IADR Abstract Archives
Threshold Light Intensity Required to Achieve Adequate Composite Cure
Objectives: This work investigates the threshold light intensity required to achieve a bottom hardness that was a minimum of 80% of the top utilizing a clinically relevant exposure time in a resin composite.
Methods: Shade and mold thickness were used to modulate the light intensity at the bottom of a composite block. An experimental composite was prepared that was subdivided and pigmented to varied shade and opacity targets. Delrin molds that ranged in thickness from 2.0 to 4.5mm were used. The molds were filled with composite, pressed flat with a sheet of clear film on the top and bottom, placed on a radiometer and exposed for 10sec with a LED light tuned to an output of 1000 mW/cm2. The intensity of the light coming through the bottom of the composite was measured at 9.5sec. The bottom and top Barcol hardness was measured.
Results: The ratio of bottom to top (R) was calculated as a metric of cure. The R was plotted versus the bottom light intensity. The data was regressed by an asymptotic model: R=A–Be-Cx where R=hardness ratio, A=maximum hardness ratio, B,C=constants and x=intensity of light at the bottom of the composite. The model and fit are: R=0.99+1.50e-0.14x, Lack-of-fit: p=0.204. Lack-of-fit test was used to assess the model fit. If the p-value is less than the selected alpha-level (0.05), evidence exists that the model does not accurately fit the data. The graph below (figure 1) shows the plotted data, the model, the fit, and the threshold intensity calculated from the model to achieve 80% R.
Conclusions: The model was demonstrated to fit the data. This study demonstrated that a minimum light intensity of approximately 15 mW/cm2 was required for a 10sec exposure time to achieve 80% of the top hardness.
Methods: Shade and mold thickness were used to modulate the light intensity at the bottom of a composite block. An experimental composite was prepared that was subdivided and pigmented to varied shade and opacity targets. Delrin molds that ranged in thickness from 2.0 to 4.5mm were used. The molds were filled with composite, pressed flat with a sheet of clear film on the top and bottom, placed on a radiometer and exposed for 10sec with a LED light tuned to an output of 1000 mW/cm2. The intensity of the light coming through the bottom of the composite was measured at 9.5sec. The bottom and top Barcol hardness was measured.
Results: The ratio of bottom to top (R) was calculated as a metric of cure. The R was plotted versus the bottom light intensity. The data was regressed by an asymptotic model: R=A–Be-Cx where R=hardness ratio, A=maximum hardness ratio, B,C=constants and x=intensity of light at the bottom of the composite. The model and fit are: R=0.99+1.50e-0.14x, Lack-of-fit: p=0.204. Lack-of-fit test was used to assess the model fit. If the p-value is less than the selected alpha-level (0.05), evidence exists that the model does not accurately fit the data. The graph below (figure 1) shows the plotted data, the model, the fit, and the threshold intensity calculated from the model to achieve 80% R.
Conclusions: The model was demonstrated to fit the data. This study demonstrated that a minimum light intensity of approximately 15 mW/cm2 was required for a 10sec exposure time to achieve 80% of the top hardness.
IMAGES
2093617_File000000.JPG
2093617_File000000.JPG