Effect of abutment height on retention of single cement-retained, wide- and narrow-platform implant-supported restorations

In contrast to prepared natural dentin abutments, little is known concerning factors influencing the retention of fixed prostheses cemented to implant abutments. The aim of this study was to investigate the effect of implant abutment height on the retention of single castings cemented to wide and narrow platform implant abutments. Thirty-six parallel-sided abutments (Biohorizon Straight Abutment) of narrow platform (NP) and wide platform (WP) sizes with their analogs were used. In each group of platform size, abutments were prepared with axial wall heights of 5, 4, 3, 2 mm (n=9). On the whole 72 castings were constructed, which incorporated an attachment to allow removal. Castings were cemented to abutments with TempBond®. A uniaxial tensile force was applied to the crown using an Instron machine until cement failure occurred. Analysis of variance of the models were fit to determine the effect of height of abutment of the restorations on the mean tensile strength (α=0.05). The mean peak removal force for corresponding abutments was significantly different (P < 0.05): (1) with platform sizes: WP > NP; (2) with alteration of axial wall height for NP: 5 mm > 4 mm > 3 mm = 2 mm and for WP: 5 mm > 4 mm = 3 mm = 2 mm. The retention of NP cement-retained restorations is influenced by the wall height but not in same manner as WP. Restorations of narrow-platform size with longer abutment exhibited higher tensile resistance to dislodgement.