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PubMed2004

Influence of phosphoric acid pretreatment on self-etching bond strengths.

PURPOSE: The purpose of this investigation was to evaluate the influence of phosphoric acid pretreatment on shear bond strength of two self-etching bonding systems to enamel and dentin. MATERIALS AND METHODS: Forty-eight extracted third human molar teeth were mounted, embedded into polystyrene resin, polished with 600-grit aluminum oxide papers, and randomly divided into four groups (n = 12): group 1-Clearfil Liner Bond 2V (Kuraray Co. Ltd., Osaka, Japan); group 2-One Up Bond F (Tokuyama Corp., Tokyo, Japan); group 3-phosphoric acid (Condicionador Dental Gel, Dentsply Ind. Com. LTDA, Rio de Janeiro, Brazil) and Clearfil Liner Bond 2V; group 4-phosphoric acid and One Up Bond F. In groups 3 and 4 the substrate was pre-etched for 15 seconds with 37% phosphoric acid, rinsed, and dried with an air stream. In all groups adhesive systems were applied according to manufacturers' instructions and light cured; then a restorative composite resin (TPH Spectrum, Dentsply Ind. Com. LTDA) was placed in a polytef matrix and cured. The specimens were stored in humidity for 7 days at 37 degrees C. The shear bond strength test was performed in a universal test machine with a crosshead speed of 0.5 mm/min. All procedures were repeated for the dentin evaluation. Mean values were analyzed with two-way analysis of variance and Duncan tests (p < .05). RESULTS: The values obtained are listed in decreasing order: enamel-group 3 = 24.6 MPa, group 4 = 23.6 MPa, group 1 = 19.2 MPa, group 2 = 8.5 MPa; dentin-group 1 = 17.2 MPa, group 2 = 16.1 MPa, group 4 = 13.1 MPa, group 3 = 11.3 MPa. CONCLUSIONS: Under the conditions of this study, enamel etching with 37% phosphoric acid provided statistically significant higher shear bond strength values, regardless of the adhesive system. However, in dentin, for Clearfil Liner Bond 2V, phosphoric acid pretreatment negatively affected bond strength values. CLINICAL SIGNIFICANCE: The use of self-etching systems in composite-to-enamel bonding restorative techniques still needs improvement when compared with the high bond strengths obtained with phosphoric acid treatment. However, lower shear bond strengths were observed in dentin when phosphoric acid was used in association with either adhesive system.

Acid Etching, Dental↗
PubMed2003

Determination of free silica in dust particles: effect of particle size for the X-ray diffraction and phosphoric acid methods.

The X-ray diffraction method and the phosphoric acid method are widely used to determine the fraction of free silica (mainly quartz and other silica polymorphs) in respirable dust sampled in working environments in Japan. In this study, we clarified the size effect of quartz dust for the X-ray diffraction method and the phosphoric acid method using size controlled quartz samples. The quartz samples were classified into 6 fractions with different size ranges: 1 microm and smaller, 1 to 3 microm, 3 to 5 microm, 5 to 7 microm, 7 to 10 microm and 10 microm and larger. Both of the determination methods were affected by the particle size, and especially particles smaller than 3 microm fairly dissolved in hot phosphoric acid and reduced X-ray diffraction intensity remarkably. If the content of these fine particles in the standard quartz sample is lower than that of the test samples, the fraction of free silica may be underestimated by these methods. For this reason, the standard quartz sample should have a representative size distribution of the field samples. The dust samples containing quartz were collected at a foundry and dissolved by phosphoric acid to remove non-quartz materials. The size fractions of dissolved samples were 50% for 5-10 microm, 25% for 3-5 microm, 20% for 1-3 microm and 5% for 1 microm and smaller. As the size distribution is similar to the present standard sample widely used in Japan, we concluded that the standard sample is suitable for these determination methods.

Dust↗
PubMed2004

Activated carbon from peach stones using phosphoric acid activation at medium temperatures.

In the present study, the activation features of phosphoric acid have been investigated using waste peach stones as the raw material in the production of granular activated carbon. Thermogravimetry/differential thermal analysis was conducted to characterize the thermal behavior of peach stone and titration method was used to evaluate the adsorption capacity of the produced activated carbon. It was observed that the iodine value of the activated carbon increased with activation temperature. However, temperatures higher than 500 degrees C caused a thermal destruction, which resulted in the decrease of the adsorption capacity. Activation longer than 1.5 h at 500 degrees C resulted in thermal degradation of the porous structure of the activated carbon. The adsorption capacity was enhanced with increasing of amounts of phosphoric acid, however, excessive phosphoric acid caused a decrease in the iodine value. In addition, it was found that the carbon yields generally decreased with activation temperature and activation time. Scanning electron microscopy analysis was conducted to observe the changes in the poros structure of the activated carbon produced in different temperatures. Activation of carbon by phosphoric acid was found to be superior to that by CaCl2 and gas activation. The activated carbon produced from peach stone was applied as an adsorbent in the treatment of synthesized wastewater containing cadmium ion and its adsorption capacity was found to be as good as that of the commercial one.

