Fracture resistance of overlays of upper premolars restored by two types of pressable ceramics.

INTRODUCTION: There is a lack of scientific evidence about the fracture resistance properties of the newly introduced pressable type zirconia-reinforced lithium silicate when partial coverage is indicated for upper premolars. OBJECTIVE: The aim of the study is to evaluate the fracture resistance and fractographic analysis of lithium disilicate and zirconia-reinforced lithium silicate used in overlays.MATERIALS AND METHODS: Twenty-six duplicated epoxy resin dies were prepared following overlay preparation guidelines. The specimens were divided into two groups to be restored with lithium disilicate (IPS e.max Press) or zirconia-reinforced lithium silicate (Vita Ambria) (n=13 each). Cemented overlays were subjected to thermomechanical fatigue, and the load to fracture was tested by using a universal testing machine. The normality of the fracture resistance was checked using the Shapiro‒Wilk test and Q‒Q plots.RESULTS: when comparing overlays restored with lithium disilicate and those restored with zirconia-reinforced lithium silicate, the comparison was statistically significant. Group of overlays restored with zirconia-reinforced lithium silicate showed higher mean fracture load of 1218.69. CONCLUSIONS: The newly introduced zirconia-reinforced lithium silicate had higher fracture resistance than did the lithium disilcate and could be an alternative for partial coverage restoration.KEYWORDS: Fracture resistance, Lithium disilicate, Zirconia-reinforced lithium silicate, partial coverage restorations.RUNNING TITLE: Fracture resistance of two ceramic materials in overlays.