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Biomedical subjects

N Barghi

Publications and source records attributed to N Barghi.

At least 37 records · Page 2Linked to original sources
PubMed1992

Postcementation marginal fit of a new ceramic foil crown system.

The in vitro marginal fit of a new foil crown was investigated. Ten standardized polycarbonate master dies filled with 30 wt% carbon having a 90-degree butt joint margin were used to evaluate the marginal fit of Sunrise porcelain foil crowns. The crown specimens were made on stone dies and treated with three coats of die spacer. After fabrication, they were adjusted, cemented with zinc phosphate cement to their respective master dies with 5 kg loading for 10 minutes and stored in water. A Gaertner traveling microscope was used to measure the marginal fit of each specimen. Readings were recorded at five locations randomly marked but equally dividing the margin on each crown, and the overall mean for the crowns was then calculated. The results from the 50 areas revealed a mean marginal discrepancy of 25.3 microns, and this compared favorably with the discrepancies reported for other ceramic crown systems.

Crowns↗
PubMed1992

Effects of posterior teeth replacement on temporomandibular joint sounds: a preliminary report.

Previous reports have shown the prevalence of jaw clicking to be significantly higher in a population with missing posterior teeth compared with an dentulous population. This study presents a 2- to 5-year assessment of the effects of posterior teeth replacement on the amplitude of jaw clicking in subjects who were asymptomatic in all respects except jaw clicking. Patients requiring removable partial dentures (RPDs) were clinically and anamnestically examined and temporomandibular joint (TMJ) sounds were recorded using a modified stethoscope attached to an adjustable headgear. Amplified signals were displayed on a strip chart recorder. The amplitude of TMJ sounds at preinsertion of RPDs were 27.5 +/- 17.7 dB at opening, and 11.1 +/- 12.7 dB at closing. Similar values after prosthesis insertion were 15.8 +/- 17.0 dB and 7.4 +/- 7.5 dB, respectively. Paired t test analyses showed significant differences in the amplitude of sound for opening and closing before inserting the prosthesis (p = 0.003) and for opening before and after treatment (p = 0.014). Following replacement of posterior teeth, the clicking amplitude decreased in 68% of recordings, remained unchanged in 11%, and increased in 21%.

Adult↗
PubMed1991

Dimensional changes in casting titanium removable partial denture frameworks.

The difficulties encountered in casting titanium and its alloys have until recently hindered any widespread use of titanium in restorative dentistry. Now both equipment and materials are available for the routine use of titanium in the dental laboratory. This study used one of the casting systems and examined dimensional changes that occur during the construction of a removable partial denture framework. Nineteen castings were measured for horizontal and vertical plane changes. Results show these castings to have cross arch contraction, vertical plane expansion, and near neutral anterio-posterior change. It seems that pure titanium is within the range of dimension changes generally accepted for base metal removable partial denture alloys of the nickel-chromium variety.

Dental Casting Investment↗
PubMed1991

Effect of fitting adjustments on compressive strength of a new foil crown system.

The effect of die spacing and precementation internal adjustments on the compressive strength of a new ceramic foil crown system was examined in vitro. Twenty-four ceramic foil crowns were made for identical stylized master dies made of polycarbonate filled with 30 wt% carbon. One half of the stone working dies were coated with die spacer and the remaining were left untreated. A special foil used for these crowns was adapted to the working dies under 2500 psi loading. A sculpturing device was used to standardize the size and shape of the ceramic foil crowns. Only crowns made on dies coated with die spacer received precementation fitting adjustment. All crowns in the two groups were cemented with zinc phosphate cement and were subjected to compressive force until fracture occurred. Compressive strength data were analyzed and compared. Results showed that the use of die spacer and internal adjustments increased the compressive strength of the new ceramic foil crown.

Crowns↗
PubMed1990

Influence of ceramic thickness on the polymerization of light-cured resin cement.

The curing of two light-activated resin cements under two ceramic materials was examined to assess the influence of ceramic thickness on polymerization. The degree of resin cure was determined by microhardness measurements (Knoop) on resin cement samples cured under five ceramic thicknesses with light exposures of 30 to 120 seconds. These cements cured under thin ceramic specimens with recommended exposures. With thick ceramics, both cements cured better under the glass-ceramic, but neither reached a level of maximum cure under the porcelain.

Ceramics↗
PubMed1990

The influence of condensation method on porosity and shade of body porcelain.

Condensation of porcelain is an important laboratory variable that can affect a variety of physical properties in metal ceramic restorations. This study examined four methods of condensation (brush with vibration, ultrasonic vibration, spatulation, and noncondensation) to evaluate their effects on porosity and color. Standardized 12 x 12 mm acetate plastic squares were invested and cast with Olympia alloy. After oxidation, the metal substructures received one of the following opaque and body porcelains: Ceramco II G Series, Will-Ceram V-Series, Vita VMK-68, or Jelenko. The examination of each sample consisted of three parts: (1) apparent specific gravity analysis (porosity); (2) tristimulus colorimeter analysis; and (3) subjective observer color analysis. No statistical differences (p less than or equal to 0.05) in apparent specific gravity were found between methods of condensation within any of the four porcelains. Statistical differences (p less than or equal to 0.05) in color were noted between methods of condensation within several of the porcelains by both the tristimulus colorimeter and the subjective observers.

