Biomedical subjects

J Y Thompson

Publications and source records attributed to J Y Thompson.

18 recordsLinked to original sources

PubMed2002

Effect of novel filler particles on the mechanical and wear properties of dental composites.

OBJECTIVES: The purpose of this study was to investigate the method of producing pre-polymerized fused-fiber filler modified composite (PP-FFMC) particles and the effectiveness of incorporating these novel filler particles into dental composites. METHODS: Fused-fiber filler (FFF) blocks were impregnated with composite by two different methods. Three-point flexure tests were utilized to determine which was more effective. In order to assess the effect of the addition of PP-FFMC particles, two Bis-GMA/TEGDMA based conventional composite compositions were utilized as baselines, to which the novel particles were added. Mechanical and wear tests were performed to determine the fracture toughness, biaxial flexure strength, and in vitro wear of the materials. RESULTS: Mechanical testing showed that the addition of PP-FFMC particles decreased the strength and toughness of the conventional composites. Wear tests indicated that addition of the same particles improved the wear behavior of the conventional composites. SEM analysis of the fracture surfaces indicated that the PP-FFMC particles were incorporated without creating porosity, and that fracture was transgranular through the reinforcing particles. Microscopic flaws observed in the novel particles are the likely explanation for the observed strength and toughness values. SIGNIFICANCE: The results indicate that PP-FFMC particles have the potential to improve the wear properties of dental composites, however, they adversely affect the fracture behavior. Existing processing techniques for these particles, which introduce imperfections, limit their current usefulness.

Aluminum Oxide↗

PubMed2001

Free-electron laser etching of dental enamel.

OBJECTIVE: The purpose of this study was to evaluate the Mark-III free-electron laser as a means of etching enamel surfaces, with potential application to resin bonding. METHODS: The FEL was tuned to wavelengths ranging from 3.0 to 9.2 microm. Specific wavelengths that are resonantly absorbed by phosphates, proteins, and water were used. First, bovine enamel was polished and exposed to static FEL exposures. Lased enamel was examined using scanning electron microscopy (SEM). Additional bovine enamel specimens were exposed to FEL at similar wavelengths, but with rastering to create treated rectangular areas on each specimen. Surface roughness was evaluated using profilometry and atomic force microscopy (AFM). Composite was bonded to the lased enamel, and shear bond strengths were determined using an Instron universal testing machine. As a control, the surface roughness of, and shear bond strengths to, acid-etched enamel were determined. RESULTS: Static FEL exposures caused changes in the enamel ranging from an etched appearance to pits, cracks, and frank cratering. The surface roughness of lased enamel was much greater than that of acid-etched enamel, and was qualitatively different as well. Shear bond strengths of resin to acid-etched enamel were significantly higher than bond strengths to lased enamel. CONCLUSIONS: Under the conditions used in this study, the FEL did not offer a practical and effective method of etching enamel for resin bonding. However, the ability of the FEL to deliver many specific wavelengths makes it an interesting tool for further research of laser effects on tooth structure.

Acid Etching, Dental↗

PubMed2000

Mechanical properties of a dental ceramic coated by RF magnetron sputtering.

Metal and ceramic thin film coatings were deposited onto a dental ceramic via radio frequency (RF) magnetron sputtering. The objectives of the study were to determine if a coherent interface could be produced between the coating and the substrate and if the coating significantly would improve the mechanical properties of the ceramic. Thin films of Au, Al, and AlN were deposited in this study. Mechanical testing results indicated that a significant improvement in flexural strength was observed with both Au and Al coatings while significant improvements in the flexural modulus were observed with all three materials. SEM analysis indicated that the interfaces were coherent and also suggested two mechanisms (crack bridging and crack blunting) that could be responsible for the enhanced mechanical properties.

Aluminum↗

PubMed2000

Effect of finishing technique on the microleakage and surface texture of resin-modified glass ionomer restorative materials.

