Preparation of fluoride substituted apatite cements as the building blocks for tooth enamel restoration

Fluoride substituted apatite cement (fs-AC) was synthesized by using the cement powders of tetracalcium phosphate (TTCP) and sodium fluoride (NaF), and the cement powders were mixed with diluted phosphoric acid (H₃PO₄) as cement liquid to form fs-AC paste. The fs-AC paste could be directly filled into the carious cavities to repair damaged dental enamel. The results indicated that the fs-AC paste was changed into fluorapatite crystals with the atom molar ratio for calcium to phosphorus of 1.66 and the F ion amount of 3 wt% after self-hardening for 2 days. The solubility of fs-AC in Tris-HCl solution (pH 6) was slightly lower than hydroxyapatite cement (HAC) that was similar to the apatite in enamel, indicating the fs-AC was much insensitive to the weakly acidic solution than the apatite in enamel. The fs-AC was tightly combined with the enamel surface because of the chemical reaction between the fs-AC and the apatite in enamel after the caries cavities was filled with fs-AC. The extracts of fs-AC caused no cytotoxicity on L929 cells, which satisfied the relevant criterion on dental biomaterials, revealing good cytocompatibility. The fs-AC had potential prospect for the reconstitution of carious lesion of dental enamel.     

Determination of optical properties of oxidative bleaching human dental tissue samples using optical coherence tomography

Oxidative bleaching changes of human teeth induced changes in the optical properties of dental tissue. We introduced 1310 nm wavelengths of optical coherence tomography (OCT) attenuation coefficient method which is a relatively novel and rarely reported methodology to measure the correlation coefficient during the teeth oxidative bleaching procedure. And the quantitative parameters of enamel optical thickness and disruption of the entrance signal (DES) were extracted from the OCT images. The attenuation coefficient of the bleached tissue is 6.2 mm⁻¹ which is significant (p < 0.001) higher than that unbleached sample is 1.4 mm⁻¹. But attenuation coefficient varied significantly (p < 0.001) between 5.9 and 1.5 mm⁻¹ in dentine which is downtrend. Furthermore, the persistence of bleaching oxidation in 35% hydrogen peroxide-induced optical thickness of enamel is similar with unbleached tissue which may indicate the refractive index of enamel is unchanged. Moreover, disruption of the entrance signal (DES) analysis showed that remarkable difference was appeared at enamel surface. The results indicate that optical properties of oxidative bleaching human dental tissue can be determined by attenuation coefficient using OCT system.     

Alterations in enamel remineralization in vitro induced by blue light

Blue light, especially from LED devices, is a very frequently used tool in dental procedures. However, the investigations of its effects on dental enamel are focused primarily on enamel demineralization and fluoride retention. Despite the fact that this spectral region can inhibit enamel demineralization, the effects of the irradiation on demineralized enamel are not known. For this reason, we evaluated the effects of blue LED on remineralization of dental enamel. Artificial lesions were formed in bovine dental enamel blocks by immersing the samples in undersaturated acetate buffer. The lesions were irradiated with blue LED (455 nm, 1.38 W/cm², 13.75 J/cm², and 10 s) and remineralization was induced by pH-cycling process. Cross-sectional hardness was used to asses mineral changes after remineralization. Non-irradiated enamel lesions presented higher mineral content than irradiated ones. Furthermore, the mineral content of irradiated group was not significantly different from the lesion samples that were not submitted to the remineralization process. Results obtained in the present study show that the blue light is not innocuous for the dental enamel and inhibition of its remineralization can occur.     

Design of highly nonlinear dispersion flattened hexagonal photonic crystal fibers for dental optical coherence tomography applications

In this paper, we propose a highly nonlinear dispersion flattened hexagonal photonic crystal fiber (HNDF-HPCF) with nonlinear coefficients as large as 57.5W⁻¹ km⁻¹ at 1.31 μm wavelength for dental optical coherence tomography (OCT) applications. This HNDF-HPCF offers not only large nonlinear coefficient but also very flat dispersion slope and very low confinement losses. Using these characteristics of our proposed PCF, it is shown through simulations by using finite difference method with an anisotropic perfectly matched boundary layer that this PCF offers the efficient supercontinuum (SC) generation for dental OCT applications at 1.31 μm wavelength using a picosecond pulse easily produced by commercially available less expensive laser sources. Coherent length of light source using SC is found 10 μm and the spatial resolutions in the depth direction for dental applications of OCT are found about 6.1 μm for enamel and 6.5 μm for dentin.     

