Biomedical subjects

D H Pashley

Publications and source records attributed to D H Pashley.

At least 91 records · Page 5Linked to original sources

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↗

PubMed2000

Buffering action of human dentin in vitro.

PURPOSE: The purpose of this study was to determine the relative contributions of the mineral and organic phases of dentin to its total buffering capacity and to compare the buffering abilities of normal and caries-affected dentin for acids used in adhesive dentistry. MATERIALS AND METHODS: Disks of normal and caries-affected human coronal dentin 0.6 mm thick were prepared. Fifty microL of various acids were applied to the surface of mineralized or completely demineralized dentin for varying lengths of time. They were collected from the surface and combined with water rinses to permit titration of the total amount of acid applied, the amount recovered, the total amount that was taken up by the dentin, and the amount that diffused across dentin into 1 mL of water. Equal volumes of acids were applied to mineralized or demineralized dentin powder or hydroxyapatite powder. RESULTS: About 88% to 90% of applied acid was recovered from the surface; only 10% to 12% of the acid was taken up by dentin. Of the H+ that was taken up, only 1% to 2% actually diffused across 0.6 mm of dentin. Increasing the application time of 37% phosphoric acid did not increase the amount of H+ that diffused across dentin. Increasing the concentration of phosphoric acid from 10% to 65% produced only slight increases in H+ diffusion across dentin. There was no difference in the buffering capacity of normal vs caries-affected dentin disks. Almost all of the buffering capacity of dentin is due to its mineral phase. CONCLUSION: The high buffering capacity of dentin and the high reactivity of H+ insure that little H+ diffuses through dentin more than 0.6 mm thick.

Analysis of Variance↗

PubMed2000

Bonding of a self-etching primer to non-carious cervical sclerotic dentin: interfacial ultrastructure and microtensile bond strength evaluation.

PURPOSE: The objectives of this study were 1) to examine the ultrastructural features of the resin-sclerotic dentin interface following the application of Clearfil Liner Bond II sigma to natural cervical wedge-shaped lesions, and 2) to evaluate the regional tensile bond strength of this self-etching primer at different locations on natural and artificially-created cervical lesions. MATERIALS AND METHODS: Deep cervical natural lesions were bonded using the self-etching primer. Micromorphology of the bonded interface at different locations within the lesions were examined using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and scanning transmission electron microscopy/energy dispersive x-ray analysis (STEM/EDX). Ultrastructural features were further compared with the use of the same self-etching primer on artificial lesions created in sound cervical dentin. A nontrimming technique was used to evaluate the regional tensile bond strength from the occlusal, gingival, and the deepest central part of both natural and artificial cervical lesions. Beams with a mean area of 0.46 +/- 0.03 mm2 were prepared and were pulled to failure using a Bencor Multi-T testing device attached to an Instron universal tester. Bond strength results were evaluated using a two-way ANOVA design. RESULTS: A hypermineralized layer devoid of intact, banded collagen was invariably present on the surface of the natural lesions. Depending upon its thickness at different locations of the lesion, the action of a self-etching primer may be limited to this surface layer alone, producing a hybridized hypermineralized surface layer. Penetration of the self-etching primer into the underlying sclerotic dentin produced a hybridized complex containing a hybridized hypermineralized surface layer as well as a subsurface layer of hybridized intertubular dentin. Bacterial colonization of the lesion surface resulted in the formation of an additional zone of hybridized intermicrobial matrix over the surface of the lesions. Dentinal tubules remained blocked with sclerotic casts, and resin tags were rarely observed. Regional tensile bond strength results showed that the overall bond strength to natural sclerotic dentin was about 20% lower than sound cervical dentin, but was independent of the different locations within the lesions from which bond strength was evaluated. CONCLUSION: There were four factors that may have influenced the overall decrease in bond strength in natural cervical sclerotic lesions: a) the presence of a hybridized intermicrobial matrix together with entrapped bacteria may have weakened the bonds, b) inability of a self-etching primer to etch through a thick, hypermineralized surface layer, c) presence of a layer of possibly remineralized, denatured collagen at the base of the hypermineralized surface layer, and d) retention of acid-resistant sclerotic casts that obliterate the tubular lumina and prevent effective resin tag formation.

