Rudolph D J, Dominguez P D, Ahn K, Thinh T
Department of Orthodontics, UCLA School of Dentistry, CHS 90024, USA.
Angle Orthod. 1998 Apr;68(2):133-8; discussion 139-40. doi: 10.1043/0003-3219(1998)068<0133:TUOTTI>2.3.CO;2.
Intermaxillary tooth-size discrepancies can be assessed using a diagnostic setup or predicted using a mathematical formula, such as the Bolton analysis. However, variations in tooth thickness may produce inaccuracies in the Bolton analysis ratio. To date, no method for incorporating tooth thickness into discrepancy prediction has been proposed. The purpose of this study was to design and test a new method of predicting anterior tooth-size discrepancy that takes into account tooth thickness and width. Forty-four positioner setup models were set to ideal overbite (2.5 mm) and occlusion (Class I canine relationship). Interproximal gaps between the maxillary or mandibular central incisors were allowed in order to optimize tip and torque. The mesiodistal width of all anterior teeth and the labiolingual thickness of the maxillary incisors were measured on these idealized setups to the nearest 0.1 mm. Actual intermaxillary anterior ratios were then calculated. A new method of prediction was developed by assuming a linear relationship between tooth thickness and ideal intermaxillary ratio. Errors in Bolton's method were compared with the new method. The results showed wide variations in mesiodistal tooth widths, tooth thicknesses, and intermaxillary anterior ratios in orthodontically treated patients. The correlation coefficient between the intermaxillary ratio and tooth thickness was r = 0.68 when tooth thickness was < 2.75 mm, and r = 0.28 when tooth thickness was > or = 2.75 mm. The mean absolute errors in predicting the actual intermaxillary ideal ratio was 1.29 +/- 0.81 for Bolton's ratio and 0.84 +/- 0.46 for the new prediction formula. These new formulas were better than Bolton's ratio in predicting tooth-size discrepancies (p = 0.003). Tooth thickness combined with mesiodistal width may be useful in predicting intermaxillary tooth-size discrepancies.
上下颌牙齿大小差异可通过诊断性排牙或使用数学公式（如Bolton分析）进行预测。然而，牙齿厚度的变化可能会导致Bolton分析比率出现误差。迄今为止，尚未提出将牙齿厚度纳入差异预测的方法。本研究的目的是设计并测试一种新的预测前牙大小差异的方法，该方法要考虑到牙齿的厚度和宽度。44个定位器排牙模型被设置为理想的覆合（2.5毫米）和咬合关系（I类尖牙关系）。上颌或下颌中切牙之间留出邻间隙，以优化牙尖和转矩。在这些理想化模型上测量所有前牙的近远中宽度以及上颌切牙的唇舌厚度，精确到最接近的0.1毫米。然后计算实际的上下颌前牙比率。通过假设牙齿厚度与理想上下颌比率之间存在线性关系，开发了一种新的预测方法。将Bolton方法的误差与新方法进行比较。结果显示，在接受正畸治疗的患者中，前牙的近远中宽度、牙齿厚度和上下颌前牙比率存在很大差异。当牙齿厚度<2.75毫米时，上下颌比率与牙齿厚度之间的相关系数r = 0.68；当牙齿厚度≥2.75毫米时，r = 0.28。预测实际上下颌理想比率时，Bolton比率的平均绝对误差为1.29±0.81，新预测公式的平均绝对误差为0.84±0.46。在预测牙齿大小差异方面，这些新公式优于Bolton比率（p = 0.003）。牙齿厚度与近远中宽度相结合可能有助于预测上下颌牙齿大小差异。
