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Biomedical subjects

K C Chan

Publications and source records attributed to K C Chan.

At least 145 records · Page 8Linked to original sources
PubMed1980

Marginal leakage of compacted gold, composite resin, and high-copper amalgam restorations.

Amalgam and compacted gold were found to have the least marginal leakage in Class V cavities. Composite resin with acid etching performed at an acceptable level. Without acid etching the marginal seal was unsatisfactory. The following conclusions can be drawn: 1. High-copper amalgam and compacted gold are the materials of choice for Class V restorations when esthetics are not of primary concern. 2. If composite resins are to be used, they should be placed with an acid-etch technique.

Acid Etching, Dental↗
PubMed1980

Auxiliary retention for intracoronal cast gold restorations.

The retention of Class V inlays cemented to cavities in extracted teeth was significantly increased by placing opposing retentive grooves in the inlays and cavity walls. The set cement formed a bridge between the two retentive grooves.

Dental Bonding↗
PubMed1980

The ability of foods to stain two composite resins.

In this bench study, coffee and soy sauce stained composite resin restorations to a significantly greater degree than did tea or cola beverage. Generally, the greatest degree of staining with all samples occurred during the first week of the study time. The stain penetration was superficial and was estimated to be 5 mu or less.

Carbonated Beverages↗
PubMed1980

The cutting effectiveness of carbide fissure burs on teeth.

The cutting effectiveness of the burs decreased with time. While the multivariate analysis of variance showed an overall difference among the three groups, these differences appeared to be due to the shape of the curves (the linear and quadratic components) rather than to their average location (the mean). Therefore there were no significant differences in cutting among the three types of burs tested. The SEM photomicrographs showed that there was no gross bur damage after the burs were used for cutting tooth structure. The cutting mechanism of a carbide bur on tooth structure needs further investigation.

Carbon↗
PubMed1980

Effect of clinical finishing procedures on amalgam microstructure.

Spherical amalgam specimens were burnished, burnished-polished, polished (wet), or polished (dry). The amalgams were sectioned normal to the prepared surface, elemental analyses were made at a series of depths from the surface with the electron microprobe and the phase fractions were calculated. Significant variations in phase distributions exist within 100 micrometers of the surface.

Chemical Phenomena↗
PubMed1979

Acid etch bonded cast orthodontic retainers.

We have described a technique which involves the use of a cast orthodontic retaining appliance bonded by the acid etch technique and composite resin for semipermanent retention. The technique provides an alternative form of treatment which offers some unique advantages over previous retentive techniques.

Acid Etching, Dental↗
PubMed1979

Comparison of the retentive strength of two cast gold pin techniques.

The retention contributed by the use of pins with gold castings can be substantially increased by the technique of placing a threaded pin in the dentin and making a casting with a threaded receptacle to fit the pin. The basis for the improvement is the greater retention of threaded pins to dentin compared to that of smooth, cemented pins that are part of the casting. The limitation on the retention achieved with the new technique is the cohesive strength of the cement. Zinc phosphate cement provided the highest retention, and EBA and polycarboxylate cements provided lower and similar retention when threaded pins were cemented to threaded receptacles.

Cementation↗
PubMed1979

Influence of temperature on ionic sparing effect and cell-associated cations in the moderate halophile, Micrococcus varians var. halophilus.

Cells of the moderately halophilic Micrococcus varians var. halophilus grew well in a chemically defined medium containing 1 to 3 M NaCl and 0.0103 M K+. The requirement for NaCl could be partially replaced by K+,:Li+ and Cs+. The efficiency of the sparing effect of these cations for NaCl was in order of K+ GReater than Li+ greater than Cs+. Increase in growth temperature was found to enchance the sparing effect of Li+ and Cs+ but not that of K+. Over the range of NaCl concentrations in which the cells grew well, cell-Na+ concentrations were similar to the medium NaCl concentrations while cellK+ concentrations were several-fold that in the medium. Cell-bound Na+ and K+ concentrations increased proportionally with medium NaCl concentration and growth temperature. The temperature-dependent cation accumulation was more obvious with K+ than Na+. The cell-associated Na+ + K+ concentrations were almost as high as or slightly higher than the external media which contained appropriate levels of NaCl regardless of the growth temperature.

