Biomedical subjects

David H Pashley

Publications and source records attributed to David H Pashley.

At least 73 records · Page 4Linked to original sources

PubMed2005

Effect of resin hydrophilicity on tracer penetration. A preliminary study.

PURPOSE: To evaluate, by transmission electron microscopy, the extent of silver nitrate penetration into four polymerized resin blends with increasing degree of hydrophilicity after a period of 24 hours. METHODS: The uncured resin was polymerized in an experimental composite inlay processing chamber under a pressurized nitrogen atmosphere maintained at 551.6 KPa and light-activated for one complete cycle at 125 degrees C for 10 minutes. The resin blocks were sectioned occluso-gingivally into multiple 0.9 x 0.9 x 5 mm resin beams, and immersed in 50% basic, ammoniacal silver nitrate for 24 hours, exposed to a photodeveloping solution and prepared for transmission electron microscopy. The percentage distributions of silver deposits were compared using Kruskal-Wallis one-way analysis of variance (ANOVA) on ranks and Dunn's multiple comparison tests. RESULTS: No silver uptake occurred in the two most hydrophobic resins (Groups 1 & 2). The percentage distributions of silver deposits in the more hydrophilic Group 3 (6.23 +/- 1.35%) and 4 (5.08 +/- 1.09%) resins were significantly higher (P < 0.05) than were found in the more hydrophobic resins but Groups 3 and 4 were not significantly different from each other. The intensity of silver uptake increased with hydrophilicity of the resin blends. TEM examination revealed two types of silver deposits: fine spotted-type silver grains, and islands of interconnecting electron-dense clusters of silver grains. Phase separation of resin components was observed in Group 4 resin blends.

Analysis of Variance↗

PubMed2005

Application of biologically-oriented dentin bonding principles to the use of endodontic irrigants.

PURPOSE: To compare the removal of smear layer and the structure of the hybrid layer formed after the use of EDTA or MTAD solutions when used as a final flush. METHODS: Single-rooted extracted premolars (n=18) were collected and treated for root canal therapy using NaOCl irrigation followed by a final rinse of 17% EDTA, Biopure MTAD, or saline (negative control). The roots were obturated with gutta-percha and a hydrophilic HEMA-containing root canal sealer. The TEM specimens were impregnated with 50% silver nitrate to visualize sealing imperfections and nanoleakage. The structure of the coronal, middle and apical parts of root canal walls was examined using transmission electron microscopy. RESULTS: After NaOCl irrigation, a final rinse with BioPure MTAD or 17% EDTA completely removed the 2 microm-thick smear layer on mechanically instrumented root canal walls. The BioPure MTAD hybrid layer was thicker than the 17% EDTA hybrid layer. Both the BioPure MTAD and EDTA caused a collapse of the dentin matrix structure which impeded sealer infiltration and the formation of high quality hybrid layer bonding. The hybrid layers created in smear layer-covered dentin exhibited less potential for nanoleakage than the MTAD or EDTA hybrid layers.

Bicuspid↗

PubMed2005

Durability of resin-dentin bonds related to water and oil storage.

PURPOSE: To evaluate the long-term effects of etching time, adhesive system and storage condition on resin bond strength to dentin. METHODS: Twenty-five extracted human third molars had a flat dentin surface exposed. Two total-etch adhesives, Single Bond (SB) and One-Step (OS), and one self-etching adhesive system, Clearfil Liner Bond 2V (CL), were used. The adhesives were bonded to dentin according to their respective manufacturer's instructions. Additional groups of SB and OS systems were created, in which the phosphoric acid etching time was doubled (30 seconds). After bonding, build-up crowns were constructed incrementally with Z250 resin composite and the teeth were stored for 24 hours in distilled water at 37 degrees C. The teeth were serially and vertically sectioned to obtain several bonded beams with approximately 0.8 mm2 of cross-sectional area. Beams were tested in microtensile (0.6 mm/minute) either immediately (control) or after storage for 6 months or 1 year in either distilled water or mineral oil. Data were analyzed by ANOVA and Tukey's multiple comparison tests. RESULTS: Significant reductions (P< 0.05) in bond strength were observed after both long-term storage periods in water for all the materials, regardless of the etching time for SB and OS. Bond strengths were either preserved or increased in specimens stored in oil.

Acrylic Resins↗

PubMed2004

Effects of solvents on the early stage stiffening rate of demineralized dentin matrix.

