Biomedical subjects
G J Mount
Publications and source records attributed to G J Mount.
Clinical performance of glass-ionomers.
Glass-ionomers were introduced to the profession 20 years ago and have been shown to be a very useful adjunct to restorative dentistry. Their major advantages include the ion exchange adhesion to both enamel and dentine and a continuing fluoride release throughout the life of the restoration. The chemistry of the setting reaction is essentially an acid/base reaction but recent research has introduced variations in an effort to improve clinical handling. Small additions of resin increase the physical properties to a degree and allow for a light-initiated setting mechanism. However, it is essential that the acid/base reaction remains dominant if the full advantages of the glass-ionomer are to be retained. The material has multiple uses in dentistry and it shows a high degree of biocompatibility to the pulp and surrounding soft tissues. The main limitation at this time is a relatively low fracture resistance but it is possible to protect it through lamination with stronger materials if the need arises. This paper examines the essential parameters for successful clinical placement and comments on its longevity.
A new cavity classification.
With the development of adhesive restorative materials and a far better understanding of the action of the fluoride ion it is suggested that the time has arrived for a reassessment of the traditional cavity classification as set out by G.V. Black over one hundred years ago. When preventive measures and remineralization fail and a carious lesion has progressed through the enamel into the dentine there is a need to remove the infected dentine, and possibly some of the affected dentine as well, to eliminate cavitation and avoid further accumulation of plaque. In most situations this will involve removal of enamel to achieve access to the infected dentine but, in the presence of fluoride, both enamel and dentine are capable of being remineralized and therefore conserved, at least to a degree. The principle of minimal extension must be encouraged to allow maximum preservation of natural tooth structure. A new cavity classification is proposed which is designed to make the most of the potential for healing which is inherent in both enamel and dentine. However, it must be accepted that a considerable proportion of restorative dentistry is carried out to replace failed restorations and, in this case, cavity design will be complicated by existing loss of tooth structure.
Electron probe microanalysis and transverse microradiography studies of artificial lesions in enamel and dentin: a comparative study.
In cardiology and research involving the interactions between restorative materials and dental hard tissues, it is important for small changes in tooth mineral content to be measurable. Currently, transverse microradiography (TMR) is the most accepted tool for the above purpose. Electron Probe Microanalysis (EPMA) can yield both qualitative identification of elements and quantitative compositional information. The purpose of this study was to compare the mineral distribution in well-defined artificial lesions, in dentin and enamel, by the use of both TMR and EPMA on the same sample. The good correlation between the two sets of data validates EPMA as a technique and helps in the interpretation of its results. The data from TMR analysis are expressed as vol% of mineral, while EPMA gives the levels of Ca and phosphate in wt%. The conversion between the two sets of data is complicated by the fact that local density is, as yet, unknown.
A study of glass-ionomer cement and its interface with enamel and dentin using a low-temperature, high-resolution scanning electron microscopic technique.
This report describes a method of immobilizing the water contained in glass-ionomer cement and dental hard tissues and stabilizing the delicate organic component of dentin. With this method, the intact interface between glass-ionomer and dental hard tissues can be observed under scanning electron microscope with few of the artifacts that are caused by the desiccation associated with conventional scanning electron microscopic studies. There was a distinct zone of interaction between the glass-ionomer cement and enamel and dentin. Under severe thermal stress, glass-ionomer cement failed cohesively, leaving an intact interface with enamel and dentin. Machine-mixed glass-ionomer cements displayed a high level of porosity. Some glass particles were separated from the matrix, and there was evidence that some are dislodged from the matrix during specimen preparation.
A revised classification of carious lesions by site and size.
The present classification used by the profession for the identification of carious lesions was devised by Black about 100 years ago. It was based, in part, on the location of the lesion but was modified to take into account the materials that were available for restoration. Over the last 20 years, there has been considerable modification of these materials; adhesion between the restoration and tooth structure is now possible, and the understanding of the relevance of fluoride and other ions in the prevention and repair of caries has improved. It would be logical at this time to adopt a new classification based on the site of the carious lesion and the extent to which it has progressed. More relevant detail could be recorded for each restoration, and this would be of value both for personal records and epidemiologic studies. The proposal is a simple digital system that is compatible with the use of computers for record keeping.
Longevity in glass-ionomer restorations: review of a successful technique.
