Bone and cortical bone characteristics of mandibular retromolar trigone and anterior ramus region for miniscrew insertion in adults

Background: to date, no quantitative and qualitative assessment of the skeletal characteristics of MRTARR has been performed for miniscrew insertion. The aim of this study was to evaluate bone depth, cortical bone thickness and vestibulo-lingual bone dimension of mandibular retromolar trigone, an anatomical area positioned distally to the second mandibular molar, recently documented in literature as a strategic insertion site for orthodontic miniscrews. Methods: the sample included cBct records of 60 adult subjects (mean age 32.8 ± 8.2) retrospectively evaluated, including 30 males (mean age 33,4 ± 8.6) and 30 females (31,7 ± 9,1) selected from the digital archive of a private practice. the cbct exams were preselected if the examined subjects fulfilled the following selection criteria: caucasian subjects, age between 20 and 45y.o., absence of: periodontal disease, metallic restorations in the first and second permanent mandibular premolars and molars, missing teeth except for third molar, genetic syndromes, craniofacial dysmorphisms, facial trauma, and previous orthognathic surgery treatment. All cbct examinations were performed with i-cat cbct scanner (imaging Sciences international, Hatfield, Pa). each exam was converted into DicoM format and processed with Osirix Medical imaging software. The following procedure was used in order to obtain proper view sections of MRTARR for quantitative and qualitative bone characteristics evalu- ation. on reproducible sagittal scan views, bone depth and cortical bone thickness were evaluated on specific lines parallel and 45° angulated to the occlusal plane and at 3 and at 6mm dislocated from it. Vestibo-lingual bone dimension was computed in 4 different cross section scans and at 3 different level of depth (0, 6 and 11mm). Results: all the considered insertion sites showed on aver- age more than 10mm of bone depth. Significant differences (p<.05) were found comparing bone depth in cross-sectional scans at different inclinations (parallel vs 45° oriented com- pared to the occlusal plane). this finding suggests that the insertion with a parallel disposition to the occlusal plane is potentially safer compared with a 45° insertion inclination modality. No significant difference of bone depth was found comparing cross sectional scans with the same orientation (par- allel or 45° inclined) but at a different dislocation (3 vs 6mm) from the occlusal plane. Vestibulo-lingual bone dimension evaluation showed adequate values for miniscrew insertion. coNclUSioNS: Mrtarr can be successfully used as a miniscrew insertion site for different clinical appli- cations. retromolar trigone and anterior ramus region showed enough bone quantity and adequate bone quality for safe mini-screw insertion in adults. Miniscrew insertion with a parallel orientation to the occlusal plane offers increased bone depth compared to the 45° insertion orienta- tion. Vestibo-lingual bone dimension showed a significant reduction in the posterior regions. Considering the average cortical bone thickness, pre-drilling is always recommended before screw insertion.