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ABSTRACT: To investigate the effects of fluoride (F), calcium-phosphate-monofluorophosphate-urea (CPMU) mineralising solution, and casein on plaque pH and calcium (Ca), phosphate (P) and F content, and the ability of plaque to induce carious lesions in enamel.
Plaque microcosms were cultured in cariogenic growth conditions on enamel specimens for 28d in a "multiplaque artificial mouth". The plaques were supplied 5 times daily with 10% sucrose (1.5 ml over 6 min) over a 12h period followed by a 12h rest period. Duplicate plaques were pulsed with 0, 1000, 3000 and 5000 ppm F (1.5 ml over 6 min) or 2% w/v casein (1.25 ml over 30 min) twice daily. One of each pair was also pulsed with CPMU (1.5 ml over 6 min). Plaque pH was monitored during growth. After 28 days' culture, plaque Ca, P and F levels were quantified and lesion depth in enamel was measured by backscattered electron SEM.
F pulses raised the plaque pH, which was otherwise below 4 during sucrose pulsing, while CPMU hastened and raised the recovery pH. Plaque Ca, P and F levels substantially increased with increasing concentrations of applied F, particularly in the presence of CPMU (P < 0.01). In the absence of either F or CPMU, enamel lesions were formed with extensive enamel loss.
CPMU and F supplied to plaque microcosms substantially reduce plaque cariogenicity to enamel under highly cariogenic experimental conditions. This was associated with an increase in plaque pH, plaque F and Ca levels.
The New Zealand dental journal 03/2011; 107(1):12-8.
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ABSTRACT: Dental plaque bacteria form complex and robust cell aggregates which cannot be counted accurately using epifluorescence microscopy. This causes a significant problem for quantifying their viability. The aim of the investigation was to develop a fluorescence assay to quantify the viable biomass of dental plaque biofilms. Using an artificial mouth system, microcosm plaques were grown under a range of fluoride and mineralizing conditions, and were treated with the oral antiseptics chlorhexidine (CHX) and Listerine. Plaques were harvested, made into suspension and stained in microtitre plates with a di-chromatic fluorescent stain (Live/Dead BacLight). The percentage of viable biomass was calculated from the regression data generated from a viability standard. The standard was constructed using different proportions of viable (green fluorescence) and non-viable (red fluorescence) plaque bacteria, and growth conditions for optimizing green fluorescence were investigated. The results from the assay showed that fluoride at 1000 and 3000 ppm promoted plaque viability by at least 15%, from approximately 45 to 60%, and at 5000 ppm to approximately 87% (P<0.05). Plaques treated with Listerine and CHX from d 0 yielded insufficient biomass to be tested for viability, however 14 d post-treatment, viability was comparable to untreated plaques (approximately 55%, P>0.05). Treatment with Listerine and CHX from d 3 reduced biomass but not viability. Development of this assay enabled viability of plaque bacteria which cannot be resolved with epifluorescence microscopy to be evaluated. It offers a rapid alternative to epifluorescence microscopy and could be applied to nonoral bacteria.
Journal of Microbiological Methods 06/2007; 69(3):489-96. · 2.09 Impact Factor
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ABSTRACT: A better appreciation of the properties of carious dentine would be of clinical advantage in carious assessment and management. The aim of this study is to understand the deterioration of the mechanical properties of carious dentine as a result of bacterial demineralising process as well as change in dentine structures observed under scanning electronic microscope. Eight primary molar teeth with untreated carious dentine were axially sectioned and fine polished for nano-indentation. On each specimen, six lines of indentation, evenly distributed through the lesion, were made from the pulp to lesion cavity floor parallel to tubule direction using nano-indentation (Ultra Micro Indentation System, UMIS-2000), while another two indentation lines were made on an adjacent region of sound dentine in the same manner. All tests were conducted on hydrated specimens. Hardness and elastic modulus decreased significantly and progressively toward the cavity floor varying from 0.56 to 0.001 GPa and 14.55 to 0.015 GPa, respectively. The change in mechanical properties was in a specific pattern as a function of lesion depth, in which the hardness could be fitted to an exponential function, while the variation of the elastic modulus across the entire lesion was fitted to a power law relationship. More critical evaluation of the elastic modulus data indicated that two distinct exponential functions provided an excellent fit to the results. These changes in elastic modulus also matched the structural changes seen across a lesion, which were associated with a change from primarily peritubular to intertubular dissolution.
