Hygroscopic and hydrolytic effects in dental polymer networks.

Polymerization shrinkage and polymerization shrinkage stress in polymer-based restoratives

Study of water sorption, solubility and modulus of elasticity of light-cured dimethacrylate-based dental resins

Effects of resin hydrophilicity on water sorption and changes in modulus of elasticity.

Influence of food-simulating solutions and surface finish on susceptibility to staining of aesthetic restorative materials

Polymethacrylate networks were made by copolymerization of a range of compositions of bis-GMA and triethylene glycol dimethacrylate (TEGDM). Polymerization was initiated both by heating with benzoyl peroxide or by photopolymerization (lambda greater than 400 nm) using camphoroquinone as sensitizer. The uptake of water increased from 3 to 6% as the proportion of TEGDM increased from 0 to 1.0. Intermediate compositions took up less water than would be predicted from the law of mixtures. Volumetric changes were determined and clinical significance discussed. A copolymer prepared by photopolymerization took up more water as the temperature was increased from 24-60 degrees C. In this range, values of the diffusion coefficient (D) conformed to the Arrhenius equation, D = Do exp (-E/RT), giving E = 42-46 kJ/mol and Do = 0.13 cm2 s-1.

Water sorption of polymethacrylate networks: bis-GMA/TEGDM copolymers.

The wear of a composite restorative material in the oral cavity was followed by examining impressions by scanning electron microscopy. It was demonstrated that filler particles protrude from the polymeric matrix and, eventually, are lost leaving holes in the surface. A measure of the rate of wear was obtained by following the recession of the matrix on the faces of a large prominent particle. For a restoration that had been in place for 7 years, the average rate of wear over a further period of several months was estimated to be about 0.1 microns/day. For comparison, the gross wear of 2 mm over the entire 7-year period gives a greater average rate of wear of 0.8 microns/day.

Microscopic observations of the wear of a tooth restorative composite in vivo

Composite materials were made by sedimention of ceramic powders in methyl methacrylate which was then polymerized by gamma-irradiation. Inclusion of 4-methacryloxyethyl trimellitic anhydride (4-META) generally was found to result in an increase in Knoop hardness number, Young's modulus, and transverse strength. Most emphasis was placed on transverse strength which was found to be increased by ca. 30% by inclusion of 4-META (5 wt %) in composites made with silanated LiAlSiO4. However an abrupt decrease in strength was found for composites with greater than ca. 83 wt % silanated LiAlSiO4. This was shown by fractography to be due to increased porosity and dewetting at the higher filler contents. Fractography also indicated that inclusion of 4-META results in a more coherent polymeric matrix. Further evidence for greater coherence was obtained by showing that 4-META confers resistance to disintegration by chloroform.

A new coupling agent for composite materials: 4-methacryloxyethyl trimellitic anhydride.

For convenience in clinical manipulation, it is the practice to fabricate PMMA prostheses from mixtures of powder and monomer. When the monomer is subsequently polymerized an unusual 2-phase polymeric material results in which grains of PMMA are dispersed in a matrix of the same polymer.



The mechanical properties of the 2-phase materials are inferior in certain respects relative to 1-phase polymers.



The purpose of the present work is to evaluate the failure of 2-phase materials by microscopical examination of their fracture surfaces. A granular microstructure was clearly distinguishable and a distinction made between materials which fail exclusively by transgranular fracture and others which additionally exhibit intergranular fracture.



In order to interpret markings observed on the fracture surfaces of the complex 2-phase systems a study was made of the influence of molecular weight on the fractography of 1-phase PMMA. Molecular weight was reduced by degradation of samples by exposure to γ-rays. The spacing of periodic rib markings on fracture surfaces was found to decrease with molecular weight and this relationship used to provide an estimate of the molecular weight of polymer in the matrix of 2-phase materials.

D. T. Turner

Papers

Water sorption of polymethacrylate networks: bis-GMA/TEGDM copolymers.

Microscopic observations of the wear of a tooth restorative composite in vivo

A new coupling agent for composite materials: 4-methacryloxyethyl trimellitic anhydride.

Fractography of poly(methyl methacrylates).

Intergranular cracking of a weak two‐phase polymethyl methacrylate