Biomedical subjects

David M Parker

Publications and source records attributed to David M Parker.

9 recordsLinked to original sources

PubMed2006

Recurrent rectal diverticulitis.

Diverticular involvement of the colon is very common in the United States. Patients present with asymptomatic diverticuli and may have complications of these, spanning the spectrum of uncomplicated diverticulitis to an acute surgical abdominal as a result of feculent peritonitis. We discuss a patient requiring low anterior resection for intractable symptoms resulting from recurrent rectal diverticulitis as well as a review of the limited literature on the subject of diverticular disease of the rectum.

Colon, Descending↗

PubMed2005

An investigation of some food-approved polymers as agents to inhibit hydroxyapatite dissolution.

Dental erosion involves dissolution of the hydroxyapatite fraction of enamel and dentine, so agents that reduce the dissolution rate of hydroxyapatite could find application in food products aimed at reducing erosion. This study was performed to test some common food ingredients and additives for their effect on the dissolution rate of hydroxyapatite in a citric acid solution representative of soft drinks. Pyrophosphate, tripolyphosphate and a linear chain polyphosphate (average 25 phosphate units) significantly reduced the hydroxyapatite dissolution rate by 35, 46 and 64%, respectively. Xanthan gum and carboxymethylcellulose significantly reduced the hydroxyapatite dissolution rate by 29 and 16%, respectively. The protective effect may be ascribed to the binding of condensed phosphate or to the formation of an adsorbed layer of gum at the hydroxyapatite surface. Several other common food additives had no statistically significant effect on the hydroxyapatite dissolution rate. Polyphosphate exhibited a considerable persistence of action, causing a reduction in the dissolution rate for 3 h after treatment. Tripolyphosphate was slightly persistent, and pyrophosphate and xanthan gum did not exhibit a substantial persistence of action. A solution containing polyphosphate and xanthan gum reduced the hydroxyapatite dissolution rate by 70% and exhibited a similar persistence of action to the solution containing only polyphosphate. These compounds are suggested to have potential as erosion-reducing agents in soft drinks.

Buffers↗

PubMed2004

In vitro demineralization/remineralization cycles at human tooth enamel surfaces investigated by AFM and nanoindentation.

The early stages of enamel surface dissolution (erosion) are of high scientific relevance; however, little is known about if and to what extent these early stages, which result in the softening of the enamel surface, are reversible. The present study investigated the possible rehardening of surface softened enamel in two separate experiments in vitro, employing physiologically relevant demineralization and remineralization times and remineralizing solutions possessing chemical properties close to those of human saliva. Atomic force microscopy (AFM) based nanoindentation has been used to study the nanomechanical properties and the ultrastructure of polished enamel samples as affected by demineralization/remineralization cycles. In contradiction to previous studies employing microhardness techniques, no enamel rehardening has been observed after remineralization; however, the demineralization schemes used in the present study (short treatments with a citric acid buffer) are not comparable to the ones used in previous studies, making a comparison difficult. A mineral deposition after remineralization on softened enamel samples has been observed by AFM; however, a protective effect of this deposited layer could not be revealed. The exposure of softened enamel samples to either a remineralizing solution or a mineral water led to an improved acid resistance of these samples as shown in a demineralization/remineralization cycle. The present study has demonstrated that AFM based nanoindentation is a useful tool to investigate the demineralization and remineralization of surface softened enamel with high accuracy.

Dental Enamel↗

PubMed2004

Susceptibility of deciduous and permanent enamel to dietary acid-induced erosion studied with atomic force microscopy nanoindentation.

