Biomedical subjects
Publications and source records attributed to D R Beech.
Since its inception, in 1986, the Australian Vigilance System has had voluntary and compulsory components. The voluntary component is the Therapeutic Device Problem Reporting Scheme and the compulsory one is requirements on sponsors to report as a condition of entry on the Australian Register of Therapeutic Goods. In addition, reports produced worldwide are actively monitored for their applicability to Australia.
This study was undertaken to determine if the time after which teeth are extracted influences the tensile bond strength of a glass ionomer (Fuji II: GC) and a dentin bonding agent (Scotchbond Self Cure; 3M) to dentin. Within 20 min of extraction, 14 teeth were bonded with glass ionomer and 13 teeth with Scotchbond Self Cure plus a composite material (Clearfil; Kuraray), by attachment of orthodontic brackets to prepared dentin surfaces. The bonds were fractured in tension, and yielded values of 3.7 MPa for glass ionomer and 1.08 MPa for Scotchbond Self Cure + Clearfil. These data were significantly different (P less than 0.002) from data previously obtained from the use of old teeth, from which values of 2.20 MPa and 1.82 MPa for glass ionomer and Clearfil + Scotchbond Self Cure, respectively, were obtained. It was concluded that the time after extraction can significantly change bond strengths to dentin, but that the direction and magnitude of these changes depend on the adhesive system used.
Despite concerns and claims that the smear layer on dentin is undesirable for bonding, supportive evidence is lacking. The clinical efficacy of various agents for smear layer removal and the effect of smear layer removal on the bond strengths of a glass-ionomer cement and three representative dentin bonding agents were examined. For all but one dentin bonding agent (Gluma), a 15-second treatment with 17% EDTA caused a reduction in bond strength. For Gluma, no significant bond was obtained without EDTA treatment. While Gluma probably bonds via dentinal collagen, the other materials interact primarily with dentinal calcium. Removal of the smear layer for adhesives reliant on the presence of calcium is therefore undesirable. The clinical effects of some agents proposed for smear layer removal were examined by SEM of replicas.
Six different composite resin restorative materials were placed in posterior Class I and Class II cavities and evaluated at one and two years after placement for colour, marginal discoloration, and wear. Wear was determined by comparison with standard models and by SEM. All materials darkened over the study period but remained an acceptable match. Marginal discoloration increased. The trend of relative wear was in accordance with predictions from fracture mechanics. Insufficient restorations in one material were available at two years for it to be included in the results. The microfine materials used in this study suffered surface damage (micro-chipping) in high stress areas, again consistent with fracture mechanics predictions.
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The chemistry and structure of the dimethacrylate resins and the nature of the filler systems in dental composite resins are reviewed in relation to their influence on the setting behaviour, dimensional stability, aesthetics, fracture behaviour and adhesive potential. It is clear that a deeper understanding of the structure of the polymeric matrix and the mechanism of clinical wear is required. As a result of ongoing research in this area and with the development of dentine adhesives, the future prospects of composite resins are encouraging.
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A method for accelerating the dissolution and erosion of 'acidic' dental cements has been developed which gave relative solubilities in accordance with in vivo observations, in contrast to the conventional test. It involves subjecting 24-h-old specimens to a jet of dilute acid (lactic or citric) and determining weight loss. The relative ranking for 'acidic' cements in the apparatus and in vivo was: glass ionomer less than silicophosphate less than zinc phosphate less than polycarboxylate. The method was not valid for reinforced zinc oxide/eugenol/EBA cements. Of the two polycarboxylate cements studied, a brand which has the acid in the powder was found to be more soluble than the conventional material. It is proposed that the method be the basis of a new solubility/erosion test in national and international standards for 'acidic' dental cements.
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Mechanical and adhesive properties of polycarboxylate and glass ionomer cements were studied. Water had an adverse effect on the compressive and tensile strengths of both materials. Both cements showed good bonding to enamel and dentine. Bonds between polycarboxylate cement and sterling silver were strong enough to cause cohesive failure of the cement rather than adhesive failure, when the specimens were tested. Surface cleaning and conditioning with 5% sodium hypochlorite solution showed an improvement in the bonds of the cements to dentine and they were significantly stronger than the bonds formed after the use of 50% citric acid solution (ASPA conditioner.)