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Biomedical subjects

T F Watson

Publications and source records attributed to T F Watson.

At least 73 records · Page 4Linked to original sources
PubMed1993

Light-cured glass ionomer cement as a retrograde root seal.

A light-cured ionomer cement was investigated as a retrograde root seal, without a retrograde cavity. This was compared with the material used in a retrograde cavity, and with a conventional glass ionomer cement, as a seal. The adaptation and sealing ability of the test materials were assessed using a confocal optical microscope with a fluorescent dye. The root canals of 40 extracted human single-rooted teeth were prepared and filled with gutta-percha and sealer. All the teeth were subsequently apicected, then divided into four equal groups. In one group, a retrograde cavity was prepared, and the light-cured glass ionomer cement was placed as a retrograde root filling. No retrograde cavities were prepared in the three remaining groups. The light-cured glass ionomer cement was applied directly onto the apicected root face. Two different thicknesses of light-cured glass ionomer cement were tested, a thin layer (approximately 1 mm) in one group, and a thicker layer (> 1 mm) in another group. A conventional glass ionomer cement was used in the last group, and applied directly onto the root face in a single thickness (approximately 1 mm). In the group where the light-cured glass ionomer cement was used in a retrograde cavity, the material was often well adapted to one cavity wall, but gaps were found on the opposite wall. The light-cured and conventional glass ionomer cement retrograde root seals were well adapted to the root face, regardless of the thickness of material used. The thinly applied (approximately 1 mm) light-cured glass ionomer cement retrograde root seals permitted the least leakage.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1992

In vivo confocal microscopy in clinical dental research: an initial appraisal.

Until recently, the in vivo microscopic investigation of intraoral tissues at high resolution has been virtually impossible. Confocal microscopy enables high-resolution imaging to be achieved below semitransparent surfaces in intact living specimens, but this may still be impractical for intraoral applications because of the need to stabilize the sample. The development of a steadying objective (x 240 overall mag.) which is held against the sample surface and is focused by moving internal elements, avoids the need for fine adjustment of the living sample under the microscope to achieve a change of focus. It is therefore more comfortable and also reduces the problems of movement due to the pulse. The objective was used with a tandem scanning microscope, with images recorded via a SIT video camera. Using this system internal tooth structure (e.g. enamel prisms/adhesive restoration interfaces) and the lining cells of the gingival crevice through to the junctional epithelium may be examined. It is also possible to image the oral mucous membrane, focusing to the capillary loops in the basal layers, where streaming red blood cells can be seen. Access is limited to the anterior regions as far back as the premolar teeth. Applications could include caries research, soft and hard tissue responses to biomaterials (e.g. implants), wound healing and monitoring the effect of periodontal treatment regimens. This new technique offers numerous exciting opportunities for the microscopic investigation of many clinical operative procedures in vivo, allowing the response of the tissues to be non-destructively monitored, over time, at high resolution.

Composite Resins↗
PubMed1992

A confocal microscopic evaluation of the interface between Syntac adhesive and tooth tissue.

The aim of this study was to microscopically evaluate the effect of dentine smear layer thickness, tubular orientation and immediate stress application on a modern dentine bonding agent. Eighty mesial and distal wedge-shaped cavities were cut into dentine/cementum cervically in 40 extracted human lower third molars. The thickness of the dentine smear layer was reduced by polishing the cavity surface in half the samples. Each component of the bonding agent (Syntac: Ivoclar Vivadent) was labelled with a fluorescent dye, the unfilled resin being light cured for 30 s with the composite restoration placed in one increment and light cured for 40 s. The samples were longitudinally sectioned using a slow speed diamond saw underwater, either immediately or 24 h post placement. The sectioned surfaces were then viewed using a confocal optical microscope. The thickness of the smeared layer only effected the penetration of adhesive in dentine tubules which were separated from the pulp chamber by the cavity design. These areas were well filled with adhesive; however, areas communicating with the pulp chamber showed no penetration differences due to smear layer reduction by polishing. The interdependence of the adhesive components was illustrated by failure to achieve a well-impregnated tooth/adhesive hybrid layer when the materials were incorrectly handled. The Syntac/dentine interface was generally able to withstand the stress of sectioning immediately post placement, but showed signs of failure in the cavity line angle when the applied stresses were greatly increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Acrylic Resins↗
PubMed1991

Applications of confocal scanning optical microscopy to dentistry.

Confocal optical microscopy is now a well recognised technique in the fields of biological and materials science. This type of light microscope can be considered as being midway between optical and electron microscopy. Confocal or scanning optical microscopes can make high resolution, thin, optical sections within semitransparent samples such as biological tissues. Surface images of samples can be produced which are similar in character to those of the SEM, but without many of the problems of specimen preparation. The improved resolution and removal of out-of-focus blur allows much more information to be gained from fluorescence microscopy techniques, with the images capable of 3-D reconstruction of the sample. There are basically two types of confocal optical microscope: the laser scanning type (CLSM) and the real-time direct view of tandem scanning microscopes (TSM). The former are best suited to immunofluorescence microscopy, whilst the latter are more appropriate for high-speed reflection imaging, having originally been developed for in vivo microscopy.

