Work simplification techniques make easy methods not so hard to find.

PURPOSE: To consider changes in the physical properties of mouthguard materials with the change of temperature, shock-absorbing examination and Shore hardness measurement of existing MG materials and other elastic materials were carried out. METHODS: Both examinations were done under two temperature conditions: at room temperature (25 degrees C) and simulated intraoral temperature (37 degrees C). In addition, a comparative study of the relation between Shore hardness and shock absorption of the materials was made. A self-made drop impact machine was used for the shock-absorbing examination. The thickness of a sample was assumed to be 3 mm. The loading was applied by dropping 3 kinds of steel ball, phi 10 mm (4.0 g), phi 15 mm (13.7 g), and phi 20 mm (32.6 g) from a height of 60 cm. The shock absorption of all materials was compared by the maximum impact force. Shore hardness was measured based on the JIS standard. RESULTS: The shock absorption of each material showed a different tendency depending on the loading condition. Furthermore, the shock absorption of the same material showed different results depending on the temperature condition. Shore hardness measurements tended to show low values with the condition of 37 degrees C for all materials. CONCLUSION: From the relation between shock absorption and Shore hardness, it was confirmed that there is a correlation between hardness and the maximum impact force in the materials that showed shock absorption by elastic deformation. Some materials showed high shock absorption compared with existing MG materials.

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PubMed2006

Effect of low O2-gas transmission rate barrier films on knoop hardness and toothbrush abrasion of resin cements.

PURPOSE: To investigate the influence of utilizing films with different oxygen transmission rates (O2-GTR) on Knoop hardness and toothbrush abrasion of resin cements for luting. METHODS: Four dual-activated, composite-type resin cements, and a chemically activated PMMA-type resin cement, were used. Three different types of barrier films (Techbarrier HI, Harden Film N130, and Lix-2) were used. Resin cement was mixed and inserted into a cylindrical mold (4 mm in diameter, 3 mm in height), then chemically activated. The specimens were stored in the dark at 37 +/- 1 degrees C, 90 +/- 5%RH conditions for 1 hour. Knoop hardness on the top surface of the resin cement was measured with a microhardness tester. The top surface of specimens (8 mm in diameter, 3 mm in height) polymerized under the same conditions were used for toothbrush abrasion testing. One-way ANOVA followed by Tukey HSD test (P< 0.05) were done. RESULTS: When the cement surface was covered by low O2-GTR film, a significant increase in Knoop hardness and resistance to toothbrush abrasion was observed for the dual activated, composite-type resin cements, but not for the chemically activated PMMA type resin cement. From the results of this study, the use of low O2-GTR matrix barrier films for the dual activated, composite-type resin cements could be effective in eliminating the oxygen inhibited layer on the cement surface.

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PubMed2005

[20 rules for hard nucleus phacoemulsification].

The mature cataract with hard nucleus still represents one of the most difficult task for modern phacoemulsification. The author presents some practical advise concerning both less experienced and experienced surgeons.

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