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Abstract
The aim of the present study was to evaluate the effect of filler size and loading, storage condition (wet and dry), and storage time on both hardness and color changes of light cured composites. Also, the relationship between hardness and color changes was assessed.
A total of 90 disc shaped specimens were fabricated. The specimens were divided into 3 main groups, 30 specimens each, according to the type of resin-composite used (Te-Econom, Heliomolar and Filtek Supreme). Each group was further subdivided into three subgroups, 15 specimens each, according to the storage condition to which they were subjected (S); namely S1 where specimens were stored in a dry dark tight sealed container, and S2 where specimens stored in a wet condition namely; in de-ionized water contained within a dark bottle. Each subgroup was further subdivided into three subgroups, 5 specimens each, according to the storage period (P) where P1 denotes for one month storage period, P2 denotes for three months storage period and P3 denotes for six months storage period.
All specimens were stored for 24 hours at room temperature 37 ± 1°C and 100% relative humidity, and then subjected to microhardness measurement using a Vicker’s microhardness tester and color measurement using a spectrophotometer. The baseline readings were recorded. Following that, each group was stored in the assigned condition for the selected period of time. At the end of the assigned storage period, the test specimens were stored in tea solution for 7 days. Then, the specimens were removed, rinsed, blotted dry and subjected to microhardness and color measurement. The change in hardness value was calculated for each sample according to the following formula:
ΔVHN= VHN (baseline) – VHN (after treatment).
While, color difference ΔE*= was calculated for each sample using the following equation:
∆E* = {(∆L*) ² + (∆a*) ² + (∆b*) ²} ½
The results of the current study revealed that, the hardness of all tested resin-composites decreased when stored in both conditions, at all assigned periods. The highest reduction in the hardness was recorded by Heliomolar, followed by Filtek Supreme, followed by Te-Econom which recorded the lowest values. For all tested resin-composites, perceptible color change was observed when stored in both conditions, at all assigned periods. However, the greatest perceptible color change was observed by Filtek Supreme, followed by Te-Econom, and then Heliomolar recorded the lowest values.
Regarding the relationship between the intrinsic discoloration and color change a positive relationship was found between them.
Conclusions:
Under the conditions of the current study, the following conclusions could be derived:
1- The type of composite has an influence on the color change and hardness of the tested materials regardless the storage condition and period.
2- The storage condition strongly influence the color and hardness of all tested resin-composites with the wet condition disturbing color more than the dry one, independent of the composite type or the storage period.
3- The storage period has an obvious role on the color changes and hardness of all tested materials in spite of the type of composite and the storage condition assigned.
4- A positive correlation was found between color and hardness changes in the present study.
Recommendations:
1. General change in color and decrease in hardness reported in the present study suggested that partial replacement of parts of old resin-composite restorations may not be regarded as an adequate solution.
2. Further studies for old to fresh resin-composite bonding are to be carried out to clarify the potentials of the sealing and bonding of the formed joint which may either support or contradict the results of the present study.
3. Despite the fact that composites have the advantage of accepting additions, this addition may not be considered a right choice according to our results as it may not provide the restoration with the esthetic quality required or physical standard accepted by the profession.
4. In the current study, although the decrease in hardness reported was insignificant from the baseline, a significant decrease may be recorded if longer periods are investigated. Therefore, new studies are called for in order to verify if longer periods of aging change these results.