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Biomedical subjects

M G Duncanson

Publications and source records attributed to M G Duncanson.

At least 73 records · Page 4Linked to original sources
PubMed1981

In vitro analysis of self-shearing retentive pins.

Combining stress, analysis, microscopic examination, mechanical testing of the shear mechanism, and retention of the Reten Pin leads to the following conclusions: 1. The suggested 0.006 inch pin-channel mismatch induces high lateral and apical stresses. Microscopically, this was seen to correlate with injury to the dentin. 2. The degree of retention was increased by using a smaller pin-channel mismatch. This correlates with smaller stresses and reduced dentinal damage. 3. The shear mechanism acts in a uniform manner, with a relatively small variation from the mean. It is suggested that for the best results the manufacturer should supply larger twist drills and pins with a somewhat deeper self-shearing groove to minimize apical involvement during shearing of the handle from the pin.

Dental Pins↗
PubMed1981

The diametral tensile strengths of various composite resins.

The products exhibiting the greatest tensile strength values were those systems which provided measuring devices enabling the dentist to more accurately control the amounts of material to be mixed. Statistical analysis supported this finding; the means of the powder/liquid and paste/liquid systems formed a group that was significantly different from the five paste/paste systems. This indicates that accurate measurement of components could represent one important factor in the ultimate strength of a composite resin. There was no apparent correlation between average density and mean diametral tensile strength for the seven systems compared in this study.

Chemical Phenomena↗
PubMed1981

Wetting effects of surface treatments on inlay wax-investment combinations.

Gypsum-bonded and phosphate-bonded investments were applied to wax surfaces which were untreated, treated by buffing with cotton moistened with a die lubricant containing organic solvent, or treatment with a wax pattern cleaner. Contact angles between the investment material and wax surfaces were measured and compared. The treatment of a wax pattern with a surface tension reducing agent significantly increases the degree of wetting by both gypsum- and phosphate-bonded investments.

Calcium Sulfate↗
PubMed1980

Effects of cast gold surface finishing on plaque retention.

The relationship between the surface finish on cast gold restorations and the amount of plaque deposited on that surface was examined. Six different finishes were tested. The rough finish was found to accumulate significantly less plaque than the other finishes. Every finish exhibited some plaque accumulation, even after the first 24 hours. Each finish accumulated progressively more plaque at each successive time interval.

Adult↗
PubMed1980

A comparison of six impression syringes.

Five manually operated, and one air-activated, syringes were evaluated and compared. When used with polyether or polysulfide, some disposable syringes were found to require in excess of 100 pounds of force to operate. The metal reusable syringe required only 13 and 21 pounds, respectively, with the same materials; the air-activated syringe required none. There was no significant difference among the syringes with regard to bubble entrapment during impression making. There was a significant difference found in this regard among the five experienced dentists. The air-activated syringe was most easily controlled, as evidenced by the significantly smaller number of tracing errors made with it.

Air↗
PubMed1980

Retention and resistance of preparations for cast restorations.

Five preparation designs were tested for retention and resistance. Retention values for all partial veneer crowns were significantly lower than those for the complete veneer crown. Resistance values increased significantly with the addition of grooves and/or extension of axial surface coverage. Addition of grooves and/or extension of axial surface coverage produced small increases in retention values but marked increases in resistance values.

Crowns↗
PubMed1976

Comparative stability of two removable die systems.

The comparative stability of two removable die systems was evaluated. Under controlled conditions, ten casts, each with two removable dies, were constructed for each system for a total of 20 casts and 40 removable dies. Base-line pre- and postsectioning measurements to within 0.0001 inch in horizontal and vertical planes were recorded and differences calculated. Each die was removed and re-placed 30 times prior to any postsectioning measurement. The results indicated small inconsistent horizontal deviations and consistent vertical deviations for both systems. The Pindex system deviations were slightly less than those of the Di-Lok system, although t test values preclude any conclusion of significance. The results of this investigation indicate the need for dentists and dental laboratory technicians to exercise care in the utilization of any removable die system so as to obtain optimum accuracy and stability in the relationships of the components of that system.

Dental Casting Technique↗
PubMed1976

Nonprecious metal alloys for fixed restorative dentistry.

Non-noble alloys are available for use in the fabrication of cast restorations. These alloys are not necessarily designed for subsequent application of porcelain. Because they are promoted for use in place of the traditional gold alloys, significant changes in technique and armamentarium are necessary. Casting of acceptable clinical quality can be obtained, but not without additional equipment and personnel training. Obtaining casting of gold alloy quality on a routine basis may not be easily achieved. Casting into detail is possible (see Fig. 5), although greater surface roughness of the casting may be observed with the non-noble alloys. A high polish is possible (Fig. 6), however technicians and clinicians accustomed to and expert in polishing single or multiple gold alloy castings will require time and training to adjust to the somewhat more difficult and time-consuming techniques required in the polishing of non-noble alloys. Well fitting castings of the non-noble alloys require investments capable of greater thermal and/or hygroscopic expansion. The solidification shrinkage in non-noble alloys is greater than that of gold alloys. The clinician may find casting of these alloys to be "tight-fitting" on insertion. At present, because additional time and armamentarioum may be required, laboratory fees for the non-noble metal casting may not be any more economical than those of cast gold alloys. Therefore, the clinician and patient may benefit little with regard to reduced fees for restorations constructed of these alloys. In conclusion, the non-noble metals may find increased use in fixed restorative dentistry as expertise develops to the level at which usage of these products becomes routine. These is still considerable clinical information needed as to the durability and corrosion resistance of these alloys. Some work has been work has been done on the corrosion of these alloys, but much data remains to be obtained. Soldering these alloys is difficult and requires training of the technician in the required usage of special solders. The following facts should be considered in casting and finishing non-noble alloys for single and multiple unit casting in dentistry. 1. Silicate or phosphate bonding investments are required. 2. Recognition of proper casting appearance of the molten alloy is essential. 3. Additional armamentarium is required to obtain casting temperatures necessary. 4. Polishing procedures are more laborious and require harder abrasives. 5...

Crowns↗
PubMed1975

Viscoelastic properties of human dentin.

Stress relaxation measurements were performed on thick-walled cylinders of radicular human dentin. The experimentally measured relaxation moduli were used to obtain an approximation to the logarithmic distribution function of relaxation times. This distribution function was used to predict the behavior of other viscoelastic properties. In particular, the prediction of the strain and strain rate dependence of the modulus was determined and compared with experimental results.

Dentin↗