Standard Cavities Research Articles

Broadband ferromagnetic resonance system and methods for ultrathin magnetic films

Spintronics requires the development of magnetic thin film structures having a wide range of magnetic properties. Ferromagnetic resonance (FMR) is a well understood experimental technique that has proven to be an invaluable tool to probe the static and dynamic magnetic properties of ultrathin films, multilayer nanostructures, and superlattices. In order to achieve a full characterization of thin film materials, one needs to carry out FMR measurements at a wide range of microwave frequencies. In this paper, we show that one does not have to use a broadband vector network analyzer; similar performance can be achieved by using a broadband microwave signal generator, a coplanar waveguide, and a broadband microwave detector. To obtain a good signal to noise ratio, one needs to employ a modulation technique in order to use lock-in detection; in this paper, we use low frequency external field modulation (105Hz) and microwave power amplitude pulse modulation (10kHz). The sensitivity and the performance of this broadband microwave system is demonstrated on two types of samples: molecular beam epitaxy grown single crystal GaAs(001)/Fe/Au and sputter deposited textured Si(111)/Ta/Ru/Co/Ru superlattice structures. The samples were mounted on a coplanar waveguide, allowing one a broadband measurement, ~0.1–50GHz, of DC field swept FMR signals. The results are compared to traditional field swept, field modulated measurements in microwave cavity resonators. Despite the fact that the FMR signal can be very different from that obtained by standard microwave cavities, we show that the analysis of the FMR signal is fairly simple using an admixture of the in-phase and out-of-phase components of rf susceptibility and that the resulting fitted magnetic parameters are in excellent agreement. Additionally, we demonstrate that microwave power amplitude pulse modulation can be used to greatly speed up data collection times, especially for very weak and broad FMR signals.

Effect of smear layer on the push-out bond strength of two different compositions of white mineral trioxide aggregate.

The aim of this in vitro study was to evaluate the effect of smear layer on the push-out bond strength of white mineral trioxide aggregate (WMTA) with and without disodium hydrogen phosphate (Na2HPO4). Dentin discs with standard cavities were obtained from extracted human single-rooted teeth and divided to 4 groups (n=15) according to the irrigation regimen and the canal filling material. In groups 1 and 3, canals were irrigated with normal saline; in groups 2 and 4, irrigation method included sodium hypochlorite (NaOCl) and then ethylenediaminetetra-acetic acid (EDTA). The canals were filled with WMTA in first and second groups and with WMTA+Na2HPO4; in groups 3 and 4. The samples were wrapped in wet gauze and incubated in 37°C for 3 days. The push-out bond strength was then measured by means of the Universal Testing Machine and the failure modes were examined under stereomicroscope at 40× magnification. Tow-way ANOVA was used to evaluate the effect of material type and smear layer removal. Post hoc Tukey test was used for the two-by-two comparison of the groups. The greatest and lowest mean±standard deviation for push-out bond strength were observed in groups 4 (4.54±1.14 MPa) and 1 (1.44±0.96 MPa), respectively. The effect of removing the smear layer on the push-out bond strength of WMTA+Na2HPO4 was significant (P=0.01), but not for WMTA (P=0.52). Interestingly, there was significant difference between groups 1, 3 and 2, 4 (P<0.05). The failure mode for all experimental groups was of mixed type. Under circumstances of this in vitro study, removal of smear layer increases push-out bond strength when Na2HPO4 is added to WMTA.

Effect of two different types of fibers on the fracture resistance of endodontically treated molars restored with composite resin.

