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Biomedical subjects

W A Walker

Publications and source records attributed to W A Walker.

At least 19 recordsLinked to original sources
PubMed1998

Effects of eugenol and noneugenol endodontic sealer cements on post retention.

Resin cements are sometimes recommended to enhance the retention of posts in endodontically treated teeth. Many sealer cements used in endodontics contain eugenol, however, which has been shown to inhibit the polymerization of resins. The purpose of this study was to evaluate the effects of a eugenol and a noneugenol sealer cement on the retention of posts. Sixty extracted canines were divided equally into four groups. Each tooth received conventional endodontic therapy and was prepared to receive a post. Two sealer cements were used in obturation: one contained eugenol and one was eugenol-free. The posts were cemented with either zinc phosphate cement or resin cement. Each combination of sealer and post cement was tested for retention on an Instron testing machine. The type of sealer used had no effect on post retention with either cement. Post retention was significantly greater with the zinc phosphate cement than the resin cement.

Analysis of Variance↗
PubMed1998

A comparison of amounts of apically extruded debris using handpiece-driven nickel-titanium instrument systems.

One hundred single-rooted teeth were instrumented with Lightspeed, Profile .04 Taper Series 29, and NT McXIM instruments according to the recommendations of the manufacturers, and Flex-R files using the balanced force technique. Groups were comparable with respect to average curvature, canal length, and major and minor foramen size. A standard amount of irrigant was used for each tooth. Apically extruded debris and irrigant were collected and weighed. Debris was desiccated before being weighed. There were no statistically significant differences among the four groups with respect to total extruded debris. The amount of extruded debris was positively correlated with the amount of irrigant extruded. Factors such as canal length, curvature, and foramen size did not affect the amount of debris extruded.

Analysis of Variance↗
PubMed1998

An evaluation of canal morphology at different levels of root resection in mandibular incisors.

One hundred randomly selected mandibular incisors were examined to assess the prevalence and location of two canals and to describe the canal anatomy that may be encountered during apical surgery. Sections of the root were cut at 1, 2, and 3 mm from the apex, simulating a 20-degree beveled surgical resection. The sections were digitally imaged at x 50 magnification, and canal dimensions were measured using imaging software. The prevalence of two canals was 2% at 1 mm, 0% at 2 mm, and 1% at 3 mm. At these levels in the roots, the canal was rarely divided by hard tooth structure. An isthmus of tissue was present 20% of the time at 1 mm, 30% at 2 mm, and 55% at 3 mm. Four distinct canal types were noted: (i) round, (ii) oval, (iii) long oval, and (iv) ribbon. In 75% of the teeth, the canal shapes varied from one level to the next. The more coronally the root-end resection was made, the more elongated the canal tended to become.

Dental Pulp Cavity↗
PubMed1998

Microleakage of TERM used with sodium perborate/water and sodium perborate/superoxol in the "walking bleach" technique.

This study compared the sealing ability of TERM as an interim restoration for the "walking bleach" technique when using either sodium perborate/water or sodium perborate/superoxol. Thirty-three extracted maxillary premolars were restored with TERM after placing either a cotton pellet (control), a paste of sodium perborate and water, or a paste of sodium perborate and superoxol in the chamber. Microleakage was assessed at 24 h, 8 days, and 15 days using a fluid filtration method. Statistical analysis revealed both "walking bleach" groups had significantly higher numbers of teeth demonstrating microleakage than the control group. There was no statistically significant difference in microleakage between the two "walking bleach" groups. The results of this study indicated that the temporary restorative material, TERM, provided an unsatisfactory seal when used with either walking bleach technique. When used over a cotton pellet, TERM provided an excellent seal.

Borates↗
PubMed1998

Immaturity of gastrointestinal host defense in newborns and gastrointestinal disease states.

Not only is the gastrointestinal tract the largest immune organ in the body, but it also contains one of the most important and interesting immunologic compartments. Host protection against pathogens and injurious agents by the gastrointestinal tract is essential for an individual's survival. The intestinal mucosal immune system, which is linked with other mucosal surfaces and together represents the common mucosal immune system, prevents the passage of potentially harmful antigens and pathogens into the systemic circulation of the host. In a healthy host, antigens crossing the mucosal barrier in physiologic quantities evoke the appropriate immune response, which includes polymeric IgA antibody production to the antigen and systemic tolerance.

Animals↗
PubMed1997

Effect of tip design of nickel-titanium and stainless steel files on root canal preparation.

