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Biomedical subjects

A H Tjan

Publications and source records attributed to A H Tjan.

At least 55 records · Page 3Linked to original sources
PubMed1988

Temperature rise produced by various visible light generators through dentinal barriers.

This study evaluated and compared the heat generated by seven brands of light-curing units by measuring the temperature elevation from the ambient temperature through the use of a digital thermocouple-thermometer with a needle probe placed at three locations in the dentin. The results of this study indicated a wide range of differences in temperature rise among the tested light-curing units. In all three locations of probe placement, the Translux unit produced the least temperature elevation.

Dental Restoration, Permanent↗
PubMed1988

Effect of contaminants on the adhesion of light-bodied silicones to putty silicones in putty-wash impression technique.

This study was concerned with the adhesion of a light-bodied silicone to a putty silicone in a putty-wash impression technique when the preliminary putty impression was contaminated with human saliva or residues from acrylic resins used in the fabrication of provisional restorations by direct technique. Data indicated that condensation and addition silicones differed in their susceptibility toward the tested contaminants. Salivary contamination and chemical residues from the autopolymerizing acrylic resins weakened the bond strength and caused adhesive failure dependent upon the type of silicone impression material used.

Acrylic Resins↗
PubMed1988

Interfacial bond strengths between layers of visible light-activated composites.

The bond strengths between composite layers either cured to themselves or to other types (classes) of composites of similar or different brands were measured by using a direct tensile test (true tension). The diametral compression test for tension for each material tested was also conducted according to ADA specification No. 27. The values were used for comparison. 1. The interfacial bond strengths were generally found to be higher than the cohesive strengths of the weaker materials when cured to different types of composites or of the weak region in the specimen when composites were cured to themselves. 2. The cohesive tensile failure of the materials occurred at much lower stress levels than their corresponding diametral tensile strength (ranging from 1/4 to 1/3 of the diametral strength). 3. When two types of composites were bonded together the cohesive failure occurred consistently within the materials with lower diametral strength. Correlation was observed between the values of cohesive strength of material measured with true tension and the diametral test. 4. A urethane dimethacrylate microfilled composite bonded weakly to BIS-GMA composite, therefore, their combined use should be avoided. 5. Incremental placement produced a clinically acceptable bond strength because it exceeded or was at least comparable to the cohesive strength of the material.

Composite Resins↗
PubMed1988

Reversible hydrocolloid: the standard of excellence.

Reversible hydrocolloid is the oldest elastic dental impression material and, with the appropriate methodology, the advantages outweigh the disadvantages. Skill, care, and comprehension of the physical properties of the materials ensure success.

Agar↗
PubMed1988

Effects of four lubricants used during incremental insertion of two types of visible light-activated composites.

The effect of alcohols, bonding resins, or dentin adhesives on the adhesive bond between the layers of visible light-activated composites when used as lubricant for composite instruments was investigated. The results of this study indicated that alcohols are not compatible with certain BIS-GMA-based and UEDMA-based composite systems (Herculite and Heliomolar composites were used for this investigation). Use of ethanol as a lubricant caused pure adhesive failure and low bond strength in UEDMA-based composite (Heliomolar), indicating that the bond strength was less than the cohesive strength of the composite. A bonding resin of a similar brand (or the same system) used to lubricate the composite instrument did not affect the bond strength of the bonded composite specimens. In light of this study, a bonding resin of the same resin system as the composite may be the most suitable and reliable material to be used for lubricating the composite instrument.

1-Propanol↗
PubMed1988

Dental material artifacts on MR images.

Magnetic resonance (MR) imaging of the head and neck is becoming an important aid in evaluating pathologic conditions of the brain, midface, and pharynx. Certain dental materials cause artifacts during MR imaging of the lower midface. These artifacts can obscure the normal anatomy. This study describes the degree of artifact production caused by various materials commonly used in dental restorations. Of the materials tested, those causing artifacts were made of stainless steel, such as orthodontic bands used for braces, and pins or posts that are commonly drilled into teeth to provide structure or stability before filling. Materials used as temporary or permanent fillings or crowns--such as amalgam, gold alloy, aluminum, microfilled resin, and polyvinyl acrylics--did not cause artifacts in the images.

Dental Materials↗
PubMed1987

Effects of various cementation methods on the retention of prefabricated posts.

