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T F Watson

Publications and source records attributed to T F Watson.

At least 55 records · Page 3Linked to original sources
PubMed1998

A comparison of two histological validating techniques for occlusal caries.

UNLABELLED: Validation of a diagnostic technique is important to establish whether it actually measures what it is purported to measure. However, the accuracy of the validation technique per se can influence the apparent accuracy of the diagnostic technique. OBJECTIVES: The aim of this study was to describe two alternative histological validating techniques for occlusal caries and to compare quantitative depth measurements of carious lesions taken using each method. METHODS: Thirty sections (mean thickness 0.67 mm) were cut to include two to four discrete sites in 10 freshly extracted teeth. The first histological validating technique used a microfocal X-ray unit to produce magnified high definition radiographic images of the sections or 'macroradiographs'. An image analysis system was used to make quantitative measurements of the lesions (if present) with respect to the enamel-dentine junction (EDJ). The second validating technique used a confocal microscope to image beneath the cut surface of the section. Quantitative measurements were taken from the fluorescence images of both sides of each section and a mean depth measurement calculated. RESULTS: Complete agreement was found between the two validating techniques for the subjective interpretation of the presence and extent of caries. A strong positive relationship was found between the two histological validating techniques for depth measurements made of dentine caries from the EDJ (r = 0.93, P < 0.001). Depth measurements made from the macroradiographs were greater than from the confocal fluorescence images (mean difference = 0.41 mm). CONCLUSIONS: Both validating techniques enable the identification of sound sites, those with enamel caries and dentine caries. However, quantitative assessments made with each technique could result in disagreement.

Adult↗
PubMed1998

Interfacial characteristics of resin-modified glass-ionomer materials: a study on fluid permeability using confocal fluorescence microscopy.

The tooth interface with resin-modified glass-ionomer cements (RM GICs) is poorly understood. This study examined the interface, especially with dentin. Cervical cavities in extracted teeth were restored with Fuji II LC, Vitremer, Photac-Fil, or a conventional GIC, Fuji Cap II. Fluorescent dye was placed in the pulp chambers for 3 hrs before the specimens were sectioned. Examination of the tooth/material interface with a confocal microscope showed that dye uptake by the restoration varied among materials. A "structureless", non-particulate, highly-stained layer of GIC was observed next to dentin in Fuji II LC. This layer varied in width, was prominent where the dentin tubules were cut "end-on" and in areas closer to the pulp, and was not seen adjacent to enamel. Vitremer showed minimal dye uptake, and the "structureless" layer was barely discernible. Photac-Fil showed more uniform uptake and absence of this layer. Cracking of enamel was also noted with these materials. The conventional GIC did not show any dye uptake, presence of a "structureless" layer, or enamel cracking. We elucidated the potential mechanisms involved in the formation of a "structureless" interfacial layer in Fuji II LC by studying the variables of cavity design, surface pre-treatment, water content of the tooth, time for it to develop, early finishing, and coating of the restoration. This layer, the "absorption layer", is probably related to water flux within the maturing cement, depending on environmental moisture changes and communication with the pulp in a wet tooth. The "micropermeability model" was useful in this study of the interfacial characteristics of RM GICs.

Absorption↗
PubMed1998

Conventional glass ionomers as posterior restorations. A status report for the American Journal of Dentistry.

The search for a material to replace amalgam continues as a major quest in materials science. Resin composites may offer one solution but an alternative class of material, the glass ionomer cements (GICs) may have some potential for fulfilling this role. GICs were first introduced to the dental profession in 1976, and have now become an accepted part of the dental armamentarium, especially for use in low load bearing situations. They possess a low coefficient of thermal expansion similar to that of tooth structure, physicochemical bonding to both enamel and dentin, and the release of fluoride ions into the adjacent tooth tissue. These properties help to reduce marginal leakage and may contribute to a reduced incidence of recurrent decay in the restored tooth. Fluoride released into the ambient fluids has a caries-preventive effect in neighboring teeth by enhancing remineralization and inhibiting demineralization of the dental hard tissues. The main criticisms of the GICs are their brittleness, poor surface polish, porosity and surface wear. To overcome some of these deficiencies, considerable attention has been directed at improving their physical properties, especially with the addition of metal powders, the metal-modified GICs. Different metal powders have been tried, including alloys of silver and tin, pure silver, gold, titanium, palladium and stainless steel. There is conflicting data as to whether or not these materials are sufficiently strong for use in high stress restorations, especially their potential use as replacement materials for amalgam fillings.

Bicuspid↗
PubMed1997

The effects of surface machining on heat cured acrylic resin and two soft denture base materials: a scanning electron microscope and confocal microscope evaluation.

