A Comparative Study of the Photosensitizer Penetration into Artificial Caries Lesions in Dentin Measured by the Confocal Raman Microscopy

This study utilized the confocal Raman microspectroscopy (CRM) technique for the first time to investigate the degree of the penetration of toluidine blue‐orto (TBO) in artificial caries lesions produced by two distinct caries‐inducing models. The dentin specimens (n = 10) were divided into three groups: control, in vitro and in situ. Thereafter, the lesion depth and the demineralization level were evaluated by cross‐sectional microhardness (CSMH). CRM mapping across the dentin surface was assessed after the dye application. The CSMH and CRM data were analyzed by t‐test and ANOVA, respectively (P < 0.05). The values of the lesion depth and the demineralization areas were higher for in situ samples (P < 0.05). The TBO penetration values (μm) for the control, in vitro and in situ groups were 44.8 ± 5.6, 46.1 ± 4.5 and 51.2 ± 8.5, respectively. There were no statistically significant differences among the groups (P > 0.05). The rate of TBO penetration was detected up to about <50 μm and the demineralization level did not influence the results. These results have showed promising parameters to develop new protocols for deep caries lesions management using photodynamic antimicrobial chemotherapy.     

Antimicrobial photodynamic therapy as a strategy to arrest enamel demineralization: a short-term study on incipient caries in a rat model

In this study we developed a rat model of incipient caries to investigate the short-term effects of antimicrobial photodynamic therapy (aPDT) on oral microbiota regulation and demineralization arrestment. Twenty-nine male rats were submitted to caries induction. Early carious lesion was confirmed by optical coherence tomography (OCT) 5 days after experiment beginning in five animals. The remaining animals (n = 24) were randomly divided into two groups: control (n = 12), animals were untreated; and aPDT (n = 12), animals were treated with 100 μM of methylene blue for 5 min and irradiated by a light emitting diode at λ = 645 ± 30 nm, fluence rate of 480 mW cm(-2) and exposure time of 3 min. Bacterial burden was evaluated before, immediately after, 3, 7 and 10 days following treatment, and total number of microaerophilic bacteria was counted. OCT was also used to quantify teeth demineralization. A significant bacterial decrease of about 1.6 log was observed immediately after aPDT. Besides, bacterial load in aPDT group remained lower than control until 10 days post-treatment (P < 0.05) and variation of optical attenuation coefficient before and after aPDT was 15%, corroborating to caries arrestment. Put together, these findings suggest that aPDT was competent to reduce cariogenic bacteria and to avoid further mineral loss.     

Effects of Cerium and Combination of Fluoride and Cerium on the Hydrolysis of Hydroxyapatite and Calcium Hydrogen Phosphate

Researches have indicated that fluoride aided in decreasing the solubility of enamel of teeth and preventing caries through converting hydroxyapatite (HAP) to less dissoluble fluoroapatite (FAP). However, The toxicity of fluoride is not negligible. Recent studies^[1] suggested that rare-earth elements (for instance,lanthanum, cerium, etc.) might play an important role in enamel demineralization reduction. However, the effect of these rare-earth elements on the solubility of HAP and calcium hydrogen phosphate (CaHPO₄·2H₂O, DCPD),which are the major inorganic compositions in enamel, remains unclear. The purpose of this paper was to investigate the characteristics of the hydrolysis of DCPD and HAP under 37℃ when hydrolyzed (a) in solutions containing cerium alone, and (b) in solutions containing fluoride followed by solutions containing cerium, respectively.     

Enhanced penetration of fluoride particles into bovine enamel by combining dielectrophoresis with AC electroosmosis

