Aim
Evaluate effect of conical hybrid stock and computer-aided design/computer-aided manufacturing (CAD/CAM) abutments on the strain developed around implant and the screw loosening.
Patients and methods
Sixteen epoxy resin blocks containing implant assembly (fixture, abutment, abutment screw, cemented zirconia crown) divided into two equal groups (eight blocks) in each group as fallow: group (A): eight blocks with implants attached to Stock abutment with conical hybrid connection to retain the crown to the implant. Group (B): Eight blocks with implants attached to customized CAD/CAM milled abutment with the same size and connection to retain the crown to the implant. The samples were subjected to dynamic cyclic loading 150 000 cycles using chewing simulator. A digital torque gauge was used to evaluate screw loosening by measuring removal torque value (RTV) before and after cyclic loading. Strain gauge was installed around implants in buccal, palatal aspects of each implant, and a load of 100 N was applied vertically and another load of 65 N was applied obliquely by using universal testing machine and the strain was determined using strain meter.
Results
For GA, percentage of initial removal torque loss (RTL) was (17.988 ± 1.248%) and significantly increased after loading (30.763 ± 1.176%). For GB, percentage of initial removal torque loss was (24.350 ± 1.239%) and increased significantly after loading (33.313 ± 2.840%). For strain results under vertical and oblique loading, there was no statistically significant difference in both groups in stock and cad cam abutments and the strain measurement under oblique loading were significantly higher than the strains measured under vertical loading in both groups.
Conclusions
Screw loosening occurred in both stock abutments and CAD/CAM abutments but CAD/CAM abutments yielded greater removal torque reduction (RTV) reduction% than the stock abutments and stock abutments showed little stress values around implant than CAD/CAM abutment without statistically significant difference. Off-axial loads will generate more stresses around implants.