PURPOSE: The purpose of this study was to evaluate the effects of wet and dry finishing/polishing procedures on the microleakage and surface texture of resin-modified glass ionomer (RMGI) restorative materials. MATERIALS AND METHODS: Class V cavity preparations were made at the cemento-enamel junction (CEJ) on the buccal and lingual surface of 30 extracted human molars. The teeth were restored in three groups of 10 (20 preparations in each group) using Fuji II LC and Vitremer, both RMGIs, and Fuji II, a capsulated conventional glass ionomer cement (control). One restoration per tooth was finished/polished with copious applications of water and the other was finished/polished without water. All restorations were finished/polished using a sequence of four abrasive disks. Finishing/polishing was initiated according to manufacturers' instructions-immediately after light-curing Fuji II LC and Vitremer, and 15min after placement for Fuji II. The specimens were thermocycled and subjected to a silver nitrate leakage test. Each tooth was sectioned buccolingually and examined with an optical microscope at 40x to determine the extent of microleakage at enamel and dentin margins. The data were subjected to a non-parametric statistical analysis. To evaluate surface roughness after polishing, three disks each of Vitremer and Fuji II LC were fabricated in Teflon molds. One disk of each material was not finished/polished (control). The others were finished/polished using Sof-Lex abrasive disks. One specimen of each material was kept wet during all finishing/polishing procedures, while the other was kept dry. Atomic force microscopy was used to determine the average roughness (R(a)) of the specimens. RESULTS: For each material, microleakage at the enamel margin was very slight. Leakage of the conventional glass ionomer Fuji II was severe at dentin margins. Statistical analysis indicated that both Vitremer and Fuji II LC had significantly less leakage than Fuji II, and that Vitremer had significantly less leakage than Fuji II LC (p<0.05). Leakage at enamel margins was significantly less than at dentin margins. Differences related to wet and dry polishing were not statistically significant. Profilometry data indicated that polished specimens were rougher than those cured against a Mylar strip. Wet polishing created greater surface roughness than dry polishing. CONCLUSIONS: RMGIs rather than conventional glass ionomers should be used in Class V cavity sites to allow immediate finishing and to reduce the incidence of microleakage. Dry finishing of RMGIs with abrasive disks is recommended because it produces a smoother surface and does not contribute to microleakage. However, wet finishing of conventional glass ionomers is still recommended to avoid desiccation.

Composite Resins↗

PubMed1999

Effect of acid etching and collagen removal on dentin wettability and roughness.

It was recently reported that removal of the collagen network from etched dentin does not affect dentin bond strengths. The aim of this study was to determine if the removal of the collagen fibers results in changes in dentin roughness and wettability. Twenty cary-free extracted human third molars were sectioned parallel to the occlusal surface to expose either superficial or deep dentin. Dentin was ground flat through 600-grit SiC abrasive paper under water to provide uniform surfaces. Observed contact angle measurements were performed to assess wettability by using the axisymmetric drop shape analysis technique using water and a water-based primer. Average roughness was determined with a profilometer. The specimens were analyzed just after being ground, after etching with 35% H(3)PO(4) gel for 15 s, and after etching and deproteinization with 5% NaOCl for 2 min. Data were analyzed with two-way ANOVA and Newman-Keuls multiple comparison t test procedure. Etching resulted in an increase in surface roughness and dentin wettability. For deep dentin, collagen removal did not influence the average roughness, but it resulted in a significantly greater degree of wettability. The degree of wettability for deep dentin was greater than for superficial dentin.

Acid Etching, Dental↗

PubMed1999

An ultra-morphological characterization of collagen-depleted etched dentin.