Acid Etching, Dental↗

PubMed2000

Comparative microtensile bond strength and SEM analysis of bonding to wet and dry dentin.

PURPOSE: To compare bond strengths of resins to acid-etched wet vs. dry dentin. MATERIALS AND METHODS: Human third molars were bonded with One-Step (OS), Single Bond (SB) or Clearfil PhotoBond (PB) under control moist or air-dried (5 s air blast) conditions. Tensile bond strengths were tested using the microtensile bond testing method. Scanning electron microscopy was done to evaluate the quality and thickness of the hybrid layers following polishing and acid plus NaOCl-challenge. RESULTS: The tensile bond strengths of OS, SB and PB were significantly (P < 0.01) lower (8-19 MPa) to air-dried dentin than to moist dentin (39-50 MPa). No hybrid layers were seen in the air-dried specimens bonded with OS or SB, while relatively thin hybrid layers were produced by PB. In contrast, moist dentin produced high bond strengths with all bonding systems and created thicker, acid/NaOCl-resistant hybrid layers. These results support the predictions of a previously published morphologic model and offer a morphologic explanation for the differences in bond strengths between wet vs. dry bonds.

Acid Etching, Dental↗

PubMed1999

A novel approach to AFM characterization of adhesive tooth-biomaterial interfaces.

A novel approach is proposed for studying tooth-biomaterial interactions with high resolution. Thus far, polished interfaces examined by AFM have not disclosed much detail, mainly due to the destruction of soft surface texture and the smearing of polishing debris across the interface that obscures the actual ultra-structure. Therefore the practical utility of diamond-knife microtomy as a sample preparation technique for imaging tooth-biomaterial interfaces by AFM with high resolution was tested in this study and compared to that of ultra-fine mechanical polishing techniques. The AFM images clearly demonstrated the enhanced potential of diamond-knife microtomy for nondestructively producing clean cross-sections through interfaces that allow the interfacial ultra-structure to be imaged by AFM with a resolution equaling that of TEM. This novel approach opens the field to the full range of scanning probe microscopy, including physical and chemical surface characterization of interfaces with a mix of soft and hard substrates.

Dental Cements↗

PubMed1999

Changes in root surface temperatures with in vitro use of the system B HeatSource.

The purpose of this study was to measure root surface temperatures while using the System B HeatSource at various temperature settings. A split-tooth model of a human maxillary central incisor was prepared with 10 thermocouples to record root surface temperatures at 1-mm increments from the root apex. A System B HeatSource model 1005 was used to warm and compact gutta-percha to within 3 mm of the working length using the Buchanan technique. Twenty obturations were recorded at each of the following temperature settings: 250 degrees, 300 degrees, 350 degrees, 400 degrees, 450 degrees, 500 degrees, 550 degrees, and 600 degrees C. Examination of the mean temperatures recorded for each position and at each temperature setting revealed that the thermocouple 5 mm from the apex (T5) detected the highest increases in root surface temperatures. Only this site exceeded the 10 degrees C rise in temperature for one full minute that could cause damage to the supporting structures. The range of instantaneous temperatures at this site was 8.85 to 12.06 degrees C, with a mean of 10.62 +/- 0.93 degrees C. The results of this in vitro study indicate that any temperature setting of the System B HeatSource at or above 250 degrees C has the potential to cause the root surface temperature to rise 10 degrees C. Whether this occurs in vivo or if it does is maintained long enough to cause any tissue damage remains to be determined.

Body Temperature↗

PubMed1999

Effect of removal of surface collagen fibrils on resin-dentin bonding.