It is just 20 years since glass-ionomer cements were introduced to the profession as a restorative material capable of an ion exchange adhesion to tooth structure as well as a continuing fluoride release. At the time of presentation there was considerable publicity, but, in retrospect, it is likely that the materials were marketed prematurely, before there had been a great deal of clinical investigation. The clinical short-term results were rather disappointing, particularly in relation to esthetics, because the original version lacked translucency. In the next few years, some manufacturers worked to refine the product and improve the properties and achieved reasonable results. In the early 1980s, it was shown that the main problem with both esthetics and physical properties was the need to maintain a proper water balance in the material during the early setting phase. Once this problem was identified and overcome, it became possible to achieve excellent results, but these have not been reported frequently. This article discusses a method of placement that will lead to acceptable glass-ionomer restorations and shows a series of restorations that are up to 15 years old.
Changes to Dyract restorative resin immersed in various media.
PURPOSE: To examine changes in weight, strength, fluoride release, and surface changes to the polyacid-modified resin composite Dyract after immersion in various media for periods up to 16 weeks. MATERIALS AND METHODS: Properties investigated were change in weight, strength, release of fluoride ions, and surface changes. Specimens were immersed in reverse osmosis deionized water (ROW) and in acetate buffer solutions containing calcium hydrogen orthophosphate. The acetate media were of pH3, pH5 and pH7. All solutions were maintained at 37 degrees C without agitation. Solutions were changed weekly and retained for fluoride analysis and specimens were weighed each week. After periods of 1, 2, 3, 4, 8, 12 and 16 weeks, some specimens were subjected to shear punch testing and SEM examination. RESULTS: All specimens except those in pH3 medium gained weight for the first 2-5 weeks after which weight was lost until all specimens weighed less than at the commencement of the study. The specimens in pH3 medium lost considerable weight from weeks 1 and 2. SEM examination showed disintegration of the surface of all specimens examined. Fluoride release peaked at 1 week in all specimens except those in pH3 medium. Fluoride release was highest in pH3 media (approximately 46 ppm) after 1 week and remained high for 7 weeks, after which it was reduced to about 50% of the initial release. Specimens stored in ROW and pH5 media released approximately 5 ppm after 1 week, and this was reduced to approximately 1 ppm (pH7) and 2 ppm (ROW) by week 6.
The strength of auto-cured and light-cured materials. The shear punch test.
This paper examines the versatility of the shear punch test as described by Roydhouse and suggests that it should be considered as an alternative to the present standard compressive strength test for glass ionomer cements and flexural strength for composite resins. The shear punch test can be used for examining small thin specimens, about 1.0 mm thick and 8.0 mm in diameter, of both auto-cured and light-cured restorative materials such as composite resins and glass ionomer cements. The preparation of the specimen is simple and does not require a precision mould or subsequent machining to size except that, after curing, it may need to be abraded gently to obtain flat parallel test surfaces. The test apparatus consists of a punch approximately 3.0 mm in diameter opposing a true fitting matching die. The specimen is supported over the die section and the punch is advanced through it in a compression cage. The formula used to calculate the shear strength allows for variation in specimen thickness and thus provides comparative data between materials. It also allows examination of the effects of variations in manipulation, maturation and storage of each material. It is suggested this test should be considered as an alternative to the present compression and flexural strength tests because it would provide a single strength test for a range of restorative materials being manipulated under a variety of circumstances. It is of particular significance for testing the light-cured materials because it examines a specimen size below that of the diameter of the exit window of a normal clinical light curing unit and also at a thickness where depth of cure of the material is not a problem.
Confusion in the use of terms.
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Glass-ionomer cement restorations.
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Some physical and biological properties of glass ionomer cement.
It has become apparent through both clinical use and laboratory experiments that the glass ionomer cements have several highly desirable properties. They show a continuing fluoride release and the ability to take up further fluoride under favourable conditions. The presence of fluoride also helps to inhibit plaque formation. The adhesion between tooth structure and cement also results in almost complete prevention of the bacterial micro-leakage. Also, the cement itself is so highly bio-compatible that it is now being used as a bone substitute and it has become apparent that there is no need to place a sub-lining under a glass ionomer restoration. Recent research is leading to the development of self curing cements with enhanced physical properties so that, in the presence of the above advantages, their use in clinical dentistry is rapidly expanding. Glass ionomer cements are of great value for any restoration which is not under undue occlusal stress and they work well also as a long term temporary restoration in the presence of a high caries rate, where zinc oxide and eugenol used to be the material of choice.
