ABSTRACT
OBJECTIVE: In this study a simple non-contact method was developed to measure the polymerization shrinkage of dental composites. METHODS: A gas pycnometer was used to determine the volumes of specimens prior to and after photopolymerization and from which the total volumetric shrinkage could be determined. RESULTS: Four commercial composites were studied and were found to have polymerization shrinkages varying from 1.6 to 2.5%. The method was found to be labour efficient and produced reproducible results with a standard deviation of approximately 10%. SIGNIFICANCE: This method is appropriate for shrinkage measurements where only the total amount shrinkage is required and in particular for the measurement of shrinkage of photocured materials which are sensitive to water absorption.
Subject(s)
Composite Resins/chemistry , Materials Testing/methods , Materials Testing/instrumentation , Polymers/chemistry , Specific GravityABSTRACT
The combined use of an enrichment broth and gene amplification following simple DNA extraction to detect toxigenic strains of Clostridium difficile in feces was investigated by examining feces from 329 cases of suspected C. difficile infection. DNA was extracted by heating the washed centrifuged deposit from the broth in a microwave oven. For comparison, specimens were tested concurrently using standard methods for culture and cytotoxin testing. Amplified fragments were identified by molecular weight estimation, restriction enzyme digestion patterns and Southern blot hybridization. The combination of an enrichment broth followed by gene amplification was shown to be a sensitive, specific and rapid method for detecting toxigenic strains of C. difficile in feces. Use of the method in diagnostic laboratories may require the development of improved detection and verification systems for the amplified gene fragment.
