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Biomedical subjects

E Lynch

Publications and source records attributed to E Lynch.

At least 37 records · Page 2Linked to original sources
PubMed1998

Persistent loss of thermoregulation in the rat induced by 3,4-methylenedioxymethamphetamine (MDMA or "Ecstasy") but not by fenfluramine.

Using radio-biotelemetry, the timecourse of recovery and sensitivity to ambient temperature (Ta) of the thermogenic response of methylenedioxymethamphetamine (MDMA or "Ecstasy") was examined. Ambient temperatures of 17 and 22 degrees C produced very different response profiles, with the lower temperature producing a hypothermic response to 10 and 15 mg/kg doses of MDMA, and the higher temperature producing a profound hyperthermia to the same doses. Although the peak responses to the drug had subsided within 5 h of administration, residual effects, in the form of an elevation of body temperature during the "low" phase of the diurnal cycle, were present for a further 48 h. Long-lasting disruption of the thermoregulatory system following a short series of MDMA administrations (10 mg/kg once per day for 4 days) was shown by exposing the rats in the undrugged state to a thermoregulatory challenge, consisting of 60-min exposure to a Ta of 30 degrees C, at 1 week before, and at 4 weeks and 14 weeks after the drug administration. MDMA-treated rats showed a prolonged hyperthermic response to the challenge at both post-drug intervals compared with fenfluramine-treated rats and saline-treated controls. Thus, the results indicate both that MDMA's thermogenic effects are more sensitive to Ta than previously demonstrated, and that the serotonergic neurotoxicity of the drug may produce long-lasting changes in thermoregulatory mechanisms.

Amphetamine↗
PubMed1998

The isolation of Actinomyces naeslundii from sound root surfaces and root carious lesions.

The isolation of Actinomyces naeslundii from sound, exposed root surfaces (n = 56) and soft and leathery root carious lesions (n = 71) was investigated. Root carious lesions were sampled after the removal of overlying plaque. Supragingival plaque or carious dentine was sampled using a sterile excavator, the samples were disaggregated and cultured on both selective and non-selective media. A. naeslundii isolates were identified to the genospecies using specific antisera. Significantly greater numbers and proportions of A. naeslundii genospecies 2 than A. naeslundii genospecies 1 were isolated from all sites sampled. There was no significant difference between the numbers and proportions of the two genospecies isolated from leathery and soft lesions. The relationship between the presence of A. naeslundii genospecies and aciduric and acidogenic organisms was investigated. Those sound exposed root surfaces from which A. naeslundii genospecies 1 and/or 2 were isolated yielded significantly lower numbers of lactobacilli and yeasts than the surfaces from which A. naeslundii were not isolated. This difference was also found in leathery lesions but not soft root carious lesions. The microflora of soft root carious lesions was found to comprise primarily gram-positive pleomorphic rods which formed 70+/-7.8% of the flora, while in plaque from exposed root surfaces and in infected dentine from leathery lesions the gram-positive pleomorphic rods represented only 35% of the flora.

Actinomyces↗
PubMed1997

Multicomponent spectroscopic investigations of salivary antioxidant consumption by an oral rinse preparation containing the stable free radical species chlorine dioxide (ClO2.).

A multicomponent evaluation of the oxidative consumption of salivary biomolecules by a commercially-available oral rinse preparation containing an admixture of the stable free radical species chlorine dioxide (ClO2.) with chlorite anion (ClO2-) has been investigated using high resolution 1H NMR spectroscopy. The results obtained demonstrated that ClO2. and/or ClO2- present in this preparation effected the oxidative decarboxylation of salivary pyruvate (to acetate and CO2). Experiments conducted on chemical model systems confirmed the oxidative decarboxylation of pyruvate by this oral rinse, and also demonstrated that urate, thiocyanate anion, and the amino acids cysteine and methionine (precursors to volatile sulphur compounds responsible for oral malodour), were oxidatively consumed. The biochemical, periodontal and therapeutic significance of the results are discussed.