To compare the in vitro fracture resistance of endodontically treated molars with mesio-occluso-distal (MOD) cavities restored with two different types of fibers. Sixty extracted human mandibular first molars were selected for the study and randomly assigned to six groups (n = 10). Group 1 served as the control. In groups 2 through 6, endodontic access and standard MOD cavities were prepared. Following root canal treatment, group 2 was left unrestored. In group 3, the teeth were restored with composite resin (Venus, Heraeus Kulzer). In group 4, flowable composite resin (Venus, Heraeus Kulzer) was used before restoring the teeth with composite resin. In group 5, leno-woven ultrahigh molecular weight polyethylene ribbon fiber (Ribbond) was inserted in the flowable resin in a buccal to lingual direction, and the teeth were then restored with composite resin. In group 6, translucent glass fiber (Vectris, Ivoclar) was adapted over the flowable resin in the bucco-lingual direction and restored with composite resin. The specimens were stored in 100% humidity at 37°C for 1 day. Compressive loading of the teeth was performed using a universal testing machine at a crosshead speed of 0.5 mm/min. The mean load necessary to fracture the samples was recorded in Newtons (N). Data were subjected to analysis of variance (ANOVA) and Duncan's post-hoc test, where significance was set at p < 0.001. The highest and the lowest mean fracture strengths were found in sound teeth (1598.8 N) and unrestored teeth (393.7 N), respectively. The mean load necessary to fracture the samples was 958.6 N in the polyethylene ribbon group (group 5), 913.2 N in the glass-fiber group (group 6), 699.7 N in teeth restored with flowable resin and composite (group 4), and 729.3 N in group 3 with composite resin alone. Statistical analysis showed significantly higher fracture resistance of both the fiber groups compared to composite resin alone (p < 0.001). Both polyethylene ribbon and glass fiber under MOD composite restorations significantly increased fracture strength with no statistical difference between the two groups. Therefore, both polyethylene- and glassfiber- reinforced composites can be used for access cavity restorations in teeth with weakened cusps.

An in vitro comparison of root canal length determination by DentaPort ZX and iPex apex locators.

Aim:The aim of the present study is to evaluate and to compare the accuracy of two electronic apex locators (EALs): DentaPort ZX and iPex, at a position 0.5 mm short of the apical foramen.Materials and Methods:Thirty single-rooted, mandibular premolar teeth were selected. Standard access cavities were prepared and the actual length (AL) was calculated. The samples were then embedded in alginate and the electronic measurements were determined and recorded.Results:The results obtained showed that in determining the root canal length with a tolerance level of ±0.5 mm, i.e., AL ± 0.5 mm, DentaPort ZX was accurate in 93.3% of the samples and iPex was accurate in 90% of the samples at a position 0.5 mm short of the apical foramen.Conclusion:A strong correlation was seen between the two electronic methods and AL and also in between the two EALs, showing the possibility of their use to measure the root canal length. No statistically significant difference was found between both the apex locators.

W-band orientation selective DEER measurements on a Gd3+/nitroxide mixed-labeled protein dimer with a dual mode cavity

Double electron–electron resonance (DEER) at W-band (95GHz) was applied to measure the distance between a pair of nitroxide and Gd3+ chelate spin labels, about 6nm apart, in a homodimer of the protein ERp29. While high-field DEER measurements on systems with such mixed labels can be highly attractive in terms of sensitivity and the potential to access long distances, a major difficulty arises from the large frequency spacing (about 700MHz) between the narrow, intense signal of the Gd3+ central transition and the nitroxide signal. This is particularly problematic when using standard single-mode cavities. Here we show that a novel dual-mode cavity that matches this large frequency separation dramatically increases the sensitivity of DEER measurements, allowing evolution times as long as 12μs in a protein. This opens the possibility of accessing distances of 8nm and longer. In addition, orientation selection can be resolved and analyzed, thus providing additional structural information. In the case of W-band DEER on a Gd3+–nitroxide pair, only two angles and their distributions have to be determined, which is a much simpler problem to solve than the five angles and their distributions associated with two nitroxide spin labels.

