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.     

Argon laser induced changes to the carbonate content of enamel

Argon laser irradiation can be used to cure orthodontic brackets onto teeth in significantly less time than conventional curing lights. In addition, it has been shown that the argon laser seems to impart a demineralization resistance to the enamel. The purpose of this study was to use surface science techniques to ascertain if this demineralization resistance is possibly a result of a decrease in the carbonate content of enamel. Eleven mandibular third molars previously scheduled for extraction were collected and used in the present study. The teeth were sectioned in two and randomly assigned to either the argon laser (457-502 nm; 250 mW cm⁻²) or the control (no treatment) group. The sections assigned to the argon laser group were cured for 10 s and analyzed. To exaggerate any potential changes the experimental sections were then exposed to a further 110 s of argon laser irradiation. Surface analysis was performed using X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The results showed no statistically significant change in the carbonate content of enamel after argon laser irradiation (p > 0.05). Thus, it is suggested that any demineralization resistance imparted to the enamel surface by argon laser irradiation is not due to alterations in carbonate content.     

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.     

Absorption and thermal study of dental enamel when irradiated with Nd:YAG laser with the aim of caries prevention

It is widely recognized that Nd:YAG can increase enamel resistance to demineralization; however, the safe parameters and conditions that enable the application of Nd:YAG laser irradiation in vivo are still unknown. The aim of this study was to determine a dye as a photoabsorber for Nd:YAG laser and to verify in vitro a safe condition of Nd:YAG irradiation for caries prevention. Fifty-eight human teeth were selected. In a first morphological study, four dyes (waterproof India ink., iron oxide, caries indicator and coal paste) were tested before Nd:YAG laser irradiation, under two different irradiation conditions: 60 mJ/pulse and 10 Hz (84.9 J/cm²); 80 mJ/pulse and 10 Hz (113.1 J/cm²). In a second study, the enamel surface and pulp chamber temperatures were evaluated during laser irradiations. All dyes produced enamel surface melting, with the exception of the caries indicator, and coal paste was the only dye that could be completely removed. All irradiation conditions produced temperature increases of up to 615.08°C on the enamel surface. Nd:YAG laser irradiation at 60 mJ/pulse, 10 Hz and 84.9 J/cm² promoted no harmful temperature increase in the pulp chamber (ANOVA, p < 0.05). Among all dyes tested, the coal paste was an efficient photoabsorber for Nd:YAG irradiation, considered feasible for clinical practice. Nd:YAG laser at 84.9 J/cm² can be indicated as a safe parameter for use in caries prevention.     

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.     

Color changes in CR-39 nuclear track detector by gamma and laser irradiation

A study of the effect of gamma and laser irradiation on the color changes of polyallyl diglycol (CR-39) solid-state nuclear track detector was performed. CR-39 detector samples were classified into two main groups. The first group was irradiated with gamma doses at levels between 20 and 300 kGy, whereas the second group was exposed to infrared laser radiation with energy fluences at levels between 0.71 and 8.53 J/cm². The transmission of these samples in the wavelength range 300–2500 nm, as well as any color changes, was studied. Using the transmission data, both the tristimulus and the coordinate values of the Commission Internationale de l'Eclairage (CIE) LAB were calculated. Also, the color differences between the non-irradiated samples and those irradiated with different gamma or laser doses were calculated. The results indicate that the CR-39 detector acquires color changes under gamma or laser irradiation, but it has more response to color changes by gamma irradiation. In addition, structural property studies using infrared spectroscopy were performed. The results indicate that the irradiation of a CR-39 detector with gamma or laser radiations causes the cleavage of the carbonate linkage that can be attributed to the ?H abstraction from the backbone of the polymer, associated with the formation of CO₂ and ?OH with varying intensities.     