OBJECTIVES: To monitor the stiffening rate of demineralized dentin matrix at the early stages after exposure to different neat solvents. METHODS: Dentin beams approximately 0.8x0.7x8.0 mm were obtained from human third molars. After covering their ends with resin composite, the middle exposed length of 4.0mm (gauge-length) was demineralized in 0.5 M EDTA (pH 7.0) for 7 days. The specimens were gripped by a testing machine, pre-loaded to 10 g and cyclically stressed in tension to 5% strain, for 30 repeated cycles (total 20 min) at 0.6 mm/min while immersed in water (control). Then, water was replaced by either 100% acetone, methanol, ethanol, propanol, HEMA or air and the specimens subjected to the same cyclic protocol. The maximum apparent modulus of elasticity (E(Max)) was calculated for every cycle, plotted as a function of time and subjected to regression analysis. Stiffening rate was calculated as changes in E (min). Regression analysis examined the relationship between E and time for each solvent. Data were analyzed by one-way ANOVA and Student-Newman-Keuls test at alpha=0.05. RESULTS: Regression analysis showed that E increased significantly with time in all water-free solvents (R2=0.8-0.99). Stiffening rate was higher for acetone (0.9 MPa/min) and ethanol (0.8 MPa/min), intermediate for air (0.7 MPa/min), methanol (0.6 MPa/min) and propanol (0.5 MPa/min), lower for HEMA (0.2 MPa/min) and practically none for water (0.07 MPa/min) with p<0.05. CONCLUSIONS: The solvent-induced stiffening rate of demineralized dentin matrix is both time and solvent-dependent. The ability of solvents to promptly stiffen the demineralized dentin matrix may be important in maintaining the resin-infiltrated matrix expanded during the solvent evaporation stage of resin bonding.

1-Propanol↗

PubMed2004

Tensile strength and microhardness of treated human dentin.

OBJECTIVES: To determine the ultimate tensile strength and Knoop hardness of mineralized, EDTA-treated, sodium hypochlorite (NaOCl)-treated, EDTA-treated resin-infiltrated, and NaOCl-treated resin-infiltrated dentin. METHODS: Dumbell-shaped specimens with a cross-sectional area of 0.5 mm2 were prepared from the crowns of extracted human third molars. Specimens were randomly assigned to the following experimental groups: (1) mineralized dentin; (2) 0.5 M EDTA-demineralized dentin, pH 7/5 days; (3) 5% NaOCl-deproteinized dentin/2 days; (4) EDTA-treated, Single Bond resin-infiltrated dentin; (5) NaOCl-treated, Single Bond resin-infiltrated dentin. All specimens were tested in tension in a Vitrodyne testing machine at 0.6 mm/min. Knoop microhardness was measured on the fractured edges of specimens in groups 1, 3, 4, and 5. Results were analyzed by ANOVA and SNK tests (p < 0.05). RESULTS: Both EDTA and NaOCl treatments caused significant reductions in the tensile strength and microhardness of mineralized dentin (p < 0.05) with the largest reductions observed after NaOCl treatment (p < 0.05) Resin infiltration of treated dentin resulted in moderate increase of its tensile strength and microhardness, however, the original mineralized values were not recovered (p < 0.05). SIGNIFICANCE: Whenever dentin surfaces are treated with EDTA or NaOCl prior to a clinical bonding procedure, clinicians must be aware that a weak layer may be present at the interface, which may lead to premature failures of resin/dentin bonds.

Analysis of Variance↗

PubMed2004

Water movement in the hybrid layer after different dentin treatments.

