Evaluation of the effect of axial wall modification and coping design on the retention of cement-retained implant-supported crowns

Because of compromised angulations of implants, the abutments are sometimes prepared. The purpose of this study was to investigate the effect of removing one wall of the implant abutment on the retention of cement-retained crowns. Four prefabricated abutments were attached to analogues and embedded in acrylic resin blocks. The first abutment was left intact. Axial walls were partially removed from the remaining abutments to produce abutments with three walls. The screw access channel for the first and second abutments were completely filled with composite resin. For the third and fourth abutments, only partial filling was done. Wax-up models were made by CAD/CAM. Ten cast copings were fabricated for each abutment. The copings of fourth abutment had an extension into the screw access channel. Copings were cemented with Temp Bond. The castings were removed from the abutment using an Instron machine, and the peak removal force was recorded. A one-way ANOVA was used to test for a significant difference followed by the pairwise comparisons. The abutments with opened screw access channel had a significantly higher retention than the two other abutments. The abutment with removed wall and no engagement into the hole by the castings exhibited the highest retention. Preserving the opening of screw access channel significantly increases the retention where one of the axial walls of implant abutments for cement-retained restorations is removed during preparation.