PHOTOELASTIC STRESS PATTERNS PRODUCED BY IMPLANT-RETAINED OVERDENTURES

Statement of problem. When 2 implants are used to support a removable overdenture, optimal stress distribution to minimize forces to the imp lants is desired. Purpose. This study used photoelastic analysis to co mpare the stress patterns generated around implants with 2 retention m echanisms. Material and methods. Two root form implants were anchored in a photoelastic mandible and a removable overdenture was fabricated. The denture was lined with a resilient layer of impression material t o simulate oral mucosa. Attachment of the denture to the implants was varied by using ball/O-ring and bar-clip attachments. Vertical and obl ique occlusal forces from 10 to 200 lb were applied unilaterally to th e right and left first molars. Resultant stress distributions in the p hotoelastic mandible were photographed and evaluated. Results. With ve rtical forces, the ball/O-ring attachment transferred minimal stress t o both implants. Vertical forces applied to the bar-clip overdenture c reated immediate stress patterns of greater magnitude and concentratio n on both implants. A posterior oblique load resulted in similar stres s patterns to both systems with slightly greater stress to the bar-cli p overdenture. Conclusions. Within the limits of this study, ball/O ri ng attachments transferred less stress to implants than the bar-clip a ttachments when the photoelastic model was subjected to a posterior ve rtical load.