Load transfer characteristics of unilateral distal extension removable partial dentures with polyacetal resin supporting components

BACKGROUND

To photoelastically examine load transfer by unilateral distal extension removable partial dentures with supporting and retentive components made of the lower stiffness polyacetal resins.

METHODS

A mandibular photoelastic model, with edentulous space distal to the right second premolar and missing the left first molar, was constructed to determine the load transmission characteristics of a unilateral distal extension base removable partial denture. Individual simulants were used for tooth structure, periodontal ligament, and alveolar bone. Three designs were fabricated: a major connector and clasps made from polyacetal resin, a metal framework as the major connector with polyacetal resin clasp and denture base, and a traditional metal framework I-bar removable partial denture. Simulated posterior bilateral and unilateral occlusal loads were applied to the removable partial dentures.

RESULTS

Under bilateral and left side unilateral loading, the highest stress was observed adjacent to the left side posterior teeth with the polyacetal removable partial denture. The lowest stress was seen with the traditional metal framework. Unilateral loads on the right edentulous region produced similar distributed stress under the denture base with all three designs but a somewhat higher intensity with the polyacetal framework.

CONCLUSIONS

The polyacetal resin removable partial denture concentrated the highest stresses to the abutment and the bone. The traditional metal framework I-bar removable partial denture most equitably distributed force. The hybrid design that combined a metal framework and polyacetal clasp and denture base may be a viable alternative when aesthetics are of primary concern.

An exploration of Pap smear history and behavior of patients with newly diagnosed cervical cancer in Taiwan

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Background: The national health insurance policy has provided a yearly Pap smear for women >= 30 years old since 1994 in Taiwan, yet the coverage rate is still unsatisfactory. The purpose of this study is (1) to investigate the Pap smear screening history of women newly diagnosed with cervical cancer and (2) to examine factors that influence participation in Pap smear screening program in these women. Methods: Patients primarily treated for cervical cancer at Chang Gung Memorial Hospital between November 2006 and June 2007 were enrolled into this prospective study. Questionnaires included (1) socio-demographic data, and (2) knowledge on Pap smear and cervical cancer. Results: Two hundred sixty-nine patients were eligible for analysis. The median age was 51 years old (range, 25–83). Of the 269 patients, 147 (54.6%) had never had a Pap smear before diagnosis, and 35 (13.0%) did not know about Pap smear. Socio-demographic factors that significantly influenced number of previous Pap smear screening (0 vs >=1) were education level, income less than 600 U.S. dollars per month, menopaused, multiple sexual partners, and increase number of sexual partners of the male consort. Of the 147 never received Pap women, the most common reasons were thought that Pap smear screening was not necessary (46.3%), embarrassment (42.0%), busy (43.5%), and worry about the screening findings (20.4%). Of the 122 patients who have received Pap smear, 56.6% patients thought that Pap smear screening was necessary, 35.2% patients worried about the disease, 24.6% were alert on their check-ups, and 20.5% did the screening for the convenience to nearby clinics. Conclusions: Public health organizations in Taiwan should put more efforts to provide women in low education level, low income and multiple sexual partners with information on Pap smear.

No significant financial relationships to disclose.

Anticancer oncolytic activity of respiratory syncytial virus

Oncolytic virotherapy is an emerging bio-therapeutic platform for cancer treatment, which is based on selective infection/killing of cancer cells by viruses. Herein we identify the human respiratory syncytial virus (RSV) as an oncolytic virus. Using prostate cancer models, we show dramatic enhancement of RSV infectivity in vitro in the androgen-independent, highly metastatic PC-3 human prostate cancer cells compared to the non-tumorigenic RWPE-1 human prostate cells. The oncolytic efficiency of RSV was established in vivo using human prostate tumor xenografts in nude mice. Intra-tumoral and intra-peritoneal injections of RSV led to a significant regression of prostate tumors. Furthermore, enhanced viral burden in PC-3 cells led to selective destruction of PC-3 cancer cells in vitro and in xenograft tumors in vivo due to apoptosis triggered by the down-regulation of NF-κB activity (and the resulting loss of anti-apoptotic function of NF-κB) in RSV-infected PC-3 cells. The intrinsic (mitochondrial) pathway constitutes the major apoptotic pathway; however, the death-receptor-dependent extrinsic pathway, mediated by the paracrine/autocrine action of tumor necrosis factor-α produced from infected cells, also partly contributed to apoptosis. Thus, the oncolytic property of RSV can potentially be exploited to develop targeted therapeutics for the clinical management of prostate tumors.

Force spectroscopy of hepatocytic extracellular matrix components

We present atomic force microscopy and force spectroscopy data of live hepatocytes (HEPG2/C3A liver cell line) grown in Eagle's Minimum Essential Medium, a complex solution of salts and amino acids commonly used for cell culture. Contact-mode imaging and force spectroscopy of this system allowed correlation of cell morphology and extracellular matrix (ECM) properties with substrate properties. Force spectroscopy analysis of cellular "footprints" indicated that the cells secrete large polymers (e.g., 3.5mum contour length and estimated MW 1000kDa) onto their substrate surface. Although definitive identification of the polymers has not yet been achieved, fluorescent-labeled antibody staining has specified the presence of ECM proteins such as collagen and laminin in the cellular footprints. The stretched polymers appear to be much larger than single molecules of known ECM components, such as collagen and heparan sulfate proteoglycan, thus suggesting that the cells create larger entangled, macromolecular structures from smaller components. There is strong evidence which suggests that the composition of the ECM is greatly influenced by the hydrophobicity of the substrate surface, with preferential production and/or adsorption of larger macromolecules on hydrophobic surfaces.

Unexpected power-law stress relaxation of entangled ring polymers

After many years of intense research, most aspects of the motion of entangled polymers have been understood. Long linear and branched polymers have a characteristic entanglement plateau and their stress relaxes by chain reptation or branch retraction, respectively. In both mechanisms, the presence of chain ends is essential. But how do entangled polymers without ends relax their stress? Using properly purified high-molar-mass ring polymers, we demonstrate that these materials exhibit self-similar dynamics, yielding a power-law stress relaxation. However, trace amounts of linear chains at a concentration almost two decades below their overlap cause an enhanced mechanical response. An entanglement plateau is recovered at higher concentrations of linear chains. These results constitute an important step towards solving an outstanding problem of polymer science and are useful for manipulating properties of materials ranging from DNA to polycarbonate. They also provide possible directions for tuning the rheology of entangled polymers.