Search PubMed⌕ Search

Biomedical subjects

A H Tjan

Publications and source records attributed to A H Tjan.

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

Fracture resistance of composite and amalgam cores retained by pins coated with new adhesive resins.

This study determined the effects of coating pins with either Panavia EX or with 4-META (Cover-Up) materials on the fracture resistance of pin-retained amalgam and composite cores. Gold-plated stainless steel (TMS) and titanium (Filpin) self-threading pins were used. Findings of this study corroborated the findings of several other studies that the use of pins reduces the fracture resistance of restorations. However, coating the pins with adhesion promoters such as Panavia EX and 4-META materials has been found to be effective in improving the fracture resistance. Cross-preference was observed between TMS and Filpin pins; that is, Panavia material coating was more effective with TMS pins, while 4-META was more effective with Filpin pins.

Adhesives↗
PubMed1992

Dimensional accuracy and bond strength of addition silicones.

A cross-matching study was conducted to evaluate the effect on dimensional accuracy and tensile bond strength between the materials when intermixing brands of addition silicone impression materials in a putty-wash impression. Three brands of putty-wash systems (Reprosil, Permagum, and Express), which formed nine possible combinations, were involved in this study. The dimensional accuracy was estimated from stone casts recovered from impressions of a standardized stainless steel master model. Findings indicated no adverse effect on the bond between putty and light-bodied materials of different brands. Statistical analysis indicated significant differences. However, because the actual differences in percent deviations between the intermixed groups and their respective reference groups are very small, they are presumed to be insignificant clinically.

Analysis of Variance↗
PubMed1992

Effect of eugenol-containing endodontic sealer on retention of prefabricated posts luted with adhesive composite resin cement.

Reported studies have implicated eugenol in the reduction in retention of restorations luted with chemically cured composite resin cement. This study investigated the effect of residual eugenol in the root canal on the retention of ParaPost dowels cemented with Panavia EX composite resin. An attempt was also made to identify and to determine the most effective cleansing procedure. Findings of this study demonstrated a substantial decrease in retention of posts luted with Panavia composite resin cement in the presence of eugenol. Irrigation with ethyl alcohol (ethanol) or etching with 37% phosphoric acid gel was found to be effective in restoring the resistance to dislodgment of the posts, but alcohol produced the most consistent and reliable results.

Acetone↗
PubMed1992

Margin designs and fracture resistance of incisal resin composite restorations.

This study measured the resistance to fracture of Class IV resin composite restorations prepared with either butt joints, bevels, or chamfer margins. Seventy extracted intact, non-carious maxillary central incisors, of approximately the same size, were collected and randomly divided into the following seven groups: 90 degrees butt joint (control)), 1 and 2 mm 45 degrees bevels, 1 and 2 mm 60 degrees bevels, and 1 and 2 mm chamfer margins. The teeth were restored with a hybrid resin composite and tested in an Instron Universal testing machine in a compressive mode at 45 degrees to the long axis. Statistical analysis indicated that there were no significant differences between the control group and any of the 1 mm bevel or chamfer margins and that the 2 mm bevel and chamfer margins yielded the highest fracture resistance.

Analysis of Variance↗
PubMed1991

Effects of strain rate on the behavior of elastomeric impression.

The effects of strain rate on the ultimate tensile strength, ultimate elongation at fracture, and elastic recovery of five commonly used elastomeric dental impression materials were studied. Each specimen was prepared by standard mixing techniques, placed for setting in a standard ASTM mold, removed, trimmed, and mounted in an Instron testing unit. Tensile load was applied and plotted on a load versus displacement curve as the specimen was stretched axially until rupture. Five specimens of each material were tested, respectively, at strain rates of 100, 200, and 500 mm/min crosshead speed. Specimens were then removed, reassembled, and measured with an electronic caliper to assess the elastic recovery; measurements were repeated after 1 minute, 30 minutes, 1 hour, and 24 hours. Findings of this study indicated that (1) polysulfide materials exhibited the greatest amount of deformation, and the lowest tensile strengths of the materials studied; (2) higher tensile strengths were observed with higher strain rates; and (3) polysulfide materials showed the greatest amount of elongation at rupture, with the highest values occurring at the higher strain rates.

Analysis of Variance↗
PubMed1991

Microleakage of composite resin cores treated with various dentin bonding systems.

