Fracture resistance of defective amalgam restorations repaired with a resin based-composite material

My thesis title is, “Fracture resistance of defective amalgam restorations repaired with a resin based-composite material.” This can be translated as, “The strength of broken teeth with a large silver filling (amalgam) repaired with a tooth-colored filling (resin-based composite material).” Lower first molars are one of the largest teeth in the mouth and have 5 cusps (2 bumps towards the cheek, one towards the back of the tooth, and 2 towards the tongue-side). Large silver fillings are sometimes placed in these teeth that span through the top center of the tooth and the front and back ends of the tooth. If the filling spans over half the width of the tooth, it is usually in need of a crown or “cap” that will be cemented over the top of the tooth for protection. It is common to see molars with large silver fillings that have been left alone with no crown coverage. At times, the cusps surrounding the filling may weaken and fracture. When this occurs, the dentist will usually remove the remaining silver filling and replace it with a new silver or tooth-colored filling, and then cover it with a crown. This study investigated the amount of force needed to break the tooth after repairing these silver fillings with tooth-colored fillings at the cusp fracture versus removing the silver filling entirely and replacing it with a tooth-colored filling. This is important because this can minimize the amount of healthy tooth structure you might damage when removing an old filling, while also testing the strength of the more conservative, less expensive approach of repair.

In this study, molars were filled with silver restorations, fractures were made by cutting/drilling the cusp off to simulate a fracture. These defects were repaired or replaced with tooth-colored resin composite according to their assigned group and aged by cyclic loading at 65N for 500,000 cycles in a 37C water bath using a wear machine, which was the equivalent of two years. Then the molars were continuously loaded until fracture using the Zwick Universal testing machine.

This study showed that the replacement of these defects was stronger than repairing, but repairing these defects could still be an alternative option of treatment, thus treating the tooth conservatively and possibly extending the lifespan of the tooth.