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PubMed1991

Scanning electron microscopy observations on the penetration and structure of resin tags in bleached and unbleached bovine enamel.

The purpose of this study was to determine the effect of hydrogen peroxide on the ability of composite resin to penetrate bovine enamel etched with phosphoric acid. In a previous investigation, the flattened enamel surfaces of extracted bovine incisors were immersed in either saline (control) or 35% hydrogen peroxide (experimental) for 5 or 30 min before or after acid etching with 37% phosphoric acid gel for 60 s. A standard-sized light-cured resin cylinder was then bonded to the enamel surface. The specimens were stored in a water bath at 37 degrees C for 1 day or 7 days, after which the enamel-resin bond was tensile tested to failure. Sixteen of the failed specimens (eight control and eight experimental) were randomly selected for the present scanning electron microscopic study to evaluate the appearance of the resin tags at the resin-enamel interface. In the control specimens, the tags were well defined and contiguous with resin which was uniformly adherent to the enamel surface. In the experimental specimens, large areas of the enamel surface were free of resin. When tags were present, they were fragmented, poorly defined, and penetrated to a lesser depth than in the saline controls. The changes observed suggest that there may be interaction between resin and residual peroxide at or near the enamel surface.

Acid Etching, Dental↗
PubMed2003

Influence of the frequency of Er:YAG laser on the bond strength of dental enamel.

OBJECTIVE: The present study had the aim of evaluating the influence of different frequencies of the Er:YAG laser on adhesive resistance of enamel and one restorative system. BACKGROUND DATA: There have been no reports of studies assessing the influence of the pulse frequency variation of the Er:YAG laser on adhesive resistance of the enamel/resin interface. MATERIALS AND METHODS: Fifty surfaces of enamel from extracted human third molars were planed and divided into five groups at random. Enamel surface treatment was realized by the Er:YAG laser at 80-mJ power and 1-, 2-, 3-, and 4-Hz pulse frequencies, followed by etching. For the control group, only acid conditioning with 37% phosphoric acid for 15 sec was used. The Single Bond/Filtek Z250 system was chosen for the fabrication of the specimens, which were stored in 100% relative humidity for 24 h, at 37 degrees C. The specimens were submitted to tensile resistance tests using a Universal Testing Machine (50 Kgf and 0.5 mm/min). RESULTS: The mean values in MPa were 1 Hz, 25.58 (+/-6.16); 2 Hz, 25.58 (+/-3.79); 3 Hz, 21.34 (+/-3.78); 4 Hz, 21.17 (+/-3.13); and phosphoric acid only, 22.44 (+/-7.0). Data were submitted to statistical analysis using ANOVA, and there was no significant difference in tensile resistance between the studied groups. CONCLUSION: The results suggest that the Er:YAG laser, with 80-mJ power associated with acid conditioning at 1-, 2-, 3-, and 4-Hz frequencies, did not present significant improvement in tensile bonding of enamel, as compared to acid conditioning only.

Acid Etching, Dental↗
PubMedDate not supplied

In vitro bracket bond strength to acid-etched or air-abraded enamel.

PURPOSE: This study evaluated, in vitro, the capacity of a dentin bonding agent to improve the bond strength of orthodontic brackets using air abrasion enamel preparation. METHODS: Each of the enamel surfaces received a different treatment prior to bonding procedures. Group 1 received acid-etched with 38% phosphoric acid for 30 seconds. Group 2 received acid-etched with 38% phosphoric acid for 30 seconds, dentin bonding agent (Scotchbond MultiPurpose) applied after rinse completed. Group 3 received abrasion-etched (particle size 50 microns, 120 psi). Group 4 received abrasion-etched, dentin bonding agent applied after etching completed. Unfilled adhesive resin (Ormco light cured sealant) was applied followed by a premolar bracket (Ormco meshed mini-twin) with adhesive (Ormco light cured adhesive) placed on the back. Shear bond strengths were measured using an INSTRON machine and the site of bond failure was determined under 3X magnification. RESULTS: The shear bond strength obtained with a traditional acid-etch, in vitro, was not improved significantly by the use of a dentin bonding agent. Air abraded surfaces showed very low bond strengths with all treatments. CONCLUSIONS: Tested in vitro, air-abraded surfaces provide clinically unacceptable bond strength when compared to acid-etched enamel surfaces.

