Abstract
PURPOSE: The objective of this study was to investigate the primary stability of zirconia implants using varying drilling protocols, with a focus on the impact of thread cutting on insertion torque in both mixed (D2/D3) and soft (D4) bone types. The study aimed to evaluate whether reducing thread cutting could increase insertion torque and consequently improve primary stability. METHODS: Four drilling protocols were developed, each varying in the degree of thread cutting: no thread cut, one-third thread cut, two-thirds thread cut, and full thread cut. Implants were placed into fresh porcine hip and tibia bones simulating D2/D3 and D4 bone. The protocols followed each implant system's manufacturer recommendations. Insertion torque was measured using a torque indicator, and statistical analysis was conducted with the Mann-Whitney U test, with p < 0.05 considered statistically significant. RESULTS: Significant differences in primary stability were observed between implant systems and drilling protocols, particularly in D4 bone. Three of the four implant systems showed improved primary stability in D4 bone when the thread cut was reduced (p < 0.05). One system achieved the recommended insertion torque with a full thread cut. In contrast, in D2/D3 bone, all implant systems required a full thread cut to remain within the manufacturer's torque guidelines. CONCLUSIONS: Zirconia implant systems exhibit substantial variability in primary stability based on the selected drilling protocol and bone quality. Reducing thread cutting demonstrated improved stability in soft bone. However, excessive torque should be avoided to prevent mechanical failure, especially in systems with lower fracture resistance.