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Biomedical subjects

J McCool

Publications and source records attributed to J McCool.

11 recordsLinked to original sources
PubMed2006

Silk based biomaterials to heal critical sized femur defects.

Bone auto- and allografts have inherent drawbacks, therefore the treatment of non-unions and critical size defects in load bearing long bones would benefit from the use of osteopromotive biodegradable, biocompatible and mechanically durable matrices to enhance migration or delivery of cell populations and/or morphogens/cytokines. Silk fibroin biomaterial scaffolds were evaluated as osteopromotive matrices in critical sized mid-femoral segmental defects in nude rats. Four treatment groups were assessed over 8 weeks in vivo: silk scaffolds (SS) with human mesenchymal stem cells (hMSCs) that had previously been differentiated along an osteoblastic lineage in vitro (group I; pdHMSC/SS); SS with undifferentiated hMSCs (group II; udHMSC/SS); SS alone (group III; SS); and empty defects (group IV). When hMSCs were cultured in vitro in osteogenic medium for 5 weeks, bone formation was characterized with bimodal peak activities for alkaline phosphatase at 2 and 4 weeks. Calcium deposition started after 1 week and progressively increased to peak at 4 weeks, reaching cumulative levels of deposited calcium at 16 mug per mg scaffold wet weight. In vivo osteogenesis was characterized by almost bridged defects with newly formed bone after 8 weeks in group I. Significantly (P < 0.01) greater bone volumes were observed with the pdHMSC/SS (group I) implants than with groups II, III or IV. These three groups failed to induce substantial new bone formation and resulted in the ingrowth of cells with fibroblast-like morphology into the defect zone. The implantation of pdHMSC/SS resulted in significantly (P < 0.05) greater maximal load and torque when compared to the other treatment regimens. The pdHMSC/SS implants demonstrated osteogenic ability in vitro and capacity to thrive towards the healing of critical size femoral segmental defects in vivo. Thus, these new constructs provide an alternative protein-based biomaterial for load bearing applications.

Alkaline Phosphatase↗
PubMed2004

Interface effects on mechanical properties of particle-reinforced composites.

OBJECTIVES: Effective bonding between the filler and matrix components typically improves the mechanical properties of polymer composites containing inorganic fillers. The aim of this study was to test the hypothesis that composite flexural modulus, flexure strength, and toughness are directly proportional to filler-matrix interfacial shear strength. METHODS: The resin matrix component of the experimental composite consisted of a 60:40 blend of BisGMA:TEGDMA. Two levels of photoinitiator components were used: 0.15, and 0.5%. Raman spectroscopy was used to determine degree of cure, and thermogravimetry (TGA) was used to quantify the degree of silane, rubber, or polymer attachment to silica and glass particles. Filler-matrix interfacial shear strengths were measured using a microbond test. Composites containing glass particles with various surface treatments were prepared and the modulus, flexure strength, and fracture toughness of these materials obtained using standard methods. Mechanical properties were measured on dry and soaked specimens. RESULTS: The interfacial strength was greatest for the 5% MPS treated silica, and it increased for polymers prepared with 0.5% initiator compared with 0.15% initiator concentrations. For the mechanical properties measured, the authors found that: (1) the flexural modulus was independent of the type of filler surface treatment, though flexural strength and toughness were highest for the silanated glass; (2) rubber at the interface, whether bonded to the filler and matrix or not, did not improve toughness; (3) less grafting of resin to silanated filler particles was observed when the initiator concentration decreased. SIGNIFICANCE: These findings suggest that increasing the strength of the bond between filler and matrix will not result in improvements in the mechanical properties of particulate-reinforced composites in contrast to fiber-reinforced composites. Also, contraction stresses in the 0.5 vs 0.15% initiator concentration composites may be responsible for increases in interfacial shear strengths, moduli, and flexural strengths.

Composite Resins↗
PubMed2001

Fatigue of restorative materials.