Adsorption↗
PubMed1982

The effect of 50 per cent phosphoric acid on oral soft tissues.

The effect of 50 per cent phosphoric acid on oral soft tissue was studied in two investigations. In the first investigation the buccal mucosa of three rats was studied after contact with phosphoric acid for 1, 5 and 10 minutes respectively. The material of the second investigation comprised of 26 patients from whom 31 pairs of premolars were planned to be extracted for orthodontic reasons. Phosphoric acid was applied for 90 seconds on one tooth and its buccal gingival margin in each pair of teeth. After a period varying between 1 and 7 days the tooth and a section of the gingiva were extracted and prepared for microscopic examination. The second tooth in each pair was the control tooth. The study showed that only a relatively long acid application time resulted in obvious histologic changes in the mucous membrane. The phosphoric acid gave no demonstrable gingival reaction in the patients.

Acid Etching, Dental↗
PubMed1999

Evaluation of the EPA exposure assessment for phosphoric acid.

The philosophy of this paper is that the Environmental Protection Agency's (EPA) 1990 exposure assessment for phosphoric acid is not based on sound science and therefore does not accurately characterize the eutrophication potential of phosphoric acid releases from Toxic Release Inventory (TRI) reporting facilities. This error propagates the myth that eutrophication is triggered by the release of phosphoric acid from facilities reporting releases in the TRI. A detailed evaluation of EPA's 1990 exposure assessment for phosphoric acid reveals critical flaws in their applied methodology. Significant methodological improvements detailed in this paper fundamentally alter EPA's 1990 exposure assessment and demonstrate that, contrary to EPA's conclusion, these sources of phosphoric acid do not have the potential to trigger eutrophication in surface waters. Therefore, when sound scientific principles are applied in this comparative exposure assessment, EPA's policy maintaining phosphoric acid on the TRI list is inappropriate.

Agrochemicals↗
PubMed2003

Evaluation of sodium bisulphate and phosphoric acid as urine acidifiers for cats.

Eighteen cats were used to compare the urine acidifying properties of sodium bisulphate to phosphoric acid. Acidifying agents were added at one of three concentrations (0.4, 0.6, or 0.8%, as-is basis). Cats were offered a commercial diet to determine basal urinary pH, and then again for a 1 week period between blocks 1 and 2. Cats were acclimated to the diets for 6 days, and urine samples were collected on day 7 at 0, 4, and 8 h postfeeding to obtain pre- and postprandial urinary pH. Intakes of diets containing sodium bisulphate tended (P < 0.07) to be lower than intakes of diets containing phosphoric acid. Cats consuming the 0.8% phosphoric acid diet had higher (P < 0.05) food intakes than cats consuming either the 0.4 or 0.6% phosphoric acid-containing diets. There was significant (P = 0.01) linear and quadratic response for food intake in cats consuming the sodium bisulphate-containing diet. Cats consuming the 0.4 and 0.8% phosphoric acid-containing diets tended (P = 0.07) to have higher water intakes than cats consuming the 0.6% phosphoric acid-containing diet. There were no differences (P > 0.05) in urine pH and specific gravity between cats fed the different acidifier types. Cats consuming the 0.6% phosphoric acid-containing diet tended (P = 0.07) to have a higher urine pH 8 h post-feeding than cats consuming the 0.4 and 0.8% phosphoric acid-containing diets. Urine pH was highest at 4 h post-feeding except for cats fed the 0.4% sodium bisulphate- and the 0.6% phosphoric acid-containing diets. No differences (P > 0.05) between acidifiers were found in faecal score or in faecal dry matter and organic matter concentrations. A quadratic response was detected in faecal score for cats consuming the phosphoric acid-containing diets. Cats consuming the 0.6% phosphoric acid diet tended (P = 0.06) to have a lower faecal score than cats consuming the 0.4 and 0.8% phosphoric acid diets. For faecal dry matter, a linear trend was detected in cats consuming the sodium bisulphate (P = 0.08) and phosphoric acid-containing (P = 0.04) diets. Sodium bisulphate and phosphoric acid generally behaved in a similar fashion when incorporated in dry cat diets.

Acid-Base Equilibrium↗
PubMed2006

Ion conduction mechanisms and thermal properties of hydrated and anhydrous phosphoric acids studied with 1H, 2H, and 31P NMR.

