Methods: Thirty non-carious human molar teeth were used. Teeth were embedded in acrylic resin blocks up to 2 mm below to cemento-enamel junction. Standard Class I inlay cavities were prepared and teeth were randomly divided into three groups (n=10): (1) feldspathic-ceramic (CEREC Blocks, Sirona) group; (2) resin nano-ceramic (Lava Ultimate, 3M ESPE) group; (3) Leucite glass-ceramic (IPS Empress CAD, Ivoclar Vivadent) group. After making CEREC optical impressions, restorations were designed (CEREC SW 4.0, Sirona) and milled (CEREC inLab MC XL, Sirona). The inlay restorations were adhesively cemented with a dual polymerizing resin cement (Rely X Ultimate, 3M ESPE) and stored in distilized water at room temperature for a week. All the specimens were subjected to accelerated UV-aging for 300 hours. After accelerated aging specimens were subjected to a compressive load until fracture at a crosshead speed of 0.5 mm/min by using an universal testing machine. Statistical analyses were performed by using Kruskal-Wallis statistical test (P<0.05).
Results: The highest fracture resistance mean value was found for the resin nano-ceramic group (1524.83±393.90 N). The leucite glass-ceramic (1364.23±545.57 N) and feldspathic ceramic groups (1231.83±312.82 N) followed this group respectively. However there is no significant difference among the test groups (P=0.301).
Conclusions: The new resin nano-ceramic material has improved the fracture strength of Class I inlay restorations. So it can be an alternative restorative material for posterior region.