Microglial TLR4 Mediates White Matter Injury in a Combined Model of Diesel Exhaust Exposure and Cerebral Hypoperfusion.

BACKGROUND: Air pollution particulate matter exposure and chronic cerebral hypoperfusion (CCH) contribute to white matter toxicity through shared mechanisms of neuroinflammation, oxidative stress, and myelin breakdown. Prior studies showed that exposure of mice to joint particulate matter and CCH caused supra-additive injury to corpus callosum white matter. This study examines the role of TLR4 (toll-like receptor 4) signaling in mediating neurotoxicity and myelin damage observed in joint particulate matter and CCH exposures. METHODS: Experiments utilized a novel murine model of inducible monocyte/microglia-specific TLR4 knockout (i-mTLR4-ko). Bilateral carotid artery stenosis (BCAS) was induced surgically to model CCH. TLR4-intact (control) and i-mTLR4-ko mice were exposed to 8 weeks of either aerosolized diesel exhaust particulate (DEP) or filtered air (FA) in 8 experimental groups: (1) control/FA (n=10), (2) control/DEP (n=10), (3) control/FA+BCAS (n=9), (4) control/DEP+BCAS (n=10), (5) i-mTLR4-ko/FA (n=9), (6) i-mTLR4-ko/DEP (n=8), (7) i-mTLR4-ko/FA+BCAS (n=8), and (8) i-mTLR4-ko/DEP+BCAS (n=10). Corpus callosum levels of 4-hydroxynonenal, 8-Oxo-2'-deoxyguanosine, Iba-1 (ionized calcium-binding adapter molecule 1), and dMBP (degraded myelin basic protein) were assayed via immunofluorescence to measure oxidative stress, neuroinflammation, and myelin breakdown, respectively. RESULTS: Compared with control/FA mice, control/DEP+BCAS mice exhibited increased dMBP (41%; P<0.01), Iba-1 (51%; P<0.0001), 4-hydroxynonenal (100%; P<0.0001), and 8-Oxo-2'-deoxyguanosine (65%; P<0.05). I-mTLR4 knockout attenuated responses to DEP/BCAS for all markers. CONCLUSIONS: i-mTLR4-ko markedly reduced neuroinflammation and oxidative stress and attenuated white matter degradation following DEP and CCH exposures. This suggests a potential role for targeting TLR4 signaling in individuals with vascular cognitive impairment, particularly those exposed to substantial ambient air pollution.

Fracture toughness of yttria-stabilized zirconia sintered in conventional and microwave ovens.

STATEMENT OF PROBLEM: The fabrication of zirconium dioxide (ZrO2) dental prosthetic substructures requires an extended sintering process (8 to 10 hours) in a conventional oven. Microwave sintering is a shorter process (2 hours) than conventional sintering. PURPOSE: The purpose of this study was to compare the fracture toughness of 3 mol % Y2O3-stabilized ZrO2 sintered in a conventional or microwave oven. MATERIAL AND METHODS: Partially sintered ZrO2 specimens from 3 manufacturers, KaVo, Lava 3M, and Crystal HS were milled (KaVo Everest engine) and randomly divided into 2 groups: conventional sintering and microwave sintering (n=16 per group). The specimens were sintered according to the manufacturers' recommendations and stored in artificial saliva for 10 days. Fracture toughness was determined by using a 4-point bend test, and load to fracture was recorded. Mean fracture toughness for each material was calculated. A 2-way ANOVA followed by the Tukey HDS post hoc test was used to assess the significance of sintering and material effects on fracture toughness, including an interaction between the 2 factors (α=.05). RESULTS: The 2-way ANOVA suggested a significant main effect for ZrO2 manufacturer (P<.001). The post hoc Tukey HSD test indicated that mean fracture toughness for the KaVo ZrO2 (5.85 MPa·m(1/2) ±1.29) was significantly higher than for Lava 3M (5.19 MPa·m(1/2) ±0.47) and Crystal HS (4.94 MPa·m(1/2) ±0.66) (P<.05) and no significant difference was observed between Lava 3M and Crystal HS (P>.05). The main effect of the sintering process (Conventional [5.30 MPa·m(1/2) ±1.00] or Microwave [5.36 MPa·m(1/2) ±0.92]) was not significant (P=.76), and there was no interaction between sintering and ZrO2 manufacturer (P=.91). CONCLUSIONS: Based on the results of this study, no statistically significant difference was observed in the fracture toughness of ZrO2 sintered in microwave or conventional ovens.

