FRACTURE RESISTANCE OF CAD/CAM FABRICATED IMPLANT - SUPPORTED ALL - CERAMIC CROWNS CEMENTED ON READY AND CUSTOM MADE ZIRCONIA ABUTMENTS

Statement of the problem: Despite their outstanding esthetic characteristics, the adequacy of implant-supported all-ceramic crowns under occlusal loads in the posterior segment of the jaw remains questionable.
Aim of the study: Evaluation of the fracture resistance of different CAD/CAM fabricated implant-supported all-ceramic monolithic posterior crowns cemented on ready and custom made zirconia abutments.
Materials and methods: 30 internal connection titanium dummy implants were embedded in epoxy resin and randomly divided into three groups (n=10 each) according to the crown material used; Group I: Polycrystalline ceramic (Katana Zirconia), Group II: Hybrid ceramic (Vita Enamic) and Group III: Lithium disilicate glass ceramic (IPS e.max CAD).All crowns were CAD/CAM fabricated as monolithic maxillary right first premolar.In each group, five crowns were cemented on ready made zirconia abutments (subgroup A) while the other five were cemented on custom made zirconia abutments (subgroup B). All samples were thermocycled (5o to 55o,10 seconds dwell time) then compressively loaded under axial static load till fracture using a universal testing machine with a loadcell of 5 kN at a cross-head speed of 1mm/min. The load required to fracture was recorded in Newton and failure modes were visually analyzed. Statistical analyses were performed by Two-way ANOVA and Tukey’s post-hoc test.( P ≤ 0.05)
Results: Fracture resistance of implant-supported all-ceramic monolithic posterior crowns was statistically significantly affected by the ceramic crown material and abutment type (P<0.001). Either with ready or custom-made zirconia abutments; zirconia crowns recorded the statistically significantly highest fracture resistance mean value followed by IPS e.max CAD ones while Vita Enamic crowns recorded the lowest values with no statistically significant difference between them and IPS e.max CAD crowns. Zirconia and Vita Enamic crowns cemented on custom made abutments recorded statistically significantly higher mean fracture resistance values than those cemented on ready made one. However, IPS e.max Cad crowns cemented on both abutment types showed statistically insignificant difference. Different failure modes were observed among the tested ceramic crowns without fracture of any abutment.
Conclusions: All tested implant-supported all-ceramic monolithic posterior crowns cemented on ready and custom made zirconia abutments had the potential to withstand the physiologic occlusal forces in the premolar region with the superiority of the zirconia crowns cemented on custom made zirconia abutments.