Failure due to fatigue manifests itself in dental prostheses and restorations as wear, fractured margins, delaminated coatings, and bulk fracture. Mechanisms responsible for fatigue-induced failure depend on material ductility: Brittle materials are susceptible to catastrophic failure, while ductile materials utilize their plasticity to reduce stress concentrations at the crack tip. Because of the expense associated with the replacement of failed restorations, there is a strong desire on the part of basic scientists and clinicians to evaluate the resistance of materials to fatigue in laboratory tests. Test variables include fatigue-loading mode and test environment, such as soaking in water. The outcome variable is typically fracture strength, and these data typically fit the Weibull distribution. Analysis of fatigue data permits predictive inferences to be made concerning the survival of structures fabricated from restorative materials under specified loading conditions. Although many dental-restorative materials are routinely evaluated, only limited use has been made of fatigue data collected in vitro: Wear of materials and the survival of porcelain restorations has been modeled by both fracture mechanics and probabilistic approaches. A need still exists for a clinical failure database and for the development of valid test methods for the evaluation of composite materials.

Compomers↗
PubMed1999

Focus of doctor-patient communication in follow-up consultations for patients treated surgically for colorectal cancer.

A series of consultations between patients treated surgically for colorectal cancer and their hospital consultants were examined to establish the main focus of the consultation at various stages in the post-surgical period. The results showed that follow-up consultations were predominantly doctor driven. Patients interviewed less than 12 months since the time of surgery (short-term group) were more likely to receive a longer consultation with a significantly higher number of verbal interactions (questions, responses) than patients more than 12 months since surgery at the time of interview (long-term group). Furthermore, patients in the short-term group played a greater participatory role within consultations than patients in the long-term group. The predominant focus throughout all consultations was biomedical, with little attention afforded to patients' expressions of post-operative anxiety. At present, it appears that out-patient consultations play a minimal role in either detecting or addressing psychosocial morbidity amongst colorectal cancer patients in the post-surgical period.

Aged↗
PubMed1998

Dimensional stability of record bases fabricated from light-polymerized composite using two methods.

STATEMENT OF PROBLEM: Record bases fabricated from resin-based composite, which undergoes polymerization shrinkage during curing, can distort during curing to produce significant gaps along the posterior border. PURPOSE: This study evaluated the pattern of gap formation that occurs over the palatal area of a maxillary record base fabricated from light-cured composite (Triad), and determined whether changes in the fabrication method affects the size and pattern of gap formation. Effects of composite width and passage of time on gap formation were also analyzed. MATERIAL AND METHODS: Twenty record bases were fabricated with two methods: (1) according to the manufacturer's directions, the entire surface of the record base was exposed to the curing light; and (2) the palatal area of the record base was covered with foil to prevent light penetration, and the base was light cured in three stages with readaptation of the uncured composite between stages. Ten record bases from each group were tested 1 hour after fabrication; the remaining 10 from each group were tested 7 days after fabrication. Measurements of adaptation were made at three points representing the right and left ridge crests and midpalatal areas. The first measurement was taken at the posterior border and subsequent measurements were made at 5 mm increments after reduction of the posterior border of the cast and record base with a model trimmer. RESULTS: Dimensional changes were observed in both procedures. The largest discrepancy occurred at the posterior border of record bases fabricated using method 1. Mean gap formation at the posterior border in this group after 1 hour was 454, 729, and 334 microm and 483, 841, and 330 microm after 7 days at points A, B, and C, respectively. Record bases fabricated with procedure 2 demonstrated mean gap sizes at the posterior border after 1 hour of 219, 421, and 208 microm and 267, 403, and 192 microm after 7 days at points A, B, and C, respectively. No significant influence of composite width on gap size was found. CONCLUSION: The average gap size due to stage curing (method 2) was never greater than the corresponding gap that arose from the use of the manufacturer's recommendations (method 1). Limiting the amount of surface area exposed to the curing light and readapting the uncured composite to the cast between curing episodes can significantly reduce the mean gap size occurring at the posterior border.

Acrylic Resins↗
PubMed1996

Purchasing a cycle helmet: are retailers providing adequate advice?