Magnetic resonance imaging of white matter response to diesel exhaust particles.

Air pollution is associated with risks of dementia and accelerated cognitive decline. Rodent air pollution models have shown white matter vulnerability. This study uses diffusion tensor imaging (DTI) to quantify changes to white matter microstructure and tractography in multiple myelinated regions after exposure to diesel exhaust particulate (DEP). Adult C57BL/6 male mice were exposed to re-aerosolized DEP (NIST SRM 2975) at a concentration of 100 ug/m3 for 200 hours. Ex-vivo MRI analysis and fractional anisotropy (FA)-aided white matter tractography were conducted to study the effect of DEP exposure on the brain white matter tracts. Immunohistochemistry was used to assess myelin and axonal structure. DEP exposure for 8 weeks altered myelin composition in multiple regions. Diffusion tensor imaging (DTI) showed decreased FA in the corpus callosum (30%), external capsule (15%), internal capsule (15%), and cingulum (31 %). Separate immunohistochemistry analyses confirmed prior findings. Myelin basic protein (MBP) was decreased (corpus callosum: 28%, external capsule: 29%), and degraded MPB increased (corpus callosum: 32%, external capsule: 53%) in the DEP group. White matter is highly susceptible to chronic DEP exposure. This study demonstrates the utility of DTI as a neuroanatomical tool in the context of air pollution and white matter myelin vulnerability.

Home-Based Respiratory Physiotherapy and Telephone-Based Psychological Support for COVID-19 Survivors in Peru: Protocol for a Randomized Controlled Trial.

BACKGROUND: Both pulmonary and mental health are affected following hospitalization for COVID-19 pneumonia. Pulmonary rehabilitation therapy has demonstrated benefits in improving mental health, but no validated combined programs that include mental health have been proposed. OBJECTIVE: This article presents the design of a trial that aimed to assess whether the participation in a combined rehabilitation program that includes home-based respiratory physiotherapy and telephone-based psychological support is associated with a greater improvement of pulmonary and mental health outcomes 7-12 weeks after COVID-19 hospitalization discharge compared with posthospital usual care provided by a public Peruvian hospital. METHODS: WAYRA (the word for air in the Quechua language) was an open-label, unblinded, two-arm randomized controlled trial. We recruited 108 participants aged 18-75 years who were discharged from the hospital after COVID-19 pneumonia that required >6 liters/minute of supplemental oxygen during treatment. Participants were randomly assigned at a 1:1 ratio to receive the combined rehabilitation program or usual posthospital care provided by a public Peruvian hospital. The intervention consisted of 12 at-home respiratory rehabilitation sessions and 6 telephone-based psychological sessions. The primary outcome was the 6-minute walk distance. Secondary outcomes included lung function, mental health status (depression, anxiety, and trauma), and quality of life. Outcomes were assessed at baseline (before randomization) and at 7 and 12 weeks after hospital discharge to assess the difference between arms. RESULTS: This study was funded by the Peruvian National Council of Science Technology and Technology Innovation in July 2020. Ethics approval was obtained on September 2, 2020. Recruitment and data collection occurred between October 2020 and June 2021. Results are expected to be published by the end of 2022. CONCLUSIONS: WAYRA was the first randomized controlled trial evaluating combined pulmonary-mental health rehabilitation for hospitalized COVID-19 survivors in resource-limited settings, potentially providing a foundation for the cost-effective scale-up of similar multidisciplinary rehabilitation programs. TRIAL REGISTRATION: ClinicalTrials.gov NCT04649736; https://clinicaltrials.gov/ct2/show/NCT04649736. INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID): RR1-10.2196/36001.

