Effects of potassium oxalate on knoop hardness of etch-and-rinse adhesives.

The objective of this study was to determine whether the hardness of etch-and-rinse adhesives may be affected by the pretreatment of acid-etched dentin with potassium oxalate desensitizer. Unerupted human third molars were cut into crown segments by removing the occlusal enamel and roots. The pulp chamber of these crown segments was connected to a syringe barrel filled with phosphate-buffered saline so that the moisture of dentin was maintained during the bonding procedures. Three etch-and-rinse adhesives-two two-step systems (Adper Single Bond 2 [SB], One-Step [OS]) and one three-step system (Adper Scotchbond Multi-Purpose [MP])-were applied to acid-etched dentin that had been treated (experimental groups) or not (control groups) with potassium oxalate (BisBlock). The Knoop hardness (KHN) of adhesives was taken at different sites of the outer surface of the adhesive-bonded dentin. The KHN of the three tested adhesives applied to acid-etched dentin treated with potassium oxalate was significantly lower than that exhibited by the respective controls (not treated with oxalate; p<0.05). Regardless of the adhesive, the treatment with potassium oxalate reduced the adhesives' KHN (p<0.05), with the OS system exhibiting the lowest KHN compared with the MP and SB systems.

In vivo preservation of the hybrid layer by chlorhexidine.

Host-derived proteases have been reported to degrade the collagen matrix of incompletely-resin-infiltrated dentin. This study tested the hypothesis that interfacial degradation of resin-dentin bonds may be prevented or delayed by the application of chlorhexidine (CHX), a matrix metalloproteinase inhibitor, to dentin after phosphoric acid-etching. Contralateral pairs of resin-bonded Class I restorations in non-carious third molars were kept under intra-oral function for 14 months. Preservation of resin-dentin bonds was assessed by microtensile bond strength tests and TEM examination. In vivo bond strength remained stable in the CHX-treated specimens, while bond strength decreased significantly in control teeth. Resin-infiltrated dentin in CHX-treated specimens exhibited normal structural integrity of the collagen network. Conversely, progressive disintegration of the fibrillar network was identified in control specimens. Auto-degradation of collagen matrices can occur in resin-infiltrated dentin, but may be prevented by the application of a synthetic protease inhibitor, such as chlorhexidine.

Chlorhexidine preserves dentin bond in vitro.

Loss of hybrid layer integrity compromises resin-dentin bond stability. Matrix metalloproteinases (MMPs) may be partially responsible for hybrid layer degradation. Since chlorhexidine inhibits MMPs, we hypothesized that chlorhexidine would decelerate the loss of resin-dentin bonds. Class I preparations in extracted third molars were sectioned into two halves. One half was customarily restored (etch-and-rinse adhesive/resin composite), and the other was treated with 2% chlorhexidine after being acid-etched before restoration. Specimens were stored in artificial saliva with/without protease inhibitors. Microtensile bond strengths and failure mode distribution under SEM were analyzed immediately after specimens' preparation and 6 months later. With chlorhexidine, significantly better preservation of bond strength was observed after 6 months; protease inhibitors in the storage medium had no effect. Failure analysis showed significantly less failure in the hybrid layer with chlorhexidine, compared with controls after 6 months. In conclusion, this in vitro study suggests that chlorhexidine might be useful for the preservation of dentin bond strength.

Polymerization kinetics of pre-heated composite.

Temperature affects the polymerization behavior of dimethacrylate-based materials. This study describes the influence of pre-polymerization temperature and exposure duration on polymerization kinetics of a commercial dental photo-activated composite at the top and at 2-mm depth. We used the temperature-controlled stage of a diamond-attenuated-total-reflectance unit to pre-set composite temperature between 3 degrees and 60 degrees C. Composite was light-exposed by a conventional quartz-tungsten-halogen curing unit for 5, 10, 20, or 40 sec. Real-time conversion, maximum conversion rate (R(p)(max)), time to achieve R(p)(max), and conversion at R(p)(max) were calculated from infrared spectra. Composite pre-warming enhanced maximal polymerization rate and overall monomer conversion (top significantly greater than 2 mm). Time when R(p)(max) occurred did not change with temperature, but occurred sooner at the top than at 2-mm depth. Conversion at R(p)(max) increased with temperature, allowing more of the reaction to occur prior to vitrification than at room temperature.

