Fracture strength of minimally prepared all-ceramic CEREC crowns after simulating 5 years of service

Objectives To examine the strength and mode of fracture of traditionally and minimally prepared all-ceramic resin bonded CAD/CAM crowns after fatigue loading. Methods Thirty human maxillary molars were used and divided in three groups namely; traditional crown preparation group (I), minimal crown preparation group (II) and occlusal veneer preparation group (III). A leucite reinforced glass ceramic (IPS Empress CAD) was used for fabricating the crowns. The CEREC InEOS system (v3.10) was used for scanning, designing and milling. Five years of clinical service were simulated and the fracture strength of the crowns was measured. One-way ANOVA and Kruskal-Wallis test were used for data analysis (α=0.05). Results The mean fracture strength and SD in Group I was 1070N (±181) and in Group II 1110N (±222). One-way ANOVA analysis showed no statistically significant difference between the two groups (p>0.05). In Group III all restorations developed cracks during TCML and were not subjected to fracture loading. Three of the traditionally designed crowns (Group I) and 4 of the minimally designed crowns (Group II) developed surface cracks during TCML. Significance Minimal all-ceramic resin-bonded crowns can potentially form a viable restorative option as they demonstrated comparable strength to traditional all-ceramic crowns. However, this should be interpreted with caution as a number of crowns showed cracks after 5 years of simulated service. All the occlusal veneers developed cracks during simulation and further investigation is needed for this to be considered a viable option.