An in vitro study to compare the transverse strength of thermopressed and conventional compression-molded polymethylmethacrylate polymers.

Statement of Problem: Acrylic resins have been in the center stage of Prosthodontics for more than half a century. The flexural fatigue failure of denture base materials is the primary mode of clinical failure. Hence there is a need for superior physical and mechanical properties. Purpose: This in vitro study compared the transverse strength of specimens of thermopressed injection-molded and conventional compression-molded polymethylmethacrylate polymers and examined the morphology and microstructure of fractured acrylic specimens. Materials and Methods: The following denture base resins were examined: Brecrystal (Thermopressed injection-molded, modified polymethylmethacrylate) and Pyrax (compression molded, control group). Specimens of each material were tested according to the American Society for Testing and Materials standard D790-03 for flexural strength testing of reinforced plastics and subsequently examined under SEM. The data was analyzed with Student unpaired t test. Results: Flexural strength of Brecrystal (82.08 ± 1.27 MPa) was significantly higher than Pyrax (72.76 ± 0.97 MPa). The tested denture base materials fulfilled the requirements regarding flexural strength (>65 MPa). The scanning electron microscopy image of Brecrystal revealed a ductile fracture with crazing. The fracture pattern of control group specimens exhibited poorly defined crystallographic planes with a high degree of disorganization. Conclusion: Flexural strength of Brecrystal was significantly higher than the control group. Brecrystal showed a higher mean transverse strength value of 82.08 ± 1.27 MPa and a more homogenous pattern at microscopic level. Based on flexural strength properties and handling characteristics, Brecrystal may prove to be an useful alternative to conventional denture base resins.

Zirconium for esthetic rehabilitation: An overview.

The demand for esthetic restorations has resulted in an increased use of dental ceramics for anterior and posterior restorations. A few decades ago, all-ceramic restorations were restricted to treatment in the anterior region, but now all-ceramic restorations can be made anywhere in the dentition. The properties of traditional ceramic materials, however, have limited their use to single crowns; larger restorations have been inadvisable because of insufficient strength. In attempts to meet the requirements for dental materials and improve strength and toughness, several new ceramic materials and techniques have been developed during the past few decades The paper reviews the current literature on dental zirconia with respect to survival, properties, marginal fit, cementation, esthetics and suggests clinical recommendations for their use.

Enhancement of radionuclide induced cytotoxicity by 2-deoxy-D-glucose in human tumor cell lines.

The efficacy of targeted radiotherapy can be enhanced by selective delivery of radionuclide to the tumors and/or by differentially enhancing the manifestation of radiation damage in tumors. Our earlier studies have shown that the 2-deoxy-D-glucose (2-DG), an inhibitor of glucose transport and glycolytic ATP production, selectively enhances the cytotoxicity of external beam radiation in tumor cells. Therefore, it is suggested that 2-DG may also enhance the cytotoxic effects of radionuclides selectively in tumor cells, thereby improving the efficacy of radionuclide therapy. In vitro studies on breast carcinoma (MDA-MB-468) and glioma (U-87) cell lines, has been carried out to verify this proposition. Clonogenicity (macrocolony assay), cell proliferation, cytogenetic damage (micronuclei formation) and apoptosis were investigated as parameters of radiation response. Mean inactivation dose D (dose required to reduce the survival from 1 to 0.37), was 48 MBq/ml and 96 MBq/ml for 99 mTc, treated MDA-MB-468 and U-87, respectively. The dose response of growth inhibition, induction of micronuclei formation and apoptosis observed under these conditions, were correlated well with the changes in cell survival. Presence of 2-DG (5 mM) during radionuclide exposure (24 hrs), reduced the survival by nearly 2 folds in MDA-MB-468 (from 48.5 MBq to 18.5 MBq) and by 1.6 folds in U-87 cells (from 96 MBq to 66 Mbq). These results clearly show that the presence of 2-DG during radionuclide exposure, significantly enhances the cytotoxicity, by increasing mitotic as well as interphase death. Further studies to understand the mechanisms of radio-sensitization by 2-DG and preclinical studies using tumor-bearing animals, are required for optimizing the treatment schedule.

Alterations in radiation induced cell cycle perturbations by 2-deoxy-D-glucose in human tumor cell lines.

In the present studies, effects of glucose analogue, 2-deoxy-D-glucose (2-DG) on radiation-induced cell cycle perturbations were investigated in human tumor cell lines. In unirradiated cells, the levels of cyclin B1 in G2 phase were significantly higher in both the glioma cell lines as compared to squamous carcinoma cells. Upon irradiation with Co60 gamma-rays (2 Gy), the cyclin B1 levels were reduced in U87 cells, while no significant changes could be observed in other cell lines, which correlated well with the transient G2 delay observed under these conditions by the BrdU pulse chase measurements. 2-DG (5 mM, 2 hr) induced accumulation of cells in the G2 phase and a time-dependent increase in the levels of cyclin B1 in both the glioma cell lines, while significant changes could not be observed in any of the squamous carcinoma cell lines. 2-DG enhanced the cyclin B1 level further in all the cell lines following irradiation, albeit to different extents. Interestingly, an increase in the unscheduled expression of B1 levels in G1 phase 48 hr after irradiation was observed in all the cell lines investigated. 2-DG also increased the levels of cyclin D1 at 24 hr in BMG-1 cell line. These observations imply that 2-DG-induced alterations in the cell cycle progression are partly responsible for its radiomodifying effects.

Ventilatory support for infants in emergency and in the intensive care unit.

Pediatric anesthesia and intensive care management has improved dramatically over the past two decades. Improved understanding of the pathophysiology underlying newborn surgical emergencies, new medications and new modes of ventilatory support have all contributed to better patient outcome. The authors have reviewed the anatomy and physiology of the infant airway, indications for and principles of endotracheal intubation, the management of newborn surgical emergencies, indications for post-operative ventilatory support, different modes of mechanical ventilation available, complications of mechanical ventilation with weaning parameters and extubation criteria. The introduction of nitric oxide and the implications of extracorpreal membrane oxygenation in the management of newborn emergency refractory to conventional ventilation are discussed.