Effect of the photo-activation method on polymerization shrinkage of restorative composites.

This study measured the gap that resulted from polymerization shrinkage of seven restorative resin composites after curing by three different methods. Contraction behavior, according to the specimen region, was also characterized. The materials used for this study were Alert (Jeneric/Pentron, Wallingford, CT 06492, USA), Surefil (Dentsply Caulk, Milford, DE 19963, USA), P60 (3M Dental Products, St Paul, MN 55144, USA), Z250 (3M), Z100 (3M), Definite (Degussa-Hüls, Hanau, Germany) and Flow-it (Jeneric/Pentron). The composite was placed in a circular brass mold 7 mm in diameter and 2 mm in height. Photo-activation was performed by a) continuous light (500 mW/cm2) for 40 seconds; b) stepped light with low intensity (150 mW/cm2) for 10 seconds and high intensity (500 mW/cm2) for 30 seconds and c) intermittent light (450 mW/cm2) for 60 seconds. The top and bottom surfaces were then polished and after 24 +/- 1 hours, the contraction gap was measured by SEM at variable pressure (LEO 435 VP, Cambridge, England). Results were analyzed by ANOVA and the means compared by Tukey's test (5%). The results demonstrated 1) the continuous light method presented the greatest gap values (15.88 microm), while the other methods demonstrated lower polymerization shrinkage values (stepped light, 13.26 microm; intermittent light, 12.79 microm); 2) restorative composites shrunk more at the bottom surface (15.84 microm) than at the top surface (12.11 microm) and (3) the composites Alert (12.02 microm), Surefil (11.86 microm), Z250 (10.81 microm) and P60 (10.17 microm) presented the least contraction gaps, followed by Z100 (15.84 microm) and Definite (14.06 microm) and finally Flow-it (23.09 microm) low viscosity composite, which had the greatest mean value.

A morphological and tensile bond strength evaluation of an unfilled adhesive with low-viscosity composites and a filled adhesive in one and two coats.

OBJECTIVE: The purpose of this study was to measure the tensile bond strength (TBS) testing of resin composite to dentin of three low-viscosity composites, in association with an unfilled adhesive, and a filled adhesive one and two coats respectively, and to evaluate and compare the SEM morphological observations. METHODS: The labial surface of 120 bovine lower incisors were ground to obtain a flat dentin surface allowing demarcation of a 4 mm diameter area with adhesive tape. The teeth were randomly divided in six groups of 20 each. The dentin of each ground surface was etched with 35% H(3)PO(4) for 15s, followed by application of the respective adhesive: Single Bond (SB) for Groups 1, 2, 3 and 6; Optibond Solo (OS) for Groups 4 and 5. In Groups 1 and 4, a resin composite rod with a wire loop was luted directly to the adhesive surface with Z100. Group 2 received an intermediate layer of Flow It (FI) composite; Group 3 received an intermediate layer of Protect Liner F (PLF) composite; Group 5 received a second coat of OS; and Group 6 received an intermediate layer of an experimental low-viscosity composite (EM). A resin composite rod was luted to the surface of each specimen with Z100 resin composite. All specimens were stored in distilled water at 37 degrees C for 24h prior to TBS testing. Each specimen was inspected by SEM and classified according to adhesive or cohesive failure mode. One specimen of each group was cut longitudinally, polished and prepared for SEM observation. RESULTS: The TBS values were: Group 1 (7.86MPa+/-2.28), Group 2 (7.62MPa+/-1.85), Group 3 (7.60MPa+/-2.14), Group 4 (7.96MPa+/-2.36), Group 5 (7.50MPa+/-2.70) and Group 6 (7.18MPa+/-2.40). No significant statistical differences were observed among the groups. However, the analyses of the failure mode presented a considerable variation. SIGNIFICANCE: The use of a filled adhesive or an unfilled adhesive along with a low-viscosity composite as an intermediate layer may provide a stress absorbing layer, whereby improving the preservation of the bonded interface area.