Neurotoxicity of Diesel Exhaust Particles.

BACKGROUND: Air pollution particulate matter (PM) is strongly associated with risks of accelerated cognitive decline, dementia and Alzheimer's disease. Ambient PM batches have variable neurotoxicity by collection site and season, which limits replicability of findings within and between research groups for analysis of mechanisms and interventions. Diesel exhaust particles (DEP) offer a replicable model that we define in further detail. OBJECTIVE: Define dose- and time course neurotoxic responses of mice to DEP from the National Institute of Science and Technology (NIST) for neurotoxic responses shared by DEP and ambient PM. METHODS: For dose-response, adult C57BL/6 male mice were exposed to 0, 25, 50, and 100µg/m3 of re-aerosolized DEP (NIST SRM 2975) for 5 h. Then, mice were exposed to 100µg/m3 DEP for 5, 100, and 200 h and assayed for amyloid-ß peptides, inflammation, oxidative damage, and microglial activity and morphology. RESULTS: DEP exposure at 100µg/m3 for 5 h, but not lower doses, caused oxidative damage, complement and microglia activation in cerebral cortex and corpus callosum. Longer DEP exposure for 8 weeks/200 h caused further oxidative damage, increased soluble Aß, white matter injury, and microglial soma enlargement that differed by cortical layer. CONCLUSION: Exposure to 100µg/m3 DEP NIST SRM 2975 caused robust neurotoxic responses that are shared with prior studies using DEP or ambient PM0.2. DEP provides a replicable model to study neurotoxic mechanisms of ambient PM and interventions relevant to cognitive decline and dementia.

Human perception of dental porcelain translucency correlated to spectrophotometric measurements.

PURPOSE: This study evaluated the relationship between instrumental measurements and subjective visual assessment of differences in dental porcelain translucency. MATERIALS AND METHODS: Unshaded feldspathic porcelain was used with controlled amounts of tin oxide to create two groups of 12-mm diameter disks with incremental changes in opacity. Contrast ratio (CR = Yb/Yw) was determined with a spectrophotometer, and used as a measure of porcelain translucency (Group A = 0.20 to 0.40; Group B = 0.6-0.8). Within each group, there were 14 specimens with 11 CRs. Three observer groups (first year dental students, residents, faculty with >10 years of shade matching experience) were recruited to assess the translucency between porcelain disks under two lighting conditions (reflected light, transmitted light). Each subject's ability to distinguish between specimens of differing translucency was determined. Descriptive statistics and three-way ANOVA followed by a post-hoc Tukey-Kramer test were used to evaluate the translucency perception threshold (TPT) of subjects (alpha= 0.05). RESULTS: The overall mean TPT (DeltaC) was 0.07, while 50% of the subjects could perceive a 0.06 CR difference between porcelain specimens. Three-way ANOVA revealed a significant difference in translucency perception among the observer groups (p < 0.0001), whereas the main effects for porcelain opacity (p= 0.3038) and lighting condition (p= 0.0645) were not significant, and no significant interactions were found. Post-hoc Tukey-Kramer test indicated that the mean TPT observed in the faculty group (DeltaC = 0.04) was significantly lower than those observed in student (DeltaC = 0.09) and resident groups (DeltaC = 0.08), while there was no significant difference between students and residents. CONCLUSIONS: The overall mean TPT of all subjects was 0.07, and 50% of the study population perceived a 0.06 CR difference in translucency. Increased shade matching experience (> or =10 years) significantly improved the ability to perceive differences in translucency; however, neither the viewing condition nor porcelain opacity affected the perceived translucency threshold.