Low-fluence CO2 laser irradiation decreases enamel solubility

This study investigated whether subablative-pulsed CO₂ laser (10.6 μm) irradiation, using fluences lower than 1 J/cm², was capable of reducing enamel acid solubility. Fifty-one samples of bovine dental enamel were divided into three groups: control group, which was not irradiated (CG); group laser A (LA) irradiated with 0.3 J/cm²; and group laser B (LB) irradiated with 0.7 J/cm². After irradiation, the samples were subjected to demineralization in an acetate buffer solution and were then analyzed by SEM. A finite-element model was used to calculate the temperature increase. The calcium and phosphorous content in the demineralization solution were measured with an ICP-OES. ANOVA and the t-test pairwise comparison (p < 0.016) revealed that LB showed significantly lower mean Ca and P content values in the demineralization solution than other groups. A reduction in the enamel solubility can be obtained with pulsed CO₂ laser irradiation (0.7 J/cm², 135 mJ/pulse, 74 Hz, 100 μs) without any surface photomodification and a less than 2°C temperature increase at a 3-mm depth from the surface.     

Raman and IR reflection micro‐spectroscopic study of Er:YAG laser treated permanent and deciduous human teeth

Permanent and deciduous human teeth treated by a dental Er‐doped yttrium‐aluminium‐garnet pulse laser (λ = 2940 nm) as well as by classical drilling tools under conditions typical of the clinical practice were studied by ultraviolet Raman and Fourier transform infrared (FTIR) reflection microspectroscopy. Enamel was analyzed by both spectroscopic methods, whereas dentine was studied only by FTIR reflection because of the high level of photoluminescence continuum background even when a wavelength of 325 nm was used in inelastic light scattering experiments. The applied energy and pulse frequency of the dental laser varied between 200 and 500 mJ and between 10 and 30 Hz, respectively. The most important result is that after the laser treatment, the hydroxyapatite structure in both permanent and deciduous enamel is preserved: the apatite Ca‐P‐O framework remains intact, and the content of channel OH^‐ groups is not changed within experimental uncertainties. The calcium‐phosphate framework of dentine also exhibits negligible laser‐induced changes. The only alterations in enamel induced by laser as well as by mechanical drilling are reduction of the amount of CO₃^2‐ in apatite and changes in the protein conformation. The laser impact on the organic material and carbonate groups is strongest for laser power of 8 W; for powers of 4 or 5 W, the combination of higher pulse energy and lower pulse frequency has less impact than the combination of lower energy and higher frequency. No differences between deciduous and permanent teeth in their resistivity to laser irradiation with λ = 2940 nm were detected. Copyright © 2013 John Wiley & Sons, Ltd.     

Experimental investigation of variability of ultraviolet fluxes at the earth's surface

Some results of two years of regular measurements of UV radiation at the earth's surface in Siberia (56.5^o N, 85^o E) are given. It is shown that the presence of snow cover increases the UV irradiation of the earth by scattered radiation by 9–15%. In cloudless but windy weather, quasi-periodic fluctuations of UV irradiation with periods of 5–15 min and with fluctuation swings of 1–10% are observed. Low-level, heavy cloudiness in summer considerably reduces (by an average of 30–35%) UV irradiation, especially when the sun is low (down to 30^o). Mid-and upper-level clouds increase the UV irradiation of the earth by scattered radiation. When the sun is high (30–50^o) and there is heavy cloudiness, this increase can reach 28% in the UV-A spectral range. Tomsk State University. Academician V. D. Kuznetsov Siberian Physics and Technology Institute, Tomsk State University. Institute of Optical Monitoring, Siberian Branch of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 71–74, September, 1998.     

