Biomedical subjects

D H Pashley

Publications and source records attributed to D H Pashley.

At least 109 records · Page 6Linked to original sources

PubMed1998

Microleakage of endodontically treated teeth restored with posts.

A fluid filtration system using 15 psi of pressure on the penetrating fluid was used to quantify the amount of microleakage of a stainless-steel post and a carbon-fiber post system, each placed with various cements. Statistical analysis showed that there was a significant difference in microleakage between the cements (p < 0.001). Zinc phosphate cement showed the most microleakage, whereas C & B Metabond cement showed the least. There was no significant difference in microleakage between the stainless-steel and carbon-fiber posts. The results of this study showed that both posts, when cemented with dentin-bonding resin cements (C & B Metabond and Panavia-21), exhibited less microleakage than when cemented with non-dentin-bonding cements (glass ionomer and zinc phosphate).

Analysis of Variance↗

PubMed1998

Effects of HEMA on water evaporation from water-HEMA mixtures.

OBJECTIVES: The aims of this research were: (1) to determine the relative rates of evaporation of water and HEMA, and (2) to determine the effects of increasing concentrations of HEMA on the rate of evaporation of water from water and HEMA mixtures. METHODS: Ten microliters of each solution (100% H2O, 75% H2O-25% HEMA, 50% H2O-50% HEMA, 25% HEMA, 100% HEMA) were placed on the pan of a thermogravimetric analysis instrument held at 37 degrees C. The rate of spontaneous weight loss was measured as a function of time and relative humidity (RH) and compared statistically using ANOVA and Scheffé F test. RESULTS: The rate of evaporation of pure water was 32-fold higher than that of 100% HEMA. Addition of HEMA to water lowered the rate of evaporation of water from the water-HEMA mixtures in a manner that was proportional to its effect on lowering the vapor pressure of water (p < 0.05 comparing 50% HEMA with 75% HEMA). The rate of evaporation of water from water-HEMA mixtures was higher (p < 0.05) when the ambient gas was at 0% RH than when it was at 51% RH. SIGNIFICANCE: The results indicate that as water evaporates from water-HEMA mixtures, the concentration of HEMA rises because it is relatively non-volatile. This rise in HEMA concentration lowers the vapor pressure of water making it more difficult to remove the last amounts of water. This residual water may interfere with polymerization of adhesive monomers, thereby lowering the quality of the hybrid layer.

Analysis of Variance↗

PubMed1998

The effects of Pain-Free Desensitizer on dentine permeability and tubule occlusion over time, in vitro.

The purpose of this in vitro study was to evaluate the efficacy of a new resin emulsion (Pain-Free Desensitizer) treatment for dentine hypersensitivity, for its ability to decrease dentine permeability. Crown segments were prepared from extracted, unerupted human 3rd molars by horizontal sectioning to remove occlusal enamel and the roots. The specimens were allocated in one of two groups: In group 1, the dentine surface was acid-etched to simulate the patent tubules of hypersensitive dentine. In group 2, the mineralized dentine surface was polished free of smear layer using a hydroxyapatite paste and ultrasonication. The hydraulic conductance of each specimen was then measured to obtain a pretreatment of control value. After a single treatment with resin desensitizer, the permeability was remeasured at 5 min, 1 day, 1 week and 1 month. Between measurements, the specimens were stored in buffer solution to simulate the solubilizing effects of saliva. Parallel specimens were followed by SEM examination. The results showed that a single treatment with resin desensitizer produced large, immediate, reductions in dentine permeability in both acid-etched and mineralized surfaces. In the acid-etched (group 1) specimens, the permeability returned to control values within 7 days, while the permeability of the group 2 specimens remained low even after 30 days of soaking. This simple treatment for occluding dentinal tubules may provide sufficient temporary reduction in dentine permeability to permit the development of natural desensitization.

Analysis of Variance↗

PubMed1997

The disintegration of superEBA cement in solutions with adjusted pH and osmolarity.

This study determined the disintegration of fast-set SuperEBA cement using ANSI/ADA Specification No. 30 (Spec #30) as well as modifications in pH, osmolarity, time before immersion, and duration of immersion that mimic the clinical, endodontic application of this material. After immersion intervals of 24 h, 1 wk, 1 m, 3 m, or 6 m, specimens were desiccated and weighed. The preimmersion and postdehydration weights were obtained to the nearest 1.0 mg and the percent weight loss from preimmersion levels was calculated. Adjusting the osmolarity to the physiologic level of 300 mOsm/kg resulted in significantly less weight loss (p < 0.05) than the control group in distilled water (no modification of Spec #30). The pH of the storage solution was found to be a significant factor in weight loss. As the acidity and the time of immersion increased, the weight loss also significantly increased with the greatest weight loss of 19.81% at pH 5.5 after 6 m storage. Immersion within 10 min of mixing was not significantly different (p > 0.05) in weight from the control of 1 h set-time. The 24 h weight loss measurements for the pHs of 5.5 and 6.4 were greater than the 1.5% allowed by Spec #30. All other 24 h measurements were less than the 1.5%.

