The effect of artificial aging on Martens hardness and indentation modulus of different dental CAD/CAM restorative materials

Abstract

OBJECTIVES
To determine the Martens hardness parameters for five different classes of CAD/CAM restorative materials after storage in water and thermo-cycling.
MATERIALS AND METHODS
Lithium disilicate ceramic IPS e.max CAD (EX), silicate ceramic IPS Empress CAD (EC), a polymer infiltrated interpenetrating network material (hybrid material) VITA Enamic (VE), two compact filled composites Lava Ultimate (LU), experimental material (EM), two low filled resin composites Katana Avencia (KA), Ambarino High-Class (AH) and ultra-low/unfilled acrylic polymers CAD-Temp (CT), Telio CAD (TC), breCAM.HIPC (BC) were tested. Specimens were stored in water at 37 °C for 30, 60, 90, 120 days and afterwards thermo-cycled (30,000×, 5 °C/55 °C). Martens hardness (HM) and indentation modulus (E$_{IT}$) were longitudinally investigated after each storage time. For structural analysis, each material was analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX).
RESULTS
The groups of unfilled polymers/ultra-low filled composite (CT, TC, BC) followed by low (KA, AH) and compact filled resin composites (LU, EM) showed the lowest HM and E$_{IT}$ values (p < 0.001). The highest values presented ceramics (EX, EC) followed by hybrid material (VE) (p < 0.001). High influence on the Martens hardness parameters was exerted by the aging duration (HM: η$_{P}$$^{2}$ = 0.108, p < 0.001; E$_{IT}$: η$_{P}$$^{2}$ = 0.074, p < 0.001). Structural analyses of resin composites revealed big differences in shape, size and distribution of filler particles.
CONCLUSIONS
The tested CAD/CAM materials showed differences in Martens hardness and indentation modulus pursuant to the material class. Ceramics showed highest values, followed by the hybrid material. For resin composites the Martens hardness and indentation modulus increased with the filler content. Artificial aging affected CAD/CAM materials differently. Some materials tested are prone to aging, the Martens hardness and indentation modulus decreased after thermo-cycling.