Lasers effects on enamel for caries prevention

The aim of this study was to ascertain whether laser irradiation is able to reduce caries incidence. For this purpose, the effects of laser on enamel and on fluoride uptake were discussed. Current literature regarding the preventive effect of laser irradiation on dental hard tissue has been reviewed. An evaluation of the results of the available in vitro and in vivo studies on the efficacy of anticaries and induced changes on enamel by laser irradiation were also performed. Articles were selected using the Medline, Web of Science, Embase, and Cochrane databases, and the results of these studies were described. The most common lasers employed for caries prevention on enamel are Nd:YAG; CO₂; Er:YAG; Er,Cr:YSGG; and argon. The percentage of inhibition of dental caries varied from 30 to 97.2%, and the association with fluoride has demonstrated the best results on inhibition of caries development. Laser irradiation under specific conditions can change the crystallographic properties of apatite crystals, increasing the acid resistance of lased enamel. The combined treatment of laser irradiation with fluoride propitiates an expressive fluoride uptake, reducing the progression of carieslike lesions, and this treatment is more effective than laser or fluoride alone. Available data suggest that lasers combined with fluoride is a promising treatment in caries prevention.     

NO 3 2− and CO 2 − centers in synthetic hydroxyapatite: Features of the formation under γ- and UV-irradiations

The EPR studies of synthetic hydroxyapatite containing carbonate and nitrate ions exposed to γ-ray and UV irradiations have been performed. It has been found that γ irradiation leads to the formation of both NO₃²⁻ and CO₂⁻ paramagnetic centers, while the UV irradiation induces only NO₃²⁻ centers. To explain this fact, the hypothesis has been proposed, according to which in the hydroxyapatites studied, there coexist complexes consisting of nitrate ions and shallow electron traps that serve as sources of secondary electrons during UV irradiation. The EPR spectroscopy parameters (g and A) of the detected centers have been determined and compared with similar centers in hydroxyapatite with a different impurity composition. The study of the thermal stability of the centers has demonstrated that, in the temperature range 20–300°C, the NO₃²⁻ centers formed by UV irradiation are more stable than the same centers created by γ-ray irradiation.     

Enhanced photosensitivity in sol–gel derived 20GeO2:80SiO2 thin films

We investigate the photosensitivity of binary 20GeO₂:80SiO₂ (germanosilicate) inorganic films. The samples have been fabricated by the sol–gel spin-coating method and the densification has been performed by rapid thermal annealing at various temperatures ranging from 500 °C to 1000 °C. The –OH absorption bands in the Fourier-transform infrared (FTIR) spectra and the refractive-index data show that the films annealed below 900 °C are porous and the films annealed at 900 °C and above are dense. An ultraviolet (UV) KrF laser at 248 nm has been used to induce the change in the refractive index of the samples. We have achieved a large refractive-index change (Δn) of 0.0098 after UV illumination in excess of 1 min for our dense germanosilicate films. This UV-induced refractive-index change is attributed to the formation of GeE’/SiE’ centers from Ge–Ge/Si–Si (neutral oxygen monovacancy) and Ge²⁺ centers and to the creation of oxygen deficiency related defects. From our experiments, the oxygen deficiency related defects correspond to the absorption band at 620–740 cm^-1 in the FTIR spectra and these are the defects which make a large contribution to Δn. The attenuation coefficient of the as-deposited and UV-illuminated dense samples is about 0.42 dB/cm at 1550 nm. For porous samples, UV exposure has densified the samples to some extent. PACS 82.50.Hp; 71.23.Cq; 81.20.Fw     

Changes in dental enamel oven heated or irradiated with Er,Cr:YSGG laser. Analysis by FTIR

This study evaluated the change that occurs in dental enamel under action of oven heating or Er,Cr:YSGG laser irradiation aiming to obtain a structure more resistant to demineralization. Enamel powder was obtained from bovine teeth. Samples were subjected to oven heating at temperatures of 200, 400, 600, 800, and 1000°C or during laser irradiation with energy densities of 7.53, 10.95, and 13.74 J/cm². The infrared thermography was used to measure the surface temperature generated in the solid samples of enamel during lasers irradiation. The samples were analyzed by Fourier transform infrared spectroscopy (FTIR), which shows changes on enamel oven heated or laser irradiated, due to treatments, related to carbonates, adsorbed water and hydroxyl content. These compositional effects were more evident in lased samples. These changes may alter the material properties such as its solubility, and decrese of demineralization that is important for caries prevention.     