Flexural and fatigue strengths of denture base resin.

STATEMENT OF PROBLEM: Mechanical properties of denture acrylic resins are important for the clinical success of multiple types of prostheses. Acrylic resins must be strong and resilient so as to withstand impact. Few studies utilize cyclic loads to characterize material response to repeated stress. PURPOSE: The purpose of this study was to evaluate static and dynamic flexure properties of a variety of acrylic resins utilized in the fabrication of prostheses: (1) heat-polymerized polymethyl methacrylate (PMMA), powder-liquid type, and (2) a newly introduced, visible light-polymerized urethane dimethacrylate dough type. MATERIAL AND METHODS: Twenty rectangular bars each of 4 PMMA acrylic resin materials (Diamond D, Fricke HI-I, Lucitone 199, Nature-Cryl Hi-Plus) and 1 urethane dimethacrylate (Eclipse) were fabricated and stored in 100% humidity for 30 days. Half of the specimens for each group were submitted to a static 3-point flexure test. The other half was submitted to cycling loading at 5 Hz for 10(4) cycles. Data were analyzed using 1-way ANOVA and 2-way ANOVA, followed by Tukey HSD or Bonferroni post hoc tests when necessary (alpha=.05). RESULTS: Mean static flexure strength (SDs) in MPa were: Eclipse, 127.11 (5.83); Diamond D, 84.92 (5.10); Lucitone 199, 83.96 (11.96); HI-I, 79.54 (5.84); and Nature-Cryl Hi-Plus, 75.82 (6.96). Mean flexural strengths (SDs) in MPa postcycling were: Eclipse, 113.36 (31.29); Diamond D, 88.26 (5.46); Nature-Cryl Hi-Plus, 81.86 (4.93); HI-I, 79.18 (6.60); and Lucitone 199, 74.34 (4.95). CONCLUSIONS: The visible light-polymerized urethane dimethacrylate resin (Eclipse) showed greater flexure strength than all PMMA heat-polymerized resins for both static and cycled groups (P<.001). Yet the Eclipse material had lower load limits, and demonstrated brittle-type behavior and greater standard deviations. The heat-polymerized PMMA materials did not significantly differ from each other after static or cyclic testing.

An in vitro comparison of vertical marginal gaps of CAD/CAM titanium and conventional cast restorations.

PURPOSE: To determine if there was a significant difference between the vertical marginal openings of cast restorations, computer-aided design, and computer-aided machining restorations. MATERIALS AND METHODS: Ten working dies were created from a single master die and used to fabricate ten restorations in each of the following groups: computer-aided design/computer-assisted machining (CAD/CAM), WAX/CAM, and WAX/CAST. The CAD/CAM titanium restorations were fabricated using the scanning and crown design modules of the KaVo Everest system. The WAX/CAM titanium restorations were fabricated using the double scan technique with the KaVo Everest system. The WAX/CAST high noble copings were fabricated using the conventional lost wax casting technique. The restorations were seated on the master die, and high-resolution digital photographs were made of the marginal area on all four sides. The vertical marginal opening was then measured using a calibrated digital software program. One-way ANOVA and Tukey's post hoc tests were used to determine the presence of statistically significant differences. RESULTS: The vertical margin openings were CAD/CAM: 79.43 +/- 25.46 microm; WAX/CAM: 73.12 +/- 24.15 microm; WAX/CAST: 23.91 +/- 9.80 microm. There was a statistically significant difference between the WAX/CAST group and the remaining groups. CONCLUSIONS: There was no difference between the vertical marginal gaps of the CAD/CAM and WAX/CAM. The WAX/CAST technique resulted in smaller vertical marginal gaps than either CAD/CAM or WAX/CAM.

Tensile fatigue limits of prosthodontic adhesives.