PURPOSE: To evaluate the ultramorphology of superficial and deep dentin after etching with 35% phosphoric acid (H3PO4) and after etching with 35% H3PO4 followed by deproteinization with 5% sodium hypochlorite (NaOCl). MATERIALS AND METHODS: Two dentin disks (superficial and deep dentin) were obtained from each of 10 extracted human third molars by slow-speed sectioning. Dentin was polished with wet 600-grit SiC abrasive paper for 1 min to provide smooth surfaces. The occlusal surface of each disk was etched with 35% H3PO4 for 15 s and thoroughly rinsed. The specimens were kept moist and analyzed using Atomic Force Microscopy (AFM). Half of the specimens were deproteinized by rubbing with 5% NaOCl for 2 min, followed by a 30 s rinse with deionized water. After AFM analysis of the deproteinized specimens, all disks were fixed in a solution of glutaraldehyde and paraformaldehyde, dehydrated in ethanol and dried in hexamethyldisilazane. The dentin disks were then mounted on aluminum stubs for field-emission scanning electron microscope (FESEM) observation. RESULTS: The surface of etched dentin displayed a granular layer of silica, which did not reach the peritubular collagen area. The silica was more uniformly distributed in superficial dentin than in deep dentin. In spite of the silica deposition, the intertubular porosity remained unobstructed when observed at high magnification. Under a lateral view, intertubular dentin was demineralized to a depth of 2.0 to 2.5 microns for superficial dentin, and 2.5 to 3.0 microns for deep dentin. Deproteinization with 5% NaOCl removed the exposed collagen both for superficial and deep dentin. The number of open tubules was greater for deep dentin. Deproteinization of superficial dentin revealed an extensive labyrinth of lateral secondary tubules and anastomoses, which opened on the intertubular region and on the peritubular area close to the surface. This phenomenon decreased the area of exposed intertubular dentin as compared to etched specimens. In deproteinized deep dentin, the lateral anastomotic tubules were not consistently observed on the intertubular area, but were easily depicted on the peritubular area.

Acid Etching, Dental↗

PubMed1998

Microscopic and energy dipersive x-ray analysis of surface adaptation of dental cements to dental ceramic surfaces.

STATEMENT OF PROBLEM: Clinical failure rates reported for acid etched/resin-bonded ceramic restorations are significantly lower than those reported for restorations luted with traditional cements. This improved clinical performance may be associated with greater adaptation of the resin cements to the ceramic surfaces. PURPOSE: The objective of this study was to determine whether the use of resin cements accompanied by acid etching results in improved adaptation when compared with the use of zinc phosphate or glass ionomer cements. RESULTS: The results of this experiment indicate that superior adaptation of cement to ceramic is produced by acid etching and luting with resin cement. In addition, the results lead to the hypothesis that the high clinical failure rates reported for zinc phosphate or glass ionomer luted restorations are due either to incomplete adaptation or to failure within the cement. CONCLUSION: The findings indicate that the use of resin cements accompanied by acid etching of the ceramic surface is the preferred technique for clinical placement of all-ceramic restorations.

Acid Etching, Dental↗

PubMed1998

A characterization of first-generation flowable composites.

A plethora of new low-viscosity composite resin materials, or flowable composites, have been marketed during the last two years, but little has been published about them. The authors describe research in which they compared the properties--filler, depth or cure, flow, wear, compressive strength, diametral tensile strength, indented biaxial flexure strength and toughness--of flowable and hybrid composites. Mechanical property tests (ISO 4049, ISO/DIS 6872) of eight flowable composites and two hybrid composites were conducted. The flowable composite with the least flow was similar to traditional composites. Mechanical properties were generally about 60 to 90 percent of those of conventional composites. The authors conclude that flowable materials should be used with caution in high-stress applications for restorative dentistry.

Chemical Phenomena↗

PubMed1997

Dental materials citations: Part B, July to December 1996.

OBJECTIVE: A search was conducted in biomedical journals from July 1996 to December 1996 to identify dental materials publications and sort them into major categories. They were compared by frequency in different journals and in different categories during recent years. METHODS: Tables of contents for 16 primary and 51 secondary journals were inspected from July to December of 1996 and were divided into 17 categories. The frequencies of citations for primary journals and for different citation categories were examined over a four-year period from 1993 to 1996. RESULTS: There were 334 total citations from July to December 1996. The greatest number of citations continued to involve bonding (n = 159) and resin-based (composites; glass ionomers) restorative materials (n = 158). The numbers of articles by journal and by category were very similar over the last four years. The average number of articles per year was 531 +/- 15. SIGNIFICANCE: The literature citations compiled in this list provide a supplement for researchers and academicians to the current electronic databases.

