comparison of screw access channel obturation on the retention of implant-supported fixed restorations

introduction: a limited number of studies have evaluated factors influencing the retention of fixed prostheses cemented to implant abutments. the aim of this study was to compare the effect of varying degrees of screw access channel obturation on retention of implant-supported cast fixed restorations. materials  & methods: in this experimental study, 40 implant abutments with a diameter of 4.5 mm were connected to implant analogues and mounted in acrylic resin blocks. the samples were divided into four groups randomly. in groups 1, 2 and 3, the access channels were obturated with a 1-mm, 2-mm and 3-mm free space and in group 4 the access channels were obturated completely with silicone material and the copings were cemented with a temporary bonding agent containing eugenol. after thermocycling, the retention of the samples was evaluated in a universal testing machine under 5000 n at a strain rate of 5 mm/min. data were analyzed with one-way anova and post hoc lsd test (α = 0.05). results: the mean retention for the group with abutment access channel completely obturated was less than that in others. one-way anova showed statistically significant differences between the groups (p value = 0.032). the difference between the group with completely obturated access channels and the other groups was significant (p value < 0.05); however, the differences between the groups obturated with 1- mm , 2-mm and 3-mm free spaces were not statistically significant (p value > 0.05). conclusion: the retention of castings cemented to implant abutments might be influenced by the obturation mode of screw access channel. complete obturation of access channel with poly vinyl siloxane results in a decrease in retention.