Composite resin post and cores have gained widespread acceptance as an alternative for cast-gold post and core systems. A prefabricated metal post is generally used. Substantial microleakage at the interface between the composite resin core and the dentin substrate may occur. A tight and impervious bond between the dentin and the restorative material is critical for the longevity of core restorations. This study compared the microleakage of composite resin cores treated with various dentin bonding agents, including the recently developed Gluma, Tenure, and Scotchbond 2. The results indicated that Tenure and Scotchbond 2 bonding agents were most effective in reducing microleakage, followed by Gluma and conventional Scotchbond (Dual Cure) bonding agents. Although all proprietary dentin bonding systems used in this study significantly reduced microleakage, no system was capable of preventing microleakage completely.

Analysis of Variance↗
PubMed1991

Microleakage of crowns cemented with glass ionomer cement: effects of preparation finish and conditioning with polyacrylic acid.

This study compared the marginal leakage of cast gold complete crowns cemented with glass ionomer and with zinc phosphate cement. The effect of polishing the preparations and conditioning with polyacrylic acid was also evaluated for glass ionomer cement. The cast gold crowns cemented with glass ionomer cement demonstrated significantly lower marginal leakage than did those with zinc phosphate cement. The extent of microleakage was not substantially different between crowns when the preparations were polished and conditioned with polyacrylic acid.

Acrylic Resins↗
PubMed1991

Effects of reheating on the accuracy of addition silicone putty-wash impressions.

The effect of the relatively high thermal contraction of addition silicones (polyvinylsiloxane) on the accuracy of stone casts was evaluated using the putty/wash relining impression technique and acrylic resin trays. Impressions were made at 37 degrees C and were divided into two groups. One group was poured at room temperature (22 degrees +/- 2 degrees C) and another group was reheated to 37 degrees C before pouring. Measurement of the dimensional changes failed to reveal improved accuracy of the stone casts poured at the same temperature as that reached during impression making. On the basis of this limited sample, it can be concluded that reheating the impression using the putty/wash relining technique did not improve the accuracy of the stone cast.

Acrylic Resins↗
PubMed1991

Marginal accuracy of complete crowns made from alternative casting alloys.

The marginal accuracy of complete cast crowns made from five alternative casting alloys was measured and compared with that of crowns made from the traditional type III high-gold alloy. The alternative alloys studied were low-gold-palladium, high palladium, silver-palladium, nickel-chrome-molybdenum, and copper-aluminum. The findings indicated that Ag-Pd alloy crowns exhibited the best marginal accuracy among the alternative alloys tested. However, their marginal discrepancy value was still slightly higher than that of crowns made of type III high-gold alloy. Conversely, Ni-Cr-Mo alloy crowns exhibited the poorest marginal accuracy.

Cementation↗
PubMed1991

Microleakage at gingival margins of Class V composite resin restorations rebonded with various low-viscosity resin systems.

The failure of a composite resin restoration to seal at its interface with unetched tooth structures, resulting from polymerization shrinkage, creates an unwanted marginal microleakage. Rebonding with a low-viscosity resin system has been recommended to reseal the marginal gap and to reduce microleakage. Since no particular resin system is commercially available, any low-viscosity resin has been utilized for this purpose. However, findings of this study seem to indicate the importance of selecting the appropriate resin system to optimize the outcome of this rebonding procedure, emphasizing the lowest viscosity and good wettability of the system. With proper selection of the resin system, this rebonding procedure can significantly reduce the microleakage at gingival unetched margins of Class V composite restorations.

Analysis of Variance↗
PubMed1990

Microleakage at gingival dentin margins of Class V composite restorations lined with light-cured glass ionomer cement.

This study compared the microleakage of light-cured and auto-set glass ionomer liners used in Class V composite laminated glass ionomer restorations by determining the amount of microleakage at the gingival cementum/dentin margins. Standardized nonundercut V-shaped Class V cavities with gingival margins below the cementoenamel junction were prepared on the mesial and distal surfaces of 40 molars, establishing a total of 80 cavities, which were randomly divided into four groups. Each was lined with glass ionomers: group 1, Ketac-Bond (ESPE-Premier), which served as the control; group 2, XR-Ionomer (Kerr); group 3, XR-Ionomer with polyacrylic acid (PAA) pretreatment (Kerr); and group 4, Vitrabond (3M). Specimens were thermocycled for 300 cycles in 0.5% aqueous solution of basic fuchsin between 4 and 55 C with a 1-minute dwell time, and individually embedded in an epoxy resin. Statistical analysis indicated no differences among groups using the light-cured glass ionomer (groups 2 to 4), and they showed significantly less leakage than the control (group 1) at P less than 0.00001). Removal of the smear layer using 10% polyacrylic acid solution did not influence microleakage in restorations with light-cured glass ionomer liners.

