title: Calcium hypochlorite as a disinfecting additive for dental stone.
abstract: BACKGROUND
  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.
  
  
  OBJECTIVE
  This study was undertaken in an attempt to develop a dental stone with disinfecting properties and adequate compressive and tensile strengths.
  
  
  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 (alpha < or =.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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: School of Dentistry, University of Minnesota, Minneapolis, MN, USA.
authors.forename: Jonathan O
authors.initials: JO
authors.lastname: Twomey
authors.forename: Khalid M
authors.initials: KM
authors.lastname: Abdelaziz
authors.forename: Edward C
authors.initials: EC
authors.lastname: Combe
authors.forename: Dwight L
authors.initials: DL
authors.lastname: Anderson
mesh_terms: D000704:Analysis of Variance; D017103:Bacillus Phages / Q000187:drug effects; D017610:Calcium Compounds / Q000494:pharmacology; D002133:Calcium Sulfate / Q000737:chemistry; D019245:Compressive Strength; D019551:Dental Disinfectants / Q000494:pharmacology; D003799:Dental Stress Analysis; D008422:Materials Testing; D003765:Models, Dental; D018709:Statistics, Nonparametric; D013718:Tensile Strength
chemical_list: D017610:Calcium Compounds; D019551:Dental Disinfectants; C004488:calcium hypochlorite; D002133:Calcium Sulfate