Dental Bonding↗

PubMed1997

Dental materials citations: Part A, January to June 1997.

OBJECTIVE: A search was conducted in biomedical journals published from January 1997 to June 1997 to identify all dental materials publications and sort them into major categories. METHODS: Tables of contents for 79 journals for the period of January to June, 1997 were inspected and divided into 17 categories. Citations were analyzed by both frequency in journals and in categories, as well as compared to frequencies for previous years. RESULTS: A total of 445 citations were detected in 79 journals for the period January 1997 to June 1997. Certain journals (n = 19) demonstrated a higher citation frequency (> or = 10 citations for 6 months) and represented 77.8% of all citations. The greatest number of citations continued to involve bonding (n = 97), resin-based restorative materials (composites; glass ionomers) (n = 95), prosthodontic materials (n = 51), and pulp protection/luting materials (n = 48). Frequencies by category were very similar to those for the last four years. SIGNIFICANCE: The compiled literature citations provide a supplement for researchers and academicians seeking information in existing electronic databases.

Ceramics↗

PubMed1996

Mechanical properties of a new mica-based machinable glass ceramic for CAD/CAM restorations.

Machinable ceramics (Vita Mark II and Dicor MGC) exhibit good short-term clinical performance, but long-term in vivo fracture resistance is still being monitored. The relatively low fracture toughness of currently available machinable ceramics restricts their use to conservative inlays and onlays. A new machinable glass ceramic (MGC-F) has been developed (Corning Inc.) with enhanced fluorescence and machinability. The purpose of this study was to characterize and compare key mechanical properties of MGC-F to Dicor MGC-Light, Dicor MGC-Dark, and Vita Mark II glass ceramics. The mean fracture toughness and indented biaxial flexure strength of MGC-F were each significantly greater (p < or = 0.01) than that of Dicor MGC-Light, Dicor MGC-Dark, and Vita Mark II ceramic materials. The results of this study indicate the potential for better in vivo fracture resistance of MGC-F compared with existing machinable ceramic materials for CAD/CAM restorations.

Aluminum Silicates↗

PubMed1996

Dental materials citations: Part A, January to June 1996.

OBJECTIVE: A search was conducted to identify the dental materials publications that appeared in biomedical journals from January 1996 to June 1996 and to compare the frequency of citations among the different categories. METHODS: The tables of contents of 16 primary journals and 48 secondary journals were examined to identify dental materials articles that were published from January to June 1996. These citations were divided into 17 categories and the numbers of citations in each category were compared. To assess the usefulness of the citation listing, a survey of Academy of Dental Materials subscribers was conducted (n = 153 of 382 or 40.1% have responded to date). RESULTS: As in previous years, the greatest number of citations were found in categories of bonding (n = 83) and resin-based restorative materials such as composites and resin-reinforced glass ionomers (n = 80). Results of the reader survey indicated that 84.3% of the respondents have used the citations lists, and 95.4% feel that its publication should be continued. SIGNIFICANCE: The literature compiled in this list serves to supplement the electronic indexing mechanisms so that academicians and researchers can have ready access to the current literature in the field of dental materials.

Animals↗

PubMed1996

Review of dental materials citations: Part B, July to December 1995.

OBJECTIVE: A lag of many months occurs between journal issue publication and updates to electronic databases. The objective of this literature analysis was to identify and categorize all of the dental materials citations in biomedical journals that were published from July 1995 through December 1995. METHODS: Seventeen primary and 51 secondary journals were searched using their tables of contents to detect and record dental materials publications from July to December of 1995. Those journals that were typically rich in dental materials articles were classified as primary ones. Citations were categorized into 17 topics and divided into subsections. The review excluded case reports, most literature related primarily to dental implants, and most articles on biomedical materials used outside of the field of general dentistry. RESULTS: The greatest number of citations was related to topics of dentin bonding and resin-based restorative filling materials (composites and glass ionomers). There was no major change in the number of dental materials publications per year reported from 1993 (n = 786) to 1995 (n = 751). SIGNIFICANCE: This citation list provides a comprehensive resource for use by academicians and researchers to bridge the gap between initial publication and access to electronic searching methods for major databases.