Application of the Doehlert Design to Optimize the Signal Obtained in Photochemically Induced Fluorescence for the Determination of Eight Phenylureas

This work describes the optimization of a photochemically induced method for the detection of eight phenylureas has been developed by response surface methodology (RSM). These pesticides do not show native fluorescence but they were photolyzed into strongly fluorescent photoproducts under UV irradiation. The effect of the main variables affecting the yield of the photoderivatization reaction, and hence the fluorescence intensity, such as solvent, UV irradiation time and pH were optimized for each pesticide. A Doehlert design was applied in order to obtain maximum intensity fluorescence using response surface methodology. In general, a maximum was found for all pesticides using MeOH as organic solvent, except for diuron, whereas the effect of pH and irradiation time was different, according to each pesticide. Finally, the addition of β-cyclodextrin upon the photochemically induced fluorescence intensity was investigate. The fluorescence intensity was only improved for monolinuron at a concentration of 4 × 10⁻³ M of β-cyclodextrin.     

Precipitation of gold nanoparticles on the quartz surface modified by titanium (IV) butoxide

Gold nanoparticles have been precipitated on the surface of quartz slides covered with titanium (IV) butoxide. UV irradiation of modified quartz slides immersed into water solutions of hydrogen tetrachloroaurate of different concentrations (2.5 × 10⁻⁴–1.0 × 10⁻² M) has been used for this purpose. Properties of produced samples have been investigated by UV–Vis spectroscopy, IR spectroscopy, SEM-EDX, TGA, and AFM. According to the obtained data, produced gold particles are distributed on modified quartz surface very uniformly and the average size of gold particles is about 30–50 nm.     

Effects of mesoporous structure and UV irradiation on in vitro bioactivity of titania coatings

Mesoporous titania coatings (MTCs) with a pore size of 4.75 nm were prepared on Ti6Al4V substrates by a sol-gel process, and then irradiated with UV light at room temperature for 2 h. The effects of mesoporous structure and UV irradiation on the in vitro bioactivity were investigated. Simulated body fluid (SBF) tests reveal that the MTCs exhibit a high apatite-forming ability, which may be attributed to the following reasons: (i) the BET surface area of the MTCs is ∼190 m²/g, resulting in a greater density of Ti-OH groups than that without mesoporous structure; (ii) theoretical analysis reveals that the mesoporous structure can improve the driving force and nucleation rate of apatite precipitation in SBF. As compared with the MTCs, the UV-irradiated coatings do not exhibit any change in phase components and surface morphologies. However, the apatite-forming ability is higher on the UV irradiation coatings than on the MTCs because of the increase of Ti-OH groups and the improvement of wettability after UV irradiation. In addition, the investigation of the MG63 cell proliferation on the both substrates was performed. The results indicate that the MTCs before and after UV irradiation exhibit a good biocompatibility and are fit for the MG63 cell proliferation.     

A new method for characterization of thermal properties of human enamel and dentine: Influence of microstructure

For better selection of “tooth-like” dental restorative materials, it is of great importance to evaluate the thermal properties of the human tooth. A simple method capable of non-destructively characterizing the thermal properties of the individual layers (dentine and enamel) of human tooth is presented. The traditional method of monotonic heating regime was combined with infrared thermography to measure the thermal diffusivities of enamel and dentine layers without physically separating them, with 4.08 (±0.178) × 10⁷ m²/s measured for enamel and 2.01 (±0.050) × 10⁷ m²/s for dentine. Correspondingly, the thermal conductivity was calculated to be 0.81 W/mK (enamel) and 0.48 W/mK (dentine). To examine the dependence of thermal conductivity on the configuration of dentine microstructure (microtubules), the Maxwell-Eucken and Parallel models of effective thermal conductivity are employed. The effective thermal conductivity of dentine in the direction parallel to tubules was found to be about 1.1 times higher than that perpendicular to the tubules, indicating weak anisotropy. By adopting the Series model, the bulk thermal conductivity of enamel and dentine layers is estimated to be 0.57 W/mK.     

