Primary and Secondary Stability of Extrashort (4-mm) Implants in the Edentulous Mandible: Preliminary Results of a Prospective Clinical Trial

Purpose: To compare the primary and secondary stability of conventional (≥ 8-mm) and extrashort (4-mm) implants in edentulous patients using different methods of assessment. Materials and Methods: Patients underwent implant surgery and were randomly allocated into two groups: test, with two conventional implants in the anterior region and two extrashort (4-mm) implants in the posterior region; and control, with two conventional (≥ 8-mm) implants in the anterior region only. Primary stability (S1–implant placement) was assessed by insertion torque, implant stability quotient (ISQ, Osstell), and damping capacity (PTV, Periotest), while secondary stability (S2²¹—21 days after S1; and S2^clip—at prosthetic loading, ± 3 months after S1) was evaluated by ISQ and PTV. The statistical significance level was set at P < .05. Results: Fifty conventional implants and 24 extrashort implants were placed in 25 patients. The overall survival rate was 97.3%. There was no statistically significant difference between the insertion torque of conventional and extrashort implants (P > .05). PTV values were significantly lower for conventional implants only at S2^clip (P = .041). ISQ values were significantly greater for conventional implants at S1 (P = .004), whereas at S2²¹ and S2^clip, no differences were found (P = .413 and P = .490, respectively). Damping capacity showed no significant differences between S1–S2²¹ and S1–S2^clip. ISQ values showed a significant increase of stability between S1–S2^clip, for conventional (P = .022) and extrashort (P = .005) implants, which was different from that observed between S1–S2²¹. There was a moderate negative correlation between the PTV and ISQ variables (r = 0.5) of extrashort implants, and between the PTV and insertion torque (r = –0.3) of conventional implants. For extrashort implants, there was a null correlation between ISQ and torque (r = 0.0). There was a moderately positive correlation between ISQ and torque (r = 0.3) in the conventional implant group. Conclusion: The results suggest that extrashort and conventional implants present similar primary and secondary stability values and may similarly influence restorative protocols.