Acid Etching, Dental↗
PubMed2002

Etching conditions for resin-modified glass ionomer cement for orthodontic brackets.

This study reports the tensile bond strength of orthodontic eyelets (RMO, Inc, Denver, Colo) bonded to human extracted teeth with a resin-modified glass ionomer cement (RMGIC) (Fuji Ortho LC, GC America, Alsip, Ill) and various acid etchants (Etch-37 and All-Etch, Bisco, Schaumburg, Ill; Ultra Etch, 3M Unitek, St Paul, Minn) for enamel preparation before bonding. The enamel etch conditions were as follows: 37% phosphoric acid with silica; 37% phosphoric acid, silica-free; 10% phosphoric acid, silica-free; 10% polyacrylic acid; and unetched enamel. Bond strength was measured by pulling in tension on the eyelet with a 0.018-in steel wire perpendicular to the enamel surface with a testing machine (Instron model 1125, Canton, Mass) at a speed of 2 mm/min. A light-cured resin cement (Transbond XT, 3M Unitek, Monrovia, Calif) applied to enamel etched with 37% phosphoric acid containing silica served as a control. Each group included 30 specimens. The Weibull distribution (m) was used for statistical analysis with a 90% CI. The different etchants used with RMGIC did not affect tensile bond strength. The resin cement group had the highest tensile strength. Significantly lower bond strengths were observed when glass ionomer cement was used to bond orthodontic attachments to nonetched teeth. However, unlike resin cement, RMGIC can bond effectively to etched teeth in a moist environment without an additional bonding agent.

Acid Etching, Dental↗
PubMed2000

Bond strengths of self-etching primer adhesives to in vitro-demineralized dentin following mineralizing treatment.

PURPOSE: The purpose of this study was to determine if treatment of experimentally demineralized dentin with a calcium phosphate precipitating (CPP) solution could restore the bond strength of self-etching adhesives to that of normal mineralized control values. MATERIALS AND METHODS: The occlusal surfaces of human teeth were exposed for bonding. The teeth were assigned to a mineralized control group or one of three demineralized (40% phosphoric acid for 60 s) experimental groups. One of the experimental groups remained untreated, while the other two were treated with the CPP solutions for either 1 or 10 min. All experimental groups were then chemically dehydrated with ascending acetone concentrations to prevent shrinkage prior to bonding with Clearfil Liner Bond 2 (LB2) or MacBond II (MBII). Composite buildups were made and vertically, serially sectioned into multiple slabs about 0.7 mm thick. Each slab was then trimmed for microtensile bond testing and SEM examination. RESULTS: Both self-etching adhesives produced high bond strengths to control mineralized dentin (ca 42 and 37 MPa for LB2 and MBII, respectively). Acid etching with 40% phosphoric acid for 60 s followed by chemical dehydration significantly lowered (p < 0.05) bond strength to 26 and 27 MPa for LB2 and MBII, respectively, and created hybrid layers between 7 and 8 microns thick. When the demineralized dentin was treated with the CPP solution for 1 min, the bond strengths increased (p < 0.05) to 39 for LB2 and 42 MPa for MBII, and the hybrid layers were 11 microns thick. Increasing the CPP treatment time to 10 min lowered (p < 0.05) bond strengths but increased the hybrid layer thickness to 16 to 20 microns. CONCLUSION: The use of calcium phosphate precipitating solutions may permit higher bond strengths of self-etching primers to demineralized (e.g., caries-affected) dentin.

Acid Etching, Dental↗
PubMed1999

Combinations of etchants, composite resins, and bracket systems: an important choice in orthodontic bonding procedures.

