A method for defining targets in contemporary incisor inclination correction

Abstract

Different craniofacial properties require individual targets in incisor inclination. These requirements are mostly scheduled on the basis of cephalometric diagnosis, but, however, performed using straightwire appliances, which refer to third-order angles and not to cephalometric data. The objective of this study was to analyze the relationship between incisor third-order angles, incisor inclination, and skeletal craniofacial findings in untreated ideal occlusion subjects with natural dentoalveolar compensation of skeletal variation, in order to link the field of cephalometric assessment of incisor inclination with that of contemporary orthodontic incisor inclination correction. This study utilized lateral cephalograms and corresponding dental casts of 69 untreated Caucasians (21 males and 48 females between 12 and 35 years of age) with neutral (Angle Class I) molar and canine relationships and an incisor relationship that was sagittaly and vertically considered as ideal by three orthodontists (i.e. well supported by the antagonistic teeth and without the need for either deep or open bite correction). Upper (U1) and lower (L1) axial incisor inclinations were assessed with reference to the cephalometric lines NA and NL, and NB and ML, respectively. Sagittal and vertical skeletal relationships were classified using SNA (SNB) and NSL-ML (NSL-NL) angles. Third-order angles (U1TA and L1TA) were derived from direct dental cast measurements using an incisor inclination-recording appliance. The relationships between cephalometric and third-order measurements evaluated by calculating Pearson product-moment correlation coefficients (a = 0.05) showed strong correlations between cephalometric axial inclination data (U1NA/deg, L1NB/deg, U1NA/mm, L1NB/mm, U1NL, and L1ML) and sagittal-skeletal data, but no significant relationship between skeletal-vertical findings and incisor inclination. The mean U1TA was 4.9 (standard deviation [SD] 5.85) and the mean L1TA -3.0 (SD 6.9) degrees. Regression analyses were used for axial inclination (ANB angle designated as the independent variable) and for third-order data (U1NA, L1NB, U1NL, and L1ML designated as independent variables). Based on the correlations found in this study, a novel method for defining targets in upper and lower incisor third-order correction according to natural standards is presented. As a consequence, third-order movements can be adapted to cephalometric diagnosis with enhanced accuracy.