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Biomedical subjects

O F Makinson

Publications and source records attributed to O F Makinson.

At least 19 recordsLinked to original sources
PubMed1998

Enamel cracks. The role of enamel lamellae in caries initiation.

Lamellae or cracks are distributed throughout tooth enamel in both deciduous and permanent dentitions. While earlier authors postulated that lamellae may be pathways of entry for caries, no evidence was adduced and the theory appears to have been discounted. The present study seeks to show that, at least in some cases, lamellae are permeable to dyes, may be associated with caries initiated in the dentine, supporting the hypothesis of Hardwick and Manly of lamellae penetration by Streptococcus mutans and lactobacilli. The enamel lamellae are shown to be a permeable pathway allowing caries-producing bacteria access to the dentine-enamel junction. Caries can thus be established within the tooth without visible evidence at the surface.

Azo Compounds↗
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↗
PubMed1993

A microscopic examination of bond surfaces in failed electrolytically etched cast metal fixed prostheses.

The aims of this investigation were to examine the patterns of resin cement failure between debonded electrolytically etched (Maryland) bridge retainers and their respective abutment teeth and to determine if the clinical assessment of bond failure corresponded to the types of failure observed in the scanning electron microscope. Twenty-eight (18 anterior and 10 posterior), debonded bridges were examined. The results indicated that the classification of bond failures at the clinical level did not correspond to the SEM assessments of failure. It appeared from the specimens examined that loss of retention occurred as a result of resin failure within the cement layer close to the enamel-resin interface. Only one metal retainer specimen showed a small area of resin-metal failure. There appeared to be no differences in the patterns of resin failure between anterior and posterior bridges. The observations also indicated that the resin cements used for bridge cementation adhered well to electrolytically etched retainer surfaces.

Composite Resins↗
PubMed1992

Dental treatment and dental health. Part 2. An alternative philosophy and some new treatment modalities in operative dentistry.

In this, the second of two papers on the relationships between dental treatment and dental health, the philosophical basis of Minimum Intervention Dentistry is presented. This approach to patient care has several distinct treatment modalities. These range from preventive measures and fissure sealants, through monitoring carious lesions for active progression or arrest, to minimal cavity designs such as tunnel preparations and preventive resin restorations which employ adhesive dental restorative materials. This paper discusses these techniques and the implications of this change in philosophy for dental teaching, research and manpower considerations.

Dental Caries↗
PubMed1992

Comparative elasticity tests for elastomeric (non putty) impression materials.

This study was conducted to evaluate the methods used for measuring the elastic recovery of various elastomeric impression materials. One brand from each chemical group was selected to allow relative ranking of the results from each deforming test mode. For compression tests, the polysulphide and silicone specimens made in metal moulds gave significantly less set than those made in acrylic moulds; this was not so for the polysiloxane and polyether specimens. For polysulphide and polyether materials, the set in compression was greater using the BSI balanced beam method than for an optical method without inertia or load effects; this was not so for silicone or polysiloxane materials. The elastic recovery of the materials did not alter significantly after ten minutes of strain release, except in tensile tests, where the elastic recovery continued to change for twenty minutes. The rank ordering of the deformation set showed a relative correlation for the compression test, a new tensile test method, and bend and torsion testing methods. Thus only one method is needed to determine set per cent.

Dental Impression Materials↗
PubMed1992

Dental treatment and dental health. Part 1. A review of studies in support of a philosophy of Minimum Intervention Dentistry.

An international movement emerged in 1986-1987 which heralded a major change in the role of conservative dentistry. This shift was away from the traditional operative dentistry, with its relatively frequent replacement of restorations, to a concept of 'Minimum Intervention Dentistry', which advocates the use of adhesive dental materials, remineralization techniques and monitoring of initial carious lesions. The move away from some of Black's concepts started as investigations examined the dental health of patients in the National Health Service of Great Britain. These investigations, and the report of the Committee of Enquiry into Unnecessary Dental Treatment, have resulted in an extensive re-education programme being initiated by the British Department of Health and Social Security in conjunction with the British Dental Association. This paper, and a subsequent one, were written to enable widespread dissemination of these ideologies to Australian practitioners. While they may appear provocative to some, these papers were merely meant to stimulate discussion on the implications of this research for dentistry in this country. In this paper the results from the British investigations are presented, as is a discussion of some of the outcomes of this and other related research.

Australia↗
PubMed1992

Some parameters for testing deformation of elastomeric impression materials.

