The proportion of cancellous bone as predictive factor for early marginal bone loss around implants in the posterior part of the mandible.

AIM: This study envisaged to explain early marginal bone loss (first years of function) around implants in the posterior area of the mandible by the local bone quality (ratio cortical vs. cancellous bone). MATERIAL AND METHODS: Four hundred and twenty-three Branemark MKIII implants inserted in the posterior region of the mandible were examined, retrospectively, on intra-oral radiographs taken at abutment connection, and 1 and 3-4 years after loading. The quality of the bone was assessed on cone beam or multi-slice CTs. The bone quality was determined by the relative proportions of cortical and trabecular bone at the insertion site. Cortical bone was defined as a clearly white structure without a trabecular pattern. Trabecular bone was defined as the structure between the two cortical plates. The width of both structures was measured at 1, 3, 5, and 7 mm away from the crest of the alveolar bone and converted in to relative proportions. Other parameters (smoking, history of periodontitis, dehiscence, pre-tapping, submerged healing, etc.) were retrieved from the patients record. RESULTS: At abutment connection, the mesial and distal marginal bone level was located 0.7 (+/-0.7) and 0.8 (+/-0.7) mm apically to the implant-abutment junction. At 1 year and 3-4 years of loading implants placed in a mandible consisting of <30% of cancellous bone had lost 1.49 and 1.83 mm, respectively. Implants placed in jawbone consisting of more than 60% of cancellous bone lost 0.74 and 0.91 mm after 1 year and 3-4 years of loading. The bone-level changes (both first year as well as after 3-4 years) were significantly less when the implant was placed in sites with a higher proportion of cancellous bone. Other parameters were significantly less important. CONCLUSIONS: Very cortical bone could jeopardize the long-term stability of the marginal bone surrounding implants placed in the posterior region of the mandible. A correlation between marginal bone loss and the proportion of cortical bone was demonstrated around Branemark implants. At present, no comparable studies are available, and therefore, it cannot be excluded that similar events take place around other implant systems.