OBJECTIVES: The aim of this study was to evaluate the effects of NaOCl at removing the demineralized layer by examining the morphology of the hybrid layer and measuring shear bond strengths after different dentin treatments. METHODS: Dentin disks were treated with: (1) 35% phosphoric acid (PA) 20 s; (2) PA treatment followed by 1.5% NaOCl, 2 min; (3) PA treatment, followed by a 10% NaOCl immersion for 120 h. SEM was used to analyze the morphology of dentin and its interface with dentin bonding agents (DBAs), while shear bond strength tests were used to measure adhesion. All specimens were then fractured into two halves: One half was inspected under SEM; the other half was sequentially placed in 10% PA followed by 12.5% NaOCl for 70 h, to remove all dentin from the resin replica of the original bonded interface. RESULTS: SEM observations showed that collagen fibrils were completely removed from the acid-etched surface by NaOCl treatment. The diameter and the size of dentinal tubules and the number of lateral branches of the tubules were increased following NaOCl treatment. NaOCl applied on dentin smear layers did not significantly modify their SEM morphology. Resin tags were larger in diameter after phosphoric acid/NaOCl treatment than after only phosphoric acid treatment. Resin-infiltrated dentin-layers were only observed after the single phosphoric acid (i.e. conventional etching) procedure, and were not observed after combined phosphoric acid/NaOCl treatment. Etched/NaOCl samples showed a lower bond strength using Scotchbond MP and 3M Single Bond, but were higher in Optibond FL and unmodified in Prime & Bond 2.0 groups when compared with acid-etched controls. Treatment of etched dentin with NaOCl for 120 h produced an unusual type of resin infiltration of mineralized dentin that could be called a "reverse hybrid layer" which may explain the mechanism of resin bonding to NaOCl treated dentin. SIGNIFICANCE: The use of acidic conditioners for exposure of the collagen matrix exposes a soft delicate mesh that can collapse, thereby interfering with resin infiltration. If acid-etching is followed by NaOCl treatment, high bond strengths can be achieved via "reverse hybrid layer" formation, a proposed new mechanism of micromechanical resin retention. This mechanism is not yet recommended for clinical use but demonstrates a new type of resin retention.

Adolescent↗

PubMed1999

Effect of water content on the physical properties of model dentine primer and bonding resins.

OBJECTIVE: Primers and adhesives containing hydroxyethyl methacrylate (HEMA) are placed on moist dentine even though several studies indicate that water may interfere with the polymerization reaction. The purpose of this study was to evaluate the influence of increasing amounts of water on the physical properties of a model dentine primer resin (HEMA) and model dentine bonding resin (a mixture of HEMA and Bis-GMA). METHODS: Miniature (ca 10 x 0.5 mm (long x thick) hour-glass shaped and parallel-sided specimens were created by casting the monomer or comonomer mixtures into appropriately shaped moulds. The water content was either 0, 5, 9, 17 or 29 vol%. One hour after polymerization, half the specimens were subjected to physical testing under dry conditions. The other half were immersed in water for 24 h and then tested while wet. The ultimate tensile strength (UTS), modulus of elasticity (E), percent elongation at failure, and toughness were calculated. RESULTS: The properties of the dry-stored primer and bonding resins were not altered by water incorporation up to 9 vol%. Higher water content lowered the physical properties (P < 0.05). Immersion of primers polymers in water for 24 h significantly decreased their properties. Water immersion of the bonding resins was unaffected only for specimens containing 0 or 5 vol% water. CONCLUSIONS: The plasticizing effects of extrinsic water are far more important than the effects of intrinsic water in poly-HEMA resin. Hybrid layers composed primarily of poly-HEMA would be expected to be more elastic than those made with bifunctional, cross-linked polymer chains.

Bisphenol A-Glycidyl Methacrylate↗

PubMed1999

Regional measurement of resin-dentin bonding as an array.

