Biomedical subjects

T F Watson

Publications and source records attributed to T F Watson.

At least 19 recordsLinked to original sources

PubMed2007

The penetration of RealSeal primer and Tubliseal into root canal dentinal tubules: a confocal microscopic study.

AIM: To compare penetration depth into dentinal tubules of RealSeal with that of a well-established endodontic sealer (Tubliseal) by means of confocal microscopy. METHODOLOGY: Twenty sound extracted, single-rooted premolars were selected. Following completion of root canal instrumentation, the teeth were divided into two groups using a stratified sampling method, ranking teeth according to size. In group 1, 10 teeth were filled with Gutta-percha and Tubliseal using cold lateral condensation. In group 2, 10 teeth were filled with RealSeal. Both sealers were labelled with Rhodamine B dye. The teeth were sectioned parallel to their long axis resulting in 20 specimens per group. Confocal microscopy was used to assess the penetration depths of the sealers at three sites for each specimen (coronal, middle and apical). Data were analysed statistically using Stata Release 9.1. RESULTS: The penetration depth of RealSeal in each one of the thirds of the root canal was found to be higher than that of Tubliseal (P < 0.05). The penetration depths of the two sealers was found to be significantly different (P = 0.001). The mean penetration value for the RealSeal group was 908.8 microm whereas the mean value for the Tubliseal group was 139.5 microm. CONCLUSIONS: The penetration depth of RealSeal into the root dentinal tubules is significantly greater than that of Tubliseal.

Bicuspid↗

PubMed2006

A novel real-time confocal imaging technique for examining host-implant interfacial shear failure patterns.

In clinical practice, implant failure usually occurs at the biomaterial-host tissue interface, typically involving both biomechanical and biochemical mechanisms. By definition, any new 'bioactive' material will bond to living bone but, prior to clinical use, interface formation, performance, longevity and failure pattern characterizations are necessary. The common missing link in many biomaterial interface investigations is imaging at the point of presumed loaded failure. The novel real-time confocal technique described here allows bond strength, formation rate, longevity and bone-material interface failure pattern characterization for a wide range of biomaterials capable of forming tissue interfaces, in one real-time imaged microshear stress process, conducted using imaging frame matched load/displacement data acquisition under relatively normal near in vivo environmental conditions. The technique, validated by post-failure scanning electron microscopy imaging, revealed that more slowly reacting melt-derived 45S5 glass materials produced stronger and more stable long-term interfaces than faster reacting microporous bioactive sol-gel glasses.

Biocompatible Materials↗

PubMed2006

Microhardness as a predictor of sound and carious dentine removal using alumina air abrasion.

Clinical air abrasion is known to remove dental hard tissues effectively. The aim of this study was to quantify and compare the efficiency of alumina air abrasion in the removal of sound and carious dentine. Twelve non-cavitated carious lesions in freshly extracted molars were bisected mesiodistally. The Knoop hardness number (KHN) was measured on the cut sample surface at 250-microm intervals along a line running axially through the centre of the lesion, from the enamel-dentine junction to the pulp including both sound and carious tissue. The cut surface was then abraded over the same path using alumina particles (27 microm). Powder flow rates, pressure, distance and the angle of the nozzle to the tooth were kept constant throughout the experiment. Non-contact surface profilometry and surface analysis software were used to calculate the rate of dentine removal at the site of each KHN measurement. The results showed that dentine Knoop hardness can be used as a predictor of the rate of dentine removal, with a Somers' D value of 0.826. Carious dentine with a low KHN was removed less efficiently than the hard sound dentine with a higher KHN. Thus, dentists should be aware that air abrasion systems using alumina particles remove healthy dentine more efficiently than carious dentine, with the associated implications for clinical caries excavation and cavity preparation.

Air Abrasion, Dental↗

PubMed2005

Penetration of bonding resins into fibre-reinforced composite posts: a confocal microscopic study.