Animals↗

PubMed1996

Effects of flaw size and auto-glaze treatment on porcelain strength.

The functional surfaces of porcelain restorations are often ground to adjust occlusion. This removes the surface glaze and introduces flaws. Re-firing the restoration before final placement produces a self-glaze layer on the surface that may reduce the extent of damage caused by grinding. The objectives of this study were to determine whether re-firing after grinding increases the strength of dental porcelain and to determine whether the effectiveness of this treatment was dependent on the initial flaw size. Six groups, each containing 12 disk specimens, were prepared from experimental body porcelain (No. 36, J.F. Jelenko & Co., Armonk, NY). The specimens were fired under vacuum, ground to a thickness of 1 mm with 240-grit SiC abrasive, and polished through 600-grit on the surface to be subjected to tensile stress. Control Group A consisted of 12 non-indented specimens. Flaws were induced in the remaining groups by means of a Vickers indenter under the following loads: 3.9 N (Group B), 7.8 N (Group C), 11.8 N (Group D), 15.7 N (Group E), and 19.6 N (Group F). Following indentation, half of the specimens from each group were re-fired. The flexure strength of each specimen was determined by means of a piston-on-three-ball biaxial fixture. The TTEST procedure of SAS (1985) indicated a significant difference between the mean strength values of glazed and non-glazed specimens in Group E only (p = 0.55, 0.24, 0.13, 0.07, 0.01, and 0.69 for Groups A to F, respectively). ANOVA with the GLM procedure of SAS (1985) revealed that the mean strength values of groups subjected to five indentation loads were not significantly different (p = 0.45 for glazed specimens and p = 1.00 for non-glazed specimens). These findings support those of Fairhurst et al. (1992) for specimens with smaller flaws that were induced by grinding with 1 micron abrasive grit. The results of the current study indicate that re-firing of porcelain with large surface flaws does not significantly increase the flexural strength.

Analysis of Variance↗

PubMed1995

Review of dental materials citations: Part A, January to June 1995.

OBJECTIVE: Electronic databases are an excellent resource for identifying relevant references for research and education projects. However, these databases are not yet a substitute for direct inspection of the literature because: (a) there still is a lag of many months between journal issue publication and updates of the database, and (b) most databases selectively report a portion of the entire literature. The objective was to identify and categorize all the dental materials citations in biomedical journals that were published from January 1995 through June 1995. METHODS: Seventeen primary and 56 secondary dental journals were manually searched via their tables of contents to detect dental materials publications from January to June of 1995. Dental materials citations were categorized into 17 major sections and further divided into several subsections. The review excluded case reports and literature primarily related to dental implants or biomedical materials outside of dentistry. RESULTS: Three hundred-sixty-nine citations were identified. The greatest number of citations were associated with dentin bonding, composites, and glass ionomers. There was no significant increase in dental materials publications vs. the number reported for 1994. SIGNIFICANCE: This list provides a comprehensive source for review by academicians and researchers to bridge the gap between initial publication and electronic citation.

Dental Materials↗

PubMed1994

Effect of surface etching on the flexure strength and fracture toughness of Dicor disks containing controlled flaws.