Analysis of Variance↗

PubMed1997

Effects of cross-sectional area on resin-enamel tensile bond strength.

OBJECTIVE: It was hypothesized that there is an inverse relationship between resin-enamel bond strength and bonded cross-sectional area, and that there are regional differences in resin-enamel bond strength. METHODS: The facial and lingual surfaces of extracted human third molars were ground down 0.3 mm using 240 grit abrasive paper and were then bonded with either Clearfil Liner Bond 2 or Scotchbond Multi-Purpose Plus adhesive systems using the manufacturer's instructions. The bonded surfaces then received a resin composite build-up. After 24 h of storage in water, the bonded teeth were vertically serially sectioned into 1.0 mm thick slabs using a diamond saw, and the bonded surface area at the resin-enamel interface was varied from 0.5 to 3.0 mm2 using a diamond saw under microscopic observation. The trimmed region was varied from the occlusal third of the facial or lingual enamel to the middle third, to the cervical third. The trimmed specimens were then glued to a Bencor Multi-T device, placed in an Instron testing machine and stressed to failure at 1 mm/min. A three-factor ANOVA was used to compare bond strengths (buccal vs. lingual, occlusal vs. middle vs. cervical-third, vs. materials). Regression analysis was used to examine the relationship between bond strength and bonded cross-sectional area for each material on occlusal enamel. RESULTS: For both bonding systems, there was a highly significant (p < 0.001) inverse exponential relationship between tensile bond strength (y axis) and bonded cross-sectional area (x axis) with y intercepts of 51 and 59 MPa for Clearfill Liner Bond 2 and Multi-Purpose Plus, respectively. Using both materials, the highest bond strengths were measured in the occlusal third, which were significantly higher (p < 0.05) than those made to cervical enamel. SIGNIFICANCE: Like resin-dentin bonds, resin-enamel bonds exhibit an inverse relationship with cross-sectional area. This relationship becomes more apparent at bonded surface areas below 2 mm2 and is probably due to reductions in the number of interfacial stress-raisers as samples are made smaller.

Analysis of Variance↗

PubMed1997

Dentine permeability and dentine adhesion.

OBJECTIVES: The objectives of this paper are to review the structure of dentine as it pertains to adhesive bonding and to describe the importance of resin permeation into dentinal tubules and into spaces created between collagen fibrils by acid-etching during resin bonding. The advantages and disadvantages of separate acid-etching, priming and adhesive applications are discussed. DATA SOURCES: Although not an exhaustive review, the concepts included in the review were obtained from the dentine bonding literature. STUDY SELECTION: Attempts were made to critically evaluate what is known about dentine permeability and adhesion and what remains to be discovered. Speculations were made on a number of controversial issues that are not yet resolved. CONCLUSIONS: Acid-etching of dentine produces profound changes in the chemical composition and physical properties of the matrix which can influence the quality of resin-dentine bonds, their strength and perhaps their durability.

Acid Etching, Dental↗

PubMed1997

Effects of fluoride on structure and function of canine gastric mucosa.

These studies were done to determine the effects of fluoride (F) on the structure and function of the canine gastric mucosa and the possible protective effects of 16,16-dimethyl-prostaglandin E2 (dmPGE2). A portion of the stomach with its vascular supply intact was mounted in a two-compartment chamber, one side of which contained a control solution. Minor effects were caused by exposure to 1 mmol/liter F. Both 5 and 10 mmol/liter F caused marked increases in the fluxes of water and Na, K, and H ions; mucus secretion; and tissue swelling and redness. The extent of these changes did not increase appreciably upon exposure to 50 or 100 mmol/liter F. Histological findings included marked thinning of the surface cell layer, reduced uptake of PAS stain, localized exfoliation and necrosis of surface cells, acute gastritis, and edema. It was concluded that: (1) the threshold F concentration for effects on the structure and function of the gastric mucosa was approximately 1 mmol/liter; (2) the maximum or near-maximum effects were caused by 10 mmol/liter F; (3) the effects persisted for at least 6 hr after the exposure; and (4) dmPGE2 (0.5 microg/ml) did not attenuate the effects induced by F.

