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Biomedical subjects

V A Marker

Publications and source records attributed to V A Marker.

At least 19 recordsLinked to original sources
PubMed2001

Effect of handpiece tip design on the cutting efficiency of an air abrasion system.

PURPOSE: The aim of this study was to evaluate the effect of nozzle angle and tip diameter on the cutting efficiency of an air abrasion system. MATERIALS AND METHODS: Thirty-six extracted human third molars were air-abraded with the PrepStar microabrasion machine using a handpiece with either 80 degrees or 45 degrees nozzle angles with 0.38 or 0.48 mm tip orifice diameters. The following parameters were held constant: abrasive particle size (27 microm), air pressure (80 psi), distance (2 mm) and duration (15 seconds). The cutting efficiency was compared using enamel, dentin and cementum substrates. Width and depth of the cutting patterns were analyzed and measured using scanning electron micrographs. RESULTS: Statistical analysis using three-way ANOVA and Duncan's Multiple Range test revealed that the width of the cuts was significantly greater when the cavities were prepared using the 45 degrees nozzle angle. Significantly deeper cavities were produced with the 80 degrees nozzle angle. The tip orifice of the nozzle influenced the cutting efficiency in softer substrates, dentin and cementum. Precise removal of hard tissue is best accomplished using the 80 degrees angle nozzle tips for all types of tooth surfaces, enamel, dentin and cementum.

Air Abrasion, Dental↗
PubMed1999

A pilot study to evaluate different palate materials for maxillary complete dentures with xerostomic patients.

PURPOSE: The hypothesis tested in this pilot study was that materials used for the palatal region of a maxillary denture affect the comfort of the maxillary denture in xerostomic patients. MATERIALS AND METHODS: Xerostomic complete denture wearers were selected to test three different maxillary dentures that were made with different palatal materials. Each denture was worn for a period of 2 weeks. The Kapur Index was used to measure retention. The Oral Health Index Profile (OHIP) was used to determine the patient's perception of each denture after the 2-week period. At the end of the study, the patients were asked to select which of the three dentures they would like as their primary denture. RESULTS: All participants chose the metal-palate dentures, and 4 of 5 selected the titanium-palate denture as their primary denture. Statistical analysis of the OHIP demonstrated that the metal-palate dentures were perceived as being more comfortable than the acrylic-resin dentures. CONCLUSION: This pilot study suggests that for xerostomic patients who have worn complete dentures, their selection of a metal-palate denture as their primary prosthesis strongly suggests that these dentures have properties that make them more comfortable to the patient than acrylic dentures. Subjective patient measurements supported this conclusion that the metal-palate dentures were preferable, while the evaluation method available to the clinician failed to discriminate among the prostheses.

Acrylic Resins↗
PubMed1997

Comparison of titanium and cobalt-chromium removable partial denture clasps.

STATEMENT OF PROBLEM: The use of titanium alloys for removable partial dentures is an increasingly popular application. While the flexibility of titanium would allow for cast clasps to be placed in deeper undercuts than advisable with cobalt-chromium, it is possible that the retentive forces of the titanium clasp might not maintain sufficient retention after repeated flexing of the clasp arm during insertion and removal of the partial denture. PURPOSE: This study assessed the characteristics of cast clasps made of titanium and titanium alloys to determine whether these materials are suitable alternatives for removable partial denture applications. MATERIAL AND METHODS: Removable partial denture clasps at two undercut depths were fabricated from commercially pure titanium, titanium alloy (Ti-6A1-4V), and cobalt-chromium. Loss of retention force was measured as the clasps underwent 3 years of simulated clinical use. The data were subjected to ANOVA and Scheffé's tests to determine differences. Evidence of casting defects and porosity was evaluated by radiographic examination and nonparametric statistics. SEM microscopy was used to observe surface characteristics that were described qualitatively. RESULTS: For the 0.75 mm undercut specimens, there was less loss of retention for clasps made from pure titanium and titanium alloy than for cobalt-chromium clasps. Porosity was more apparent in the pure titanium and titanium alloy clasps than in those made from cobalt-chromium, but the amount of porosity did not correspond to evidence of fractures or permanent deformation. CONCLUSIONS: The long-term retentive resiliency of the pure titanium and titanium alloy clasps suggests that these materials are suitable for removable partial dentures.

Alloys↗
PubMed1995

Review of the 1994 dental materials literature.

