Enamel Sections Research Articles

Effect of a test dentifrice containing nano-sized calcium carbonate on remineralization of enamel lesions in vitro

The efficacy of a test dentifrice containing nano-sized (several tens to hundreds of nm) calcium carbonate (hereafter NC) on enamel lesion remineralization was studied in an in vitro system that employed collagen-coated wells for cell culture, as a model of oral surfaces for NC retention. The well surfaces were treated with the test dentifrice and briefly rinsed with distilled water. Thin sections of enamel with artificial subsurface demineralization were remineralized in the plate wells containing remineralizing solution. The dentifrice treatment was repeated twice a day (in the morning and evening) for 20 days. After remineralization, microradiographic analysis was performed to evaluate the rate of lesion remineralization on the sections. The test dentifrice showed a statistically significant mineral gain (48.8% decrease in DeltaZ % x microm from the baseline value), indicating lesion remineralization, whereas the placebo dentifrice without NC did not. An elevated Ca concentration in the remineralizing solution was also observed after a single treatment with the test dentifrice. We conclude that the test dentifrice has potential to remineralize incipient enamel lesions due to the unique properties of NC, which is retained on oral surfaces, thereafter releasing Ca ions into oral fluids (saliva, plaque).

High resolution analysis of uranium and thorium concentration as well as U-series isotope distributions in a Neanderthal tooth from Payre (Ardèche, France) using laser ablation ICP-MS

We have mapped U ( 238U) and Th ( 232Th) elemental concentrations as well as U-series isotope distributions in a Neanderthal tooth from the Middle Palaeolithic site of Payre using laser ablation ICP-MS. The U-concentrations in an enamel section varied between 1 and 1500 ppb. The U-concentration maps show that U-migration through the external enamel surface is minute, the bulk of the uranium having migrated internally via the dentine into the enamel. The uranium migration and uptake is critically dependent on the mineralogical structure of the enamel. Increased U-concentrations are observed along lineaments, some of which are associated with cracks, and others may be related to intra-prismatic zones or structural weaknesses reaching from the dentine into the enamel. The uranium concentrations in the dentine vary between about 25,000 and 45,000 ppb. Our systematic mapping of U-concentration and U-series isotopes provides insight into the time domain of U-accumulation. Most of the uranium was accumulated in an early stage of burial, with some much later overprints. None of the uranium concentration and U-series profiles across the root of the tooth complied with a single stage diffusion–adsorption (D–A) model that is used for quality control in U-series dating of bones and teeth. Nevertheless, in the domains that yielded the oldest apparent U-series age estimates, U-leaching could be excluded. This means that the oldest apparent U-series ages of around 200 ka represent a minimum age for this Neanderthal specimen. This is in good agreement with independent age assessments (200–230 ka) for the archaeological layer, in which it was found. The Th elemental concentrations in the dental tissues were generally low (between about 1 and 20 ppb), and show little relationship with the nature of the tissue.

Unlocking evidence of early diet from tooth enamel

Recent developments in microspatial analysis of enamel chemistry provide the resolution needed to reconstruct detailed chronological records of an individual's early life history. Evidence of nutritional history, residential mobility, and exposure to heavy metals can potentially be retrieved from archaeological and even fossil teeth. Understanding the pattern and timing of incorporation of each trace element or stable isotope into enamel is crucial to the interpretation of the primary data. Here, we use laser ablation inductively coupled plasma mass spectrometry and ArcGIS software to map variation in calcium-normalized strontium intensities across thin sections of enamel from exfoliated deciduous teeth. Differences in calcium-normalized strontium intensities across each tooth reflect variation in tooth mineralization, implying that sampling location must be taken into account in interpreting results. Chronologically consistent shifts in calcium-normalized strontium intensities in teeth from children with known nursing histories reflect the onset and duration of breastfeeding and the introduction of nonmaternal sources of food. This tool is likely to be valuable for studying weaning and nursing behavior in the past. The distribution of normalized strontium intensities presented here is consistent with a model for the differential incorporation of strontium and calcium into enamel during the secretory and maturational phases of formation.