Because of conflicting published data, the temperature rise in four elastomeric materials was measured with a thermistor during setting in the oral cavity and in metal and plastic moulds of varying shapes and volumes for 'elastic set' specimens. The clinical temperature rise was 2-3 degrees C higher in the molar region than anteriorly, except for the polysiloxane. The temperature range attained in the set materials varied from 29 degrees C to nearly 35 degrees C for clinical and in vitro specimens. The average time taken by a group of operators to remove this type of impression from the mouth was five seconds. In a custom tray with light and heavy viscosity materials, the syringe material layer was only 0-0.15 mm thick and, essentially, the heavy viscosity material provided the elastic components for the impression.

Dental Impression Materials↗
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

Replacement of low copper amalgams by a group of general dental practitioners.

The replacement of low copper amalgams was studied in a number of general practices in Adelaide in 1975 duplicating, by design, the method of a similar Canadian study. The results of this study are in surprising agreement with the Canadian data, and are still relevant to modern practice as the high copper alloys have not proven to have greatly superior longevity. This study involved 60 dentists who, over 271 working days, replaced an average of 6.7 amalgam surfaces/dentist/day. This is equivalent to 1541 amalgam surfaces replaced/dentist/year. In addition, the reasons given for the removal of existing amalgam restorations were closely congruent with those given by the Canadian dentists. This study also indicated that many of these restorations increased in size. This is evident through restorations extending from two surfaces to involve three surfaces.

Adolescent↗
PubMed1991

The effect on radiographic definition of X-ray tube movement.

This study was designed to measure the vibration of three X-ray tubes in simulated clinical conditions and the effect of this on image quality. Vibration was measured by exposing film to an X-ray beam collimated by a lead diaphragm with a pin-hole. Exposures were made of a test specimen with the X-ray tubes stationary and while oscillating after positioning by vertical, lateral and forward movements. The damping time for the X-ray tube to stop oscillating varied with the machine from 3 s to 102 s. The radiographic patterns caused by tube oscillation varied from closed loops to figure of eight movements with periodicities of between 0.5 and 1.0 s. Amplitudes of up to 5.9 mm were recorded; they were greater in a horizontal direction and affected by arm extension. Images of bone trabeculae and of small holes drilled in the proximal surfaces of two teeth were little affected by tube movement. Only under magnification was the definition of a ball-bearing seen to be slightly less distinct, with less than 1% variation in size. These effects are likely to be of little clinical significance.

Oscillometry↗
PubMed1991

Color change in light-cured resins exposed to daylight.

The clinical yellowing of anterior composite resin restorations with time is often the cause for their replacement. This work examined in vitro the effect of sunlight and water separately and together on color changes in the lighter shades of 16 resins. The natural radiation (ultraviolet and visible) was greater than would be expected in clinical use, and the color changes were generally only slight for most resins, as judged by standardized photographic recording and visual inspection of transparencies over time. The changes were greater when sunlight and water were combined. The light-cured surface was less affected than the distal surface. The hydrolysis action by water was particularly marked for one resin, which also showed a high release of camphoroquinone-type catalyst. Marked clinical discoloration may be as much or more affected by absorption of food colorants than by sunlight and water.

Color↗
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

Operating illumination to differentiate dental hard tissues.

This in vitro study was designed to evaluate the ability of fluorescent tubes and dental lights to help operators distinguish tissues (fissures), differentiate between tissues (at the dentinoenamel junction or between carious and sound dentin), and distinguish form of a tooth preparation (Class II and Class V cavities). Operators with "normal" color vision ranked the lights in order of preference for each type of specimen. In general, for the fluorescent illuminants, operators preferred lights with high color temperature values and high color rendering index values. A small group of color-blind observers indicated a preference for an illuminant of low color temperature and low color rendering index value. For dental lights, operators preferred a higher color temperature for examining fissures, the dentinoenamel junction, and the cavity preparation. No particular illuminant was preferred for distinguishing between carious and sound dentin. Many observers had difficulty in choosing a preferred dental luminaire.

Color↗
PubMed1989

Colour changes on curing light-activated anterior restorative resins.

With many composite resins operators may notice a change in colour after light curing the restoration. Three types of specimen--a disc, a simulated Class III and a veneer--were made using a series of composite resins. Generally, resins became lighter or more translucent on irradiation. This was not only true for a range of resins from a single company but also the extent of the change was brand dependent. For most resins the opacity decreased with curing and most of this change occurred with a 20 seconds cure. The reflectance was approximately 50 per cent greater for resins placed over a white background than on a dark background for the thin disc specimens.

Color↗