AIM: To compare the penetration of two different bonding resins applied for different contact times, on glass reinforced-reinforced composite root canal posts showing an interpenetrating polymer network (IPN) or cross-linked polymer matrix. The research hypothesis was that the bonding resins were equally able to penetrate into the IPN post whereas less penetration was evident into the cross-linked post. In addition, the prolonged contact time of the bonding resin on the surface of post was assumed to increase the resin penetration. METHODOLOGY: A total of 36 posts, comprising 18 IPN posts (everStick Post) and 18 cross-linked posts (C Post Millennium) were divided into 12 groups of three posts. All posts had a diameter of 1.2 mm. Both bonding resins (Scotchbond Multi Purpose Plus and Stick Resin) were labelled with Rhodamine B for determination of the resin penetration into the post. After contact times of 1, 30 and 300 s the bonding resins were light cured for 60 s. Penetration of bonding resins into three sections of each post was measured by confocal scanning light microscope. The influences of post and type of adhesive resin on resin diffusion into the polymer matrix of the post were assessed by nonparametric methods. RESULTS: For C Post Millennium and for 1 s contact time, no penetration of bonding resins into the polymer matrix of posts occurred in any section of any post. For the everStick Post, penetration was always noted after 300 s contact (mean 22.8 microm) and nearly always after 30 s contact (mean 3.5 microm), with very little difference between the two adhesives. The degree of penetration into everStick Posts was invariably greater after 300 s contact than after 30 s (P < 0.001). Both sets of results were highly significantly greater than the zero penetration recorded using C Post Millennium or 1 s contact time (P < 0.001). CONCLUSIONS: The ability of bonding resins to penetrate into everStick Post with IPN polymer matrix may give the opportunity to establish a good link between fibre-reinforced composite posts, luting cements and composite cores.

Composite Resins↗

PubMed2005

A study of the rheological properties of endodontic sealers.

AIM: To test the hypothesis that there would be no statistically significant difference in viscosity-related measures of endodontic sealers or change in these with strain rate, internal diameter or powder : liquid ratio in a capillary system. METHODOLOGY: Materials used were Apexit, Tubliseal EWT, Grossman's sealer and Ketac-endo. Viscosity-related measures were tested in a two-plate test, and in a capillary rheometer. The mean values (n = 12) for thickness and diameter of material formed between two glass plates were tested with one-way analysis of variance. Pressure was applied to a capillary rheometer at strain rates 5 and 10 mm min(-1) in tubes of internal diameter 0.6 and 1.2 mm. RESULTS: Tubliseal EWT had a thinner film thickness than the other sealers (alpha = 0.05). The difference in diameter between Tubliseal EWT and the other sealers was significant apart from Apexit. Increased strain rate gave a significant increase (alpha = 0.05) in the flow of all sealers. Narrower tubes produced increased velocity, which was significant for all sealers, and reduced volumetric flow, which was significant for all sealers except Grossman's 2 : 1 (Wilcoxon signed rank test). Reduction in powder : liquid ratio of Grossman's significantly increased flow in narrow tubes and at higher strain rate (Mann-Whitney test). CONCLUSION: There was a significant difference between the flow of Tubliseal EWT and the other sealers tested in the two-plate test; capillary flow was affected by sealer, internal diameter, strain rate and powder : liquid ratio. The null hypotheses were rejected.

Calcium Hydroxide↗

PubMed2005

Microtensile bond strengths to enamel of self-etching and one bottle adhesive systems.

