Biomedical subjects

A H Tjan

Publications and source records attributed to A H Tjan.

At least 19 recordsLinked to original sources

PubMed1994

Effects of thermocycling, load-cycling, and blood contamination on cemented implant abutments.

This study compared the effects of thermocycling, load-cycling, and human blood contamination on the retentive strength of five different cements for luting posts to root-form implants. For each cement, 10 specimens (controls) were stored in an incubator, 10 specimens were thermocycled, 10 specimens were subjected to cyclic compressive loading, 10 specimens were subjected to a combination of thermocycling and cyclic compressive loading, and 10 specimens were contaminated with blood before cementation, then exposed to a combination of thermocycling and compressive loading. After 70 hours, retentive tests were performed on the Instron machine, and data were recorded in kilograms. Significant retentive differences were identified among the cements and with load-cycling, but minimal effect on the retentive strength was demonstrated from thermocycling. Blood contamination in combination with thermocycling and load-cycling adversely affected the retentive strengths of all of the cements and could be a major cause of abutment failure in dental implants.

Analysis of Variance↗

PubMed1993

Temperature rise at root surface during post-space preparation.

This study compared the changes in temperature at the root surface of extracted human central incisors during post-space preparation using the following reamers (1) Peeso, (2) Kurer, (3) Gates-Glidden, (4) Para-Post, and (5) diamond burs. A mean temperature rise ranging from 2.3 degrees C to 15.6 degrees C from the baseline of approximately 28 degrees C was recorded. Peeso reamers recorded the highest temperatures followed by Kurer system and diamond burs, whereas Gates-Glidden and Para-Post systems were the lowest.

Analysis of Variance↗

PubMed1993

Microleakage of posterior composite resin restorations using beta quartz glass-ceramic inserts.

The effectiveness of using beta quartz glass-ceramic inserts in Class II composite resin restorations to prevent microleakage at the gingival cementum margins was investigated. Class II cavities were prepared on both mesial and distal sides of ten extracted teeth with the gingival margins placed on cementum. Both cavities were then restored with a composite resin in exactly the same manner, except that one received a glass ceramic insert and the other did not. The specimens were then thermocycled in basic fuchsin solution, embedded in epoxy resin and sectioned. The extent of dye penetration at the gingival cementum margins was then assessed and scored. The result indicated that the use of a glass-ceramic insert substantially reduced the microleakage of gingival cementum margins of composite resin restorations.

Ceramics↗

PubMed1992

Marginal leakage of cast gold crowns luted with an adhesive resin cement.

The microleakage of cast gold complete crowns cemented with Panavia EX cement was evaluated and compared with those luted with a standard zinc phosphate cement. The effect of water immersion of specimens for 30 and 90 days was also investigated. The finding of this study indicated that crowns cemented with Panavia EX cement exhibited substantially less marginal leakage than those cemented with zinc phosphate cement. No significant difference in marginal leakage was observed between 30-day and 90-day water immersion of crowns cemented with Panavia EX cement.

Adhesives↗

PubMed1992

Effect of various incremental techniques on the marginal adaptation of class II composite resin restorations.

The effects of various placement techniques on the formation of microgaps were compared at the gingival margins of class II composite resin restorations. Three incremental techniques (occlusogingival layering, oblique layering, and faciolingual layering) and two one-bulk techniques of placing composite resin were studied. In the first one-bulk placement technique the composite resin was photocured occlusally; in the second one-bulk technique the composite resin was irradiated from three directions; facial, lingual, and occlusal. None of the incremental placement techniques improved the adaptation at the gingival margin compared with a one-bulk technique irradiated occlusally. However, the one-bulk placement technique that was irradiated from three directions created a substantial marginal discrepancy.

Acid Etching, Dental↗

PubMed1992

Seating and retention of complete crowns with a new adhesive resin cement.

The retentive property of cast gold complete crowns cemented with an adhesive resin cement (Panavia Ex) was compared with retention of crowns cemented with zinc phosphate cement (Flecks) and the conventional resin cement (Comspan). The effect of these agents on seating of crowns also was evaluated. Panavia cement exhibited the highest retentive strength, with values almost twice those obtained with zinc phosphate cement. However, the difference in mean retention values of crowns cemented with Comspan cement or with zinc phosphate cement was not statistically significant. Both resin cements used in this study provided better seating of crowns than did zinc phosphate cement.

Adhesives↗

PubMed1992

Effect of tray space on the accuracy of monophasic polyvinylsiloxane impressions.

The effect of tray space on the dimensional accuracy and stability of impressions made from four brands of monophasic polyvinyl siloxane material was assessed on the recovered stone casts by quantitative and qualitative methods. In general, both evaluation methods agreed that tray space and repeat pour did not affect the accuracy of the dies for individual castings. But disagreement was observed in the findings for fixed partial dentures (FPDs). Quantitative measurement of the interpreparation (IP) dimensions did suggest the possibility of a potential problem when a FPD is cast in one piece because of a significantly reduced distance between the two abutments. However, from the findings of this study it can be concluded that a rigid stock tray can be used with a monophasic polyvinyl siloxane impression material.

Analysis of Variance↗

PubMed1992

Accuracy and bond strength of reversible with irreversible hydrocolloid impression systems: a comparative study.

Combinations of three reversible hydrocolloids with five irreversible hydrocolloids were evaluated for dimensional accuracy and bond strength. A stainless steel model representing two teeth prepared for a fixed partial denture was designed for an accuracy study. The recordings were made with a measuring microscope, and the tensile bond strength was determined with an Instron Universal Testing instrument. The accuracy of these materials was clinically acceptable, and the resulting models were suitable. The materials distributed by a common supplier exhibited better tensile strength, although one irreversible hydrocolloid, Jeltrate, performed well in the noncompanion combination groups. This reversible with irreversible hydrocolloid combination impression has an advantage compared with the traditional reversible hydrocolloid impression, because it does not require elaborate, expensive conditioning equipment and water cooled trays.

Agar↗

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↗