Influence of cervical preflaring on determination of apical file size in the palatal roots of maxillary molars

PURPOSE: The aim of this study was to investigate the influence of cervical preflaring in determining the initial apical file (IAF) in the palatal roots of maxillary molars, and to determine the morphologic shape of the canal 1 mm short of the apex. METHODS: After preparing standard access cavities the group 1 received the IAF without cervical preflaring (WCP). In groups 2 to 5, preflaring was performed with Gates-Glidden (GG), Anatomic Endodontics Technology (AET), GT Rotary Files (GT) and LA Axxes (LA), respectively. Each canal was sized using manual K-files, starting with size 08 files, and making passive movements until the WL was reached. File sizes were increased until a binding sensation was felt at the WL. The IAF area and the area of the root canal were measured to verify the percentage occupied by the IAF inside the canal in each sample by SEM. The morphologic shape of the root canal was classified as circular, oval or flattened. Statistical analysis was performed by ANOVA/Tukey test (P GT=AET>GG>WCP. The morphologic shape was predominantly oval. CONCLUSION: The type of cervical preflaring used interferes in the determination of IAF.

Influence of several fibre‐reinforced composite restoration techniques on cusp movement and fracture strength of molar teeth

To compare mean cusp movement in molar teeth with endodontic access and mesial-occlusal-distal (MOD) cavities before and after restoration with several fibre-reinforced composite restoration techniques under loading and to evaluate the effect of restoration technique on fracture strength. Reference points were marked at the mesial cusp ridges of extracted human mandibular molar teeth. Digital images were taken under loading (300 N) using a stereomicroscope (Leica MZ16A; Wetzlar, Germany). Three-dimensional (3D) distances between the reference points were recorded (Leica, Stereo-Explorer, 2.1) as controls. Standard MOD cavities were prepared and restored as follows (n = 10), group 1: composite restoration (Clearfil AP-X; Kuraray, Tokyo, Japan); group 2: cavity lined with polyethylene fibre (Ribbond, Ribbond Inc., Seattle, WA, USA) in combination with flowable resin (Protect-Liner F; Kuraray, Tokyo, Japan) before composite restoration; group 3: polyethylene fibre inserted on occlusal surface of the tooth from buccal to lingual after finishing the composite restoration; group 4: missing walls were restored with composite resin and inner surfaces of the axial walls were then reinforced with polyethylene fibre placed circumferentially before the composite restoration. The restored teeth were re-loaded, digital images were re-taken and the 3D distance between the reference points was recorded in μm. Comparisons of the restoration techniques, the effectiveness of restoration for each group were analysed statistically (Kruskall-Wallis, paired-samples t-test). The teeth were then loaded until failure (5 mm min(-1) ), the data were recorded (N) and analysed statistically (Kruskall-Wallis test). A significant difference occurred amongst the groups in terms of cusp movement (P = 0.018). All the groups revealed a decrease in inter-cuspal width when compared to their initial records. The mean values of these decreases were as follows: group 1 17.6 (P = 0.003), group 2 6.7 (not sig), group 3 6.6 (not sig) and group 4 0.85 (not sig) μm. No significant difference was found amongst the fracture strength values (P = 0.22). In group 1, 90% of the fractures were non-restorable, whereas in group 3 100% of the fractures were restorable. Regardless of restoration technique, fibre reinforcement of composite restorations decreased cusp movement in molar teeth with MOD and endodontic access cavities but did not affect fracture strength.

Formulation of Percolating Thermal Underfill by Sequential Convective Gap Filling