The objectives of this investigation were: (1) to compare the shear bond strengths (SBS) of metal, ceramic, and plastic brackets using different concentrations of maleic and phosphoric acid gels and aqueous solutions, and (2) to determine if a relationship exists between the type of acid etchant and the location of resin after debonding. A sample of 210 bovine incisors was divided among three different bracket groups (Victory series metal, Transcend 6000 ceramic, Spirit MB plastic). Prior to bonding, enamel was acid-etched using 37% phosphoric acid (H3PO4) gel and aqueous solution, 10% maleic acid gel and aqueous solution, 10% H3PO4 gel and aqueous solution, or 2% H3PO4 aqueous solution. SBS testing and the adhesive remnant index (ARI) score provided insight into the effects of the bonding process on enamel. Resin tags associated with each etchant type were inspected under scanning electron microscopy (SEM). Statistical analyses (level of significance, p = 0.05) of the data showed significant differences among groups. It was concluded that specific acid-composite-bracket combinations are recommended for use in clinical orthodontic practice in order to achieve efficient bonding.

Acid Etching, Dental↗
PubMed2003

Effect of dentinal pretreatments on coronal dentin primary carious lesions: a field emission SEM study.

The aim of the study was the morphological analysis of coronal dentin caries and the modifications induced by different pretreatments with phosphoric acid or sodium hypochlorite. Carious dentin specimens were obtained from human molars affected by carious lesions. Specimens were divided in four groups and submitted to: (1) untreated; (2) 35% phosphoric acid for 15 s; (3) 35% phosphoric acid for 15 s and 5% sodium hypochlorite for 2 min; (4) sodium hypochlorite for 5 min. Specimens were observed under high-resolution SEM. Different areas were identified within the carious lesion: a deeper, inner region revealing closed highly mineralized tubules, and a more superficial outer layer showing an increasing demineralization rate toward the surface of the lesion. Phosphoric acid followed by NaOCl treatment removed all collagen fibrils from greatly altered carious outer-dentin layer. The 5-min treatment with sodium hypochlorite affected both inner and outer dentin, removing all collagen fibrils and increasing the porosities of deeper intertubular hypermineralized dentin. FEISEM analysis confirmed that only inner carious dentin after phosphoric acid treatment may be considered a suitable substrate for dentinal bonding system. On the contrary, the outer dentin is an unstable substrate for any type of bonding systems and must be avoided/removed from any surface before conditioner application.

Acid Etching, Dental↗
PubMed2002

Acid washing and stabilization of an artificial arsenic-contaminated soil.

An acid-washing process was studied on a laboratory scale to extract the bulk of arsenic(V) from a highly contaminated Kuroboku soil (Andosol) so as to minimize the risk of arsenic to human health and the environment. The sorption and desorption behavior of arsenic in the soil suggested the possibility of arsenic leaching under acidic conditions. Artificially contaminated Kuroboku soil (2830 mg As/kg soil) was washed with different concentrations of hydrogen fluoride, phosphoric acid, sulfuric acid, hydrogen chloride, nitric acid, perchloric acid, hydrogen bromide, acetic acid, hydrogen peroxide, 3:1 hydrogen chloride-nitric acid, or 2:1 nitric acid-perchloric acid. Phosphoric acid proved to be most promising as an extractant, attaining 99.9% arsenic extraction at 9.4% acid concentration in 6 h. Sulfuric acid also attained high percentage extraction. The arsenic extraction by these acids reached equilibrium within 2 h. Elovich-type equation best described most of the kinetic data for dissolution of soil components as well as for extraction of arsenic. Dissolution of the soil components could be minimized by ceasing acid washing in 2 h. The acid-washed soil was further stabilized by the addition of lanthanum, cerium, and iron(III) salts or their oxides or hydroxides which form insoluble complex with arsenic. Both salts and oxides of lanthanum and cerium were effective in immobilizing arsenic in the soil attaining less than 0.01 mg/l As in the leaching test.

