Effects of Drilling Protocol and Bone Density on the Stability of Implants According to Different Macrogeometries of the Implant Used: Results of an In Vitro Study

Purpose: To assess the effects of drilling protocol and bone density on the primary stability of implants with different macrogeometries currently used in clinical practice. Materials and Methods: This in vitro study compared the designs of two implants: Biomimetic Coral, a parallel-walled design with a slightly expanded platform and a symmetric progressive thread; and tapered Biomimetic Ocean, a reverse coronal design with an asymmetric progressive thread. The drilling alternatives were grouped according to the standard sequence for each type, plus an extra drill for hard bone, using laminated blocks with different densities. The insertion torques and implant stability quotient (ISQ) values were obtained with a surgical motor and resonance frequency analysis (RFA), respectively. Results: A total of 120 implants (n = 60 Ocean, n = 60 Coral) were inserted and analyzed without registering any deviation from the protocol. The Coral implants presented significantly higher insertion torque values (P .001), consistent with optimal osseointegration, for the standard drill, the dense bone drill, and the screw tap. Insertion torque was not affected by the drilling sequence (P = .124), and the effect of interaction between the implant design and drilling sequence was not significant (P = .940). Statistically significant differences were observed in insertion torque values due to the type of implant but not due to the bone density. The ISQ values were significantly higher (P .001) for the Coral design. In both the Ocean and Coral implants, ISQ was affected by the drilling sequence (P .001), as the ISQ values were higher in the standard sequence with screw tap drilling than in the standard sequence with a dense bone drill. A positive correlation was found between the insertion torque and ISQ values. Conclusion: The macrogeometry of the implant and the drilling sequence have a significant effect on both primary stability values (ISQ and insertion torque). The values for the Coral implant were statistically higher but still within the range required to achieve proper osseointegration. These results support the drilling sequence recommended by the manufacturer for this type of implant, using larger-diameter drills and screw taps in sites with harder or cortical bone. Keywords: dental implants, drilling sequence, implant stability quotient, insertion torque, macrogeometry, screw tap