Comparision 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.