Tensile fatigue limits and ultimate tensile strengths of some prosthodontic adhesive systems were determined. Ni-Cr-Be cylinders were: electro-etched, chemically etched, and sand-blasted prior to being bonded end-to-end with BIS-GMA and 4-META adhesives. Bonded specimens were stored in distilled de-ionized water for three days prior to being tested. Fifteen paired specimens per group were subjected to a cyclic tensile load for 1000 cycles. Tensile fatigue limits were determined by the staircase method. Five specimens per group were tested for ultimate tensile strength. In addition, those specimens which survived the 1000 cycles during fatigue testing were also tested for ultimate tensile strength. Statistical evaluations to compare tensile fatigue limits and ultimate tensile strengths for fatigued and non-fatigued specimens were then performed. The results indicated that the tensile fatigue limit and the ratio of fatigue limit to ultimate tensile strength of the sand-blasted, 4-META adhesive system were significantly lower than those of the other systems tested. The application of a cyclic load significantly decreased the ultimate tensile bond strength of the 4-META adhesive. Application of a cyclic load had no significant effect on the ultimate tensile bond strengths of the BIS-GMA systems tested.

Measurement of water sorption by resin composite adhesives with near-infrared spectroscopy.

Spectroscopic methodology was used to follow the water uptake of disks of two resin composite luting agents during long-term storage. Fourier-transform near-infrared (FT-NIR) spectroscopy was used for collection of spectra over the 4200-6500 cm-1 spectral region. The 5200-cm-1 absorption band of water was monitored initially, at 24 h, seven days, two weeks, and then monthly over a period of 12 months. The disks were stored in water, air, and desiccated conditions. Disks were also subjected to two alternate cycles (two weeks each) of hydration and desiccation. A spectral manipulation program was used for quantitation of the area under the water absorbance band. Area ratios demonstrated similar water-uptake patterns for the two adhesives. Rapid water uptake was seen within the first two weeks of storage. Alternate hydration and desiccation of the samples showed that water uptake by the filler/polymer network was partially reversible. The desiccant was unable to remove all the water from the samples, which indicated that some water was tightly held within the sample matrix. FT-NIR spectroscopy is recommended as an effective method for study of the equilibration of resin composites in water.

Analysis of debond rates of resin-bonded prostheses.

Debonding rates of 164 resin-bonded prostheses (RBP) placed from 1974 to 1985 were examined at recall. The yearly debond rates were calculated, the cumulative probability of failure was determined for the debonded RBPs, and Weibull distribution parameters were determined. For perforated prostheses, there was a high initial debond rate, followed by slowly decreasing rates for about 5 years. Increasing rates after 5 years indicated the beginning of wear-out. The Weibull parameters for the wear-out period of the perforated prostheses were: characteristic life = 128 (SE = 2) months, modulus = 1.27 (0.06), and threshold parameter = 0. Data were available for etched frameworks for 6 years and showed decreasing debond rates during this time. The characteristic life of the etched bridges was 318 (84) months. The cumulative failure data were also modeled with a cubic polynomial distribution that resulted in a U-shaped hazard function.

Coronal microleakage of permanent lingual access restorations in endodontically treated anterior teeth.

Forty-six intact extracted human anterior teeth were treated endodontically with laterally condensed gutta-percha and sealer. The teeth were restored with a base of either zinc phosphate or temporary stopping and a permanent restoration of either acid etched composite resin with GLUMA as the dentin bonding agent or with Ketac-Fil glass ionomer. The teeth were thermocycled, coated with nail varnish (except for the access), immersed in silver nitrate, developed, and sectioned longitudinally. The linear dye penetration was measured. All restorations permitted leakage into the base. All groups had specimens which leaked into the gutta-percha. There was a tendency for the glass ionomer/zinc phosphate group to leak least, but there were no statistically significant differences among the groups.

Optical detection of pulpal blood.