Fluoride deposition into the pores of enamel is necessary at high concentrations to reduce enamel demineralization and with a high degree of penetration to account for loss by ingestion. Current diffusion and electrochemical methods are inadequate for effectively transporting fluoride greater than 20 μm into enamel. The study explores the coupling of dielectrophoresis (DEP) and AC electroosmosis (ACEO) to selectively concentrate fluoride particles from fluoride gel excipients and enhance their penetration into enamel. By measuring the frequency response of approximately 10‐μm‐sized sodium fluoride particles in an aqueous gel media, appropriate frequencies for positive DEP, negative DEP, and ACEO are identified. An assembly composed of two cross‐planar interdigitated electrode (IDE) arrays with open slots is driven successively by fields at appropriate frequencies to drive fluoride particles through the slots of the IDE and into the enamel pores using a combination of DEP and ACEO methods. Fluoride uptake and penetration of 1.23% acidulated phosphate fluoride gel into bovine tooth enamel at various depths is measured using wavelength dispersive spectrometry to compare deposition by diffusion, DEP, and DEP plus ACEO. Fluoride levels in all DEP groups were significantly higher than diffusion groups at depths 10 and 20 μm. The highest fluoride concentrations at 10, 20, 50, and 100 μm depths occur under deposition conditions combining DEP with ACEO. Fluoride levels at 50 μm were equivalent to long‐term prophylactic exposure. These methods may potentially benefit populations at high risk for development of caries and periodontal disease, including underserved children and disparate groups.     

用XPS和SEM研究氟化物对牙釉质早期脱矿和再矿化的影响

用光电子能谱和扫描电镜分析体外人牙釉质片经含不同浓度氟化物的脱矿液和再矿化液处理后釉质化学成分和形态学变化。结果发现，脱矿液中单独加入低浓度氟化物不能有效抑钙和磷溶解，在有外源性钙和磷存在时，才能获得再矿化而抑制钙和磷溶解，脱矿环境中有高浓度氟，通过局部沉积氟化钙而抑制酸与牙的反应，氟促进再矿化主要表现在加速钙的沉积，同时本身参以形成氟磷灰石，提高了牙齿的耐酸能力。     

表面官能团作用下的牙釉质原位再矿化研究

采用酸蚀后的牙釉质作为早期龋缺损模型,在缺损牙釉质表面修饰-SO3-功能基团,分别在人工唾液和含氟人工唾液中进行原位再矿化的研究。利用X-射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)、能谱仪(EDS)、选区电子衍射(SAED)研究原位再矿化晶体的组成和结构。结果表明,在人工唾液和含氟人工唾液中,表面修饰的官能团均可有效促进牙釉质再矿化。在含氟人工唾液中生成了沿c轴取向生长的具有较大长径比的棒状氟羟基磷灰石(FHA),这种FHA晶体具有类牙釉质的成分和结构,对修复早期龋有重要的意义。     

Determination of oxygen with reactor neutrons

Oxygen in silicon was determined by the secondary nuclear reactions of⁶Li(n, α)T and¹⁶O(t, n)¹⁸F. Lithium fluoride was deposited in vacuum on fused quartz, covered with the sample and irradiated in a nuclear reactor. The depth profiles of¹⁸F in fused quartz and in silicon were observed, and enough depth to eliminate surface oxygen was estimated. On the basis of these results, oxygen was determined by the average cross-section method. Oxygen concentration in CZ silicon with various growing condition was 5–26 ppm and was consistent with those determined by the infrared absorption method. The detection limit of oxygen in silicon is 5 ppm.     

A Potassium Based Fluorine Containing Bioactive Glass for Use as a Desensitizing Toothpaste

Potassium releasing bioactive glasses (BAGs) may offer improved relief for dentine hypersensitivity compared to conventional sodium containing BAGs by releasing K⁺ ions for nerve desensitization and occluding dentinal tubules to prevent fluid flow within dentinal tubules. Potassium oxide was substituted for sodium oxide on a molar basis in a fluoride containing BAG used in toothpastes for treating dentine hypersensitivity. The BAG powders were then immersed in an artificial saliva at pH 7 and tris buffer and the pH rise and ion release behavior were characterized by ICP-OES and ISE. The potassium and sodium containing BAGs were characterized by XRD, DSC, FTIR and NMR. Both BAGs presented amorphous diffraction patterns and the glass transition temperature of the potassium glass was higher than that of the sodium glass. The ³¹P MAS-NMR spectra indicated a peak at 2.7 ppm corresponding to apatite and a small peak at −103 ppm indicated crystallization to fluorapatite. Both BAGs dissolved and formed apatite at similar rates, although the dissolution of the potassium glass was slightly slower and it released less fluoride as a result of partial nanocrystallization to fluorapatite upon quenching. The potassium release from the potassium ions could potentially result in nerve deactivation when used in toothpastes.     

