Tomographic analysis of the anatomical proportion between buccal cusps heights and marginal ridges depths of maxillary premolars for vertical bracket positioning

Abstract

ABSTRACT Objective There are several protocols for vertical positioning of brackets during bonding suggested in the literature; however, it is observed that even with a strict bonding protocol, the marginal ridges of the posterior teeth, mainly premolars, do not coincide at the end of levelling phase. The purpose of this retrospective study was to analyse whether there is an anatomical proportion between the height of the buccal cusp and the depth of the marginal ridges in the upper premolars using the point of greatest convexity on the buccal surface as a reference. Methods 40 CBCT scans were analysed using a 3D software. After the demarcation of 3 points of interest, linear measurements were recorded and compared on all upper premolars separately, through linear regression analysis. Results Although there was a tendency for a positive correlation between the recorded measurements, there was a high level of dispersion between points, and a high confidence interval between maximum and minimum values. The linear regression coefficients on teeth 14, 15, 24 and 25 were, respectively: 0.6527(0.508–0.797); 0.7426(0.521–0.964); 0.6205(0.436–0.805) e 0.7558(0.562–0.949). Conclusions The great level of variations, and the absence of an anatomical proportion makes clear the need for individualization of bracket bonding heights in upper premolars for a coincidence of marginal ridges at the end of the orthodontic levelling phase, and suggests that the use of a predetermined value on the buccal faces of premolars for brackets bonding it is not an accurate indicator of the levelling of marginal ridges.