During the development of the microtensile bond-testing method, large variations in bond strengths were noted among serial sections. The reason for these variations is unknown. The purpose of this work was to determine the consistency of resin-dentin bond strengths across the occlusal surface of coronal dentin by dividing composite resin buildups into an array of 1x1 mm beams, the top half consisting of composite resin, and the bottom half consisting of dentin. Extracted human third molars had the occlusal enamel removed as a single section by means of a diamond saw. Resin composite buildups were made after the dentin was bonded with either One-Step or MacBond. After being stored in 37 degrees C water for 1 day, the teeth were vertically sectioned at 1-mm increments into slabs of bonded teeth. Each slab was further subdivided by vertical sections into 1x1x8 mm beams. Each beam was assigned an x-y coordinate and tested for tensile bond strength. Two different clinicians (A and B) performed the same procedures using One-Step in a parallel study. Using One-Step, clinician A obtained a large number of zero bonds in superficial dentin but fewer in deep dentin. This resulted in a very large standard deviation in bond strengths (mean +/- SD of 22+/-20 MPa in superficial dentin and 27+/-14 MPa in deep dentin). Clinician B obtained much higher (p<0.001) and more uniform bond strengths with One-Step (56+/-13 MPa in superficial dentin and 57+/-12 MPa in deep dentin). With MacBond, there were no zero bonds and hence less variation, with a mean of 41+/-13 MPa in superficial dentin and 27+/-12 MPa (x +/- SD) in deep dentin. When pairs of Z100 resin composite cylinders were bonded together with One-Step and then sectioned into an array, there was little variation in regional bond strength (37 +/-1 MPa). Dividing bonded resin composite buildups into an array of 20 to 30 1x1x8 mm beams allows for the evaluation of uniformity of resin-dentin bonds. The method used in this study detected local regional differences in resin-dentin bond strengths. The largest differences were shown to be related to technique rather than to material. The results indicate that resin-dentin bonds may not be as homogenous as was previously thought.

Adhesiveness↗

PubMed1999

Effects of dentin depth and cavity configuration on bond strength.

During polymerization of resin composites, shrinkage stresses compete with resin-dentin bonds in a manner that can cause failure of the bond, depending upon the configuration of the cavity, its depth, and the restorative technique. The hypothesis tested in this study was that the effect of cavity configuration (C) and remaining dentin thickness (RDT) influence resin bond strength to the dentin of Class I cavity floors. The occlusal enamel was ground to expose a flat superficial dentin surface as a control (superficial dentin, C-factor = 1) in human extracted third molars. Cavities 3 mm long x 4 mm wide were prepared to a depth 2 mm below the ground dentin surfaces (deep dentin within cavity floor, C-factor = 3). To assess the relationship between C-factor and RDT, we removed the walls of cavities, making a deep flat surface for bonding (deep dentin, C-factor = 1). The teeth were restored with either Clearfil Liner Bond II (LB II), One-Step (OS), or Super-Bond D Liner (DL), followed by Clearfil Photo Posterior resin composite. After 24 hrs' storage in water, the teeth were sectioned vertically into 3 or 4 slabs (0.7 mm thick) and trimmed for the micro-tensile bond test so that we could determine the strength of the resin bonds to the pulpal floor. All groups gave high bond strengths to superficial dentin, but OS and DL gave significantly lower bond strengths to flat deep dentin when the C-factor was 1. When the C-factor was increased to 3 by the creation of a three-dimensional cavity preparation, the bond strengths of all materials fell (range, 21 to 35%), but the difference was significant (p < 0.05) only with DL. SEM observations of failure patterns showed that specimens with high bond strengths tended to exhibit cohesive failures within the hybrid layer, while specimens exhibiting low bond strengths showed failures at the top of the hybrid layer. Some adhesives do not bond well to deep dentin, making them more susceptible to polymerization shrinkage stress that develops in cavities with high C-factors.

Analysis of Variance↗

PubMed1999

Long-term durability of dentin bonds made with a self-etching primer, in vivo.

