Terminal bar apparatus disappears Surface enamel become smooth After completing mineralization: Ameloblasts secrete an organic cuticle; developmental / primary cuticle Cells of enamel organ flatten and fuse to form Reduced Enamel Epithelium (REE) 11 Root development  When the crown is completed:  Cell proliferation continues at the cervical region (at the rim of the enamel organ), forming cervical loop SR Pulp  Cells of IEE & OEE fuse to form the Hertwig’s Epithelial Root Sheath (HERS) OEE  Cervical loop – grows deeper into Cervical Loop ectomesenchyme of the dental sac, enclosing more dental papilla Ref. Fehrenbach & Popowics 12  13 Ref. Fehrenbach & Popowics Root development ….. Function of HERS Architect of the root (Shape the root) Length (Short or long) Curvature (Straight or curved) Number (Single or multiple) Thickness etc. Ref. Fehrenbach & Popowics Induce dentine formation in the root area IEE induce cells in dental papilla to differentiate into odontoblasts and form dentine IEE fails to differentiate into ameloblasts due to lack of two layers in enamel organ 14 Root development ….. IEE of HERS induce outer cells of dental papilla Differentiate into odontoblasts Secrete predentine With Dentinogenesis the root lengthens Basement membrane together with HERS disintegrates with the root dentine formation Cells may become epithelial rests of Malassez - located in mature periodontal ligament Can cause cysts May be activated in periodontal repair & regeneration 15 Ref. Fehrenbach & Popowics 16  Cementogenesis; Contact between undifferentiated cells in the dental sac with the newly formed predentine Cells of dental follicle → differentiate into Cementoblasts Fibroblasts Apposition cementoid (matrix) by cementoblasts Cementoblasts get entrapped in the cementum & become cementocytes cementoid become mature → cementum Appositional growth of cementum in the root area after HERS disintegration & the DCJ – dentinocemental induction of dental sac cells to differentiate into Cementoblasts which produce cementoid. Entrapping cells will become cementocytes. Nearby alveolar bone & periodontal ligament are also developing further. (Ref. Fehrenbach & Popowics) 17 Periodontal Ligament Alveolar Bone Cells of dental follicle → differentiate into Ectomesenchyme cells dental follicle fibroblasts → collagen fibers differentiate osteoblasts → Alveolar bone Collagen fibers immediately organise into fibre bundle First forms labial & lingual plates Rapid turnover Continued renewal Bony septa appear between the teeth to Ends of these fibers insert into outer form crypts layers of cementum & surrounding alveolar bone – called Sharpey’s fibers When teeth erupt, alveolar bone & PDL Maturation with functional occlusion matures to support the newly formed tooth 18 Formation of permanent teeth Succedaneous permanent teeth Successional dental Anteriors & premolars lamina of permanent teeth primordia On the lingual aspect of the deciduous tooth germ Replace the deciduous teeth Developing mandibular dental Non-Succedaneous permanent arch Vestib teeth ule Molars Develop from the posterior Developing extension of dental lamina primary teeth Not replacing deciduous Developi teeth ng mandible Development of the succedaneous permanent teeth in a lingual position to the primary teeth on a section of foetal mandible 19  At the 10th week of IU life – initiation occurs for permanent anterior teeth Each primordium of permanent teeth 1 to 5 appears as an extension of dental lamina lingual to primary tooth germ Origin from successional dental lamina Succedaneous - because they replace primary anteriors & molars Permanent molars are nonsuccedaneous & have no primary predecessors - Develop from a posterior extension of the dental lamina 20 Ref. Fehrenbach & Popowics  Tooth emergence & Development of the dentition Fehrenbach & Popowics After the completion of the enamel formation Ameloblasts – secrete an acellular enamel cuticle on the newly formed enamel Cell Layers of enamel organ compressed & form the reduced enamel epithelium (REE) before eruptive movements begin (appears as few layers of flattened cells)  Eruptive phase – deciduous teeth & non-succedaneous permanent teeth Bone overlying erupting tooth resorbed by osteoclasts Crown passes through the connective tissue of mucosa With movement of the crown → creates space for the extension of the root sheath Reduced enamel epithelium & oral epithelium fuse & form a solid mass of epithelial cells over the crown Central cells in this mass disintegrate with enzyme (from REE) activity and form an epithelial canal (tunnel) through which the tooth erupts A. Oral cavity before the eruption begins – enzymes from the epithelium are present