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Biomedical subjects

G P Stewart

Publications and source records attributed to G P Stewart.

At least 19 recordsLinked to original sources
PubMed2000

Evaluation of root reinforcement of endodontically treated teeth.

OBJECTIVES: The purpose of this study was to test the root reinforcing capabilities of a glass ionomer sealer and to test whether pretreatment of the instrumented canal to alter or remove the smear layer might enhance the reinforcement. STUDY DESIGN: Ninety single-canaled roots of standardized dimensions were instrumented to International Standards Organization size 45 and were analyzed for resistance to vertical fracture. Six groups were tested (n = 15). RESULTS: No significant difference in fracture resistance was observed between any of the groups. CONCLUSIONS: Under the conditions of this study, reinforcement of endodontically treated mature teeth by placement of adhesive materials in the root was not demonstrated.

Analysis of Variance↗
PubMed1997

Two-year clinical evaluation of an amalgam adhesive.

This study compared the clinical effectiveness of an amalgam adhesive as the principal mode of retention for large, complex amalgam restorations with traditional pin-retained amalgams. Restorations were evaluated for retention and reinforcement, postoperative sensitivity, marginal adaptation and recurrent decay. At the end of two years, all restorations were completely retained and rated Alfa for each of the parameters evaluated. An amalgam adhesive proved clinically effective as a suitable alternative to pin retention.

Bicuspid↗
PubMed1994

Comparison of acidulated phosphate fluoride gel and hydrofluoric acid etchants for porcelain-composite repair.

Hydrofluoric acid etches porcelain to produce a porous surface visible under scanning electron microscopy when compared to an acidulated phosphate fluoride gel. Some investigators have suggested the greater porosity of the hydrofluoric acid etch produces a greater composite-to-porcelain bond. This investigation tested that assumption with two common fluoride etchants. The etched surfaces were first viewed under scanning electron microscopy to ensure that a characteristic etch was achieved. Both etchants yielded bond strengths that produced cohesive failure of all samples. This suggested that the intraoral use of hydrofluoric acid is no more effective than the less dangerous acidulated phosphate fluoride gel.

Acid Etching, Dental↗
PubMed1994

In vitro and in vivo measurement of remaining dentin thickness.

Experiments were performed in vitro on extracted human teeth and in vivo on dog teeth to determine the accuracy of a pulse-echo mode with an ultrasonic micrometer in measuring remaining dentin thickness. The accuracy of the ultrasonic micrometer measured remaining dentin thickness was compared with direct caliper measurements in measuring human dentin discs (correlation coefficient, r = 0.99). After modification of the delay line tip (focusing tip), the device was found to be highly accurate on both prepared extracted human teeth (r = 0.87) and in vivo on dog teeth (r = 0.92). The use of ultrasonic technology to measure remaining dentin thickness looks promising. Further research needs to be performed to make the device more clinically useful.

Animals↗
PubMed1994

Effect of handpiece pressure and speed on intrapulpal temperature rise.

This study determined the effect of handpiece pressure and speed on the intrapulpal temperature rise produced during finishing. Finishing was performed on a class V amalgam restoration with a brown rubber point. The remaining dentin thickness was standardized under the restoration at 2.0 mm. Finishing was done continuously for 60 seconds with temperature rises recorded at the dentin/pulp interface every 15 seconds. All finishing was done dry. Handpiece speed (rpm's) varied from 7000-15,000 rpm's and applied pressure from 20-60 gr force. Increases in either speed or pressure can produce significant intrapulpal temperature increases over these ranges. Doubling either one produces a 50% temperature increase during finishing. Finishing at 15,000 rpm's with 60 gr force is capable of producing damaging temperature rises at the pulp after only 15 seconds finishing time.

Analysis of Variance↗
PubMed1993

Amalgam retention using pins, boxes, and Amalgambond.

The purpose of this study was to evaluate and compare the retentive strength of amalgam to tooth structure by utilizing pins, boxes, Amalgambond adhesive only, and Amalgambond adhesive plus retentive boxes. There was no statistical difference (P = 0.05) in retentive strength of the amalgam between the group utilizing pins alone and the group utilizing Amalgambond plus retentive boxes. However, both of these sample groups demonstrated statistically greater retentive strengths than either the boxes only or Amalgambond only groups.

Analysis of Variance↗
PubMed1991

Temperature rise due to finishing of direct restorative materials.

