The Minimum Radiant Exposure And Irradiance For Inducing Complete Polymerization Of Light-cured Resin Cement

Objective:Study the optical properties of LED light curing units before and after transmission of glass ceramics and the minimum radiant exposure and irradiance required to initiate complete polymerization of light-cured resin cements.Methods:6 new LED light curing units were collected.The spectra,central wavelengths and change of irradiance during working time of LED light curing units were measured by an irradiance spectrometer,the powers of the light curing units were measured by an optical power meter and then convert into the irradiance.Two kinds of glass ceramic plates(LD and LEU)were made by CAD/CAM technology.Each glass ceramic was selected with transparency HT,color A2 and A3,so there were 4 groups.Each group had 8 plates with different thickness of 0.5,1.0,1.5,2.0,2.5,3.0,3.5,4.0 mm and the same inner diameter of 10 mm,the total number was 32.The center wavelengths of the transmitted light of light curing units after transmission of glass ceramics were measured by an irradiance spectrometer,and the powers of the transmitted light of light curing units after transmission of glass ceramics were measured by an optical power meter and then convert into the irradiance.The polymerization model of light-cured resin cement was established.According to the ERL,the experimental groups and control group were established to cure 100μm resin specimens by different curing protocols,and the specimens of the control group were completely cured.The Vickers hardness of the specimens was measured by a digital microhardness tester.By comparing the Vickers hardness of the specimens of experimental groups and control group,it was judged whether the specimens of experimental groups were completely cured,thereby acquiring the minimum radiant exposure and irradiance for inducing complete polymerization of light-cured resin cement.Results:(1)In the central wavelength,the difference between the Elipar S10 standard power mode and the Bluephase N low power mode was not statistically significant(P>0.05),the difference between the S.P.E.C 3 standard power mode and the S.P.E.C 3 3K power mode was not statistically significant(P>0.05),and the difference among remaining power modes were statistically significant(P<0.05).(2)In the irradiance,the difference between the Elipar S10 standard power mode and the VALO high power mode was not statistically significant(P>0.05),and the difference among remaining power modes were statistically significant(P<0.05).(3)Light curing units with different power modes transmit glass ceramics and light curing units transmit different types of glass ceramics,the difference of central wavelength of transmitted light were statistically significant(P<0.05).(4)Light curing units with different power modes transmit glass ceramics,light curing units transmit different types,colors and thicknesses of glass ceramics,the difference of irradiance of transmitted light were statistically significant(P<0.05).(5)In the minimum radiant exposure experiment,the surface had no effect on the Vickers hardness of the light-cured resin cement(P>0.05),the radiant exposure had an effect on the Vickers hardness of the light-cured resin cement(P<0.05).The Vickers hardness of the experimental group 1 to 5 was statistically different from that of the control group(P<0.05).There was no statistically different between the Vickers hardness of the experimental group 6 and that of the control group(P>0.05).(6)In the minimum irradiance experiment,the surface had no effect on the Vickers hardness of the light-cured resin cement(P>0.05),the irradiance had an effect on the Vickers hardness of the light-cured resin cement(P<0.05).The Vickers hardness of the experimental group 3 and 4 before doubling the curing time was statistically different from that of the control group(P<0.05),and the Vickers hardness of the experimental group 3 after doubling the curing time was statistically different from that of the control group(P>0.05),the Vickers hardness of the experimental group 3after doubling the curing time was statistically different from that of the control group(P>0.05).Conclusions:(1)The power mode of light curing unit and the type of glass ceramic have effects on central wavelength of transmitted light,the color and thickness of glass ceramic have no effects on that.(2)The power mode of light cuirng unit,the type,color and thickness of glass ceramic have effects on irradiance of transmitted light.Among them,the thickness of glass ceramic has the most significant effect.The transmission performance of IPS e.max CAD is better than that of IPS Empress CAD,and the transmission performance of color A2 is better than that of color A3.(3)When the irradiance is greater than 50 mW/cm~2 and the radiant exposure is greater than 6 J/cm~2,Variolink N light-cured resin cement with thickness of 100μm and color of transparency can be induced to completely polymerize.