The purpose of this study was to evaluate the effect of modified and non-modified tip designs of both stainless steel and nickel-titanium endodontic hand files on root canal preparation. Root canals of mesial roots of extracted mandibular molars were prepared using a quarter-turn-pull technique. The experimental design permitted comparison of the effects of nickel-titanium alloy construction or file tip modification alone, with effects when these two factors were incorporated into a single file design. Transportation, centering ratio, and dentin removal were evaluated using a modified Bramante technique. Nickel-titanium files, regardless of tip design, remained significantly more centered and demonstrated less apical transportation than stainless steel files at size 25. When instrumentation was continued to size 40 apically with step-back, there were no significant differences in transportation in the apical or coronal sections. However, during instrumentation to size 40 with step-back, the combination of modified tip and nickel-titanium alloy produced significantly more transportation and dentin removal, as well as greater deviation from the center at the mid-root level than did other file designs. Thus, of the file design parameters evaluated in this study, construction from nickel-titanium was most important in defining canal configuration at small file sizes in the apical region. Although the combination of nickel-titanium and modified tip design resulted in more transportation at larger file sizes in the midroot region, such alterations in canal configuration may be of little importance clinically. Nonetheless, it is suggested that other factors, such as tactile sensation and instrumentation technique, should be considered as important as the type of alloy or tip design.

Analysis of Variance↗
PubMed1997

Determination of periodontal ligament cell viability in the oral rehydration fluid Gatorade and milks of varying fat content.

The purpose of this study was twofold: 1) to determine if the oral rehydration fluid Gatorade could serve as a suitable temporary storage medium for maintenance of periodontal ligament (PDL) cell viability on avulsed teeth and 2) to determine if fat content is related to maintenance of cell viability when milk is used as the temporary storage medium. PDL cells were cultured from extracted human teeth then incubated over timed intervals from 15 to 210 min in the oral rehydration fluid Gatorade, milks of varying fat content, and saliva. Dulbeco's Modified Eagles Medium served as the positive control while tap water served as the negative control. Cell viability was determined using a colorimetric assay that used Cell Proliferation Reagent WST-1. Results using Gatorade yielded cell viability data similar to the negative control, tap water, indicating that this oral rehydration fluid was not suitable as a temporary storage medium for the avulsed tooth. However, the fat content of milk was found to have an effect on cell viability, suggesting that milks with lower fat content may be more appropriate for maintaining PDL cell viability than milks with higher fat content.

Animals↗
PubMed1997

Subclavian artery injuries.

Thirty-two consecutive patients with subclavian artery injuries were evaluated to assess the mechanism of injury, types of repair, and results. In this series, most wounds were from firearms. Although the mortality was high (19%), most patients had the vessel repaired successfully. Associated injuries, especially to neural structures, led to significant morbidity. Principles used in dealing with these injuries should be 1) proximal and distal control prior to exposing the injury site, 2) reestablishing distal circulation through primary repair or graft placement, and 3) identifying and treating associated injuries.

Adult↗
PubMed1996

Human fetal enterocytes in vitro: modulation of the phenotype by extracellular matrix.

The differentiation of small intestinal epithelial cells may require stimulation by microenvironmental factors in vivo. In this study, the effects of mesenchymal and luminal elements in nonmalignant epithelia] cells isolated from the human fetus were studied in vitro. Enterocytes from the human fetus were cultured and microenvironmental factors were added in stages, each stage more closely approximating the microenvironment in vivo. Four stages were examined: epithelial cells derived on plastic from intestinal culture and grown as a cell clone, the same cells grown on connective tissue support, primary epithelial explants grown on fibroblasts with a laminin base, and primary epithelial explants grown on fibroblasts and laminin with n-butyrate added to the incubation medium. The epithelial cell clone dedifferentiated when grown on plastic; however, the cells expressed cytokeratins and villin as evidence of their epithelial cell origin. Human connective tissue matrix from Engelbreth-Holm-Swarm sarcoma cells (Matrigel) modulated their phenotype: alkaline phosphatase activity increased, microvilli developed on their apical surface, and the profile of insulin-like growth factor binding proteins resembled that secreted by differentiated enterocytes. Epithelial cells taken directly from the human fetus as primary cultures and grown as explants on fibroblasts and laminin expressed greater specific enzyme activities in brush border membrane fractions than the cell clone. These activities were enhanced by the luminal molecule sodium butyrate. Thus the sequential addition of connective tissue and luminal molecules to nonmalignant epithelia] cells in vitro induces a spectrum of changes in the epithelial cell phenotype toward full differentiation.

Alkaline Phosphatase↗
PubMed1996

Combined gunshot injuries of the trachea and esophagus.

During an 8-year period between 1985 and 1993, twelve patients were treated with combined gunshot wounds to the trachea and esophagus. All patients survived, but there were complications, including one tracheoesophageal fistula. Combined injuries of the trachea and esophagus should be repaired primarily, and drains do not necessarily have to be placed. The benefit of a muscle flap placed between the repairs was not confirmed in this series. Complications should be recognized early and treated aggressively to minimize damage to the airway.

Adolescent↗
PubMed1996

Coronary operations in patients with spinal cord injury.