Tracking Dietary Transitions in Weanling Baboons (Papio hamadryas anubis) Using Strontium/Calcium Ratios in Enamel

Strontium and calcium are incorporated into developing teeth in a manner that reflects changing physiological concentrations in the body. A new model predicts changes in strontium/calcium (Sr/Ca) ratios in response to dietary transitions experienced at birth and during the weaning period. Microsampling of longitudinal thin sections of tooth enamel using laser ablation inductively coupled plasma mass spectrometry provides a basis for the systematic evaluation of variation in Sr/Ca ratios within the tooth crown. Incremental growth markers in enamel are used to determine the age of onset of enamel mineralization at each sampling point. Thin sections of 5 teeth from 2 wild-caught baboons (Papio hamadryas anubis) were systematically analysed using this technique. Intra- and intertooth analyses of Sr/Ca ratios reveal a pattern of dietary development during the period of enamel formation that is consistent with observational data on the timing of weaning behaviour in anubis baboons.

The effect of a 10% carbamide peroxide bleaching agent on the phosphate concentration of tooth enamel assessed by Raman spectroscopy

The study assessed changes in phosphate concentrations of surface enamel treated with a proprietary bleaching agent ('PEROXIDE') containing 10% carbamide peroxide over a 28-day period using Raman spectroscopy. Six non-carious human molar teeth (age range 12-21 years), extracted for orthodontic reasons, were used. From the enamel face of each half tooth, a near flat enamel section, approximately 2 x 2 mm, was cut, providing 12 specimens. Each specimen was treated with 10% carbamide peroxide for 8 h day(-1) for 28 consecutive days, with Raman spectra being obtained prior to bleaching and after 7, 14, 21 and 28 days. Raman spectra were acquired on a confocal LabRam 300 spectrometer fitted with an Olympus B microscope (Olympus, Middlesex, UK). The difference in the maximum peak values for phosphate group concentrations were tested using the Friedman test (non-parametric anova) and Dunn's multiple comparison test. An intense broad band at 980 cm(-1), characteristic of phosphate groupings, was always observed. At 7 and 14 days, and again at 28 days, there was a significant decrease in the phosphate group concentration compared with base-line measurements (P < 0.05) but not at 21 days (P > 0.05). Ideally, bleaching should not be continued to a point where surface enamel is lost, and the present study suggests that a regime using 10% carbamide peroxide should not extend to 7 days.

Enamel diffusion modulated by Er:YAG laser: (Part 2). Organic matrix

Organic matrix (OM) has been hypothesized as a key player in the laser-induced retardation of enamel diffusion (LRED). Therefore, this study was aimed to quantify the contribution of OM in LRED. Four groups of enamel sections (n=10) were assigned to 'normal', 'laser treated', 'OM extracted' and 'laser+OM extraction' groups for measurement of diffusion coefficient (DC) using fluorescence recovery after photobleaching (FRAP) and fluorophores transport study (FTS). Er:YAG laser treatment and OM extraction were performed on respective groups. Sections were characterized with stereomicroscopy and polarized light microscopy. Treatment effects were statistically assessed with a factorial ANOVA. DC measured by FRAP and FTS coupled with confocal microscopy revealed the significant effect of OM (p=0.001) and laser treatment (p<0.01). After OM extraction, the laser effect on diffusion decreased about 34-75%, confirming the significant role of OM in LRED. Both FRAP and FTS may be promising tools to quantify enamel DC.

