Primary stability of dental implants placed in low-density polyurethane blocks: Undersized osteotomy versus...

Primary stability is a determinant of early implant success and becomes critical in low-density bone, where reduced trabecular support may increase micromotion risk. Undersized osteotomy and osseodensification are two commonly discussed site-preparation strategies aimed at improving initial stability through different biomechanical mechanisms.

An analytical experimental in vitro study was performed using 76 cylindrical implants (4.0×10mm) (n=38 per group) placed in type IV polyurethane blocks with a dense cortical shell. Group OS underwent an undersized osteotomy drilling sequence, while Group OD underwent osseodensification using Densah® burs operated in counterclockwise rotation. In Group OD, the final osteotomy diameter was intentionally overprepared by 0.3mm (4.3mm) relative to the implant diameter. Maximum insertion torque (Ncm) was recorded during placement. Primary stability was measured as implant stability quotient (ISQ) using the Penguin® resonance frequency analysis device (two perpendicular readings per implant; mean value used). Between-group comparisons were performed using Student's t-test for independent samples (α=0.05).

Group OS showed higher mean insertion torque than Group OD (30.66±1.71 vs 26.58±2.63 Ncm; p<0.0001). Group OD showed higher mean ISQ than Group OS (56.80±2.90 vs 52.92±3.57; p=0.00000227).

Undersized osteotomy increased insertion torque, consistent with higher rotational resistance during insertion, whereas osseodensification increased ISQ, suggesting higher construct stiffness. Both protocols may be clinically useful in low-density bone depending on the primary objective (torque-driven mechanical engagement vs RFA-derived stiffness).