PURPOSE: A dental resin material showing improved bond strength to ebur dentis and low irritation to dental pulp, having low change in volume caused by polymerization, comprising 5,6-benzo-2-methylene-1,3-dioxepane and a polymerization initiator.

CONSTITUTION: A dental resin material usable as a filler, an adhesive, resin for plate, etc., comprising 5,6-benzo-2-methylene-1,3-dioxepane shown by the formula IV obtained through a compound shown by the formula III which is prepared by reacting a compound shown by the formula I with a compound shown by the formula II, as a polymerizable component, and a polymerization initiator (preferably radical polymerization initiator or hydrous organic acid polymerization initiator, and an amount of it used is preferably 0.1W50wt% in the dental resin material), which are packed into or applied to the affected part such as tooth cavity, etc., thermally polymerized or subjected to photopolymerization, and stuck fast to the affected part.