Changes in Bone Levels Around Mini-Implants in Edentulous Arches

Purpose: To evaluate changes in marginal bone levels around maxillary and mandibular mini-implants stabilizing complete dentures and to explore possible risk factors associated with bone loss. Materials and Methods: All eligible patients from nine private dental practices were invited to participate. Panoramic radiographs were obtained postoperatively and at the follow-up examination. The changes in bone level were estimated with linear mixed models that included the factors sex, age, jaw, region (anterior versus posterior), smoking habits, and loading concept. Results: Of the 180 invited patients, 133 participated in the followup (response rate: 73.9%). Of 336 mini-implants in 54 maxillas and 402 mini-implants in 95 mandibles, 15 maxillary implants and 11 mandibular implants were lost after insertion, and 4 mandibular implants fractured. Radiographic evaluations in 11 participants were not possible. The mean marginal bone loss at the remaining 634 mini-implants in 122 patients was 0.8 mm in the maxilla and 0.5 mm in the mandible over a mean observation time of 2.2 ± 1.0 years. This difference in univariate estimation lost significance after adjusting for the other variables. Implants in former smokers showed more bone loss than implants in participants who had never smoked. Implants that were loaded 3 to 4 months after placement (delayed loading) showed more marginal bone loss than immediately loaded implants. No statistically significant differences were found between men and women, different age groups, or anterior and posterior implants. Conclusion: Mean marginal bone loss around mini-implants used to stabilize complete dentures was insignificantly higher in the maxilla than in the mandible after a mean observation period of 2.3 years. These values are comparable with marginal bone loss around standard-diameter implants. A previous smoking habit and delayed loading after implant placement with a low insertion torque were shown to be possible risk factors for bone loss. Keywords: bone loss, edentulism, mini-implant, overdenture, risk factor