Comparative evaluation of shear bond strength of two nanofilled posterior composites as core build up materials: An in vitro study

Core build up is necessary as a foundation for post endodontic restorations when the tooth structure is severely damaged, fractured or extensively carious. Core build up material should provide resistance and retention form for the coronal restoration and possess sufficient strength to resist occlusal forces. An ideal core build-up material should have physical properties similar to those of tooth structure where the occlusal biting loads are transferred to dentin. The study evaluated and compared the shear bond strength of two nanofilled resin composites Group A - Filtek Z350 XT and Group B - Filtek Bulk fill) as core build up materials. Eighteen extracted permanent human molar teeth were sectioned horizontally with a carborandum disk beneath the DEJ to expose the coronal dentin surface and finished to create a uniform flat surface. Teeth are then mounted in custom-made wax molds (size 1.5 cm height, 1.5 cm length, and 5cm breadth) by autopolymerizing pink orthodontic resin, with coronal portion of the tooth exposed. Composite is layered over unset GIC and self-etch primer is used, over which composite is layered and cured. The samples are subjected to SBS test using Instron Universal Testing Machine. Mean and standard deviation for Bulk cure was 2.6033 MPa and 1.50829 and for Z350 2.4267 MPa and 2.65740 Levene's Test for Equality of Variances was done for checking the difference between groups (p=.090). The present study concluded that Filtek Bulk fill resin composite is similar to Filtek Z350 XT for core build with no difference in shear bond strength.