Considerations for placement of mandibular buccal shelf orthodontic anchoring screw in Class III hyperdivergent and normodivergent subjects – A cone beam computed tomography study

Abstract

PurposeThe study simulated a mandibular buccal shelf (MBS) orthodontic anchoring screw insertion path and determine the effect of vertical skeletal pattern, insertion site, vertical level and insertion angle on the slope, cortical bone thickness and distance from molar root to the insertion path.Materials and methodsForty CBCT images of Class III subjects were divided equally into hyperdivergent and normodivergent groups. The slope of the MBS was measured at four different sites of insertion. Cortical bone thickness along the orthodontic anchoring screw insertion path and distance from molar root to the path were measured at different combinations of sites of insertion, vertical levels and insertion angles. Measured outcomes were compared between hypodivergent and normodivergent groups at different combinations of variables using factorial repeated ANOVA.ResultsThe cortical bone thickness and the slope of the MBS were not different between hyperdivergent and normodivergent groups. However, posterior sites had a flatter slope than that of the anterior. Higher vertical level and insertion angle resulted in thicker cortical bone and higher distance from molar root. The mesial aspect of second molar site gave a higher distance from molar root than first/second molar contact point site.ConclusionThe mesial aspect of the second molar appears to be a safe site for placement of MBS orthodontic anchoring screw as its slope was flatter and gave greater distance from molar root. Increasing vertical level or insertion angle resulted in a higher cortical bone thickness and distance from the molar root.