Introduction of a device to pre-heat composites prior to curing has prompted this study to evaluate the effect of pre-heating on the surface hardness and depth of cure of composite resins. Factors considered in this study included curing time (10, 20 and 40 seconds), curing temperature (70, 100 and 140 degrees F), curing light type (halogen and LED), and composite type (hybrid and microhybrid).
The surface hardness portion of the study included 180 samples (5 of each of 36 combinations of factors) prepared according to the ADA standard for surface hardness. Four Knoop hardness measurements were obtained from both the top and bottom surfaces, and the data was analyzed by using the two sample t-test. For both the hybrid and microhybrid, there were statistically significant increases in hardness with increases in temperature and curing time (α = 0.5, p0.4428). The LED light was statistically significantly better than the Halogen in the microhybrid group (α = 0.5, p<0.0203).
The ADA standard for surface hardness states that the bottom surface of a 2 mm sample must have 80% of the hardness of the top surface. In this study, it was noted that the standard was met in the hybrid group at any times or temperatures when using the LED. The halogen did not meet the standard at the 10 second curing time for any temperature or time, but was met at the 20 and 40 second time for all other temperatures. The microhybrid group had a very different result compared to the hybrid. Using the halogen, the standard was only met at 140 degrees and 40 seconds curing time. For the LED, the standard was met at the 40 second curing time at all temperatures, and at the 20 second time for the 70 degree sample. It should be noted that even though the standard was not met in many circumstances, the hardness values increased significantly as curing time and temperature increased.
The depth of cure portion included the same number of samples as the surface hardness portion, using the same combinations of factors. Six mm deep samples were prepared, and each sample was tested on the top surface, and at locations along the following mm increments after being sectioned: 0.5, 1.5, 2.5, 3.5, 4.5, and 5.5, or until unreliable measurements were obtained. The 0.5 and 3.5 mm increments were chosen for statistical analysis. For both composite types, there was a statistically significant increase in hardness as temperature and curing time increased (α = 0.5, p<0.0001). The
LED light performed statistically significantly better than the halogen(a = 0.5, p<0.0001).
Master of Science (MS)
Year Degree Awarded
Date (Title Page)
Library of Congress/MESH Subject Headings
Composite Resins; Dental Bonding; Dental Materials
Loma Linda University Libraries
This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.
Bond, Peter R., "The Effect of Pre-heating on Depth of Cure and Surface Hardness of Resins" (2005). Loma Linda University Electronic Theses, Dissertations & Projects. 1288.
Loma Linda University Electronic Theses and Dissertations
Loma Linda University. Del E. Webb Memorial Library. University Archives