Determination of the fluoride distribution in rabbit bone using instrumental neutron activation analysis

An instrumental neutron activation analysis (INAA) technique, based on the¹⁹F(n,)²⁰F reaction, has been development for the determination of fluoride in bone. The purpose was to study fluoride distribution in different kinds of bone samples using a rabbit model. The rationale for the study stems from the posible correlation between fluoride in bone and osteoporosis. The sodium concentration in the bone was used to correct the²⁰F peak area for the²³F(n,)²⁰F contribution. Two secondary standards, teflon tape and teflon coated dacron line, were used to quantify fluoride concentration. They proved to be stable and consistent with respect to their fluoride concentration. Bone specimens from 10 sites and two tooth samples were analyzed for fluoride. Fluoride concentration ranged from 305 ppm in the tibia long bone to 585 ppm in the humerus trochanter end and the magnitude of fluoride concentration levels is age depdentent. The detection limit of the fluoride is approximately 5 ppm using a 100 mg bone sample.     

Nature identification and morphology characterization of cation-exchange membrane fouling during conventional electrodialysis

The aim of this work was to study the effect of a concentrate solution pH value and of the composition in calcium, carbonate, and protein of a diluate solution to be treated by conventional electrodialysis on the fouling of cation-exchange membranes (CEM). It appeared that after demineralization of solutions containing CaCl(2) and CaCl(2)+Na(2)CO(3) using a concentrate solution maintained at a pH of 12, mineral fouling appeared on both sides of the CEM. The nature of the deposits was identified as calcium hydroxide and/or carbonate on both surfaces. The mineral fouling presented an aggregation-like crystal following a carnation-like pattern of aggregates of small rhombohedral crystals with CaCl(2) added alone, while CaCl(2)+Na(2)CO(3) yielded a smoother spherical crystal. Protein fouling was detected only on the CEM surface in contact with the diluate after demineralization of a solution containing CaCl(2)+Na(2)CO(3) using a concentrate pH value of 2.     

Nature identification and morphology characterization of anion-exchange membrane fouling during conventional electrodialysis

The aim of this work was to study the effect on the fouling of anion-exchange membranes (AEM) of (1) the pH value of the concentrate solution and (2) the composition in calcium, carbonate, and protein of the diluate solution to be treated by conventional electrodialysis. It appeared that after demineralization of solutions containing CaCl(2) using a concentrate solution maintained at a pH value of 7 or 12, mineral fouling appeared on the AEM surface in contact with the concentrate. The mineral deposits presented a cylindrical filament shape for conditions with a concentrate solution pH value of 7, while, for a pH value of 12, the mineral deposit had a crumbly and spongy texture formed by irregular aggregates. The nature of the fouling was identified as a calcium phosphate with or without calcium hydroxide. In addition, gel-like protein fouling was detected on the AEM surface in contact with the diluate after demineralization procedures using a concentrate pH value of 2 or 7, regardless of the mineral composition of the diluate.     

Studies on pollutants: A new reagent for the detection of fluoride

A new solid analytical reagent is reported for the detection and semiquantitative determination of traces of fluoride. A blue (λ_max 590 nm) trypan blue dye is liberated from an insoluble zirconium-trypan blue complex by the action of fluoride in dilute acetic acid medium. The detection limit is 0.8 ppm and the range of semiquantitative determination is 0.8 to 8 ppm. The method is simple and can be conveniently used for field detection of fluoride in polluted waters.     

Impact of pulsed electric field on electrodialysis process performance and membrane fouling during consecutive demineralization of a model salt solution containing a high magnesium/calcium ratio

Pulsed electric fields (PEFs), hashed modes of current consisting in the application of a constant current density during a fixed time (Ton) followed by a pause lapse (Toff), were recently demonstrated as an effective alternative for mineral fouling mitigation and process intensification during electrodialysis (ED) treatments. Recent ED studies have continuously reported a considerable mineral fouling formation on ion-exchange membranes, especially during the demineralization of solutions containing a high Mg/Ca ratio and a basified concentrate solution. The aim of this study was to evaluate the process performance under two different PEF conditions on a mineral solution containing a mineral mixture giving a high Mg(2+)/Ca(2+) ratio of 2/5. Two different pause-lapse durations (PEF ratio 1 (Ton/Toff 10s/10s); PEF ratio 0.3 (Ton/Toff 10s/33.3 s)) during consecutive ED treatments and their comparison with dc current were evaluated at a current density of 40 mA/cm(2). Our results showed that PEFs resulted in an intensification of ED process, enhancing the demineralization rates (DRs), reducing the system resistance (SR), and reducing the fouling and energy consumption (EC). PEF ratio 1 was the most optimal condition among the current regimes applied, leading to faster and higher demineralization rates due to a lower fouling and with low energy consumption during all consecutive runs.     

