Search

Artificially inducing dentinal lesions mimicking those remaining after selective excavation should allow to investigate the effects and limits of such selective excavation, for example regarding the mechanical properties of treated teeth or the remineralisation of sealed residual lesions. Such analyses might otherwise be limited by the variability of natural lesions or ethical and practical concerns. This study compared different demineralisation protocols for their suitability to induce lesions similar to natural residual caries. Twelve natural deep lesions were excavated until leathery dentin remained, and analysed for their mineral loss (ΔZ), lesion depth (LD), mineral loss ratio (R), the slope of the mineral gradient and their nano-hardness profile. Artificial lesions were induced using four different demineralisation protocols (acetic acid pH = 4.95; 0.1 M lactic acid gel pH = 5.0; 0.5 M ethylenediaminetetraacetic acid pH = 7.2; Streptococcus mutans biofilms) and their depths monitored over different demineralisation times. Lesions with depths most according to those of natural lesions were analysed using transversal microradiography. Lesions induced by acetic acid solution did not significantly differ with regards to LD, ΔZ, R and mineral profile. Seven dentin specimens were subsequently submitted to a moderately acidic (pH = 5.3) methylhydroxydiphosphonate-buffered acetate solution for 12 weeks. Natural and artificial residual lesions were similarly deep (mean ± SD: LD = 626 ± 212 and 563 ± 88 µm), demineralised (R = 19.5 ± 4.7 and 29.8 ± 4.1%), showed a flat and continuous mineral gradient (slope = 0.10 ± 0.05 and 0.13 ± 0.06 vol%/µm) and did not significantly differ regarding their nano-hardness profile. The described protocol induces lesions with mineral content and mechanical properties similar to natural residual lesions.

This in situ study investigated whether there is a relationship between gap size and wall lesion development in dentin next to 2 composite materials, and whether a clinically relevant threshold for the gap size could be established. For 21 days, 14 volunteers wore a modified occlusal splint containing human dentin samples with 5 different interfaces: 4 gaps of 50 µm, 100 µm, 200 µm, or 400 µm and 1 non-bonded interface without a gap. Eight times a day, the splint with samples was dipped in a 20% sucrose solution for 10 minutes. Before and after caries development, specimens were imaged with transversal wavelength-independent microradiography (T-WIM), and lesion depth (LD) and mineral loss (ML) were calculated at the 5 different interfaces. After correction for the confounder location (more mesial or distal), a paired t test clustered within volunteers was performed for comparison of gap widths. Results showed no trend for a relationship between the corrected lesion depth and the gap size. None of the differences in lesion depth for the different gap sizes was statistically significant. Also, the composite material (AP-X or Filtek Supreme) gave no statistically significant differences in lesion depth and mineral loss. A minimum gap size could not be established, although, in a non-bonded interface without a measurable gap, wall lesion development was never observed., (© International & American Associations for Dental Research.)

Objective: The purpose of this study was two-fold: (1) to monitor bacterial biofilm formation and bacteria-induced demineralization of dentine in situ by using electrochemical impedance spectrum (EIS); (2) to examine the relationship between EIS findings and changes in the chemical composition and ultrastructure of dentine during bacteria-induced demineralization., Methods: In this study, dentine demineralization was induced by Streptococcusmutans (ATCC 25175) in the presence of sucrose in culture medium and was monitored using two EIS measurement systems (Type A with a working electrode and Type B without a working electrode). Scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) and X-ray diffraction (XRD) were employed to examine the morphology, element contents and crystallinity of hydroxyapatite (HAP) on the dentine surface. Transverse microradiography (TMR) was used to characterize the lesion depth and degree of mineral loss during demineralization., Results: The resistance of the bulk dentine (R(d)) and the apparent resistance of dentine (R(a)) measured from the Type A and Type B EIS systems, respectively, decreased gradually with demineralization. The resistance of the biofilm formed on dentine surface was determined by fitting the EIS data with equivalent circuits. The presence of biofilm slightly increased R(a) of dentine before demineralization. However, the electrochemical behavior of biofilm did not affect the decreasing impedance of dentine with demineralization. The SEM, EDX, XRD and TMR results demonstrated that the surface and bulk dentine gradually became more porous due to the loss of minerals during demineralization, which in turn resulted in the decrease in R(d) and R(a) values obtained from EIS systems., Conclusions: This investigation highlighted EIS as a potential technique to monitor biofilm formation and bacterial-induced demineralization in situ., (Copyright 2009 Elsevier Ltd. All rights reserved.)