OBJECTIVES: Electronic databases provide strong support for research and education literature searches. However, there is still some lag in time between publication and updates of the database. The objective of this summary was to identify and categorize the 1994 dental materials scientific literature that dealt with restorative dentistry. METHODS: Seventeen primary journals were manually searched via the Tables of Contents and 88 secondary journals were manually or electronically searched. Dental materials citations were categorized into 15 major sections and several subsections, excluding case reports and literature primarily related to dental implants or biomedical materials outside of dentistry. RESULTS: Nearly twelve hundred citations were identified, the largest number being associated with composites and glass ionomers. 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

A comparison of two silicoating techniques.

PURPOSE: A major challenge of composite-coated metal restorations is creating a strong bond between the two materials. This study was conducted to compare the bond strengths between composite and metal alloys using two silicoating treatments; the Silicoater Classic and the Silicoater MD (Kulzer Inc, Irvine, CA). MATERIALS AND METHODS: The Classic uses a pyrolytically applied silica glass and the MD process is an oven sintering of a metal oxide silicate layer. Two types of specimens of three different alloys were cast (Deva4: 51Au38Pd, G-Cast: 50Au32Ag12Cu [Degussa Corp. South Plainfield, NJ]; Ticonium: 70Ni15Cr [CMP Industries, Inc, Albany NY]). The specimens were silicoated with either the Classic or the MD process and opaque resin and composite (Dentacolor, Kulzer Inc) were bonded to each surface. A total of five control and 10 thermocycled (5,040 cycles 0 degree C to 67 degrees C; dwell time, 1 minute) specimens were fabricated for each alloy and specimen type. Two bond strength tests were used; a three-point flexure test and a shear bond strength test. Data were analyzed using a multivariate analysis of variance (MANOVA) and a Tukey's multiple comparison test. RESULTS: The standard deviations of the shear bond strength values ranged from +/- 2.30 to +/- 17.82.kg; thus, there was no significant difference in these results. Bond strength ratios were calculated from the flexure strength data. After thermocycling, the Silicoater MD produced significantly higher (P < 0.05) bond strength ratio values compared with the Silicoater Classic for Deva-4 (MD, 9.6 +/- 1.5 v Classic, 4.7 +/- 0.9) and G-Cast (MD, 11.6 +/- 1.2 v Classic, 3.9 +/- 0.5) but lower values for Ticonium (MD, 4.5 +/- 0.4 v Classic, 6.9 +/- 0.9). CONCLUSION: The Silicoater MD produced higher bond strength ratio values with noble alloys, and the Silicoater Classic produced higher bond strength ratio results when base metal alloys were used, suggesting a possible correlation between the effectiveness of the coating processes and the compositions of the alloys. These findings suggest that, for optimum results, selection of the type of silicoating process should be based on the components of the alloy.

Composite Resins↗
PubMed1993

Determining amalgam marginal quality: effect of occlusal surface condition.

Currently there is no "standard" finishing and polishing procedure for dental amalgam restorations. This investigation evaluated the effect of four different finishing techniques on the durability of dental amalgam restorations as determined by the marginal breakdown. Burnishing immediately before carving or as part of the condensation process seems to improve the carving characteristics of the amalgam.

Dental Alloys↗
PubMed1993

Restoration surface roughness after air-powder polishing.

This study was conducted to evaluate the surface effects of the air-powder polisher on direct restorative materials in vivo. Hybrid composite, microfilled composite, amalgam, and glass ionomer restorations were polished for 10 seconds. Replicas of the pre-treatment and post-treatment surfaces were examined in the SEM. A visual and written rating scale was developed to evaluate surface roughness, i.e., 1 = smoothest and 7 = roughest. Micrographs (x200) of the pre- and post-treatment surfaces were evaluated as (1) randomly ordered samples and (2) paired samples. The pre-treatment ratings from the randomly ordered samples ranged from 1-7 for the microfilled and hybrid composite, and 3-7 for the glass ionomer restorations. The range of post-treatment ratings was slightly higher for the hybrid and amalgam (2-7) and the glass ionomer (4-7). Results were analyzed by the Wilcoxon ranks test, which showed that the differences between the ratings of pre and post-treatment surfaces were not significant (P < or = 0.05). A comparison between the two evaluation methods using the Spearman rank correlation (Rho) test showed a good correlation (P < or = 0.05) between the random versus paired evaluation methods and suggested that the random rating method was reliable. Thus, a 10-second exposure with the air-powder polisher does not significantly roughen the surface of the materials tested. Visual observations showed that surface changes were dependent on initial conditions, with smooth surfaces becoming rougher, and surfaces that were extremely rough generally becoming smoother.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Evaluation of the interactions between amalgam, cement and gold castings.