STATEMENT OF PROBLEM: Rough surfaces promote the adhesion and colonization of denture plaque, therefore it is important to know the character of the surface left by rotary instruments on denture base materials. As a single microscopic technique can introduce artifact, complementary microscope techniques need to be used. PURPOSE: This study investigated the surface characteristics of the machined surfaces of heat-cured acrylic resin, Molloplast B and Novus. MATERIAL AND METHODS: Scanning electron microscopy and confocal microscopy were used to investigate surfaces that had been prepared with appropriate clinical rotary instruments. Thirty samples of each material were prepared with steel and tungsten carbide burs, Molloplast stones, and Arbor bands. An analysis of variance, with the Scheffe multiple comparison of means test, was used to compare average surface roughness of the individual surfaces. RESULTS: The tungsten carbide bur produced a smoother nongrooved surface than the steel bur on acrylic resin. The roughest surfaces were produced on the soft lining materials by the Arbor band and Molloplast stone. CONCLUSIONS: The confocal microscope is a valuable complementary instrument to scanning electron microscopy and provides surface roughness data by using a noncontact method. Each type of rotary instrument produces its own characteristic surface on denture base materials.

Acrylic Resins↗
PubMed1997

In vivo changes in roughness of resin-modified glass ionomer materials.

OBJECTIVES: The clinical changes in roughness of resin-modified glass ionomer materials is relatively unknown. This study examined the in vivo wear of these materials using surface roughness as an indicator of wear patterns. METHODS: Ten patients with four cervical abrasion lesions each were selected. The four cavities in each patient were restored with Fuji II LC (GC Corp., Japan), Vitremer (3M Dental, USA), Photac-Fil (ESPE, Germany) and Fuji Cap II (GC Corp., Japan). After light-curing, the restorations were polished and left uncoated. Silicone impressions were made of the surface of each restoration after polishing, and then at 3 monthly intervals up to 24 mon after restoration placement. Gold-coated resin replicas were made from the impressions for surface wear evaluation. Quantitative assessment of wear was performed by measuring surface roughness with a confocal microscope for topographical reconstruction of the specimen surface. The effect of material at each time period was analyzed using the Kruskal-Wallis test with exact non-parametric inference. Rugosity, as determined by the center line average, was determined by image analysis. SEM images of the same surfaces provided the qualitative analysis. RESULTS: All restorations showed a cyclic distribution of rugosity with time as demonstrated by lowess plots. There were significant differences between materials at 6, 9 and 18 mon. The rugosity curves appeared to converge at 24 mon. SIGNIFICANCE: It was concluded that the in vivo surface changes in roughness of resin-modified glass ionomer materials is cyclic in nature over the first 2 y.

Adult↗
PubMed1997

The effects of maturity and dehydration shrinkage on resin-modified glass-ionomer restorations.

The dimensional change, including hygroscopic change, of adhesive dental materials is a clinically important topic, since excessive changes could cause debonding from tooth structure. The water balance of glass-ionomer cements arises mainly from their sensitivity to the environment; depending on the surroundings, they can gain or lose water, either of which can be potentially damaging. These effects become less noticeable as the cement ages. The effects of maturity of the newer resin-modified glass-ionomer materials and their responses to changes in moisture are unknown. Using confocal microscopy, we examined the effects of dehydration stress on the glass-ionomer/tooth interface in specimens of various degrees of maturity. Wedge-shaped cervical cavities in extracted teeth were restored with one of three resin-modified glass-ionomer restorative materials. The control specimens were restored with a conventional glass ionomer. The samples were left to mature, then sectioned and examined at 1 day, 1 wk, 1 mo, 3 mos, 6 mos, and 1 yr. After being sectioned, each specimen was examined immediately with a confocal microscope with water-immersion objectives so that the subsurface interfacial characteristics could be studied. The specimen was then allowed to dehydrate under the microscope, with further examinations at 15, 30, and 60 min. Generally, gap formation at the interface occurred within 15 min of dehydration. All materials showed a different pattern of gap change with maturity, probably due to the different setting mechanisms involved. All of them were susceptible to dehydration shrinkage up to 3 mos of maturity. At 6 mos and 1 yr, Fuji II and Fuji II LC showed insensitivity to dehydration. Vitremer and Photac-Fil showed less sensitivity to dehydration at 1 yr than at 6 mos. The results of this study of the maturing polymerized resin-modified cements have potential clinical implications in the handling of these materials; the addition of resin has not significantly reduced the glass ionomer's susceptibility to dehydration problems.

Analysis of Variance↗
PubMed1997

Fact and artefact in confocal microscopy.