Acids↗
PubMed2000

Bond strengths of nonrinsing adhesives.

OBJECTIVE: The purpose of this study was to determine enamel and dentin bond strengths of a nonrinsing "all-in-one" adhesive and of a nonrinsing conditioner combined with a 1-bottle adhesive. METHOD AND MATERIALS: Specimens were obtained from 240 bovine teeth ground to expose enamel or dentin surfaces. Ten enamel and 10 dentin specimens were randomly assigned to each of 12 different combinations of adhesive system (Prompt L-Pop; no etch + Prime & Bond NT; NRC + Prime & Bond NT; 36% phosphoric acid + Prime & Bond NT; no etch + Prime & Bond 2.1; 36% phosphoric acid + Prime & Bond 2.1) and restorative material (resin composite; polyacid-modified resin composite ["compomer"]). After the application of the adhesive system, a No. 5 gelatin capsule filled with the restorative material was seated against the enamel or dentin surface. After 24 hours in distilled water at 37 degrees C, the specimens were thermocycled and the shear bond strengths were measured. RESULTS: For resin composite, etching with phosphoric acid resulted in the highest bond strengths to enamel. For compomer, the highest enamel bond strengths were achieved with both phosphoric acid and Prompt L-Pop. Treating dentin with Prime & Bond NT without etching provided the highest mean bond strength for composite. For compomer, treating dentin with Prime & Bond NT resulted in the highest mean bond strengths, regardless of the conditioner. CONCLUSION: Compomer and resin composite exhibited statistically similar bond strengths. Bond strengths to dentin were significantly lower than those to enamel.

Acid Etching, Dental↗
PubMed1999

Bond strength of compomers to dentin using acidic primers.

PURPOSE: To determine the in vitro bond strengths of seven compomer/bonding agent restorative systems to human dentin. MATERIALS AND METHODS: Seven compomer/bonding agents were bonded to human dentin, stored in water at 37 degrees C for 24 hours, and debonded in tension. Bonding conditions were with and without phosphoric acid etching, with and without the use of combined primer/bonding agents, and under moist and wet bond interfaces. RESULTS: Without phosphoric acid etching, F2000/F2000 Compomer Primer/Adhesive and F2000/Single Bond Dental Adhesive System were less sensitive to dentin wetness. With moist dentin, bond strengths of Dyract/Prime & Bond 2.1, Dyract AP/Prime & Bond 2.1, Hytac/OSB light-curing, one-component bonding agent, F2000/Single Bond, and Freedom/STAE single component light-cured dentin/enamel adhesive system, were improved with phosphoric acid etching. Also, with moist dentin, the bond strength of F2000/F2000 Compomer Primer/Adhesive in the 3M Clicker dispensing system was higher without phosphoric acid etching, whereas bonds of Compoglass/Syntac Single-component were not affected by phosphoric acid etching. Bonding did not occur without primer/bonding agent, regardless of surface condition or use of phosphoric acid etching.

Acid Etching, Dental↗
PubMed2007

Chemical characteristics of aerosol mists in phosphate fertilizer manufacturing facilities.

Of the carcinogens listed by the National Toxicology Program (NTP), strong inorganic mists containing sulfuric acid were identified as a known human carcinogen. In this study, aerosol sampling was conducted at 24 locations in eight Florida phosphoric acid and concentrated fertilizer manufacturing plants and two locations as background in Winter Haven and Gainesville, Florida, using dichotomous samplers. The locations were selected where sulfuric acid mist may potentially exist, including sulfuric acid pump tank areas, belt or rotating table phosphoric acid filter floors, sulfuric acid truck loading/unloading stations, phosphoric acid production reactors (attack tanks), and a concentrated fertilizer granulator during scrubbing with a weak sulfuric acid mixture. An ion chromatography system was used to analyze sulfate and other water soluble ion species. In general, sulfate, fluoride, ammonium, and phosphate were the major species in the fertilizer facilities. For the rotating table/belt phosphoric acid filter floor, phosphate and fluoride were the dominant species for PM10, and the maximum concentrations were 170 and 106 microg/m3, respectively. For the attack tank, fluoride was the dominant species for PM10, and the maximum concentration was 462 microg/m3. At the sulfuric acid pump tank, sulfate was the dominant species, and the maximum PM10 sulfate concentration was 181 microg/m3. The concentration of PM10 sulfate including ammonium sulfate, calcium sulfate, and sulfuric acid were lower than 0.2 mg/m3 at all locations. The aerosols at the filter floor and the attack tank were acidic. The coarse mode aerosol at the sulfuric acid pump tank (an outdoor location) was acidic, whereas the fine mode aerosol was neutral to basic.

