A yellow powder with a melting point of 1,503 degrees Fahrenheit (817 °C) and a boiling point of 3434 degrees Fahrenheit (1,890 °C), bismuth trioxide is commonly found in fireworks to produce special "dragon's egg" effects. Bismuth trioxide is insoluble and thermally stable, suitable for ceramic, optic and glass applications. Although bismuth oxide can be found naturally as sphaerobismoite and mineral bismite, manufacturers synthesize bismuth trioxide by smelting lead and copper ores. Some dental materials incorporate bismuth oxide because the substance makes them easier for x-rays to distinguish from surrounding tooth structures. In addition, bismuth oxide is used to produce hydraulic silicate cement used in teeth and gum treatments such as pulp capping, pulpotomies, root canal sealing and pulp regeneration. Overexposure or prolonged ingestion of bismuth oxide may cause black spots to appear on the gums and induce excess salivation and halitosis.