Non-Thermal Effects of Microwave Oven Heating on Ground Beef Meat Studied in the Mid-Infrared Region by Fourier Transform Infrared Spectroscopy

The effects of cooking by microwave oven on the secondary structure of lipid and protein contents in bovine ground beef were investigated in the midinfrared region by Fourier transform infrared (FTIR) spectroscopy to highlight the nonthermal effects of microwave oven heating. Samples of bovine ground beef were cooked in a conventional electric oven at the temperature of 175°C for 15 min and in a microwave oven at 800 W for 1½ min. Spectra analyses of bovine meat after cooking in the conventional oven evidenced a relevant increase in intensity of the carbonyl band at 1742 cm^?1 and of the methylene group at 2921 and 2853 cm^?1 that can be attributed to the Maillard reaction. In contrast, the increase in intensity of these bands after microwave oven heating was less than that which occurred after conventional cooking, showing that the temperature in ground beef meat samples during microwave heating was less than that induced by conventional heating. Spectral analysis in the amide I, II, and III regions showed that a significant increase in intensity occurred in the region from 1660 to 1675 cm^?1 and around 1695, 1635, 1575, and 988 cm^?1 after cooking by means of a microwave oven. These features, which can be attributed to β-turns and β-sheet structures, are characteristic of disorder processes in meat protein contents and increasing transition dipole coupling due to higher contents in aggregated β-sheet structures. This result highlighted nonthermal effects of microwave oven heating in the protein's secondary structure.     

Changes induced in structure and optical properties of PM-355 nuclear track detector due to laser irradiation

PM-355 is a class of polymeric solid-state nuclear track detectors which has a lot of applications in several radiation detection fields. Samples from sheets of PM-355 have been exposed to infrared (IR) laser fluences ranging from 1 to 12.8?J/cm². The effect of IR laser radiation on the structural properties of PM-355 has been investigated using X-ray diffraction and Fourier transform infrared spectroscopy. The results indicate that the samples exhibit chain scission under the effect of laser irradiation up to 4.2?J/cm², thus producing free radicals that led to the formation of new bonds started and continued until 12.8?J/cm². This reduces the ordering structure, giving the PM-355 polymer more resilience. In addition, the laser irradiation at the fluence range 4.2–12.8?J/cm² led to a more compact structure of PM-355, which resulted in an improvement in its isotropic nature with an increase in Vickers hardness and refractive index. Further, the color changes due to laser irradiation were computed using the transmission data in the wavelength range of 370–780?nm. It is found that the color intensity, which is the color difference between the irradiated samples and the non-irradiated one, increases with increasing the laser fluence, largely depending on the proportions of the blue color component.     

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.     

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.     

Bound Energy of Water in Hard Dental Tissues

Abstract

Enamel and dentin are composed, respectively, of 3 wt% and 10 wt% of water, which exhibits different features in the tissues: loosely and tightly bound water. The objective of this study is to clarify by infrared spectroscopy, the different features of the water in heated (100–1000°C) hard dental tissues (enamel and dentin). The water band between 3800 cm^?1 and 2500 cm^?1 was analyzed by infrared spectroscopy. The area dependence of the water band with temperature was compared with the Arrhenius equation in two regions (100–400°C and 700–1000°C). The activation energy was determined for these two regions, and similar values were observed for both tissues. For enamel we obtain ?4.1±0.2 kJ/mol at 100–400 °C and ?63±9 kJ/mol at 700–1000°C; for dentin ?4.1±0.2 kJ/mol at 100–400°C and ?60±11 kJ/mol at 700–1000°C. The water loss changes the color of the tissues, hydroxyapatite crystallographic parameters, and produce ESR signals. These changes were discussed and compared with the results observed in this work and after laser irradiation. We conclude that these two activation energies could be assigned to the adsorbed (loosely bound) and trapped (tightly bound) water.     

