The physical and chemical properties of some polymeric dental materials
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A study was made of three groups of materials used in dentistryq i. e. denture base acrylics, "Gel-type" tissue conditioners and epimine resins. Conventional denture base acrylic made by curing a dough of methyl methacrylate and poly(methyl methacrylate) beads is considerably weaker than homogeneous poly(methyl methacrylate). The reasons for this were revealed by a comparison of their fracture mechanics and morphology. Phase inhomogenuity was found in denture base acrylic, the interstitial phase having lower Mv and Young's modulus than the bead phase. A viscoelastic and autoradiographic study of the denture base acrylic revealed that the two phases were interpenetrating polymer networks. It was found possible to improve the strength of denture base acrylic by the addition of methacrylic acid thus improving the 19 v of the interstitial polymer. The combination of methacrylic acid and cross-linking agent also facilitated the control of phase stiffness. Improving the molecular weight and matching the phase stiffness produces a conventional denture base material of comparable strength to homogeneous poly(methyl methacrylate)o A study of the effects on "Gel-type" tissue conditioners of an oral environment revealed the reasons for their loss of compliance during clinical use. The alcohol desorption and water absorption characteristics of the gels were studied. prom such studies and a knowledge of their chemical composition conclusions were drawn regarding the best ccr. positions for tissue conditioner gels intended for long service in the mouth. Two epimine ccnpounds, an impression rubber and a temporary crown and bridge material were studied. Their physical properties and chemical composition were determined. A car. parison of known long term behaviour of analogous resins; canbined with the determined physical properties of the epimine resins studiedt revealed some of the clinical limitations of such systems.
AuthorsCauston, Brian Edward
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