Bone modifications around porous trabecular implants inserted with or without primary stability 2 months after tooth extraction : a 3-year controlled trial

Implant primary stability has long been considered a prerequisite for successful osseointegration. However, achieving stability may be difficult when placing implants in wide postextractive bone defects. The purpose of this study was to conduct a clinical and radiographic investigation of bone modifications at porous-structured implants inserted with or without primary stability. Materials and methods: Fifty porous-structured implants were inserted in the posterior sockets of 50 consecutive patients 2 months after tooth extraction, combined with allogeneic bone and a resorbable membrane. The implants were divided into two groups according to insertion torque: spinner (spinning at 35 Ncm, n = 23) and stable (stable at 35 Ncm, n = 27). Implant stability was assessed by resonance frequency analysis from baseline to 6-month function. Follow-up took place 3 years after implant placement. Results: At baseline, the implant stability quotient was undetectable in the spinner group and averaged 75.07 \ub1 5.84 in the stable group. At uncovering, the implant stability quotient increased to 71.33 \ub1 4.42 and 77.97 \ub1 3.30 in the spinner and stable group, respectively (P < 0.001). After 6 months of loading, no between-group difference in implant stability quotient was found (P = 0.13). Marginal bone level changes were similar between groups at all follow-ups, averaging 120.41 \ub1 0.77 mm and 120.15 \ub1 0.53 mm at 36-month follow-up in the spinner and stable group, respectively (P = 0.35). No implant failed throughout the observation period. Neither biological nor mechanical complications occurred. Conclusion: Implants with a moderately rough surface and a porous-structured body may osseointegrate even without primary stability