Abstract
The Knoop hardness numbers (KHN) were measured for the composite resin specimens 1 day after curing (lday group) and 5 years after curing (5 year group: stored in 37°C artificial saliva), and the influence of the Knoop hardness on the post-irradiation color changes was investigated. Composite resin disks which were 10 mm in diameter and 1 mm in thickness, and made of the 3 M Co. light-cured composite resin Silux Plus (shades: U, Y, DY, L, G, UO, YO) were made with 20,40, and 120 seconds of light exposure through a 1 mm thick glass plate. The chromatical values of the specimens 2 hours after curing in the 1 day group and immediately after curing and 5 years after curing in the 5 year group, and the KHN of the specimens 1 day after curing in the 1 day group and 5years after curing in the 5 year group were measured. All of the data were statistically analyzed using a Student t test.
1) In the comparison of the KHN between the specimens after 1 day and 5 years in the different light-irradiation times, all of the resin shades of those after 5 years showed significantly higher values than those of after 1 day except for YO in the 20 sec. group, U and DY in the 40 sec. group and DY in the 120 sec. group.
2) In the comparison of the KHN among the shades in the different light-irradiation times, for the DY and L after 1 day and Y and G after 5 years, the KHN of the 20 second group were significantly lower than those of the 40 and 120 second groups.
3) Both in the 1 day and 5 year groups, in the 120 second group was it found that the higher the L*(lightness) values the higher the KHN of the shades were.
4) Both in the 1 day and 5 year groups, the relationship between the opacity % and KHN was cornpared among the different light-irradiation times. In the 20 second group of the 1 day group and the 40 second group of the 5 year group, the higher the opacity % the higher the KHN of the shades were. In the other groups, however, the relationship between the opacity % and KHN was low.
5) In the 5 year groups, the ΔE*ab (color difference) values between the colors immediately after curing and after 5 years were obtained, and the relationships between the ΔE* ab and KHN were compared among the different shades. In the 120 second group, the higher the KHN the lower the ΔE*ab were. However, in the 20 second and 40 second groups, the relationship between the KHN and ΔE*ab was low.