The initial stages of dental enamel demineralization by dietary acids are of particular clinical relevance. Some authors have reported a difference in the susceptibility of deciduous and permanent enamel to erosion, although other studies could not confirm these findings. The aim of the present study was therefore to investigate whether there are differences in the susceptibility of deciduous and permanent enamel to dietary acid induced erosion (demineralization). Nanoindentation combined with atomic force microscopy was used to investigate the erosive effect of four different drinks (cola, lemonade, juice drink, and water) on enamel at early stages in vitro. Surface nanohardness and reduced elastic modulus were obtained for the soft drink-treated enamel samples as a function of the exposure time. The results obtained showed that the four drinks had widely differing erosive effects due to their diverse compositions. Water did not show statistically significant changes in nanomechanical properties for all exposure times compared with untreated enamel. Exposure of enamel to cola, lemonade and the juice drink led to a statistically significant surface softening of the enamel with cola and the lemonade having a much stronger softening effect than the juice drink. For longer exposure times enamel softening increased for cola and lemonade and stayed unchanged for the juice drink. Deciduous enamel was not found to be more susceptible to erosion than permanent enamel under the conditions of the present study.

Acids↗

PubMed2003

Enamel dissolution as a function of solution degree of saturation with respect to hydroxyapatite: a nanoindentation study.

The objective of this study was to investigate human enamel dissolution as a function of degree of saturation (DS) of the surrounding solution with respect to hydroxyapatite. Nanoindentation was used to compare changes in enamel nanomechanical properties due to dissolution by two solutions. Citric acid solution (DS=0.000, pH 3.30) and citric acid solution containing calcium (299 mg/l) and phosphate (54.0 mg/l) (DS=0.032, pH 3.30) were compared with a control mineral water (DS=0.673, pH 7.48). Exposure times were 0, 120, 300, 600, 900, and 1200 s. Compared to untreated enamel, there was a statistically significant change in enamel hardness after 120 s exposure to both citric acid solutions, and in elastic modulus after 300 s exposure. The rate of change of both variables decreased with exposure time. This suggests that dissolution rate is diffusion-limited under these conditions, in agreement with previous studies. There was no statistically significant difference between the hardness or elastic modulus of enamel exposed to the two citric acid solutions at any time. This may be due to a change in solution composition during contact with the enamel.

Journal Article↗

PubMed2003

Human enamel dissolution in citric acid as a function of pH in the range 2.30< or =pH< or =6.30--a nanoindentation study.

The objective of this study was to investigate the dissolution of human enamel in citric acid solutions over a wide range of pH. The in vitro conditions are considered to be relevant to soft drink-induced enamel erosion. Nanoindentation was used to investigate changes in the nanomechanical properties of polished enamel surfaces after exposure to citric acid solutions. Solutions used had 38.1 mmol l-1 citric acid and pH greater than 2.3 but less than 6.3 (2.30 < or = pH < or = 6.30). Samples were exposed to rapidly stirred, constant composition solutions for 120 s. Statistically significant changes in enamel hardness and reduced elastic modulus were observed after exposure to all solutions. There was an approximately linear dependence of enamel hardness on solution pH for 2.90 < or = pH < or = 6.30. Below pH 2.90, enamel is thought to have reached the lowest possible hardness value. The reduction in enamel dissolution caused by an increase in pH of a soft drink is likely to be small. Product modification to reduce the erosive potential of drinks may require additional methods such as addition of calcium salts.

Citric Acid↗

PubMed2003

Enamel dissolution in citric acid as a function of calcium and phosphate concentrations and degree of saturation with respect to hydroxyapatite.

The aim of this study was to investigate enamel dissolution in citric acid solutions as a function of solution calcium and phosphate concentrations and degree of saturation with respect to hydroxyapatite (DSHA). The primary relevance of the study is the development of soft drinks with reduced erosive potential. Nanoindentation was used to investigate changes in the hardness of polished human enamel surfaces after 120 s and 300 s exposure to solutions with pH 3.30 and a range of calcium and phosphate concentrations. All solutions were undersaturated with respect to hydroxyapatite, with 0.000 < or = DSHA < or = 0.295. A complex dependence of enamel softening on calcium concentration was observed. Substantial enamel softening occurred in solutions with calcium concentrations equal to or less than 120 mm (DSHA approximately 0.104), but there was little or no statistically significant softening of the enamel for calcium concentrations over 120 mm. This condition may be applicable to soft drink formulation. Furthermore, solutions with DSHA = 0.101 and different calcium/phosphate ratios resulted in different degrees of softening of the enamel. Hence, contrary to assumptions made in many models, enamel dissolution is not simply a function of DSHA, and individual calcium and phosphate concentrations are critical.