16,16-Dimethylprostaglandin E2↗

PubMed1997

Current concepts on adhesion to dentin.

This review examines fundamental concepts in bonding to dentin. Emphasis is placed on the structure and permeability characteristics of dentin and how they may influence its interaction with adhesive resin. Several new techniques to examine the interfaces between resin and dentin are reviewed along with some of their limitations. The advantages and disadvantages of acid etchants/conditioners vs. self-etching conditioners/primers are discussed. The problems of matching the surface tension of resin-bonding systems to the surface energy of the substrate are reviewed in terms of wetting the various components of dentin. The problems associated with matching the permeability of intertubular dentin to the diffusibility of bonding reagents are explored. Speculation is advanced on how to ensure polymerization and wetting of dentinal collagen. Theoretical problems associated with dentin bonding and with bond testing are reviewed to encourage future research in this rapidly developing area.

Adhesives↗

PubMed1996

In vitro study on the dimensional changes of human dentine after demineralization.

Dentine rods measuring approximately 0.7 x 0.7 x 5.0 mm were prepared from dentine of extracted human third molars stored in saline containing 0.5% sodium azide at 4 degrees C until used. Forty specimens were demineralized in 10% citric acid plus 3% ferric chloride (w/w) solution for 8 h, then assigned to four groups (A, B, C and D) of 10 specimens each. Groups A and B were used to investigate volumetric changes after air-drying and further immersion in either water, an aqueous solution of 50% 2-hydroxymethylmethacrylate (HEMA) or 100% HEMA, followed by air-drying. Groups C and D were used to investigate the ability of 100% HEMA or 100% ethylene glycol to prevent shrinkage of demineralized dentine during exposure to air. Demineralization caused a small, non-significant (1.9%) reduction in dentine volume. Air-drying further reduced the volume by 65.6%. When demineralized, shrunken specimens were immersed in water for 24 h, they recovered their original demineralized volume. Immersion in 100% HEMA did not re-expand demineralized shrunken dentine. Specimens immersed in 50% HEMA yielded a 50% volume shrinkage when exposed to air for 24 h. Both 100% HEMA and 100% ethylene glycol were effective in preventing shrinkage of demineralized dentine. The technique used provided useful information about maximal dimensional changes that may occur at a microscopic level during adhesive dental restorative procedures.

Acid Etching, Dental↗

PubMed1996

Dimensional changes of demineralized human dentine during preparation for scanning electron microscopy.

Dentine rods measuring approx. 0.7 x 0.7 x 5.0mm were prepared from the crowns of extracted human third molars. The specimens were demineralized in 0.5 M EDTA (pH 7.0) for 3 days and their volume measured with a digital micrometer under a dissecting microscope. The specimens were randomly assigned to experimental groups and were chemically dehydrated in acetone. Next they were dried using either hexamethyldisilazane, Peldri II, or critical-point drying techniques. The dimensions of the specimens were measured again after each step and the changes in volume were expressed as a percentage of the original demineralized volume. The effects of fixing the specimens in 10% buffered formalin before dehydration with acetone were also investigated for every drying procedure. Dehydration in acetone caused a small but significant reduction in the volume of demineralized formalin-fixed specimens but unfixed specimens did not change significantly. In general, all three drying procedures caused some shrinkage in demineralized dentine specimens. Unfixed specimens exhibited a volumetric shrinkage of approx. 15-20% after drying with any of the methods. Fixed specimens shrank more than unfixed specimens after drying (25-35%). Regardless of the drying technique, the specimens shrank a further 10-20% when measured in the vacuum chamber of the scanning electron microscope. Among the three drying techniques employed, hexamethyldisilazane seems to be a very useful alternative to critical-point drying for the preparation of dentine specimens for scanning electron microscopy.

Acid Etching, Dental↗

PubMed1996

Regional bond strengths of resins to human root dentine.

