Effect of tree types of light-curing units on 5-year colour changes of light-cured composite

The purpose of this study was to determine colour changes in a composite cured with tungsten-halogen, light-emitting diode (LED) or a plasma arc after 5 years. Five specimens 10 mm in diameter and 2 mm in height were prepared using Hybrid (Clearfil AP-X) composite for each test group. The corresponding specimens were cured with a tungsten-halogen curing light, a LED unit or with a plasma arc. Specimens were stored in light-proof boxes for 5 years after the curing procedure to avoid further exposure to light and stored in 37°C in 100% humidity. Colorimetric values of the specimens immediately after curing and after 5 years were measured using colorimeter. The ΔE* _ab values varied significantly depending on the curing unit used (p < 0.001). Curing time did not affect the colour changes of the specimens (p = 0.4). The results of this study suggest that composite materials undergo measurable changes due to the curing unit exposure.     

Real‐time curing characteristics of experimental resin composites containing amorphous calcium phosphate

The real‐time polymerization of light‐curable experimental resin composites filled with amorphous calcium phosphate (ACP) was monitored. Experimental composites were based on a 2,2‐bis[4‐(2‐ethoxy‐3‐methacryloyloxy propoxy)phenyl]propane (Bis‐EMA)/triethyleneglycol dimethacrylate (TEGDMA)/2‐hydroxyethyl methacrylate (HEMA) resin photoactivated by a camphorquinone/tertiary amine system. Four ACP composites were prepared, containing 40 wt% ACP and 0/10 wt% reinforcing fillers (barium glass and silica). Additionally, two control composites were prepared which contained only reinforcing fillers (40–50 wt%). The degree of conversion (DC) was monitored in real time using a Fourier‐transform infrared (FTIR) spectrometer with an attenuated total reflectance accessory. During the light curing (1,219 mW cm^?2) for either 20 or 40 s, infrared spectra were collected from the bottom of 2‐mm‐thick composite specimens at the rate of two spectra per second over 5 min. When cured for 40 s, the ACP composites attained a high DC (89.1%–92.4%), while the DC of control composites was significantly lower (53.5%–68.4%). All materials showed a lower DC for the shorter curing time (20 s) and various extents of 5‐min postcure polymerization: 12.9%–21.5% for the ACP composites and 2.7%–5.2% for the control composites. The control composites reached the maximum reaction rate much earlier (4.1–4.3 s) and at lower DC (9.9%–10.4%) than did the ACP composites (17.4–22.0 s and 43.5%–49.3%, respectively).     

Different depth-related polymerization kinetics of dual-cure,bulk-fill composites

ObjectiveThe aim of this study was to evaluate the polymerization kinetics qualitatively and quantitatively for dual-cure bulk-fill composites in comparison with light-cure bulk-fill and traditional incremental composites at two clinically relevant depths.MethodsFive commercial dental composites were evaluated, including three dual-cure bulk-fill composites (BulkEZ, HyperFIL and Injectafil), one light-cure bulk-fill composite Filtek Bulk Fill Flowable (FBF) and one traditional incremental composite Filtek Z250 (Z250) as controls. Specimens were prepared in two different depths (0.5 mm and 5 mm) for 20 s light irradiation. Self-cure was also evaluated for the three dual-cure composites. The polymerization kinetics were measured continuously in real-time for at least 10 min using a Fourier-transform infrared spectroscopy (FTIR) with an attenuated total reflectance (ATR) accessory. The experimental kinetic data were fitted using two mathematical models — a sigmoidal function and a superposition of two exponential functions characterizing the gel phase and glass phase. The degree of conversion (DC) and the rate of polymerization were calculated for all test conditions.ResultsBoth experimental FTIR measurements and mathematical modeling revealed distinct depth-related polymerization kinetics for BulkEZ compared to the other two dual-cure composites. Specifically, BulkEZ exhibited moderately-paced polymerization kinetics at both depths while HyperFIL and Injectafil exhibited faster polymerization at 0.5 mm and slower polymerization at 5 mm. The bulk-fill FBF and incremental Z250 exhibited relatively fast polymerization at both depths, a characteristic for light-cure. The DC values at the two depths were not significantly different for BulkEZ, but significantly higher at 0.5 mm than at 5 mm for the other four composites (α = 0.05).SignificancePolymerization kinetics and their depth variation for dual-cure bulk-fill composites are material dependent. The distinct depth-related polymerization kinetics revealed for BulkEZ compared to other composites may affect their contraction stress and clinical performance.     

