Investigation of the marginal fit and fracture strength of monolithic crowns made from different materials

Aim: This study was carried out to examine the effects of cementation and aging on the marginal fit and fracture strength of monolithic crowns fabricated from three different materials. Material and Method: The steel die representing the upper first premolar used in the study was prepared on a Computer Numerical Control (CNC) lathe with an anatomical occlusal surface with a 5 mm crown length and a 1 mm chamfer line at 6° taper angle. 48 epoxy resin dies were obtained from the impression taken from the stell die with the conventional impression method. The prepared epoxy resin dies were randomly divided into three groups (n=16) and numbered. Then crowns were fabricated from different monolithic materials (feldspatic porcelain; VITABLOCS Mark II, lithium disilicate; IPS e.max CAD, zirconia; Zolid FX). The marjinal fit of the prepared crowns was evaluated an using a stereomicroscope before cementation and all crowns were cemented with adhesive resin cement. After cementation, marginal fit measurements were repeated. Half of the samples (n=8) from each group were kept in distilled water at 37°C for 24 hours. The remaining specimens were aged 5000 times with a 20-second holding time in an aging device with 5°C and 55°C water, and the marginal adaptation of the samples was re-evaluated. All specimens were subjected to the fracture test in a tensile-compression device. The data obtained were recorded in megapascal (MPa). Jamovi 2.2.5 program was used for statistical analysis. Marginal fit was evaluated with repeated measures analysis of variance and fracture strength with analysis of covariance. Results: It was determined that the effect of the type of material used, cementation and aging process on the marginal fit were statistically significant. It was determined that the aging process affected the fracture strength negatively, except for feldspatic crowns. Conclusion: It was found that the marginal fit and fracture strength values of all materials tested were within clinically acceptable limits. Keywords: Monolithic materials, aging process, cementation process, fracture strength, marginal fit.