Modification of surface pre-treatment for resin infiltration to mask natural white spot lesions

Objectives

The aims of this study were to investigate an alternative pre-treatment method for resin infiltration using 37% H₃PO₄ with a brush applicator and to evaluate the penetration effect of the infiltrant for masking the natural white spot lesions (WSLs) in human teeth.

Methods

Seventy extracted human molars and pre-molars with non-cavitated WSLs were collected. Thirty teeth met criteria of ICDAS code 2, and were sectioned, providing a total of sixty paired halves. For the control group, 15% HCl gel was applied for 120 s, and 37% H₃PO₄, gel was gently rubbed with a brush applicator for 30 s to the experimental group. Also, to evaluate the penetration effect of the infiltrant by pre-treatment, the specimens were treated with the infiltrant (Icon^®). Thicknesses of the removed surfaces and percentages of the infiltrated areas (IA%) were evaluated by CLSM, and micro-morphological changes were observed by SEM.

Results

The mean thicknesses of removed surface layers were significantly different between the control group (36 ± 7.62 μm) and the experimental group (13 ± 2.76 μm) (p < 0.001). But, the means of IA% were similar in both groups (p > 0.05). In the SEM images, the prism cores were preferentially dissolved in the control group, while the prism peripheries were preferentially dissolved in the experimental group.

Conclusions

Applying 37% H₃PO₄ gel with an applicator brush for 30 s could increase the permeability and minimize removal of the surface layer of natural WSLs. Moreover, the effect of resin infiltration was similar to the control group which was pretreated 15% HCl gel for 120 s in vitro study.

Clinical significance

For resin infiltration, applying 37% H₃PO₄ gel with a brush applicator can preserve the protective surface layers of the WSLs with reduced application time.     

EDTA or H3PO4/NaOCl dentine treatments may increase hybrid layers’ resistance to degradation: A microtensile bond strength and confocal-micropermeability study

Objectives

The aim of this study was to reduce hybrid layer degradation created with simplified dentine adhesives by using two different methods to condition the dentine surface.

Methods

A smear-layer was created on flat dentine surfaces from extracted human third molars with a 180-grit/SiC-paper. Dentine specimens were conditioned before bonding with the following procedures: 37% H₃PO₄; H₃PO₄/0.5% NaOCl; 0.1 M EDTA; 0.1 M EDTA/0.5% NaOCl. Two etch-and-rinse adhesives: (Scotchbond 1XT or Optibond Solo Plus) were applied and light-cured. Composite build-ups were constructed. The bonded teeth were sectioned into beams, stored in distilled water (24 h) or 12% NaOCl solution (90 min) and finally tested for microtensile bond strengths (μTBS). Additional dentine surfaces were conditioned and bonded as previously described. They were prepared for a pulpal-micropermeability confocal microscopy study and finally observed using confocal microscopy.

Results

μTBS results revealed that both adhesives gave high bond strengths to acid-etched dentine before, but not after a 12% NaOCl challenge. Bonds made to acid-etched or EDTA-treated dentine plus dilute NaOCl, gave high μTBS that resisted 12% NaOCl treatment, as did EDTA-treated dentine alone. A confocal micropermeability investigation showed very high micropermeability within interfaces of the H₃PO₄, etched specimens. The lowest micropermeability was observed in H₃PO₄ + 0.5% NaOCl and 0.1 M EDTA groups.

Conclusions

The use of dilute NaOCl (0.5%) after acid-etching, or the conditioning of dentine smear layers with 0.1 M EDTA (pH 7.4) produced less porous resin–dentine interfaces. These dentine-conditioning procedures improve the resistance of the resin–dentine bond sites to chemical degradation (12% NaOCl) and may result in more durable resin–dentine bonds.     

Does tin pre-treatment enhance the bond strength of adhesive systems to enamel?

Objectives

The study investigated the modification of composite-to-enamel bond strength by pre-treatment of enamel with a concentrated, acidic SnCl₂-solution.

