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A cementicle is a small, spherical or ovoid calcified mass embedded within or attached to the cementum layer on the root surface of a tooth, or lying free within the periodontal ligament. They tend to occur in elderly individuals.〔〔 There are 3 types:〔〔 * Free cementicle - not attached to cementum * Attached (sessile) cementicle - attached to the cementum surface〔 (also termed exocementosis)〔 * Embedded (interstitial) cementicle - with advancing age the cementum thickens, and the cementicle may become encorporated into the cementum layer〔 They may be visible on a radiograph (x-ray).〔 They may appear singly or in groups,〔 and are most commonly found at the tip of the root.〔 Their size is variable,〔 but generally they are small (about 0.2 mm - 0.3 mm in diameter).〔 Cementicles are usually acellular, and may contain either fibrillar or afibrillar cementum, or a mixture of both.〔 Cementicles are the result of dystrophic calcification,〔 but the reason why this takes place is unclear.〔 Cementicles are thought to form when calcification occurs around a nidus, a precipitating center. Around this nidus they slowly enlarge by further deposition of calcium salts.〔 Examples of how cementicles are thought to form include: * Calcification due to degenerative changes in the epithelial cell rests of Malassez〔 * Calcification of thrombosed (blocked) capillaries in the periodontal ligament〔 (i.e. a phlebolith)〔 * Microtrauma to Sharpey's fibres〔 causes small spicules of cementum or alveolar bone to splinter into the periodontal membrane Some do not consider these as true cementicles.〔 ==References== 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Cementicle」の詳細全文を読む スポンサード リンク
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