Biomedical subjects

D Tantbirojn

Publications and source records attributed to D Tantbirojn.

13 recordsLinked to original sources

PubMed2005

Effect of acidic food and drinks on surface hardness of enamel, dentine, and tooth-coloured filling materials.

OBJECTIVES: The purpose of this study was to determine the effect of acidic food and drinks (Cola soft drink, drinking yogurt, orange juice, sports drink, Tom-yum soup) on surface hardness of various substrates (enamel, dentine, universal composite, microfilled composite, conventional glass ionomer, resin-modified glass ionomer, polyacid-modified resin composite). METHODS: Specimens (n = 10) were alternately immersed, 5 s each, in food or drinks and in artificial saliva for 10 cycles. Baseline and post-immersion Vickers hardness were compared using paired t-test. The difference in hardness between the groups was analysed with one-way ANOVA followed by a least significant different (LSD) test. RESULTS: Cola soft drink significantly reduced surface hardness of enamel, dentine, microfilled composite, and resin modified glass ionomer (p < 0.05). Orange juice and sports drink significantly reduced surface hardness of enamel (p < 0.05). Drinking yogurt and Tom-yum soup did not reduce surface hardness of any substrate. CONCLUSION: This in vitro study confirms the erosive potential of certain acidic food and drinks that public should be aware of.

Acrylic Resins↗

PubMed2003

Fracture toughness and microhardness of a composite: do they correlate?

OBJECTIVES: Chipping and bulk fracture are major contributors in clinical failures of composite restorations. Fracture toughness (K(Ic)) quantifies susceptibility for fracture, but experimental determination is complicated. It would be beneficial for the dental community if a relatively simple experiment, such as microhardness (HK), could be used to screen composites for fracture resistance. This study explores a possible correlation between K(Ic) and HK. METHODS: Composite cylinders (4mm diameter and approximately 7 mm long) were cured for five combinations of light intensity (I, microm W/cm(2)) and curing time (T, s) to achieve a range of different total light energy densities (I x T=100 x 10, 100 x 20, 300 x 20, 300 x 40, and 700 x 60 microm W s/cm(2)). A chevron-notch was cut in the median plane of the cylinders for the fracture toughness test, which was executed in a displacement control mode at 6 micro m/s cross-head speed (sample size 4). Knoop hardness was determined at the median plane of the cylinders (sample size 6). The tests were performed 15 min and 24h after curing. RESULTS: Both the K(Ic) and HK increased with increased light energy density and storage time. Linear regression analysis indicated a strong correlation between HK and K(Ic) tested at the same time period (R(2)=0.97 and 0.90 for 15 min and 24h, respectively). The correlation became weaker between the different storage times (R(2)=0.71), indicating a change in fracture toughness and/or microhardness mechanisms. CONCLUSION: Fracture toughness of a composite cannot be simply extrapolated from microhardness.

Algorithms↗

PubMed2000

In vitro inhibition of enamel demineralization by a polymerizable amphiphilic film.

An amphiphilic coating is configured as a substantive film that has a tendency for an in-plane two-dimensional polymerization. This coating is hypothesized to protect enamel from in vitro acid decalcification, assessed through the following artificial caries model. Three regions on labial enamel of eight bovine incisors were treated with an acid resistant varnish (A), the amphiphilic coating (B), or left undisturbed (C), and the teeth were immersed for 3 wk in lactic acid gel. Mineral loss (deltaZ-value) was determined by a cross-sectional microhardness technique. deltaZ-values (mean +/- SD; volume percent mineral-microm) were: -4 +/- 24 (A), 29 +/- 69 (B), and 7,372 +/- 1,766 (C). deltaZ-value of the uncoated enamel (C) was significantly different from the other groups. Scanning electron microscopy showed enamel etched pattern from citric acid, and the coating firmly attached on enamel surface. This amphiphilic coating can inhibit enamel decalcification under the present experimental condition.

Acrylates↗

PubMed2000

Nominal shear or fracture mechanics in the assessment of composite-dentin adhesion?