Electron Spin Resonance–Native Signal in Thermally Treated Dental Tissue

Although the dosimetric Electron Spin Resonance (ESR) signal of hard tissues, particularly enamel, has been extensively studied, little attention has been paid to the native signal. This signal is known to be affected by the health of the tissue, as well as by socio–economic factors. In dental applications several clinical procedures, including the use of laser irradiation, can heat the tissue locally with side effects that must be studied. The purpose of the present work is to study the ESR signals in enamel and dentin tissues after thermal treatment with temperatures in the range of 100°C–300°C. Non‐irradiated permanent bovine teeth were studied. ESR measurements were performed with a Varian E‐4 ESR spectrometer operating in the X band range. Progressively larger ESR signals were produced in dentin tissues previously heat treated at and above 100°C. No detectable signals were observed in similarly treated enamel. The signal shows partial decay at four and six months after thermal treatment. The experimental data for dentin show a correlation with the Arrhenius function with an activation energy of (41 ± 2)10³ J/mol. After six months, the ESR signal shows a higher activation energy (67 ± 3)10³ J/mol and the decay shows a activation energy of (38 ± 2)10³ J/mol. A possible assignment of the signal origin in dentin is difficult. The water lost during thermal treatment and reincorporated during the following six months correlates with the signal gain and subsequent decay. The water lost can produce point defects in the hydroxyapatite, or structural changes in the collagen structure. The results observed here are useful for understanding the thermal effects produced in dentin by infrared laser irradiation, and provides a cautionary warning that annealing conditions in ESR studies of biological tissues should be standardized.     

In vitro study of the demineralization induced in human enamel by an acidic beverage using X-ray fluorescence spectroscopy and Raman microscopy

This study was conducted with the purpose of evaluating the demineralization effect of a widely consumed acidic soft drink, Coca-Cola®, in human enamel. This way, an in vitro model for the daily intake of this beverage was developed taking into account the intraoral environment. The evaluation of the enamel specimens was undertaken considering two approaches, the direct analysis of enamel surface and the study of specimens as cross sections. The depolarization ratio of the phosphate symmetric stretching band in Raman spectra was used to evaluate the loss of mineralization of the hydroxyapatite matrix, and the changes regarding the elemental content was performed using energy-dispersive X-ray fluorescence (EDXRF). For comparison, the Rayleigh-to-Compton ratio in EDXRF spectra of enamel samples was also determined in order to establish alterations in the average atomic number of the samples before and after erosive challenge. Considering the model applied and the timeframe of study, we determined evidences of demineralization after consumption of this drink. There was a significant increase of depolarization ratio in most of the analyzed specimens as well as a decrease of the concentration of major elements concomitant with apparent increase of the concentration of trace elements. Moreover, depths of demineralization of tens of micrometers were obtained with both spectroscopic techniques, showing consistency between the obtained results.     

The effect of irradiation angle on laser ignition of cellulose sheet in microgravity

The objective of this work was to investigate the effect of external radiation angle on radiative ignition of solid materials. A laser ignition experiment was performed in microgravity to investigate events occurring in the ignition process in a quiescent atmosphere. Filter paper was used as the test material, and it was heated by infrared radiation (CO₂ laser 10.6 μm) or near-infrared radiation (diode laser, 800.1 nm). The ignition time was determined for various irradiation angles, and the gas phase density change before ignition was observed by a Mach–Zehnder interferometer for each test condition. The results showed that the ignition by CO₂ laser occurred on the laser beam line depending on the irradiation angle, while diode laser caused a similar ignition position independent of the irradiation angle. The period from gasification to ignition with CO₂ laser was almost the same for different irradiation angles, while it varied with the irradiation angle for diode laser, and the ignition time was much shorter than that with diode laser. According to these results, it is considered that solid ignition with inclined external radiation is characterized based on (1) solid surface heating and (2) gas phase heating, and the second factor, gas phase heating, causes the different dependence of solid ignition on irradiation angle with different radiation wavelengths.     

FT‐Raman investigation of human dental enamel surfaces

FT‐Raman spectra of human enamel surfaces from sound, affected (with 1 cavity) and highly affected (with at least 3 cavities) tooth samples were analyzed by principal component analysis (PCA). Major differences between the unaffected and affected tooth samples seem to arise from the structural changes along the c‐axis of hydroxyapatite, the chief crystalline component of human dental enamel. Based on Fisher index calculations, the most discriminative value was obtained for the intensity of the only Raman active ν₂PO₄³⁻ (E₁) symmetric deformation mode at 428 cm⁻¹. Moreover, these changes can be observed through the whole tooth enamel surface, establishing a predisposition to caries correlated to chemical and structural composition of tooth enamel. No spectral changes regarding the CO₃²⁻ substitution were detected by both nondestructive FT‐Raman and FTIR (Fourier transform infrared) spectroscopy of the powdered teeth samples. Copyright © 2009 John Wiley & Sons, Ltd.     