An optical system to assess blood within the pulpal cavity was developed. The system included a light-emitting diode source, human incisor teeth, and a silicon photodiode detector. An automated syringe pump was used to flow bovine blood lengthwise through the teeth. Transmitted light intensities were recorded at a collection frequency of 20 reading/min and apparent absorbance units were calculated. The effects of blood concentration, blood flow rate, and pulp chamber size were investigated. It was found that changes in blood flow rate did not cause significant changes in transmitted light intensity. Increases in blood concentration and pulp chamber size resulted in larger absorbance values. These results suggest that photoplethysmography measurements may be sensitive to the amount of blood in the pulp chamber as it reflects the pulsatile-related expansion and contraction of capillaries within the pulp tissue.

Optical detection of hemoglobin in pulpal blood.

An in vitro, flow-through optical system was designed to measure hemoglobin (Hb) concentrations in the pulp space. The system included light-emitting diodes and a silicon photodetector positioned on opposing surfaces of human teeth. A syringe pump allowed a controlled flow of blood through the pulp chamber. The Hb concentration was computed as a nonlinear function of transmitted light intensity. Transmitted light intensities were also used as indicators of oxygenation level. Optical measurements correlated with Hb values measured by the conventional cyanmethemoglobin method (r=0.993). The mean percentage error was 5.8%, and the standard error of prediction was 0.77 g/dl for Hb concentrations ranging from 4 to 20 g/dl. Deoxygenated blood exhibited up to 31% lower transmitted intensity. Light transmission through teeth may be useful in the assessment of total Hb and blood oxygenation within the pulp chamber.

Detection of pulpal circulation in vitro by pulse oximetry.

Evaluation of pulse oximetry as a potential method of determining pulp vitality was the subject of this research. An in vitro model of pulpal circulation was fabricated to test the design for a dental pulse oximetry sensor. Blood samples equilibrated with hypoxic gas mixtures were circulated through the model by a peristaltic pump. A pulse was simulated by introduction of gas bubbles into the blood circulation. Pulse oximeter readings for saturation were recorded and compared with blood gas analysis results. Statistical analysis revealed no difference between pulse oximetry and blood gas analysis with a highly significant correlation coefficient. Clinical evaluation of this application is currently in progress.

Effect of microbial contamination and pH changes in storage solutions during in vitro assays of bonding agents.

A study of pH changes in, and microbial colonization of, storage solutions being utilized during an in vitro evaluation of luting agent solubility has been made. Microbial growth in storage solutions was observed to occur at as high as 10(5) colony-forming units (cfu)/mL after seven days' incubation. A strong time-dependent inverse correlation between pH and cfu was found, with the pH dropping to as low as 5.3 (p less than 0.01). Decreases in pH were not found in presterilized control samples (p less than 0.05). Further, it was demonstrated that presterilization with ethylene oxide or the addition of respiratory inhibitors prevented both microbial colonization and the pH drop when compared with controls (p less than 0.001). These data suggest that studies of dental materials which include incubations in various fluids should be controlled for the potential effects of micro-organisms and their effect on pH.

Short-term fluoride release/uptake of glass ionomer restoratives.

OBJECTIVES: The short-term fluoride release/uptake of four glass ionomer restoratives was measured and compared to the fluoride release after exposure to three commercial fluoride gels. METHODS: Materials tested were: 1) Ketac-Fil (ESPE GmbH); 2) Ketac-Silver (ESPE GmbH); 3) Photac-Fil (ESPE GmbH); and 4) Fuji II LC (GC Corp.). Twenty discs of each material were fabricated and stored in deionized water at 37 degrees C. Initial fluoride release was measured at 24 h intervals for 7 d, and 24 h intervals at the end of each week for 5 wk. After 6 wk, samples were divided into groups and each group was treated for 6 min with one of the following commercial fluoride gels: acidulated phosphate fluoride (APF), neutral sodium fluoride (NaF), and stannous fluoride (SnF2). Control specimens were placed in deionized water. After exposure, fluoride measurements were carried out at 24 h intervals for 7 d, and 24 h intervals at the end of 2 wk. Fluoride exposure was repeated, and measurements were again recorded over 3 wk. RESULTS: Initial fluoride release by all materials was highest during the first 24 h and decreased sharply over the first week. After exposure to APF, fluoride release increased significantly for all materials. Exposure to NaF also resulted in increased fluoride release for all materials although it was not as high as the increase recorded after exposure to APF. Exposure to SnF2 did not result in significant fluoride release by any material. SIGNIFICANCE: The results of this study suggest that certain fluoride gels may replenish fluoride within some glass ionomers and thus prolong their cariostatic potential.

