Human tooth development is a consecutive process, which includes bud stage, cap stage, bell stage and tooth root development.

人类牙齿发育是一个连续的过程，经历了蕾状期、帽状期、钟状期和牙根发育期。

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OD to 15 mm below tooth root, ie tooth zone.

从外径最外侧到齿根下15毫米，即齿区。

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After withdrawal of traction force, tooth root and periodontal tissue were gradually repaired.

停止加力后，牙根及牙周组织逐渐修复。

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In the most serious cases the enamel is worn away to such an extent that the dentine (the substance that comprises the bulk of the tooth) or even the pulp (the root) of the tooth are exposed.

BBC: NEWS | Health | Bad teeth blamed on fizzy drinks

It took 10 people to lift the sedated bear onto a make-shift operating table to have root canal done on the tooth.

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If you are removing it for prevention of tooth decay or periodontal disease such as gingivitis, which destroys the root and makes the teeth fall out then I believe it's best at night.

WSJ: How to Be a Better Flosser