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Biomedical subjects

M G Duncanson

Publications and source records attributed to M G Duncanson.

80 records · Page 5Linked to original sources
PubMedDate not supplied

Compressive viscoelastic properties of human dentin: I. Stress-relaxation behavior.

Stress-relaxation measurements were performed on specimens of radicular human dentin. The relaxation modulus showed a linear dependence on the logarithm of time and the approximation to the logarithmic distribution function of relaxation times was used to predict the behavior of other viscoelastic properties. This experimental technique provides significant criteria for the design of polymeric restorative and prosthetic materials.

Dentin↗
PubMedDate not supplied

The effect of clasp form on permanent deformation.

This study was conducted to discover whether a relationship exists between clasp width-thickness ratios and wear or deformation. Five different forms of circumferential clasps were studied. The clasps were fabricated with a 160 degree curvature around an 8-mm (diameter) cylinder and cast in Ticonium alloy. The clasps were subjected to 1500 cycles of 0.01 inch flexure. The degree of permanent deformation was not related to clasp form or width-thickness ratio. Of the five forms, only one exhibited no permanent deformation. According to Duncan's Multiple Range Test, significant differences in wear against a steel tooth model were observed among the five clasp forms evaluated (alpha = 0.05).

Chromium Alloys↗
PubMedDate not supplied

Force versus time profiles of selected heat-processed denture liners.

The potential correlation of the force versus time behavior of four resilient lining materials and their acceptance by patients was investigated. Two modified acrylic resins and two silicone denture lining materials were tested. The response of the soft lining materials to a programmed indentation test was used to define a parameter for each denture liner product. A parameter defined as the "Rebound Index," using force-time data obtained from the indentation measurements, was significantly different for the modified acrylic resins compared to the silicone materials. Improved patient acceptance was correlated with higher values of this index.

Acrylic Resins↗
PubMedDate not supplied

Effects of clasp flexure on a 4-META adhered light-polymerized composite resin.

Three specimen sets of removable partial denture claps were veneered using a composite resin with 4-META onto a 50-microns aluminum oxide air-abraded surface and flexed 0.01, 0.02, and 0.03 inches for 1,500 cycles. No veneers survived intact following 0.03-inch flexures; 58% survived 0.01-inch flexures and 44% survived 0.02-inch flexures intact. There was a significant increase in the number of veneer cracks in 0.02-inch flexed clasps compared to those flexed 0.01 inch.

Acrylic Resins↗
PubMedDate not supplied

Wettability of elastomeric impression materials: effect of selected surfactants.

This study evaluated seven classes of 65 impression materials for the effect of selected surfactants on contact angle values for high-strength stone. Uniform surfaces of the materials were treated with a surfactant, and stone samples were poured on each impression material surface. The samples were sectioned and photographed for measurement of the advancing contact angles. Statistical analysis supported four conclusions: No significant difference was found between the two surfactants. Both surfactants were significantly better than the control (water). Polyether impression materials were superior in wettability to the other elastomeric impression materials tested. With respect to contact angle, two distinct groups of impression materials emerged. Reversible hydrocolloid (47.7 +/- 1.5), irreversible hydrocolloid (36.8 +/- 8.8), and polyether (45.8 +/- 7.6) formed a hydrophilic group. A hydrophobic group consisted of the polysulfide (62.6 +/- 10.1), poly(vinyl siloxane) (71.1 +/- 12.3), condensation-reaction silicone (74.1 +/- 11.0), and polyethene (75.9 +/- 14.6) materials.

Dental Impression Materials↗
PubMedDate not supplied

Adaptation of the temporomandibular joint to altered mandibular function.

This pilot study describes responses of Sprague Dawley rats to mandibular retrusion. Lingually overcontoured crowns were cemented onto maxillary incisors to produce 3.5 mm of autoretrusion. Monitoring data indicate that activity was suppressed and nutritional intake was reduced. Histological evaluation of the 2-, 4-, 7-, and 59-day test specimens detected only a monocytic infiltrate response in the 4-day group.

Adaptation, Physiological↗
PubMedDate not supplied

Uses and properties of current glass ionomer cements: a review.

Glass ionomer cements have been used for a variety of restorative purposes. Recently, the formulation of these and other restorative materials has changed rapidly, so it is difficult to keep pace with the literature concerning effective use. A major modification to glass ionomer cements has been incorporation of resin components. This and other modifications over the years have changed some handling characteristics and physical properties of glass ionomer cements. A general review of some changes is reported here.

Dental Bonding↗