UNLABELLED: The aim of this study was to examine the morphology of the hybrid layer (HL) of bonded water-stored specimens after different chemical pre-treatments of dentin. MATERIALS AND METHODS: Twenty-seven recently extracted human molars were selected. Fifty-four dentin disks in middle/deep dentin were obtained with a slow speed saw with a diamond-impregnated disk under water lubrication. Smear layers were created with 180 grit silicon carbide under running water for 1 min. Different pre-treatments of dentin were: Group (1) no treatment; Group (2) 35% H3PO4 etch for 15 s followed by 10% glutaraldehyde for 120 s; Group (3) 37% H3PO4 etch for 15 s followed by 5% NaOCl for 120 s. Three dentin bonding agents (DBAs), Prime and Bond NT (P and B), AdmiraBond (AB), and Clearfil SE Bond (SEB) were applied in association with a resin composite following the manufacturers' directions. Each specimen was then longitudinally sectioned and polished with wet SiC papers (up to #4000 grit). Impressions of the polished dentin were immediately taken with a silicone impression material. Bonded specimens were then stored for 3 or 12 h in deionized water. Further impressions of stored specimens were taken after air-drying of specimens for 10 s. Positive replicas were obtained using a polyether impression material. All the replicas and the original specimens were inspected by SEM. RESULTS: A line of droplets (0.5-4 microm in diameter) was observed along the region of the adhesive-HL junction in all replicas of specimens stored in water, except in group 3, when P and B and AB were used. When SEB was used in each group the droplet were found in all groups except the zone of droplets was thinner. No differences in droplets dimensions were seen between 3 or 12 h water storage, or between the different dentin treatments. CONCLUSIONS: The replica procedure used in this study was able to detect water trapped in the adhesive-HL region that was released during the setting of the impression material. The droplets observed in this region support the hypothesis that there can be bidirectional water movement within the adhesive-HL complex.

Acid Etching, Dental↗

PubMed2004

Resin bonding to cervical sclerotic dentin: a review.

Several reports have indicated that resin bond strengths to noncarious sclerotic cervical dentine are lower than bonds made to normal dentine. This is thought to be due to tubule occlusion by mineral salts, preventing resin tag formation. The purpose of this review was to critically examine what is known about the structure of this type of dentine. Recent transmission electron microscopy revealed that in addition to occlusion of the tubules by mineral crystals, many parts of wedge-shaped cervical lesions contain a hypermineralised surface that resists the etching action of both self-etching primers and phosphoric acid. This layer prevents hybridisation of the underlying sclerotic dentine. In addition, bacteria are often detected on top of the hypermineralised layer. Sometimes the bacteria were embedded in a partially mineralised matrix. Acidic conditioners and resins penetrate variable distances into these multilayered structures. Examination of both sides of the failed bonds revealed a wide variation in fracture patterns that involved all of these structures. Microtensile bond strengths to the occlusal, gingival and deepest portions of these wedge-shaped lesions were significantly lower than similar areas artificially prepared in normal teeth. When resin bonds to sclerotic dentine are extended to include peripheral sound dentine, their bond strengths are probably high enough to permit retention of class V restorations by adhesion, without additional retention.

Acid Etching, Dental↗

PubMed2004

Use of self-etching adhesives to seal resected apices.

The purpose of this study was to evaluate the sealing ability of four self-etching adhesives placed over blood-contaminated/uncontaminated resected root apices without root-end preparation. Extracted maxillary incisors and canines were randomly divided into four groups of 10 teeth each. After canal preparation and resection of the apex, four self-etching adhesives (Clearfil SE Bond, One-Up Bond F, Unifil Bond, and ABF) were applied over the control and contaminated surfaces. The roots were then subjected to 15 cm of water pressure to simulate periapical microleakage stress. Data were analyzed using a two-way repeated measures, ANOVA. Positive and negative controls responded as expected. Statistical analysis indicated that there were no significant differences in the sealing effectiveness among the adhesives applied to contaminated or uncontaminated groups. All contaminated groups had significantly higher leakage (p < 0.003) than their uncontaminated pairs.

Analysis of Variance↗

PubMed2004

Effect of 2% chlorhexidine gel as an intracanal medication on the apical seal of the root-canal system.

The purpose of this study was to determine what effect intracanal medications might have on the apical seal of the root-canal system. Forty-two teeth were cleaned and shaped in a crown-down manner to a size #50 K-file. The teeth were divided into three groups: (A) immediate obturation; (B) intracanal placement of calcium hydroxide placed for 14 days; and (C) 2% chlorhexidine gel placed for 14 days. After 14 days, these materials were removed using copious irrigation and obturation was completed on groups B and C. Obturation was performed using the continuous wave of condensation technique using AH Plus sealer in all groups. Leakage was evaluated 60 days after obturation by using a fluid-filtration device. Using the one-way ANOVA test, there was no statistically significant difference in leakage between the three groups. Under the conditions of this study, 2% chlorhexidine gel and calcium hydroxide paste did not adversely affect the apical seal of the root-canal system.

Analysis of Variance↗

PubMed2004

Effect of solvents on bonding to root canal dentin.

