Critical Sensing Modalities for Hydrogen: Technical Needs and Status of the Field to Support a Changing Energy Landscape.

Decarbonization of the energy system is a key aspect of the energy transition. Energy storage in the form of chemical bonds has long been viewed as an optimal scheme for energy conversion. With advances in systems engineering, hydrogen has the potential to become a low cost, low emission, energy carrier. However, hydrogen is difficult to contain, it exhibits a low flammability limit (>40000 ppm or 4%), low ignition energy (0.02 mJ), and it is a short-lived climate forcer. Beyond commercially available sensors to ensure safety through spot checks in enclosed environments, new sensors are necessary to support the development of low emission infrastructure for production, transmission, storage, and end use. Efficient scalable broad area hydrogen monitoring motivates lowering the detection limit below that (10 ppm) of best in class commercial technologies. In this perspective, we evaluate recent advances in hydrogen gas sensing to highlight technologies that may find broad utility in the hydrogen sector. It is clear in the near term that a sensor technology suite is required to meet the variable constraints (e.g., power, size/weight, connectivity, cost) that characterize the breadth of the application space, ranging from industrial complexes to remote pipelines. This perspective is not intended to be another standard hydrogen sensor review, but rather provide a critical evaluation of technologies with detection limits preferably below 1 ppm and low power requirements. Given projections for rapid market growth, promising techniques will also be amenable to rapid development in technical readiness for commercial deployment. As such, methods that do not meet these requirements will not be considered in depth.

Effect of bleaching treatments on microleakage of Class I restorations.

OBJECTIVE: To test the effect of bleaching agents on microleakage of composite restorations. METHODS: Sixty extracted human molar class I cavities were restored using Scotchbond 1 and Filtek Z250 composite according to the manufacturer's instructions. The teeth were randomly divided into four groups (n = 15 each). Group 1 was the control group, which was not bleached. Group 2 had a once-daily bleaching treatment with 20% carbamide peroxide gel for eight hours. Group 3 had a bleaching of 6% H2O2 for 30 minutes twice a day. Group 4 had a bleaching treatment once per day with 19% percarbonate gel for eight hours. The bleaching was carried out at 37 degrees C for 14 days. Nail varnish was applied on the apical portion of the teeth only, and the specimens were immersed in a 0.1% rhodamin-B-isothiocyanate for 24 hours at 37 degrees C. After thorough rinsing with tap water, the specimens were embedded in self-curing methacrylate resin. The blocks were sectioned with a water-cooled microtome saw into three to five slices. The cuts were positioned centrally through the restorations and approximately parallel to the long axis of the tooth in the mesiodistal direction. Microleakage was evaluated at the occlusal margins of the class I restorations using a stereo microscope. RESULTS: Microleakage occurred in all groups. The percentage of sections showing leakage was 20% (Group 1), 11% (Group 2), 15% (Group 3), and 18% (Group 4). The statistical evaluation (Kruskal-Wallis test) showed no significant difference between groups (p = 0.537). CONCLUSION: Bleaching with the materials tested has no influence on microleakage of Filtek composite bonded with Scotchbond I.

Influence of the rubber dam on proximal contact strengths.

PURPOSE: The study tested the hypothesis that the application of a rubber dam influences the reconstruction of proximal contact strengths, while the corresponding contra-lateral teeth are not affected. METHODS: Seventy-four systemically and periodontally healthy subjects in need of a direct posterior composite restoration were treated with the use of a rubber dam. The proximal contact strengths (PCS) were electronically evaluated by measuring frictional forces during removal of a 50.0 +/- 5.0 microm-thick straight metal band. RESULTS: Proximal contact strengths significantly increased from 2.26 +/- 1.45N before to 3.83 +/- 2.34N after application of the rubber dam; whereas, the variation of PCS at the corresponding contacts in the contra-lateral quadrant remained within the intra-examiner variance of +/- 0.2N. Upon removal of the rubber dam, there was a statistically significantly drop in PCS from 3.54 +/- 1.87N to 2.31 +/- 1.35N. Again, there was only minimal change in the contra-lateral quadrant. It was concluded that application of the rubber dam affects proximal contact strengths.

Resin penetration through submicrometer hiatus structures: a SEM and CLSM study.

The purpose of this study was to confirm the existence of submicrometer hiatus structures and to examine the degree of resin penetration through these formations. Dentin disks 2.0 mm in thickness were sectioned from 48 human molars with the use of a microtome saw. Three different fifth-generation (total-etch, combined primer/resin) dentin adhesive systems were used to bond a light-cured, resin-based composite to the dentin disks (n = 16 each group). Bonded disks from the three groups were then sectioned. Half of each group was examined with the use of a scanning electron microscope (SEM) (n = 8), and the other half with the use of a confocal laser scanning microscope (CLSM) (n = 8). The frequency of submicrometer hiatus formation was recorded and documented with associated imaging techniques. Resin penetration within submicrometer hiati were observed in 41.7% (10/24) of SEM specimens and 83.3% (20/24) of CLSM specimens. The location and size of these structures were found to be quite uniform. Submicrometer hiati approximated 200 microm in each of the three dentin bonding systems examined. Resin penetration through submicrometer hiati does not appear to be an artifact of desiccation. These structures were clearly identified within the hybrid layer of each dentin adhesive system used in this study.

