Biaxial Flexural Strength and Modulus of Resin Luting Cements

Objectives: The purpose of this study was to evaluate the effects of curing mode and viscosity on the biaxial flexural strength (FS) and modulus (FM) of two resin luting cements. Methods: Eight experimental groups were evaluated (n = 12), among the dual-cured resin cements (Nexus 2/Kerr Corp. and Variolink II/Ivoclar Vivadent), curing modes (light activation or self-cure), and viscosities (low and high). Forty-eight resin cement discs of each product (0.5 mm thick by 6.0 mm diameter) were fabricated using impression material molds (Aquasil Ultra/Dentsply Caulk). Half the specimens were light-activated for 40 seconds (600 mW/cm², XL3000/3M ESPE), and half were allowed to self-cure. After 10 days dark storage at 37 ^oC, the biaxial flexure test of the specimens was determined using a universal testing machine (1.27 mm/min, Instron 5844). Data were statistically analyzed by three-way ANOVA and Tukey's post-hoc test at a pre-set alpha of 0.05. Results: The FS and FM means (SD) are displayed in Tables 1 and 2, respectively (MPa):

Table 1 (FS)	Nexus 2		Variolink II
Viscosity	Light-activated	Self-cured	Light-activated	Self-cured
Low	134.7 (27.4) Ab	120.9 (11.0) Ba	137.6 (22.1) Ab	117.1 (24.3) Ba
High	146.9 (18.6) Aa	120.2 (20.5) Ba	159.0 (22.0) Aa	120.0 (12.0) Ba

Table 2 (FM)	Low viscosity		High viscosity
Cement	Light-activated	Self-cured	Light-activated	Self-cured
Nexus 2	7180 (2100) Aa	5549 (864) Ba	7633 (1435) Aa	5587 (1915) Ba
Variolink II	7084 (1508) Aa	5411 (895) Ba	7575 (1980) Aa	5282 (924) Ba

Groups having similar letters are not significantly different (upper case = row; lower case = column). No significant difference was observed between resin cements for FS (p=0.50) and FM (p=0.62). Conclusions: Light-activation significantly increased FS and FM. The high viscosity versions from light-activated groups exhibited higher FS than their low viscosity versions, while the viscosity of resin cements did not change the FM.