Relation of Crown Failure Load to Flexural Strength for Dental Polymers and a Fiber Reinforced Composite Resin

Dental polymers are often advertised and selected for use in restorations based upon the flexural strength of prefabricated discs, which may not accurately reflect their performance in dental applications. The objectives of this study were, therefore, to determine whether the three-point bending (3PB) test for flexural strength would be predictive of the “crunch-the-crown” CTC test for the failure load. Three brands of polymers (Trilor, Juvora, and Pekkton) were fabricated into rectangular bars and fully contoured crowns (10 specimens of each polymer brand, 30 specimens of each shape). Bars were tested in 3PB to determine flexural strength, and crowns were CTC tested to determine failure load after luting to resin abutments. Statistical significance was evaluated by one-way ANOVA ( = 0.05) and Pearson’s correlation coefficient. The fracture mechanisms were characterized by scanning electron microscopy (SEM). There were significant differences (p Juvora [5,217 N] > Pekkton [3,023 N]) and mean flexural strengths of the bars (Trilor [468 MPa] > Juvora [197 MPa] = Pekkton [192 MPa]). There were no correlations between flexural strength and failure load. The mode of crown fracture was different between the polymers, and included deformation (Juvora), ductile-to-brittle fracture (Pekkton), and a combination of cracks and deformation (Trilor). The flexural strength was not correlated with the corresponding crown failure load. Dental practitioners should not rely on the value of flexural strength obtained from the three-point bending test, as advertised from the manufacturer, to predict the performance of polymeric crowns.