The long-term durability of bonds between adhesive resins and dentin is of significant importance for the longevity of bonded restorations. We carried out an in vivo one-year study to evaluate the durability of resin-dentin bonds in the oral cavity, as well as to test the hypothesis that the adhesive interface would show morphological changes in vivo over time. Very shallow saucer-shaped dentin cavities were prepared in 12 intact teeth of one Japanese monkey (Macaca fuscata) under general anesthesia. The cavities were restored with Clearfil Liner Bond II and Clearfil Photo Posterior resin composite. The teeth were extracted at three different times: immediately, and 180 and 360 days after placement of the restorations. One day after the monkey was killed, specimens of the three time periods were subjected to the micro-tensile bond test at a crosshead speed of 1 mm/min. The surfaces of the failed bonds were observed under a field emission scanning electron microscope (FE-SEM). Bond strength measurements in this study were successfully performed and were stable at approximately 19 MPa during the one-year testing. Scanning electron microscopic observations of the failed surfaces revealed, at the top of the hybrid layer and within the adhesive resin, porosity which increased over time. Long-term bonds can be assessed in vivo by the combined evaluation of the microtensile bond strength and SEM morphological examination of the adhesive interface.

Acid Etching, Dental↗

PubMed1999

Effect of moist vs. dry bonding to normal vs. caries-affected dentin with Scotchbond Multi-Purpose Plus.

Recent research in dentin bonding demonstrated the superiority of moist bonding over dry bonding on normal dentin, but it is unclear if this technique is also superior in bonding to caries-affected dentin. The purpose of this study was to evaluate the SEM appearance and bond strength of Scotchbond Multi-Purpose Plus (SMPP) to normal vs. caries-affected dentin bonded under moist vs. dry conditions, with and without polyalkenoic acid in the primer. Extracted carious human third molars were ground down by means of 600-grit SiC paper until the carious dentin no longer stained with caries detector solution. The flat surfaces were then primed, bonded, and built up with resin composite. After soaking in water for 1 day, the teeth were serially sectioned vertically into 5 or 6 slabs 0.7 mm thick. The bonded caries-affected areas were isolated by means of an ultrafine diamond bur to create an hourglass configuration with a cross-sectional area of 0.9 mm2. Bonded normal dentin was isolated the same way. Each specimen was attached to a Bencor device and tested in tension to failure. SMPP bonds to dry, normal dentin were only half as strong (21+/-10 MPa, x +/- SD) as those made to moist, normal dentin (42+/-9 MPa, p<0.01). There was no significant difference between bonds made to normal vs. caries-affected dentin by means of the moist technique (42+/-9 vs. 48+/-4 MPa, respectively). Removal of the polyalkenoic acid from the primer lowered (p<0.05) the bond strength of SMPP to caries-affected dentin (38+/-8 MPa). The benefits of moist bonding extend to caries-affected dentin. The polyalkenoic acid in the SMPP primer contributes to the high bond strength that can be achieved to caries-affected dentin.

Analysis of Variance↗

PubMed1999

Dentin permeability after toothbrushing with different toothpastes.

PURPOSE: To evaluate the interaction of smear layer produced during brushing and dentifrice particles. MATERIALS AND METHODS: Dentin disks were obtained from extracted human third molars. Dentin permeability was evaluated using a hydraulic pressure apparatus working at 1 psi of pressure. After preparation, each sample was connected to the hydraulic pressure apparatus to evaluate the permeability of dentin with the smear layer produced during specimen preparation. After 5 min of measurements dentin was etched with 37% phosphoric acid gel for 2 min, washed and gently dried with cotton to measure the permeability after smear layer removal. This was done to measure the maximum permeability of each specimen (expressed as 100%). Then a second smear layer was produced using a #400 carbide paper under water for 1 min. Dentin permeability of the smear layer covered dentin was then measured, and expressed as a percent of the maximum permeability of that specimen, permitting each specimen to serve as its own control. The three toothpastes used (Merfluan powder, Merfluan paste and Fluorigard) were applied on dentin surfaces using a small sponge to completely cover the dentin surface. After 5 s, each sample was connected to a mechanical device and brushed under water for 3 min with constant pressure of 250 gr using a Colgate medium toothbrush. After this treatment, each sample was gently washed with tap water, gently air dried for 3-5 s and connected with the pressure apparatus to remeasure the permeability after brushing. For SEM examination of dentin before and after treatment with toothpaste and brushing, each dentin and enamel sample was fixed in 2% buffered glutaraldehyde. RESULTS: Dentin permeability proved unaffected by dentifrice treatments. SEM observations demonstrated the presence of dentifrice particles on dentin surface and inside dentin tubules. Smear plugs produced during dentin brushing were not removed by dentifrices.

