Archform comparisons between skeletal class II and III malocclusions

Abstract

The purpose of this cross-sectional research was to explore the relationship of the mandibular dental and basal bone archforms between severe Skeletal Class II (SC2) and Skeletal Class III (SC3) malocclusions. We also compared intercanine and intermolar widths in these two malocclusion types. Thirty-three virtual pretreatment mandibular models (Skeletal Class III group) and Thirty-five Skeletal Class II group pretreatment models were created with a laser scanning system. FA (the midpoint of the facial axis of the clinical crown)and WALA points (the most prominent point on the soft-tissue ridge)were employed to produce dental and basal bone archforms, respectively. Gained scatter diagrams of the samples were processed by nonlinear regression analysis via SPSS 17.0. The mandibular dental and basal bone intercanine and intermolar widths were significantly greater in the Skeletal Class III group compared to the Skeletal Class II group. In both groups, a moderate correlation existed between dental and basal bone arch widths in the canine region, and a high correlation existed between dental and basal bone arch widths in the molar region. The coefficient of correlation of the Skeletal Class III group was greater than the Skeletal Class II group. Fourth degree, even order power functions were used as best-fit functions to fit the scatter plots. The radius of curvature was larger in Skeletal Class III malocclusions compared to Skeletal Class II malocclusions (rWALA3>rWALA2>rFA3>rFA2). In conclusion, mandibular dental and basal intercanine and intermolar widths were significantly different between the two groups. Compared with Skeletal Class II subjects, the mandibular archform was more flat for Skeletal Class III subjects.

Figure 1. A. The final WALA curve-fitting of Class II malocclusion:

a. WALA scatter diagrams of SC2 samples were processed by nonlinear regression analysis via SPSS 17.0. b. The fourth degree even order power function was utilized to analyze the curve fitting to represent the basal bone archform curves. c. The final fitting curve of WALA and the curve equation for WALA is derived: . B. The final FA curve-fitting of Class II malocclusion: a. FA scatter diagrams of SC2 samples were processed by nonlinear regression analysis via SPSS 17.0. b. The fourth degree even order power function was utilized to analyze the curve fitting to represent the dental archform curves. c. The final fitting curve of FA and the curve equation for FA is derived: . C. The final WALA curve-fitting of Class III malocclusion. The curve equation for WALA is derived: . D. The final FA curve-fitting of Class III malocclusion. The curve equation for FA is derived: .

Figure 2

A. The FA curves' comparison between skeletal Class II and III. B. The WALA curves' comparison between skeletal Class II and III. C. The FA and WALA fitting curves of SC2 group. D. The FA and WALA fitting curves of SC3 group.