Tooth Development Flashcards
What does the periodontium consist of?
- Cementum
- Periodontal ligament
- Alveolar bone
- Gingiva
Cementum - Overview? Thickness? Adherence? Properties? Cycle?
- Thin layer of calcified tissue covering radicular dentine
- 10-15um in thickness (cervically)
- 50-200um thickness (apically)
- Can exceed 600um at root apex
- Adheres to dentine and the periodontal ligament
- Capable of repair and regen
- Formed throughout life, allowing reattach of PDL
- Always a layer of uncalcified precementum
Cementum - Physical properties?
Physical properties:
- pale yellow
- dull surface
- softer than dentine
- permeable (more than dentine)
- easily abraded cervically
Cementum - Chemical composition?
65% inorganic, 23% organic and 12% water (by weight)
Inorganic:
- hydroxyapatite, with other calcium forms (thin plate like apatite crystals)
Organic:
- Col I, and non-collagen elements (sialoprotein and osteopontin)
Classification of Cementum - Different types?
- Cellular and Acellular
- Extrinsic and Intrinsic fibres
- Combination of both
- Afibrillar cementum
Classification of Cementum - Acellular vs Cellular?
Acellular: no cells - variation in arrangement - primary cementum - covers dentine - appears structureless Cellular: cells - contains cementocytes - mainly in apical area and inter-radicular areas overlying acellular cementum - secondary cementum - lacunae present - widely spaced incremental lines (variable growth times) - precementum - cementocytes (inactive) trapped in lacunae with canaliculi (oriented towards the PDL, as source of energy) - lines of Salter (incremental lines) Afibrillar: - histologically look like a dark line and between hyaline and acellular cementum
Cementum - Origin of organic matrix? Extrinsic vs Intrinsic fibres?
Extrinsic fibres: - derived from Sharpey's fibres of PDL - sharpey's fibres enter the cementum perpendicular to root surface Intrinsic fibres: - derived from cementoblasts - run parallel to root surface
Mixture of all types of cementum
Cementum - Acellular extrinsic fibre cementum? Overview? Location? Thickness?
- Mainly over cervical 2/3 of root
- Bulk cementum in premolars
- First formed cementum
- Reach 15um in thickness
- All Col fibres extrinsic
- Ground substance may be product of cementoblasts
Cementum - Cellular intrinsic fibre cementum? Insertion? Location? Speed?
- Intrinsic fibres parallel to the root surface
- No role in PDL attachment
- Apical third of root and interradicular area
- Formed slowly
Mixed fibre cementum - Overview? Orientation? Bundle sizes? Acellular vs Cellular?
Overview:
- both extrinsic and intrinsic fibres
Orientation:
- almost at right angles
Bundle sizes:
- extrinsic fibres ovoid or round (5-6um d)
- intrinsic fibres are 1-2um in diameter
Acell vs Cell:
- Acell forms slowly but well mineralised
- Cell forms quickly but less mineralised (esp at core)
Afibrillar cementum - Overview? Distribution? Mineralisation? Origin? Location?
Overview:
- no collagen fibers
- sparsely distributed
- well mineralised ground substance
- epith in origin (hyaline)
- thin, acell could overlap enamel
- found between fibrillar cementum and dentine
Cemento-Dentinal Junction - Overview? Role? Composition?
- Intermediate layer between 2 tissues
- Anchors periodontal fibres into dentine
- Innermost cementum layer, superficial layer of root dentine, intermediate cementum and hyaline
- Wide irregular spaces that may interconnect with tubules
Cementum - Attachment to the periodontal ligament?
- Fibres in the PDL run into the organic matrix of the precementum
- Mineralisation of precementum leads to incorporation of these extrinsic fibres (Sharpey’s fibres)
Cementum - Resorption and repair?
- Roots show small localised areas of resorption
- May be associated with trauma and pressure applied onto roots
- Multinuc odontoclasts
- Resorption may reach dentine
- Deficiencies resulting from resorption can be filled by deposit of cementum (reversal lines)
- Repaired cementum resembles cellular cementum (less mineralised, smaller crystals)
- Precementum like layer wide than normal precementum
Clinical consideration - Root fractures? Cementicles?
