Quantitative study of bacterial colonization of dental casts.

STATEMENT OF PROBLEM: Contamination of dental casts can occur if the record bases are improperly disinfected or inadvertently not disinfected during fabrication of a prosthesis. It is essential to develop an effective means of disinfecting dental casts from professional, medical, and legal points of view. PURPOSE: This study determined whether: (1) saliva contamination on the surface of the dental cast contributed to bacterial growth over time and (2) cleaning or disinfecting of dental casts can minimize bacterial growth. MATERIAL AND METHODS: Five dental casts were contaminated with saliva. Each cast was divided into six areas and swabbed at 15, 30, 60, 120, 180, and 240 minutes. Sheep blood agar plates were inoculated and incubated at 37 degrees C for 72 hours. Standardized dental stone cylinders were contaminated with 25 microliters of saliva and treated by rinsing in tap water, scrubbing with soap and tap water, soaking in 2% glutaraldehyde, or as controls with and without saliva contamination (n = 12). The treated dental stone cylinders were placed in individual test tubes containing 2.5 ml of sterile phosphate-buffered solution and a final dilution of 10(-4) was achieved. Sheep blood agar plates were inoculated and incubated at 37 degrees C for 24 hours. RESULTS: Contamination of dental casts did not decrease, even when allowed to sit 4 hours before handling. Results also demonstrated that rinsing saliva-treated stone cylinders for 20 seconds significantly diminished bacterial contamination. Scrubbing with soap and tap water or soaking in 2% glutaraldehyde significantly reduced the bacterial contamination of saliva-treated stone cylinders when compared with rinsing with tap water. CONCLUSION: Bacterial contamination of dental casts can occur and requires an effective method of disinfecting.

Lased and sandblasted denture base surface preparations affecting resilient liner bonding.

STATEMENT OF PROBLEM: Adhesive failure between the liner and the denture base creates an environment for potential bacterial growth and accelerated breakdown of the soft liner resulting in a deteriorating prosthesis. PURPOSE: This study evaluated the effects of a specific sandblasted or lased preparation on the interfacial bonding of polymethyl methacrylate and silicone and polyethyl methacrylate resilient liners. MATERIAL AND METHODS: Polymethyl methacrylate test specimens were fabricated and received one of three surface treatments: untreated (control), sandblasted (250 microns aluminum oxide particles), and lased (carbon dioxide). Polyethyl methacrylate and silicone resilient lining materials were applied to these surfaces and the peel strengths were determined with the American Society for Testing and Materials peelin-adhesion test. RESULTS: Altering the polymethyl methacrylate surface by sandblasting significantly reduced the peel strengths for the polymethyl methacrylate/polyethyl methacrylate and polymethyl methacrylate/silicone specimens. Altering the polymethyl methacrylate surface by delivering carbon dioxide laser energy to form a grid pattern produced lower peel strengths that were statistically significant from the controls for the polymethyl methacrylate/polyethyl methacrylate specimens, but not so for the polymethyl methacrylate/silicone specimens. Untreated polymethyl methacrylate/polyethyl methacrylate peel strengths were significantly higher than polymethyl methacrylate/silicone. CONCLUSIONS: Results of this study imply that mechanical surface preparation of denture bases before application of a resilient liner may not be warranted.