Methods

Six groups of flat human enamel specimens (n = 44 per group) were treated as follows: OB-H: H₃PO₄ etching, Optibond FL application (primer + adhesive; manufacturer's instructions); OB-S: SnCl₂ pre-treatment, Optibond FL application (primer + adhesive); OB-HS: H₃PO₄ etching + SnCl₂ pre-treatment, Optibond FL application (primer + adhesive); CF-N: Clearfil SE application (primer + bond; manufacturer's instructions); CF-H: H₃PO₄ etching, Clearfil SE application (primer + bond); CF-S: SnCl₂ pre-treatment, Clearfil SE application (primer + bond). Enamel specimens were then built up with resin composite (Clearfil Majesty Esthetic) and stored (100% humidity, 37 °C, 1 week). μTBS-measurement and failure mode analysis of one-half of the specimens were performed immediately after storage, while the other half was analysed after a thermocycling procedure (8500 cycles; 5 °C and 55 °C; dwell time 30 s). Additional specimens were prepared for SEM- and EDX-analysis.

Results

Highest values were measured for OB-H before and after thermocycling, lowest values for CF-N. Compared to OB-H treatment, OB-S treatment reduced μTBS before/after thermocycling by 23%/28% and OB-HS treatment by 8%/24% (except for OB-SH before (n.s.), all p ≤ 0.001 compared to OB-H). In the Clearfil SE treated groups pre-treatment increased μTBS significantly compared to CF-N (before/after: CF-H: +46%/+70%; CF-S: +51%/42%; all p ≤ 0.001).

Conclusion

Pre-treatment with H₃PO₄ or SnCl₂ markedly increased the μTBS of Clearfil SE to enamel. However, thermocycling partly reduced the gain in μTBS obtained by SnCl₂ pre-treatment.

Clinical significance

The application of an acidic and highly concentrated SnCl₂ solution is a good option to increase the μTBS between enamel and a resin composite mediated by an adhesive system containing the multifunctional monomer MDP.     

Self-assembly LiFePO4/polyaniline composite cathode materials with inorganic acids as dopants for lithium-ion batteries

Carbon-coated LiFePO₄ (C-LFP) composites incorporated with electrochemically-active conducting polymer polyaniline (PANI) are fabricated via a self-assembly process. Inorganic acids HCl, H₂SO₄ and H₃PO₄ are used as dopants for PANI. The C-LFP/PANI composites are characterized by thermogravimetric analysis, scanning electron microscopy, electrochemical impedance spectroscopy, Raman spectra and four-probe resistivity measurements. Our results show that a remarkable improvement in capacity and rate capability can be achieved in the C-LFP/PANI composite cathodes doped with HCl and H₃PO₄. The C-LFP/PANI-HCl composite exhibits the best electrochemical performance, which gives a ca. 15% capacity enhancement at 0.2 C and 40% enhancement at 5 C compared to the parent C-LFP. The mechanism for the enhancement has been discussed.     

Surface conditioning of natural enamel caries lesions in deciduous teeth in preparation for resin infiltration

Objectives

As a conditioning step for resin infiltration into caries lesions, the relatively impermeable surface layer should be removed using hydrochloric acid gel (15%) to achieve improved infiltration, as it could be shown for permanent teeth. It is unclear whether this etching regimen can be transferred to the deciduous dentition, where differences in surface structure have been reported. Thus, the aim of the present study was to evaluate the effect of phosphoric and hydrochloric acid gels on the surface layer reduction of natural lesions of primary teeth.

Methods

Thirty-two extracted or exfoliated primary molars with lesions confined to enamel were selected. Paired lesion halves were partially etched with either 37% phosphoric (H₃PO₄) or 15% hydrochloric acid gel (HCl) for 30 s, 60 s, 90 s, or 120 s, respectively.

Results

Etching with H₃PO₄ resulted in incomplete reduction of the surface layers in all groups [highest percentage reduction (SD) at 120 s: 54 (28)%] as observed with confocal microscopy. In contrast, surface layers could be eroded almost completely [99 (3)%] by etching with HCl for 120 s.

Conclusion

An effective erosion of the surface layer of natural enamel caries in deciduous teeth can be achieved by etching with 15% hydrochloric acid gel for 90–120 s.     

Can poly(acrylic) acid molecular weight mixtures improve the compressive fracture strength and elastic modulus of a glass-ionomer restorative?

Objectives

To optimize the compressive fracture strength (σ) and elastic modulus (E) of a glass-ionomer (GI) restorative using poly(acrylic) acid (PAA) weight average molecular weight (M_w) mixtures.