Aerosols↗
PubMed2000

Effect of etching agent on dentinal adhesive interface in primary teeth.

The purpose of this study was to evaluate in vitro the effect of a phosphoric acid etchant containing benzalkonium chloride on the dentin/adhesive interface in primary teeth. The teeth had caries lesions involving enamel and dentin, and were stored in a 2% glutaraldehyde solution for 2-4 hours. The teeth were divided into five groups of five teeth each: Group 1: Etching for 15 seconds with a semigel 32% phosphoric acid containing benzalkonium chloride; Group 2: Etching with 35% phosphoric acid for 15 seconds; Group 3: Treated with a 2% benzalkonium chloride in a alcoholic solution; Group 4: Conditioned with a 3% benzalkonium chloride in a alcoholic solution (control group); Group 5: The teeth were untreated (control group). The carious tissue was removed with a carbide bur in high-speed and copious air water spray. The overall dimensions and depths of the cavities were determined by the carious tissue removal. After the caries lesion was removed, the cavity was cleaned with an air-water spray and the dentin was treated according to the specific group. The teeth were then restored with Scotchbond Multi-Purpose Plus (3M, St. Paul, MN) and Z-100 resin-based composite (3M, St. Paul, MN) according to the manufacturer's instructions. After the teeth were restored they were stored in water for 24 hours at room temperature and the restorations polished. After storage the teeth were thermally challenged for 500 cycles in temperatures of 50 C and 550 C and then stored in 100% humidity until the sectioning procedures. The teeth were cut into two sections along the longitudinal axis through the center of the teeth and passed the mesial-distal surfaces through the restoration by using a double-face diamond disc with water coolant. The specimens were ground with 320 up to 600 grit silicon carbide paper and polished with 6 mm and 1 mm diamond paste and 0.25 pm alumina solution. The specimens were etched with 10% citric acid for 1 minute and washed with deionized water. After that, they were deproteinized with 10% NaOCl for 5 seconds. The specimens were dried at room temperature sputter-coated with gold and observed with an SEM for assessment of the morphology of the bonded interface. The interface was observed to determine the presence/absence of hybrid layer formation, resin tags, and gaps. In the groups treated only with benzalkonium chloride solutions, spaces were observed in the resin/dentin interface. Similar findings were observed in the control group, which received no treatment on the dentin before primer application. In these groups neither resin tags or hybrid layer formation was observed. The presence of an amorphous layer, which was unremoved smear layer, was noted. The group treated with 35% phosphoric acid showed a hybrid layer formation (8.15 microns). This layer was linked intimately with the peritubular and intertubular dentin. Tags formation was observed towards the pulp under the hybrid layer. In these specimens the gaps were not observed between the dentin layer and bonding materials. The total removal of the smear layer was observed using 37% phosphoric acid with benzalkonium chloride. A hybrid layer (+/- 7.32 microns) and resin-tags attached to this layer were observed similar to the group in which the 35% phosphoric acid was used. The samples showed total removal of the smear layer and no gaps were observed in the dentin/adhesive interface.

Acid Etching, Dental↗
PubMed2002

Comparison of the bond strength of composite resin to Er:YAG laser irradiated human enamel pre-treated with various methods in vitro.

