Comparative hardness and modulus of tooth-colored restoratives: a depth-sensing microindentation study.

The objective of this study was to compare the hardness and modulus of the continuum of direct tooth-colored restorative materials using a depth-sensing microindentation approach. The effects of thermal fatigue on mechanical properties were also evaluated. Six restorative materials representing the continuum were selected. They included an ormocer (Admira [AM], Voco), a giomer (Beautifil [BF], Shofu), a compomer (Dyract Extra [DE], Dentsply), a minifill composite (Esthet-X [EX], Dentsply), resin-modified (Fuji II LC [FL], GC) and highly viscous (Fuji IX [FN], GC) glass ionomer cements (GICs). Fourteen specimens (3 mm wide x 3 mm long x 2 mm deep) were made for each material. The specimens were randomly divided into two groups and treated as follows: Group A--stored in distilled water at 37 degrees C for 30 days; Group B--thermal cycled for 5000 cycles (35 degrees C [28s], 15 degrees C [2s], 35 degrees C [28s], 45 degrees C [2s]) and stored for 26.5 days. Hardness and modulus of the materials were determined using depth-sensing microindentation testing with the Instron MicroTester. Hardness was computed by dividing the peak load over the maximum projected contact area while modulus was calculated by analysis of the loading/unloading load-displacement (P-h) curves and the analytical model according to Oliver and Pharr (J. Mater. Res. 7 (1992) 1564). Results were analyzed using ANOVA/Scheffe's post hoc test and independent samples T-test (p<0.05). Hardness ranged 46.44-72.65 and 49.11-78.97 HV, while modulus ranged 7.86-12.78 and 8.12-13.13 GPa for Groups A and B, respectively. Although the ranking of mechanical properties were generally similar for both groups, disparities in statistical differences between materials were observed between Groups A and B for both hardness and modulus. For both groups, BF was significantly harder than DE, AM, FL and EX was significantly harder than FL. The modulus of FN was significantly greater than EX, DE, AM and FL was significantly stiffer than AM. With the exception of BF, no significant change in hardness and modulus was observed for all materials with thermocycling. The hardness and modulus of some glass ionomer-based/containing materials may be comparable or even superior to minifill and ormocer composites. Thermal fatigue should be considered when comparing mechanical properties between materials.