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Biomedical subjects

R DeLong

Publications and source records attributed to R DeLong.

52 records · Page 3Linked to original sources
PubMed1984

Corrosion-fatigue of the bond between nickel-chrome casting alloys and porcelain.

This study was designed to determine if corrosion-fatigue might play a part in early failure of the porcelain-fused-to-metal bonds with Ni-Cr alloys. A qualitative test was used that compared the bond strengths of a control group with those of samples subjected to corrosion-fatigue. One Au-Pd alloy was used for comparison with the Ni-Cr alloys. The bond strengths were determined with a shear-push through test in an M.T.S. hydraulic testing machine. Two additional groups of samples were tested with corrosion only and fatigue only. All samples except those used for controls were placed in an oral environment chamber that had an aerated artificial saliva circulating through it maintained at 37 degrees C. (Samples subjected to fatigue only used unaerated distilled water). Corrosion was accelerated by enforcing a potential of approximately 500 mV on the test samples. The samples subjected to fatigue were stressed with a haversine waveform with a force between 5 and 45 pounds at a rate of 200 Hz for 10(6) cycles.

Chemical Phenomena↗
PubMed1984

Cusp reinforcement by the acid-etch technique.

Strain gauges were mounted on 12 maxillary pre-molars which were subjected to a sequence of restorative procedures for MOD preparations. An occlusal stress was applied using servohydraulics, and the cuspal flexure was assessed using a strain gauge. Two bonded and three non-bonded restorative procedures were tested for each tooth. The two bonded conditions showed significantly higher cuspal reinforcement when compared with the MOD preparation and the non-bonded restorative procedures. The non-bonded restorations showed some intragroup differences, with one non-bonded composite showing useful cuspal reinforcement. However, this was much less than that afforded by the bonded technique. The deformation of the cusp under occlusal force in restorations bonded by the acid-etch technique showed much less hysteresis when compared with non-bonded restorations.

Acid Etching, Dental↗
PubMed1978

Accelerated aging due to enzymatic racemization.

Thermodynamic racemization may be a cause of aging. Racemases might accelerate the aging process. If enzymatic racemization does accelerate aging, then the use of chemical or immunological inhibitors of racemases might retard aging.

Aging↗
PubMedDate not supplied

Evaluation of factors affecting the accuracy of impressions using quantitative surface analysis.

Impression material goes from a plastic to an elastic state during setting. Movement of the impression and excessive seating pressure during this transition can cause distortion in the impressions. The purpose of this study is to determine if the impression distortion is related to movement during setting or to distortion of the putty phase in the two-step impressioning technique. A master model of a maxillary quadrant of teeth was impressed using four different procedures: 1) one-step technique without movement (1S-NM); 2) one-step technique with movement (1S-M); 3) two-step technique without movement (2S-NM); and 4) two-step technique with movement (2S-M). An artificial oral environment and surface analysis technique of the Minnesota Dental Research Center for Biomaterials and Biomechanics were used to produce the impressions and measure their accuracy. A digitized image of the first premolar of the master model was aligned with a digitized image of the first premolar of each epoxy model using AnSur. The root mean squared difference (RMS) between the aligned images is a measure of the distortion. The corresponding RMS values for the different methods were: 1S-NM = 23.7 +/- 9.21; 1S-M = 20.4 +/- 3.9; 2S-NM = 20.5 +/- 7.7; 2S-M = 21.3 +/- 4.4. Statistical analysis using a two-way analysis of variance showed no difference at the 0.05 level of significance. Pairwise comparison using the Tukey method showed that neither technique (one-step vs two-step) nor movement is a significant factor. These results showed that low seating pressure will not cause any greater distortions in the two-step impression technique than in the one-step technique, and minor movement during the setting of the impression material will no cause distortion.

Analysis of Variance↗