Comparison of Retention and Fracture Load of Endocrowns Made from Zirconia and Zirconium Lithium Silicate After Aging: An in-Vitro Study

Background: This study aimed to compare retention and fracture load in endocrowns made from zirconium lithium silicate and translucent zirconia. Methods: : Fifty-six intact human maxillary molars after being mounted in acrylic resin, were scanned to acquire biogeneric copies. Specimens underwent standard endodontic treatment and were prepared for endocrown up to 2 mm above the cementoenamel junction. The specimens were randomly divided into two groups of 28 and endocrowns were designed using biogeneric copies and milled from high-translucent zirconia disks (Zr) and zirconium lithium silicate blocks (ZLS). After cementation with dual cure resin cement, all the specimens underwent thermomechanical aging and pull-out retention test and compressive test were conducted (14 specimens were used for each test in each group, n=14) and failure modes in both tests were evaluated. Results: : Independent samples t-test showed significant difference between the retention of Zr (271.5 N ±114.31) and ZLS (654.67 N ±223.17) groups ( p value = 0.012). Compressive test results were also significantly different between Zr (7395.07 N ±1947.42) and ZLS (1618.3 N ±585) ( p = 0.002). Failure mode of retention test was primarily adhesive failure at the cement-restoration interface in Zr group and cement-tooth interface in ZLS group. Failure modes of fracture test for Zr group were 7 non-restorable fractures and one restorable fracture while 6 specimens resisted compressive loads up to 8500 N without fracture. ZLS group showed 7 restorable and 7 non-restorable failures. Conclusions: : Zr endocrowns showed significantly lower retention and higher fracture strength. Both materials seem to be suitable for fabrication of endocrown in clinical setup.