PURPOSE: To obtain the subject material with low offensive odor and irritancy, excellent in compatibility, and having high surface hardness after cured, by combining methacrylic ester polymer powder with a liquid component comprising specific compounds such as benzyl methacrylate.

CONSTITUTION: This backing material is a combination of methacrylic ester polymer powder (containing 0.01-5wt.% of a photopolymerization catalyst) with a liquid component composed of (a) 10-40wt.% of benzyl methacrylate, (b) 20-40wt.% of a compound of the formula (R is an alkyl) (pref. n-butoxyethyl methacrylate), (c) 20-70wt.% of a methacrylic acid compound having 2 to 3 methacryloyl groups in one molecule (pref. 1,6-hexanediol dimethacrylate or neopentyl glycol), and (d) a photopolymerization catalyst. A denture base obtained by using this backing material is excellent in compatibility, having sufficient mechanical strength and durability for a long period after used and also being excellent in resistance to discoloration.