Regional ultimate tensile strength and water sorption/solubility of bulk-fill and conventional resin composites: The effect of long-term water storage

Abstract

The effect of long-term water storage on the regional ultimate tensile strength (UTS), water sorption (Wsp) and water solubility (Wsl) of conventional and bulk-fill resin composites at various depths was investigated. Composite specimens light-cured from one side were sectioned into beams corresponding to different depths (1-5 mm) and stored in water for 24 h, 1 week, 1 month, 6 months or 1 year. UTS increased during the first week and then gradually decreased over time, especially in deeper regions. Bulk-fill composites initially exhibited similar UTS at all depths, whereas the UTS of conventional composites at 1 mm and 5 mm differed significantly at all time points. Wsp and Wsl increased with depth and storage time, markedly at 3-5 mm after 1 month for conventional composites and after 6 months for bulk-fill composites. The signs of degradation at depths beyond 3 mm suggested that even bulk-fill composites have suboptimal properties in layers more than 3 mm in thickness.

Polymerization shrinkage of light-cured conventional and bulk-fill composites —The effect of cavity depth and post-curing

“…During the post-curing stage, the polymerization of RBCs slowly continues even beyond 24 h and increases the degree of conversion 11,14,33) , thus increasing the depth of cure with less shrinkage in deeper layers. On the other hand, the post-cured regions were reported to absorb more water in the long term, deteriorating their mechanical properties 20) .…”

“…On the other hand, the post-curing stage continues slowly up to or beyond 24 h after light irradiation [11][12][13][14] . The post-curing stage is more pronounced in deeper layers that receive less light energy, because the extent of the light-curing stage is limited 15) and the low-density polymer matrix network allows for the internal mobility of the light-activated free radicals [16][17][18][19][20] . The proportion of light-and post-curing stages in the polymerization process would be dependent upon composite thickness, and it might affect the polymerization shrinkage behavior of RBCs, but this has not been sufficiently examined to date.…”

An Analysis of Water Sorption of Some Composites Used in Dentistry

“…However, in the results of these studies, it has been stated that water absorption is higher in regions far from the polymerization light in thicknesses of more than 2 mm. It is appropriate to apply a maximum of 3 mm composite layers when bulk-fill composites are used [12].…”