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ABSTRACT
Objective: To determine the changes in surface hardness occurring due to disinfection of denture base acrylic resins.
Materials and Method: 80 disc shaped test specimens (13 mm x 8 mm) fabricated from heat polymerised acrylic resin were subjected to Vickers' hardness test before and 15, 30, 60 and 90 days after disinfection in one of the test disinfectant solutions (1% sodium hypochlorite, 2% alkaline glutaraldehyde or 4% chlorhexidine gluconate) at room temperature for 10 minutes. The control specimens were stored in distilled water at room temperature without disinfection. Vickers' hardness test was performed on these control specimens after 15, 30, 60, and 90 days of storage in water.
Result: Mean values demonstrated a significant decrease in hardness after disinfection regardless of the disinfectant solutions used. However, this effect was reversed after 15 days of storage in water and continuous increase in hardness values for up to 60 days of water storage, after which no significant change was observed upto 90 days.
Conclusion: Chemical disinfection by immersion method significantly affects the hardness of heat polymerised acrylic resin tested. However, 4% chlorhexidine gluconate least affected the hardness of resin whereas 2% alkaline glutaraldehyde affected the hardness to a maximum. This effect was found to reverse after 15 days of storage in water.
Keywords: Vickers Hardness Number, Disinfection, Acrylic Resin, Water Immersion
INTRODUCTION
Dentists, auxiliary personnel and dental laboratory technicians may be exposed to a wide variety of harmful microorganisms during clinical and laboratory dental procedures. Prostheses in contact with oral tissues, saliva, and blood, when removed from patients' mouths at various stages of finishing, polishing and repairing procedures may be contaminated by pathogenic microorganisms which may be transmitted through direct or indirect contact or through the aerosol during trimming, finishing, and/or polishing procedures.1
Prostheses and dental appliances should be disinfected in both the dental office and laboratory and before being inserted intraorally, to eliminate cross contamination.2 However, frequent immersion of acrylic resin in disinfectants may affect the mechanical properties of the material. One property which changes to a significant level is hardness. Hardness measurements have been successfully used as an indirect method of evaluating polymerization depth of resin based materials and the degree of conversion of conventional heat polymerizing and self curing acrylic resins....