The purpose of this study was to determine the interactive effects between a dental amalgam, cements and a gold alloy and therefore evaluate cements as barriers to corrosion. There were 48 castings cemented to either simulated amalgam cores or teeth using zinc phosphate (ZnPO4) or glass polyalkenoate (ionomer) cement. An additional 12 castings were placed in direct contact with the amalgam restoration. Half of the specimens were thermocycled between 5 degrees and 50 degrees C for 12 weeks. The other half were stored at 37 degrees C for the same period of time. The specimens were then encased in epoxy resin and sectioned. The sectioned specimens were examined for cement loss, as well as evidence and extent of corrosion. Significantly more cement loss occurred with the ZnPO4 compared with the glass polyalkenoate (ionomer) cement when the castings were cemented to amalgam cores. Evidence of corrosion was apparent in all specimens; thermocycling produced significantly more corrosion than the 37 degrees C environment. The direct-contact group produced significantly more corrosion compared with the specimens where castings were cemented with ZnPO4.

Corrosion↗
PubMed1992

Solvent degradation and reduced fracture toughness in aged composites.

Qartz- and barium-glass-filled composites aged for more than one year in ethanol experienced a significant reduction in fracture toughness (K1c), essentially identical to that experienced after two months of aging. This reduction is mainly attributed to a softening of the resin matrix, but cracking within the resin and at the filler/matrix interface, as revealed by SEM microscopy, may also have contributed. No significant cracking could be seen in the composites aged in water. Composites post-cured at temperatures approaching their glass-transition temperature also experienced a reduction in K1c after alcohol storage. Storage in water for one year had little effect on the K1c of composites cured at oral temperatures, but a significant increase was observed for those post-cured at elevated temperatures. This increase is difficult to explain, but appears to involve a filler/matrix interfacial phenomenon, because it was not observed in the unfilled resin. The results of this study demonstrate that an alteration in the fracture resistance and some degradation of the filler/matrix interface, as has been observed clinically, occur after long-term exposure of dental composites to certain solvents used as food-simulating liquids.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1990

Bond strengths of high-palladium content alloys.

Palladium-based alloys have had a significant import on the fabrication of ceramometal restorations. This article compares the bond strengths of four palladium-based alloys with that of a high-noble alloy. Tests were designed to closely represent clinical situations. Bond strengths of the palladium alloys compared favorably with the high-noble metals; palladium alloys containing up to 2% gold were the best.

Dental Alloys↗
PubMed1989

[Normalizing method for determining the mode of crack-propagation in amalgams and composite resins].

A normalizing method for determining the mode of crack-propagation in a phase or component of a dental amalgam or composite resin was devised. The results calculated using the method were found to be satisfactory when the method was applied to the materials. Furthermore, details of the mode of crack-propagation in the materials which cannot be seen using pictures of the cross-section structure of the materials are revealed using the method.

Composite Resins↗
PubMed1987

Factors affecting the retention and fit of gold castings.

A study was designed to simulate clinical conditions. Several factors were evaluated for effect on retention and fit (margin adaptation) of gold castings. Twenty-six castings (13 pairs) were made by different investigators using a standard preparation but with varying fabrication techniques. One of each pair of castings was made on a spaced die and one on an unspaced die. A significant difference in the postcementation retention was observed in the varying techniques of each investigator. Retentive values varied from 29 to 129 lbs. Complete seating of the castings during cementation was improved by the use of die spacer. Castings made on the spaced dies had more retention than corresponding unspaced castings. Die spacing has positive benefit when properly used. Moderate roughness of axial surfaces improves retention when zinc phosphate cement is used. Physical properties of restorative materials are important, but the individual technique and care of each investigator has a major effect on the ultimate fit and retention of the cast restoration.

Cementation↗
PubMed1987

Strength properties of soldered joints for a gold-palladium alloy and a palladium alloy.

Strength of a soldered palladium alloy, PGC (Engelhard Corp.), and a soldered medium gold alloy, PGX (Engelhard Corp.), was examined. The results obtained were as follows: Highest strength was observed with postsoldered specimens of PGC alloy. Microstructural examination of postsoldered specimens revealed nearly pore-free solder joints with PGC and PGX alloys, and fracture appeared at the solder-alloy interface with PGC and PGX alloys. Microstructural examination of presoldered and presoldered/thermocycled specimens revealed that presoldered specimens of PGC and PGX alloys exhibited intrasolder fracture; PGX solder joints had considerably less porosity, which may explain the equivalent bond strengths of all the soldered specimens and the yield point of the controls; PGC solder joints exhibited large quantities of pores, which may explain the lower strength; pores observed in PGC alloy may be the result of the high fusing temperature of the solder; and these results indicate a need to develop a new presolder for PGC. The best result was obtained with postsoldered specimens of the PGC alloy. However, for PGX alloy, either postsolder or presolder techniques can be used.

Dental Alloys↗