Observations in Australia of the use of glass ionomer cement restorative material.
The aim of this study was to evaluate, with the aid of a questionnaire distributed to selected groups of dentists, the use of glass ionomer cement in different types of proximal restorations and further to evaluate any complications observed with the use of GIC. Few dentists responded in the 'Often' category regarding the observation of secondary caries or gingival inflammation in association with GIC fillings compared with about three-quarters of the dentists who reported on posterior composite resin restorations. Tunnel cavities had been prepared and restored by 54 per cent of the dentists, simple proximal restorations in primary molars by 89 per cent and 'sandwich' restorations by 69 per cent. Few dentists with at least two years experience with tunnel restorations observed biological complications, but fracture of the marginal ridge was reported in the 'Often' category by 12 per cent. Among the dentists with at least five years experience with proximal restorations in primary molars 59 per cent of the operators mentioned more complications with these than with amalgam restorations. Biological complications were not a great problem with glass ionomer/composite laminates but wear or dissolution of the proximal GIC surface was recorded in the 'Often' section by 14 per cent of those placing them.
Glass ionomer cements and future research.
Once a root surface lesion has extended into tooth structure beyond the point at which it can be successfully remineralized it is necessary to carry out traditional restorative procedures. Often the extent of the lesion is difficult to define and development of a pulp exposure is an ever present risk. Access may be difficult and placement of a restorative material, such as amalgam, which requires positive condensation for correct placement, poses a problem. The principal requirement of a restoration in such a lesion is that it should completely seal the restoration/tooth interface and prevent the ingress of further bacteria or bacterial nutrients. As there will be no occlusal load, physical properties of the restorative material are not significant. As these lesions will often occur on anterior teeth it is desirable that the material be reasonably esthetic although there will be no need for a great depth of translucency. The modern trend to light curing of restorative materials facilitates placement but there are situations with these lesions where it is difficult or impossible to obtain proper access for the light and an auto cure material may be indicated. Because the patient who presents with root surface lesions is likely to pose a continuing problem, it is desirable that the restorative material have some degree of in-built protection against further demineralization. An ongoing fluoride release is very desirable. Glass ionomer cement fulfils all the above requirements and is therefore at present the material of choice. Either the original auto cure cement or the newer dual cure materials will provide a complete marginal seal with a continuing fluoride release throughout the life of the restoration and both varieties are sufficiently esthetic to be entirely acceptable.
Clinical placement of modern glass-ionomer cements.
The main advantages of glass-ionomer cement are its ionic exchange with dentin and enamel and its continuous fluoride release, which acts as an effective anticariogenic agent. The new dual-curing (light-activated) cements have enhanced physical properties and excellent esthetics, so the situations in which they can be placed as a complete restoration are greatly increased. If the occlusal load is too great to use glass-ionomer cement alone, the dual-curing cements are ideal for the lamination technique, in which the cement is used as a dentinal substitute and is covered with composite resin. This paper discusses the clinical placement techniques required to ensure success with either technique.
Microleakage in the sandwich technique.
This study assessed the microleakage and if it was possible to reproduce the success that is seen in the oral cavity with properly placed "sandwich" restorations. Simulated Class V erosion lesions were prepared in extracted human molar teeth and restored using a Type III glass ionomer lining cement mixed mechanically at a high powder:liquid ratio of 3:1 or greater with resin composite laminated to it leaving cement exposed at the gingival margin. To update the technique for modern materials a dual cure glass ionomer lining cement was placed in a second series with resin composite laminated to it completely covering the gingival margin. The restorations were stored in water for two weeks before temperature cycled and immersed in dye. The results showed minimal leakage relative to most other published studies and that most leakage was related to the setting shrinkage of the resin composite.
Efficiency of protective sealants for glass ionomer cements.
This study compared the efficiency of protective sealants for glass ionomer cements. Scotchbond 2, Visar Seal, an experimental light activated silicone and Ketac Glaze were evaluated using liquid scintillation spectrometry. The results showed that Ketac Glaze was a very effective sealant for the newly placed glass ionomer cement and the resin component of Scotchbond 2 is in the same range.