Dentistry, Operative↗
PubMed1991

The adaptation and sealing ability of light-cured glass ionomer retrograde root fillings.

The adaptation and sealing ability of a light-cured glass ionomer cement when used as a retrograde root filling was assessed using a confocal optical microscope with and without a fluorescent dye. This material was compared with a conventional glass ionomer cement and amalgam. The root canals of 60 extracted human single-rooted teeth were prepared and filled with gutta-percha and sealer. All the teeth were apicected, retrograde cavities were prepared, and then divided into three groups of 20 teeth each and filled with the test materials. The light-cured glass ionomer cement was well adapted to the retrograde cavity and apicected root surface. Within the retrograde cavity the cement was often well adapted to one wall, but gaps were found on the opposite cavity wall. This was probably caused by the polymerization contraction of the material. In contrast, the amalgam retrograde root fillings were poorly adapted to the cavities, with gaps between the cavity walls and amalgam. This group exhibited the poorest sealing ability as measured by the extent of dye penetration. The conventional glass ionomer cement was often found smeared over the root face, and there were unfilled voids at the base of some retrograde cavities. The results of the dye leakage study were analysed statistically. The sealing ability of the light-cured glass ionomer cement was significantly better than that of amalgam (P less than 0.001). The dye penetration around the light-cured glass ionomer cement and the conventional glass ionomer cement was not significantly different (P greater than 0.05). However, the sealing ability of the conventional glass ionomer cement was significantly better than that of amalgam (P less than 0.05).

Analysis of Variance↗
PubMed1991

Tandem-scanning microscopy of slow-speed enamel cutting interactions.

The aim of this study was to observe the subsurface microstructure of dental enamel during cutting procedures. Real-time confocal scanning optical microscopy, with a tandem-scanning reflected-light microscope, is suitable for making high-resolution images of enamel prisms in intact teeth under near-normal conditions. Blocks of enamel were held on a micro-positioning stage and advanced toward the tip of a diamond knife. The orientation of the samples was varied to simulate common clinical cutting conditions. Oil immersion objectives were used with the knife rigidly mounted in a specially made carrier. This was attached to the objective below its end-lens. The images were recorded with a sensitive video camera and cassette recorder for analysis of the cutting interactions at a slow playback speed. The presence of decussating enamel prisms was particularly effective at slowing crack propagation when loading was applied in an appropriate direction. Residual subsurface cracking was seen when the blade had finished cutting. This was most pronounced in regions where the enamel prisms were cut transverse to their long axis; this was equivalent to the preparation of the cervical margin of an approximately cavity. Where there is surface adhesion to enamel (e.g., glass-ionomer cements), residual subsurface cracking will produce a weakened substrate for bonding that could have important implications for restoration longevity.

Carbon↗
PubMed1991

The interfacial region of the tooth/glass ionomer restoration: a confocal optical microscope study.

The dynamic interactions between the tooth tissues and a glass ionomer cement were investigated, using fluorescent markers incorporated into components of glass ionomer restorations. A confocal optical microscope was used to examine the tooth/restoration interface. Samples were examined at specific intervals after restoration to determine the effect of maturation of the glass ionomer matrix. Loss of fluorescent dye from the glass ionomer restoration into the subjacent dentin indicated fluid movement across the interface during maturation. To determine the effect of shrinkage from water loss on the integrity of the tooth/restoration interface, restored teeth were maintained fully hydrated and then allowed to dry. Substantial cracking at the enamel margins after drying of the set restoration indicated the strength of the attachment to enamel and also cautioned against excessive clinical drying.

Dental Bonding↗
PubMed1991

Confocal light microscopic techniques for examining dental operative procedures and dental materials. A status report for the American Journal of Dentistry.

A new form of light microscopy is compared with the current microscopic techniques for examining restorative dental procedures and dental materials. Confocal microscopy enables thin optical sections to be made below the surface of semi-transparent specimens with improved resolution. This paper reviews the different types of confocal microscopes, identifying the strengths and weaknesses of the various instruments. It also reviews some of the techniques for specimen preparation and the control of factors influencing image quality.

Dental Materials↗
PubMed1990

Fluorescence in the tandem scanning microscope.

Our studies have shown that the fluorescence mode can be used to good effect in both tandem scanning microscopes (TSM: direct view confocal microscopes) as well as confocal scanning laser microscopes (CSLM). Applications are presented which show that the two great advantages of TSM are real-time viewing and real colour, which allow faster use and interpretation. CSLM are complementary, not competitive, being currently more sophisticated for low-level fluorescence work. This is equally possible with available TSM, but requires further development using CCD cameras and image-processing systems.