Enamel diffusion modulated by Er:YAG laser: (Part 1)—FRAP

Several studies have demonstrated the caries protective effect of lasers by strengthening enamel crystalline structure. However, the effect of laser on enamel diffusion (ED) remains unclear. Objectives This study aimed to quantify the laser-induced alteration of diffusion coefficients (DC) in enamel using fluorescence recovery after photobleaching (FRAP). Methods Eleven caries-free enamel sections were characterized morphologically using stereomicroscopy, polarized light microscopy and scanning electron microscopy, before and after laser treatment with Er:YAG laser 50 mJ × 5 s × 5 Hz. With 20 μM fluorescein, DCs were measured ( n = 11) by FRAP coupled with confocal microscopy. Results The DCs measured were 2.89 ± 0.61 × 10 −7 cm 2/s and 4.076 ± 0.73 × 10 −7 cm 2/s, at the lased and unlased areas, respectively ( p = 0.001). Conclusions This study has confirmed the reduction of ED as a potential mechanism involved in laser-induced caries prevention. FRAP was demonstrated to be a promising technique for evaluating diffusion-related phenomenon in enamel.

The anti-caries efficacy of a silica-based fluoride toothpaste containing zinc citrate, triclosan, vitamin E and sunflower oil

Aim: To evaluate the ability of a new fluoridated toothpaste, containing 1450 ppm fluoride (as sodium fluoride), vitamin E and sunflower oil, to reduce the acid-dissolution of sound dental enamel (demineralisation study), promote remineralisation of demineralised enamel (remineralisation study) and deliver and incorporate fluoride into demineralised enamel (fluoride uptake), when compared to a clinically-tested fluoride toothpaste and a non-fluoride negative control toothpaste. Methods: The de- and remineralisation studies both utilised pH cycling protocols. In the demineralisation study, sound enamel sections were used and efficacy was measured by calcium analysis of experimental solutions. For the remineralisation study, artificial carious lesions were microradiographed before and after pH-cycling. For fluoride-uptake, lesions were immersed in slurries of the toothpastes and subsequently, an acid-etching technique was used to sample the lesions. Results: Expressed as mean values (SD), for the new fluoride toothpaste, the positive and negative controls respectively were: demin study, calcium demineralisation rate = 0.0980 (0.010), 0.110 (0.009) and 0.493 (0.043) μg Ca.mm-2.h-1; remin study, Δ;Z = 20.7 (16.6), 24.6 (14.9) and −34.7 (13.1) %; F-uptake = 27.8 (1.56), 29.6 (2.00) and 1.06 (0.430) μg F.cm-2. Compared with the negative control, both the positive control and the test toothpaste significantly reduced enamel demineralisation and increased both remineralisation and fluoride uptake to enamel. There were no significant differences between the new fluoride toothpaste and positive control. Conclusion: Fluoride delivered from the new silica-based toothpaste containing vitamin E and sunflower oil was as effective as that delivered from a clinically proven toothpaste.

Effect of Bleaching on Dental Hard Tissues: A Raman and IR Spectroscopic Study

The effect of two bleaching materials on dental enamel was studied by vibrational spectroscopy. Human molar enamel sections parallel to the dentin-enamel junction were one-side polished and treated with bleaching agents containing 38% hydrogen peroxide (Opalescence Xtra Boost) or 20% carbamide peroxide (Opalescence PF 20%). Then the crystalline structure and molecular inclusions of the bleached samples were analyzed by Raman scattering and attenuated total reflectance infrared spectroscopy. No spectral difference was observed between the unbleached enamel and that bleached with the two different agents, which indicates no significant occurrence of structural or chemical changes in enamel apatite due to bleaching.

The Effect of Bleaching on the Elastic Modulus of Bovine Enamel

The purpose of this study was to determine the elastic modulus of enamel during bleaching procedure with the use of an ultrasonic device. Enamel sections were obtained from freshly extracted bovine incisors. Specimens were exposed to 10% carbamide peroxide for two hours, followed by an application of a fluoride-containing toothpaste for five minutes and stored in artificial saliva (pH 7.0). An ultrasonic device was used to measure the sound velocities of longitudinal and shear waves as well as elastic modulus. The mean elastic modulus of bleached enamel decreased with time, from 15.5 GPa to 10.1 GPa. Conversely, the elastic modulus of bleached enamel followed by application of a fluoride-containing toothpaste increased with time, from 15.2 GPa to 20.2 GPa. Results of this study indicated that a decrease in elastic modulus associated with bleaching occurred, and that fluoride-containing toothpaste reversed this effect.