BACKGROUND: The risk of heart disease in patients with spinal cord injury is similar to that in the general population. The physiologic derangements raise special problems in patients with SCI having coronary operations. METHODS: From January 1980 to May 1995, we performed coronary artery bypass procedures on 20 patients with SCI; 4 were tetraplegic and the remainder were paraplegic. The indication for operation was angina: unstable (13), exertional (4), or postinfarctional (3). Bowel and bladder care was given immediately before operation; operating room tables were double padded and a pelvic wrap was used to protect the back. Electric wheelchairs were used for early mobilization. RESULTS: Vasomotor instability from cardiopulmonary bypass was not present in patients with SCI. Pharmacologic support was required in the operating room by 4 patients for low vascular resistance, but in only one case in the intensive care unit. One patient required ventilation support for more than 24 hours. All patients were able to cough effectively. No thoracic wound complications occurred. There were three operative deaths, all in patients with multiple risk factors. The acute hospital stay averaged 9.3 days; patients were then transferred to an SCI unit for rehabilitation, were upper-extremity weight bearing was restricted for 2 to 4 weeks. CONCLUSIONS: Patients should not be denied coronary artery bypass procedures because of an SCI, but their special needs must be managed properly.

Adult↗
PubMed1996

Development of immune function in the intestine and its role in neonatal diseases.

This review has traced the ontogeny of the human mucosal immune system, speculating that appropriate gut immune responses are essential in preventing many significant neonatal enteric diseases. Because the gastrointestinal tract serves as the portal of entry for many potential antigens, its mucosal immune function is essential in controlling antigenic responses and ensuring systemic tolerance. A thorough under standing of the development of the entire immune system is essential in defining intestinal mucosal immune function. From the protective barrier covering the enterocyte to the intraepithelial T lymphocytes, these components work together to limit antigen passage from the gut lumen to the underlying immune cells and, thus, promote normal immunity and tolerance. When abnormalities exist or when this immune barrier has not matured fully, conditions afflicting newborns, especially preterm infants, occur. Necrotizing enterocolitis, milk-protein enteropathy, and enteric bacterial infections are only three clinical examples of how aberrant gut immune-mediated defenses may have a significant role in their pathogenesis. In clinical practice, it is not only important to recognize these conditions at their onset but also to understand the basis for the underlying illness and identify newborns who are at an increased risk of acquiring them.

Bacterial Adhesion↗
PubMed1996

A comparison of sealer placement techniques in curved canals.

Sealer placement techniques have not been examined in teeth with curved canals prepared with Lightspeed instruments. Three traditional methods of placing sealer were studied, using 45 extracted human single-rooted teeth, divided into 3 groups of 15. Root canal preparations were made with Light-speed nickel-titanium, engine-driven instruments. AH26 sealer was applied with either K-file, lentulo spiral, or master gutta-percha cone. Radiographs were taken after sealer placement and analyzed for amount of canal sealer fill. The teeth were then obturated with laterally condensed gutta-percha, chemically cleared, photographed, and analyzed for total canal wall sealer coverage. The results showed a statistically significant difference in canal sealer fill among the three groups before obturation, but there was no statistical difference in canal wall coverage among the three groups after obturation. None of the examined methods exceeded an average of 62.5% wall coverage of sealer after obturation. This suggests that complete wall coverage after obturation may not be possible.

Analysis of Variance↗
PubMed1996

Exogenous nucleotides alter the proliferation, differentiation and apoptosis of human small intestinal epithelium.

The turnover of intestinal epithelial cells is a finely regulated process extending from undifferentiated crypt stem cells to terminally differentiated villus cells. The final phase of this maturation process is apoptosis and extrusion. Recent studies have shown that programmed cell death (PCD) occurs not only in senescent cells and in rapidly developing tissues but also in response to cellular stress preventing damaged cells from entering uncontrolled proliferation without repair. This study examined the role of exogenous nucleotides on cell proliferation, differentiation and apoptosis in organ cultures of human fetal small intestine. The addition of adenosine monophosphate (AMP), a putative stress reactant, to the culture media resulted in the suppression of crypt cell proliferation followed by the restoration of differentiation and the induction of apoptosis across a broad range of villus epithelium when compared with controls without added nucleotide. In contrast, the addition to cytidine monophosphate (CMP) to the culture media did not increase apoptosis, despite the nucleotide being taken up by the fetal small intestine in a similar dose- and time-dependent manner to AMP. Furthermore, Bax mRNA, an apoptosis-inducer gene, was increased with addition of AMP, suggesting that the induction of apoptosis may be channeled through the p53 pathway. These results suggest that a specific exogenous nucleotide, AMP, may have an important role in controlling the dynamic balance of cellular turnover in the developing human small intestine.

Adenosine Monophosphate↗
PubMed1996

Combined tracheal and esophageal trauma from gunshot wounds.

During a 5-year period between 1988 and 1993, nine patients with combined tracheal and esophageal injuries were treated at our institution. All injuries resulted from gunshot wounds and all were repaired. All patients survived, but complications included one tracheoesophageal fistula. Combined injuries of the trachea and esophagus should be repaired primarily, and drains do not necessarily have to be placed. The benefits of a muscle flap placed between the repairs were not confirmed in this series. Complications should be recognized early and treated aggressively to minimize damage to the airway.

Adolescent↗