This study addresses the anticipated problem of discriminating among high-performing dentin adhesives. The simplicity of the nominal shear bond test, despite being heavily criticized, has made it a routine procedure for the determination of bonding efficacy. A fracture mechanics approach has been suggested as a better assessment of bonding efficacy (Versluis et al., 1997). However, experimental complexity is a major limitation. It is hypothesized that a new, simplified interfacial fracture toughness test (Lin, 1994) will evaluate bonding agents differently if compared with the traditional shear bond test. Therefore, the objective of this study was to compare the performances of six dentin bonding agents subjected to the interfacial fracture toughness test (critical plane strain energy release rate) or to the nominal shear bond test (shear bond strength). Their performances were also characterized by scanning electron micrography of the fracture surfaces for evidence of dentin cohesive failure. Statistical analyses showed only marginal differences between these determinants of the two tests. However, when the analysis was applied only to the materials that had 100% frequency of dentin cohesive failure in shear testing, which also had high bonding efficacy, the difference in adhesive strengths between the two tests became significant. The reliability of the nominal shear test is questioned when dentin cohesive failure occurs, which usually is associated with high bonding efficacy. Since it is expected that bonding efficacy will increase further, the interfacial fracture toughness test is the preferred methodology to distinguish among high-performing dentin adhesives.

Adhesiveness↗

PubMed2000

Optical scattering power for characterization of mineral loss.

Mineral loss in early caries cannot be measured without invasive procedures. To quantify mineral loss without sectioning the tooth, one must determine the optical scattering of the enamel. Using enamel white-spot lesions, we hypothesize that the optical scattering power (Sp) of the demineralized enamel would provide a quantitative estimate of mineral loss. Enamel slabs were demineralized to produce artificial white spots. The data were acquired by means of a Charge-Coupled Device (CCD) camera and image-processing software. For the purpose of comparison, mineral loss (deltaZ) of the demineralized samples was determined by the use of a microhardness approach after the samples were sectioned. The scattering power correlated well with deltaZ (r2 = 0.82). In contrast, simple reflectance of the demineralized samples correlated poorly with deltaZ (r2 = 0.22). The validity of using scattering power to measure demineralization has been confirmed by a three-dimensional Monte Carlo Simulation.

Animals↗

PubMed1999

Theoretical considerations of contraction stress.

Polymerization shrinkage of composite restorative materials causes clinical concerns because it introduces residual stresses in restored teeth. These stresses can, among other things, propagate enamel cracks, bring about microleakage, and cause postoperative sensitivity. The amount of shrinkage stress does not depend only on how much a composite contracts, but also on the elastic modulus ("stiffness") of the composite, the shape of the cavity, the established bonding between the tooth and restoration, etc. The relationships between these many factors can be described by universal physical laws. To analyze shrinkage stresses, theoretical models must be used that relate the various shrinkage properties and clinical conditions via physical laws. Models will assist us to rethink and optimize established paths to clinical success.

Composite Resins↗

PubMed1998

Spatial chemical analysis of dental stain using wavelength dispersive spectrometry.

Six extracted human teeth with naturally-formed neglected stain were analyzed for chemical constituents using wavelength dispersive spectrometry (WDS), an electron microprobe technique. Spatial distribution, within a few microm resolution, of the compositional elements was obtained by line and map analyses, which provided relative concentrations of the elements in stain-enamel complex. Absolute concentrations at different locations across a specimen were obtained from quantitative analysis. Results showed that these neglected stains were highly calcified and contained a significant amount of organic matter (C, N, O, S), with traces of Fe and Cu. The tooth surface underneath the stain layer could be easily distinguished by the higher Ca and P content, as well as by finite amounts of C and S. Corresponding areas of high concentrations between S and Fe/Cu were observed, which suggested the complex of sulfur and metal ions as possible color-forming species. S was found to diffuse into surface enamel in the range of 10 microm.

