Effect of Altered Cervical Thread Pitch on the Primary Stability of Dental Implants

Background: The macrogeometry and shape of dental implants strongly influence primary stability, which may at times result in excessively high insertion torque. This in vitro study aimed to evaluate whether increasing coronal thread density could reduce insertion torque without compromising primary stability. Methods: Two conical implants with identical macrogeometry and surface characteristics (Ø 4.2 × 11.5 mm) differed only in the thread pitch of the coronal 3 mm: a modified version (27% more coronal threads; Group 1) and a standard, commercially available version (Group 2). Thirty implants of each design were inserted into high-density (D1; 40 PCF; pounds per cubic foot) and low-density (D3; 20 PCF) polyurethane blocks (n = 120). Insertion torque (IT) and implant stability quotient (ISQ, measured by resonance frequency analysis) were recorded. Group comparisons used the Kruskal-Wallis test, and a generalized linear model (GLM) assessed the independent effects of IT and design on ISQ in D1 bone. Results: In D1 bone, Group 2 showed higher IT (median 74.0 vs. 63.5 N·cm; p < 0.001) and ISQ (mean 79.1 vs. 77.4; p ≤ 0.030). The GLM identified IT as a negative predictor of ISQ (β = -0.267 per 1 N·cm; p < 0.001), and Group 2 was associated with higher ISQ (+3.90; p < 0.001). In D3 bone, Group 2 again exhibited higher IT (median 37.5 vs. 33.0 N·cm; p < 0.001), while ISQ values were similar between designs (all p > 0.35). Conclusions: Increasing coronal thread density lowers insertion torque without reducing stability in softer bone and maintains sufficient ISQ for immediate loading in dense bone, making the design advantageous for varied bone qualities.