Influence of Screw Access Channel on All Ceramic Cement-Retained Implant Supported Posterior Crowns

statement of the problemThe presence of a screw access channel on the occlusal surface of implant-supported all ceramic crowns may reduce the fracture resistance of the restoration. Purpose Evaluate the effect of screw access channel on the fracture resistance, fracture pattern and defects at the fracture origin after subjecting to vertical compression load on cement retained implant posterior crowns. Material and methodsFour parallel groups, eight specimens each, were examined in this study. The specimens were subjected to thermal cycling corresponding to one year clinical service, and then were subjected to fracture resistance testing & fractographic analysis. The specimens were grouped as follows, Group A restorationswere constructed with lithium disilicate glass ceramic with no occlusal access channel. Group B restorations were constructed with lithium disilicate glassceramic with screw access channel at the center of their occlusal surfaces. Group C restorationswere constructed with zirconium oxide ceramic with no occlusal access channel. Group D restorationswere constructed with zirconium oxide ceramic with screw access channel at the center of their occlusal surfaces. Results The highest mean (SD) fracture resistance was 6193.71627.2 N recorded in group C followed by 3282.591006.07 N recordedin group D, then 2528.44453.54 N recorded in group A and the lowest mean fracture resistance was 2458.75230.28 N recorded in group B. Conclusion occlusal screw access channel had no significant effect on lithium disilicate glass ceramic and had a significant effect on zirconium oxide ceramics.