Correlation between drilling torque and cone-beam CT gray values: an exploratory clinical study on bone density assessment using a measurement drill

Accurate assessment of bone density at the implant site is essential for implant planning. Several studies have supported the use of gray values (GV) derived from cone-beam computed tomography (CBCT) as a preoperative assessment parameter. In this clinical study, we aimed to verify the correlation between drilling torque values (DTV) ​​and GV and to assess the effectiveness of a novel method for evaluating cancellous bone density. Data from 10 patients who underwent preoperative CBCT for implant planning were analyzed. The region of interest (ROI) was set to a square area of cancellous bone located 4 mm below the cortical bone at the planned implant insertion site. The GV of this area was calculated. During implant surgery, a 2-mm diameter bone socket was prepared. After removing the cortical bone with a pilot drill, the DTV of the ROI was measured using a dedicated bone density measurement drill. Correlations among GV, DTV, and the implant stability quotient (ISQ) were examined. A significant correlation was observed between GV and DTV (r = 0.82, p = 0.0010), whereas no significant correlation was found between DTV and the ISQ. This study demonstrated a correlation between DTV and GV in cancellous bone, suggesting that intraoperative bone mineral density assessment via DTV measurement may be an effective method for guiding implant treatment. Japan Registry of Clinical Trials (jRCT), jRCTs062240101. Registered on 26 December 2024.