High-resolution confocal microscopic images may be made of either the surface of a sample or beneath the surface. These images can be likened to optical tomograms, giving thin (> 0.35 micron) slices up to 200 microns below the surface of a transparent tissue: With microscopes running under normal conditions, the optical section thickness will be > 1 micron and the effective penetration into enamel and dentin a maximum of 100 microns. For maximum resolution, high-quality, high-numerical-aperture objectives should be used. Refractive index matching of the lens immersion media and the substrate will avoid distortions of images in the optical axis. Such errors could occur when imaging a considerable distance (> 40 microns) into a cell containing water, with an oil immersion objective above the cover slip. Care should be taken in the interpretation of computerized z axis reconstructions made from serial optical sections: Their validity should be checked with equivalent views made with the sample oriented in the same direction as the reconstruction. The use of fluorescent dyes in microscopy is a very powerful investigative technique. It is important that the dyes used not be labile and that they be well-fixed to the materials being examined, or the images may indicate the dye distribution rather than the material to which it is "attached". Multiple labeling experiments must have crossover control experiments to verify the distribution of the individual dyes. Valuable information can often be gained by combining information from both reflection and fluorescence images. Two-photon laser excitation of dyes gives the potential for greater depth penetration and improved resolution.

Artifacts↗
PubMed1996

Pattern of transmission of laser light in teeth.

This study examined the transmission of helium neon laser light in 20 dog and human teeth. The effect of probe position and angulation was observed both macroscopically and at a microscopic level using confocal microscopy. In all teeth in both species, laser light was transmitted through teeth to the pulpal surface with the light following the path of the enamel prisms and dentinal tubules. Probe angulation did not affect the pattern of light transmission, nor did probe position; however, the position of the probe on the tooth surface determined which section of the pulp was illuminated. Enamel and dentine together are able to collect and distribute light within the tooth, with both enamel prisms and dentinal tubules acting as optical fibres.

Absorption↗
PubMed1995

Sealing ability of potential retrograde root filling materials.

The sealing ability of two potential retrograde root filling materials, a light-cured glass ionomer cement (Vitrebond) and a reinforced zinc oxide-eugenol cement (Kalzinol) was compared with that of amalgam using three methods of assessment: bacterial leakage, confocal microscopy and Indian ink leakage. the root canals of 80 extracted human single-rooted teeth were prepared. All the teeth were apicected, retrograde cavities were prepared and then divided into four equal groups of 20 teeth. The teeth were sterilised by autoclaving and the retrograde cavities filled with the test materials. In the control group, retrograde cavities in 10 teeth were left unfilled while cavities in another 10 teeth were sealed with cyanoacrylate cement. The teeth were first subjected to a bacterial leakage test using Enterococcus faecalis as a leakage marker. After which, the adaptation of the retrograde root fillings was assessed using a confocal optical microscope. Finally, the teeth were processed for the Indian ink leakage test. Bacterial leakage occurred in more teeth filled with amalgam compared with both Vitrebond and Kalzinol (P<0.001), between which there were no differences. With confocal microscopy, the size of the marginal gap was largest with amalgam and smallest with Vitrebond; all differences were statistically significant (<0.001). Finally, there was more Indian ink penetration with amalgam compared with both Vitrebond and Kalzinol (P<0.001) but there were no differences between Vitrebond and Kalzinol. Although there were individual differences within samples, overall, the three methods of assessment produced similar results. The sealing ability of Vitrebond and Kalzinol was similar and both materials were better than amalgam.

Carbon↗
PubMed1995

The influence of bur blade concentricity on high-speed tooth-cutting interactions: a video-rate confocal microscopic study.

This study aimed to determine the degree of eccentricity between different tungsten carbide bur manufacturing techniques and to study the effect of bur inaccuracy on dental enamel. Error in bur concentricity may arise from malalignment of the steel shaft and carbide head in a two-piece construction bur. Cutting blades rotate at multiple radii from the shaft axis, potentially producing vibrations and damage to the cut substrate. Techniques now allow for the manufacture of one-piece tungsten carbide burs with strength adequate to withstand lateral loading. A comparison of tungsten carbide dental cutting tools revealed the true extent of concentricity errors. Variation in alignment of the cutting head and shaft in the two-part constructions incurred between 20 and 50 microns of additional axial error. High-speed cutting interactions with dental enamel between carbide burs were studied by means of a video-rate confocal microscope. A cutting stage fitted to a Tandem Scanning Microscope (TSM) allowed for real-time dynamic image acquisition. Images were captured and retrieved by means of a low-light-level camera recording directly to S-VHS videotape. Videotape showing the interactions of high-speed rotary cutting instruments (at 120,000 rpm) were taken under simulated normal wet-cutting environments, and the consequent damage to the tooth tissue was observed as it occurred. Concentrically engineered bur types produced a superior quality cut surface at the entry, exit, and advancing front aspects of a cavity, as well as less subsurface cracking. Imaging of the coolant water film local to recent cutting operations showed regular spherical cutting debris of 6 to 18 microns diameter from the concentric tools, whereas the less-well-engineered burs produced ragged, irregular chips, with 25-40 microns diameter debris, indicating far more aggressive cutting actions. This study has shown that there is reduced substrate damage with high-concentricity carbide burs.

