Effect of hot-Water Immersion on Flexural Strength of CAD/CAM Composite-Resin

Objectives: This study examined effect of hot water immersion on flexural strength of CAD/CAM composite-resin blocks.
Methods: Three commercially available CAD/CAM composite-resin blocks [Cerasmart 300 (GC, C300), KATANA AVENCIA P Block (Kuraray-Noritake, KAP), VITA Enamic (VITA, ENA)] were used.
Forty-five rectangular specimens (4.0±0.2×1.2±0.2×14.0±0.2mm) were cut from each composite-resin block, then randomly divided into three groups (n=15 each). One group was subjected to Soxhlet extractor at 90±5°C in deionized water for 28 days. Another group was immersed in deionized water at 37±2°C for 28 days. The remaining group was kept in air at 23±2°C for one day. Three-point flexural strengths (FS) were determined after each storage period at 23±2°C, and the results were analyzed (ANOVA/Scheffé, p<0.05). The surface morphology of specimens after the FS test were examined using SEM.
Results: The results are summarized in the table. Significant effects of the composite-resin blocks (F=368.2441, p<0.001) and storage conditions (F=34.9064, p<0.001) were found on FS. For C300, the specimen stored in hot water was lower FS than other conditions (p<0.05). For KAP, the specimens stored in air showed greater FS than other conditions (p<0.05). There were no significant differences in FS among three storage conditions in ENA (p>0.05). ENA specimens stored in both air and water immersion had lower FS than those of other blocks (p<0.05). The FS of KAP after hot water immersion was greater than those of the other blocks (p<0.05). And ENA showed the lowest FS among the blocks tested (p<0.05). SEM photographs indicated that there was plenty of pits on specimens kept in hot water compared to other specimens in all blocks.
Conclusions: Although the hot water immersion accelerated to deteriorate the surface texture of all composite-resin blocks, the effect of hot water immersion on FS was depending upon the products under the present experimental conditions.