for tissue disintegration B. Fusion of the REE with oral epithelium C. Disintegration of central fused tissues leaving a tunnel for tooth movement Fehrenbach & Popowics D. Coronal fused tissues peel back from the crown during eruption leaving initial junctional epithelium Eruptive phase – deciduous teeth & non-succedaneous permanent teeth…. Tooth eruption achieved without exposing the surrounding connective tissue & any haemorrhage This tissue disintegration can cause an inflammatory response May lead to tenderness & oedema of soft tissues Discomfort in teething – can affect infants & young adults Succedaneous Permanent teeth eruption Develop lingual to the primary teeth Successional lamina disintegrates Pre-eruptive movements move the tooth buds Most anterior teeth lingual to the roots of the primary teeth Exception: maxillary incisors - move to a more labial position as they erupt Premolars occupy a place between primary roots  Shedding (Exfoliation) of Deciduous Teeth Loss of primary teeth should occur first: this involves Osteoclasts will resorb the alveolar bone between the primary and permanent teeth Mesenchymal tissues will form odontoclasts which will resorb the dentin and cementum of the roots of the primary tooth Fibroclasts will destroy collagen fibres of periodontal tissues Periodontal ligament remodelled continuously by fibroblast and fibroclast activity to accommodate the eruption process Hydrolytic enzymes Ruffled border Intermittent Crown passes through the connective tissue of mucosa (tight/loose) With movement of the crown → creates space for the extension of the root sheath Reduced enamel epithelium & oral epithelium fuse & form a solid mass of epithelial cells over the crown Central cells in this mass disintegrate with enzyme (from REE) activity and form an epithelial canal (tunnel) through which the tooth erupts  Nasmyth membrane A residue on newly erupted teeth REE Oral epithelium Enamel/dental cuticle Can cause extrinsic stains with foodstuff – (green-gray) Usually wears off with chewing & proper brushing Reassurance Rarely - Selective polishing Developmental disturbances during eruption Dentigerous cyst Forms around a crown of a non- erupted impacted or developing tooth Most common – 3rd molars Initially – asymptomatic When larger can cause Displaced teeth Jaw fracture pain Complete removal Eruption cyst Dentigerous cyst in a partially erupted tooth Fluctuant, blue vesicle like gingival lesion Disintegrate with eruption: no treatment required - reassurance  Anomalies in Primary & Permanent dentition Can occur at any stage of tooth development Considerable variations may observe in Number → Anodontia (less/missing), Supernumerary teeth (more) → Microdontia (small), Macrodontia (large) Size → Gemination, Fusion, Concrescence, Dilacerations, Talon cusp, Shape Dense in Dente, Dense invaginatus & Taurodontism → Amelogenesis imperfecta, Environmental enamel hypoplasia, Structure Dentinogenesis imperfecta, Dentine dysplasia, Hypercementosis 29  Number Developmental anomalies during Initiation stage Anodontia Hyperdontia Lack of initiation within the dental Abnormal initiation within the lamina dental lamina can form an (Failure of teeth to develop) excessive number of tooth Partial buds → Supernumerary teeth Hypodontia (having less than 6 congenitally missing teeth) Oligodontia (≥6 congenitally missing teeth) Complete 30 Supernumerary teeth: Number Odontome Compound odontome Complex odontome Masses of irregular denticles (multiple small tooth-like Disorganized mass of dental structures in a circumscribe tissue soft tissue stroma) 31  Size Shape Abnormal Morphodifferentiation Dense in Dente (Dens Invaginatus) Microdontia – Smaller Peg lateral Size & shape Macrodontia - Larger Dense evaginatus (extra cusps) 32  Shape Double teeth Gemination Fusion Twinning in the crown area – broader, Twinning in the crown area – broader, falsely macrodontic tooth falsely macrodontic tooth Number of teeth usually normal (1ry or 2ry) Common with primary anterior teeth Splitting can be detected as a cleft in incisal Number of teeth – one less edge (varying depth) or Two crowns Radiographs - Two distinct pulp cavities Radiographs - Large single-rooted tooth with enamel, dentine & pulp united in with one pulp cavity radiographs Usually in the crown, but root area also 33 Apposition & Maturation stage Structure Dentinogenesis imperfecta Amelogenesis imperfecta Enamel opacities Dentin Dysplasia Chronological Enamel hypoplasia Turner’s tooth 34  Root formation stage Dilaceration Enamel pearl Hypercementosis Concrescence Accessory roots 35  Other Developmental Anomalies Eruption cyst ▪ Cysts: Submerged teeth Ankylosis ▪ Neoplasia: What can you do? 36