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



Sixty 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 (1.7Hz, 49N, 600000 cycles, 1500 thermo-cycles) and then submitted to cyclic isometric stepwise loading (5Hz) until completion of 105000 cycles or failure after 5000 cycles at 200N, followed by 20000 cycles at 400N, 600N, 800N, 1000N and 1200N. 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).



The 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.



Veneering of CAD-CAM RNC restorations has no influence on their fatigue resistance except when monolithic crowns are modified on their occlusal central groove.
Division of Cariology and Endodontology, School of Dentistry, University of Geneva, Geneva, Switzerland. Electronic address: giovanni.rocca@unige.ch.
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GT
Rocca
Division of Cariology and Endodontology, School of Dentistry, University of Geneva, Geneva, Switzerland.
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Sedlakova
Division of Cariology and Endodontology, School of Dentistry, University of Geneva, Geneva, Switzerland.
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CM
Saratti
Laboratory of Biomechanics, Department of Mechanics, Biomechanics and Mechatronics, Faculty of Mechanical Engineering, Czech Technical University, Prague, Czech Republic.
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Sedlacek
Division of Cariology and Endodontology, School of Dentistry, University of Geneva, Geneva, Switzerland.
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Gregor
Division of Cariology and Endodontology, School of Dentistry, University of Geneva, Geneva, Switzerland.
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Rizcalla
ACTA, Amsterdam, The Netherlands.
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Feilzer
Division of Cariology and Endodontology, School of Dentistry, University of Geneva, Geneva, Switzerland.
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Krejci
D003188:Composite Resins; D017076:Computer-Aided Design; D003442:Crowns; D003776:Dental Porcelain; D003799:Dental Stress Analysis
D003188:Composite Resins; D003776:Dental Porcelain
CAD/CAM; Endocrown; Endodontically treated teeth; Fatigue; Fractography; Lava Ultimate; Veenering