Dentin↗

PubMed1999

Bonding to caries-affected dentin using self-etching primers.

PURPOSE: To evaluate resin bond strengths to caries-affected versus normal dentin using three self-etching primer adhesive systems. MATERIALS AND METHODS: Carious lesions were excavated and then bonded with one of three self-etching primer adhesive systems (Clearfil Liner Bond 2, Clearfil Liner Bond 2V, A.R.T. Bond). A crown was then built up using a resin composite to a height of 4 mm. Five to six serial slabs approximately 0.7 mm thick were sectioned perpendicular to the bonded surface. The bonded caries-affected or normal dentin areas were isolated to create an hourglass configuration with a cross-sectional area of approximately 1 mm2. The specimens were subjected to tensile stress at a crosshead speed of 1.2 mm/min. The bonded interfaces to caries-affected and normal dentin were examined with an SEM. RESULTS: Clearfil Liner Bond 2 and Clearfil Liner Bond 2V produced high bond strengths to normal dentin, but significantly lower bonds than to caries-affected dentin. (P < 0.05). For A.R.T. Bond, there was no statistically significant difference between types of dentin. All three bonding systems produced thin (+/- 0.5-1.5 microns) hybrid layers in normal dentin. When used on caries-affected dentin, all self-etching primer systems produced hybrid layers that were twice as thick as those produced in normal dentin.

Acid Etching, Dental↗

PubMed1999

The microtensile bond test: a review.

PURPOSE: The purpose of this review is to describe all of the various modifications of the microtensile bond test in one paper, so that investigators can select the modification that best suits their needs. METHODS: The essence of the microtensile test is the division of resin-bonded teeth into slabs between 0.5 and 1.0 mm thick that are then trimmed in such a manner that tensile force will be concentrated on the bonded interface during testing. Among the many advantages of the technique are that each tooth produces multiple specimens. Further, there is no need for a matrix to limit the bonded surface area, since the area is determined by the dimensions of the trimmed specimens. RESULTS: The various modifications of the microtensile test have been used to measure differences in regional bond strength across occlusal dentin, down the external surface of teeth from crown through roots, down the internal surface of root canals from cervical to apical thirds, as well as to compare normal vs caries-affected occlusal dentin and normal vs sclerotic cervical dentin. The technique is ideal for evaluating the long-term durability of resin-hard-tissue bonds. CONCLUSION: The microtensile test methods offer versatility that cannot be achieved by conventional methods. It is more labor-intensive than conventional testing, but holds great potential for providing insight into the strength of adhesion of restorative materials to clinically relevant sites and substrates.

Dental Bonding↗

PubMed1999

Durability of resin-dentin bonds.

PURPOSE: The purpose of this study was to determine if the durability of resin-dentin bonds could be evaluated more quickly if the bond specimen was divided into 1 x 1 x 8 mm beams incubated at 37 degrees C for a 90-day period. MATERIALS AND METHODS: Extracted human third molars were prepared for bonding by removing the occlusal surface near the dento-enamel junction (superficial dentin group) or near the pulp (deep dentin group). The teeth were bonded either with MacBond, One Step or Clearfil Liner Bond 2, and then builtup to form a flat resin composite crown. After 24 hours in water, each buildup was vertically divided into slabs 1 mm thick, the top half of which was resin, with the bottom half as dentin. Each slab was then vertically sectioned at 1-mm increments to create 1 x 1 x 8-mm beams of resin-bonded dentin. They were incubated for 1 day or 90 days at 37 degrees C, followed by measurement of the tensile bond strengths. The results were analyzed by the Least-Squares Means method at the 95% confidence level. RESULTS: MacBond gave the highest (p < 0.05) 1-day bond strengths to superficial dentin, but significantly lower bond strengths were measured in deep dentin. There were no significant differences in the bond strengths of either One Step or Clearfil Liner Bond 2 to superficial vs deep dentin at 1 day, but at 90 days their bond strengths to deep dentin had fallen significantly (p < 0.05). Prepolymerized cylinders of resin composite bonded together with One Step showed little variation in bond strength over the 90-day experiment. SEM examination of the failed bonds showed increased porosity in intertubular dentin over time. CONCLUSION: The results indicate that division of large specimens into many small beams accelerated the deterioration of bond strength in deep dentin in all three bonding systems and in both superficial and deep dentin in the MacBond treated specimens. This method seems promising for studying the durability of resin-dentin bonds.