Methods

174 PAA solutions were prepared (four control PAA M_ws at three PAA concentrations (25, 35 and 45%) (n = 12) and six M_w mixtures (Groups A-F at nine blend ratios and three PAA concentrations (n = 162))). The viscosity (η) of each PAA solution was determined using a digital viscometer. The PAA solutions were hand-mixed with a commercial GI restorative powder (Ionofil Molar; Voco, Cuxhaven, Germany) and σ and E were determined using cylindrical (6 mm height, 4 mm diameter) specimens (n = 20) at 24 h. Data were analyzed using analyses of variance (ANOVA) (three-, two- and one-way) and regression analyses at p < 0.05.

Results

The three- and two-way ANOVAs highlighted significant effects of M_w mixture, blend ratio and PAA concentration (all p < 0.0001) on the η, σ and E data. Regression analyses showed significant increases in η, σ and E (p < 0.0001) with increasing M_w from Groups A to F. There was no significant effect of blend ratio on the σ data for Groups A (p = 0.178), D (p = 0.747) and F (p = 0.107) and on the E data (p > 0.083).

Significance

The current approach to improving the mechanical properties of GI restoratives using PAA M_w mixtures is encouraging, however, further manipulation of the GI restorative system by optimizing PAA M_w mixtures, blend ratios and PAA concentrations is required to elicit further improvements in σ and E without impacting upon the η of the PAA solution.     

ElectroBond application may improve wetting characteristics of etched dentine

Objective

To assess the efficacy of an electrically assisted application technique on dentine wettability (water contact angle measurements) and to determine the promoted surface roughness of dentine after applying 37% phosphoric acid etching, a self-etching primer or a self-etching adhesive system.

Methods

Wettability was assessed on 30 caries-free extracted human third molars. Specimens were sectioned parallel to the occlusal surface to expose moderately deep dentine and ground flat (water-wet 180-grit SiC) to provide uniform flat surfaces. 37% H₃PO₄, Clearfil SE Bond (CSEB) primer or Prompt-L-Pop (PLP) adhesive system were applied on dentine surfaces. In half of the specimens, the electric impulse-assisted application technique/ElectroBond-assisted application was followed. Contact angle measurements were performed to assess wettability using the Axisymmetric Drop Shape Analysis technique. Additional surfaces were conditioned for atomic force microscopy (AFM) analysis. Two-way ANOVA, Student's t and Student-Newman-Keuls tests were performed (P < 0.05).

Results

PLP-treated dentine showed the highest intertubular roughness and the lowest dentine wettability. ElectroBond application reduced water contact angles when dentine was treated with H₃PO₄ or Clearfil SE Bond primer, but not when dentine was treated with PLP.

Conclusions

The use of electric current improved wettability of dentine surface following application of phosphoric acid and a mild self-etch primer, but not self-etch adhesive.     

The effect of doping Mg on the structure and electrochemical properties of Li3V2(PO4)3 cathode materials for lithium-ion batteries

The Mg-doped Li₃V_2−xMg_x(PO₄)₃ (x = 0.00, 0.01, 0.02, 0.05, 0.10, 0.20, 0.30, 0.33, 0.50, 1.00 and 1.33) compounds have been prepared by a sol–gel method in reducing atmosphere (70%Ar + 30%H₂) using citric acid as a chelating agent and a carbon source coated on the samples. The Mg-doped effects on the structural and electrochemical performance of Li₃V₂(PO₄)₃ are investigated by X-ray diffraction, galvanostatic, charge/discharge and four-point probe measurement method. The Li₃V_2−xMg_x(PO₄)₃ solid solution phase can exist stable in the composition range between x = 0.00 and 0.27. The simple improve mechanism of the electrochemical performance for Mg-doped Li₃V_2−xMg_x(PO₄)₃ system is discussed too. In the Mg-doped Li₃V_2−xMg_x(PO₄)₃ system, at a lower charge/discharge rate (0.1C), the cycle performance has no much improvement with the increasing Mg doping content. However, at higher rates, there has an excited improvement in both cycle performance and rate capability due to the increase of electrical conductivity (more than one order of magnitude). At 5C charge/discharge rate, for the Li₃V_1.95Mg_0.05(PO₄)₃ sample, the discharge capacities for the 1st and 100th cycle were 138.9 and 123.3 mAh g⁻¹. The discharge capacity retention reached to 89% (more than 51% for undoped Li₃V₂(PO₄)₃ system). More important is that, except for the first 15 cycles, the discharge capacities kept almost a constant. Based on the excellent electrochemical performance, Li₃V_1.95Mg_0.05(PO₄)₃ will be a promising cathode material for rechargeable lithium-ion batteries.     