Effect of antimicrobial agents on the micromorphology of primary dentin.

The use of disinfectants on the dentin surface contributes to superficial cleaning and removal of remaining microorganisms of the carious process. However, the effect of these agents on the adhesion of resin materials to the dentin surface of primary teeth has not been established. This study evaluated the dentin micromorphological effects due to the use of antimicrobial agents in the different depths of dentin. Twenty-five buccal surfaces of primary molars were prepared from the sectioned teeth, ground flat and polished with silicon carbide paper of different grits. The surfaces were treated with 32% phosphoric acid with benzalkonium chloride (Bisco), 35% phosphoric acid gel (3 M), 3% benzalkonium chloride solution by itself or 10% maleic acid. All agents were applied for 15 seconds on the dentin surface. The samples were washed with distilled water, dried and coated with gold for observation of the dentin surface with the scanning electron microscope. The samples were subdivided according to the dentin depth in upper, middle and lower areas. The following was observed: presence of smear layer, opening of the dentin tubules, and inter and intratubular dentin morphology. The effects of the antimicrobial agents were compared in the different depths of the dentin. The results demonstrated that the surface conditioned with 3% benzalkonium chloride solution presented few disclosed dentin tubules. The use of the 32% phosphoric acid with benzalkonium chloride completely removed the smear layer and increased the diameter of the dentin tubule openings. The 35% phosphoric acid totally exposed the tubules in the upper area of the analyzed surface but partially exposed them in the middle and lower areas. The 10% maleic acid totally removed the smear layer, left all the tubules opened and conditioned the intertubular dentin. It was concluded that in the different depths of the dentin surface, conditioning with 10% maleic acid in primary teeth showed the most consistent micromorphological characteristics compared to the other agents used in this study.

How wet should dentin be? Comparison of methods to remove excess water during moist bonding.

PURPOSE: The aim of this study was to evaluate the shear bond strength of two adhesive systems when applied on dentin surfaces with different degrees of wetness. MATERIALS AND METHODS: Two-hundred ten dentin specimens were used. After conditioning with 35% phosphoric acid gel and washing, seven methods of drying dentin were used: 30 s air spray (groups 1 and 2), 5 s air spray (groups 3 and 4), dry cotton pellets (groups 7 and 8), wet cotton pellets (groups 9 and 10), microbrush (groups 11 and 12), absorbent paper (groups 13 and 14). The last group was not dried; the dentin surfaces were left overwet (groups 5 and 6). Prime & Bond 2.1 adhesive was applied on the odd-numbered groups and Scotchbond Multi Purpose on the even-numbered groups. Z100 composite cylinders were bonded to the adhesive and the specimens were subjected to a shear bond test. RESULTS: The Least-Squares Means test was used to compare the following results, where different letters indicate significantly different mean values: Group 9 (G9) = 23.2 MPa (a), G3 = 21.3 MPa (ab), G2 = 19.5 MPa (bc), G10 = 18.6 MPa (bc), G14 = 16.3 MPa (cd), G8 = 16.1 MPa (cd), G4 = 14.6 MPa (de), G13 = 14.0 MPa (de), G11 = 13.9 MPa (de), G7 = 13.5 MPa (de), G12 = 12.1 MPa (e), G1 = 8.2 MPa (f), G5 = 2.7 MPa (g), G6 = 2.4 MPa (g). CONCLUSION: The adhesion values were affected both by the degree of dentin wetness and by the adhesive systems.

Influence of loading types on the shear strength of the dentin-resin interface bonding.