To understand the behaviors of phosphoric acids in fuel cells, the ion conduction mechanisms of phosphoric acids in condensed states without free water and in a monomer state with water were studied by measuring the ionic conductivity (sigma) using AC impedance, thermal properties, and self-diffusion coefficients (D) and spin-lattice relaxation times (T1) with multinuclear NMR. The self-diffusion coefficient of the protons (H+ or H3O+), H2O, and H located around the phosphate were always larger than the diffusion coefficients of the phosphates and the disparity increased with increasing phosphate concentration. The diffusion coefficients of the samples containing D2O paralleled those in the protonated samples. Since the 1H NMR T1 values exhibited a minimum with temperature, it was possible to determine the correlation times and they were found to be of nanosecond order for a distance of nanometer order for a flip. The agreement of the ionic conductivities measured directly and those calculated from the diffusion coefficients indicates that the ion conduction obeys the Nernst-Einstein equation in the condensed phosphoric acids. The proton diffusion plays a dominant role in the ion conduction, especially in the condensed phosphoric acids.

Journal Article↗
PubMed2002

Activated carbons prepared from phosphoric acid activation of grain sorghum.

The production of activated carbons from grain sorghum with phosphoric acid activation has been studied by means of two processes, i.e., one-stage and two-stage. The former comprises simultaneous carbonization and activation after impregnation; the latter, the carbonization of the precursor at 300 degrees C for 15 min, followed by the activation of the resultant char after impregnation with phosphoric acid. The preparation conditions, e.g., activation duration, phosphoric acid concentration, and activation temperature, have been varied to determine the optimal processing conditions. The optimal activation conditions for the highest surface areas have been determined to be 600 and 500 degrees C with a phosphoric acid concentration of 35% for the one-stage and two-stage processes, respectively. The two-stage process has been found to greatly enhance the porosity development, especially the microporosity.

Carbon Compounds, Inorganic↗
PubMed1995

Scanning electron microscopic study and shear bond strength measurement with 5% and 37% phosphoric acid.

Direct bonding of orthodontic attachments has become a clinical reality with the application of the acid etch technique, using 37% phosphoric acid. The objective of this study was to detect the etch pattern with scanning electron microscopy and the shear bond strength with a Hounsefield tensometer (Nene Instruments Ltd., Northampton, England) by using 37% and 5% phosphoric acid (H3PO4). It was observed that with 5% H3PO4 there was minimal enamel loss compared with 37% H3PO4. There was no significant difference in shear bond strength, when enamel surface was etched with 5% H3PO4 and 37% H3PO4.

Acid Etching, Dental↗
PubMed2005

A theoretical study of 31P NMR chemical shielding models for concentrated phosphoric acid solution.

Calculations on the hydrates, dimer, and trimer of phosphoric acid were carried out in an effort to obtain a viable model of the phosphorus NMR chemical shielding in 85% phosphoric acid solution. The theoretical approaches used the gauge-including-atomic-orbital (GIAO) 6-311+G(nd,p) basis set at both scaled density functional theory (sB3LYP) and estimated infinite order Møller-Plesset (EMPI) approaches and with the aug-cc-pvtz basis in the sB3LYP approach. Shieldings and hydrogen bonding stabilization energies are similar in the three approaches and indicate that the faster sB3LYP/6-311+G(nd,p) approach can be used with larger systems. The changes in shielding compared to the isolated species are small and suggest that the undissociated acid dihydrate could serve as a model entity for modeling the phosphorus shielding in concentrated phosphoric acid solution.

Journal Article↗
PubMedDate not supplied

The deposition of hygroscopic phosphoric acid aerosols in ciliated airways of man.

The hygroscopic growth of phosphoric acid aerosol (Dc greater than 0.5 micron) within the human tracheobronchial tree is modeled to investigate changes in deposition characteristics when compared to nonhygroscopic aerosols of identical preinspired size. Phosphoric acid particles are assumed to grow in a stepwise fashion to 99% relative humidity (RH) within conducting airways of the lung, having initially reached equilibrium at 90% RH (T = 37 degrees C) in the trachea. Deposition efficiencies for growth and no growth are calculated from theoretical equations for inertial impaction, sedimentation and diffusion. The results show that neglecting the growth of an inhaled phosphoric acid aerosol may result in underestimation of the total deliverable dose by a factor of as much as 600-700%. Significant differences in regional deposition sites for hygroscopic or nonhygroscopic aerosols are predicted. Increased deposition efficiencies imply that measured physical properties (respirable fraction, aerodynamic diameter) of aerosols alone are not sufficient to assess deposition characteristics within the lung; hygroscopic growth must also be considered.

Aerosols↗