Cesium↗
PubMed1978

The effect of surface finish on the anodic polarization of a conventional spherical amalgam.

The corrosion of carved, burnished, polished, and burnished--polished samples of a conventional spherical amalgam was studied by anodic polarization in Ringer's solution. The effect of the variation of the mercury content from 40 to 60 wt% on the corrosion of burnished or polished samples was also investigated. It was found that burnished and burnished--polished samples corrode the least and carved samples the most. The current-density peak associated with gamma2 was of greater magnitude in polished specimens than in burnished specimens throughout the range of mercury concentrations investigated. It is hypothesized that lower porosity and more ready passivation of the surface due to a high amount of gamma2 are the reasons that burnished samples corroded less than polished samples in this anodic polarization test.

Corrosion↗
PubMed1978

Dentinal crazing and interpin distance.

All three types of self-threading plus cause dentinal crazing. The frequency and degree of damage done to the dentin varies significantly between the three types of pins and depends upon the differences in the diameters of the drill and the pin. When two or more pins are placed in dentin, the potential for dentinal damage increases. Minikin pins (0.019-inch diameter) caused the least damage, in terms of both degree and frequency. The optimum and safe interpin distance using Minikin pins suggested by this study is 3 mm. Minim and Regular pins (0.023- and 0.031-inch diameters, respectively) caused more injury than Minikin pins. The Regular pins showed more damaging effects on dentin than Minim pins, both in terms of degree and frequency. On the basis of this study, the minimum interpin distance using Minim or Regular pins should be 5 mm. These minimum interpin distances are applicable only in situations where the dentin is not dehydrated or embrittled due to endodontic treatment. In teeth that have been endodontically treated, it would be advisable to use only the smallest self-threading pins and possibly increase the interpin distance if two or more pins are to be used.

Dental Pins↗
PubMed1978

The strength of multilayer and repaired composite resin.

Composite resin surfaces that formed against a plastic matrix or that polymerized while exposed to air were excellent substrates for the adhesion of new resin. Samples formed by the addition of composite resin to a cut surface had a tensile strength of one half of the cohesive strength of the resin. Coating the cut surface with a thin layer of unfilled resin enhanced bonding of the second composite resin layer. The use of a thin layer of unfilled catalyst resin as a bonding agent caused the most rapid development of strength and the greatest strength in samples tested after 7 days.

Adhesiveness↗
PubMed1978

Microleakage and enamel finish.

Cavity preparations that are finished with hand instruments allow significantly less marginal leakage than those which are completed only with rotary instruments. This does not mean that hand-instruments walls are perfectly smooth; it only means that these walls allow less marginal leakage. Cavity preparations restored with composite resin showed more marginal leakage than those restored with amalgam. Also, the degree of marginal leakage was greater in cavity preparations restored with composite resin than in those restored with amalgam. Cavity preparations are more prone to marginal leakage at sharply defined cavosurface acute angles than at the smooth or straight surfaces of the cavity. This pattern of marginal leakage was true for both amalgam restorations and composite restorations, but the degree of marginal leakage was greater when composite resin was used as a restorative material. Since less marginal leakage was found in the finished cavity preparations, it is obvious that all cavity preparations must be finished with hand instruments. This may not completely eliminate the problem of marginal leakage, but it will reduce the potential secondary caries both in degree and frequency. Also, since sharply defined acute angles did exhibit more marginal leakage, this part of the cavity preparation needs special attention. With amalgam and composite restorations at least, these angles should not be sharply defined but should be slightly round, so that better condensation of restorative materials can be obtained. This may reduce the degree of marginal leakage.

Composite Resins↗