Objectives: Tubules dominate the microstructure of dentin, and in crowns of human teeth they are surrounded by thick mineralized peritubular cuffs of high stiffness. Here we examine the three-dimensional (3D) arrangement of tubules in relation to enamel on the buccal and lingual aspects of intact premolars and molars. Specifically we investigate the angular orientation of tubules relative to the plane of the junction of dentin with enamel (DEJ) by means of wet, non-destructive and high-resolution phase-contrast (coherent) tomography., Methods: Enamel capped dentin samples (n=16), cut from the buccal and lingual surfaces of upper and lower premolar and molar teeth, were imaged in water by high-resolution synchrotron-based phase-contrast X-ray radiography. Reconstructed 3D virtual images were co-aligned with respect to the DEJ plane. The average tubule orientation was determined at increasing distances from the DEJ, based on integrated projections onto orthogonal virtual planes. The angle and curl of the tubules were determined every 100 microm to a depth of 1.4mm beneath the DEJ., Results: Most tubules do not extend at right angles from the DEJ. Even when they do, tubules always change their orientations substantially within the first half-millimeter zone beneath the DEJ, both on the buccal and lingual aspects of premolar and molar teeth. Tubules also tend to curl and twist within this zone. Student t-tests indicate that lower teeth seem to have greater tilts in the tubule orientations relative to the DEJ normal with an average angle of 42 degrees (+/-2.0 degrees), whereas upper teeth exhibit a smaller change of orientation, with an average of 32 degrees (+/-2.1 degrees)., Significance: Tubules are a central characteristic of dentin, with important implications on how it is arranged and what the properties are. Knowing about the path that tubules follow is important for various reasons, ranging form improving control over restorative procedures to understanding or simulating the mechanical properties of teeth. At increasing depths of dentin beneath enamel, tubules are significantly tilted relative to the DEJ norm, which may be important to understand clinical challenges such as sensitivity, effectiveness of bonding techniques or prediction of possible paths for bacterial invasion. Our data show dissimilar average tubule angles of upper versus lower teeth with respect to the DEJ which presumably contributes to different shear responses of the tissue under function. The degree to which this may warrant improved restoratives or new adhesive techniques to enhance adhesive restorations merits further investigation.

Purpose: To examine an association between coloration (red, pink) resulting from staining with Caries Detector Dye (CDD) and the corresponding mineral density in dentin caries lesions determined by transverse microradiography (TMR)., Methods: CDD coloration of the lesion sections (approx. 190 microm) prepared from extracted caries teeth was photographed, and the corresponding relative mineral densities (RMD: relative values to the sound dentin) were obtained by TMR. A parallel study was performed using artificially demineralized and then remineralized dentin lesions., Results: The mean RMD values in the naturally black-pigmented, red- and pink-stained portions were 46 +/- 26.7%, 64 +/- 24.5%, and 80 +/- 15.1%, respectively. There were statistical differences in the RMD values among the three portions, as well as a wider range of RMD value distributions in the red and black-pigmented portions than in the pink portion.Even among the black-pigmented and red portions, much higher RMD values more than 90% were observed in several lesions, which were close to the mineral density of the sound (unaffected) dentin tissue. On the other hand, the remineralized surface layer of artificially demineralized lesions did not show the red coloration, and there seemed a threshold value of mineral density (approx. 21%), beyond which the red coloration was not observed. Similar threshold value was noted in the remineralized lesion body. This study showed a remarkable discrepancy regarding the RMD value for the red staining behavior between the naturally occurring caries and artificial carious lesion.

There is no consensus about the definition and progression of outer and wall lesions in secondary caries. In this study we investigated whether lesion progression is influenced by an adjacent composite restoration and whether wall lesions develop at the composite-tooth interface. In order to study the appearance and progression of approximal primary caries lesions and lesions next to composite restorations, 16 samples were placed in a full denture of each of 8 subjects. Each denture housed 4 restored and 4 unrestored enamel samples and similarly 8 dentin samples. All samples were distributed over 2 sample holders, in each of which 4 approximal spaces were simulated. Every 4 weeks the sample holders were microradiographed using transversal wavelength independent microradiography and lesion depth was measured. At the end of the study, after 20 weeks, the lesion depth of the outer lesions was 0-350 microm for enamel and 0-750 microm for dentin. The estimated difference in progression between secondary and primary lesions (1.1 microm/4 weeks, 95% CI: -9.2 to 11.4 microm) was not statistically significant (p = 0.83). Secondary outer lesions appeared and progressed as primary caries lesions. No clear wall lesions were found next to composite, but they were observed next to acrylic resin., (2007 S. Karger AG, Basel)

This study was undertaken to examine the effects of the antiepileptics phenytoin and zonisamide on changes in the mineral density of the incisor and bone mineral density (BMD) of the mandibular head, and on the rate of dentin formation using histomorphometric measurements. After repeated administration of phenytoin or zonisamide to male growing rats, the mineral density of the lower incisors and mandibular head were determined by analyzing microradiographs and dentin formation rates were determined by histomorphometric measurements. Results showed a significant decrease in the mean values of BMD of the mandibular head and lower incisors in groups treated with phenytoin or zonisamide compared with the vehicle-treated group (p < 0.05). The percent rates of decrease in mineral density of the incisors for phenytoin and zonisamide were 6.8% and 4.0%, respectively. Phenytoin and zonisamide significantly reduced the dentin formation rate for the mesial and distal areas compared with the vehicle-treated group. Thus, epileptic children who are treated over a long period with antiepileptics, especially at primary school age, should ensure good oral hygiene so as not to suffer bone loss, edentulism or gingival overgrowth., (2004 Prous Science.)