Calcium↗

PubMed2002

Influence of soft drinks on the thickness and morphology of in situ acquired pellicle layer on enamel.

Diet-induced demineralization is a key factor in tooth enamel loss, with soft drinks being a significant aetiological agent. In the oral environment, the acquired pellicle layer might modify the demineralization potential of drinks. The objectives of this exploratory in situ study were to determine the influence of soft drinks, volunteers, and exposure times on the thickness and morphology of pellicle layers using an atomic force microscope (AFM). Polished uninterrupted third molars were partly taped and exposed to the oral environment for periods of 2 and 5 days, respectively. Each day 1L of either mineral water, a "toothkind" blackcurrant drink, a "prototype" blackcurrant drink, or orange juice was consumed in this four-way crossover, single-center study. Subsequently the tape was removed and the surfaces imaged with an AFM before and after chemical cleaning. The pellicle layer morphology and thickness were investigated. The maximum pellicle layer thickness was observed after the consumption of the prototype blackcurrant drink, followed by the toothkind blackcurrant drink, orange juice, and water on days 2 and 5, respectively. A three-way ANOVA at the 95% confidence level showed statistically significant differences between the pellicle layer thicknesses, factors being drinks (p=0.0046), exposure time (p=0.0009), and volunteers (p=0.0244). Depending on the volunteer either a uniform or a patchy pellicle layer was observed. This demonstrates that AFM is a useful tool in obtaining simultaneously qualitative and quantitative data of in situ acquired pellicle layers.

Beverages↗

PubMedDate not supplied

Porcine dermal collagen (Permacol) for abdominal wall reconstruction.

OBJECTIVE: A review of Eisenhower Army Medical Center's experience using Permacol (Tissue Science Laboratories, Covington, Georgia) for the repair of abdominal wall defects. METHODS: Retrospective review of medical records of patients undergoing abdominal wall reconstruction with Permacol. RESULTS: From July 30, 2003 to February 12, 2005, 9 patients underwent repair of complicated fascial defects with Permacol. Indications for surgery included reoperative incisional hernia repair after removal of a infected mesh (3 patients), reconstruction of a fascial defect after resection of an abdominal wall tumor (2 patients), incisional hernia repair in a patient with a previous abdominal wall infection after a primary incisional hernia repair (1 patient), incisional hernia repair in a patient with an ostomy and an open midline wound (1 patient), emergent repair of incisional hernia with strangulated bowel and multiple intra-abdominal abscesses (1 patient), and excision of infected mesh and drainage of intra-abdominal abscess with synchronous repair of the abdominal wall defect (1 patient). At a median follow-up of 18.2 months, 1 recurrent hernia existed after intentional removal of the Permacol. This patient developed an abdominal wall abscess 7 months after hernia repair secondary to erosion from a suture. Overall, 1 patient developed exposure of the Permacol after a skin dehiscence. The wound was treated with local wound care, and the Permacol was salvaged. Despite the presence of contamination (wound classification II, III, or IV) in 5 of 9 patients (56%), no infectious complications occurred. CONCLUSION: Complex reconstruction of the abdominal wall can be associated with a high complication rate. Placement of a permanent prosthetic mesh in a contaminated field is associated with a high rate of wound infections and subsequent mesh removal. Permacol becomes incorporated by tissue ingrowth and neovascularization. Permacol is a safe and acceptable alternative to prosthetic mesh in the repair of complicated abdominal wall defects.

Abdominal Abscess↗