Development of amperometric arsine gas sensor using gold-modified diamond electrodes

Amperometric gas sensor of arsine was developed using gold-modified diamond electrodes as the working electrodes. The detection method was conducted in high concentration of H₂SO₄. The reaction was declared based on two oxidation steps, involving oxidation of As³⁻ to As⁰ at mild potential in strong acid, followed by electrochemical oxidation of As⁰ to As³⁺ at gold-based electrodes. Linear calibration curve was observed in the concentration range of 5–50 ppb (r² = 0.985) with detection limit of ∼4.43 ppb (S/N = 3). Current decreasing of measurement was found ∼5.5% for 5 measurements. However, better stability was observed after the 5th measurement, indicated that the sensor could be applied for long time measurement. Investigation to several possible interference gasses, i.e. SO₂, H₂S, NO, NO₂, CO, O₃ and H₂ indicated no significant interference of the gas to arsine measurements.     

Comparison of sealant and infiltrant penetration into pit and fissure caries lesions in vitro

Objectives

The aim of this in vitro study was to evaluate the penetration of an infiltrant and a sealant, when applied as recommended, into fissure caries lesions.

Methods

The fissure systems of extracted human teeth were classified according to the international caries detection and assessment system (ICDAS, codes: 0, 1, 2). Within each ICDAS-code ten teeth were either etched with 37% H₃PO₄-gel for 60 s and subsequently sealed (‘Fissure Sealing’; Helioseal; Ivoclar Vivadent) or etched with 15% HCl-gel for 120 s and subsequently infiltrated (‘Resin Infiltration’; Icon; DMG). Additionally, ten teeth with ICDAS-code 2 were etched with 37% H₃PO₄-gel for 120 s and infiltrated (‘Soft-Etch-Infiltration’). Specimens were cut perpendicular to their surfaces, polished, and confocal microscopic images were obtained. Lesion depths (LD_max) and penetration depths (PD_max) were measured and percentage penetration was calculated as PP_max = PD_max/LD_max × 100.

Results

Baseline LD_max [median (interquartile range)] for ICDAS-code 2 lesions was 1192 (805–1512) μm. In ICDAS-code 2 lesions PP_max was significantly higher for specimens treated with ‘Resin Infiltration’ [41 (30–78)%] compared to ‘Soft-Etch-Infiltration’ [11 (0–21)%] or ‘Fissure Sealing’ [5 (0–9)%] (p < 0.05; Mann–Whitney test). PP_max did not differ significantly between groups in ICDAS-code 0 and 1 lesions (p > 0.05).

Conclusion

The fissure sealant when applied after etching with H₃PO₄-gel only penetrates superficially into non-cavitated fissure caries lesions. Penetration of an infiltrant is superior in particular after etching with HCl-gel.

Clinical significance

Compared with sealing, infiltration of fissure caries lesions leads to more deeply infiltrated lesions, which might in turn result in superior abilities to hamper caries progression.     

The effect of pretreatment of Vulcan XC-72R carbon on morphology and electrochemical oxygen reduction kinetics of supported Pd nano-particle in acidic electrolyte

The influence of chemical pretreatment of carbon support for oxygen reduction on palladium nano-particles in acidic electrolyte was studied. Vulcan XC-72R carbon as catalyst support for palladium nano-particles was pretreated with 5% HNO₃, 0.07 M H₃PO₄, 0.2 M KOH and 10% H₂O₂. The effect of treatment on the properties of the carbon support was studied by N₂ adsorption and X-ray photoelectron spectroscopy (XPS). It was found that chemical treatment significantly changed the surface chemical properties and surface area of the carbon support. The surface area and pore volume of 5% HNO₃ and 10% H₂O₂ treated carbon supports were drastically decreased due to the oxidative nature of treatment. Ethylene glycol (EG) reduction method was used to synthesise 20% Pd on pr-treated and un-treated carbon supports. Differences in catalyst morphology were characterized using X-ray diffraction, energy dispersive X-ray analysis and transmission electron microscope techniques. It was observed that by using a mild reducing agent, namely EG, well-dispersed and nano-size Pd particles could be achieved during catalyst synthesis. The electrocatalytic activity of different Pd/C catalysts towards the oxygen reduction reaction (ORR) was examined by cyclic voltammetry (CV) on a rotating ring-disc electrode (RRDE) and compared with E-Tek 20% Pd/C catalyst under identical experimental conditions. The kinetics of ORR on these electrocatalysts predominantly involved a four-electron step reduction with the first electron transfer being the rate-determining step. However, the observed specific activity, mass activity and amount of hydrogen peroxide produced during ORR were greatly influenced by the pretreatment employed for carbon support.     