Effect of cavity preparation instruments (oscillating or rotating) on the composite-dentin interface in primary teeth.

OBJECTIVES: To evaluate the effect of preparation of instruments on the interfacial integrity between cavity wall and composite restoration. METHODS: Two class II slot preparations were done in 10 primary teeth either with SonicSys or with a conventional bur. The cavities were filled using an adhesive system. One layer of a flowable composite and one layer of a condensable composite were applied. The specimens were analyzed by confocal laser scanning microscopy. RESULTS: In the SonicSys group the mean thickness of the hybrid layer was 6.12 (0.60) microm; in the control group it was 6.04 (0.63) microm. The difference was not statistically significant. Two fractures were observed in one tooth of each group. These were located only in the enamel. The cavity margins were beveled in all specimens. SIGNIFICANCE: Compared to conventional preparations, cavity preparation with SonicSys has no deleterious effect on the integrity of the interface.

The nanoleakage phenomenon: influence of moist vs dry bonding.

PURPOSE: To assess the degree of nanoleakage of Class V preparations restored with three bonding agents using wet and dry bonding. MATERIALS AND METHODS: Standardized Class V cavities were prepared in 66 human molars with cervical margins located in dentin. The composite was placed using one of three different dentin bonding agents with a moist or dry bonding technique (n = 11 per group). The teeth were stored in a 1% rhodamin-B solution for 24 h at 20 degrees C, then rinsed with water, embedded in methacrylate, and sectioned parallel to the long axis of the tooth, separating the restorations into two parts. A confocal laser scanning microscope (CLSM) was used to visualize the layer 10 microm under the prepared surface of the section. The lengths of the dye-penetrated pathways were measured, representing the amount of nanoleakage. RESULTS: Differences in nanoleakage between the tested materials were proven to be statistically significant. The effect of drying had a significant influence on both the acetone-based and the ethanol-based material, but not on the water-based bonding resin. CONCLUSION: Dentin drying may have an influence on nanoleakage, depending upon the nature of the individual bonding agent.

An in vitro investigation to optimize the quality of compomer-based fissure sealants.

PURPOSE: To evaluate if the in vitro quality of preventive fissure sealants made with compomer-based materials can be improved by modifying the method of application. METHODS: Delton resin-based sealant, Dyract Flow and Dyract Seal compomers were used. The manufacturer's instructions were modified by prolonging the application time of the materials used and by applying the sealer in two layers. Extracted caries-free human molars were fissure sealed under standardized conditions and then exposed to a thermocycling procedure and a dye penetration test. Following the preparation of ground slices the samples were assessed by means of a light microscope and a scanning electron microscope. Statistical analysis of the results was done using a chi-square test. RESULTS: The modified application of the two-compomer-based fissure sealers improved distinctly the quality of such fissure sealants. This was observed with respect to the criteria sealing ability, absence of pores in the sealant and complete filling of the fissure in wide as well as in narrow fissures. Compomer-based fissure sealants applied with the modified technique were equal to conventional resin-based composite fissure sealants regarding sealing ability and complete filling of the fissure. With respect to absence of pores, compomer-based sealants were superior to resin-based composite sealants.

Cleaning efficacy of a manual toothbrush with tapered filaments.

PURPOSE: To compare the cleaning efficacy of (A): a newly developed manual toothbrush with tapered filaments (meridol, GABA International, CH-Münchenstein) with (B): a standard flat trim manual toothbrush (ADA reference toothbrush) in vivo. MATERIALS AND METHODS: 87 healthy participants took part in this study. Subjects were asked to abstain from all oral hygiene procedures for 48 hours. After plaque was scored (Turesky modification of the Quigley Hein Index), the subjects brushed their teeth under supervision with the two manual toothbrushes according to a split-mouth design. In total, a cleaning time of two minutes was given for the whole procedure with an alert after every 30 seconds. Immediately after brushing, plaque was scored again by the same investigator, who was blind with respect to the toothbrush used. RESULTS: Using the non-parametric Wilcoxon test for paired samples (p<0.05) the overall plaque scores were reduced for (A) from 1.95+/-0.48 to 1.02+/-0.41 (p<0.001), and (B) from 1.93+/-0.52 to 1.09+/-0.44 (p<0.001). At proximal surfaces the plaque scores were reduced (A) from 2.02+/-0.49 to 1.11+/-0.43 (p<0.001) and (B) from 2.01+/-0.52 to 1.20+/-0.45 (p<0.001). The relative plaque reductions overall were (A) 47.4+/-18.0% and (B) 44.1+/-15.6% (p=0.039), at proximal surfaces (A) 44.2+/-18.8% and (B) 40.5+/-15.9% (p=0.015), and at lingual surfaces (A) 30.6+/-28.1% and (B) 24.0+/-27.1% (p=0.016). CONCLUSION: Both brushes removed a significant amount of plaque. Overall and in areas difficult to reach, the meridol toothbrush was superior to the ADA reference brush.

