The mean gray value of each rescaled ROI was measured on the three orthogonal planes: axial, coronal, and sagittal, totaling three ROIs per implant site. The average of the rescaled gray values for the three ROIs was computed for each implant site.

Data were analyzed by descriptive and inferential statistics using the software XLSTAT version 2018 (Addinsoft SARL, New York, USA), and a two-tailed significance level of 0.05 was adopted. Spearman correlation coefficients were used to test the association among assessment methods of bone quality (intra-surgical tactile evaluation, CT visual assessment, mean gray values) and primary stability (insertion torque). One-way ANOVA followed by Tukey HSD was used to test the variation of mean gray values (average of ROIs) as a function of arch (maxilla, mandible), dental region (premolar, molar), insertion torque (< 15 N cm, 15 to 35 N cm, > 35 N cm), and bone types (1, 2, 3, 4) as classified by CT visual assessment and by intra-surgical tactile evaluation.