Low overpotential reduction of dinitrogen to ammonia in aqueous media

The molecular nitrogen fixation to ammonia is one of the most important processes in chemistry. In this connection, our aim was to realize an electrochemical reaction under extremely mild conditions in an aqueous media for the first time. The reduction of dinitrogen was achieved on a polypyrrole electrode in aqueous 0.1 M Li₂SO₄/0.03 M H⁺ solution at 60 bar N₂-pressure. The reaction product was only ammonia and the ammonia formation efficiency depends strongly on the applied pressure, temperature, electrode potential, supporting electrolyte, film thickness of polymer electrode, as well as on the amount of proton source added to the electrolyte medium. The maximum yield of NH₃ was 53 μM obtained at −0.165 V_NHE after 5 h of electrolysis.     

Concentrations of and application protocols for hydrogen peroxide bleaching gels: Effects on pulp cell viability and whitening efficacy

Objectives

To assess the whitening effectiveness and the trans-enamel/trans-dentinal toxicity of experimental tooth-bleaching protocols on pulp cells.

Methods

Enamel/dentine discs individually adapted to trans-well devices were placed on cultured odontoblast-like cells (MDPC-23) or human dental pulp cells (HDPCs). The following groups were formed: G1 – no treatment (control); G2 to G4 – 35% H₂O₂, 3 × 15, 1 × 15, and 1 × 5 min, respectively; and G5 to G7 – 17.5% H₂O₂, 3 × 15, 1 × 15, and 1 × 5 min, respectively. Cell viability and morphology were evaluated immediately after bleaching (T1) and 72 h thereafter (T2). Oxidative stress and cell membrane damage were also assessed (T1). The amount of H₂O₂ in culture medium was quantified (Mann–Whitney; α = 5%) and colour change (ΔE) of enamel was analysed after 3 sessions (Tukey's test; α = 5%).

Results

Cell viability reduction, H₂O₂ diffusion, cell morphology alteration, oxidative stress, and cell membrane damage occurred in a concentration-/time-dependent fashion. The cell viability reduction was significant in all groups for HDPCs and only for G2, G3, and G5 in MDPC-23 cells compared with G1. Significant cell viability and morphology recovery were observed in all groups at T2, except for G2 in HDPCs. The highest ΔE value was found in G2. However, all groups presented significant ΔE increases compared with G1.

Conclusion

Shortening the contact time of a 35%-H₂O₂ gel for 5 min, or reducing its concentration to 17.5% and applying it for 45, 15, or 5 min produce gradual tooth colour change associated with reduced trans-enamel and trans-dentinal cytotoxicity to pulp cells.

Clinical significance

The experimental protocols tested in the present study provided significant tooth-bleaching improvement associated with decreased toxicity to pulp cells, which may be an interesting alternative to be tested in clinical situations intended to reduce tooth sensitivity and pulp damage.     

Stabilization of dentin matrix after cross-linking treatments,in vitro

Objectives

To evaluate the effect of EDC on elastic modulus (E), MMPs activity, hydroxyproline (HYP) release and thermal denaturation temperature of demineralized dentin collagen.

Methods

Dentin beams were obtained from human molars and completely demineralized in 10 wt% H₃PO₄ for 18 h. The initial E and MMP activity were determined with three-point bending and microcolorimetric assay, respectively. Extra demineralized beams were dehydrated and the initial dry mass (DM) was determined. All the beams were distributed into groups (n = 10) and treated for 30 s or 60 s with: water, 0.5 M, 1 M or 2 M EDC or 10% glutaraldehyde (GA). After treatment, the new E and MMP activity were redetermined. The beams submitted to DM measurements were storage for 1 week in artificial saliva, after that the mass loss and HYP release were evaluated. The collagen thermal denaturation temperature (TDT) was determined by DSC analysis. Data for E, MMP activity and HYP release were submitted to Wilcoxon and Kruskal–Wallis or Mann–Whitney tests. Mass loss and TDT data were submitted to ANOVA and Tukey tests at the 5% of significance.

Results

EDC was able to significantly increase collagen stiffness in 60 s. 10% GA groups obtained the highest E values after both 30 and 60 s. All cross-linking agents decreased MMP activity and HYP release and increased TDT temperature. Significant differences were identified among EDC groups after 30 or 60 s of cross-linking, 1 M or 2 M EDC showed the lowest MMP activity.

