PubMed · 14852632
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C H LAZARUS. 1951. Amalgam.. https://pubmed.ncbi.nlm.nih.gov/14852632/
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UNLABELLED: Electron beam irradiation can be used to influence the properties of polymers. It was the aim of this study to investigate whether PMMA denture base materials can benefit from irradiation in order to have increased fracture toughness, work of fracture or hardness. Rectangular specimens of heat-and auto-curing denture base materials were electron beam irradiated (post-cured) with 25, 100 and 200 kGy using an electron acceleration of 10 MeV or 4.5 MeV respectively. Fracture toughness, work of fracture, Vickers hardness and colour changes were measured and compared with not-irradiated specimens. The toughness, work of fracture and hardness increased using 10 MeV with a dose of 25 kGy and with 100 kGy using 4.5 MeV. However, the clinical use may not benefit from the observed small changes. Higher dosage (200 kGy) decreased the values significantly. The colour changes reached a level which was found to be not clinically acceptable. CONCLUSION: PMMA denture base materials do not benefit from post-curing with electron beam irradiation.
OBJECTIVES: Since the introduction of poly(methyl methacrylate) as a denture base material, it has suffered from having relatively poor mechanical properties. Many methods of improving its strength and toughness have been investigated. Most of these have not been adopted due to: increased cost, the need for specialist processing equipment or increased laboratory time due to more complicated procedures. Glass flake has been used as a reinforcing agent in many industrial polymers, but is as yet untested with denture base acrylic materials. The aim of this study is to evaluate the effect of adding glass flake to denture base acrylic powder on the fracture toughness of the set material. METHODS: Glass flake was added in 5, 10 or 20% w/w to Trevalon denture base powder. The material was mixed, flasked, packed and processed in a manner typical for a denture base material. Fracture toughness was determined using a double torsion test technique. RESULTS: The addition of glass flake gave up to a 69% increase in fracture toughness compared to plain Trevalon material. The addition of 5% glass flake lead to an improvement in fracture toughness that was statistically significant compared to both plain Trevalon and the 10 and 20% groups. SIGNIFICANCE: The significant improvement in fracture toughness of a denture base acrylic material using glass flake is an extremely promising result. Other mechanical properties will require testing before glass flake can be recommended as a reinforcing agent for denture base acrylic materials.
OBJECTIVES: To investigate by questionnaire, the use and selection of materials and techniques for the placement of direct restorations and the provision of endodontics and bleaching by dental practitioners in the North West of England and Scotland. METHODS: A questionnaire was sent to 1,000 general dental practitioners selected at random from dentists in Scotland and the North West of England. Non-responders were sent another questionnaire after a period of 4 weeks had elapsed. RESULTS: A total of 701 usable questionnaires were returned, giving a response rate of 70%. The most commonly used material for the restoration of Class II cavities in premolar and permanent molar teeth was amalgam (n = 605, 86%) and (n = 634, 90%) respectively. Many practitioners (n = 419, 60%) felt amalgam should continue to be used but a majority (n = 374, 66%) remained unconvinced about the merits of amalgam bonding. A minority (n = 63, 9%) of practitioners used predominantly directly placed resin composite rather than amalgam to restore Class II cavities in premolar and permanent molar teeth. Home-based vital bleaching was provided by a significant number (n = 245, 35%) of practitioners with only 18% (n = 123) providing practice-based bleaching. The most commonly used endodontic obturation technique was cold lateral condensation (n = 527, 75%) with 61% (n = 425) of respondents not using rubber dam routinely for endodontics. CONCLUSIONS: For the practitioners in this survey, amalgam was the most frequently selected direct restorative material. Few practitioners used amalgam bonding let alone direct resin composite for posterior restorations. Home-based rather than practice-based bleaching procedures were preferred, as were more traditional endodontic obturation techniques.