Root fractures: - repaired by cementum callus (resorption and repair answer) Cementicles: - attached or free - apical and middle thirds - furcation areas
Early tooth development - Initiation? Process? Basic?
Initiation:
- locations of teeth are established by the appearance of tooth germs
- tooth germs appear along the dental lamina (invagination in the oral mucosa)
Early tooth development - Morphogenesis? Process? Basic?
Morphogenesis:
- shape of the teeth determined
- cell proliferation and movement determine shape
Early tooth development - Histogenesis? Process? Basic?
Histogenesis:
- differentiation of cells takes place to produce full formed dental tissues
- histo begins during morpho as all phases overlap
Early tooth development - Overview?
Early tooth development:
- primitive oral cavity, mesenchymal condensation underneath the dental epithelium takes place
- ectomesenchymal in origin (from neural tube)
Early tooth development - 6 weeks in utero - processes?
- Thickening of the oral epithelium
- Invagination of the epith into the mesenchyme to form the primary epith band
- maxillary and mandibular processes with a developing tongue
Early tooth development - 7 weeks in utero? Division? Lamina?
Primary epith bands divides into 2:
- vestibular lamina (buccally)
- dental lamina (lingually)
Vestibular lamina:
- contributes to the development of the vestibule
- vestibules delineate the lips and cheeks from the tooth bearing regions
- degeneration of the central epith cells producing a sulcus
Dental lamina:
- contributes to teeth formation
Early tooth development - 8 weeks in utero?
- Swellings (tooth bud) develop on the deep surface of the dental lamina
- Each swelling is surrounded by mesenchymal condensation
Early tooth development - Tooth germ formation? Stages?
- Tooth germs are classified into stages (bud, cap, early and late bell stage)
- Odontogenesis is a continuous procedure
Tooth germ formation - Bud stage?
Bud stage:
- enamel organ appears as a simple ovid epith mass
- surrounded by mesenchyme
- mesenchyme separated from the epith by a base mem
Tooth germ formation - Cap stage? 11 weeks in utero? Process?
Cap stage:
- morphogenesis progresses
- invagination of the deeper surface of enamel organ
- peripheral cells start to be arranged as external and internal enamel epith
- central cells more rounded
- dental papilla and dental follicle also present
Tooth germ formation - Cap stage? 12 weeks in utero? Formation?
Cap stage:
- central cells in the enamel organ become separated (stellate reticulum)
- (cuboidal) external enamel epith cells (form)
- (columnar) internal enamel epith cells (form)
- prolif of surrounding mesenchyme
- dental papilla/follicle
Tooth germ formation - Early bell stage? 14 weeks in utero? Progression? Dental follicle composition?
Early bell stage:
- shape of the internal enamel epith decides the crown shape
- mitotic activity at different sites affects the folding
- contribution of available spaces and mechanical forces
- dental lamina breaks (epith rests of serrez)
Dental follicle:
- inner vascular fibrocellular condensation
- loose connective tissue layer
- outer vascular layer lining the alveolus
(presence of permanent tooth bud, at the same time as the primary dentition)
Tooth germ formation - Early bell stage? 14 weeks in utero? Layers?
Early bell stage: 4 distinct layers;
- external enamel epith
- stellate reticulum
- stratum intermedium
- internal enamel epith
Tooth germ formation - external enamel epithelium? Forms the? Separation? Organelles?
External enamel epith:
- forms the outer layer of cells in enamel organ
- base mem separates cells from mesenchyme (follicle)
- desmosomes and gap junction
Tooth germ formation - Cervical loop? Overview?
Overview:
- is at the growing margin of enamel organ
- lies at the junction between inner and outer enamel epith
Tooth germ formation - Stellate reticulum? Overview?
Shape? Organelles? Role?
Overview:
- intercellular spaces become fluid filled
- star shaped branching
- prominent nuc, little endoplasmic and few mito
- developed golgi and microvilli (secretion)
- glycosaminoglycans
- synth collagen
Role:
- stellate reticulum protects the underlying tissues and maintains tooth shape
- balance between hydrostatic Pa of stellate and papilla
- effect crown outline