Implant-Supported Fixed Partial Dentures with Posterior Cantilevers: In Vitro Study of Mechanical Behavior

Rehabilitation with dental implants is not always possible due to the lack of bone quality or quantity, in many cases due to bone atrophy or the morbidity of regenerative treatments. We find ourselves in situations of performing dental prostheses with cantilevers in order to rehabilitate our patients, thus simplifying the treatment. The aim of this study was to analyze the mechanical behavior of four types of fixed partial dentures with posterior cantilevers on two dental implants (convergent collar and transmucosal internal connection) through an in vitro study (compressive loading and cyclic loading). This study comprised four groups (n = 76): in Group 1, the prosthesis was screwed directly to the implant platform (DS; n = 19); in Group 2, the prosthesis was screwed to the telescopic interface on the implant head (INS; n = 19); in Group 3, the prosthesis was cemented to the telescopic abutment (INC; n = 19); and in Group 4, the prosthesis was cemented to the abutment (DC; n = 19). The sets were subjected to a cyclic loading test (80 N load for 240,000 cycles) and compressive loading test (100 KN load at a displacement rate of 0.5 mm/min), applying the load until failure occurred to any of the components at the abutment-prosthesis-implant interface. Subsequently, an optical microscopy analysis was performed to obtain more data on what had occurred in each group. Results: Group 1 (direct screw-retained prosthesis, DS) obtained the highest mean strength value of 663.5 +/- 196.0 N. The other three groups were very homogeneous: 428.4 +/- 63.1 N for Group 2 (INS), 486.7 +/- 67.8 N for Group 3 (INC), and 458.9 +/- 38.9 N for Group 4 (DC). The mean strength was significantly dependent on the type of connection (p < 0.001), and this difference was similar for all of the test conditions (cyclic and compressive loading) (p = 0.689). Implant-borne prostheses with convergent collars and transmucosal internal connections with posterior cantilevers screwed directly to the implant connection are a good solution in cases where implant placement cannot avoid extensions.