The long-term success of resin cementation of post/cores is likely increased with improvement in resin-root canal dentin bonding. The adverse effect of some irrigation constituents (NaOCl, H2O2) or medications (eugenol) on the bond strengths of resins to dentin have been reported. The purpose of this in vitro study was to evaluate the effect of two gutta-percha solvents (chloroform versus halothane) on microtensile bond strength to root canal dentin. Thirty, extracted, human, single-rooted teeth were instrumented to a #70 file and randomly divided into 3 groups of 10 each. The root canals were treated with water, chloroform, or halothane for 60 s. All root canals were obturated using C&B Metabond. After 24 h of storage in distilled water, serial 1-mm-thick cross-sections were cut and trimmed. Microtensile bond strength to apical, middle, and coronal root canal dentin were measured using an Instron machine. Using pooled data, the results indicated that water-treated roots had significantly higher resin-dentin bond strengths compared with chloroform or halothane treatment groups (control: 23.9 MPa; chloroform: 18.3 MPa; halothane: 17 MPa; p < 0.05). Gutta-percha solvents have an adverse effect on bond strengths of adhesive cements to root canal dentin.

Analysis of Variance↗

PubMed2004

Sealing ability of One-Up Bond and MTA with and without a secondary seal as furcation perforation repair materials.

This study investigated the ability of One-Up Bond alone and mineral trioxide aggregate (MTA), with and without a secondary seal of One-Up Bond or SuperEBA to seal saucer-shaped perforation defects in human molars. Cusps were removed, roots were amputated, and endodontic therapy completed on 40 extracted teeth. A cylindrical hole was made in each tooth from the furcation area to the chamber, into which a section of steel tubing was cemented. Intracoronal saucer-shaped defects were created over the perforation. The teeth were restored with MTA, One-Up Bond, or MTA with a secondary seal of One-Up Bond or SuperEBA. The integrity of the seal was evaluated by fluid filtration. MTA alone leaked significantly more than One-Up Bond or MTA with either secondary seal at 24 h. At 1 month, MTA, MTA plus One-Up Bond, and One-Up Bond alone were equivalent.

Aluminum Compounds↗

PubMed2004

Identification of resected root-end dentinal cracks: a comparative study of transillumination and dyes.

The dilemma of diagnosing and possibly treating dentinal cracks continues to present a challenge in endodontics. The purpose of this in vitro study was to compare the effectiveness of transillumination and dyes in identifying root-end dentinal cracks. Fifty maxillary central incisors were decoronated, and the canals were instrumented to an ISO size 50 at the working length. The apical 3 mm of the roots was resected, and cracks were artificially created in the apical dentin. Four independent examiners evaluated the root ends at x8 magnification with a surgical operating microscope using transillumination (group 1), sodium fluorescein dye (group 2), caries detect dye (group 3), methylene blue dye (group 4), and methylene blue plus transillumination (group 5). The examiners' ability to identify root ends correctly with and without cracks was analyzed by comparing the data with the predetermined standard (cracked and noncracked) using logistic regression analysis. All techniques used were shown to be more effective than random chance at diagnosing cracks. The areas under the curve of the different techniques were as follows: transillumination, 0.81 (95% confidence interval [CI], 0.69-0.93); sodium fluorescein, 0.72 (95% CI, 0.58-0.86); caries detector, 0.76 (95% CI, 0.63-0.89); methylene blue, 0.70 (95% CI, 0.55-0.84); and methylene blue plus transillumination, 0.82 (95% CI, 0.70-0.94). Thus, the crack assessment techniques that gave the best discrimination between cracked and noncracked specimens, regardless of rater, was methylene blue plus transillumination. This study emphasizes the usefulness of transillumination along with magnification in detecting dentinal cracks.

Area Under Curve↗

PubMed2004

Effects of pre- and post-bonding hydration on bond strength to dentin.