Continuous determination of hydrogen fluoride in air with the fluoride-selective electrode

Hydrogen fluoride in a standard or sample gas stream at 200 ml min^?1 permeates through a teflon membrane (0.8 μm pore size, 0.08 mm thick) into an absorption solution (citrate/acetate buffer at pH 5.4) flowing at 30 ml min^?1. The fluoride produced is measured with the fluoride-selective electrode. The response time is about 12 min. The absorption efficiency of hydrogen fluoride is about 70% between 6.5 and 0.25 ppm by volume (5.2 and 0.2 mg m^?3). In this range, the Nernst equation is valid with a relative standard deviation of less than 1.8%. The lower determination limit for hydrogen fluoride is 0.1 ppm (0.08 mg m^?3).     

Quantitative laser-induced breakdown spectroscopy analysis of calcified tissue samples

We report on the application of laser-induced breakdown spectroscopy (LIBS) to the analysis of important minerals and the accumulation of potentially toxic elements in calcified tissue, to trace e.g. the influence of environmental exposure, and other medical or biological factors. This theme was exemplified for quantitative detection and mapping of Al, Pb and Sr in representative samples, including teeth (first teeth of infants, second teeth of children and teeth of adults) and bones (tibia and femur). In addition to identifying and quantifying major and trace elements in the tissues, one- and two-dimensional profiles and maps were generated. Such maps (a) provide time/concentration relations, (b) allow to follow mineralisation of the hydroxyapatite matrix and the migration of the elements within it and (c) enable to identify disease states, such as caries in teeth. In order to obtain quantitative calibration, reference samples in the form of pressed pellets with calcified tissue-equivalent material (majority compound of pellets is CaCO₃) were used whose physical properties closely resembled hydroxyapatite. Compounds of Al, Sr and Pb were added to the pellets, containing atomic concentrations in the range 100–10 000 ppm relative to the Ca content of the matrix. Analytical results based on this calibration against artificial samples for the trace elements under investigation agree with literature values, and with our atomic absorption spectroscopy (AAS) cross-validation measurements.     

Fluoride determination by magnesium atomic absorption inhibition—release effects

The pH characteristics of fluoride inhibited magnesium atomic absorption signals distinguish them from other anions commonly present. The new technique involves addition of magnesium chloride and then acid to the sample solution while monitoring the magnesium atomic absorption signal. The signal enhancement due to the pH effect is proportional to flouride concentration. A sensitivity of 0.10 absorbance units/ppm F and a determination limit of 0.3 ppm F were found. Tap water fluoride determination results compare well with those for established methods. Various data point to a mechanism involving simple displacement of flouride in the refractory compound to form hydrogen fluoride.     

The role of salivary peptides in dental caries

Dental caries is a complex disease, characterized by demineralization of tooth structure. With a protective role, several salivary phosphopeptides appear to be involved in remineralization processes, delaying the loss of tooth structure. In this work we have correlated peptide saliva composition with dental caries susceptibility through the analysis of saliva and hydroxyapatite-adsorbed salivary peptides samples. Saliva samples were obtained from two groups, a caries-free and a cariessusceptible group, and were analysed using HPLC-MS and a sequential extraction with 6 m of guanidine followed by tri fluoroacetate. Data analysis has allowed us to verify a strong correlation between large amounts phosphopeptides (PRP1/3, histatin 1 and statherin), and the absence of dental caries, which reinforces the importance of these peptides in the maintenance of tooth integrity. In addition, in the caries-susceptible group a high number of peptide fragments was observed, suggesting a high proteolytic activity.     