Electrochemical evidence of the adsorption of alkanethiols on two sites on Ag(111)

We present spectroscopic and electrochemical results consistent with the adsorption of alkanethiols on two sites and the formation of a very densely packed, stable, monolayer on Ag(111). A surface coverage of alkanethiols of 8.5 (±0.4)×10^?10 mol cm^?2 was calculated from the charge associated with the reduction of a monolayer of alkanethiols. Alkanethiol modified Ag(111) electrodes were found to have lower capacitances than the alkanethiol modified Au(111) electrodes. The lower capacitances are due to the higher surface concentration of alkanethiols on Ag(111). The very low intensity of the methylene CH stretching bands of alkanethiols with alkane chains of four to nine carbons chemisorbed on Ag(111) suggests a vertical orientation of all-trans alkane chains. No vibrational evidence of oxidation of the chemisorbed alkanethiols was found after exposure to air for up to 6 weeks. A fine structure consisting of two current peaks was observed in all cyclic voltammograms of the reduction of chemisorbed alkanethiols. This revealed that the reduction of chemisorbed alkanethiols occurs in two steps on Ag(111). Chronoamperometric measurements also support a two-step reductive desorption of alkanethiols. The high surface concentration of alkanethiols and the orientation of the alkane chains suggest that the fine structure in the voltammograms is due to the reduction of the alkanethiols from two adsorption sites.     

A comparative evaluation of ion release characteristics of three different dental varnishes containing fluoride either with CPP-ACP or bioactive glass

ObjectiveTo compare ion release characteristics of three different dental varnishes either containing CPP-ACP and fluoride (CPP-ACPF, MI Varnish GC, Japan), bioactive glass and fluoride (BGAF, Dentsply Sirona USA) or fluoride alone (NUPRO White, Dentsply Sirona USA) using fluoride-Ion Selective Electrode (F-ISE), Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES), X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), ¹⁹F and ³¹P Magic Angle Spinning-Nuclear Magnetic Resonance (MAS-NMR).MethodsA thin layer (0.0674 ± 0.0005 g) of each varnish (20 × 25 mm in area) was spread on a roughened glass slide (n = 7). They were separately immersed in 10 ml Tris buffer (0.06 M, pH = 7.30), and changed after 1, 2, 4, 6, 24 and 48 h. Fluoride-ion concentration at each time using the F-ISE, whilst calcium and phosphate release were investigated using ICP-OES. XRD, FTIR. MAS-NMR analyses were also performed before and after immersion.ResultsThe cumulative F-ion release was significantly higher in CPP-ACPF (1.113 mmol/g) > BGAF(0.638) > F(0.112) (p < 0.001). The cumulative calcium and phosphorus were higher in the CPP-ACPF (0.137 mmol/g, 0.119) than BGAF (0.067, 0.015) (p < 0.001) respectively. The XRD and ¹⁹F MAS-NMR confirmed the presence of NaF peaks in all cases before immersion. There were less prominent signal and appearance of fluorapatite crystals after immersion. ¹⁹F MAS-NMR revealed CaF₂ formation after immersion in both CPP-ACPF and BGAF. ³¹P MAS-NMR showed phosphate signals in both CPP-ACPF and BGAF before immersion. FTIR failed to show any signs of apatite formation.SignificanceBoth CPP-ACP and bioactive glass enhanced ion release without compromising the bioavailability of fluoride. The CPP-ACPF varnish had the most promising ion release.     

Degree of orientations of collagen fibers and bone apatite crystals in rat femora by infrared dichroism imaging

ObjectivesThe degree of orientations of collagen fibers and bone apatite crystals affects bone strength. We demonstrated that collagen fibers were aligned along the long axis of bone and that the degree of collagen fiber orientation changed with aging using infrared (IR) dichroism imaging. In this study, we developed a technique for evaluating bone apatite crystal orientation using IR dichroism imaging to investigate the relationships between collagen fiber and bone apatite crystal orientations.MethodsFemora were harvested from male Sprague Dawley rats of different ages (6, 12, and 33 weeks); they were then embedded in poly (methyl methacrylate) and sectioned with a microtome into 3-μm longitudinal sections. The angle-dependent Fourier transform infrared (FTIR) spectra for sections were collected using FTIR imaging, and collagen fiber and bone apatite crystal orientations in the sections were assessed using IR dichroism imaging.ResultsCollagen fibers and poorly crystalline apatite in the femoral cortical bone were longitudinally aligned; however, the stoichiometric hydroxyapatite crystal and all of the bone apatite were not aligned. The degree of poorly crystalline apatite orientation was higher in 33-week-old rats than in 6-week-old rats.ConclusionsPoorly crystalline apatite in the rat femoral cortical bone was aligned along the collagen fibers. The degree of poorly crystalline apatite orientation and collagen fiber orientation in the femoral cortical bone increased until at least 33 weeks; meanwhile, on aging, the stoichiometric hydroxyapatite crystal was not longitudinally aligned.     

