"CT EVALUATION OF CORTICAL BONE THICKNESS AND DENSITY FOR ORTHODONTIC MINI-IMPLANT PLACEMENT”

Introduction: There is the evidence that cortical bone thickness(CBT) and cortical bone quality(CBQ) can have a strong impact on primary stability and overall success of mini-implants. This study evaluated quantity(thickness) and quality(density) differences of cortical bone between interradicular sites to provide guidelines for mini-implant placement. Material and method: The maxilla or mandibula CT scans of 45 patients treated at the Department of Orthodontics of “Sapienza” University of Rome were selected. The selected patients were divided in two groups: adolescent group(aG)(range 12-18 years) and adult group(AG)(range19-50years). Using SimPlant software (Materialise, Leuven, Belgium),a program that allows reconstruction of 3D models and images of anatomical structures along planes and curves from data acquired with CT, the CBT and CBQ was measured at 2,4,6 and 8 mm intervals apical to the alveolar crest at each interradicular sites in both maxilla and mandible. A cube of 1mm was used to measure the density of cortical bone at each level. The CBT values were described in millimeters(mm) and CBQ values in Hounsfield units (HU). Data was evaluated using a statistical analysis software (SPSS® software (Statistical Package for Social Science, IBM Corporation, NY-USA). Quantitative data of each group was described with mean values. Considering the values of thickness and density , the T-test was used to determine the influence of different gender , age and arch on CBT and CBQ values. The significance was set at P≤.05. Correlations between thickness , density and level of measurements were tested with the Pearson correlation coefficient. The significance was set at P≤.01. Results: Considering CBT in aG the average values ranged from 1.19mm to 1.83mm; in AG the average values ranged from 1.25mm to 1.99mm. Considering CBQ in aG the average values ranged from 910.03HU to 1461.61HU; in AG the average values ranged from 777.43HU to 1327.90HU. The mandibular CBT was higher both on the vestibular(P≤.000)and lingual/palatal side(P≤.013). The mandibular CBQ was higher both on the vestibular(P≤.000)and lingual/palatal side(P≤.027). In the male CBT and CQB were higher than female both on the vestibular and lingual/palatal side with in each case an equal significance value(P≤.000). Comparing , finally, the CBT and CBQ values of aG and AG , the aG showed a higher thickness and bone density but the data was statistically significant only comparing the lingual/palatal CBT(P≤.001). Conclusion: The results of the present study demonstrated an higher CBT and CBQ values in the mandibular interradicular sites of adolescent males.