In 3D chip stacks, heat dissipation through wiring layers and the bonding interface contributes to the total temperature gradient. The effective thermal impedance of micro solder-ball arrays filled with a poorly-conducting silica underfill can be as high as 30 K*mm2/W, three times the value of a thermal grease interface. Efforts to improve the underfill conductivity to 5 W/(m*K) are underway, which would translate into in a significant interface-resistance reduction. To achieve thermal conductivities &amp;gt;1 W/(m*K), alumina particles were introduced in capillary underfills at particle loadings above the percolation threshold, but at these loading levels the high viscosity of the resulting underfill no longer permits capillary filling. We propose a novel sequential gap-filling method. Particles are suspended in a carrier fluid at a low concentration (0.1 vol%). Using forced convection, the suspension is injected into the cavity formed between the IC dies by the C4 array. A filter element at the cavity outlet triggers particle accumulation in the cavity. The particles form a percolation network with an effective thermal conductivity of &amp;gt;1 W/(m*K). Next an evaporation step removes the carrier fluid, and the exposed pores between the particles are refilled with a particle-free adhesive using capillary forces. Finally, the matrix is cured at 65 °C. 10x10 mm2 standard and micro-C4 cavities (&amp;gt;30 μm) can be completely filled in 2 min at 0.2 bar, resulting in a homogeneous volumetric fill of 36%. Percolation was identified by SEM inspection. For the micro-C4 arrays filler particles of &amp;lt; 10 μm were used. Uniform particle filling is precluded because of the longer filling time due to the small pore sizes. Particle trapping sites are introduced to form local stacks that provide an additional drainage network to guarantee acceptable filling times. Effective thermal-conductivity values of the percolating thermal underfill method proposed here are reported.

Simulation and experimental analysis of large area substrate overmolding with epoxy molding compounds

This paper presents new experimental and numerical methods to characterize the transfer overmolding of substrates with epoxy polymer. We investigated Multi Chip Modules on ceramic panels as well as on printed circuit boards encapsulated as a Mold Array Package (MAP). Experiments show that the polymer flow during the overmolding process depends significantly on the mold height: While standard MAP-type mold cavities are filled homogeneously and symmetrically in most cases, low cavity heights (<500 μm) can cause the flow front to concentrate on a few flow paths (flow front fingering). We developed a numerical method to describe this inhomogeneous polymer flow. The reason for flow front fingering seems to be local variations of polymer viscosity which enforces a necking on distinct flow paths. Fingering can cause the formation of air traps and excessive wire sweep. We also developed new experimental methods to measure the pressure distribution within cavities: our sensor is based on commercially available, passive pressure sensitive films from FUJUFILM and is operational at temperatures up to 180°.

High-frequency EPR applications of open nonradiative resonators

A new class of open single-mode cavities, the nonradiative (NR) resonators, has recently been proposed in order to overcome the limitations of standard cylindrical cavities and Fabry-Perot resonators at millimeter wavelengths. This paper presents the first applications of a NR resonator in W-band pulsed electron paramagnetic resonance spectroscopy. It consists of a cylindrical cavity having a lateral aperture that represents about 35% of its total height. Electron-spin-echo measurements performed on different samples show that the signal-to-noise ratio and the optimal pulse length obtained with the proposed device are comparable to those obtained with the closed cavity used in the commercial W-band spectrometer, at both cryogenic and room temperature. Similar results have been obtained for paramagnetic species optically activated by means of an optical fiber inserted in the aperture of the resonator. The insertion losses estimated for the probe employed with the NR resonator are higher than those of the commercial probe, hence, demonstrating that the proposed cavity holds the promise of improved resonator performance.

A New Concept of Open ${\rm TE}_{011}$ Cavity

The confinement properties of the open structure formed crossing a circular waveguide perpendicular to a parallel-plate waveguide are discussed, highlighting the fundamental differences with respect to the common high-frequency resonators. The structure supports a TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">011</sub> mode that appears suited for millimeter- and submillimeter-wave applications. The experimental characterization of this mode in a configuration resonating at 281 GHz is described in detail. The observed resonance exhibits state-of-the-art performances. The properties of the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">011</sub> mode are studied in terms of the geometry, calculating the mode chart and the related quality factor and power-to-field conversion efficiency. The mode chart is then determined for configurations including a sample holder, where one of the waveguides is filled with a low-loss dielectric material. In addition to excellent merit figures, the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">011</sub> mode shows a relevant stability with respect to the geometrical imperfections and to the insertion of a sample holder. The obtained results demonstrate that the proposed single-mode resonator competes with the standard cavities in terms of performances, versatility, and simplicity.

