Studies on prosthetic materials-measurement of the rheological properties of acrylic resins
Başlık çevirisi mevcut değil.
- Tez No: 400621
- Danışmanlar: PROF. DR. ALAN HARRISON
- Tez Türü: Doktora
- Konular: Diş Hekimliği, Dentistry
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1992
- Dil: İngilizce
- Üniversite: Unıversıty Of Brıstol
- Enstitü: Yurtdışı Enstitü
- Ana Bilim Dalı: Protez Ana Bilim Dalı
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: Belirtilmemiş.
Özet
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Özet (Çeviri)
Over the centuries a variety of materials have been used for the construction of dentures. The historical development of these materials from the early dentures carved from ivory, bone, and wood up to the latest acrylic resins have been discussed in this study. Today, well-fitting dentures are produced by low cost, easy manipulation and construction methods with excellent aesthetics. However, current denture base materials are still not ideal in every respect and there is a need for further research and development. Most acrylic resin denture base systems are supplied in a poly(methyl methacrylate) powder and methyl methacrylate liquid form. When these two components are mixed the mass passes through a series of stages viz: (i) sandy (H) stringy (iii) doughy (manipulation stage) and (iv) rubbery. Moulding or fabricating dentures is mostly carried out by the dough moulding press/pack technique. In this technique, a polymer/monomer mix during the dough packing stage is forced by the application of pressure to flow into, fill and conform to the shape of the mould. Ideally the packing manipulation stage should be as long as possible and the dough should exhibit good flow characteristics to give optimum packing plasticity. Properties which relate to the flow of the materials are known as rheological properties. The changing rheological properties during dough formation of acrylic resin denture base materials are thus important factors in the successful handling of these materials and can influence the accuracy and quality of the moulded denture. The rheological characteristics of acrylic resin denture base polymers are presented in this study. When the polymer and monomer are mixed, the mixture is at its lowest viscosity and highest flow. The viscosity increases and the penetration decreases at different rates with respect to increases of time. The material has shown that it behaves as a pseudoplastic fluid, that is, the viscosity decreases as the shear rate increases. There is an increase of viscosity with increasing temperature. Polymerisation plays a part in dough formation and the formation of the dough is related to evaporation of the monomer. The amount of residual monomer available in a reacting polymer decreases as the time interval from mixing to setting increases. The materials used in this study are characterised in respect of their constituents, mean powder particle size and distribution, molecular weight averages and distributions and glass transition temperature; their effect on the rheological changes under the same conditions have been shown. Considerable differences are observed in penetration, viscosity, doughing and manipulation times. The comparison of polymers indicates a higher viscosity for higher molecular weight. The smaller particles saturate with monomer more readily and give higher viscosity and lower flow. No correlation has been found between rheological properties and glass transition temperature of the materials investigated. The rheological properties are evaluated using different methods (i) probing following ASTM F451-76 and hole penetration following BS 2487:1989 (ISO 1567:1988), (ii) needle penetrometer, (iii) oscillating rheometer. The results indicate that although each of the methods is capable of evaluating the flow properties of the unprocessed polymers, the penetrometer has many advantages and would be ideal for a packing plasticity 'standard' test.
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