The Impact of Cement Type on the Fracture Resistance of Cad-cam Anterior Crowns

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Background: The increasing use of chairside computer-aided design and computer-aided manufacturing (CAD-CAM) technologies has expanded the range of restorative materials and luting agents available for anterior restorations. However, the interaction between restorative material composition and cementation protocol may substantially influence the mechanical performance of CAD-CAM crowns. Objectives: This thesis aimed to evaluate the effect of luting agent selection on the fracture resistance of CAD-CAM maxillary central incisor crowns. Two in vitro studies investigated (1) resin-matrix ceramic crowns cemented with adhesive resin cements or resin-modified glass ionomer (RMGI) cements and (2) conventional lithium disilicate and virgilite-containing lithium disilicate crowns cemented with different adhesive resin cements. Materials and Methods: In the first study, 90 resin-matrix ceramic crowns were fabricated and allocated to six cementation groups (n=15), including three adhesive resin cements and three RMGI cements. Following 10,000 thermocycles, specimens were loaded to failure, and fracture resistance was analyzed using nonparametric statistics. In the second study, 60 CAD-CAM crowns were fabricated from conventional lithium disilicate or virgilite-containing lithium disilicate and divided into five groups (n=12) according to restorative material and resin cement. After 30 days of water storage at 37 °C, crowns were subjected to compressive loading until fracture, and the results were analyzed using one-way ANOVA and Tukey HSD tests. Results: In the first study, fracture resistance differed significantly among cement groups (p<0.001). Adhesive resin cements generally provided higher fracture resistance than RMGI cements, with RelyX Unicem 2 showing the highest median fracture resistance (1574.89 N), followed by Panavia V5 (1296.21 N). In the second study, conventional lithium disilicate cemented with Multilink Automix exhibited the highest mean fracture resistance (946.35 ± 155.85 N). Among virgilite-containing lithium disilicate crowns, the highest value was obtained with Unicem (819.59 ± 232 N), whereas Calibra resulted in the lowest fracture resistance (567.94 ± 184.95 N). Conclusions: The fracture resistance of CAD-CAM anterior crowns is dependent on both restorative material and luting agent. Adhesive resin cements enhanced the fracture resistance of resin-matrix ceramic crowns compared with RMGI cements. Conventional lithium disilicate demonstrated higher fracture resistance than virgilite-containing lithium disilicate under the tested conditions, while the performance of virgilite-containing restorations was strongly influenced by resin cement selection. These findings emphasize that optimal clinical performance requires consideration of the restorative material–cement combination rather than material selection alone.

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