title: Cast erosion from the cleaning of debris after the use of a cast trimmer.
abstract: BACKGROUND
  Whether using tap water to rinse off debris will make a clinical difference to the surface detail of a gypsum cast is unknown. In addition, how best to remove debris from the cast is unknown.
  
  
  OBJECTIVE
  The purpose of this in vitro study was to evaluate the efficiency of different methods of cleaning a gypsum cast after trimming and the effect of short-term exposure to tap water on the surface quality of the cast.
  
  
  METHODS
  A die fitting American National Standards Institute/American Dental Association specification 25 (International Standards Organization specification 6873) for dental gypsum products was embedded in a Dentoform with the machined lines positioned at the same level as the occlusal surface of the posterior teeth. A flat plate was used to ensure that the plane of occlusion for the die was at the same position as the posterior teeth. Forty polyvinyl siloxane impressions of the Dentoform were made and poured with vacuum-mixed improved Type IV dental stone. Each cast was inspected for the accurate reproduction of the lines. The base of the 2-stage pour was trimmed with a cast trimmer with water, and surface debris was removed by rinsing by hand under tap water for 10 seconds, by brushing the cast with a soft toothbrush for 10 seconds, or by resoaking the cast and using a soft camel hair brush in slurry water for 10 seconds. The amount of debris was evaluated on a scale of 1 to 4, and the quality of the 20-μm line was evaluated on a scale of 1 to 4 under ×15 magnification. The nonparametric Kruskal-Wallis ranks test was used to identify significant differences among the different cleaning methods (α=.05).
  
  
  RESULTS
  Results of the Kruskal-Wallis and Kruskal-Wallis Z-value tests demonstrated that all cleaning methods produced cleaner casts than were observed for uncleansed controls (P<.001), but no differences in debris removal were found among the different cleaning methods (.065≤P≤.901). The ability to see the quality of a 20-μm line (P=.974) was not statistically different among the groups.
  
  
  CONCLUSIONS
  Rinsing the cast under flowing tap water and brushing, or hand washing under flowing tap water, or using a soft camel hair brush in slurry water for 10 seconds had no noticeable effects on the quality of a 20-μm line, and all 3 methods resulted in a clean cast.
authors.affiliation: Associate Professor, Section of Prosthodontics, Department of Adult Restorative Dentistry, University of Nebraska Medical Center College of Dentistry, Omaha, Neb. Electronic address: phansen@unmc.edu.
authors.forename: Paul A
authors.initials: PA
authors.lastname: Hansen
authors.affiliation: Research Service, Veterans Affairs Nebraska-Western Iowa Healthcare System, Omaha, Neb; and Professor, Section of Biomaterials, Department of Adult Restorative Dentistry, University of Nebraska Medical Center College of Dentistry, Omaha, Neb.
authors.forename: Mark W
authors.initials: MW
authors.lastname: Beatty
mesh_terms: D002133:Calcium Sulfate; D003735:Dental Casting Technique / Q000295:instrumentation*; D003764:Dental Materials; D006801:Humans; D066298:In Vitro Techniques
chemical_list: D003764:Dental Materials; D002133:Calcium Sulfate