Specimens (2 mm in thickness and 10 mm in diameter) were prepared in split stainless steel rings. After baseline measurements of color were made as described below, the specimens were aged artificially in a weathering machine (Atlas Ci35 Weather-Ometer) with exposure to a controlled-irradiance xenon arc filtered through borate borosilicate glass at 0.55 W/m2/nm @ 340 nm, a black panel temperature of 70 °C (light) and 38 °C (dark), dry bulb temperature of 47 °C (light) and 38 °C (dark), and humidity of 50% (light) and 95% (dark). The test cycle was 40 min light only, 20 min light plus front water spray, 60 min light only, and 60 min dark plus back water spray. Specimens were evaluated for changes for an energy exposure of 150 kJ/m2 @ 340 nm. CIE L*a*b* relative to CIE standard illuminant C was measured against white backgrounds on a reflection spectrophotometer (Macbeth 7000) at baseline and after each aging interval. Delta E* was calculated.


Polymerization shrinkage

Density of specimens before and after polymerization was calculated by a water displacement technique using a 2-mL pyncometer. The change in density was the volumetric shrinkage. Linear shrinkage was calculated by dividing volumetric shrinkage by three.

Depth of cure

SUMMARY OF RESULTS

The composites tested had values of delta-E* less than 3.3; thus, all of the composites tested had non-perceptible changes in color after accelerated aging. Depth of cure values of the composites ranged from 4.5 to 6.0 mm, all of which are considered adequate. Values of linear polymerization shrinkage varied from 0.8 to 1.8%. Values less than 2% are considered average. Values less than 1% are considered excellent. Values of water sorption ranged from 12 to 18 µg/mm3, all of which are considered acceptable.