Modified A Line: A New Guide To Position Maxillary Central Incisor

Introduction - The aim of the study is to identify the ideal position of maxillary central incisor as defined by soft tissue thickness of the upper lip, using modified A-line. Materials and methods-30 standardized lateral cephalograms of adult orthodontically treated patients were studied. Patients with esthetically pleasing profile, competent lips, average growth pattern, ANB range in 2-4º and Angle’s class I molar relationship were selected. Cephalometric landmarks were located and U1 position with respect to modified A line, A-Pog line, N-Pog line and SN plane was studied. Results-The mean value of U1 to modified A- line is -0.5mm. The observed mean values for U1 to A-Pog, U1 to N-Pog and U1 to SN plane are 5.98mm, 6.98mm and 103.78º respectively. Conclusion-The modified A- line, based on horizontal plane (HP) and soft tissue thickness of the upper lip at point A can be used as an objective cephalometric tool for positioning maxillary central incisor.