A castable glass-ceramic system for single tooth crowns has recently been introduced. The system promises improved aesthetics and excellent fit and has the potential to replace traditional single unit metal and ceramo-metal restorations. This project seeks to determine what microstructural changes occur during heat treatment of the material. Specifically, changes in crystallinity and preferred orientation will be determined by x-ray diffraction. Significant alterations will be characterized by scanning electron microscopy. These structural changes will be correlated with dimensional changes in three orthogonal directions to determine if there are anisotropic changes. A preliminary study to see how these factors alter fit will be conducted.