Light Transmission Through Indirect Restorative Materials

Objectives: A 2⁵ full factorial design of experiment (DOE) was used to determine the influence of material, shade, translucency, sample thickness, and light-to-sample distance on the amount of light transmitted through restorative materials (irradiance). The relationship between these factors influences the cure of cement under a restoration.
Methods: Materials: 3M™ ESPE™ Lava™ Ultimate CAD/CAM Restorative (LVU), IPS e.max^® CAD (EMX), and 3M ESPE Sinfony™ Indirect Lab Composite (SFY). Three shades at both high and low translucencies were cut and polished into 1, 2, or 3 mm thick tiles (n=3). Samples were illuminated (3M ESPE Elipar™ S10 LED Curing light) at varying distances (0, 3, and 6 mm), and irradiance (mW/cm²) was recorded (MARC^® Resin Calibrator). Regression analysis was performed (p<0.05).
Results: Table 1 shows pooled irradiance data and results of statistical analysis of the factorial design model. All factors were significant and are listed in order of their impact (larger F-ratio denotes a greater impact). All 2-way interactions were significant (p<0.05 for all) except for material*thickness (p=0.137) and material*distance (p=0.432).
Conclusions: All individual factors and most 2-way interactions studied have a statistically significant effect on the amount of light transmitted through the samples, with thickness, translucency, and light-to-sample distance having the greatest impact. Irradiance data demonstrates the practical impact of the variables. Interactions with the most significant effects included: translucency*material and thickness*distance. These factors should be carefully considered when light curing cements in restorations.