Instantaneous and Selective Bare Eye Detection of Inorganic Fluoride Ion by Coumarin–Pyrazole‐Based Receptors

A series of rationally designed coumarin–pyrazole‐based scaffolds, equipped with N―H and C―H hydrogen bond donors ( R1–R5 ) and containing various electron‐withdrawing groups at key positions, are synthesized and characterized in order to investigate their inorganic fluoride binding properties in highly competitive media (1:1 DMSO–water). Only one, 3‐{4‐[(2,4‐dinitrophenyl)‐hydrazonomethyl]‐1‐phenyl‐1H‐pyrazol‐3‐yl}‐chromen‐2‐one ( R1 ), of the five compounds synthesized, is found to be capable to selectively detect inorganic fluoride via naked eye amongst other anionic species in aqueous media. Qualitative and spectroscopic studies exhibit that receptor R1 has the potential of showing instantaneous change of color from yellow to pink upon addition of sodium fluoride (0.95 ppm) in aqueous media, at concentration lower than that recommended by World Health Organization (1 ppm). Intensity of color increases with increasing fluoride concentration till 5 ppm, beyond which intensity of color change becomes saturated. This has established the applicability of this receptor for assessment of the level of fluoride in water. Anion binding studies carried out by UV–visible titration portrayed substantial bathochromic peak shift from 410 to 495 nm, upon addition of varying concentrations of aqueous sodium fluoride solution, which has validated the color change. Jobs plot data confirmed 1:1 stoichiometry between R1 and fluoride ion. ¹H‐NMR investigation reveals that the deprotonation of N―H hydrogen donor group of receptor R1 and its interaction with fluoride ion is responsible for the observed color change.     

Comparison of Fracture Load of the Four Translucent Zirconia Crowns

Recently, translucent zirconia has become the most prevalent material used as a restorative material. This study aimed to compare the crown fracture load of the four most common different translucent zirconia brands available in the market at 1.5 mm thickness. Standardized tooth preparations for a full ceramic crown were designed digitally with software (AutoCAD) by placing a 1.0 mm chamfer margin and 1.5 mm occluso-cervical curvature for the crown sample manufacturing. Stylized crowns were chosen to control the thickness of the crown. The axial and occlusal thickness were standardized to 1.5 mm thickness except at the central pit, which was 1.3 mm thick. The STL file for the tooth dies was prepared using software (3Shape TRIOS^® Patient Monitoring, Copenhagen, Denmark). The tooth dies were printed with a resin material (NextDent Model 2.0, Vertex-Dental B.V., Soesterberg, The Netherlands) using a 3D printing software (3D Sprint^® Client Version 3.0.0.2494) from a 3D printer (NextDent™ 5100, Vertex-Dental B.V., Soesterberg, The Netherlands). The printing layer thickness was 50 µm. Then, a total of twenty-eight (N = 28) stylized crowns were milled out of AmannGirrbach (Amann Girrbach GmbH, Pforzheim, Germany) (n = 7), Cercon HT (Dentsply Sirona, Bensheim, Germany) (n = 7), Cercon XT (Dentsply Sirona, Bensheim, Germany) (n = 7), and Vita YZ XT (Zahnfabrik, Bäd Sackingen, Germany) (n = 7). Following sintering the crowns, sandblasting was performed and they were bonded to the tooth dies with the resin cement (RelyX U-200, 3M ESPE, Seefeld, Germany) and permitted to self-cure under finger pressure for 6 min. The crowns were loaded on the occlusal surface in a universal testing machine (MTS Centurion) with a stainless-steel ball indenter (7 mm radius) with a loading rate of 1 mm/min to contact the stylized crowns on each of the four cusps until failure. A rubber sheet (1.5 mm thickness) was positioned between the crown and indenter, which helped with the load distribution. Statistical analysis was done using SPSS version 20 (IBM Company, Chicago, USA). The fracture loads were analyzed using Dunnett’s T3 test, and the number of cracks was analyzed using the Mann–Whitney U test among the groups. The significant level was set at p value = 0.05. The mean fracture loads were 3086.54 ± 441.74 N, 4804.94 ± 70.12 N, 3317.76 ± 199.80 N, and 2921.87 ± 349.67 N for AmannGirrbac, Cercon HT, Cercon XT, and Vita YZ XT, respectively. The mean fracture loads for the surfaces with the greatest number of cracks (excluding the occlusal surfaces) were on the lingual surface for AmannGirrbach and Cercon HT, on the distal and mesial for Cercon XT, and on the buccal for Vita YZ XT. We found that the AmannGirrbach had the most overall cracks. Cercon XT had the greatest number of occlusal cracks and appeared to be the most shattered. Cercon HT had the least number of cracks. In conclusion, Cercon HT presented the best strength properties, the highest fracture load, and no visible cracks. AmannGirrbach presented the lowest strength properties.