CBCT comparison of buccal shelf bone thickness in adult Dravidian population at various sites, depths and angulation - A retrospective study.

INTRODUCTION: It is important to understand the variations in the bone thickness of the buccal shelf region among different ethnic groups, as these variations will influence the placement and success of the buccal shelf mini-screw. OBJECTIVES: The primary objective was to analyse the total buccal bone and cortical bone thickness of the mandibular buccal shelf region (MBS) at various depths, mesiodistal positions and angulations in Dravidian population and to find the best site for insertion of buccal shelf mini-implant. MATERIAL AND METHODS: This was a retrospective study done on 30 cone-beam computed tomography samples collected from 30 subjects, aged 16 to 25 years and of Dravidian origin, who reported for orthodontic treatment. The total bone and cortical bone thicknesses of the buccal shelf regions were evaluated in relation to the Disto-Buccal cusp of 1st Molar (DB1M), Mesio-Buccal cusp of 1st Molar (MB1M), and Disto-Buccal cusp of 2nd Molar (DB2M) at the depths of 4mm, 8mm and 12mm from cemento-enamel junction (CEJ). The total bone thickness and the clearance from the root and cortical bone thickness were assessed at angulations of 30, 45 and 60 degrees from 5mm below the root apex. ANOVA and Post Hoc tests were done to compare the bone thickness measurements. Kappa statistics was done to assess the intraobserver reliability. Pearson's correlation test was done to find the correlation between growth pattern and thickness of the bone. RESULTS: The mean age group of the included sample was 20.5 years. Maximum total bone thickness was observed at a depth of 8mm in relation to the MB2M (6.41+/-0.29mm) and 12mm in relation to the DB2M 6.56+/-0.28mm and the P value was 0.000. Maximum bone thickness was present in the DB2M at 30 degrees followed by DB2M 45 degrees of 11.42+/-0.35mm and 10.89+/-0.3mm and the P value was 0.000. The maximum clearance from the root was observed at 30 degrees and 45 degrees in the DB2M with 5.35+/-0.2mm and 5.18+/-0.27mm, the P value was 0.014 when comparing angulation 30 and 45 degrees . The DB2M had a cortical bone thickness of 2.97+/-0.15mm and 2.8+/-0.2mm at 45 degrees and 60 degrees and was statistically significant. CONCLUSIONS: The insertion site with optimal bone quantity was observed in relation to the buccal aspect of distobuccal cusp of 2nd molar at depth of 8mm or greater with a preferred angulation of 30-45 degrees to have adequate clearance from the molar tooth roots and to penetrate a region of cortical bone of minimum 2mm.