PURPOSE: This study tested the hypothesis that the hydration condition of the tooth during bonding or storage may affect the bond strength of a single-step, self-etching adhesive to dentin. MATERIALS AND METHODS: Twelve extracted human third molars were transversally sectioned to expose flat, mid-dentin surfaces. Six teeth were dehydrated in ascending ethanol concentrations for several days while 6 teeth were kept hydrated in distilled water. The teeth were bonded with the single-step, self-etching adhesive One-Up Bond F (Tokuyama, Japan) according to directions. Resin composite buildups were constructed incrementally with Z 250 (3M ESPE). The bonded hydrated and dehydrated teeth were then divided into 2 subgroups and stored either in distilled water or in a dry condition for 24 h before being prepared for the microtensile bond strength test. Bonded beams of approximately 0.8 mm2 were tested in tension at 0.5 mm/min in a testing machine. Separate dentin disks were bonded with the adhesive and prepared for transmission electron microscopy (TEM). RESULTS: Bond strengths of specimens stored in water were: 25.0 +/- 10.6 and 18.9 +/- 9.1 MPa for hydrated and dehydrated teeth, respectively. Bond strengths of specimens stored dry were significantly higher (p < 0.001): 46.1 +/- 21.4 and 40.9 +/- 19.1, for hydrated and dehydrated teeth, respectively. Two-way ANOVA showed that previous hydration condition of the teeth had no effect on the bond strength, regardless of the storage condition (p > 0.05). However, storage of the bonded teeth in water caused significant reductions in the bond strength, regardless of the previous hydration condition of the teeth. TEM showed massive silver nitrate impregnation in the adhesive layer of water-stored specimens. CONCLUSIONS: Postbonding water exposure had a highlysignificant effect on bond strength of the single-step, self-etching adhesive.

Analysis of Variance↗

PubMed2004

Bonding to root caries by a self-etching adhesive system containing MDPB.

PURPOSE: To evaluate the bonding of an experimental antibacterial fluoride-releasing adhesive system (ABF) to normal and carious dentin in human teeth with Class V root caries. METHODS: Mesiodistal sectioning removed the buccal enamel, superficial dentin and much of the carious dentin in 21 extracted human bicuspids with root surface caries. The surfaces of normal coronal and root dentin, and caries-affected and caries-infected dentin were ground with wet 600-grit SiC paper to create a standardized smear layer. Tooth surfaces were treated with the ABF according to manufacturer's instructions, and then covered with excess resin composite. After immersion in 37 degrees C water for 24 hours, the restored teeth were horizontally sectioned into serial slabs that were trimmed into hourglass shapes to isolate the bonded area to the test substrates, and then their bond strengths were measured by the microtensile bond test, and the interfaces examined by SEM and TEM. The bond strengths were statistically compared with ANOVA and Fisher's PLSD (P < 0.05). RESULTS: The bond strengths of ABF to caries-affected and caries-infected dentin were significantly lower than those to normal coronal and root dentin. SEM micrographs revealed that the hybrid layers in caries-affected and caries-infected dentin were more porous compared to the hybrid layer in normal coronal and root dentin. TEM micrographs showed that bacteria that had invaded the dentin were embedded in this adhesive monomer in caries-infected dentin. CLINICAL SIGNIFICANCE: Although the bond strength of ABF adhesive system to root carious dentin is lower than that of normal dentin, the antibacterial and fluoride-releasing properties of ABF may contribute to prevent caries progression and inhibit secondary caries.

Acid Etching, Dental↗

PubMed2004

Effects of storage media on mechanical properties of adhesive systems.

PURPOSE: To evaluate the effects of water vs. oil storage on the mechanical properties of dental adhesives over 3 and 6 months. METHODS: Adhesive resin sheets were prepared by pouring either Single Bond (SB), One-Step (OS) or Clearfil Liner Bond 2V (CL) into a mold measuring 15 x 15 x 0.8 mm. After solvent evaporation, the adhesives were light-cured, removed from the mold and trimmed to either hourglass or I-beam shapes that were used to determine the true stress (TS) and modulus of elasticity (E), respectively. Control adhesive specimens were subjected to tensile testing at 0.6 mm/minute after 24 hours of immersion in distilled water. Experimental specimens were stored at 37 degrees C in either distilled water or mineral oil and tested after 3 and 6 months. The data were analyzed by two-way ANOVA and Tukey's test. RESULTS: Storage in water significantly decreased the TS and E of SB and OS specimens after 3 and 6 months (P < 0.05), but did not cause significant changes in either TS or E of CL specimens in the same periods (P > 0.05). Storage in oil significantly increased the TS of the three adhesives after 3 and 6 months (P > 0.05), and the same trend was observed for E value of CL sample (P > 0.05). CLINICAL SIGNIFICANCE: Exposure of cured adhesive systems to long-term immersion in water caused marked reduction in their mechanical properties. Reduced mechanical properties of the adhesive system may compromise resin/dentin bonds and have a clinical implication on the longevity of adhesive restorations.

Adhesiveness↗

PubMed2004

Nanoleakage types and potential implications: evidence from unfilled and filled adhesives with the same resin composition.