Calcinosis↗

PubMed1998

In vitro enamel and cementum fluoride uptake from three fluoride-containing composites.

The incorporation of fluoride into restorations is desirable because of its cariostatic action. The purpose of this study was to determine fluoride release and fluoride uptake by enamel and cementum from three visible light-cured fluoride-containing composites. Seven circular discs of each composite were prepared and the amount of fluoride released into distilled water was determined at daily intervals for 14 days and then after 30, 60 and 90 days. The fluoride concentration in enamel and cementum was determined in three successive depths by an acid etch biopsy procedure. The composite slabs were made and ligated to the enamel and cementum surfaces and the teeth were immersed in synthetic saliva for 7 days. After removal of the composite slabs, three successive biopsies were again performed. Then the teeth were immersed in 1 M KOH for 24 h and similar biopsies done. The fluoride concentrations were adjusted to standardized depths of 10microm, and the total and bound fluoride uptake calculated. The amounts of fluoride released were significantly different among the three composites. The fluoride released decreased sharply after 1 day and then gradually reached a plateau. As for the enamel and cementum fluoride uptake, FluorEver showed the largest uptake followed by FluoroCore and then Pertac-Hybrid.

Acid Etching, Dental↗

PubMed1998

Do dental composites always shrink toward the light?

Many of the current light-curing composite restorative techniques are rationalized in compliance with the theory that composite shrinks toward the light. Shrinkage directed toward the margins is believed to be responsible for the observed improved marginal properties. However, the dental literature does not consistently support this theory. Experimental determination of contraction patterns is very difficult. In this study, a finite element technique is used to analyze the direction of composite shrinkage as it cures. The process of polymerization can be characterized by pre- and post-gel phases. The stress developed in a restoration can be relieved quickly by the flow of material still in the pre-gel phase. Residual stresses arise after gelation. Both auto- as well as photo-curing composites were analyzed. In photo-curing composites, the gel-point varies throughout the material with the intensity of the light. Experimentally determined light transmittance data for different materials were used in the simulation. Degree of cure and time-dependent shrinkage properties were also included from experimental measurements. The analysis showed that the shrinkage direction was not significantly affected by the orientation of the incoming curing light, but instead was mostly determined by the bonding of the restoration to the tooth and by the free surfaces. Consequently, differences between the contraction patterns of auto- and photo-cure were minimal. It was concluded that composite does not shrink toward the light, but that the direction is predominantly determined by cavity shape and bond quality. Improved marginal properties should be pursued by the optimization of other factors, such as the polymerization process, the curing procedure, and the bond quality. The direction of shrinkage vectors in response to light position does not seem to be an appropriate criterion for the optimization of marginal quality.

Animals↗

PubMed1998

Stain removal efficacy: an in vitro evaluation using quantitative image analysis.

OBJECTIVE: This study developed a computer image analysis technique as a quantitative means to measure changes in dental stain after brushing with various dentifrices. METHOD AND MATERIALS: Enamel specimens with naturally occurring mature stain were cut from bovine incisors. The specimens were subjected to in vitro toothbrushing with one of the four tested groups, consisting of two dentifrices that make claims of stain removal (Aquafresh Whitening and Rembrandt Sensitive), a regular dentifrice, (Aquafresh Triple Protection), and water. Digital images of stain specimens were recorded under standardized lighting conditions and analyzed with an image analysis software. The area-intensity stain determinant, which accounted for the reflected intensity and the corresponding areas of stain, was computed. Stain removal efficacy was calculated based on the difference in area-intensity stain determinant before and after brushing. RESULTS: Brushing with any of the tested dentifrices removed more stain than did brushing with water alone. The finding that brushing with a regular dentifrice resulted in higher stain removal efficacy than brushing with water seems to indicate a role for abrasivity. Aquafresh Whitening had a higher stain removal efficacy than did Rembrandt for the removal of mature calcified stain used in this study. However, there were certain stains that none of the dentifrices removed. CONCLUSION: Computer image analysis provides an objective and quantitative measurement to distinguish in vitro stain removal efficacy of dentifrices.

