Introduction: Internal adaptation is the space between the restoration and tooth preparation. Nakamura reported the closer the adaptation between a ceramic restoration and its abutment, the greater a crown's resistance to fracture. Ideal internal adaptation is as minimal as possible while still allowing for complete seating of the restoration. Objective: This study compared the internal adaptation of maxillary anterior crowns milled from four different materials on a 3-axis milling machine. It was hypothesized there would be no difference between the test groups.