Comparative investigation of diode pumping for continuous-wave and mode-locked Cr^3+:LiCAF lasers

Cr3+ doped colquiriites are promising solid-state gain media for developing inexpensive and highly efficient tunable continuous-wave (cw) and femtosecond lasers. Among Cr3+ doped colquiriites, Cr3+:LiCAF has superior thermal properties enabling high-power operation with standard laser cavities. In this study we present detailed laser experiments with Cr3+:LiCAF, which achieve laser performance approaching that of the much more expensive Ti:sapphire laser technology. Inexpensive, new, multimode (~1.5 W) and single-mode (~150 mW) diode lasers were used as pump sources. With multimode diode pumping, cw output powers exceeding 1 W and mode-locked pulse energies as high as 2.8 nJ were obtained. Using single-mode diode pumping, up to 280 mW of cw output power with 54% slope efficiency and continuous tuning between 765 and 865 nm were demonstrated. In cw mode-locking, 72 fs, 1.4 nJ pulses were obtained, and an electrical-to-optical conversion efficiency of 7.8% was demonstrated.

Assembly of two novel Lindqvist polyoxoanion-templated coordination polymers with standard honeycomb cavities

Two novel polyoxometalate(POM)-templated coordination polymers: [Cu 2(phnz) 3][M 6O 19] (M = Mo for 1, W for 2; phnz = phenazine), have been hydrothermally synthesized and characterized by routine physical methods and single crystal X-ray diffraction. In the compounds, Lindqvist POMs as templates induce the [Cu 2(phnz) 3] complexes to 2D hexagonal metal-organic framework (MOF), which represents 6 3 topologies of dimensions ca. 13.515 × 13.515 × 13.515 Å. Furthermore, the 2D sheets are held together by Lindqvist POMs into 3D supramolecular networks with 1D channel, and Lindqvist POMs site in the channels. The successful syntheses and isolation of two compounds provide a novel example of the utility of POM clusters as templates for self-assembly extended framework with cavities.

Evaluation of the risk of a stripping perforation with gates-glidden drills: serial versus crown-down sequences

The aim of this study was to evaluate the remaining dentine/cementum thickness using Gates-Glidden burs in serial and crown-down sequences and to observe which of the two sequences is the safest for preparing mesial roots of molars. Thirty-six left and right human mandibular first molars were selected. Standard access cavities were made and initially explored with Flexofiles sizes 10 and 15 until the tip was visible at the apex. The teeth were embedded in a muffle specially developed for this study using a PVC tube with two parallel metal rods in its lid. Each tooth-block was sectioned 3 mm apically to the furcation using a low-speed saw with a diamond disc. The tooth-block was examined under a microscope and an initial image was captured by a digital video system with 8 X and 12 X magnifications. Finally, the tooth-blocks were reassembled in the muffle so that the canals could be instrumented. After instrumentation the area of each mesial canal as well as the smallest distance to the root furcation were measured again. The mesio-buccal canals (crown-down order) and the mesio-lingual canals (serial sequence) presented an average area of 0.46 +/- 0.16 mm(2) and 0.88 +/- 0.27 mm(2) (P < 0.01), respectively. The mean values of the smallest distance to the furcation for the mesio-buccal and mesio-lingual canals were 0.66 +/- 0.19 mm and 0.39 +/- 0.13 mm (P < 0.01), respectively. The remaining dentine/cementum thickness using Gates-Glidden burs was greater in the crown-down sequence than in the serial sequence.

Effect of temporary filling materials on repair bond strengths of composite resins