Small differences in the shear bond test can make critical differences in the bonding strength values. The purpose of this study was to compare the influence of the orthodontic-looped wire, stainless steel tape and chisel systems used in shear bonding tests to verify the resistance in the dentin-resin interface. Forty-eight human teeth were used and divided in three groups. The teeth were ground until a flat smooth surface was achieved, that was delimited with an adhesive tape containing a hole of 4 mm diameter. After, the dentine surface was treated with Scotchbond Multi Purpose and the composite Z-100 was applied in layers, through a stainless steel mold. The samples were stored at 37 degrees C and 100% of relative humidity for 24 h and, then, submitted to 500 thermal cycles. After, they were taken to an universal test machine (Otto Wolpert) with crosshead speed of 6 mm/min. The results were statistically analyzed using a Tukey's test (p\lt 0.05). The orthodontic-looped wire determined the highest values of shear bond (13.33 MPa), following by chisel (7.81 MPa) and stainless steel tape (4.87 MPa). The debonding values depend on a complex stress combination produced during the loading of the samples. Small variations in test methodologies give statistically different values for shear bond strength. Different shear strength methods in vitro make the comparative clinical performance of the resin filling materials difficult.

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.

Effect of storage and acid etching on the tensile bond strength of composite resins to glass ionomer cement.

This in vitro study evaluates the effect of storage time and acid etching on the tensile bond strength of glass ionomer cement to composite resins. The bonded assemblies were stored at 100% relative humidity and 37 degrees C for 1 hour, 1 day, 1 week, 1 month and 3 months. The test specimen was loaded at tension to failure on an Otto Wolpert-Werke testing instrument with a crosshead speed of 6 mm/min. The results showed a significant statistical difference for etched Vidrion F when compared to etched Ketac Bond at all storage periods. The unetched samples were statistically similar at 3 months, with the highest values for Vidrion F.

Influence of adhesive systems on the bonding of dental amalgam to glass ionomer cement.

STATEMENT OF PROBLEM: Dental amalgam restorations have traditionally been retained in cavity preparations by surgical procedures called retention form. In this procedure healthy dental structure is usually removed to create adequate retention. The increasing use of bonding systems for restorative procedures may result in more conservative cavity preparations. PURPOSE: The purpose of this study was to evaluate the tensile bond strength of the amalgam to glass ionomer cement under the influence of three adhesive systems (Panavia-EX, Vidrion F fresh mix, and Alpha Seal). MATERIAL AND METHODS: The bonded assemblies were stored in an environment of 100% relative humidity and 37 degrees C for 24-hour and 30-day storage periods. The test specimen was loaded in tension to failure on a universal testing machine with a crosshead speed of 6 mm/min. RESULTS: The results revealed that in the 24-hour period without acid etch fresh Vidrion F and Panavia Ex adhesives were stronger than autopolymerizing sealant. Panavia Ex adhesive was stronger in the 24-hour period with acid etch. CONCLUSIONS: The 30-day period with acid etch revealed no statistical difference among the adhesives. In the 30-day period without acid etch, the fresh Vidrion F adhesive recorded the greatest tensile bond strength.

Resin bond strength with different methods to remove excess water from the dentin.

