PubMed · 4873082
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D E Redqwell. 1968. Simple injection moulding.. https://pubmed.ncbi.nlm.nih.gov/4873082/
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OBJECTIVE: To determine the efficacy of 3 types of polymer-based saliva substitutes in reducing oral dryness in patients with Sjögren's syndrome (SS). METHODS: Subjective efficacy of 3 different saliva substitutes (determined by self-administered questionnaire) was evaluated in a double-blind, placebo-controlled trial in 43 patients with primary and secondary SS. High-viscosity versus low-viscosity xanthan gum-based saliva substitutes were also compared in 33 SS patients. Salivary flow rates (SFR) were determined to examine correlations between the SFR and the subjective efficacy of the saliva substitute. RESULTS: Neither the saliva substitutes nor the placebo was truly effective. Preference for a particular saliva substitute over placebo was equally distributed among the 3 types of substitutes. The SFR of patients who preferred polyacrylic acid-based saliva substitutes was lower than that in patients who preferred the porcine mucin-based substitute (P < 0.05). Patients whose oral dryness was reduced by low-viscoelastic substitutes had a low stimulated SFR ( < 0.20 ml/minute; P < 0.05). CONCLUSION: The optimal properties of a saliva substitute are not the same for all patients with SS, but are dependent on such parameters as the individual SFR. Thus, to determine the best saliva substitute for a particular patient, it is necessary to have the patient try a number of substitutes of different viscoelastic properties.
OBJECTIVES: Investigators have reported on the measurement of fracture toughness (K(lc)) of dental composites using a variety of testing methods. However, fracture toughness has been shown to be dependent upon several variables, including crack-tip sharpness and specimen geometry. This study was designed to compare the fracture toughness values obtained for two experimental and three commercial posterior composites, using four popular testing methods. METHODS: The four methods for testing fracture toughness included single-edge notched, compact tension, short rod with chevron notch and double torsion. The results were compared by ANOVA and Tukey's multiple comparison test (p < or = 0.05). RESULTS: The values obtained from the short rod test were significantly higher than those from the three other tests. Evaluation of the load-deflection curves and fracture surfaces suggested that the data for this test may not have been valid because a stable crack growth region could not be identified. In general, the fracture toughness results obtained from the double torsion test were lower than values obtained from the single-edge notched and compact tension methods. The double torsion test was the most difficult to conduct, resulting in only a 50% success rate. SIGNIFICANCE: The double torsion test, though possibly the most technique-sensitive of the four fracture toughness methods evaluated provides the most information about crack initiation and propagation and may be most indicative of the true fracture toughness of dental composites.