Significance

Cross-linking agents are capable of preventing dentin collagen degradation. EDC treatment may be clinically useful to increase resin-dentin stability.     

Effects of sodium sulfamate on electrodeposition of Cu(In,Ga)Se2 thin film

Cu(In,Ga)Se₂ thin films have been prepared by electrodeposition from chloride electrolytes using sodium sulfamate as a complexing agent. Cyclic voltammograms indicate that sodium sulfamate can inhibit the reduction of Cu²⁺, Cu⁺ and H₂SeO₃, and accordingly hinder the formation of copper selenides. EDS analysis reveals that with the increase of sodium sulfamate concentration in the bath, atom ratio (Cu + Se)/(In + Ga) decreases while gallium content increases, and the film composition transforms from Cu-rich to Cu-poor. SEM and Raman spectra also show that copper selenides phases in electrodeposited films diminish with the increase of sodium sulfamate concentration.     

Preparation of bioactive titania films on titanium metal via anodic oxidation

ObjectivesTo research the crystal structure and surface morphology of anodic films on titanium metal in different electrolytes under various electrochemical conditions and investigate the effect of the crystal structure of the oxide films on apatite-forming ability in simulated body fluid (SBF).MethodsTitanium oxide films were prepared using an anodic oxidation method on the surface of titanium metal in four different electrolytes: sulfuric acid, acetic acid, phosphoric acid and sodium sulfate solutions with different voltages for 1 min at room temperature.ResultsAnodic films that consisted of rutile and/or anatase phases with porous structures were formed on titanium metal after anodizing in H₂SO₄ and Na₂SO₄ electrolytes, while amorphous titania films were produced after anodizing in CH₃COOH and H₃PO₄ electrolytes. Titanium metal with the anatase and/or rutile crystal structure films showed excellent apatite-forming ability and produced a compact apatite layer covering all the surface of titanium after soaking in SBF for 7 d, but titanium metal with amorphous titania layers was not able to induce apatite formation.SignificanceThe resultant apatite layer formed on titanium metal in SBF could enhance the bonding strength between living tissue and the implant. Anodic oxidation is believed to be an effective method for preparing bioactive titanium metal as an artificial bone substitute even under load-bearing conditions.     

Slow progression of dentin bond degradation during one-year water storage under simulated pulpal pressure

Objectives

To evaluate the dentin bond durability of simplified adhesives after one-year (1 y) under water storage and simulated pulpal pressure.

Methods

Class I cavities were prepared in sixty human third molars with the pulpal wall located in mid-coronal dentin. The roots were cut off to expose the pulpal chamber, and the teeth were assembled in a pulpal pressure simulator device. A two-step etch-and-rinse adhesive (Single Bond 2/SB), a two-step self-etch adhesive (Clearfil SE Bond/CSE), a three-step self-etch adhesive (Adper Scotchbond SE/SSE) and three all-in-one adhesives (Adper Easy Bond/EB, Clearfil S³ Bond/S3 and Adhese One/AO) were applied according to manufacturer? instructions. No enamel pre-etching was used for the self-etch systems. The cavities were filled with a composite (Z250, 3M ESPE) in four to five horizontal increments and individually cured. Immediately after the final cure, pulpal pressure was set to 15 cm H₂O. After 24 h and 1 y under simulate pulpal pressure the teeth were cut following a ‘nontrimming’ microtensile test technique (n = 30) and tested in tension. Kruskall–Wallis and post hoc multiple comparisons were used at α = 0.05. Weibull statistics was applied to SB, CSE and EB. Fractographic analysis of debonded specimens was performed using scanning electron microscopy.

Results

At 24 h and 1 y periods, SB showed higher bond strength means than all the others adhesives tested. CSE was not statistically different from EB at 24 h and from EB and SB at 1 y. EB showed bond strength statistically higher than the other three self-etch adhesives, which were not statistically different from each other at 24 h. AO showed significantly lower bond strength than all tested materials after 1 y. For all adhesives the mean bond strength at 1 y were not statistically different from the values measured at 24 h (p > 0.05). Shifts in failure mode patterns and Weibull modulus decrease indicate some degree of bond degradation after the 1 y storage period.