BACKGROUND AND OBJECTIVE: We have reported that the application of ultrasonic scalers on the Er:YAG laser-irradiated enamel surface achieved bond strengths of approximately 16 MPa. However, it is reported that a bond strength of 20 MPa is needed to prevent the marginal gaps, so the tensile bond strength (TBS) of composite resin to the Er:YAG laser-irradiated enamel is still insufficient. STUDY DESIGN/MATERIALS AND METHODS: Various methods (phosphoric acid etching, air scaling, ultrasonic scaling, air powder polishing, combination with phosphoric acid etching, and prior mechanical removal methods) were tested as a technique to increase TBS of composite resins to the Er:YAG irradiated enamel. RESULTS: Both the methods of mechanical removal following Er:YAG laser irradiation and the phosphoric acid etching following irradiation and mechanical removal had significant effects on TBS. TBS in the group with acid etching following air powder polishing showed highest value, 22.0 MPa. CONCLUSION: The application of phosphoric acid etching following mechanical removal of Er:YAG laser irradiation was effective to achieve high bond strength.

Acid Etching, Dental↗
PubMed2005

Mechanistic studies with 2-C-methyl-D-erythritol 4-phosphate synthase from Escherichia coli.

The mechanism of the reaction catalyzed by 2-C-methyl-d-erythritol 4-phosphate (MEP) synthase from Escherichia coli has been studied by steady-state and single-turnover kinetic experiments for the 1-deoxy-d-xylulose 5-phosphoric acid (DXP) analogues, 1,1,1-trifluoro-1-deoxy-d-xylulose 5-phosphoric acid (CF(3)-DXP), 1,1-difluoro-1-deoxy-d-xylulose 5-phosphoric acid (CF(2)-DXP), 1-fluoro-1-deoxy-d-xylulose 5-phosphoric acid (CF-DXP), and 1,2-dideoxy-d-hexulose 6-phosphate (Et-DXP). CF(3)-DXP, CF(2)-DXP, and Et-DXP were poor inhibitors, most likely because of the increase in steric bulk at C1 of DXP. The three analogues were also poor substrates for the enzyme. In contrast, CF-DXP was a good substrate (k(cat)(CF)(-)(DXP) = 37 +/- 2 s(-)(1), K(m)(CF)(-)(DXP) = 227 +/- 25 microM) for MEP synthase when compared to DXP (k(cat)(DXP) = 29 +/- 1 s(-)(1), K(m)(DXP) = 45 +/- 4 microM). A primary deuterium isotope effect was observed under single-turnover conditions when CF-DXP was incubated with 4S-[(2)H]NADPH ((H)k/(D)k = 1.34 +/-0.01), whereas no isotope effect was observed upon incubation with DXP and 4S-[(2)H]NADPH ((H)k/(D)k = 1.02 +/- 0.02). The reaction did not exhibit burst kinetics for either substrate, indicating that product release is not rate-limiting. These studies suggest that positive charge does not develop at C2 of DXP during catalysis. In addition, the isotope effect with CF-DXP and 4S-[(2)H]NADPH but not DXP indicates that the rearrangement step, which precedes hydride transfer, is rate-limiting for DXP but becomes partially rate-limiting for CF-DXP. Thus, rearrangement appears to be enhanced by substitution of a hydrogen atom in the methyl group of DXP by fluorine. These observations are consistent with a retro-aldol/aldol mechanism for the rearrangement during conversion of DXP to MEP.

Acetaldehyde↗
PubMed1997

Etching of young permanent teeth with acid gel--a comparison between the effect of 15 seconds & 60 seconds of etching.