UNLABELLED: This study compared the enamel bond strengths of self-etching and one bottle adhesives, and evaluated microscopically their debonding modes. Evaluated systems were: Self-etch--Prompt L-Pop (LP); one bottle, total etch--Single Bond (SB), Prime & Bond NT (PB); compomer--Hytac Aplitip (HA), F2000 (F2); resin composite- Reference 21 Aplitip (R2), Herculite XRV (XRV), Esthet.X (EX); in the following combinations: LP/HA; LP/R2; SB/F2; SB/XRV; PB/EX. Flat surfaces of enamel were ground on caries free extracted third molars. An adhesive resin was applied to this surface and a restorative material built on it. The teeth were sectioned longitudinally into 1 mm thick specimens and trimmed to a 1 mm2 area at the enamel/adhesive interface. For each material combination, 10 specimens were tested. Microtensile bond strengths were determined at 0.5 mm min(-1). Fractured specimens were examined using confocal and scanning electron microscopy to determine failure modes. Bond strength data was analysed using Kaplan-Meier survival analysis, a log-rank test and a Bonferroni multiple comparison. Failure mode data was analysed with a chi2 test. The interface of additional fluorescent-labelled specimens was examined by laser scanning confocal microscopy. The bond strength data showed significant differences: LP/R2 > LP/HA, SB/F2 and PB/EX; SB/F2 < LP/HA, SB/XRV and PB/EX. Both compomers principally exhibited cohesive failure. Resin composite materials showed more complex failure modes. Fluorescence images demonstrated interfacial characteristics consistent with the failure modes observed. SIGNIFICANCE: bond strength was not influenced by the use of self-etch or one bottle adhesives.

Adhesives↗

PubMed2004

An in vitro investigation of microtensile bond strengths of two dentine adhesives to caries-affected dentine.

OBJECTIVES: To compare the micro-tensile bond strengths of two different adhesive systems (ABF (Clearfil Protect Bond), Kuraray Medical Inc., Tokyo, Japan) and Prime & Bond NT (PBNT, Dentsply, Konstanz, Germany) bonded to caries-affected dentine retained after chemo-mechanical caries removal using Carisolv gel, with that retained after excavation using conventional hand instrumentation. METHOD: Twenty, adult, human extracted carious teeth were used in this split tooth study with bur-cut cavities in sound dentine acting as controls. After clinical caries excavation, the occlusal cavities in each experimental group were restored with either bonding system plus composite. Matchstick-shaped samples through the bond interfaces were sectioned and microtensile bond strengths recorded. Scanning electron microscopy (SEM) was used to ascertain the mode of failure at the restoration-dentine interface. RESULTS: Statistical analysis of the bond strength data showed that for the ABF group, there was no difference in bond strengths between the controls and Carisolv group but these values were significantly higher than those for the hand-excavated samples. PBNT samples showed no significant differences in any of the three test groups, with wider ranging data sets. SEM analysis indicated a variety of failures at the interface including cohesive failures within the caries-affected dentine itself. CONCLUSIONS: From the data generated by this study it could be concluded that microtensile bond strengths of PBNT/composite restorations to caries-affected dentine in clinical cavities were statistically comparable to those to sound dentine. In the ABF/composite restored group (self-etched), the use of conventional hand excavation appeared to weaken the bond strength to the remaining caries-affected dentine. However, the use of Carisolv gel excavation did not compromise bond strengths to caries-affected dentine in either group tested.

Adhesiveness↗

PubMed2004

The surface effects of erosion and abrasion on dentine with and without a protective layer.

OBJECTIVE: The aim of this in situ study was to investigate with four imaging modalities whether covering dentine with adhesive resins could protect against erosion from acids. The objectives were to observe and quantify the effects of acids and the soft tissues, especially the tongue, on dentine and the bonding agents using four assessment techniques: qualitative assessment with SEM, surface roughness and thickness of resin with the TSM and volume loss with the laser profilometer. DESIGN: An in situ investigation using extracted dentine sections embedded in splints held on the palate of 10 volunteers. The dentine sections were protected by two resins and subjected to a tooth wear regime. RESULTS: Both Seal and Protect and Opitbond Solo protected the tooth surfaces from a tooth wear regime. There were no statistical differences between the control surfaces and those protected with dentine bonding agents for resin thickness, roughness and profilometry. The appearance of the slabs under both confocal and SEM showed that the material remained in place despite a vigorous wear regime and therefore protected the tooth surface. CONCLUSIONS: For patients with uncontrolled erosion or tooth wear, applying a dentine bonding agent to exposed dentine is a practical option to prevent further damage.

