[Influence of light irradiation mode on microhardness of dual cured resin cements].

Purpose: To investigate the influence of different light irradiation modes on microhardness of dual-curing resin cements.

Methods: The cylindrical specimens (1 mm in thickness and 7.5 mm in diameter) of 5 self-adhesive resin cements (Biscem, Clearfil SA Cement, G-CEM LinkAce, Maxcem Elite and RelyX U100) and 2 universal resin cements(DUOLINK and Nexus 3) were irradiated respectively by a continuous mode (light-curing for 20 s) and a delayed mode (light-curing 5 s + auto-curing 60 s + light-curing 20 s), and then they were placed dry in a light-proof thermostat at 37 degrees centigrade. Surface microhardness of specimen was detected at 0.5, 24 h and 4 weeks post-irradiation. After that period of time, all specimens were soaked in ethanol for 24 h, their hardness were detected again, and the percentage of hardness reduction after soaking were calculated. Data were analyzed by SPSS 16.0 software package.

Results: The hardness of all resin cements under both irradiation modes increased mainly within 24 h post-irradiation. The irradiation mode did not affect the hardness of all resin cements 4 weeks after irradiation significantly (P>0.05), except for Biscem. However, after ethanol softening, 5 self-adhesive resin cements cured by the continuous mode had higher hardness reduction percentage than that cured by delayed mode (P<0.05); while hardness reduction percentage of 2 universal resin cements had no significant difference between continuous and delayed cure modes (P>0.05).

Conclusions: The self-adhesive resin cements cured by delayed mode had better anti-softening ability. Supported by Nanjing Medical Science and Technology Development Fund (ZKX09035), Nanjing Science and Technology Development Fund (201001083) and Nanjing Medical Science and Technology Development Fund (YKK10125).