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Biomedical subjects

A H Tjan

Publications and source records attributed to A H Tjan.

At least 73 records · Page 4Linked to original sources
PubMed1985

Internal escape channel to improve the seating of full crowns with various marginal configurations: a follow-up study.

The effectiveness of an internal escape channel in improving the marginal adaptation of full crowns with various marginal configuration was investigated. Full crowns with 90-degree shoulders had a vertical discrepancy comparable to those of crowns with accentuated finish lines. Although an internal escape channel significantly improved the seating of a full crown with a 90-degree shoulder and 45-degree level, its vertical discrepancy was much higher than those of crowns with an accentuated finish line or a 90-degree shoulder.

Cementation↗
PubMed1985

Resistance to root fracture of dowel channels with various thicknesses of buccal dentin walls.

The significance of the amount of remaining buccal dentin plate of the dowel channel in resisting root fracture under horizontally directed load was investigated. Forty cast gold dowels and cores were made for four groups of dowel channels that had, respectively, 1 mm, 2 mm, 3 mm, and 1 mm with a 60-degree bevel (collar) of the remaining buccal dentin at the entrance of the canal. An Instron tester in compressive mode was used to produce the horizontal force. Although significant differences in the failure loads for the four groups were not found, dowel channels with 1 mm of remaining buccal dentin walls were apparently more prone to fracture under horizontal impact than those that had 2 or 3 mm of buccal dentin walls. Contrary to popular belief, the addition of a metal collar did not enhance the resistance to root fracture.

Crowns↗
PubMed1984

Comparison of retentive properties of dowel forms after application of intermittent torsional forces.

Four different forms of cast-gold dowels (round parallel-sided, round parallel-sided with antirotational keyways, tapered, and ovoid parallel-sided) were subjected to intermittent horizontal and vertical rotational forces prior to tensile testing. The results of this experiment indicated that ovoid parallel-sided dowels were the most retentive. Tapered dowels were found to be the least retentive. The addition of antirotational features to the round parallel-sided dowel did not improve the retentive values. The retentive properties of the round parallel-sided dowels, with or without antirotational features, were not statistically different from the ovoid parallel-sided dowels. Sandblasting the finished castings prior to cementation increased retention.

Crowns↗
PubMed1984

The effect of a corrugated channel on the retentive properties of an obturator-reinforced composite resin dowel-core system.

A study was conducted to compare the retentive properties of the obturator-reinforced composite resin dowel and core systems with and without corrugated dentin surfaces in the dowel channels. A commercially available tap with a diameter of about 1.4 mm and a thread groove depth of 100 micron was used to accomplish this dentin roughening. To compare whether methods of placement affect the retentive capacities of this dowel and core system, a Lentulo spiral, Jiffy tube, and Centrix C-R syringe were used to insert the resin mixes into the corrugated channels. The following conclusions can be drawn. By corrugating or roughening the dentin surface of the prepared channel, the retentive properties of this dowel and core system are significantly increased. In this system using minimal amounts of composite resin, the three methods of placement exhibited no significant difference in retention. The retentive failure seemed to occur at the resin-tooth interface. Increasing the degree of corrugation (deeper grooves) increased the retention, but caution must be exercised to prevent weakening the tooth.

Crowns↗
PubMed1984

Some esthetic factors in a smile.

A survey of the characteristics of an open smile was conducted with 454 full-face photographs of randomly selected dental and dental hygiene students. Findings show that an average smile exhibits approximately the full length of the maxillary anterior teeth, has the incisal curve of the teeth parallel to the inner curvature of the lower lip, has the incisal curve of the maxillary anterior teeth touching slightly or missing slightly the lower lip, and displays the six upper anterior teeth and premolars. Consideration of the characteristics may be useful in improving the esthetics of restorations.

Adult↗
PubMed1983

Retentive properties of some simplified dowel-core systems to cast gold dowel and core.

The retentive capacity of three groups of dowel and core systems was compared by subjecting them to tensile loading. The following conclusions were made. Retentive values for Parapost dowels were significantly higher than those of both cast-gold and reinforced composite resin dowels and cores. Surface configuration of dowels appeared to be an important factor in retention. No significant differences were observed in the retentive values between cast-gold and obturator-reinforced composite resin dowels and cores. Retentive failure of the obturator-reinforced composite resin system always occurred in the composite resin-dentin interface.

Cementation↗
PubMed1982

The internal escape channel: a solution to incomplete seating of full cast crowns.

An experiment was conducted to investigate the effect of internal escape channels and perimetric occlusal bevel on the completeness of seating of full veneer cast-gold crown during cementation. Twenty-four crowns were fabricated on Ivorine dies and cemented by standardized procedures. Two experimental groups were reused to study the effect of the addition of a perimetric occlusal bevel. The vertical dimension was significantly reduced in all four test groups when compared with the control. We concluded that an internal escape channel improves the complete seating of a full veneer cast-gold crown.

Crowns↗
PubMed1981

Effect of multiple axial grooves on the marginal adaptation of full cast-gold crowns.

Twenty-seven crowns were fabricated on the standardized ivorine dies to determine the effect of multiple axial grooves. No grooves were placed on the control (group I). In groups II and III, respectively, two and four grooves were replaced. The mean value of the occlusal cement film thickness was used to appraise the vertical discrepancy (lack of seating) of the crown on the die. This value was obtained by averaging seven measurements of the occlusal cement film thickness taken at different areas. These measurements were recorded from the photomicrographs at x 100 magnification. There were significant differences between the control group and both test groups. Results of this study show that the presence of the grooves has an adverse effect on the seating of full cast-gold crowns.

Cementation↗
PubMed1980

The effect of thermal stress on the marginal seal of cast gold full crowns.

An experiment was conducted to observe the effect of fluctuations in temperature on the marginal seal of full veneer cast gold crowns. Forty crowns were fabricated and allotted into two groups of 20 crowns each. One group was cemented with zinc phosphate and the other group, with zinc polycarboxylate cement. Ten crowns from each group were subjected to thermal stress of fluctuating temperatures (4 and 60 C) and the remaining ten crowns from each group were held at the constant temperature of 37 +/- 1 C. The experiment demonstrated the following results: --Microleakage was evident in all groups. --The degree of microleakage with zinc phosphate was less than with zinc polycarboxylate cement. --Contrary to the claim that zinc polycarboxylate cement adheres to enamel through chelation, we were unable to observe better results. The degree of penetration of dye in the tooth-cement interfaces of crowns cemented with zinc polycarboxylate was not less despite the remaining layers of enamel for bonding. The cause of microleakage with cast gold restorations is apparently multifactorial. Research should formulate a luting agent which forms a strong bond to gold alloy and tooth substrate and has a high tensile and shearing strength.

Crowns↗
PubMed1979

Biogeometric guide to groove placement on three-quarter crown preparations.

An attempt has been made to establish a practical guide to placing the grooves on a three-quarter crown which fulfills biologic, mechanical, and structural requirements. It is our intention to refine and adjust groove placement to biologic and practical limitations in the hopes of ending some of the confusion and difficulty in partial veneer preparations.

Crowns↗