2D mapping of texture and lattice parameters of dental enamel

We have used synchrotron X-ray diffraction to study the texture and the change in lattice parameter as a function of position in a cross section of human dental enamel. Our study is the first to map changes in preferred orientation and lattice parameter as a function of position within enamel across a whole tooth section with such high resolution. Synchrotron X-ray diffraction with a micro-focused beam spot was used to collect two-dimensional (2D) diffraction images at 150 μm spatial resolution over the entire tooth crown. Contour maps of the texture and lattice parameter distribution of the hydroxyapatite phase were produced from Rietveld refinement of diffraction patterns generated by azimuthally sectioning and integrating the 2D images. The 002 Debye ring showed the largest variation in intensity. This variation is indicative of preferred orientation. Areas of high crystallite alignment on the tooth cusps match the expected biting surfaces. Additionally we found a large variation in lattice parameter when travelling from the enamel surface to the enamel-dentine junction. We believe this to be due to a change in the chemical composition within the tooth. The results provide a new insight on the texture and lattice parameter profiles within enamel.

The Effects of Three Different Pastes on Enamel Caries Formation and Lesion Depth Progression-An In Vitro Study

ABSTRACT Prevention of initiation and interruption in progression of early lesions are the desirable modes of caries management. Fluoride dentifrices and casein phosphopeptides are known to inhibit demineralization and enhance remineralization. The present study was conducted with the objective to investigate the effects of fluoridated dentifrice, non-fluoridated dentifrice and casein phosphopeptide amorphous calcium phosphate paste on enamel caries formation and lesion depth progression.228 tooth sections derived from extracted human permanent molars.were used The study was carried out in 3 phases where in each phase the enamel sections were treated for 14 days twice a day for 3 minutes with respective agents, followed by acid demineralization using 0.05 M acetic acid resulting in lesions. The depths of the lesions were measured using stereomicroscope. The mean lesion depths of three test groups were compared with each other as well as with control group at the end of each phase. Comparison of mean lesion depths of different groups was carried out using analysis of variance (ANOVA) and student's unpaired-t-test. The fluoridated dentifrice group had significantly lesser mean lesion depth than control group in all the three phases (P&lt;0.05). In second phase, non-fluoridated dentifrice and CPP-ACP paste groups had significantly lesser mean lesion depths than control groups (P&lt;0.05). The study demonstrated that twice a day application of fluoridated dentifrice provides substantial protective effect against lesion formation and lesion depth progression. The study could not demonstrate any additional ability of CPP-ACP paste in reducing lesions depth progression and effect was similar to non-fluoridated dentifrice group.

Effect of Fluoride in Phosphate Buffer Solution on Bonding to Artificially Carious Enamel

The purpose of the present study was to evaluate the effect of fluoride on resin bonding to artificially carious enamel. Specimens from demineralized human enamel sections were prepared using two commercially available adhesives (Clearfil SE Bond, Kuraray; Single Bond, 3M) and a composite resin (Clearfil AP-X, Kuraray) according to manufacturers' instructions. They were then immersed in phosphate buffered saline solution with varied fluoride concentrations at 0, 0.1, 0.5, 1, and 10 ppm. After immersion in each solution for one, three, or seven days, microshear bond strength was measured. The bond strengths of both adhesive systems to artificially carious enamel significantly increased after immersion in fluoride-phosphate buffer solution. Based on the findings obtained, we thus proposed not to remove the white enamel lesions for bonding in the clinic. They might be preserved and treated using fluoride applications.