Objective: To demonstrate the progression of crater growth during repeated sequential application of an Er:YAG laser to enamel and dentine, monitored using X-ray microtomography (XMT)., Design: A single centre study in which laser craters were created in blocks cut from human enamel and/or dentine under standardised and known conditions and then studied using XMT to obtain visualisation and quantification of the effects., Setting: University setting, UK, 2001., Main Outcome Measures: Success was judged by an ability to obtain useful 3D XMT reconstructions of the blocks during crater development, and to make measurements from these data. These measurements were compared with data obtained from similar studies using different measurement techniques., Results: Time sequences of 2D and 3D images were obtained which demonstrated the progression of laser craters in enamel and dentine. Quantitative measurements from these data enabled values to be derived for the rate of progression of crater depth per unit energy, and the volume of hard tissue removed per unit energy. These values were compared with data derived from other studies and shown to be broadly comparable. However, the present study is unique in that these values were obtained from a series of measurements of the same craters over time., Conclusions: 3D X-ray microtomography is shown to be a useful tool for quantitative measurements in dental research. For the Er:YAG laser, the relationship of laser crater depth and volume of mineral removed to applied energy was found to be linear.

The Er:YAG laser, with or without phosphoric acid, is used to promote enamel surface changes to increase restorative material retention. However, such irradiation might induce subsurface enamel damage. In the present study, X-ray microtomography was used to compare the subsurface enamel beneath laser and acid conditioned; laser-only etched and acid-only etched surfaces. Laser and acid conditioning increased the etching depth, but did not induce significant damage in the enamel subsurface. Analysis of the laser-only etched enamel subsurface revealed a small reduction in mineral concentration suggesting an increase in porosity, allowing greater penetration of acid and resulting in an increased acid-etch depth.

In cardiology and research involving the interactions between restorative materials and dental hard tissues, it is important for small changes in tooth mineral content to be measurable. Currently, transverse microradiography (TMR) is the most accepted tool for the above purpose. Electron Probe Microanalysis (EPMA) can yield both qualitative identification of elements and quantitative compositional information. The purpose of this study was to compare the mineral distribution in well-defined artificial lesions, in dentin and enamel, by the use of both TMR and EPMA on the same sample. The good correlation between the two sets of data validates EPMA as a technique and helps in the interpretation of its results. The data from TMR analysis are expressed as vol% of mineral, while EPMA gives the levels of Ca and phosphate in wt%. The conversion between the two sets of data is complicated by the fact that local density is, as yet, unknown.

Three aspects of quantitative transverse microradiography are described and discussed: (1) the average mineral loss parameter of enamel or dentin lesions (R) in vol%; (2) mineral distribution visualization of lesions by means of a computer-assisted videodensitometric (CAV) method; and (3) the microradiography of hyper-remineralized lesions. "R", defined as the average amount of mineral lost (or gained) in a lesion per unit lesion length, is a useful parameter in dental caries. The results show that, in vitro, R is about constant over the demineralization period for enamel and dentin. This was found even for quite different dissolution kinetics. R is strongly reduced by the presence of small amounts of fluoride in the demineralizing system. R of dentin lesions is smaller than for enamel lesions. We conclude that the mineral loss value (delta Z) and the lesion depth (ld) are in general dependent parameters during in vitro or in situ studies on enamel or dentin. During lesion formation, mineral loss from the lesion and acid penetration in the tissue are obviously linked. This is possible only if the mineral content in the lesion does not change very much after passage of the lesion front. The CAV method presented is illustrated for enamel lesions formed in vitro and in situ.

Transverse microradiography (TMR) of thin sections is the principal method for determining mineral changes in experimental lesions. Because it has become also the standard by which newly-developed methods are validated, demands on all steps of the procedure are high. Thin sections of enamel and dentin require high-precision cutting or lapping to preserve surface structures, but their different brittleness and elasticity preclude a uniform procedure. Image analysis permits the measurement of fine details at a micron scale, but because most studies are aimed at overall mineral changes, they are usually lost on broadening of the scan areas and averaging of experimental groups. Small errors in repositioning of the scan areas for repetitive measurements may yield distorted lesion profiles, while quantitative data such as the integrated mineral loss are hardly influenced. A major reason for "irreproducibility" of TMR are the different definitions of the lesion parameters as used by various research groups. We recommend that these definitions be agreed on if the full potential of TMR as an international standard is to be utilized.

