a Graduate student, Department of Orthodontics, Hospital Sant Joan de Déu, University of Barcelona, Barcelona, Spain.
Angle Orthod. 2014 Jan;84(1):24-9. doi: 10.2319/030513-183.1. Epub 2013 Jul 24.
To test the null hypotheses that children with unilateral agenesis of the mandibular second premolar (MnP2) do not show (1) greater distal angulation of the unerupted antimere and (2) delayed tooth formation compared with children without agenesis.
Panoramic radiographs of 38 patients with unilateral aplasia of MnP2 were retrospectively examined and compared to a non-agenesic control group of 82 patients. Ages ranged from 8 to 15 years. Contralateral mandibular deciduous second molars were present for all participants. Each unerupted MnP2 was traced, and its developmental stage and angulation were recorded (measured with the distal angle and the premolar-molar angle). Dental age was evaluated using the Haavikko method. Student's t-test was performed to identify significant differences between the compared groups. The significance level for statistical testing was set at P < .05.
The results indicated a 9.5° decrease in the distal angle and a 13.2° increase in the premolar-molar angle for the unerupted MnP2 in the agenesis sample. This was a highly statistically significant difference (P < .001 and P < .0001, respectively) compared with the MnP2 inclinations in the control sample. The delay in dental age was significantly greater in patients with agenesis (2.1 years) compared with the delay in the control group (1.5 years) (P < .001).
Both null hypotheses are rejected. The results of this study statistically support the hypothesis that aplasia of MnP2, distally displaced MnP2s, and delayed tooth formation are part of a genetically related pattern of dental anomalies.
检验以下两个零假设，即单侧下颌第二前磨牙（MnP2）缺失的儿童（1）未萌出对侧磨牙的远中倾斜角度更大，以及（2）牙形成时间延迟，与无缺失的儿童相比并无差异。
回顾性分析了 38 例单侧 MnP2 发育不全患者的全景片，并与 82 例非缺失对照组患者进行比较。患者年龄 8 至 15 岁，所有患者的对侧下颌乳磨牙均存在。对所有参与者的未萌出 MnP2 进行追踪，并记录其发育阶段和倾斜角度（通过远中角和前磨牙-磨牙角测量）。使用 Haavikko 方法评估牙龄。采用 Student's t 检验比较两组间的差异。统计检验的显著性水平设定为 P <.05。
结果表明，缺失组中未萌出的 MnP2 的远中角减小了 9.5°，前磨牙-磨牙角增大了 13.2°。与对照组 MnP2 的倾斜度相比，这具有高度统计学意义的差异（P <.001 和 P <.0001）。与对照组相比，缺失组患者的牙龄延迟显著更大（2.1 年）（P <.001）。
两个零假设均被拒绝。本研究的结果从统计学上支持了以下假说，即 MnP2 缺失、远中移位的 MnP2 和牙形成时间延迟是与遗传相关的牙齿异常模式的一部分。