Study of the dynamics of the absorption spectra of human tooth enamel and dentine under heating and ablation by submillisecond pulse radiation of an erbium laser with a generation wavelength of 2.79 μm

We studied the absorption spectrum of intact human tooth enamel and dentine in the range of 0.26–10 μm. We present the infrared absorption spectra of destruction products of human tooth enamel and dentine by submillisecond laser pulses on a crystal of yttrium-scandium-gallium garnet, activated by chrome and erbium ions with a wavelength of 2.79 μm. We discuss the effect of water spraying on the mechanism of laser ablation and the infrared absorption spectra. We report for the first time transformations observed in the absorption spectra of human tooth enamel in the wavelength range of 2.5–3.5 μm under its heating to +700°C.     

Transient 3D/2D simulation of laser-induced ablation of silicon

A numerical software has been developed to simulate heating, enthalpy-based phase changes and ablation of silicon during pulsed or continuous-wave laser irradiation. The unsteady heat transfer equation is solved by finite differences in two or three dimensions with full resolution of the thin liquid layer. An intelligent adaptive grid refinement and a semi-analytic treatment of the surface elements have been implemented to simulate laser cuts with lots of laser pulses in moderate computing time. The code has been successfully verified by comparisons with an analytic solution and with experimental data. Details of the mathematical model, the implementation in Matlab^®and comparisons with experimental laser cuts are presented in this paper.     

Advances in luminescence instrument systems

We report on recent advances in the development of luminescence measurement systems and techniques at Risø. These include: (1) optical stimulation units based on new-generation powerful blue light (470 nm) emitting diodes providing up to 28 mW/cm² for OSL measurements; (2) an infrared (830 nm) laser diode unit providing up to 400 mW/cm² for stimulation of feldspars; and finally (3) an optical stimulation attachment based on a focused solid state green (532 nm) laser for rapid OSL measurements of individual sand-sized single grains of a sample. Facilities for heating samples during beta irradiation and performing linearly modulated OSL measurements have also been incorporated into the system.     

Study of the effects of unsupervised over‐the counter whitening products on dental enamel using μ‐Raman and μ‐EDXRF spectroscopies

The purpose of this in vitro study was to assess whether the mineralization degree and elemental content in tooth enamel are altered when bleaching the teeth with two different over‐the‐counter bleaching gels, exceeding the recommendations of the manufacturer. In order to perform this evaluation, 12 healthy teeth were used, six samples were treated with Teeth Whitening Home Kit, and the other six samples were treated with WHITE! (Bingo‐UK) bought in online shopping sites, for the period of 39 days. The pH of each product and the elemental content of each sample, before and after, were obtained by energy dispersive X‐ray spectrometry and phosphate (PO₄^3‐) profile was evaluated with Raman spectroscopy. Data was analyzed accordingly to a pre‐established plan with a mixed‐model ANOVA for repeated measures, significance was set at 5%. Both products were markedly acidic and below enamel critical level of 5.5. Moreover, seven days after treatment, demineralization was significant, wherein at the end of the study the degree of demineralization seems to be permanent. Copyright © 2015 John Wiley & Sons, Ltd.     

激光轰击过程中纳米碳管复合光限幅材料组成及结构的演变研究

光限幅材料在激光轰击过程中的稳定性将在很大程度上决定其实用化价值。文章采用红外(IR)光谱、拉曼(Raman)光谱、透射电子显微镜(TEM)及孔结构分析等测试方法对纳米碳管(CNTs)复合光限幅材料在激光轰击过程中组成、结构的演变进行跟踪研究。结果表明,在强激光轰击下,复合体系中二氧化硅(SiO₂)基质的组成未发生显著改变且网络结构趋于完整,具有较好的稳定性。掺杂CNTs石墨化程度提高,SiO₂凝胶玻璃基质对其起一定的保护作用。轰击过程产生的热效应使得SiO₂颗粒长大,由其堆积而成的孔随之增大。