The effects of fixed and removable implant-stabilised prostheses on posterior mandibular residual ridge resorption.

This study investigated the change over time in the area of the posterior mandibular residual ridge in patients wearing either i) mandibular overdentures stabilised by two implants (Brånemark System; Nobel Biocare, Göteborg, Sweden) connected by a bar, or ii) mandibular fixed cantilever prostheses stabilised on five or six implants. Proportional measurements were made in order to compare the area of the residual ridge with an area of bone uninfluenced by resorption. Measurements were made by digitising tracings of panoramic radiographs that were taken shortly after implant insertion and up to seven years later. With the use of overdentures, the posterior bone area index reduced by a mean of 1.1% per annum, while a mean bone area index increase of 1.6% per annum was demonstrated in association with fixed prostheses. A multiple linear regression model was fitted to predict the change in posterior area from type of prosthesis, gender, age, years of edentulism and initial height of the mandible. The model was only significant for initial height of mandible (P = 0.04) and type of prosthesis (P = 0.0001). In conclusion, patients rehabilitated with implant-stabilised mandibular overdentures demonstrated low rates of posterior mandibular residual ridge resorption, while patients rehabilitated with implant-stabilised mandibular fixed cantilever prostheses demonstrated bone apposition in the same area.