CBCT Evaluation of Cortical Bone Thickness in the Nasal Floor and Lateral Wall: Considerations for Implant Anchorage—A Retrospective Multicentre Study

<b>Background/Objectives:</b> Primary implant stability depends on cortical bone thickness. While alveolar cortices are well studied, little is known about the nasal floor and lateral wall, which may provide alternative anchorage in atrophic maxillae. <b>Methods:</b> This retrospective, multicenter study analyzed 149 anonymized CBCT scans (83 women, 66 men; mean age 52.6 ± 13.5 years). Cortical thickness was measured at six reproducible anatomical points (A-F) defined by chosen landmarks. Measurements were taken on coronal planes aligned with implant anchorage point of interest (POI) using gray-value thresholding. Intra- and inter-observer reliability was excellent (ICC = 0.89 and 0.84). Post hoc power analysis confirmed >80% power to detect 0.15 mm differences. Non-parametric tests and mixed-effects models assessed variability and risk factors. <b>Results:</b> Thickness varied significantly by site (<i>p</i> < 0.001). The thickest cortices were at point A (median 1.36 mm, IQR 1.10-1.61) and point F (1.35 mm, 1.14-1.57), the thinnest at point B (1.15 mm, 0.96-1.32). Cortical thickness was slightly lower in men (<i>p</i> = 0.048) and decreased with age (-0.005 mm/year, <i>p</i> = 0.010). No significant associations were detected with smoking, diabetes, or thyroid disease. <b>Conclusions:</b> The anterior nasal spine and lateral wall near the sinus junction provide the greatest cortical thickness, supporting their use as potential implant anchorage sites in atrophic maxillae.