Journal of Biomechanics 08/2005; 38(7):1535-42. · 2.43 Impact Factor
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ABSTRACT: The conditions under which mechanical properties of dentine are tested influence the values recorded. The aims of this study were to examine the effect of hydration on the mechanical properties of primary carious dentine and to provide information on changes in hardness and modulus of elasticity change caused by the demineralizing caries process in dentine. Three primary molar teeth with untreated carious dentine were prepared for nano-indentation tests under both wet and dry conditions. Further tests were conducted on eight primary molars with untreated carious dentine under hydrated conditions. The mechanical properties of dehydrated carious dentine increased approximately 10-fold for hardness and 100-fold for the modulus of elasticity compared with hydrated dentine. The hardness and elastic modulus of the carious primary dentine deteriorated progressively toward the lesion cavity floor, ranging from 0.001 to 0.52 GPa and from 0.015 to 14.55 GPa, respectively, and could be fitted to a simple linear relationship when plotted in logarithmic scale vs. distance. The total depth of dentine affected was around 1100 microm parallel to the tubule direction. This depth was significantly greater than observed subjectively, implying that the demineralization process is more advanced than might be suspected on simple clinical examination.
European Journal Of Oral Sciences 07/2004; 112(3):231-6. · 1.88 Impact Factor
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ABSTRACT: The deterioration of the mechanical properties of carious dentine was assumed to be associated with the decrease in mineral content due to the carious process. This study aimed to compare the mechanical properties of carious dentine studied by an ultra-micro-indentation-system (UMIS) and the mineral content determined using backscattered scanning electron (BSE) imaging. Eight axial sectioned and fine polished primary molar teeth with untreated carious dentine were measured for hardness and elastic modulus using the UMIS. On each specimen two centrally located linear arrays of indentations were made from the pulp to lesion cavity floor, followed by the capture of a BSE image using a solid-state detector. The BSE intensity at the same spot as the indentation array on each specimen was analysed and compared to the UMIS results. The results show that the mechanical properties of dentine are dependent on its mineral content. The decrease in mechanical properties of carious dentine, namely hardness and elastic modulus are directly linked to the reduction in its mineral content (r2 = 0.93 and 0.92, respectively). The relationship between dentine hardness and elastic modulus values (y) can be expressed as an exponential function of the mineral content in wt.% (x) that is y = ae(bx).
Archives of Oral Biology 06/2004; 49(5):369-78. · 1.60 Impact Factor
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ABSTRACT: Backscattered electron-scanning electron microscope (BSE-SEM) imaging has been recommended as a reliable tool to quantify the mineralisation state of calcified tissues and is commonly used in bone studies. The aim of this study is to investigate the use of BSE imaging to quantitatively analyse the mineral content of sound and carious dentine. Eight primary molars with untreated carious dentine were embedded in resin, axially sectioned and fine polished for this study. The BSE images were from a solid-state detector in an SEM operating at 1.5Torr gas pressure. BSE images of a number of different elements and compounds with atomic number ranged from 4 to 26 were analysed prior to the test to calibrate the experimental conditions and an enamel-carbon block. The mineral analysis was based on the change in BSE intensity (measured in graylevels). The results showed that variation in graylevels accurately represented difference in the atomic number and BSE coefficient of the test materials. The mineral content of sound primary dentine in the most regions was 59.3+/-5.5 wt.%, but it decreased gradually to be just 41.82+/-6.74 wt.% adjacent to the pulp. The carious dentine showed a marked reduction in mineral content which proceeded progressively toward the cavity floor, in which the minimum value of less than 10 wt.% was normally found in the outer layer of the lesion. The results show that BSE imaging is a simple and reliable technique that can be used to quantify the mineral content of sound and carious dentine. More importantly the variable pressure SEM offers an approach to minimize the impact of dehydration on carious dentine specimens.
Archives of Oral Biology 03/2004; 49(2):99-107. · 1.60 Impact Factor
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ABSTRACT: Understanding the mechanical properties of dentine is of importance as adhesive restorative materials mainly achieve their bonding to the tooth structure through dentine. The current study measures the hardness and modulus of elasticity of primary molar dentine using an Ultra-Micro-Indentation System (UMIS), which allows the dentine to remain hydrated and thus is assumed to be closer to the in vivo conditions.
Eight sound primary molar teeth were axially sectioned, embedded in resin and fine polished. Two linear arrays of indentations were done on coronal dentine, from the pulp wall to dentino-enamel junction (DEJ) parallel to the tubule direction under a force load of 25mN.
The mean hardness and elastic modulus of the dentine nearest the pulp wall was 0.52+/-0.24 and 11.59+/-3.95GPa, respectively, which was significantly lower than those of dentine in the middle area, which was 0.85+/-0.19 and 17.06+/-3.09GPa, respectively, and the dentine nearest DEJ, which was 0.91+/-0.15 and 16.33+/-3.83GPa, respectively. There is a statistically significant linear correlation between the hardness and modulus of elasticity.
The hardness and modulus of elasticity of dentine decreases with decreasing distance from the pulp. This is of importance to clinicians because an extension of cavity preparation towards the pulp may lead to less mechanical support for a restoration.
Journal of Dentistry 06/2003; 31(4):261-7. · 2.95 Impact Factor
