Comparison of diametral tensile strength of microwave and oven-dried investment materials

Statement of problem. Microwave drying technique for investment materials is believed to be timesaving by accelerating the elimination of free water content. Purpose. This study compared the diametral tensile strength of 4 investment materials used in removable partial denture framework fabrication. The investment materials were subjected to microwave and conventional oven drying at different time intervals. Material and Methods. Type III partial denture casting investments (Wirovest, Wiroplus, Biosint, PH2) were tested. A total of 160 specimens were prepared in cylindrical form at a height of 40 mm and a diameter of 20 mm, in accordance with the manufacturers' recommendations. Forty specimens were prepared from each product; 20 specimens were dried at 230 degrees C for 1 hour in an electric furnace, the other 20 were dried in a microwave oven for 10 minutes at 600 W. The dried specimens were tested at 2- and 4-hour intervals in diametral compression at a crosshead speed of 0.5 cm/min. Results. The microwave drying technique resulted in greater diametral tensile strength values for all investment materials. Conclusion. Within the limitations of this study, microwave drying of type III dental investment materials at 600 W for 10 minutes was, apart from strengthening the material, timesaving for the dental laboratory.