Analysis of Variance↗
PubMed1990

Effectiveness of nitric-NPG as a conditioning agent for enamel.

This in vitro study was designed to measure the bond strength of composite resin to enamel treated with various regimes of HNO3-NPG (N-phenylglycine and glycidylmethacrylate) followed by application of PMDM (pyromellitic dianhydride and 2-hydroxyethyl methacrylate). Forty freshly extracted human teeth were prepared with a flat area entirely in enamel on the proximal surface and then divided into five groups. Group 1 was treated with 37% H3PO4, Group 2 with 2.5% HNO3-NPG while rubbing the enamel with the solution, Group 3 with 2.5% HNO3-NPG without rubbing, Group 4 with 37% H3PO4 plus 2.5% HNO3-NPG with rubbing, and Group 5 with 5% HNO3-NPG without rubbing. After drying, PMDM solution was applied to each specimen for 60 seconds. Unfilled resin was applied, cured for 20 seconds, and the composite resin was placed and cured from all sides for a total of 120 seconds. After water bath storage for 7 days, specimens were tested on an Instron machine at a crosshead speed of 2.0mm/min. The highest shear bond strengths measured were for Group 1 (22.7 MPa), followed by Group 2 (20.92 MPa). The lowest bond strength recorded was for Group 3 (14.43 MPa). The results of this study indicate that enamel surfaces treated with 2.5% HNO3-NPG solution, if the solution is rubbed during application, produce a bond strength comparable to that achieved by H3PO4 conditioning.

Acid Etching, Dental↗
PubMed1989

The vertical dimensional change resulting from polishing or glazing porcelain.

Studies have shown that polishing porcelain can produce a smooth surface similar to that resulting from a natural glaze. It has been reported that glazing porcelain causes changes in the occlusal vertical dimension. This study evaluated the changes in vertical dimension after natural glazing and polishing procedures. Twenty uniform-size tricuspid porcelain-fused-to-metal crowns were constructed on a mandibular typodont tooth. A inch steel ball was cradled between the three cusps, and the occlusal vertical dimension was measured from the top of the steel ball to the base of the castings. Contact areas were marked and lightly removed. Ten crowns received natural glazing and the remaining 10 were polished with a Shofu polishing kit. Measurements of occlusal vertical dimension were repeated. All of the crowns showed a loss of occlusal vertical dimension. The mean loss for polished crowns was significantly higher than that recorded for the glazed crowns.

Crowns↗
PubMed1987

Comparison of fracture strength of porcelain-veneered-to-high noble and base metal alloys.

Sixty crowns were cast from a commercial high noble and base metal alloy. The porcelain applied to the crowns was fired 10 times and fractured under gradual application of load. The fracture strength of the porcelain-veneered-to-base metal and high noble alloys subjected to repeated firings was compared. The results were: The fracture strength of porcelain-veneered-to-high noble alloys remained relatively constant for five firings but decreased significantly as the firings increased to 10. Ten firings did not significantly affect the fracture strength of porcelain-veneered-to-base metal alloys. Porcelain-veneered-to-base metal alloy crowns had a higher fracture strength compared with high noble alloy crowns.

Crowns↗
PubMed1987

The effect of function and rest on the amplitude of the TMJ click.

It has been suggested that simple resting and therapeutic exercises may be beneficial in reducing or eliminating clicking on the TMJ during mandibular movements. In the reported experiments the effects of short periods of exercise and rest on the amplitude of the TMJ clicking in non-dysfunction subjects was recorded and compared. This preliminary study suggests that the TMJ clicking sound is affected unpredictably under different imposed conditions.

Adult↗
PubMed1985

Effects of batch variation on shade of dental porcelain.

Three different batches of three commercially available porcelains were applied to 36 specimens of two noble alloys. The shades were visually compared by nine observers. Results indicated the following. No color differences were found among specimens of individual batches. Discerning color changes were observed among three batches of one brand of porcelain. The porcelain fired in the laboratory may not match the manufacturer's standard shade guide. Batch to batch variation of porcelain may necessitate the fabrication of customized shade tabs with fresh batches of porcelain.

Chemical Phenomena↗
PubMed1985

Marginal distortion of cast restorations induced by cementation.

Eleven full veneer crowns were directly constructed on brass stylized dies. Crown marginal openings and vertical heights were measured before and after cementation with zinc phosphate cement. The following results were established. The marginal opening of complete veneer gold crowns increased during cementation. The vertical heights of well fitting crowns also increased significantly after cementation.

Crowns↗