PURPOSE: To compare nanoleakage patterns of an unfilled (OS; One-Step), a 6 wt% spherical silica-filled (OSs; One-Step Plus) and a 15 wt% glass-filled (OSg) version of a two-step, acetone-based self-priming adhesive. Permeability of bonded dentin treated with OS and OSs was also examined. METHODS: Deep, coronal dentin from extracted third molars were etched and bonded using these adhesives. One-mm thick sections were immersed in 50 wt% ammoniacal silver nitrate (pH 9.5) for 24 hours. Unstained, undemineralized sections were examined by TEM. The permeability of dentin bonded with OS and OSs were investigated at 20 cm of H2O hydrostatic pressure and compared with the osmotic conductance determined with 4.8 M CaCl2 at zero hydrostatic pressure. Composite-dentin beams bonded with OS, OSs and OSg that were fractured after microtensile bond testing were examined by SEM. RESULTS: Two types of nanoleakage patterns were recognized along the resin-dentin interfaces. The reticular type consisted of discontinuous islands of silver deposits and was exclusively seen in hybrid layers. The spotted type consisted of isolated silver grains and was evident throughout the hybrid and adhesive layers in OS. These two patterns were seen to variable extents in the two filled adhesive versions OSs and OSg and their distribution was independent of one another. OS and OSs bonded dentin were permeable to fluid filtration. However, part of this fluid movement was due to the permeability of the adhesive layer, as demonstrated by osmotic fluid conductance in the absence of hydrostatic pressure. Fractographic analysis revealed denuded collagen fibrils within fractured hybrid layers that were indicative of incomplete resin infiltration.

Acetone↗

PubMed2004

In vitro evaporative vs. convective water flux across human dentin before and after conditioning and placement of glass-ionomer cements.

PURPOSE: To assess the convective and evaporative fluid movement across glass-ionomer treated dentin. METHODS: Crown segments made from extracted human teeth, were divided into two groups of 14 teeth each. Each segment was cemented onto a plexiglass slab penetrated by a stainless steel tube, permitting filling of the pulp chamber with water. This set-up was attached to a device that measured fluid movement through the dentin in the crown segment. The experimental design involved repeated measurements of convective and evaporative fluid movements in each of the following conditions: smear layer-covered dentin, conditioned dentin, dentin after placement of one of two glass-ionomers (Fuji IX or Ketac-Molar), with and without a protective coating. The same water fluxes were remeasured after storage of the samples for 24 hours in distilled water. RESULTS: Statistical analysis of the results using ANOVA indicated a significant difference between the two measured water fluxes (P < 0.001). There was also a significant difference between the two materials (P < 0.001), with Ketac-Molar allowing higher permeability than Fuji IX. Conditioning the dentin surface with polyacrylic acid increased the convective water flux (P < 0.05) but did not change the evaporative water flux. Placement of the glass-ionomer material did not change the rate of spontaneous evaporation of water from the dentin, but the application of a coating agent reduced the evaporative water loss. These values were not significantly different when the specimens were stored for 24 hours.

Acrylic Resins↗

PubMed2004

Single-step, self-etch adhesives behave as permeable membranes after polymerization. Part I. Bond strength and morphologic evidence.

PURPOSE: To test the hypotheses that microtensile bond strengths of single-step, self-etch adhesives to hydrated dentin are adversely affected by delayed-activation of a light-cured composite, as well as the use of a chemical-cured composite. METHODS: Seven commercially available and one experimental single-step, self-etch adhesives were bonded to hydrated human dentin. A dual-cured composite was used and activated using: [1] the light-cured mode (base paste only-control), [2] the chemical-cured mode (base and catalyst pastes, in the dark); and [3] delayed light-activation (base syringe only, left on top of cured adhesives in the dark for 20 minutes before activation). After microtensile bond strength evaluation, fractured samples were examined using SEM. Intact, unstressed interfaces of [1] and [3] were examined with TEM. Microtensile bond strengths were also evaluated for selected adhesives bonded to dehydrated dentin and coupled with the composite activated by [2] or [3]. RESULTS: For all adhesives, bond strengths decreased significantly to bonded hydrated dentin when the composites were activated with [2] or [3] (P< 0.001). Whereas the hybrid layer-adhesive interface was intact, water-blisters that developed along the adhesive-composite interface in these two modes were responsible for the decline in bond strength. When bonded to dehydrated dentin, delayed light-activation of the light-cured composite did not result in compromised bond strength. The results of chemical-cured composites improved but were more variable and system-dependent.

Composite Resins↗