Previous studies have shown an increase in the failure load of Dicor glass-ceramic crowns of up to 97% when they were etched with NH4HF2 and luted with a resin-based cement compared with the use of unetched crowns luted with zinc phosphate cement. The objective of this study was to evaluate the effect of the acid-etch treatment on the flexure strength and fracture toughness of Dicor glass-ceramic specimens containing controlled flaws. Annealed disks were divided into two groups of 14 each, and microcracks were induced in the surface with a Vickers indenter. Seven specimens from each sample set were etched with 10% NH4HF2 (Dicor etching gel) and were fractured in air using a piston-on-three-ball biaxial fixture. Fracture toughness values were determined from the flexure strengths and fractographic measurements of fracture-initiating flaws. Analysis of data by ANOVA and the Tukey's Studentized Range Test revealed no significant difference (p > 0.05) in the mean flexure strength or fracture toughness of the etched and unetched samples within group A or group B. For the sample groups tested, flaw modification by etching had no effect on the flexure strength or on the fracture toughness of Dicor specimens containing controlled flaws.

Acid Etching, Dental↗

PubMed1994

Fracture surface characterization of clinically failed all-ceramic crowns.

The goal of this study was to establish a protocol for the retrieval and fractographic analysis of failed restorations, and to compare the fracture surface features of clinically failed ceramic restorations and with those of controlled laboratory test specimens fabricated from the same materials. Ten fractured Dicor crowns and 12 fractured Cerestore crows were retrieved and analyzed. Optical microscopy of the failed crowns revealed that the critical segments of nine of the 10 (90%) Dicor crowns and nine of the 12 (75%) Cerestore crowns were acceptable for fractographic analysis. Twelve disks of each material were fabricated as controls and fractured by bi-axial flexure for analysis of the similarities and/or differences between the fractographic features of fractured clinical crowns and the disks. Each of the 10 Dicor crowns was observed to fail along the internal surface. For 78% of the Cerestore crowns, failure initiation occurred at the porcelain/core interface or inside the core material. Critical flaw sizes of the failed Dicor crowns ranged from 127 to 272 microns. Failure stresses of the Dicor crowns, estimated by fractographic techniques and fracture mechanics relationships, ranged from 65 to 94 MPa. Estimated failure stresses for two of the Cerestore crowns which had failure initiation sites in the porcelain layer were 15 and 68 MPa. It is concluded that the fracture initiation sites of dental ceramics are controlled primarily by the location and size of the critical flaw, and not by specimen thickness.

Aluminum Oxide↗

PubMedDate not supplied

Effect of thermal and mechanical load cycling on microtensile bond strength of a total-etch adhesive system.

To evaluate the effect of thermal and mechanical cycles on dentin bond strength to cervical margins of Class II restorations, 80 box-type Class II cavities were prepared on the surfaces of bovine incisors. The cavities were restored with Single Bond (3M-ESPE) and Z-250 composite (3M-ESPE) according to manufacturer's instructions. The incisors were divided into four groups: G1-Control, G2- Thermal cycling (2,000 cycles, 5 degrees C-55 degrees C), G3- Mechanical cycling (100,000 cycles; 50N) and G4- Thermal and mechanical cycling (2,000 cycles 5 degrees C-55 degrees C/100,000 cycles; 50N). The restorations were sectioned perpendicular to the cervical bonded interface into 0.7 +/- 0.2 mm-thick slabs. The slabs were further trimmed at the interface to 1.4 +/- 0.2 mm with a fine diamond bur to produce a cross-sectional surface area of 1 mm2. All specimens were then subjected to microtensile bond testing. Means and standard deviations were expressed in MPa. The bond strength data were analyzed by one-way ANOVA and Fisher's PLSD test (p<0.05). Fracture mode analysis was performed using SEM. Bond strengths were significantly lower when thermal and mechanical cycling were performed [G4-2.41 (8.57)] when compared to the other groups [G1-28.15 (14.03); G2-27.60 (10.14); G3-27.59 (8.67)]. No differences were observed among Groups 1, 2 and 3. Interfacial fracture of the control (G1) and thermocycling (G2) groups mainly occurred between the deepest portion of the adhesive resin and the top layer of the demineralized dentin (Interphase). Mixed failure was predominant and increased when mechanical cycling was applied (G3 and G4).

Acid Etching, Dental↗