Calcium hypochlorite as a disinfecting additive for dental stone

Statement of problem. Dental casts come into direct contact with impression materials and other items that are contaminated by saliva and blood from a patient's mouth, leaving the casts susceptible to cross-contamination. Topical methods of disinfecting casts are difficult to control, while immersion methods are potentially destructive. Thus, an additional method to control cross-contamination between patients and laboratory personnel is needed. Purpose. This study was undertaken in an attempt to develop a dental stone with disinfecting properties and adequate compressive and tensile strengths. Material and methods. Calcium hypochlorite [Ca(OCl)2] in aqueous solution in concentrations from 0 to 1.5% was tested as a disinfecting additive to type V dental stone. The compressive and tensile strength properties of the modified stone were measured (MPa) using a universal testing machine at a consistency similar to unmodified stone. Strength data were analyzed by 1-way ANOVA and post hoc Tukey-Kramer procedure (α ≤ .05). To measure the disinfecting ability, the effect on Bacillis subtilis bacteriophage phi29 was tested in triplicate to find the minimum concentration at which no phage was detected. Additionally, 3 impressions were disinfected with CaviCide, and 3 impressions rinsed in water served as controls. Results. In general, the effect of adding the disinfectant to the stone was a decrease in strength. Exceptions were the dry compressive strength, for which there was a significant increase in strength (P=.048) at 0.5%, and the wet compressive and wet tensile strength, which showed no significant difference between the 1.5% and the control. When Ca(OCl)2 was added at the concentration 0.5% (2765 ppm available chlorine), the gypsum had acceptable mechanical properties; dry compressive strength was 78.86 ± 4.12 MPa, and dry tensile strength was 10.64 ± 1.27 MPa, compared to control values of 67.85 ± 6.28 and 13.41 ± 1.24 MPa, respectively. At concentrations of 0.3% and higher (36 1650 ppm of available chlorine), calcium hypochlorite was able to completely inactivate phi29. Conclusion. It is possible to prepare a type V dental stone that contains a disinfectant, has adequate mechanical properties, and will reduce numbers of residual microorganisms. For example, stone mixed with water containing 0.5% Ca(OCl)2 meets these criteria.