CHARACTERISTICS OF THE BUCCAL SHELF FOR THE INSTALLATION OF MINISCREWS IN CHILEAN INDIVIDUALS AGED 15-45 YEARS: A DESCRIPTIVE STUDY

Introduction: Orthodontic mini-screws allow complex therapeutic objectives to be achieved conservatively, so their use in clinical practice has increased considerably in recent years. The most important aspect to consider is the stability when installing it, related to the thickness of the cortical bone in the area where it is implanted. In the mandible, it has been seen that the area with the highest success rate is that of the buccal shelf (BS). Several studies have proposed variation in its location and bone thickness according to the characteristics of each patient. Objective: To describe the characteristics of the mandibular vestibular balcony (Buccal Shelf or BS) through the study of CBCT in individuals between 15-45 years of age in the Metropolitan Region of Santiago de Chile. Materials and Methods: Full-head CBCT images of 159 patients aged 15 to 45 years were analyzed, categorized into 3 groups classified according to age between 15-24 years; 25-34 years; 35-45 years. The patients’ facial pattern was measured based on Steiner’s S-N-Go-Gn angle, where it was classified into three ranges; less than 30 degrees, between 30 and 34 degrees, greater than 34 degrees and were analyzed with BlueSkyPlan software4. For the statistical tests, the normality in the distribution of the data was first analyzed through the Shapiro-Wilk test. For the comparison between variables, the Kruskal Wallis test was used with Bonferroni’s multiple comparisons test. The Horos v. 3. 3. 5 program was used for measurements of alveolar cortical thickness and the angle formed by the cortical contour of the BS in relation to the axial axis of the respective molar. All images were obtained with a KODAK 9500 CT scanner and stored in DICOM files. Results: The distance from the cortical to the tooth root increases from mesial to distal and as depth increases. When assessing the distance from the cortical to the inferior alveolar nerve, it also increases from mesial to distal, but decreases as the depth of the site increases. The greatest distance is from the vestibular cortical of the distal site of the second mandibular molar at 7mm depth to the root of the same tooth and, also, the vestibular cortical of the distal site of the second mandibular molar at 5 mm depth to the alveolar nerve. Conclusion: From mesial to distal in this area, the slope of the vestibular balcony increases, becoming flatter; likewise, the distance to the molar root and mandibular alveolar nerve measured from the alveolar cortical also increases. This may be due to the principle of mandibular growth and physiological characteristics of the posterior mandibular area. Different facial patterns show differences in the anatomy of the vestibular balcony, mainly in the angle of the vestibular balcony, but not in the thickness of the alveolar cortical bone in this area. It is important to consider that the variations found in other studies may be due primarily to racial differences.