This book is concern about the Cuspal deflection which represents interactions between the polymerization shrinkage stresses of the composite resin and the compliance of the cavity wall, which may cause failure during curing composite restoration or act as a preloading, facilitating tooth fracture under occlusal loads. It has been reported that placing resin composites in MOD cavities leads to inward deflection of the cusps, and the amount of cuspal deflection differed according to the materials and filling techniques used.This book is conducted to evaluate and compare the cuspal deflection between four newly low-shrinkage restorative resin composites SDR®(Smart Dentin Replacement), high viscosity Bulk fill QuiXfil®, high viscosity nano-hybrid Tetric EvoCeram® Bulk Fill and Universal Nano-hybrid Tetric EvoCeram®, and the effect of different water storage periods on cuspal deflection. Cuspal deflection was calculated by measuring the intercuspal distance between the indexed cusp tips using Newly modern Method.