Para-Post dowels were cemented by using combinations of cement, cleansing agents, and dentinal treatments. The comparative retentive strengths were as follows: 1. Para-Post posts cemented with composite into mechanically corrugated post spaces recorded the greatest retention. 2. The retention of the posts cemented with composite into post spaces rinsed with 1 ml of 17% EDTA with a pH of 7.5 and followed immediately by 1 ml of 5.25% NaOCl was lowest. 3. The retention of the posts secured with zinc phosphate into mechanically corrugated post spaces was significantly higher than with untapped post spaces. 4. The retentive strength of the posts placed with glass-ionomer cement into post spaces, irrigated with 1 ml of 40% polyacrylic acid solution, and rinsed with distilled water was comparable to that of posts secured with zinc phosphate cement without roughened post spaces.

Cementation↗
PubMed1987

The efficacy of resin-compatible cavity varnishes in reducing dentin permeability to free monomer.

The effectiveness of three resin-compatible cavity varnishes in reducing the dentin permeability to free monomer liquid was evaluated by means of a dentin disk mounted within a pressurized split-chamber diffusion device filled with low-viscosity aliphatic dimethacrylate. Substantial reduction in dentin permeability was obtained with all of the products tested (Microjoin, Cavi-Line, and Universal). This study suggests their likely effectiveness as a protective barrier against permeation of free monomer into the dental pulp.

Collodion↗
PubMed1987

Comparing effects of tray treatment on the accuracy of dies.

The effects of tray treatments on the accuracy of dies from addition silicone impressions were investigated. Tray treatments included custom acrylic resin tray with adhesive, perforated custom acrylic resin tray without adhesive, and perforated custom acrylic resin tray with adhesive. No appreciable differences were found in the complete crowns among the three tray treatments on the first pours. Significant statistical differences observed in the MOD and occlusal inlays were nonetheless of questionable clinical significance. Adhesives are advisable if the impressions are poured repeatedly, however, to minimize accidental separation of the impression from the tray. The second casts were less accurate with complete crowns and MOD inlays when perforated trays were used without adhesives.

Acrylic Resins↗
PubMed1987

Marginal accuracy of temporary composite crowns.

An in vitro study was conducted to quantitatively compare the marginal adaptation of temporary crowns made from Protemp material with those made from Scutan, Provisional, and Trim materials. A direct technique was used to make temporary restorations on prepared teeth with an impression as a matrix. Protem, Trim, and Provisional materials produced temporary crowns of comparable accuracy. Crowns made from Scutan material had open margins.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1987

Bond strength of composite to metal mediated by metal adhesive promoters.

The effectiveness of three metal primers in promoting the adhesive bond of composites to alloy systems commonly used in making ceramometal restorations was investigated. The results of this study indicated that the bond strengths attained with these tested metal primers are in general not high. Further research is needed for the development of a metal primer with an improved adhesive strength. Until then, dentists should continue to use the current methods of undercutting and roughening the metal surface in order to achieve additional retention.

Adhesives↗
PubMed1987

Effects of resin-compatible cavity varnishes on the polymerization of visible light-cured composites.

The effects of three proprietary resin-compatible cavity varnishes on the polymerization of two visible light-cured composites were investigated. A conventional varnish (Copalite) was included for the sake of comparison. The four cavity varnishes showed no significant difference in average hardness values of the light-cured composites when cured against completely set varnish. It was also found there was no statistical difference in the thickness of the uncured resin layer when the light-cured composites were cured against all four partially set cavity varnishes. The average thickness of the uncured resin layer in Silux was found to be significantly higher than that of Command Ultrafine. Based upon the hardness and thickness evaluations, the data of this study suggest that none of the four cavity varnishes (including Copalite) affected the hardness of the composites when allowed to set completely before the composite was applied. In contrast, all four tested cavity varnishes showed a softening of resin at the interface when the composites were cured against a partially set varnish. It is important therefore to permit the cavity varnish to dry completely before applying composite.

Composite Resins↗
PubMed1986

Clinically oriented evaluation of the accuracy of commonly used impression materials.

The elastomeric impression materials used in this study exhibited comparable clinical accuracy when properly handled. In general, they were significantly more accurate than reversible hydrocolloid. In fact, because of their excellent dimensional stability, impressions made with addition curing silicone-base or polyether rubber impression materials remained accurate even after 1 week. Elastomeric impression materials have established themselves with reversible hydrocolloids as elastic impression materials that are capable of producing clinically accurate dies with an excellent replication of surface detail.

Colloids↗
PubMed1985

Comparison of internal escape channels with die spacing and occlusal venting.

The effectiveness of the following procedures in improving the seating of full cast crowns were compared: internal escape channels, die spacing, occlusal venting, and a combination of die spacing with an escape channel. All techniques were shown to be similar in effectiveness. Die spacing produced the least consistent results. An internal escape channel, occlusal venting, die spacing, or a combination of an escape channel and die spacing did not influence the retention of full cast crowns.

Cementation↗