A clinical experimental simulation of changes in intercanine width associated with the correction of crowding: a pilot study.

The purpose of this article is was to introduce a mathematical model, investigating the anticipated changes in intercanine width associated with the resolution of crowding, using the leeway space. A linear regression formula was computed to predict the change per millimetre of 'intercanine tip space deficiency'. After digitizing 61 mandibular casts, 14 co-ordinates per model were used to fit an 'individualized optimal curve' consisting of either a hyperbolic cosine function or parabola anteriorly and a third degree polynomial function bilaterally. The total amount of tooth material was measured between the cusp tips of the canine teeth and subtracted from the available intercanine tip arch length to render the intercanine tip space deficiency. This value was then used to allocate patients to an experimental [31 subjects, 14 boys and 17 girls, mean age 11.7 years, standard deviation (SD) 1.4 years] or a control (30 subjects, 10 boys and 20 girls, mean age 11.6 years, SD 1.1 years) group. After digitally aligning the incisors and canines on the selected optimal curve, the new intercanine width was calculated. Significant differences (P < 0.001) in intercanine expansion were found between both groups (control group: mean -0.07 mm, SD 0.31 mm; experimental group: mean 1.13 mm, SD 0.51 mm) due to a clinically significant increase of approximately 0.6 mm in intercanine width (y) per millimetre of calculated intercanine tip space deficiency (x), leading to the following regression formula: y = 0.09 + 0.52x.