Effect of Abutment Changes on Retention of Implant Crowns

Objectives: Factors affecting retention of fixed prostheses to natural abutments are well understood. In contrast, little is know concerning factors influencing the retention of fixed prostheses cemented to implant abutments. The purpose of this study was to investigate the effect that varying implant abutment wall height, platform size and screw access channel filling method has on the retention of castings cemented with TempBond to implant abutments. Methods: Four 15o pre-angled abutments (Brånemark System® Replace Select Esthetic) of each platform size - narrow (NP), regular (RP) and wide (WP) were used. In each group of the abutments the labial axial wall was either; unadjusted, one-third removed, two-thirds removed or completely removed. The screw access channels were either fully or partially filled with a vinyl polysiloxane impression material, Memosil (Heraeus Kulzer). For each abutment a casting incorporating an attachment to allow removal was constructed. Castings were cemented with TempBond. The tensile force required to separate the cemented castings from the abutments was measured using an Instron Universal testing machine. Results: The mean peak removal force for comparable abutments was significantly different (p<0.05): (1) Where the screw access channel was completely filled with Memosil compared to those partially filled with Memosil (2) With platform sizes - WP>RP>NP (3) With alteration of axial wall height - 1/3>0>2/3>3/3. Conclusions: The amount of retention of castings cemented to implant abutments with TempBond is influenced by the filling modality of the screw access channel, implant platform size and the wall height of the abutment.