Alkanes↗

PubMed1999

Distribution of nanofillers from a simplified-step adhesive in acid-conditioned dentin.

PURPOSE: This in vitro study examined the interfacial ultrastructure of a nanofilled, simplified-step adhesive (Prime & Bond NT, Dentsply), to determine the distribution of nanofillers within the collagen network of the hybrid layer. MATERIALS AND METHODS: Twenty-four dentin discs were divided into two groups and bonded using two recommended conditioning techniques: Group I, NRC (Non-Rinse Conditioner), and Group II, Conditioner 36 (colloidal silica thickened 36% phosphoric acid). Following conditioning, a single coat of adhesive was applied and light-cured. Dentin discs were then bonded to form disc-pairs and processed for TEM examination. Demineralized, ultrathin sections were examined stained or unstained. Non-demineralized sections were used for STEM/EDX analysis of elemental distribution across the resin-dentin interface. In addition, four dentin discs were bonded with a generic adhesive (HEMA/TBBO) for TEM examination of stained collagen and proteoglycans. RESULTS: In unstained sections of both groups, nanofillers from the adhesive layer were congested around patent tubular orifices, but were not found within the interfibrillar spaces of the hybrid layer. EDX analysis of silicon (Si) showed predominant distribution within the adhesive layer and tubular orifices. Phosphorus (P) was present within the hybrid layer and adhesive layer in Group II. CONCLUSION: It is hypothesized that a) aggregation of the nanofillers within the adhesive resulted in filler clusters that are too large to infiltrate the interfibrillar spaces of the hybrid layer; and b) retention of ground substance within the demineralized intertubular collagen matrix may also have prevented the infiltration of the nanofillers.

Acid Etching, Dental↗

PubMed1999

Hybridization effectiveness of a two-step versus a three-step smear layer removing adhesive system examined correlatively by TEM and AFM.

PURPOSE: The objectives of this study were (1) to compare the hybridization effectiveness of two adhesive systems that are applied in respectively three and two steps, and (2) to determine the best resin-dentin interface preparation technique for atomic force microscopy (AFM). MATERIALS AND METHODS: The resin-dentin interface produced by the three-step OptiBond Dual-Cure (Kerr) and its simplified two-step successor OptiBond Solo (Kerr) was ultramorphologically examined using transmission electron microscopy (TEM) and AFM. Four different methods were used to prepare interface specimens for AFM: (1) polishing to a 0.1-micron finish with a silicon oxide suspension, (2) polishing to a 0.05-micron finish with an aluminum oxide suspension, (3) argon-ion etching, and (4) sectioning with a diamond knife. RESULTS: Both TEM and AFM demonstrated that some collapse of the exposed collagen fibril network, due to gentle postconditioning air-drying of the dentin surface, may not have been totally recovered through hybridization by the two-step adhesive formulation as opposed to the three-step precursor. From the four interface preparation methods, only diamond-knife sectioning revealed sufficient ultramorphologic detail and high resolution that can capitalize on the high resolution offered by AFM. CONCLUSION: First, the findings suggest that simplifying the application procedure of adhesives by combining the primer and adhesive resin into a single application step may reduce hybridization effectiveness. Future research should confirm this effect for other two- versus three-step adhesive systems. Second, diamond-knife sectioning should be used for future topographic imaging and physicomechanical testing of resin-dentin interfaces by AFM.

Bisphenol A-Glycidyl Methacrylate↗