Mechanical properties of resin-ceramic CAD/CAM restorative materials

Statement of problem. The recent development of polymer-based computer-aided design and computer-aided manufactured (CAD/CAM) milling blocks and the limited availability of independent studies on these materials make it pertinent to evaluate their properties and identify potential strengths and limitations. Purpose. The purpose of this in vitro study was to determine and compare mechanical properties (flexural strength, flexural modulus, modulus of resilience) and compare the margin edge quality of recently introduced polymer-based CAD/CAM materials with some of their commercially available composite resin and ceramic counterparts. Material and methods. The materials studied were Lava Ultimate Restorative (LVU; 3M ESPE), Enamic (ENA; Vita Zahnfabrik), Cerasmart (CES; GC Dental Products), IPS Empress CAD (EMP; lvoclar Vivadent AG), Vitablocs Mark II (VM2; Vita Zahnfabrik), and Paradigm MZ100 Block (MZ1; 3M ESPE). Polished 4x1x13.5 mm bars (n=25) were prepared from standard-sized milling blocks of each tested material. The bars were subjected to a 3-point flexural test on a 10-mm span with a crosshead speed of 0.5 mm/min. In addition, 42 conventional monolithic crowns (7 per material) were milled. Margin edge quality was observed by means of macrophotography and optical microscopy, providing a qualitative visual assessment and a measurement of existing roughness. The results were analyzed by ANOVA followed by the Tukey HSD test (alpha=.05). Results. The mean flexural strength of the tested materials ranged from 105 +/- 9 MPa (VM2) to 219 +/- 20 MPa (CES). The mean flexural modulus ranged from 8 +/- 0.25 GPa (CES) to 32 +/- 1.9 GPa (EMP). The mean modulus of resilience ranged from 0.21 +/- 0.02 MPa (VM2) to 3.07 +/- 0.45 MPa (CES). The qualitative assessment of margin edge roughness revealed visible differences among the tested materials, with mean roughness measurements ranging from 60 +/- 16 mu m (CES) to 190 +/- 15 mu m (EMP).The material factor had a significant effect on the mean flexural strength (P<.001), flexural modulus (P<.001), modulus of resilience (P<.001), and margin edge roughness (P<.001) of the tested specimens. Conclusions. The new-generation polymer-based materials tested in this study exhibited significantly higher flexural strength and modulus of resilience, along with lower flexural modulus values compared with the tested ceramic or hybrid materials. Crowns milled from the new resin-based blocks seemed to exhibit visibly smoother margins compared with the ceramic materials studied.