OBJECTIVES: The aim of this study was to examine the selling of cycle helmets in retail stores with particular reference to the adequacy of advice offered about the fit and securing of helmets. METHODS: All 55 retail outlets selling cycle helmets in Christchurch, New Zealand were studied by participant observation. A research entered each store as a prospective customer and requested assistance to purchase a helmet. She took detailed field notes of the ensuing encounter and these were subsequently transcribed, coded, and analysed. RESULTS: Adequate advice for helmet purchase was given in less than half of the stores. In general the sales assistants in specialist cycle shops were better informed and gave more adequate advice than those in department stores. Those who have good advice also tended to be more good advice also tended to be more active in helping with fitting the helmet. Knowledge about safety standards was apparent in one third of sales assistants. Few stores displayed information for customers about the correct fit of cycle helmets. CONCLUSIONS: These findings suggest that the advice and assistance being given to ensure that cycle helmets fit properly is often inadequate and thus the helmets may fail to fulfil their purpose in preventing injury. Consultation between retailers and policy makers is a necessary first step to improving this situation.

Adolescent↗
PubMed1994

The effect of three commercially available dentifrices containing triclosan on supragingival plaque formation and gingivitis: a six month clinical study.

In order to compare the antiplaque and antigingivitis activity of three commercially-available triclosan containing dentifrices with that of a placebo dentifrice without triclosan, a double-blind clinical study was conducted on 194 subjects over six months. Following baseline supragingival plaque and gingivitis examinations and a complete oral prophylaxis, subjects were stratified by their whole mouth baseline plaque (modified Quigley-Hein) and gingivitis (modified Löe-Silness) scores and then randomly assigned to one of four dentifrice using groups. Plaque and gingivitis examinations were then performed after six weeks, three months and six months use of the dentifrices. Subjects brushed twice daily in their customary manner. The triclosan/soluble pyrophosphate and the triclosan/zinc citrate commercially available dentifrices did not provide statistically significant reductions in either supragingival plaque accumulation or gingivitis at any of the examination intervals, as compared to the placebo dentifrice. The subjects using the commercially available triclosan/copolymer dentifrice had, after six months, statistically significant reductions in supragingival plaque (11.3 per cent), plaque severity (18.8 per cent), gingivitis (19.9 per cent) and gingivitis severity (27.8 per cent), as compared to the placebo dentifrice.

Adolescent↗
PubMed1994

Efficacy of a dentifrice containing potassium nitrate, soluble pyrophosphate, PVM/MA copolymer, and sodium fluoride on dentinal hypersensitivity: a twelve-week clinical study.

The effect on dentinal hypersensitivity from the use of a dentifrice containing 5.0% potassium nitrate, 1.3% soluble pyrophosphate, 1.5% PVM/MA copolymer, and 0.243% sodium fluoride in a silica base over a twelve-week period was compared to a matching placebo dentifrice without potassium nitrate. A total of sixty-seven subjects were entered into the study, and stratified into two balanced groups according to their baseline mean thermal (threshold) temperature (Thermodontic Stimulator) and baseline mean tactile (Yeaple Probe) sensitivity scores. The two groups were randomly assigned to use either the potassium nitrate/copolymer/pyrophosphate dentifrice or the placebo dentifrice. The two groups were well balanced with regard to their mean baseline thermal and tactile sensitivity scores, sex and age. Subjects were instructed to brush their teeth twice daily (morning and evening) for one minute with their assigned dentifrice and a commercially available soft-bristled toothbrush. Dentinal hypersensitivity examinations, which included tactile sensitivity, threshold thermal sensitivity, pain thermal sensitivity, air blast, and a visual analog scale were conducted at baseline, six weeks, and twelve weeks. All examinations were conducted by the same dental examiner. After six weeks' use of their assigned products, those subjects in the potassium nitrate/copolymer/pyrophosphate dentifrice group demonstrated statistically significant improvements (p < 0.01), as compared to the placebo dentifrice, in the following parameters: 1) tactile; 2) thermal (threshold and pain); and 3) air blast. After twelve weeks' use of their assigned products, those subjects in the potassium nitrate/copolymer/pyrophosphate dentifrice group again demonstrated statistically significant improvements (p < 0.01), in tactile, thermal (threshold and pain) and air blast sensitivity, as compared to the placebo dentifrice. It was concluded from this study that a dentifrice containing 5.0% potassium nitrate, 1.3% soluble pyrophosphate, 1.5% PVM/MA copolymer, and 0.243% sodium fluoride in a silica base is a clinically effective treatment for reducing dentinal hypersensitivity.

Adult↗
PubMed1994

Anticalculus efficacy of a dentifrice containing potassium nitrate, soluble pyrophosphate, PVM/MA copolymer, and sodium fluoride in a silica base: a twelve-week clinical study.