Photogreying of TiO<Subscript>2</Subscript> nanoparticles

Photogreying, the change in brightness on UV irradiation in the absence of oxygen, of TiO₂ nanoparticulate dispersions is shown to depend on the nature of the liquid, consistent with a surface reaction. Measurements on a series of TiO₂ particles (mainly 75×10 nm) dispersed in, e.g., alkyl benzoate correlate well with those on the same TiO₂’s dispersed in a second liquid (e.g. propan-2-ol). Photogreying in propan-2-ol is paralleled by photocatalytic-oxidation activity, indicating a common origin – UV-generation of charge carriers. Further, photogreying parallels Ti³⁺ formation. Hence, although appearance and the visible spectra of photogreyed particles both differ from those of Ti³⁺ in ≤10 nm colloidal TiO₂, we suggest that photogreying is caused by capture of UV excited electrons to form Ti³⁺. Surface treatment reduces photogreying, and we speculate that differences between uncoated samples reflect differences in the number of potentially reducible Ti’s.     

Self-cleaning characteristics on a thin-film surface with nanotube arrays of anodic titanium oxide

Self-cleaning of a surface of nanotube arrays of anodic titanium oxide (ATO) is demonstrated. The ATO was prepared in fluoride ion containing sulfate electrolytes with a structure of 0.4 μm length, 100 nm pores diameter, 120 nm interpore distance, 25 nm pore wall thickness, a 8×10⁹ pores cm⁻² pore density, and 68.2% porosity. Prepared as thin films either directly from a Ti foil or on a glass substrate, these arrays have the property that water drops spread quickly over the surface of the films without irradiation. In contrast, a flat anatase TiO₂ film requires irradiation with UV light for several minutes before the contact angle decreases to zero. The observed self-cleaning behavior of the ATO thin films is due to the capillary effect of the nanochannel structure and the superhydrophilic property of the anatase TiO₂ surface inside the tube.     

Signal processing for radiation dosimetry using EPR in dental enamel: comparison of three methods

We are reporting an alternative method of extracting useful dose information from complex EPR spectra of dental enamel. Digital differentiation of the initial first derivative spectrum followed by filtering is used to clearly distinguish the radiation-induced signal from the native background signal. The peak-to-peak height of the resulting second derivative of the signal is then measured as an indication of absorbed dose. This method does not require preliminary elimination of the native background signal, and is not effected by any uncertainty in the determination of the background signal or by errors resulting from the subtraction of two signals of comparable magnitude. Ten enamel samples were irradiated with known doses in the range of 250–10⁵ mGy. There was agreement for all the samples, within the typical experimental error of ±10% for EPR dosimetry in dental enamel, between the doses determined by two common techniques using native signal subtraction and the doses determined by the new second derivative method proposed here.     

Caries resistance of lased human root surface with 10.6 μm CO2 laser-thermal,morphological, and microhardness analysis

Although the cariostatic effects of CO₂ laser on enamel have been shown, its effects on root surface demineralization remains uncertain. The objectives of this in vitro research was to establish safe parameters for a pulsed 10.6 μm CO₂ laser and to evaluate its effect on morphological features of the root surface, as well as on the reduction of root demineralization. Ninety-five human root surfaces were randomly divided into five groups: G1-No treatment (control); G2—2.5 J/cm²; G3—4.0 J/cm²; G4—5.0 J/cm²; and G5—6.0 J/cm². Intrapulpal temperature was evaluated during root surface irradiation by a thermocouple and morphological changes were evaluated by SEM. After the surface treatment, the specimens were submitted to a 7-day pH-cycling model. Subsequently, the cross-sectional Knoop microhardness values were measured. For all irradiated groups, intrapulpal temperature changes were less than 1.5°C. Scanning electron microscopy images indicated that fluences as low as 4.0 J/cm² were sufficient to induce morphological changes in the root surface. Additionally, for fluences reaching or exceeding 4.0 J/cm², laser-induced inhibitory effects on root surface demineralization were observed. It was concluded that laser energy density in the range of 4.0 to 6.0 J/cm² could be applied to a dental root to reduce demineralization of this surface without compromising pulp vitality.     

Hydrogen Bond and 19F NMR Chemical Shift Akisotropy in Apatite

Abstract

The fluoroapatite minerals, Ca₅-F(PO₄)₃ usually contain some hydroxyis, instead of fluorine. From infrared spectra it was concluded, that there are weak hydrogen bonds OH … F along apatite hexagonal axis¹. In order to receive more detailed information about the character of F^?and OH^?bonds with the nearest atoms in apatites we studied the nuclear magnetic resonance (NMR) spectra of protons and fluorines in natural apatite single crystal, in which approximately 15% of fluorines is substituted by hydroxyis.