Department of Pediatric Dentistry, College of Dentistry, University of Tennessee, 875 Union Avenue, Memphis, TN 38163, United States.
Arch Oral Biol. 2011 Jul;56(7):687-94. doi: 10.1016/j.archoralbio.2010.12.005. Epub 2011 Jan 17.
Tooth formation normally progresses symmetrically between sides; the goal in this study was to test the clinical impression that left-right asymmetry in tooth formation is elevated in children with simple hypodontia.
Data from panoramic X-rays of American white children (5-14 years of age) with simple hypodontia (n=158) were compared to a comparable group from the same practises with all teeth present (n=206). Children with hypodontia were otherwise phenotypically normal, with no cleft or recognized syndrome. Crown-root formation of each tooth (ignoring third molars) was scored using an 11-grade scheme. Analysis relied on chi-square goodness-of-fit tests and odds ratios.
Hypodontia typically occurs unilaterally; it is more common in girls than boys; and it most frequently affects second premolars (omitting third molars). No evidence of a side preference was found as regards absence of the tooth or tooth formation. Tooth formation was decidedly more frequently asymmetric in those with hypodontia, though again the distribution by side was random in the sample. Summed over all tooth types, asymmetric formation occurred in 18.6% of cases with hypodontia compared to 11.9% in controls, and this is significant by chi-square (P=0.03), with an odds ratio of 1.43 (CL: 1.02, 2.04). All tooth types exhibit elevated developmental asymmetry in the hypodontic sample despite only one or a few teeth being agenic.
Increased asymmetry suggests a breakdown in the rigour of developmental timing in cases with simple hypodontia. In concert with increased frequencies of other growth issues in such cases, such as side differences in size and morphology, hypodontia is best viewed as a symptom of an anatomically broad relaxation of developmental canalization between homologous structures, not an isolated dental feature.
牙齿的正常发育通常是双侧对称的；本研究的目的是检验一种临床印象，即单侧简单缺牙儿童的牙齿发育左右不对称程度较高。
比较了美国白人儿童（5-14 岁）单侧简单缺牙（n=158）的全景 X 光片数据和来自同一诊所的所有牙齿正常的可比组（n=206）。除了缺牙外，缺牙儿童的表型均正常，无裂隙或公认的综合征。使用 11 级评分方案对每个牙齿（忽略第三磨牙）的牙冠-牙根形成进行评分。分析依赖于卡方拟合优度检验和优势比。
缺牙通常发生在单侧；女性多于男性；最常影响第二前磨牙（忽略第三磨牙）。在牙齿缺失或牙齿发育方面，没有发现侧偏的证据。尽管在样本中，牙齿缺失的分布是随机的，但缺牙者的牙齿发育明显更不对称。在所有牙齿类型中，缺牙者的不对称形成发生率为 18.6%，对照组为 11.9%，这具有统计学意义（卡方检验，P=0.03），优势比为 1.43（置信区间：1.02，2.04）。尽管只有一颗或几颗牙齿缺失，但在缺牙样本中，所有牙齿类型都表现出发育不对称性增加。
增加的不对称性表明，在单侧简单缺牙的情况下，发育时间的严格性出现了崩溃。与这种情况下其他生长问题的频率增加（如大小和形态的侧差异）一致，缺牙最好被视为同源结构之间发育管道化的解剖广泛放松的症状，而不是孤立的牙齿特征。