Endodontic access cavities sometimes can be prepared through a permanent composite restoration. Between the appointments, temporary cements are used to seal access cavities and may have negative effect on bonding of further composite restoration. The purpose of this study was to compare shear bond strength of composite to composite which had been in contact with various temporary filling materials. Standard cavities were prepared on 160 acrylic resin blocks, obturated with composite resin (Clearfil AP-X, Kuraray, Japan) and randomly divided into eight groups (n = 20). Group 1 received no treatment. From group 2-8, composite surfaces were covered with the following cements temporarily: Zinc-oxide/calcium-sulphate (Cavit-G, ESPE, Germany), two different Zinc-Oxide-Eugenol materials (ZnOE, Cavex, Holland and IRM, Dentsply, USA), Zinc-phosphate cement (Adhesor, Spofa-Dental, Germany), Zinc-polycarboxylate cement (Adhesor-Carbofine, Spofa-Dental, Germany), Glass-Ionomer-Cement (Argion-Molar, Voco, Germany), or light curing temporary material (Clip, Voco, Germany). The cements were removed mechanically after 1 week storage in distilled water at 37 degrees C and composite surfaces were treated with a self-etch adhesive system (SE-Bond, Kuraray, Japan). Composite resin build-ups were created on composite surfaces. Shear bond strength values were measured using universal testing machine at crosshead speed of 1 mm/min. The data was calculated in MPa and statistically analyzed using one-way ANOVA and Tukey tests. Eugenol-containing cements significantly reduced shear bond strengths of composite to composite (p < 0.05), while the other temporary materials had no adverse effect on shear bond strength (p > 0.05). These findings suggested that temporary filling materials except eugenol-containing materials have no negative effect on composite repair bond strengths.

Streptococcus mutans-induced secondary caries adjacent to glass ionomer cement, composite resin and amalgam restorations in vitro

The aim of this study was to define, in vitro, the potential to inhibit secondary caries of restorative materials currently used in dental practice. Standard cavities were prepared on the buccal and lingual surfaces of fifty extracted human third molars. The teeth were randomly divided into five groups, each one restored with one of the following materials: glass ionomer cement (GIC); amalgam; light-cured composite resin; ion-releasing composite; and light-cured, fluoride-containing composite resin. The teeth were thermocycled, sterilized with gamma irradiation, exposed to a cariogenic challenge using a bacterial system using Streptococcus mutans, and then prepared for microscopic observation. The following parameters were measured in each lesion formed: extension, depth, and caries inhibition area. The outer lesions developed showed an intact surface layer and had a rectangular shape. Wall lesions were not observed inside the cavities. After Analysis of Variance and Component of Variance Models Analysis, it was observed that the GIC group had the smallest lesions and the greatest number of caries inhibition areas. The lesions developed around Amalgam and Ariston pHc restorations had an intermediate size and the largest lesions were observed around Z-100 and Heliomolar restorations. It may be concluded that the restorative materials GIC, amalgam and ion-releasing composites may reduce secondary caries formation.

Comparison of microleakages of photo-cured composites using three different light sources: halogen lamp, LED and argon laser: an in vitro study

In this study, we compared the microleakage of composite fillings cured with halogen bulb, LED and argon ion laser (488 nm). Twenty-four extracted human molars were divided randomly in three groups. Six cavities were prepared on the coronal part of each tooth. Standard cavities (1.7 x 2 mm) were prepared. Cavities were acid etched, sealed with Scotch Bond 1 and filled by a hybrid composite. Cavities were exposed to one light source, thermocycled and immersed in a 2% methylene blue dye solution. Dye penetration in the leakage of cavities was recorded using a digital optical microscope. Mean values of percentage of dye penetrations in microleakages of cavities were 49.303 +/- 5.178% for cavities cured with LED, 44.486 +/- 6.075% with halogen bulb and 36.647 +/- 5.936% for those cured by argon laser. Statistically significant difference exists between cavities cured by halogen vs LED (P < 0.01), halogen vs laser (P < 0.001) and LED vs laser (P < 0.001). The lowest microleakage was observed in the cavities and composites cured with argon ion laser.