OBJECTIVES: The demand for restoration of root dentine defects such as cervical erosion and root caries has significantly increased recently, but there is limited information on the performance of the adhesive resins to radicular dentine. The purpose of this study was to measure the regional tensile bond strength (TBS) of composite bonded to human root and coronal dentine, and to observe the interface between resin and root dentine by SEM. METHODS: Human extracted cuspid teeth were used to measure TBS with a new microtensile bond test. Enamel and cementum were removed from the labial tooth surfaces to form a long cavity preparation into dentine from the mid-crown to the apex of the root within the same tooth. All Bond 2 (all etch technique) or Imperva Bond (no etch) was bonded to dentine surfaces and covered with Protect Liner resin composite. The resin-bonded teeth were serially sliced into 16 sections at right angles to the long axis of the tooth, and the bonded surfaces were trimmed to give a bonded surface area of 1 mm2 for TBS testing. RESULTS: All Bond 2 bond strengths to coronal and apical dentine showed high values (23.5 MPa) but the bond strength was significantly lower on cervical root dentine. Imperva Bond produced a relatively high tensile bond strength to all regional areas. SEM showed that the thickness of the resin-infiltrated layer formed by All Bond 2 in root dentine was less than coronal areas. Resin infiltration with Imperva Bond was always less than 0.5 micron. The results suggest that high TBS values can be obtained with minimal resin infiltration in root dentine.

Acid Etching, Dental↗

PubMed1996

Fluid shifts across human dentine in vitro in response to hydrodynamic stimuli.

Most authorities agree that the hydrodynamic theory of dentine sensitivity best explains the stimulus-response relations of most painful stimuli. However, as the usual hydrodynamic stimuli are so different, it has been impossible to compare them. The equivalency of hydrodynamic stimuli can be evaluated from measurements of the fluid movement induced in vitro and relating this to the hydraulic conductance (Lp) of the same dentine specimen. From this determination, a common denominator is obtained which is equivalent to the hydrostatic pressure that would be required to cause the same magnitude of fluid movement. The purpose of this study was to measure the direction and magnitude of fluid shifts across dentine in extracted human crown segments with a flat, dentine occlusal surface in response to the following hydrodynamic stimuli; air blast, 56 degrees C water, 2 degrees C water, tactile and osmotic. In acid-etched superficial dentine, which simulates hypersensitive dentine, the largest to the smallest fluid flows obtained were: hot > cold > air blast > osmotic > tactile. When these were converted to equivalency units, the ranking of stimuli from strongest to weakest was hot > cold > air blast > osmotic > tactile. This new approach to comparing hydrodynamic stimuli should be verified in vivo.

Acid Etching, Dental↗

PubMed1996

An assessment of the ability of various materials to seal furcation canals in molar teeth.

Ninety-seven maxillary and mandibular molar teeth were evaluated for the presence of naturally occurring furcation canals using the fluid filtration method. Only one specimen demonstrated a naturally occurring patent furcation canal. An artificial furcation canal was created with a 0.33-mm drill bit in the 96 teeth lacking naturally occurring furcation canals. Fluid filtration measurements were made before and after the artificial canal was made, and these served as the negative and positive controls for each tooth. The 96 teeth were randomly divided into eight equal groups, and the floor of the pulp chambers was sealed using 3 mm of either Tytin or Dispersalloy amalgams, Vitremer, FluoroCore, gutta-percha with sealer, Tytin with Ali-Bond 2 or Amalgambond, or Dispersalloy with Ali-Bond 2. Analysis of measured microleakage at 3 months indicated that Tytin amalgam used alone had significantly more microleakage than all other materials; however, this difference did not exist when bonding agents were used with Tytin. All materials leaked significantly less than the positive controls.

Dental Leakage↗

PubMed1996

Push-out strength and SEM evaluation of resin composite bonded to internal cervical dentin.

The bond strength of a resin composite used with a dual-cured dentin bonding system to internal cervical bovine dentin was evaluated using a direct or indirect placement technique. Teeth were sectioned transversely to produce 4 mm-thick specimens. The root canals were enlarged to a standardized taper, treated with a dentin bonding system, and filled with a light-cured resin composite using either direct, incremental composite placement or indirect composite placement of a pre-polymerized composite inlay. The debond stress of indirectly placed restorations using a composite inlay was 8.5 (SD +/- 2.7) MPa which was significantly greater (p < 0.0001) than the value of 5.0 (SD +/- 1.9) MPa for composite placed in a conventional, incremental manner. SEM evaluation revealed the indirect placement technique demonstrated increased resin tag density and length as compared to the direct technique. Enhanced retention of resin composite to endodontically prepared dentin treated with a dentin bonding system was obtained by using a composite inlay technique as opposed to direct, incremental buildup of the material.

Acid Etching, Dental↗

PubMed1996

Regional strengths of bonding agents to cervical sclerotic root dentin.