Composite restorations are prone to develop secondary caries if a gap exists between tissue and restoration. The aim of this article was to quantify the effects of a fluoridating and non-F composite on secondary dentine caries in vitro as a function of time. The mineral loss in dentine was assessed in an artificial gap of 200 microns width at the composite/dentine interface; the samples were demineralised in a carboxymethylcellulose gel (pH = 5, 37 degrees C) for 8 weeks. Once a week the mineral content of the samples was determined using non-destructive wavelength-independent microradiography (WIM). After 8 weeks transversal microradiography (TMR) was done on the samples to investigate the mineral distribution of the dentine lesions. The WIM results show that the fluoride-releasing composite decreased the dentine demineralisation statistically significantly with respect of the non-F control by approximately 45%. The mineral loss values are found to be strictly proportional to time; the demineralisation reduction is expected to continue over extended periods of clinical relevance. The TMR results show that the fluoridating composite reduced the mineral loss values significantly with respect to the non-F control by approximately 55%, but had a negligible effect on the lesion depth values. This study indicates that WIM is an accurate and reliable technique to measure in vitro secondary dentine caries next to a composite restoration as a function of time.

Tests of the efficacy of therapeutic agents for caries repair or prevention in vitro or in situ should be performed as realistically as possible. This implies the non-destructive assessment of mineral changes in whole teeth. In this study, Wavelength-independent Microradiography (WIM), a non-destructive form of microradiography that uses polychromatic x-rays, was tested for its use in following mineral changes during demineralization of whole teeth. Since the method was, in a previous paper, only tested on flat samples of about 0.3 mm in thickness, the present study aimed to adapt and test WIM for use on thicker samples. This was done in three steps: In the first step, natural surfaces were introduced. The mineral content of enamel and dentin samples about 0.3 mm in thickness and with natural (curved) surfaces was determined by WIM, and the result was compared with mineral measurements performed with Longitudinal Microradiography (LMR). A correlation of 0.98 was found for both the enamel and the dentin samples. In the second step, the thickness of whole teeth was added. Thick tooth sections were simulated by addition of a 5-mm block of dentin to such thin enamel and dentin samples. Mineral measurements with WIM of the samples plus the dentin block were compared with mineral measurements of the thin samples (without block). A correlation of 0.97 was found for enamel, and one of 0.90 was found for dentin. Finally, in a third step, the demineralization of whole premolars was followed as a function of time.

Wavelength-independent Microradiography (WIM), described in this paper, used polychromatic, high-energy (less than or equal to 60 kV) x-rays for determination of mineral concentrations in tooth material non-destructively. This was done with the aid of a reference step-wedge made of 94% aluminum, 6% zinc. The mass attenuation coefficient of this material has a wavelength-independent ratio to the mass attenuation coefficients of enamel and dentin. With this method, mineral concentrations of enamel and dentin samples, with a thickness up to 500 microns, were determined at 20- and at 60-kV tube voltage. The samples were demineralized for 72 and 144 h and measured again. Comparison of the data showed that mineral quantification was within 1.5%, independent of the x-rays used. Finally, these mineral concentrations--obtained from the Wavelength-independent Microradiography--were compared with measurements of the same samples by Longitudinal Microradiography. A correlation of 0.99 was found for enamel and one of 0.96 for dentin.

The preparation of ground sections for the quantitative microradiographic study of dentine was carried out either by hand or by machine using a new technique of fixing the sections to the holder by a soluble adhesive. After setting up a method of control for the plano-parallelism of the sections, the times of preparation and the quality of the sections obtained with both methods were compared: engine grinding gave the best results in terms of both quantity and quality.

One method of quantitating mineral content in thin sections of dental hard tissue is microdensitometry of contact radiographs. This method is often applied to analysis of artificial caries lesions. Because there is great inter- and intra-tooth variability, a single microdensitometric scan will not accurately reflect the content or distribution of mineral within an individual lesion, or within a group of lesions. To increase the number of replicates than can be handled routinely, a computer-driven microdensitometer has been used with a step series of aluminum and enamel to quantitate mineral content values at approximately 1-micron intervals. Accurate assessment of an individual lesion was made possible by averaging multiple scans of the lesion on each of several thin sections prepared from the lesion. Mean mineral profiles of treatment groups were then made from the profiles of the individual lesion. These data reduction techniques allowed for a large number of replicates to be used in the measurement of remineralization. The computerized microdensitometric system described here was developed to allow for an objective, quantitative analysis of the mineral content of dental hard tissue.