Adult↗

PubMed2004

Molecular analysis of the microflora associated with dental caries.

Molecular techniques have revealed many novel, presumed unculturable, taxa in oral infections. The aim of this study was to characterize the bacterial community of the middle and advancing front of carious dental lesions by cultural and molecular analyses. Samples were collected with a hand excavator from five teeth with carious lesions involving dentine. Samples were cultured on blood agar and Rogosa agar incubated in air plus 5% CO(2) and on fastidious anaerobe agar anaerobically. DNA was also extracted directly from the samples and 16S rRNA genes were amplified by PCR with universal primers. PCR products were singularized by cloning, and the cloned inserts and cultured isolates were identified by 16S rRNA gene sequence analysis. We identified 95 taxa among the 496 isolates and 1,577 clones sequenced; 44 taxa were detected by the molecular method alone; 31 taxa were previously undescribed. Only three taxa, Streptococcus mutans, Rothia dentocariosa, and an unnamed Propionibacterium sp., were found in all five samples. The predominant taxa by anaerobic cultivation were the novel Propionibacterium sp. (18%), Olsenella profusa (14%), and Lactobacillus rhamnosus (8%). The predominant taxa in the molecular analysis were Streptococcus mutans (16%), Lactobacillus gasseri/johnsonii (13%), and Lactobacillus rhamnosus (8%). There was no significant difference between the compositions of the microflora in the middle and advancing front samples (P < 0.05, Wilcoxon matched pairs, signed ranks test). In conclusion, combined cultural and molecular analyses have shown that a diverse bacterial community is found in dentinal caries and that numerous novel taxa are present.

Adult↗

PubMed2004

Water-dependent interfacial transition zone in resin-modified glass-ionomer cement/dentin interfaces.

The function of the interfacial transition zone (absorption layer) in resin-modified glass-ionomer cements bonded to deep dentin remains obscure. This study tested the hypotheses that the absorption layer is formed only in the presence of water derived from hydrated dentin and allows for better bonding of resin-modified glass-ionomer cements to dentin. Ten percent polyacrylic acid-conditioned, hydrated, and dehydrated deep dentin specimens were bonded with 2 resin-modified glass-ionomer cements and sealed with resins to prevent environmental water gain or loss. A non-particulate absorption layer was identified over hydrated dentin only, and was clearly discernible from the hybrid layer when bonded interfaces were examined with transmission electron microscopy. This layer was relatively more resistant to dehydration stresses, and remained intact over the dentin surface after tensile testing. The absorption layer mediates better bonding of resin-modified glass-ionomer cements to deep dentin, and functions as a stress-relieving layer to reduce stresses induced by desiccation and shrinkage.

Compomers↗

PubMed2002

New imaging modes for lenslet-array tandem scanning microscopes.

The tandem scanning microscope permits confocal images to be obtained in real time and viewed directly by eye. The light budget of these instruments may be increased from a few percent to a few tens of percent by incorporating an array of microlenses so as to increase the amount of illumination light that reaches the specimen. These instruments are configured for fluorescence imaging together with laser illumination. We describe how the versatility of the instrument may be enhanced to permit the use of incoherent light sources as well as extending the imaging modes to include bright-field reflection.

Dentin↗

PubMed2002

Video-rate confocal endoscopy.

Rigid endoscopes provide high quality optical images of reasonably accessible regions of the inner body, especially regions such as the aero-digestive and genital tracts. In order to enhance the versatility of these instruments we describe a development that permits confocal endoscopic images to be obtained - along with traditional endoscopic images - in real-time, from within the living patient. The system is based around a host lenslet-array tandem scanning microscope, which is capable of producing images viewed directly by eye. These types of confocal microscope are configured for fluorescence imaging together with laser illumination. Hard and soft tissues in the mouth were imaged using this combined system.

