Three dimensional anatomical exploration of the anterior hard palate at the level of the third ruga for the placement of mini-implants--a cone-beam CT study

The aim of this retrospective investigation was to measure vertical bone thickness on the hard palate, determine areas with adequate bone for the insertion of orthodontic mini-implants (MIs), and provide clinical guidelines for identification of those areas. Pre-treatment records of 1007 patients were reviewed by a single examiner. A total of 125 records fulfilled the inclusion criteria and were further investigated. Bone measurements were performed on cone-beam computed tomography scans, at a 90° angle to the bone surface, on 28 predetermined and standardized points on the hard palate. Bone thickness at various areas was associated to clinically identifiable areas on the hard palate by means of pre-treatment plaster models. Bone thickness ranged between 1.51 and 13.86 mm (total thickness) and 0.33 and 1.65 mm (cortical bone thickness), respectively. Bone thickness was highest in the anterior palate and decreased significantly towards more posterior areas. Plaster model analysis revealed that bone thickness was highest at the level of the third palatal ruga. The areas on the anterior palate with adequate bone thickness for successful insertion of orthodontic MI correspond to the region of the third palatal ruga. These results provide stable and clinically identifiable landmarks for the insertion of palatal MIs.