The distal invagination of maxillary molars can create a bit of a challenge when adapting a matrix band. There are lots of matrix options, but if your normal armamentarium is a Tofflemire and band, then an application of a little Dycal can help out. Just a dab applied with a perio probe to fill the space. Then smooth carbide to clean up the flash. This can be removed with an interproximal carver at the time of amalgam carving or later with a scaler. Having this tip in the bag helps one practice Restoratively Driven Endodontics.