Residual disease after re-excision for tumour-positive surgical margins in both ductal carcinoma in situ and invasive carcinoma of the breast: The effect of time.

BACKGROUND AND OBJECTIVES: To assess the effect of time on finding residual breast cancer in re-excision specimens after non-radical breast-conserving surgery for both DCIS and invasive breast carcinoma. METHODS: 315 breast-conserving surgical procedures with tumour-positive margins were retrospectively reviewed. The significance of association between the presence of finding residual tumour in the re-excision specimen and mean time interval was calculated with Student's t-test. A multivariate logistic regression model was used to assess the independent relative risk of time on presence of residual tumour. RESULTS: Residual tumour was found in 240 (76.2%) of the re-excision specimens. For primary invasive carcinomas time was a risk-reducing factor for finding residual disease (OR 0.89, 95% CI 0.82-0.98, P = 0.01). If invasive carcinoma was transected, the absence of residual disease was significantly related with a longer mean time interval (OR 0.98, 95% CI 0.95-0.99, P = 0.04). CONCLUSIONS: An increased time interval between primary surgery and re-excision for tumour-positive surgical margins for invasive carcinoma is associated with a decreased incidence of finding residual tumour. This could be explained by inflammatory responses after surgical trauma. For DCIS there was no influence of time on finding residual tumour, which could be explained by a more protective microenvironment of DCIS or re-growth of surviving malignant cells.

Apparent viscosities of setting elastomers.

The flow behavior of five elastomeric impression materials was determined by extrusion viscometry. Initial viscosity ranged from 400 to 5,100 poise at a shear rate of 2.2 reciprocal seconds. All of the elastomers showed initial non-Newtonian behavior and increased viscosity with time.

Extrusion of rheometry of fluid materials.

A capillary extrusion rheometer was developed and tested using Newtonian oils of known viscosity and seven endodontic sealers. The described apparatus and technique appear appropriate for comparative assessment of the rheological characteristics of a variety of fluid dental materials.

Stress relaxation of interim restoratives.

Stress relaxation of four temporary restoratives was studied. In the vicinity of ambient mouth temperature, the relaxation characteristics of an unmodified zinc oxide-eugenol cement were more favorable than those of IRM and Cavit. The plastic behavior of gutta-percha temporary stopping precluded assessment of its relaxation at temperatures in excess of 22 degrees C.

The rheologic properties of endodontic sealers.

The rheologic properties of seven endodontic sealers were investigated with a rotational viscometer. The effects of time and rate of shear on the measured viscosities were determined. Results indicated that one material exhibited Newtonian behavior, whereas the others were characterized by pseudoplasticity.

Effect of ultrasonic instrumentation on the retention of simulated cast crowns.

The effect of ultrasonic instrumentation on the retention of cemented cast restorations was studied. Forces required to dislodge castings from specimen assemblies subjected to ultrasonic vibrations did not differ significantly from those required to cause failure of noninstrumented specimens. The results indicate that clinical application of the ultrasonic device would not affect adversely the retention of properly cemented and well fitting cast restorations.

Stress relaxation of dental amalgam alloys.

Short-term stress relaxation of four dental amalgam alloys was studied. Test materials included two conventional lathe-cut restoratives, a spherical alloy, and a dispersed phase product. Specimens were 24-hr-old 4 X 8-mm cylinders. The specimens were compressed and held at constant strain on development of a stress (So) of 28 MN/m2. Subsequent stress relaxation (Dt) was recorded for 60 sec. Data were obtained at eight nominal temperatures between 0 and 55 degrees C. Over the experimental temperature range, fractional stress losses at 60 sec (Dt/So/60) for specimens made from lathe-cut alloys increased from 10% to 58%. The spherical material and the dispersed phase alloy showed fractional stress losses (Dt/So/60) ranging from 9% to 47% and 9% to 31%, respectively. It would appear that particle morphology and alloy composition affect stress-relaxation behavior of dental amalgam. Stress decay patterns enhance significantly the mechanical characterization of amalgam alloys.

Short-term stress-relaxation behavior of nonmetallic restoratives.

The rheological behavior of five nonmetallic dental materials was studied. Short-term stress relaxation was found to be strongly dependent on time and temperature. Relaxation behavior of the test materials conformed well to simple mathematical models.