牙齿发育异常分类

这是一个关于牙齿发育异常分类的思维导图，分为牙缺组（牙齿发育不全 tooth agenesis）与牙多生组（额外牙 supernumerary teeth）两大类别。牙缺组包含无牙症（Anodontia）与少牙症（Hypodontia /oligodontia）。无牙症指全部牙齿完全缺失，属于罕见情况，需要注意部分缺牙这一叫法并不准确。少牙症存在一定流行病学特点，当上颌两颗牙齿缺失时，需要重点监测上颌尖牙异位萌出；病因多为多基因家族遗传，可伴发外胚层发育不良与唐氏综合征；临床管理需要儿科牙科、修复科以及正畸科组成多学科团队协同处理。多生牙组又叫做额外牙，流行病学显示乳牙期患病率 0.8%，恒牙期为 2%，男性发病多于女性，在上颌前牙区最为多见，还和颅锁骨发育不全、唇腭裂存在关联，半数乳牙期多生牙后续会发展为恒牙期多生牙。发病理论认为起源于牙板的突起，属于第三牙列。多生牙可依据外形、生长位置、生长方向进一步细分。它对牙列会产生不同影响，如果没有不良症状只需定期拍片随访；造成牙列拥挤时要拔除形态较差的牙齿；出现牙齿移位扭转，拔除后还要正畸固定，复发风险偏高；另外多生牙阻滞也是恒牙埋伏阻生最常见诱因。无论正在学习口腔医学的在校学生还是从事儿童牙科的临床医师，都可以借助这份内容梳理牙齿数目发育异常的相关知识点。

牙齿发育异常分类

• Hypodontia group (tooth agenesis)
  • Anodontia
    • Definition: Complete absence of all teeth. Rare.
    • Note: Partial anodontia is a misnomer.
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  • Hypodontia (oligodontia)
    • Epidemiology
    • Feature: Monitor maxillary canine ectopic eruption when upper 2 missing
    • Aetiology: Polygenic familial inheritance; linked with ectodermal dysplasia & Down s
    • Management
      • Care: Multidisciplinary team (paediatric dentistry, restorative, orthodontics)
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• Hyperdontia group (supernumerary teeth)
  • Alias: Supernumerary teeth
  • Epidemiology
    • Primary dentition:0.8%; Secondary dentition:2%. M > F
    • Most common: premaxillary region; associated with cleidocranial dysostosis & CLP
    • 50% of primary supernumeraries develop permanent supernumeraries
  • Aetiology theories: Offshoot of dental lamina; third dentition
  • Classification (Table 3.2)
    • By shape: Conical (peg-shaped), Tuberculate (barrel-shaped), Supplemental
    • By position: Mesiodens, Distomolar, Paramolar
    • By orientation: upright, inverted, etc.
  • Effects on dentition & Rx
    • No adverse effect: periodic radiographic surveillance; extract if erupted
    • Crowding: extract tooth with poor crown/root form or displaced apex
    • Displacement / rotation: remove supernumerary + fixed appliance; high relapse
    • Failure of eruption (the commonest cause for permanent tooth impaction)
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