Bond strength and surface characterization of a Ni-Cr-Be alloy.

OBJECTIVES: Since resin composite cements adhere directly to base metal surfaces, the composition and integrity of the surface oxide layer is considered critical for adequate bonding. The aims of this study were to determine the tensile bond strength, and assess predominant surface oxides and oxide layer depth on the surface of a Ni-Cr-Be alloy after subjecting the alloy to various surface treatments. METHODS: Cylinders of Ni-Cr-Be (Rexillium III, Jeneric/Pentron) were cast and the following test groups were investigated: Group 0: no furnace oxidation, no air abrasion; Group 1: air fired, starting temperature 650 degrees C, ending temperature 1000 degrees C (1 min hold); Group 2: same firing sequence under vacuum; Group 3: same air firing sequence followed by air abrasion with 50 micrometers Al2O3; Group 4: vacuum fired, air abraded with 50 micrometers Al2O3; Group 5: air fired, air abraded with 280 micrometers Al2O3; Group 6: vacuum fired, air abraded with 280 micrometers Al2O3; Group 7: no furnace oxidation, air abraded with 50 micrometers Al2O3; and Group 8: no furnace oxidation, air abraded with 280 micrometers Al2O3. The oxide composition of three cylinders per group was analyzed with x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). Twenty cylinders from each group were bonded together with Panavia 21 (Kuraray), stored in water for 30 d, and tensile tested. Data were analyzed using one-way ANOVA and Duncan's Multiple-Range test (p=0.05). RESULTS: Furnace oxidation brought Be to the surface and increased the oxide thickness. Air abrasion removed the oxide layer and resulted in surfaces containing significant amounts of Al2O3. Bond strengths for Group 0 were significantly lower than bond strengths for Groups 1, 3, 4, 5, 6, 8, but not significantly different from bond strengths for Groups 2 and 7 (p<0.05). SIGNIFICANCE: Results of this study suggest differences in oxide composition and thickness due to various surface treatments. Furnace oxidation did not significantly affect bond strength and may not be required as a separate step for metal preparation if a resin adhesive is used.

Review of dentinal bonding in vitro: the substrate.

This article reviews common substrates and testing conditions used in dentinal bond strength studies in vitro. The available literature supports the use of freshly extracted, hydrated human teeth for studies in vitro. No one testing condition has proven superior accuracy over the others. Evidence is presented to support the implementation of infection control measures when handling the substrates.

Topical fluoride and glass ionomer microhardness.

PURPOSE: To evaluate the effect of topical fluoride gels on the microhardness of three glass ionomer cements. MATERIALS AND METHODS: Cylinders of Ketac-Silver, Photac-Fil, and Fuji II LC were fabricated, stored in distilled water at 37 degrees C for 48 hours, and exposed to a neutral sodium fluoride gel (Karigel-N), and acidulated orthophosphoric acid gel (Karigel), and a stannous fluoride gel (Omni) at 37 degrees C for 36 hours. Knoop hardness was then recorded. RESULTS: Statistical analysis showed significant differences (P<0.01) between groups related to material and treatment Ketac-Silver did not demonstrate significant differences in hardness, whereas exposure to APF decreased the Knoop hardness of Fuji II LC and Photac-Fil.