This type of filling is made of acrylic and a specific type of glass material. This material is most commonly used for fillings below the gum line and fillings in young children (drilling is still required). Glass ionomers release fluoride, which can help protect the tooth from further decay. However, this material is weaker than composite resin, more susceptible to wear, and prone to fracture. Glass ionomers generally last five years or less with comparable costs. The newest ones have an even better lifespan and, when placed in appropriate areas. are equal to composites.