Influence of cervical preflaring on apical file size determination in maxillary lateral incisors

The purpose of this study was to investigate the influence of cervical preflaring on determination of the initial apical file in maxillary lateral incisors. Forty human lateral incisors with complete root formation were used. After standard access cavities, a size 06 K-file was inserted into each canal until the apical foramen was reached. The WL (WL) was set 1 mm short of the apical foramen. Four groups (n=10) were formed at random, according to the type of cervical preflaring performed. Group 1 received the initial apical instrument without previous preflaring of the cervical and middle root canal thirds. Group 2 had the cervical and middle root canal thirds enlarged with nickel-titanium Orifice Opener instruments. Group 3 had the cervical and middle root canal thirds enlarged with Gates-Glidden drills. Titanium-nitrite treated, stainless steel LA Axxess burs were used for preflaring the cervical and middle root canal thirds of group 4. Each canal was sized using manual K-files, starting with size 08 files with passive movements until the WL was reached. File sizes were increased until a binding sensation was felt at the WL, and the instrument size was recorded for each tooth. The apical region was then observed under a stereoscopic magnifier, images were recorded digitally and the differences between root canal and maximum file diameters were recorded (in mm) for each sample. Significant differences were found between the groups regarding the anatomical diameter at the WL and the first file to bind the canal (p = 0.01). The major discrepancy was found when no preflaring was performed (0.1882 mm average). Canals preflared with Orifice Opener instruments (0.0485 mm average) and Gates-Glidden drills (0.1074 mm average) also showed great discrepancy. The LA Axxess burs produced the smallest differences between anatomical diameter and first file to bind (0.0119 mm average). Instrument binding technique for determining anatomical diameter at WL was not accurate. Preflaring of the cervical and middle thirds of the root canal improved anatomical diameter determination; the instrument used for preflaring played a major role on determination of the anatomical diameter at the WL. Canals preflared with LA Axxess burs created a more accurate relationship between file size and anatomical diameter.

Evaluation of dentin permeability after light activated internal dental bleaching

The aim of this in vitro study was to assess quantitatively the dentin permeability of human teeth after intracoronal bleaching therapy with 35% hydrogen peroxide activated by LEDs, halogen lamp or using the walking bleach technique. Forty human maxillary central incisors had standard access cavities performed and the cervical thirds of the canals were prepared with Gates-Glidden drills up to a size 130. Roots were resected between the coronal and middle thirds and the apical portions were discarded. A glass ionomer, 2 mm thick cervical plug was placed inside the canal, at the cement-enamel junction level. Group I received 35% hydrogen peroxide gel activated by LEDs. Group II was submitted to 35% hydrogen peroxide gel activated by halogen lamp. Group III received 35% hydrogen peroxide gel and the walking bleach technique was followed. Group IV (control) received a dry cotton pellet inside the pulp chamber with temporary restoration. Dentinal permeability was quantified by copper ion penetration. Linear measurements were obtained by analysis of digital images under x 5 magnification. Mean values and SD for the experimental groups were: I, 7.1% (+/-3.2%); II, 8.4% (+/-3.0%); III, 9.1% (+/-3.0%); IV, 1.3% (+/-2.8%). One-way ANOVA was used to analyze the results. Results showed an increase of permeability values for groups I, II and III when compared to group IV (control); however, no statistical differences were found between the three tested bleaching techniques. It can be concluded that 35% hydrogen peroxide activated by LED, halogen lamp or used following the walking bleach technique produced similar increase in dentinal permeability.

Properties of trapped electromagnetic modes in coupled waveguides

The existence of trapped modes in coupled electromagnetic waveguides is experimentally investigated for configurations with different degrees of symmetry supporting hybrid modes. The occurrence of confined solutions in such open geometries is proven to be much more general than demonstrated so far, as predicted by Goldstone and Jaffe [J. Goldstone and R. L. Jaffe, Phys. Rev. B 45, 14100 (1992)]. The identification of the observed modes is based on the numerical modeling of the relative vector fields. The experimental results make evident that an increasing aperture of the configuration can improve the confinement of the mode instead of generating additional leakage channels. In particular, long-lived trapped modes can be easily obtained in geometries with a large aperture. Their resonance parameters can compete with those of standard close cavities working at millimeter wavelengths. The role of the symmetry on the properties of these trapped modes is discussed in detail.