Fatigue behavior of resin-modified monolithic CAD-CAM RNC crowns and endocrowns

- No significant differences were found in terms of fatigue resistance between crowns and endocrowns.
- Monolithic crowns performed better than the buccal-occlusal veneered counterparts.
- Endocrowns fractured predominantly with a mesio-distal wedge-opening fracture (82%).
- Partial cusp fractures were observed above all in crowns (70%).

ObjectiveTo evaluate the influence of different types of modifications with resin on fatigue resistance and failure behavior of CAD-CAM resin nano ceramic (RNC) restorations for maxillary first premolars.MethodsSixty standardized resin composite root dies received CAD-CAM RNC endocrowns (n = 30) and crowns (n = 30) (Lava Ultimate, 3M Espe). Restorations were divided into six groups: full anatomic endocrowns (group A) and crowns (group D), buccal resin veneered endocrowns (group B) and crowns (group E) and buccal resin veneered endocrowns (group C) and crowns (group F) with a central groove resin filling. A nano-hybrid resin composite was used to veneer the restorations (Filtek Supreme, 3M Espe). All specimens were first submitted to thermo-mechanical cyclic loading (1.7 Hz, 49 N, 600 000 cycles, 1500 thermo-cycles) and then submitted to cyclic isometric stepwise loading (5 Hz) until completion of 105 000 cycles or failure after 5000 cycles at 200 N, followed by 20 000 cycles at 400 N, 600 N, 800 N, 1000 N and 1200 N. In case of fracture, fragments were analyzed using SEM and modes of failure were determined. Results were statistically analyzed by Kaplan-Meier life survival analysis and log rank test (p = 0.05).ResultsThe differences in survival between groups were not statistically significant, except between groups D and F (p = 0.039). Endocrowns fractured predominantly with a mesio-distal wedge-opening fracture (82%). Partial cusp fractures were observed above all in crowns (70%). Analysis of the fractured specimens revealed that the origin of the fracture was mainly at the occlusal contact points of the stepwise loading.SignificanceVeneering of CAD-CAM RNC restorations has no influence on their fatigue resistance except when monolithic crowns are modified on their occlusal central groove.