Conclusion

One-year of simulated pulpal pressure did not affect dentin bond strength of simplified adhesives in Class I restorations. Signs of degradation were only revealed by fractographic analysis and reliability parameters.     

Analysis of the mechanism for electrodeposition of the ZnSe phase on Cu substrate

Electrodeposition mechanism of selenium, zinc and ZnSe phase was studied with the electrochemical techniques. The chronoamperometry and voltammetry were combined with quartz crystal microbalance technique to analyse the deposition processes. It was found that they strongly depend on the applied potentials. The deposition of pure Se starts at 0 V vs. saturated calomel electrode (SCE) and the efficiency of this process decreases due to H₂Se formation and hydrogen evolution when the more negative potentials are reached. The voltammetric and microgravimetric measurements suggest that the deposition of Zn from the bath containing both ions, follows selenium deposition and synthesis of ZnSe is initiated at −0.6 V vs. SCE. The chronoamperometric transients combined with microgravimetry confirmed the range of potentials in which Se and ZnSe are deposited. Below −0.84 V vs. SCE the formation of H₂Se was observed. Then H₂Se may react with Zn²⁺ ions and another mechanism of ZnSe synthesis is possible.     

Effect of temperature on water sorption and solubility of dental adhesive resins

Objective

This study examined the effect of temperature on water sorption and solubility characteristics of four commercial dental adhesives. The null hypothesis tested was that temperature has no effect on the water sorption and solubility characteristics of these adhesives.

Methods

The tested materials were: three-step etch-and-rinse (All-Bond 2, AB), two-step etch-and-rinse (One-Step, OS), two-step self-etch (Clearfil SE Bond, SE) and one-step self-etch (Clearfil S3 Bond, S3) adhesives. Seven resin disks (6 mm in diameter × 1 mm in thickness) were prepared from each tested material and were stored in deionized water at 23 °C, 37 °C and 55 °C. Water sorption and solubility of the resin disks were measured before and after water immersion and desiccation following two consecutive sorption and desorption cycles. The water sorption and solubility values obtained were analyzed using two-way ANOVA and Tukey's multiple comparison tests. The relationships between maximum water sorption, solubility and kinetics of water diffusion with temperature were evaluated by means of Pearson correlation statistic.

Results

OS exhibited the highest water sorption and solubility values in the second sorption–desorption cycle at 55 °C (p < 0.001). This is followed by S3, SE and AB with no significant difference between SE and AB. Significant positive correlations were observed between maximum water sorption (r = 0.307, p < 0.01), solubility (r = 0.244, p < 0.05), water sorption (r = 0.651, p < 0.001) and desorption (r = 0.733, p < 0.001) diffusion coefficients (obtained using Fick's law of diffusion) with temperature in the second cycle.

Significance

High temperatures increased water sorption of simplified adhesives. Such water sorption may contribute to the failure of resin–dentin bonds.     

Physical chemical effects of zinc on in vitro enamel demineralization

Objectives

Zinc salts are formulated into oral health products as antibacterial agents, yet their interaction with enamel is not clearly understood. The aim was to investigate the effect of zinc concentration [Zn²⁺] on the in vitro demineralization of enamel during exposure to caries-simulating conditions. Furthermore, the possible mechanism of zinc's action for reducing demineralization was determined.

Methods

Enamel blocks and synthetic hydroxyapatite (HAp) were demineralized in a range of zinc-containing acidic solutions (0–3565 ppm [Zn²⁺]) at pH 4.0 and 37 °C. Inductively coupled-plasma optical emission spectroscopy (ICP-OES) was used to measure ion release into solution. Enamel blocks were analysed by Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR), and HAp by X-ray diffraction (XRD) and neutron diffraction (ND).

Results

ICP-OES analysis of the acidic solutions showed a decrease in [Ca²⁺] and [PO₄³⁻] release with increasing [Zn²⁺]. FTIR revealed a α-hopeite (α-Zn₃(PO₄)₂.4H₂O)-like phase on the enamel surfaces at >107 ppm [Zn²⁺]. XRD and ND analysis confirmed a zinc-phosphate phase present alongside the HAp.

Conclusions

This study confirms that zinc reduces enamel demineralization. Under the conditions studied, zinc acts predominantly on enamel surfaces at PO₄³⁻ sites in the HAp lattice to possibly form an α-hopeite-like phase.

Clinical significance

These results have a significant implication on the understanding of the fundamental chemistry of zinc in toothpastes and demonstrate its therapeutic potential in preventing tooth mineral loss.