Effectiveness of high-power LEDs to polymerize resin cements through ceramics: An in vitro study

Statement of problem The cementation of ceramic veneers using light-polymerized resin cement is largely dependent on the proper light activation of the cement. Light activation using high irradiance could shorten the time required to lute multiple restorations. Purpose The purpose of this in vitro study was to evaluate the light transmission of dental light-polymerizing units through ceramic cylinders and its effect on the polymerization kinetics of a resin cement. Material and methods Ceramic ingots (IPS Empress Esthetic, shade ET1) were sectioned to produce cylinders 0.5, 1.0, and 2.0 mm thick. Two light-emitting diode units were evaluated: SmartLite Focus and Valo Cordless, the latter used in either Standard or Xtra Power (XP) modes. Light transmission (average of irradiance, total energy, and light-emission profile) through the cylinders was measured (n=3). The polymerization kinetics of a resin cement light polymerized through the ceramic was monitored for 5 minutes (n=3). The degree of conversion was measured again after 72 hours. Data were individually analyzed with 2-way ANOVA and the Tukey HSD test (α=.05). Results Valo at XP presented the highest values of irradiance and SmartLite the lowest, irrespective of the ceramic thickness. Regarding the total energy, XP showed the lowest values. The total energy and irradiance lessened with the increase in ceramic thickness. In general, except for Valo at XP, the ceramic thickness did not affect the degree of conversion. Valo at XP and interposing 2.0 mm ceramic resulted in the lowest values of Rp_max. Conclusions The reduction of total energy and irradiance by ceramic interposition had only a slight effect on polymerization kinetics.