Effect of microwave disinfection on some properties of gypsum products

Abstract

ABSTRACT
Background: Dental casts can be contaminated by saliva and blood from patient’s mouth through impression
materials, record bases, trial dentures...etc. Different methods were used to disinfect the dental cast; e.g. immersing
in, spraying with, or incorporating the disinfectant directly into the dental stone powder. These methods produced an
adverse affect on the properties of dental stone. This study was intended to evaluate the effect of different methods
of microwave disinfection; immersing in water, NaCl solution, or in dry air on the reproduction of details and surface
hardness of type III and type IV gypsum products at different time intervals.
Materials and methods: A microwave oven was used to disinfect type III and IV dental stone at 850 watt for 10
minutes while immersed in water, 40 % Sodium chloride solution, and in dry air during the disinfection procedure.
Surface hardness of the dental stone samples was evaluated by using the Brinell hardness test at different time
intervals; after 1hour, 2 hours, 24 hours, and after one week of start of mixing. Reproduction of details of the dental
stone samples was also evaluated.
Results: The surface hardness was significantly different for all the test groups at different time intervals except for the
water group after 1 and 2 hour for type III dental stone. The dry air group and water group were insignificantly
different after1hr for type IV dental stone. The test for reproduction of details showed no significant difference for all
the test groups except for NaCl group which was significantly different, the score was 2 which was clinical
insignificant.
Conclusion: Microwave disinfection can be used for dental stone casts while in dry air for type III & immersed in water
for type IV, with no effect on reproduction of details and with least adverse effects on the surface hardness of the
gypsum products.
Key words: Gypsum, microwave, disinfection, surface hardness. (J Bagh Coll Dentistry 2009; 21(4):47-52)