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Biomedical subjects

G J Mount

Publications and source records attributed to G J Mount.

At least 37 records · Page 2Linked to original sources
PubMed1997

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.

Cariostatic Agents↗
PubMed1996

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.

Composite Resins↗
PubMed1995

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.

Animals↗
PubMed1994

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.

Australia↗
PubMed1994

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.

Adhesiveness↗
PubMed1993

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.

Composite Resins↗
PubMed1992

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.

Composite Resins↗
PubMed1992

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.

Chi-Square Distribution↗
PubMed1991

The aged in dentistry.

Statistics show clearly the greying of our population and the profession must face the inevitable modifications to the delivery of dental care which will follow. We have spent many years fighting the high caries rate of youngsters and teenagers but, quite suddenly, that battle seems to be virtually won. Now we are faced with an ageing population who, with our help, have retained their teeth to an advanced age and they do not want to part with them. In fact, changing a patient to full dentures after the age of forty years is a very traumatic occurrence to both patient and operator. The profession now has two major problems to deal with in the area of restorative dentistry for the ageing patient. Firstly, teeth which have been retained but are heavily restored because of ongoing caries and bulk loss of tooth structure as a result of splitting or the application of careless restorative techniques. Secondly, the onset of root surface caries following migration of the epithelial attachment and exposure of root surfaces combined with a reduction in the efficacy of oral hygiene measures. Both problems are likely to appear after the age of sixty years and the patient may live for another twenty or thirty years in a gentle medical and physical decline. Maintenance of dental health presents a series of unique problems under these circumstances.

Aged↗
PubMed1991

Minimal treatment of the carious lesion.

The development of reliable adhesive technology in the oral cavity has opened the way to an entirely new approach to the treatment of active carious lesions. The initial lesion, prior to complete penetration of the enamel, can often be controlled with remineralization techniques. However, once the dentine is breached, surgical intervention is required. With modern instrumentation, including fibre-optic lighting and magnification with binocular loupes, a more surgical approach has been developed, allowing removal of caries with very limited destruction of sound tooth structure. Experience over the last 5 years has led to the development of a classification of cavity designs as well as a reliable method of instrumentation and restoration based on the use of glass-ionomer cement and composite resin. The remineralization available through the glass-ionomer cements and the adhesion developed with both the cement and composite resin allows for maintenance of the original strength of the tooth along with a high resistance to further breakdown. The classification of cavity design is presented as well as a detailed description of the suggested instrumentation for the development of the cavities.

Dental Caries↗
PubMed1990

The effect of etching on a number of glass ionomer cements.

In view of the continuing interest in the use of glass ionomer cements as a dentine substitute or base under composite resins, further investigations were carried out on the effects of the length of time of etching of the surface of the cement prior to the placement of the resin. A number of cements are available on the Australian market which are advocated for use in this technique. Each of them was subjected to etching for periods of 15, 30, 45, or 60 seconds and then stored in water for one week. Examination under a dissecting microscope and a scanning electron microscope revealed some variation in results between the different cements. It would appear that not all those materials presently marketed for this purpose are entirely suitable. Whilst 15 seconds is the preferred time for most cements, some require times up to 60 seconds to achieve the best result. Also, some of the cements showed signs of cracking, expansion and distortion after they had been stored in water for one week to allow for maturation before being prepared for viewing under the SEM. It is suggested that this group of cements is not suitable for the 'sandwich' technique.

Acid Etching, Dental↗
PubMed1990

Restorations of eroded areas.

Class V erosion lesions must be restored to reinstate esthetic appearance, overcome sensitivity, or prevent further loss of tooth structure. Restoration has been a problem, but, with the advent of adhesive techniques, it is far less traumatic. The most widely advocated method currently uses composite resin as the primary restorative material with dentin bonding agents. Type III glass ionomer lining cements are also suggested to provide bonding to the dentin. This paper details the requirements for clinical success in the restoration of the Class V erosion lesion using Type II restorative esthetic glass ionomer cements as the primary restorative material with the possible addition of composite resin as a final veneer only if circumstances warrant it.

Composite Resins↗
PubMed1990

Polyacrylic cements in dentistry.

The polyacrylic cements were first introduced to dentistry in the middle 1960's when Smith showed the value of the polyacids, in developing adhesion to enamel and dentine. Within 10 years, Wilson had advanced the concept by changing the powder from a zinc oxide to glass and at the same time varying the poly-acid used. Both cements depend on the development of complex polyacrylate chains which can be linked with metal ions and in turn can form dynamic linkages with both enamel and dentine. The original polycarboxylate cement has many desirable characteristics and is still a useful cement for luting crowns and bridges and for lining cavities. However it is no longer widely used because it has been somewhat overshadowed by the glass ionomer cements which are even more versatile and have superior physical properties. By varying the type of glass, the fluoride content of the glass and the powder/liquid ratio as well as adding inclusions of other metals such as silver they can fulfil a variety of roles in restorative dentistry. However, as with any restorative material, it is essential that the operator fully understand the requirements for successful placement. The basic rules are reviewed for each of the types currently available and the steps for clinical success are detailed.

Acrylic Resins↗
PubMed1990

Esthetics with glass-ionomer cements and the "sandwich" technique.

The Type II restorative esthetic glass-ionomer cement has not been generally regarded as a useful esthetic restorative. However, as long as its relatively slow-setting chemistry is understood and accepted and provision is made to maintain the water balance for the first 24 hours, it can be just as useful as composite resin. Taking into account the fluoride release, its tissue compatibility, and the chemical union with underlying tooth structure that is available, it is suggested that it has a valuable place in restorative routines. Manufacturers have been encouraged recently to try to produce a fast-setting cement that can be polished at the insertion appointment. A varnish to seal newly placed restorations is supplied by most manufacturers, but these are not completely waterproof. A low-viscosity, single-component, light-activated resin bonding agent has been shown to work satisfactorily as a sealant, and, with its use, it is possible to develop adequate translucency and optimal physical properties in the oral cavity.

Adult↗