OBJECTIVES: To determine the influence of the mode of cure on surface hardness of four self-adhesive resin cements used to lute indirect composite restorations.
METHODS: Five commercial dual-curing resin cements were tested: four self-adhesive cements (RelyX Unicem, 3M ESPE; Maxcem Elite, Kerr; SmartCem 2, Dentsply and G-Cem, GC), and one total-etch resin cement (RelyX ARC, 3M ESPE). Three circular specimens of each material (0.5 x 6.5mm) were prepared according to three experimental groups. Group 1: Cements were allowed to auto-cure. Group 2: Cements were photopolymerized for 40 sec (Bluephase, Ivoclar Vivadent). Group 3: Cements were photopolymerized for 80 sec. All specimens were cured through a 4 mm height resin composite cylinder (Filtek Z250 A3, 3M ESPE). Surface microhardness numbers (VHN) were obtained using a Vickers digital durometer (Buehler 2101, Lake Bluff, IL, USA), applying 100gf during 30 sec. Ten indentations were performed on each specimen 20 min after preparation. Results were analyzed by two-way ANOVA and Student-Newman-Keuls tests (p<0.05).
RESULTS: Means and standard deviations of VHNs are shown in the table. For each row, different letters indicate a significant influence of the mode of cure (p<0.05). For each column, different numbers indicate statistically different microhardness among the cements for each mode of cure (p<0.05). Superficial hardness was significantly influenced by the material tested (p<0.0001), the mode of cure (p<0.0001) and their interactions (p<0.0001).
| Autocured | Photopolymerized 40" | Photopolymerized 80" |
RelyX ARC (3M ESPE) | 17.59(3.52)a4 | 29.65 (2.94) b5 | 33.13 (2.64) c4 |
RelyX Unicem (3M ESPE) | 1.57 (0.47) a1 | 11.78 (2.20) b3 | 17.95 (2.07) c3 |
Maxcem Elite (Kerr) | 6.26 (0.59) a2 | 6.92 (0.57) b1 | 9.21 (1.22) c1 |
Smartcem 2 (Dentsply) | 5.80 (1.05) a2 | 10.16 (0.52) b2 | 12.62 (1.34) c2 |
G-Cem (GC) | 9.53 (0.45) a3 | 13.05 (0.77) b4 | 18.07 (1.01) c3 |
CONCLUSION: The total-etch resin cement, RelyX ARC, exhibited the highest microhardness values regardless the mode of cure. Photopolymerization significantly increased microhardness of all resin cements evaluated. Self-adhesive cements exhibited different behavior according to the mode of cure. RelyX Unicem was very sensitive to light irradiation showing the lowest values in the autopolymerization mode. However, the increase in hardness values of Maxcem Elite after light irradiation was not as pronounced as with the other cements.
Supported by URJC-CM-2008-BIO-3526.