Relationship between microtensile bond strength and submicron hiatus at the composite-dentin interface using CLSM visualization technique.

OBJECTIVES: "Submicron hiatus" represents a potential space between the base of the collagenous network and the mineralized dentin when it is acid etched for bonding. This study evaluated the relationship between microtensile bond strength (microTBS) and occurrence of submicron hiatus formations at the resin-dentin interface using the same specimens. METHODS: Resin-dentin bonded micro-specimens (sticks with a size of 300 microm x 300 microm x 8mm) were prepared using one of two material combinations (group I: Syntac Classic/Tetric Ceram Cavifil: n=51 group II: Prime & Bond NT/Tetric Ceram Cavifil: n=56). After labeling the primer component with a tiny amount of rhodamine-B-isothiocyanate, submicron hiatus formations were imaged nondestructively using a confocal laser scanning microscope (CLSM). Subsequently specimens were subjected to a microTBS test. RESULTS: For the influence of submicron hiatus formations on microTBS with the Syntac Classic group, the nonparametric Spearman's correlation was -0.329 at p=0.02. For the Prime & Bond NT group, the nonparametric Spearman's correlation was -0.356 at p=0.007. Analyzing the effect of submicron hiatus on without discriminating by group resulted in a Spearman's correlation coefficient of -0.341 at p=0.001; microTBS and quality of hybrid layer showed a correlation coefficient of 0.849 at p=0.001, and microTBS and quality of tag formation showed a correlation coefficient of 0.474 at p=0.001. SIGNIFICANCE: The degree of submicron hiatus formations had an influence on microtensile bond strength for both the Syntac Classic and the Prime & Bond NT group.

Relationship between microtensile bond strength and nanoleakage at the composite-dentin interface.

OBJECTIVES: This study evaluated the relationship between microtensile bond strength (microTBS) and occurrence of nanoleakage at the resin-dentin interface using the same specimens. METHODS: Resin-dentin-bonded micro-specimens (sticks with a size of 300 microm x 300 microm x 8mm) were prepared using one of two material combinations (group I: Syntac classic/Tetric Ceram Cavifil: n=57; group II: Prime & Bond NT/Spectrum TPH: n=52). After immersion of the micro-specimens in 0.1% rhodamine-B solution for 1h, nanoleakage was imaged nondestructively using a confocal laser scanning microscope (CLSM). Then the specimens were subjected to a microTBS test. RESULTS: For the influence of nanoleakage on microTBS with the Syntac classic/Tetric Ceram Cavifil group, the nonparametric Spearman correlation was 0.033 at p=0.805. For the Prime & Bond NT/Spectrum TPH group, the nonparametric Spearman correlation was 0.077 at p=0.584. SIGNIFICANCE: The degree of nanoleakage had no influence on microtensile bond strength for the Syntac classic/Tetric Ceram Cavifil or for the Prime & Bond NT/Spectrum TPH group.

Surface characteristics of dentin experimentally exposed to hydrofluoric acid.

The purpose of this study was to test the effect of hydrofluoric acid (HF) on the surface characteristics of dentin in vitro. Dentin was exposed in 50 human molars and divided into five groups according to different etching schedules: (i) no etching, (ii) 15 s HF, (iii) 15 s H3PO4, (iv) 15 s HF and 15 s H3PO4, (v) 15 s H3PO4 and 15 s HF. Teeth were examined under a scanning electron microscope equipped with energy-dispersive X-ray (EDX) or two layers of fluorescence-labeled primer followed by the composite were applied, and the teeth were sectioned and examined using confocal laser scanning microscopy (CLSM). With scanning electron microscopy, no openings of dentinal tubules were found in groups (i), (ii), and (iv). In group (v) only a few tubules were opened and in group (iii) the smear layer was completely removed and tubules appeared open. The EDX analysis revealed that fluoride was incorporated into the dentin surface when HF was used. With CLSM, distinct hybrid layers could be detected only in group (iii). In group (v) the hybrid layer appeared less established compared with group (iii). No dentin hybridization was found in groups (i), (ii), and (iv). It is concluded that HF has the ability to close the openings of dentin tubules which were opened due to etching by phosphoric acid and cannot dissolve the smear layer.