THE USE OF TOOTH THICKNESS IN PREDICTING INTERMAXILLARY TOOTH-SIZE DISCREPANCIES

Intermaxillary tooth-size discrepancies can be assessed using a diagno stic setup or predicted using a mathematical formula, such as the Bolt on analysis. However, variations in tooth thickness may produce inaccu racies in the Bolton analysis ratio. To date, no method for incorporat ing tooth thickness into discrepancy prediction has been proposed. The purpose of this study was to design and test a new method of predicti ng anterior tooth-size discrepancy that takes into account tooth thick ness and width. Forty-four positioner setup models were set to ideal o verbite (2.5 mm) and occlusion (Class I canine relationship). Interpro ximal gaps between the maxillary or mandibular central incisors were a llowed in order to optimize tip and torque. The mesiodistal width of a il anterior teeth and the labiolingual thickness of the maxillary inci sors were measured on these idealized setups to the nearest 0.1 mm. Ac tual 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 me thod were compared with the new method. The results showed wide variat ions in mesiodistal tooth widths, tooth thicknesses, and intermaxillar y 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 th ickness was greater than or equal to 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 mesiodi stal width may be useful in predicting intermaxillary tooth-size discr epancies.