Impact of Pigmentation on Depth of Cure for Resin Composites

Objectives:

Previous research has demonstrated that composite depth of cure is significantly impacted by blue light transmission and photo-initiator light absorption. Key factors that limit photo-initiator light absorption include competitive absorption and scattering of light by pigments and fillers used in the materials.  The objective of this study was to show how various pigment colors and concentrations impact the depth of cure (DOC) of a model composite system.

Methods:

A non-pigmented model resin composite system using a camphorquine/amine photo-initiator system was prepared.  Camphorquinone absorbs blue light from 400 to 500nm with peak absorbance at 470nm. Aliquots of a non-pigmented master batch were modified with 5 levels of blue, white, black, yellow or red pigment dispersions. Four replicate DOC samples were measured per ISO4049:2009.  

Results:

Table 1 shows the mean and standard deviation of the DOC versus color and concentration of the pigment.

Table 1: DOC of model composite vs color and concentration of pigment

Two way ANOVA showed that both color (p=0.000) and pigment concentration (p=0.000) significantly impacted DOC. One way ANOVA was used to determine the impact of pigment concentration for individual colors using data from the rows of table 1.  For all colors increasing concentration significantly decreased DOC (p=0.000).  One way ANOVA at fixed pigment concentrations was conducted using data from the columns of table 1.  The analysis showed the following relative DOC: blue>>white>black>yellow>red.  This trend was true for all five concentrations.  The difference in DOC between colors was statistically significant (Tukey's) at all concentration levels as well.

Conclusion:

Both pigment concentration and color significantly impact DOC.  Increased concentration, no matter the color, decreased DOC.  DOC was most negatively impacted by red>yellow,>black.> white>>blue pigments.