Analysis of Variance↗

PubMed1997

Inhibitive effect of a resin-modified glass ionomer cement on remote enamel artificial caries.

Glass ionomer cements (GICs) demonstrate the inhibition of caries lesions formed immediately adjacent to the restoration. This in vitro study was conducted to evaluate the distance at which a resin-modified GIC is able to exert its cariostatic effect on artificial enamel lesions ('remote effect'). Resin-modified GIC or bis-GMA resin was applied on the cervical third of the labial surface of 10 paired halves of bovine incisors. Specimens were separately immersed for 3 weeks in lactic acid gel which was changed every other day to reduce fluoride accumulation. Artificial lesions were examined by the cross-sectional microhardness (MHN) method. Volume percent mineral, mineral loss (delta Z value) and change in mineral content (delta M) were computed for each MHN profile, performed at distances of 0.2, 0.5, 1.0, 2.0, 4.0 and 7.0 mm from the edge of the materials. delta Z values of the resin-modified GIC group were significantly lower than those of the bis-GMA control group at all remote sites (t test, p < 0.05). The delta M caused by resin-modified GIC was more pronounced within 1.0 mm from the material which suggested that the demineralization inhibition can be divided into the near effect (< 1.0 mm). In this in vitro study, resin-modified GIC provided caries resistance in bovine enamel located at a considerable distance from the margin of the material.

Animals↗

PubMed1997

Why do shear bond tests pull out dentin?

It is widely accepted that a dentin shear bond test which pulls out dentin must mean that the adhesive strength is superior to the cohesive strength of the dentin. Using numerical modeling techniques, Van Noort et al. (1988, 1989) and DeHoff et al. (1995) alerted the scientific community that there were massive stress concentrations in the familiar dentin bond test. It is not inconceivable that these localized high tensile stresses could initiate cracks which diverge monolithically into dentin, leaving the interface unchallenged. To test this hypothesis, we developed a failure accumulation simulation program which determined localized failure interactively "on the fly" with a finite element solver, and also included brittle behavior, adhesive and cohesive failure, stochastic response, and dynamic remeshing. All of the familiar dentin bond variables were included in the simulation. A parallel experimental dentin bond test validation was run, and the fractography was examined in the scanning electron microscope for mode of failure. The simulation confirmed the tensile monolithic fracture hypothesis. It is also confirmed that dentin pull-out was partly due to the biomechanics of the test and did not necessarily mean superior adhesive strength or even that the cohesive strength of the dentin was reduced. There is clear need for a new technology for the evaluation of biological interfaces, and the present work has shown the vital role of numerical modeling in the interpretation of such experimental procedures.

Adhesiveness↗

PubMed1992

Enamel, cementum and dentin fluoride uptake from a fluoride releasing resin composite.

The purpose of this study was to determine the fluoride release by and the enamel, cementum and dentin fluoride uptake from a visible light-cured fluoride-containing resin composite. Seven circular discs of the composite were prepared and the fluoride release in distilled water determined at daily intervals for 14 days, and then after 30, 90, 180, 365 and 550 days. The baseline fluoride concentrations in enamel and cementum were determined in three successive depths by an acid etch biopsy procedure and in dentin by an abrasion biopsy procedure. Composite slabs were prepared and ligated to the enamel, cementum and dentin surfaces and the teeth were suspended in synthetic saliva for 7 or 30 days. After removal of the composite, similar biopsy procedures were performed. The teeth were then immersed in 1 M KOH for 24 hours and similar biopsies done. The fluoride concentrations were adjusted to standardized depths of 2.0 microns for enamel, 4.0 microns for cementum and 10.0 microns for dentin, and the total and bound fluoride uptake calculated. The fluoride release from the composite dropped sharply after 1 day and after 180 days reached a plateau which remained relatively constant up to 550 days. The results of this in vitro study indicated that the mineralized dental tissues acquired fluoride at various depths.

Analysis of Variance↗