Glass powder and chemical polymerization initiator

A polymerization initiator composition comprising:

• a glass powder including aluminum, silicon, strontium, fluorine, phosphorus, and at least one of copper or vanadium;
• and
• a chemical polymerization initiator,
• wherein, in the glass powder,
• a content of silicon, when converted into an amount of silicon oxide SiO2, is 20% by mass or more and 50% by mass or less,
• a content of aluminum, when converted into an amount of aluminum oxide Al2O3, is 20% by mass or more and 40% by mass or less,
• a content of strontium, when converted into an amount of strontium oxide SrO, is 15% by mass or more and 40% by mass or less,
• a content of fluorine is 1% by mass or more and 30% by mass or less,
• a content of phosphorus, when converted into an amount of phosphorus oxide P2O5, is 0.1% by mass or more and 15% by mass or less, and
• a content of at least one of copper or vanadium, when converted into an amount of copper oxide CuO or vanadium oxide V2O5, is 0.1% by mass or more and 5% by mass or less.