Endoscopy↗

PubMed2001

The measurement and prevention of erosion and abrasion.

OBJECTIVES: To develop a reproducible method to measure tooth wear and assess the protection given by dentine bonding agents in an erosive/abrasive wear regime. METHODS: Seal and Protect (Dentsply, UK) and Optibond Solo (Kerr, UK) were each applied to 20 extracted teeth and subjected to 3000 cycles in a reciprocating erosion/abrasion wear machine. A further 20 teeth, without protection, were subjected to the same wear regime and were either brushed in water or immersed in acid. Impressions were taken by a standardised technique and were scanned with a non-contacting laser profilometer. The amount of erosion was measured at the same co-ordinates before and after erosion using 2mm diameter metal discs as reference points. RESULTS: The amount of wear on Seal and Protect had a mean 24.8 microm (SD 57.4 microm) and for Solo it was 1.4 microm (24.5 microm), and this difference was statistically significant (p=0.02). There was no statistically significant difference in the wear measured on the teeth brushed in water or immersed in acid. The wear measured on the unprotected teeth was 243 microm (SD 120 microm) and was statistically significantly different to the protected surfaces (p=0.001). CONCLUSION: Both Seal and Protect and Solo protected the teeth in this wear regime and the technique could be used clinically for patients with uncontrolled dental erosion.

Analysis of Variance↗

PubMed2001

Pattern of transmission of laser light through carious molar teeth.

AIMS: The aims of this study were to investigate the pattern of transmission of laser light through carious human molar teeth, and to examine the effect on light transmission of reactions to caries in the dentine. METHODOLOGY: Sectioned carious human molars were examined whilst illuminated from their external surfaces by a helium-neon laser probe of 0.5 mm diameter. The pattern of light transmission was observed and selected specimens were photographed. The passage of light through the surrounding dentine toward the pulp space was investigated by confocal microscopy. Further carious and restored teeth were illuminated from three buccal and three lingual sites to establish the probability of light being able to reach the coronal pulp space. RESULTS: For all 31 teeth examined, it was possible to illuminate the pulp space from a position on the buccal side. The presence of intracoronal restorations did not necessarily prevent light transmission to the pulp. Confocal microscopy demonstrated conduction of light within dystrophic deposits of irregular secondary dentine. CONCLUSIONS: The presence of carious lesions or restorations in molar teeth does not necessarily interfere with transmission of laser light to the pulp space. Light is conducted within irregular secondary dentine. With appropriate probe placement, assessments of pulp health in diseased posterior teeth may be possible using laser Doppler flowmetry.

Adult↗

PubMed2001

Real-time confocal imaging, during active air abrasion -- substrate cutting.

Air abrasion cutting, using particulates accelerated in a controlled compressed gas stream, is currently being re-evaluated as a precision tissue removal technique for dental cavity preparation. The minimal vibrations and heat generated during cutting commend the technique for use in the shaping of fragile or brittle materials that are vulnerable to vibrations and thermal stresses. Traditional air abrasion studies have relied solely upon post-procedure imaging, and cutting process details have been inferred from the nature of the residual surface. In this paper, however, a real-time confocal microscopic imaging method is described, which for the first time has allowed prior target structure characterization with subsequent imaging of cutting interactions and substrate failure patterns. Using internally focusing long working distance Hill objective lenses, focusing deep to a protective microscope slide and adhesive interfaces, unhindered remote image sampling within the bulk of specimens such as tooth tissue, acrylic and brittle ceramics was possible. Moreover, areas of active cutting and inactive regions were identified within air abraded cavities during their creation. The characteristics of the finished cut surfaces were demonstrated and confirmed the findings of previous SEM studies. The method allowed direct control over all the known variables influencing cutting with particulate streams.

Air Abrasion, Dental↗

PubMed2001

Microleakage of endodontically treated teeth restored with fiber posts and composite cores after cyclic loading: a confocal microscopic study.

