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Biomedical subjects

N Barghi

Publications and source records attributed to N Barghi.

18 recordsLinked to original sources
PubMed1992

Marginal accuracy and geometry of cast titanium copings.

The biocompatibility of titanium with human tissue is well established; its potential as an alternate metal for crown restorations has yet to be fully investigated. This study measured the geometry and accuracy of coping margins cast in Ti, 99.5% chemically pure. Twenty castings with 45-degree facial and 90-degree palatal margins were made by indirect technique with a commercial system using recommended procedures. They were then cemented with ZnPO4 cement. The coping and die assemblies were embedded in resin, sectioned longitudinally, and measured with a microscope at x50 power. Casting shrinkage was characteristic, particularly along the horizontal axis in the plane of the shoulder. Although horizontal linear shrinkage of 45-degree margins was greater than that for the 90-degree form, the surface of marginal discrepancy was greatest with the 90-degree configuration.

Analysis of Variance↗
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↗
PubMed1978

A study of various factors influencing shade of bonded porcelain.

Seventy-two specimens of four commercially used precious metals were constructed. The porcelain applied to these specimens was glazed up to nine times for shade comparison. Specimens were also studied with a scanning electron microscope prior to and after application of the porcelain. The important observations from this study were: 1. The four types of precious metals looked alike after casting and surface treatment and prior to application of porcelain. 2. Porcelain-bonded-to-metal shades were not influenced by the types of precious metals used. 3. Porcelain-bonded-to-metal shades remained stable after six glazings and changed only slightly after nine firings.

Color↗
PubMed1977

Porcelain shade stability after repeated firing.

There were no color changes detected in the first five firings for both air- and vacuum-fired porcelain. Slight changes were noticed in subsequent firings. These color changes were more noticeable in the air-fired samples than in the vacuum-fired samples. However, changes in the porcelain color after repeated firing were not sufficiently significant to cause rejection of the samples. The porcelain shade remains stable with repeated firing if the firing procedure is carefully carried out.

Color↗
PubMed1976

When to glaze--an electron microscope study.

1. A smooth porcelain surface can be obtained by glazing after grinding. There is no need for sanding or polishing with a rubber wheel. 2. A low-fusing glaze gives a slightly smoother surface than a natural glaze. The low-fusing glaze may be added at any stage of polishing, and the results will be the same.

Dental Porcelain↗
PubMedDate not supplied

Thermocycling of pit and fissure sealants.

Both sealants experience early thermocyclic failure, which is manifested as marginal breakdown or separation. From the 20 to 70% failure range (Fig 5) Nuva Seal was three times as resistant to thermocyclic stressing as was Epoxylite 9075. That is, the Nuva Seal-sealed teeth had to be cycled three times more than the Epoxylite 9075-sealed teeth to effect the same failure rates. Both Epoxylite and Nuva Seal reach the same failure rate at 7,000 cycles (75% failure rate). Extremely careful visual examination is required to detect marginal separation failures of pit and fissure sealants.

Dental Materials↗
PubMedDate not supplied

Comparing two methods of moisture control in bonding to enamel: a clinical study.

Twelve patients provided a total of 36 teeth to be used in this study. Visible-light-cured composite resin tabs were applied to a flattened, acid-etched surface of each tooth. Half of the teeth were isolated with cotton rolls in conjunction with a saliva ejector; the other conjunction with a saliva ejector; the other half were isolated using a rubber dam. An equal number of teeth were treated in each group for each subject to serve as a self-control. After extraction the teeth were mounted and shear bond strength of the composite resin to enamel was determined on an Instron Testing Machine. There was a significant difference in the shear bond strength between the two experimental groups.

Acid Etching, Dental↗