The amino terminal prepolymer which possesses the viscosity under 100Pas with (i)23C, (ii) said amino terminal prepolymer (i) polyaddition possible chemical compound, 40 - 85 where (iii) at least it brings minimum radioactivity non- permeability of 3mm/mmAl weight % it consists of the bulking agent, under non existing of the polymerization initiator the root tube seal composition for hardening possible dentistry.(i)23℃で100Pas未満の粘度を有するアミノ末端プレポリマー、(ii)該アミノ末端プレポリマー(i)と重付加可能な化合物、(iii)少なくとも3mm/mmAlの最小限の放射能不透過度をもたらす40~85重量%の充填剤からなる、重合開始剤の非存在下で硬化可能な歯科用根管封止組成物。