A randomized, two-compartment calculus clinical study of twelve-weeks duration was conducted among a group of calculus-forming subjects in the St. Louis area. The purpose of this parallel and double-blind clinical study was to compare the effect of a dentifrice containing 5.0% potassium nitrate, 1.3% soluble pyrophosphate, 1.5% PVM/MA copolymer and 0.243% sodium fluoride in a silica base, to that of a placebo dentifrice, with regard to supragingival calculus formation. The study examiner, using the Volpe-Manhold Calculus Index, selected a panel of calculus-prone men and women who had completed a one-month placebo regimen. The Volpe-Manhold Calculus Index scores and the number of completely calculus-free sites were recorded. One-hundred and fifteen subjects were entered into the study. After an oral soft and hard tissue examination, the subjects were given a complete oral prophylaxis and randomly assigned to use either the placebo or test dentifrice for a 12-week home-use period. They were prohibited from using any other means of oral hygiene during the study. After completing 12 weeks of twice-daily brushing at home using their assigned toothpaste and a standard soft-bristled toothbrush, subjects were again assessed for supragingival calculus deposits and calculus-free sites. The dentifrice containing 5.0% potassium nitrate, 1.3% soluble pyrophosphate, 1.5% PVM/MA copolymer and 0.243% sodium fluoride in a silica base, inhibited supragingival calculus formation by 54.4%, as compared to a 0.243% sodium fluoride silica-based placebo dentifrice. The mean Volpe-Manhold Calculus Index scores were compared statistically and the difference indicated statistical significance at probability of 0.01 by means of an analysis of covariance (ANCOVA). The number of calculus-free sites, a second parameter of efficacy, also was compared and demonstrated an absolute difference of 32.6% in favor of the group using the dentifrice containing potassium nitrate, soluble pyrophosphate and PVM/MA copolymer compared to a placebo dentifrice (37.8% vs 5.2%, respectively). An analysis of covariance indicated that this improvement showed statistical significance at a probability of 0.01.

Adult↗
PubMed1994

Comparative efficacy of two dentifrices containing 5% potassium nitrate on dentinal sensitivity: a twelve-week clinical study.

The effect of a dentifrice containing 5.0% potassium nitrate, 1.3% soluble pyrophosphate, 1.5% PVM/MA copolymer, and 0.243% sodium fluoride in a silica base (Sensitive/Tartar Control) on dentinal hypersensitivity over a twelve-week period was compared to a commercially available dentifrice containing 5% potassium nitrate and 0.76% sodium monofluorophosphate in a dicalcium phosphate dihydrate base (Sensodyne-F). A total of ninety-seven subjects were entered into the study, and stratified into two balanced groups according to their baseline mean air sensitivity score and baseline mean tactile (Yeaple Probe) sensitivity score. The two groups were randomly assigned to use either the Sensitive/Tartar Control dentifrice or the commercially available hypersensitivity control dentifrice with potassium nitrate. The two groups were balanced with regard to their mean baseline air and tactile sensitivity scores, sex and age. Subjects were instructed to brush their teeth twice daily (morning and evening) for one minute with their assigned dentifrice and a commercially available soft-bristled toothbrush. Dentinal hypersensitivity examinations, which included tactile sensitivity, cold air blast, and a visual analog scale were conducted at baseline, six weeks, and twelve weeks. All examinations were conducted by the same dental examiner. After six weeks' use of the assigned dentifrices, there were no statistically significant differences between dentifrice groups in any of the parameters assessed (tactile, cold air blast and visual analog scale). After twelve weeks' use of the assigned products, there were no statistically significant differences between dentifrice groups in any of the parameters assessed (tactile, cold air blast and visual analog scale). Thus it can be concluded from this study that the use of a dentifrice containing 5.0% potassium nitrate, 1.3% soluble pyrophosphate, 1.5% PVM/MA copolymer, and 0.243% sodium fluoride in a silica base provides a clinically effective method of reducing dentinal hypersensitivity which is comparable in efficacy to a commercially available hypersensitivity control dentifrice containing 5% potassium nitrate and 0.76% sodium monofluorophosphate in a dicalcium phosphate dihydrate base.

Adult↗