The purpose of present study was to compare the effect of 15 seconds & 60 seconds of etching of young permanent teeth in vitro with 50% phosphoric acid gel using scanning electron microscope. 25 pairs of enamel surfaces selected for the study were divided into 3 experimental groups. The control group consisted of unetched enamel surfaces. In Group II, the effect of 50% phosphoric acid gel was compared with 37% phosphoric acid solution for 15 seconds whereas in group III, the effect of 15 seconds & 60 seconds of etching with 50% phosphoric acid gel was compared. The degree of etching pattern was evaluated by using scoring pattern from 1-3. Results showed no significant difference between the etching pattern obtained with the use of 37% solution and 50% gel for 15 seconds. But it was observed that etching with 50% for 15 seconds resulted in equal or even an enhanced etching pattern as compared to the pattern obtained in 60 seconds with 50% phosphoric acid gel.

Acid Etching, Dental↗
PubMed1978

Mechanism of adhesion of polymers to acid-etched enamel. Effect of acid concentration and washing on bond strength.

The tensile bond strengths of composites to enamel etched with various concentrations of phosphoric acid have been shown to correlate closely with the phase diagram for the system Ca(OH)2/H3PO4/H2O. Bond strengths were independent of the adhesive used and were a maximum when using approximately 20% phosphoric acid as etchant. High bond strengths were obtained with 2% phosphoric acid etchant without 'tag' formation, after short term water immersion. Washing the enamel for 60 s instead of 15 s after etching significantly increased the bond strengths obtained with 16 and 30% acid but not with 2%. Etching enamel with phosphoric acid results in deposition of calcium phosphates, which must be removed to give optimal bonding.

Acid Etching, Dental↗
PubMed1998

Effect of ceramic surface treatments on the bond of four resin luting agents to a ceramic material.

PURPOSE: This study evaluated the effect of various ceramic surface treatments on the shear bond strengths of four resin luting agents to Cerec 2 ceramic material. MATERIAL AND METHODS: Four ceramic surface treatments were performed. All groups were subjected to the control treatment, which was abrasion with No. 600 silicon carbide paper. The other three group treatments were etching with phosphoric acid gel, application of bonding agent containing silane coupler, and application of silane coupling agent after etching with phosphoric acid gel. Cerec 2 ceramic specimens were treated with one of the four methods and then cemented together with each of the four resin luting agents (Super-Bond C&B, Panavia 21, Clapearl, and Vita Cerec Duo Cement). Half of the specimens were stored in water and the other half were thermal cycled before shear bond strength testing. RESULTS: Treatment with the silane coupler improved the shear bond strength compared only with the abrasion with carbide paper (control). When the ceramic material was treated with the silane coupler or the silane coupling agent after etching with phosphoric acid gel, no significant differences in bond strength were noted between water storage and 20,000 thermal cycles for any of the four resin luting agents. After 20,000 thermal cycles, all specimens treated with the silane coupling agent with phosphoric acid gel except those cemented with Super-Bond C&B resin luting agent after etching showed cohesive failures within the ceramic. CONCLUSION: Combined surface treatment of etching with phosphoric acid and application of silane coupling agent provides the highest bond strengths of resin luting agents to Cerec 2 ceramic material after thermal cycling.

Acid Etching, Dental↗
PubMed1990

The quaternary structure of Escherichia coli inorganic pyrophosphatase is essential for phosphorylation.

The hexameric inorganic pyrophosphatase (PPase) is irreversibly inactivated by phosphoric acid monoesters. The inactivation kinetics are consistent with the formation of a dissociable complex of the phosphoric acid monoester with the enzyme, followed by phosphorylation of the dicarboxylic amino acid of its active site. PPi and its analogues, binding at the regulatory site, release the inhibitor from the active site and thus restore PPase activity. Chemically identical subunits in the hexameric PPase interact, promoting their cooperativity in a reaction with phosphoric acid monoesters. The trimeric and monomeric PPase, exhibiting full catalytic activity, form a dissociable complex with the phosphoric acid monoesters but, in contrast to the hexameric PPase, do not form a covalent bond with them. This indicates that the native hexameric structure is essential for the irreversible inactivation of Escherichia coli PPase by phosphoric acid monoesters. Possible nontraditional pathways for activity regulation of PPase are discussed.

Binding Sites↗