Four-millimeter implants supporting fixed partial dental prostheses in the severely resorbed posterior mandible: two-year results.

BACKGROUND: Reduced alveolar bone volume complicates implant dentistry. PURPOSE: In this prospective multicenter study, a new, 4-mm long Straumann SLActive implant (Ø 4.1 mm) supporting a fixed dental prosthesis (FDP) in the severely resorbed posterior mandible was evaluated for two years. MATERIAL AND METHODS: Thirty-two patients (11 men, 21 women; mean age 64.1 years) participated. Ten to 12 weeks after single-stage surgery, a screw-retained FDP was attached to three or four 4-mm implants. RESULTS AND DISCUSSION: One hundred implants were inserted. Three failed at surgery and four were lost before loading. Twenty-eight patients received FDPs (93 implants). Two patients were discontinued because of secondary exclusion criteria; therefore, 26 patients were followed up from baseline (BL). After 1 year, one patient insisted on removal of all implants and one patient died because of nonstudy-related complications. Twenty-four patients (87 implants) were eligible for examination 2 years post-loading. All implants were found to be stable [survival rate 95.7% (confidence interval, CI 88.8-98.3) after 1 year and 92.3% (CI 84.5-96.2) after 2 years]. The mean change from BL to 12 months was - 0.43 mm (CI 0.31-0.59; p < .001) and from 12 to 24 months - 0.11 mm (CI -0.01-0.23; p = .056). The survival rate is only slightly lower than in similar studies on 6 to 8.5 mm implants. This may be related to high initial stability and effective use of the residual bone volume with high primary bone-to-implant contact in dense bone structures. The surgical handling of the tested implant was found to be similar to that of implants of common length. However, the preparation procedure must be done with great care to avoid overdrilling. Careful planning and design of the prosthetic construction is mandatory to prevent unfavorable occlusion and avoid harmful shear forces. CONCLUSION: This study showed that 4 mm implants can support an FDP in severely resorbed posterior mandibles for at least 2 years and with healthy peri-implant conditions.