This paper presents results obtained from a comparative machinability study of newly invented ceramic materials for dental restorations. With the microstructure being the dominant factor on crack initiation and propagation during the fabrication process, the objective of this study is to identify the relationship between the microstructural characteristics and damage created during machining which could compromise the reliability of ceramic-made dental restorations. Glass ceramic material with tailored characteristics of microstructure is used in this study. The machining platform is milling operations where proper tool geometry and machining parameters are selected. Empirical models to correlate the cutting force and degradation of flexure strength with machining parameters are established. The aims of the research are to reduce surface cracking to yield improved surface finish (smooth < 2 mm) and to lessen strength degradation after machining. The study consists of four steps, including characterization of microstructure, identification of machining parameters, on-line monitoring of the machining operations, and evaluation of flexure strength degradation. Contributions of this study are the establishment of a procedure for carrying out the machinability assessment, and the establishment of empirical models relating the cutting force and fracture strength degradation to the cutting conditions.