Acid Etching, Dental↗
PubMed1989

Microleakage patterns of porcelain and castable ceramic laminate veneers.

This investigation evaluated the microleakage of conventional porcelain and Dicor castable ceramic laminate veneers bonded either entirely on acid-etched enamel or with the cervical margins on dentin. Three brands of light-activated composite resin cement systems were used and compared. Laminate veneers were bonded to extracted human maxillary central incisors and the extent of the marginal microleakage was measured. The findings indicated minimal marginal microleakage under both types of ceramic veneers bonded to all-enamel preparations. A markedly greater leakage at the dentin-composite resin interface was observed in veneers with cervical margins placed on dentin.

Acid Etching, Dental↗
PubMed1989

Comparison of the marginal fit of various ceramic crown systems.

This study evaluated the marginal fit of four ceramic crown systems, (1) metal ceramic crowns with a metal margin, (2) metal ceramic crowns with a porcelain facial margin, (3) Cerestore crowns, and (4) Dicor crowns. Measurements of the marginal adaptation were recorded from the facial and lingual margins by using a video-enhanced microscope with digital micrometer and image intensification in a high resolution television screen. Results indicate that all four crown systems yielded comparable and acceptable marginal fit.

Aluminum Oxide↗
PubMed1989

The polishability of posterior composites.

The polishability of six brands of posterior composites was evaluated by means of a stylus profile instrumentation and scanning electron microscopy and was compared with that of an anterior microfilled composite. A sedigraphic study was performed to estimate the size and distribution of their inorganic particles. The extent of the filler loading as well as the hardness values were also assessed to determine any relevant characteristics. Some of the findings indicated that posterior composites with large particles produced significantly higher surface roughness than those with small fiber particles. A direct correlation was also found between the hardness value and surface roughness value, indicating that a composite with higher hardness value yielded a higher roughness value.

Composite Resins↗
PubMed1989

Temperature rise in the pulp chamber during fabrication of provisional crowns.

This study measured and compared thermal changes in the pulp chamber during the fabrication of provisional crowns by direct method using various brands of autopolymerizing resin systems. The effect of curing the crowns in condensation and addition-reaction silicone putty matrices was also evaluated. The results suggested that the amount of heat transferred in the pulp chamber during the curing of resins may be damaging to the dental pulp and odontoblasts. Curing provisional resin crowns in either condensation or addition silicone putty impressions significantly reduced the temperature rise in the pulp chamber.

Crowns↗
PubMed1989

Microleakage of core materials for complete cast gold crowns.

This study evaluated the microleakage patterns of complete cast-gold crowns cemented onto teeth rebuilt with pin-retained cores made from cast gold, amalgam, composite resin, and silver-reinforced glass ionomer by using three different cements (zinc phosphate, glass ionomer, and resin cement). Crowns cemented onto unrebuilt tooth preparations with zinc phosphate cement served as controls. The cemented specimens were thermocycled between 4 degrees and 50 degrees C in waterbaths. They were then embedded in epoxy resin and sectioned. The extent of marginal microleakage was evaluated with a stereomicroscope and scored. The findings indicated that the type of luting agent used appeared to affect microleakage more than the core material. No significant differences in the degree of microleakage were found under crowns cemented onto teeth rebuilt with the four core materials when cemented with the same luting cement.

Composite Resins↗
PubMed1988

Metal-reinforced glass ionomers: their flexural and bond strengths to tooth substrates.

This study compared the flexural strengths and bond strengths to dentin and enamel of two brands of silver-reinforced glass ionomers with their respective unfilled glass-ionomer cements for luting. The results led to the following conclusions. 1. No significant differences in bond strengths to tooth substrates were recorded between silver-reinforced and unfilled glass ionomers. 2. Although the mean bond-strength values of enamel were higher than those of dentin, no statistically significant differences were observed. 3. No significant differences in bond strengths to tooth substrates were observed between the two brands of glass ionomers studied. 4. No differences in flexural strengths were recorded between the silver-reinforced glass ionomer and glass ionomer of a similar brand for luting. 5. Ketac-Silver and Ketac-Cem cements had significantly higher flexural strength than Fuji II Lumi Alloy and Fuji I cements.

Dental Bonding↗