Evaluation of L.E.D. Curing Lights on Surface Hardness And Volumetric Shrinkage

Objectives: Higher irradiance levels will produce higher surface hardness values on composite material with appropriate curing times. Higher irradiance levels with longer exposure times will produce the greatest volumetric shrinkage values.
Methods: The irradiance levels of 30 L.E.D. light curing units (LCU) were tested and compared using 2 L.E.D. radiometers. The LCU (VALO=V; Woodpecker=W) groups were divided into 3 and 2 subgroups of 6 composite discs for a total of 30 samples: V-Standard, V-High, V-Xtra, W-Soft, W-Xtra. Samples are removed from the plastic mold and marked to indicate the top/bottom. The samples then underwent surface hardness testing by the Barcol Hardness Tester on both sides post 24-hour water bath at 37 degrees C. Two additional composites were filled in a standardized Class I plastic prepped teeth and were placed in the Micro-Computed Tomography machine for volumetric shrinkage analysis.
Results: All LCUs were standardized at their respected irradiance levels.
Maximum polymerization shrinkage occurs over the longest exposure time and highest light irradiance. All curing intensities produce similar values of surface hardness given their irradiance levels and appropriated exposure times. Preliminary study on one sample showed 3.368% shrinkage levels post curing.
Barcol hardness testing measurements did not vary much between the different intensities of curing nor with the type of curing lights used.
Conclusions: Composite when not cured thoroughly can lead to the loss of the composite material and tooth decay. Light curing units are required to cure the composite effectively and efficiently. Modifications of polymerization and composite would lead to newer, low-shrinkage dental restorative materials. Further research is required with a larger sample size to gain a better understanding.