Physical Properties of CAD/CAM Hybrid Resin Blocks After Water Immersion

Objectives: Hybrid resin blocks for CAD/CAM are known as valid dental materials. CAD/CAM hybrid resin molar crowns have been adopted as the treatment covered by national health insurance in Japan last year. The materials for molar teeth are required high physical properties. Its bending strength should endure occlusal force in the daily life. For the purpose, it is essential to furnish less degradation character after water immersion to CAD/CAM hybrid resin blocks for molar teeth restoration. In this study, we aimed to evaluate the bending strength of the CAD/CAM hybrid resin blocks before and after water immersion and compare the reduction ratio of the bending strength between materials.
Methods: The materials used in this study were, CERASMART300 (CS300, GC), CERASMART (CS, GC), Lava Ultimate (LU, 3M ESPE), KZR-CAD HR2 (KZR2, YAMAKIN) and KATANA Avencia (KA, kuraray Noritake). These materials were cut in 1.2mm-thick, 4.0mm-width for three-point bending test and polished as specimens. Bending test was conducted with a crosshead speed of 1mm/min (SHIMADZU) under the following conditions i) dry storage (control, n=5), ii) storage in 37 degree C water for 7 days and 28 days (immersion, n=5). The data was analyzed by one-way ANOVA (p<0.01). The reduction ratio was calculated as the ratio of bending strength after water immersion to control.
Results: Bending strength after water immersion were decreased compared to the control in all materials significantly. Bending strength of CS300 was the highest and the reduction ratio of CS300 was the lowest among tested materials.
Conclusions: These results suggested that bending strength of hybrid resin blocks are decreased nearly 10 to 40 % by water immersion. CS300 had higher durability against water degradation than other hybrid resin blocks.