RESUMEN
Objective:To study the 3D accuracy of 4 impression materials.Methods:A metal mould with a custom tray was prepared for the measurement.Impression samples of 2 alginate and 2 rubber impression materials were prepared in the metal mould(n =3)re-spectively.The length of three tagged lines,along X,Y,Z axis directions of the samples was measured with a 3D optical scanner.Re-sults:120 min after sampling the variable rates of the length along X,Y,Z axis of Zhermark alginate samples were 3.615%,3.037%and 2.836%,those of CAVEX alginate samples were 2.836%,3.358% and 4.276% respectively;8 h after sampling the variable rates of Impregum Penta polyether rubber samples were 0.039%,0.071% and 0.057%,those of ExpressXT Penta H addition-curing silicone rubber samples were 0.033%,0.088% and 0.084% respectively.Conclusion:The variable rates of the 4 impression materi-als are in accordance with ISO1563∶1990.The variable rate of alginate impression material is greater than that of rubber.