Biomimetic remineralization of human dentin using promising innovative calcium-silicate hybrid “smart” materials

Introduction

The hypothesis was that experimental ion-leaching bioactive composites enhance remineralization of apatite-depleted dentin.

Materials and methods

Calcium-aluminosilicate (wTC-Ba) or fluoride-containing calcium-aluminosilicate (FTC-Ba) Portland-derived mineral powders were mixed with HTP-M methacrylate HEMA/TEGDMA/PAA-based resin to prepare experimental composites. Controls were Vitrebond and Gradia Direct LoFlo.Calcium- and fluoride-release, pH of soaking water, solubility and water uptake were evaluated in deionized water using material disks (8 mm diameter and 1.6 mm thick).The apatite-formation ability (bioactivity) and the ability to remineralize previously demineralized dentin were assessed by ESEM-EDX and FTIR after soaking in a phosphate-containing solution.Human dentin slices (0.8 mm thickness) were demineralized in EDTA 17% for 2 h, placed in close contact with the material disks and immersed in a phosphate-containing solution (Dulbecco's Phosphate Buffered Saline, DPBS) to assess the ability of the materials to remineralize apatite-depleted dentin.

Results

Only the experimental materials released calcium and basified the soaking water (released hydroxyl ions). A correlation between calcium release and solubility was observed. FTC-Ba composite released more fluoride than Vitrebond and formed calcium fluoride (fluorite) precipitates. Polyacrylate calcium complexes (between COO⁻ groups of polyacrylate and released calcium ions) formed at high pH.The formation of apatite was noticed only on the experimental materials, due to the combination of calcium ions provided by the materials and phosphate from the DPBS. Apatite deposits (spherulites showing Ca and P EDX peaks and IR bands due to phosphate stretching and bending) were detected early on the experimental material disks after only 24 h of soaking in DPBS.Only the experimental composites proved to have the ability to remineralize apatite-depleted dentin surfaces. After 7 days in DPBS, only the demineralized dentin treated with the experimental materials showed the appearance of carbonated apatite (IR bands at about 1400, 1020, 600 cm⁻¹). EDX compositional depth profile through the fractured demineralized dentin slices showed the reappearance of Ca and P peaks (remineralization of dentin surface) to 30-50 μm depth.

Conclusions

The ion-leachable experimental composites remineralized the human apatite-depleted dentin. Ion release promotes the formation of a bone-like carbonated-apatite on demineralized dentin within 7 days of immersion in DPBS.The use of bioactive “smart” composites containing reactive calcium-silicate Portland-derived mineral powder as tailored filler may be an innovative method for the biomimetic remineralization of apatite-depleted dentin surfaces and to prevent the demineralization of hypomineralized/carious dentin, with potentially great advantage in clinical applications.     

Synthesis and characterization of triethylene glycol dimethacrylate nanocapsules used in a self-healing bonding resin

Objectives

To date, the production of highly durable dentine bonding is still a challenge. Self-healing bonding resins may provide a new direction for the improvement of the bonding durability. The objective of the current study was to synthesize polyurethane nanocapsules encapsulated with the core material triethylene glycol dimethacrylate (TEGDMA) for use as a major component in a self-healing bonding resin.

Methods

TEGDMA nanocapsules were synthesized via interfacial polycondensation in a miniemulsion, and the TEGDMA nanocapsules were then characterized via Fourier-transform infrared (FTIR) spectrometer, field emission scanning electron microscopy (FESEM), and high-performance liquid chromatography (HPLC) to investigate the morphology, the average TEGDMA loading (DL%), and encapsulation efficiency (EE%). The mechanical property of dental adhesive with different concentrations (0, 3, 6, 9, and 12 wt%) of the TEGDMA nanocapsules were also measured, and the cytotoxicity was investigated using an MTT assay.

Results

FTIR confirmed that the TEGDMA nanocapsules were successfully synthesized. These nanocapsules showed a high drug load. The bond strength of the dental adhesive incorporated with 9 wt% TEGDMA nanocapsules was significantly higher compared with those of the other groups (P < 0.001). Moreover, the biocompatibility of the dental adhesive was not affected by the incorporation of the TEGDMA nanocapsules.

Conclusions

The current study demonstrated the successful synthesis of TEGDMA nanocapsules, and the overall properties of the dental adhesive were not compromised.