Dental Cavity Preparation↗
PubMed1995

Resin-modified glass ionomer materials. A status report for the American Journal of Dentistry.

The resin-modified glass ionomer materials are hybrid materials of traditional glass ionomer cement with a small addition of light-curing resin, and hence exhibit properties intermediate to the two, with some characteristics superior to conventional glass ionomer materials. Generally, they have the advantages of both such as adhesion to tooth structure, esthetics, fluoride release and rapid hardening by visible light. Issues surrounding other physical properties, such as the mechanism of adhesion, sensitivity to water, long-term wear and strength, need to be addressed and substantiated. There are other considerations, which are not features of the conventional materials, but are of importance with the resin-modified glass ionomer cements i.e. light-curing, which require further research to provide evidence of their behavior. The future for this group of materials is unknown, but the currently available materials appear to be promising.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1995

Resin-dentin interface of Scotchbond Multi-Purpose dentin adhesive.

PURPOSE: To evaluate the interface between dentin, Scotchbond Multi-Purpose (SMP), and resin composite (Z100) using confocal fluorescence microscopy. MATERIALS AND METHODS: Novel techniques were employed to view and record at video rate the application of the SMP primer and adhesive onto the dentin surface. The subsurface morphology of the dentin/restorative interface was also studied. To facilitate this study, the components of the adhesive system were labeled with fluorescent dyes. RESULTS: In an ideal situation, the primer and adhesive penetrated the dentin tubules, a distinct hybrid zone was formed and a thin layer of adhesive was observed at the interfacial region. However, the primed dentin surface was sensitive to disruption by the adhesive application brush during its placement, so that parts of the primer layer could be incorporated into the adhesive. This disruption could only be seen using confocal microscopy and a fluorescence labeling technique. Delamination of the primer layer was not observed when the adhesive film was thinned by air blowing. The application of an air stream to the cavity surface increased the penetration of the primer and adhesive along the dentin tubules, but also increased the thickness of the adhesive within irregularities on the cavity surface and at the cavity line angle. The cause of the problems in the handling properties of SMP may be the difference in viscosity between the two components (primer and adhesive) at the adhesive interface.

Composite Resins↗
PubMed1995

Resin-modified glass-ionomer materials. Part 1: Properties.

The resin-modified (light-cured) glassionomer cements were developed as hybrids of the conventional glass-ionomer materials to overcome some of their disadvantages. These new materials will be reviewed in two parts. This first article deals with their physical and biological properties. Part 2 will cover their clinical applications and handling.

Biocompatible Materials↗
PubMed1994

Adhesive systems: composites, dentine bonding agents and glass ionomers.

The urge by manufacturers to develop new and better materials can often leave the dentist confused as to how they work. This article seeks to describe these materials simply and how they can best be made to work; it may also help practitioners to ask representatives leading questions when presented with the latest product.

Composite Resins↗
PubMed1994

Determining the dental origins of foreign bodies in foodstuffs: applications of a new microscopic technique.

The use of confocal optical microscopes is reported as a method for histologically identifying foreign bodies, alleged to be of dental origin, found in foodstuffs. This technique offers the advantages of allowing rapid evaluation of a sample, without causing its destruction due to the production of thin sections which are normally required for conventional histology. The system has been used to identify fragments of dental origin, allegedly found by customers in foodstuffs which are marketed by a major retail chain.

Animals↗
PubMed1993

Sealing ability of a mineral trioxide aggregate when used as a root end filling material.

This in vitro study used rhodamine B fluorescent dye and a confocal microscope to evaluate the sealing ability of amalgam, super EBA, and a mineral trioxide aggregate when used as root end filling materials. Thirty single-canal teeth were cleaned, shaped, and obturated with gutta-percha and root canal sealer. After application of nail polish to the external surface, the apical 3 mm of each root was resected and 3-mm deep root end preparations were made. The roots were randomly divided into three groups and the root end preparations filled with the experimental materials. All roots were then exposed to an aqueous solution of rhodamine B fluorescent dye for 24 h, longitudinally sectioned, and the extent of dye penetration measured using a confocal microscope. Statistical analysis showed that the mineral trioxide aggregate leaked significantly less than amalgam and super EBA.

Aluminum Compounds↗