Effect of fluoride on artificial caries lesion progression and repair in human enamel: Regulation of mineral deposition and dissolution under in vivo-like conditions

Objective This study was carried out to determine in vitro the effect of fluoride on (1) the demineralization of sound human enamel and (2) the progression of artificial caries-like lesions , under relevant oral conditions. Methods Thin sections of sound human enamel were exposed to solutions undersaturated with respect to tooth enamel to a degree similar to that found in dental plaque fluid following sucrose exposure in vivo, containing fluoride concentrations (0–0.38 ppm) found in plaque fluid. Mineral changes were monitored for 98 days, using quantitative microradiography. The effect of fluoride (1.0–25.0 ppm) on the progression of artificial caries-like lesions was similarly studied. Results Fluoride concentrations of 0.19 ppm and greater were found to prevent the demineralization of sound enamel in vitro. However, significantly higher concentrations of fluoride (25.0 ppm) were required to prevent further demineralization of artificial caries-like lesions. Demineralizing solutions with intermediate fluoride concentrations (2.1–10.1 ppm) induced simultaneously remineralization in the outer portion of the lesion and demineralization in the inner portion. Simultaneous remineralization and demineralization were also observed in hydroxyapatite pellets. Conclusions Our results show that the observed effect of fluoride on enamel demineralization is not solely a function of bulk solution properties, but also depends on the caries-status of the enamel surface. A mechanistic model presented indicates that, in comparison to sound enamel surfaces, higher concentrations of fluoride are required to prevent the progression of artificial caries-like lesions under in vivo-like conditions since the diffusion of mineral ions that promote remineralization is rate-limiting.

Developmental movements of the inner enamel epithelium as derived from micromorphological features

It was the purpose of this article to analyze the (micro) morphological structure of enamel at different stages of development in order to deduce movement patterns of ameloblasts during formation of the human dental primordium. Developing enamel and overlying ameloblasts were dried and fractured for scanning electron microscopy (SEM) and sectioned for transmission electron microscopy (TEM). Specimens of human permanent enamel were either fractured and/or ground and etched to visualize the enamel rods. All specimens were viewed by SEM. Moreover, three-dimensional reconstructions were made from serial ground sections of enamel blocks to follow the enamel rods for a longer distance. In addition, the outline of the dentino-enamel junction was analyzed under the SEM after removal (using nitric acid) of the enamel cap, and in serial histological sections. Two basic movements of the inner enamel epithelium can be derived from the micromorphological features: (i) the scalloped dentino-enamel junction may be a consequence of a bulged inner enamel epithelium owing to initial spatial impediment; and (ii) the undulating path of the enamel rods may be a consequence of unequal growth of the cells in the cervical loop.

Fraunhofer diffraction of short-fiber-reinforced composites aligned by an electric field

This study aims to determine if aligned, short-fiber composites are capable of producing Fraunhofer diffraction patterns similar to those of human enamel sections and to validate the mechanism of diffraction by comparing the experimental and theoretical fiber spacings. Rectangular composite specimens were filled with short E-glass fibers (120 microm length, 15 microm diameter) to contents of 1, 5, 10, and 25% (vol%). The fibers were oriented perpendicular to the surface normal using an alternating electric field of 0.75 kV/mm. A He-Ne laser was used with thin slices of specimen placed behind a pinhole to produce diffraction patterns. The locations of the diffraction maxima were used to determine the theoretical slit spacings which were compared to the experimental slit spacings determined by microscopy. The specimens produced diffraction patterns analogous to the theoretical Fraunhofer diffraction of light through multiple slits. This was verified by comparing the theoretical spacing of the fibers calculated from the diffraction pattern with the experimental spacing of the fibers determined from the optical micrographs. This work has verified that orientation of short-fiber composites using an electric field can yield composites with sufficient order to produce Fraunhofer diffraction patterns that are qualitatively similar to the diffraction patterns of human enamel sections.

Dental enamel—a biological ceramic: regular substructures in enamel hydroxyapatite crystals revealed by atomic force microscopy

Hydroxyapatite crystals from developing rat incisor enamel and polished sections of mature human dental enamel were investigated using Atomic and Chemical Force Microscopy. Regular substructures were seen on crystals comprising ∼40 nm wide morphologically and chemically defined bands across the crystal long axes. Exposure to low pH resulted in selective dissolution between bands and the emergence of 2–3 spherical structures within each band. The spherical structures were chemically distinct exhibiting high friction in lateral force mode. Enamel crystals appear to comprise stacks of roughly hexagonal arrays of chemically or structurally distinct spherical subunits.