PURPOSE: To compare the resin bond strength using different methods to remove the excess water from the dentin while maintaining it moist. MATERIALS AND METHODS: 60 human molars were randomly divided into four treatment groups of 15 teeth each as follows: Group 1: A wet bonding technique was used as recommended by the manufacturer and was used as a control group. The exposed occlusal dentin surfaces were conditioned with 32% phosphoric acid (Uni-Etch) for 15 seconds and rinsed for 15 seconds. 40 microL of distilled water was added to standardize the content of the water on dentin surface. The conditioned dentin surfaces were gently blow-dried for 3 seconds with oil-free compressed air. The tip of the syringe was placed at 2 cm from the dentin surface. One coat of the One-Step primer/adhesive was applied to the dentin surface using a fully saturated brush tip, allowed to remain on the surface undisturbed for 3 seconds, and then gently air-dried for 3 seconds from a distance of 1 cm to remove excess solvent and water. A second coat of the primer/adhesive was applied and gently air-dried from a distance of 1 cm. The primer/adhesive was light-cured for 10 seconds. Resin composite (Z100, shade A3) was then polymerized for 40 seconds. Group 2: The dentin surface was blot-dried by applying tissue paper (Kimwipes EX-L) adjacent to the exposed area; Group 3: The excess water on the dentin surface was removed using an applicator brush (Bend-a-Brush) for 5 seconds; Group 4: A small dry hydrophilic cotton pellet was gently applied over the dentin surface to remove the excess water. The sequential steps for these three groups were similar to those of Group 1. The dentin surface remained visibly moist in all procedures. After light-curing, the specimens were thermocycled (5 degrees and 55 degrees C, 500 cycles, 30-second dwell time). The specimens were sheared and the data were analyzed using ANOVA and Tukey's test methods. The site of failure was analyzed using a stereomicroscope and a scanning electron microscope. RESULTS: ANOVA revealed that there was a statistically significant difference between the groups (P < 0.05). Turkey's test revealed that Group 1 was significantly lower than Groups 2, 3 and 4 with no difference between the last three groups (P < 0.05). All samples showed resin cohesive failures.

Influence of protecting agents on the solubility of glass ionomers.

PURPOSE: To evaluate the influence of protective agents (varnish and glaze-resin resin) on water solubility of two glass ionomer restorative cements (Chelon-Fil and Vidrion-R), with the graviometrical test (A.D.A Specification No 9). MATERIALS AND METHODS: Fifteen samples of each restorative cement were obtained and divided in one control and two experimental groups: (a) control, no protection; (b) protected with varnish; (c) protected with glaze-resin. On the two experimental groups, after the initial gelification reaction, the specimens were protected and immersed in distilled water for the period of 1 and 24 hours. RESULTS: The two glass ionomer restorative cements tested required surface protection to avoid the early solubility. Among the protective materials evaluated, the varnish was the most effective agent.

Effect of topical fluoride application on the surface roughness of composites.

The influence of fluoride solutions on the surface roughness of polished and nonpolished composites with Sof-Lex discs was verified. Concise and Herculite XR samples were exposed to the action of 1.23% acidulated phosphate fluoride rinse, 1.23% acidulated phosphate fluoride gel, and 0.2% neutral phosphate fluoride rinse for 4 min each. The average roughness values obtained by perfilometer showed that all fluoride solutions produced surface alterations in the samples. In the unpolished samples, more roughness was produced in Concise etched by 1.23% acidulated phosphate fluoride rinse. In the polished samples, the 1.23% acidulated phosphate fluoride gel produced greater alterations in Herculite XR, and the neutral rinse in Concise samples.

Base deflection and microleakage of composite restorations.

The flexural deflections of human dentin, Herculite XR, Dycal, Vidrion F, zinc phosphate base, and combinations of composite-base were determined. The influence of the flexural deflections in the marginal microleakage was also determined for the composite-base combinations. The flexural deflection test for dentin showed no statistically significant differences between the two floor cavity depths studied. There were significant differences among cements when the thickness of the base was 1 mm whereas no differences occurred at 2 mm. The composite-base combinations did not present statistical differences. There were no statistically significant differences in the microleakage levels among loaded and non-loaded specimens; however, dye penetration was visually greater in loaded samples.

Chemical etching solutions for creating micromechanical retention in resin-bonded retainers.

This study introduced three chemical etching solutions capable of producing micromechanical retention in nickel-chromium and nickel-chromium-beryllium alloys used for resin-bonded retainers. The effectiveness of the chemical etching solutions was evaluated with tensile strength tests and photographs at various magnifications with a scanning electron microscope. Chemical etching with the CG-Etch solution produced suitable and uniform microretention whereas the other solutions were not effective on all metal alloys. Significant differences (p < 0.05) relating to tensile bond strengths were noted. The CG-Etch solution gave the highest mean bond strength compared with solutions II, III, and control groups.