STATEMENT OF PROBLEM: The effectiveness of the seal obtained with carbon fiber posts and composite cores is still unclear. Both 3-step dental adhesives and self-etching adhesive primers have been suggested as adhesive systems. PURPOSE: This confocal microscopic study evaluated the microleakage of teeth endodontically treated and restored with fiber posts and composites with 3 adhesive systems. MATERIAL AND METHODS: A total of 72 human mandibular premolars were endodontically treated and divided into 6 groups of 12 teeth each. The first 3 groups were treated with an endodontic sealer containing zinc oxide-eugenol (ZOE) and restored with temporary filling materials containing ZOE. The last 3 groups were treated with ZOE-free materials. Post spaces were prepared in the root canals. The first group treated with ZOE-based materials was restored with fiber posts cemented with zinc phosphate cement and composite cores without adhesive. The other 2 groups of ZOE-treated teeth were restored with fiber posts cemented with All Bond 2 and Panavia 21 dental adhesives, respectively. The last 3 groups were restored with fiber posts cemented with All Bond 2, Panavia 21, and Panavia Fluoro cement, respectively. The teeth were loaded intermittently at 2 cycles per second in a moist environment and, after 300,000 cycles, immersed in a solution of Rhodamine B dye for 48 hours. A confocal microscope was used to observe the teeth. The ratio between the length of the interfaces observed and the length of the dye penetration was evaluated. Two teeth from each group acted as controls and were not subjected to dynamic loads. RESULTS: All resin cement groups leaked significantly less than the group cemented with zinc phosphate cement. No statistically significant difference was found between the microleakage of teeth treated with ZOE-based and non-ZOE-based materials. Teeth restored with All Bond 2 dental adhesive leaked significantly less than those restored with Panavia cement. CONCLUSION: The 3-step dental adhesive (All Bond 2) resulted in a better marginal seal than that obtained with the self-etching primers (Panavia 21 and Panavia F). The use of endodontic sealers and temporary filling materials containing ZOE had no detrimental effect on the marginal seal of carbon fiber post/composite resin core restorations.

Adhesives↗

PubMed2001

Three-point bending test of fiber posts.

Five different types of fiber posts (carbon fiber Composipost radio-opaque, quartz fiber Aestheti-Plus, carbon fiber Carbotech, glass fiber Light post, and silica fiber Snowpost) were submitted to a three-point bending test after being stored for 1 yr under three different conditions: dry storage at room temperature, storage in 37 degrees C water, and storage in bovine teeth that were endodontically treated and restored with composite resin. The posts were observed before and during the test by confocal microscopy. More voids were found within the Composipost radio-opaque than in other posts. Posts of all groups that were stored in water showed flexural strength values lower than posts that were stored dry. In all storage conditions, Carbotech posts showed higher flexural strength values than Composiposts and Snowposts, and Aestheti-Plus posts showed higher flexural strength values than Snowposts. Posts that were stored in bovine teeth showed flexural strength values similar to those of posts that were stored dry. It was concluded that fiber posts must not be in contact with oral fluids and that during the 1-yr storage in bovine teeth, they were sufficiently protected from this contact by the apical root canal filling and by the coronal composite resin filling.

Animals↗

PubMed2001

Dentine caries: take it or leave it?

In modern dentistry the primary aim when excavating carious dentine is to eradicate only the highly infected, irreversibly demineralised and denatured biomass in order to allow effective restoration of the cavity, restoration of the surface anatomy of the tooth and to prevent disease progression. However, the boundary between this superficial zone of dentine requiring excavation and the deeper, affected but repairable tissue is not always obvious either in the clinic or in the research laboratory. The inherent subjectivity in detecting this excavation boundary can result in clinically significant differences in the quality and quantity of dentine removed by different operators and makes the in vitro comparison of newer excavation techniques more difficult. This article discusses the rationale behind carious dentine excavation and the criteria available to the dentist, both clinical and laboratory, to help identify the dentine requiring removal.

Color↗