An in vitro study was performed to evaluate the effect of four variables on the temperature rise produced by the finishing of restorations. The four variables were: restorative material, finishing agent, finishing time, and depth of dentin under the restoration. Class V preparations were cut on extracted premolars and restored with amalgam, composite, or glass ionomer cement. Finishing was done with wet pumice and cup, wet pumice and a brush, a grit rubber polishing point, and an aluminum oxide- coated disc. Finishing time was continuous or intermittent for up to 1 minute. Dentin thickness under the restoration was 0.5 mm to 3.0 mm. Amalgam produced the highest temperature rises at the pulp, while composite and glass ionomer were no different than the untreated (virgin) tooth. Aluminum oxide discs produced the largest temperature rise, wet pumice with a brush the least. Temperature rise increased almost linearly with continuous finishing, while intermittent finishing significantly reduced temperature rise in all cases. Thickness of remaining dentin was only significant for the amalgam restoration, and then only at 1.0 and 0.5 mm.

Aluminum Oxide↗
PubMed1990

Mechanical properties of metal-ceramic alloys at high temperature.

Four alloys used for the construction of porcelain-fused-to-metal restorations were tested at high temperatures (1000 degrees C) so that loss of properties could be ascertained. In addition, thin flat plates of metal (30 x 11 x 1 mm) with a 9-mm recess and a metal thickness of 0.35 mm were processed for porcelain application and distortion measured at 15 points along the surface prior to and following each firing cycle. Yield and ultimate tensile strengths and elongation were determined on specimens at room temperature and at 1000 degrees C. None of the alloys tested showed a great amount of distortion during the various firing cycles, yet they showed increased change with each successive heating. The greatest distortion occurred with Jelenko "O" alloy. When the mechanical properties were compared, there was a marked loss of both yield and ultimate strength values for each alloy (Jelenko "O"-Y.S., 95.64%, U.T.S., 96.22%; Olympia--Y.S., 95.08%, U.T.S., 96.76%; Tempo--Y.S., 91.23%, U.T.S., 93.46%; Biobond II--Y.S., 83.72%, U.T.S., 86.21%). Percent elongation increased by 272% with Biobond II and 370% with Jelenko "O", whereas Tempo and Olympia increased by 120 and 155%. It is apparent that the palladium-based alloy and the nickel-chromium-based alloy have higher mechanical properties at the temperature where porcelain will be applied.

Dental Alloys↗
PubMed1983

Effects of cyanoacrylates on die stone.

An evaluation was made of the effects of the application of an increasing number of coats of cyanoacrylate on die stone. The application of one coat of cyanoacrylate adhesive on the surface of trimmed and marked dies increases the surface hardness, increases the scratch resistance, will not change the dimensions of the die appreciably, and renders the margin marking more permanent. Excess resin should be removed immediately by compressed air. The use of hardener instead of water is recommended for mixing Type IV dental stone. Use of the cyanoacrylate method will aid the dentist and the technician in achieving an accurate crown fit.

Calcium Sulfate↗
PubMed1978

Effects of polyamines and methylglyoxal bis(guanylhydrazone) on Escherichia coli ribonucleic acid polymerase and the template activity of hepatic cell nuclei in vitro.

Escherichia coli RNA polymerase was assayed with 4 mM Mg2+ and 1 mM Mn2+ using native DNA, heat-denatured DNA, histone-nucleate and isolated rat liver nuclei as the template source. With purified DNA and either or both divalent metal ions, 0.1--5 mM amine stimulated enzyme activity. Spermidine resulted in the greatest stimulation (1.7-fold at 5 mM); whereas, spermine or methylglyoxal bis(guanylhydrazone) first stimulated, then above 3 mM inhibited, the reaction. The addition of unfractionated histone to purified DNA inhibited the reaction by 90%. The subsequent addition of amines resulted in a slight stimulation in incorporation (1.5-fold) in the range of 1--3 mM amine. Alternatively, when enzyme was combined with DNA before histone, only a 20% inhibition was observed and this could be completely prevented by 3 mM spermidine. The addition of amines to isolated nuclei resulted in marked alterations in ultrastructure and Mg2+ content; however, relatively small effects on RNA polymerase activity were observed. With the E. coli enzyme, 0.1--1.0 mM amine stimulated RNA synthesis (1.5-fold) whereas, none of the amines stimulated endogeneous activity in the absence or presence of 300 mM (NH4)2SO4.

Animals↗