The regional bond strengths of three current-generation bonding systems (All Bond 2, Scotchbond Multi-Purpose, and Clearfil Liner Bond 2) were measured in natural wedge-shaped defects in the cervical area of extracted human teeth. A microtensile testing method was used to compare the strengths of resin bonds made to occlusal margins with those made to gingival margins. Controls consisted of normal teeth which had artificial wedge-shaped defects, of the same depth and dimension, created with a high-speed bur. The results indicated that there were no regional differences in bond strength, although bonds made to natural lesions were from 20 to 45% lower than those made to normal dentin in artificially created wedge-shaped defects, depending on the bonding agent. Scanning electron microscopy revealed that Clearfil Liner Bond 2 created the thinnest hybrid layers, which were difficult to measure in the natural lesions. The natural lesions contained sclerotic dentin, whereas the artificial lesions were composed of normal dentin. Although the bond strengths to sclerotic dentin were lower than those to normal dentin, the absolute values (ca. 16 to 17 MPa) were high relative to previous-generation bonding agents.

Acid Etching, Dental↗

PubMed1996

The effects of acetone, ethanol, HEMA, and air on the stiffness of human decalcified dentin matrix.

During resin-bonding procedures, dentin surfaces are treated with acidic conditioners to remove the smear layer and decalcify the surface to expose the collagen fibrils of the underlying matrix. These decalcified surfaces are then either air-dried or treated with dehydrating solvents, procedures which may modify the physical properties of the dentin matrix. The purpose of this study was to evaluate the effects of dehydration on the stiffness of the decalcified dentin matrix. Small (8 x 1.7 x 0.9 mm) beams of dentin were prepared from mid-coronal dentin of extracted human molars. The ends were covered with varnish for protection, and the specimens were placed in 0.5 M EDTA for 5 days to decalcify. The stiffness was measured by both the cantilever technique and by conventional stress-strain testing. Specimens tested by the cantilever technique were sequentially exposed to water, acetone, alcohol, HEMA, and glutaraldehyde. Specimens tested by conventional stress-strain testing were exposed either to water, acetone, or HEMA, or were allowed to air-dry. The results indicate that the stiffness of decalcified human dentin matrix is very low (ca. 7 MPa), if the specimens are wet with water. As they are dehydrated, either chemically in water-miscible organic solvents or physically in air, the stiffness increases 20- to 38-fold at low strains or three- to six-fold at high strains. These increases in modulus were rapidly reversed by rehydration in water. Exposure to glutaraldehyde also produced an increase in stiffness that was not reversible when the specimens were placed back in water.

Acetone↗

PubMed1996

Dynamics of the pulpo-dentin complex.

Dentin has a relatively high water content due to its tubular structure. Once dentin is exposed, this intratubular water is free to move in response to thermal, osmotic, evaporative, or tactile stimuli. Fluid shifts across dentin are thought to cause sufficient shear forces on odontoblasts, nerve endings, nearby fibroblasts, and blood vessels to cause significant mechanical irritation, disruption, or damage, depending on the magnitude of the fluid shift. Even in the absence of fluid shifts, the water-filled tubules provide diffusion channels for noxious (i.e., bacterial products) substances which diffuse inward toward the pulp, where they can activate the immune system, provide chemotactic stimuli, cytokine production, and produce pain and pulpal inflammation. Viewed from this perspective, dentin is a poor barrier to external irritants. However, pulpal tissues react to these challenges by increasing the activity of nerves, blood vessels, the immune system, and interstitial fluid turnover, to make the exposed dentin less permeable either physiologically, via increased outward fluid flow, or microscopically, by lining tubules with proteins, mineral deposits, or tertiary dentin, thereby enhancing the barrier properties of dentin, and providing additional protection to pulpal tissues. These reactions involve dentin and pulp, both in the initiation of the processes and in their resolution. These responses of the dental pulp to irritation of dentin demonstrate the dynamic nature of the pulpo-dentin complex.

Bacterial Toxins↗

PubMed1995

Bond strength versus dentine structure: a modelling approach.

Bond strengths of a hypothetical hydrophilic dentine-bonding agent were calculated as a function of dentine depth and resin strength to evaluate the importance of several variables in a simple model. The tested hypothesis was that the total bond strength was the sum of the strengths of resin tags, hybrid layer and surface adhesion. Each of these three variables has a range of values that can influence its relative contribution. The resulting calculations indicate the potential for higher bond strengths to deep dentine than to superficial dentine in non-vital dentine and the importance of resin strength in the development of strong bonds. Comparison of the calculated bonds with published values indicated that they were within the same order of magnitude. Such theoretical modelling of dentine bonding can identify the relative importance of variables involved in the substrate, resins and surface adhesion.

Acid Etching, Dental↗