Cementum and root development PDF

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Cementum and root formation Periodontium Tissues supporting and investing the tooth consist of - Cementum - Periodontal ligament - Bone lining the alveolar socket - Gingiva facing the tooth Periodontium respond to force - Cementum apical deposition respond to occlusal force - Periodontal ligament high turnover to respond to forces - Bone reabsorbs on the pressured side and is added on the tension side Root formation From apposition to maturation stage.  In these stages the matrices of dentine, enamel and cementum are secreted in layers  These tissues are initially secreted as a matrix that is partially calcified  Serves as a framework for later calcification Cervical loop HERS = her twigs epithelia root sheath Epithelial rests of Malassez: - Epithelial remnants of the HERS - Resides in the periodontal ligament - Clinically these remnants may become significant (possible cause of radical are cysts) Root formation via apical extension of the inner and outer epithelial layers forming HERS. HERS induces differentiation of odontoblasts from the radicular pulp which forms dentine. Root formation is almost complete, HERS is just a small tag of epithelium to become the rim of the apical foramen. Root development proceeds crown formation. - An apical root sheath forms from the cervical loop region of the enamel organ - HERS encloses the dental papilla sitting inside the dental follicle - Bi-(or more) furcation can occur to provide more than a single root without interrupting the pattern or process of root formation. Cementum = thin layer of calcified tissue covering the root, approx 50% organic 50% inorganic. Organic makeup:  90% of the organic component = type 1 collagen  Remaining collagens consist of type 3 and type 12  Many non-collagenous proteins are present in cementum: Initiation of cementum formation

Source of cementoblasts: (possible origins) 1. Infiltrating dental sac or dental follicle cells 2. HERS cell transform into cementoblasts 3. Stem cells from blood Possible signals for cementum formation:

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Loss of SR HERS HERS cell apoptosis Odontoblasts producing pre-dentine Detailed mechanism is unclear.

Evidence for cementoblastogenesis and root formation: - PDL and cementoblasts precursors reside within the dental follicle and differentiation is under control of factors in the local milieu. - HERS epithelial cells undergo epithelial-mesenchymal trans differentiation into cementoblasts during development Types of cementum and classification (according to three factors)  Based on time of formation - Primary cementum: formed before eruption - Secondary cementum: formed after eruption  Based of presence or absence of cells in the matrix - Acellular cementum / cellular cementum  Based on origin of collagen fibres in the matrix - Intrinsic fibre cementum: fibres formed by cementoblasts - Extrinsic fibre cementum: fibres resulting from incorporation of PDL fibres Acellular: - Also known as primary cementum - Produced by cementoblasts which differentiate in close proximity to the root edge adjacent to newly formed unmineralised dentine - Project collagen fibrils into dentine prior to dentine mineralisation - Mineralisation then spreads into cementum - Strong union of cementodental junction Cellular: - Also known as secondary cementum - Rapidly formed - Less mineralised than primary cementum, slow mineralisation - Deposited on dentine surface near advancing root edge - Fibres extend into dentine, but unlike primary cementum the cells become entrapped to become cementocytes occupying ‘osteocytic lacunae’ Acellular or cellular mixed cementum: - Cementum whose fibres are derived from the PDL (extrinsic) and cementoblasts (intrinsic)

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Fibres are different thicknesses Fibres run in different orientations – intrinsic parallel to root, extrinsic perpendicular to root

Acellular afibrillar cementum: - Mineralised matrix but lacks collagen - Plays no role in tooth attachment - Deposited over enamel and dentine at the cementoenamel junction Clinical: - Sharpey’s fibres can be reabsorbed and re-embedded allowing tooth movement - Cement resorbs less rapidly than bone - Cement may resorb under excessive pressure or deciduous teeth - Cement may occasionally fuse to bone - Chronic inflammation may produce hypercementosis in autoimmune diseases - Cementum is exposed in periodontal disease and may be worn away exposing sensitive dentine....