Effect of Ceramic Thickness on Light Attenuation, Degree of Conversion, Knoop Hardness, and Elastic Modulus of Four Luting Resins
This study evaluated the influence of the thickness of disilicate ceramic on the light attenuation (mW/cm2), degree of conversion (DC, %), Knoop hardness (KH, N/mm2) and the elastic modulus (E, MPa) of four luting resins. Three resin cements: RelyX Veneer (RV, 3M Oral Care, Monrovia, CA USA); Allcem Veneer APS (AC, FGM); Variolink Esthetic LC (VE, Ivoclar Vivadent, Schaan, Liechtenstein) and one flowable resin composite Tetric N-Flow (TF, Ivoclar Vivadent) were photocured for 20 seconds. The irradiance (mW/cm2) and emission spectrum (mW/cm2/nm) from a broad-spectrum LED light unit (Bluephase G2, Ivoclar Vivadent) were measured over the luting material (control) and through 0.3 mm, 0.7 mm, and 1.0 mm thick ceramic discs (e.max CAD, Ivoclar Vivadent). The LED light delivered 26.1 J/cm2 to the surface and 6.2 J/cm2 through the 1.0 mm thick ceramic. The distribution of violet and blue light across the light tip of the light-curing unit (LCU) was relatively homogeneous, but there was less violet range. The irradiance and spectral radiant power decreased significantly as the ceramic thicknesses increased (p<0.001). The luting material type had significant effect on KH and E values (p<0.001). The RV had the greatest KH and E values, and VE had the lowest. Ceramic thickness had no significant effect on KH (p=0.213) and E (p=0.130). The KH (p=0.265) and E (p=0.165) were also not influenced by the location where these measurements were made across the specimens. No significant reduction of the DC was observed as the ceramic thickness increased (p=0.311). Increasing the ceramic thickness exponentially reduced the irradiance. This reduction was more pronounced at the shorter wavelengths (violet) of light, with an 82% decrease for 1 mm-thick ceramic. Increasing the ceramic thickness did not affect the DC, irrespective of photoinitiators used in the tested resins. The position of the violet and blue LEDs within the body of the LCU did not influence KH or E in any of the resins tested. The KH and E of VE were significantly lower than the other 3 luting materials tested.SUMMARY
Objectives
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Results
Conclusion
A. Location of the blue and violet LEDs within the body of the Bluephase G2 light-curing unit; B. The positions of the five indentations made on each sample correspond to the location of the LED emitters within the light-curing unit (LCU).
Trendline graph showing the relationship between irradiance and ceramic thickness. Irradiance decreased exponentially (R2 =0.92) as the thickness increased.
A. Radiant power (mW) emitted during 20 seconds and B. emission spectrum (mW/nm) at the high mode of Bluephase G2 measured with the integrating sphere from control and through the different ceramic thicknesses. Orange line (control)— no ceramic interposition; Blue line—through 0.3 mm of ceramic. Green line—through 0.7 mm of ceramic. Gray line—through 1.0 mm of ceramic.
Two-dimensional images of the entire beam profile and at 400 nanometers (nm) and 460 nm superimposed over the 5.0 mm diameter specimens.
Mean Knoop hardness (N/mm2) and standard deviations for all resins light activated directly by the Bluephase G2 (control) and through different ceramic thicknesses. Different letters indicate significant differences (Tukey test p<0.05). Capital letters are used for comparing resin luting materials; lowercase letters compare the ceramic thickness for each resin luting material.
Mean elastic modulus (MPa) and standard deviations for all resin luting materials light activated directly by the Bluephase G2 (control) and through different thicknesses of ceramic. Different letters indicate significant differences (Tukey test p<0.05). Capital letters are used for comparing resin luting materials; lowercase letters compare the different ceramic thicknesses.
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