Near-infrared transillumination at 1310-nm for the imaging of early dental decay

New imaging technologies are needed for the early detection of dental caries (decay) in the interproximal contact sites between teeth. Previous measurements have demonstrated that dental enamel is highly transparent in the near-IR at 1300-nm. In this study, a near-IR imaging system operating at 1300-nm was used to acquire images through tooth sections of varying thickness and whole teeth in order to demonstrate the utility of a near-IR dental transillumination system for the imaging of early dental caries (decay). Simulated lesions, which model the optical scattering of natural dental caries, were placed in plano-parallel dental enamel sections. The contrast ratio between the simulated lesions and surrounding sound enamel was calculated from analysis of acquired projection images. The results show significant contrast between the lesion and the enamel (>0.35) and a spatial line profile that clearly resolves the lesion in samples as thick as 6.75-mm. This study clearly demonstrates that a near-IR transillumination system has considerable potential for the imaging of early dental decay.

Characterization of lipid in mature enamel using confocal laser scanning microscopy

Objective. To characterize the lipid components of organic matrix in mature human enamel using Confocal Laser Scanning Microscopy (CLSM) coupled with a hydrophobic fluorescent probe. Methods. Twenty-four longitudinal sections of human enamel were fixed with 3.7% paraformaldehyde (PFA), partially decalcified with 0.5 M of EDTA, and labelled with a fluorescent probe (Nile red) before CLSM characterization. Based on the fluorescence spectra of Nile red in ethanol (1 μg/ml), each enamel section was evaluated with 543 nm light source and with 590 nm long pass filter. Spectrophotometric analysis was carried out to characterize the autofluorescence and Nile red lipid fluorescence in mature enamel. Special optical parameters of the microscope were chosen to rule out the intrinsic fluorescence of the samples, and that induced by PFA. Results. The intensity of autofluorescence and PFA−induced fluorescence were negligible above 565 nm; whereas the fluorescence of Nile red peaked at around 600 nm. Lipid material was identified in the cross-striations, the lines of Retzius, the Hunter–Schreger bands, inter-prismatic spaces, and intraprismatic spaces in the mature human enamel. Conclusions. This technique successfully revealed the distribution of lipid components of organic matrix in mature human enamel and may be promising in assessing the changes of enamel organic elements in the developmental, pathological or experimental conditions.

Isotopic alteration of mammalian tooth enamel

AbstractMammalian tooth enamel carbonates from a Pliocene site at Allia Bay in northern Kenya show variable carbon and oxygen isotopic alteration. Sample screening by cathodoluminescence, prior to isotopic analysis, identified areas of extensive chemical alteration and others that were minimally altered. The luminescent patterns were used to guide sampling for the isotope study. Carbon stable isotope ratios of the apatite carbonate from luminescent enamel exteriors differ from the ratios in the enamel interiors and the magnitude of difference varies widely. The interior of the enamel usually retains the carbon isotope ratios expected based on faunal identification, but in a minority of cases, all of the enamel appears to be altered isotopically. Among fauna with an apparent mixed feeding signal, it is particularly difficult to determine whether the δ13C value is due to an actual mixed feeding strategy during life or to alteration toward sediment values. Palaeoecological reconstructions based on the δ13C values of enamel carbonate in browsing fauna would be affected, in many cases, since differences of 1‰ are significant for such reconstructions. Even so, careful selection of unaltered enamel sections should avoid this problem. Palaeodiet reconstruction would be less affected except in those cases where the alteration approaches 5‰. In such cases, a mixed feeding strategy would be the erroneous interpretation of the data. Oxygen isotope ratios in the enamel carbonates show no pattern and the retention of biogenic values is unlikely. For this reason, palaeotemperature reconstructions, based on the δ18O values of the enamel carbonate, would not be possible at this site. Copyright © 2003 John Wiley &amp; Sons, Ltd.