Animals↗
PubMed1990

The application of real-time confocal microscopy to the study of high-speed dental-bur-tooth-cutting interactions.

A tandem scanning reflected light microscope (TSM) has been used to study the cutting interactions of dental burs with enamel. Confocal microscopy produces high-resolution images of subsurface structures in semi-transparent specimens such as teeth. The TSM has a real-time imaging ability which allows the visualization of the high-speed failure of a substrate which is being machined. This paper describes the criteria for successful imaging and their implementation in the design of a stage for controlling these cutting interactions. Examples of the results achieved are given and further applications for this technique in the field of biomaterials suggested.

Dental Enamel↗
PubMed1990

A confocal microscopic study of some factors affecting the adaptation of a light-cured glass ionomer to tooth tissue.

Vitrabond consists of a conventional glass ionomer, in conjunction with a light-curing resin and hydroxy-ethylmethacrylate. This study, which used a tandem scanning reflected light microscope for confocal imaging, looked at factors affecting the adaptation of this material to tooth tissue. Wedge-shaped cervical cavities were cut and restored in three ways: (1) Vitrabond was applied as a thin sub-base and either extended onto the enamel margin or kept clear of it. P50 resin composite was then placed, following phosphoric-acid-etching of the enamel margins. (2) The dentin surfaces were conditioned with Scotchprep (maleic acid), then with the Vitrabond, the enamel was etched, and the Scotchbond 2 adhesive applied prior to addition of the P50. (3) Vitrabond was applied alone in bulk, with and without Scotchprep acid-dentin conditioning with a 1:1 (normal) and 3:1 powder:liquid ratio (P:L). Adaptation of the Vitrabond was excellent when maleic acid was used for conditioning of the dentin. When the Vitrabond was used with P50 but extended onto the enamel, the enamel margin occasionally failed. Enamel invariably fractured when the Vitrabond was used alone in bulk. An increase in the P:L ratio decreased contraction gaps when the dentin was not conditioned, but Vitrabond failed cohesively when the dentin was conditioned. The Vitrabond was very susceptible to shrinkage on dehydration. This study suggests that Vitrabond should only be applied to dentin in thin layers, should not be extended onto enamel margins, and should not be allowed to dehydrate. Maleic acid conditioning of the dentin improved adaptation.

Acid Etching, Dental↗
PubMed1989

A confocal optical microscope study of the morphology of the tooth/restoration interface using Scotchbond 2 dentin adhesive.

It is difficult to avoid specimen damage when one is preparing an adhesive/adherend interface for examination using conventional optical or scanning electron microscopy. Fluorescence imaging with a confocal optical microscope has facilitated evaluation of the distribution of Scotchbond 2 dentin adhesive, in an in vitro study with P50 composite resin used as the restorative material. The adaptation of the adhesive and restoration to the tooth was excellent. Gap formation between the restoration and the tooth was observed only when the adhesive system was used incorrectly. Contributions of the primer film former (Scotchprep) and hardening film former (Scotchbond 2) to the adhesive interface with the tooth and overlying composite restoration could be identified. The dentin smear layer was incorporated by the Scotchprep and subsequently impregnated by the Scotchbond 2. Control of the film thickness was difficult. Cracking and cohesive failure within the adhesive were observed when the film thickness exceeded 70 microns, with such thicknesses easily achieved in internal line angles. The extent of the slippery air-inhibited layer was considerable, but could be reduced if the adhesive was wiped with a cotton wool pledget. The distribution of the Scotchbond 2 within the tooth was localized to the smear layer and dentin up to 50 microns deep to it. This study has shown the penetration of Scotchbond 2 dentin adhesive within the tooth and its distribution within the restoration.

Composite Resins↗
PubMed1987

Tandem scanning reflected light microscopy: applications in clinical dental research.

The Tandem Scanning Reflected Light Microscope (TSRLM) enables the investigation of microscopic structures both at and deep to the surface of intact objects. The present paper reviews studies undertaken to determine whether the TSRLM would be usable and useful in the investigation of natural and restorative dental materials in vitro and in vivo. It was found that the TSRLM could be used to study normal and diseased dental tissues and the new materials which are used to replace lost substance. More importantly, it could be used to characterize the interface between tooth and optically translucent materials in bulk samples, giving high resolution information from not only a shallow depth of field, but at planes below cut surfaces. This makes it possible to study interfacial regions in three dimensions without the risk of delamination that must accompany the preparation of a microscopic section. The use of fluorescent markers enables more information to be derived from the tooth/adhesive interface. Studies to date indicate the need for the development of adhesion promoting agents which incorporate a fluorescent radical in their molecular structure. Preliminary work using the instrument for observation of cutting interactions between a high speed bur and a tooth indicates some useful potential in the study of cavity preparation techniques and tissue failure mechanisms. Recent developments of the TSRLM for three dimensional imaging in other dental applications are outlined. This microscope is an important advance in the microscopic assessment of adaptation of biomaterials to hard tissues.

Animals↗