Absorption↗
PubMed1997

Variation in labial shoulder geometry of metal ceramic crown preparations: a finite element analysis.

Recent studies have highlighted variations in the geometry of teeth prepared to receive metal ceramic crowns, particularly in the region of the labial shoulder, where shoulder designs have often involved less reduction than is recommended. Using two-dimensional finite element analysis, this study subjected crowns, superimposed upon preparations with clinically common labial margin designs, to loads of 200N in three different directions. The resultant stress distribution within the labial marginal porcelain was examined. Results imply that variations in the marginal preparation geometry of metal ceramic crowns influenced the stress response of the finished crown. Within the limits of this study, a crown constructed a 1.3mm chamfer preparation appeared to have the best response to a simulated load applied to the palatal/incisal surface, at 45 degrees to the long axis.

Crowns↗
PubMed1996

Assessment of shoulder dimensions and angles of porcelain bonded to metal crown preparations.

The metal ceramic crown is the most popular extracoronal restoration in the United Kingdom. These restorations may fail because of fracture or esthetics. A potential cause of failure is the quality and width of the facial shoulder preparation. In this study 24 extracted human teeth were prepared to receive metal ceramic crowns by one of three dentists. Preparations were replicated and scanned in the midfacial plane by a coordinate measuring machine with a noncontact probe. The x, y, and z surface coordinates were recorded. The results indicated a mean (+/-SD) shoulder width value of 0.752 mm (+/-0.174 mm) and a shoulder angle of 108.54 (+/-15.06) degrees. From these data it would appear that there are deficiencies in shoulder preparations, particularly in width. These inadequacies may have implications for longevity of the restoration and periodontal health in a clinical situation.

Computer Graphics↗
PubMed1996

Clinical and microbiologic evaluation of a resin modified glass ionomer cement for orthodontic bonding.

This study evaluated the clinical performance of a new resin modified glass ionomer cement, Geristore (Den-Mat Corp., Santa Maria, Calif.), for the bonding of orthodontic brackets and its effect on certain caries-associated microorganisms. This cement has been shown to possess increased mechanical properties and long-term fluoride release. There were 716 brackets bonded in 40 patients (17 males and 23 females), with a split-mouth technique and a composite resin, Phase II (Reliance, Itasca, III.), as a control. Bond failures were recorded up to 1 year. Plaque scores and plaque samples were taken from the area of the bonding adhesive in 20 patients, before, at 1 week, and 5 months after the placement of brackets. The plaque samples were investigated for the presence of Streptococcus mutans and lactobacilli. The overall bond failure rate was found to be 8.9% for Geristore and 3.1% for Phase II (p < 0.05). Labially, there was no significant difference (p > 0.05) in bond failure rate: 3.8% for Geristore and 1.7% for Phase II. The proportions of S. mutans and lactobacilli in plaque taken from around Geristore cement were reduced at 1 week and 5 months, when compared with Phase II resin, and this reduction was statistically significant (p < 0.05) at 1 week. Results of this study suggest that Geristore may be of use in the labial segments, especially in caries prone patients, in whom demineralization at debond may present an esthetic and restorative problem several years after treatment.

Adolescent↗
PubMed1995

Comparison of selected microflora of plaque and underlying carious dentine associated with primary root caries lesions.

The composition of the microflora recovered from superficial dental plaque sampled from 81 primary root caries lesions requiring restoration was compared with the microflora of the underlying, infected carious dentine. The numbers of bacteria in the plaque samples were significantly greater than in the dentine samples, and the frequency of recovery of mutans streptococci, streptococci, lactobacilli, gram-positive pleomorphic rods (primarily Actinomyces spp.), and yeasts was not significantly different between the paired samples. However, the proportion of lactobacilli and gram-positive pleomorphic rods was significantly greater in the dentine, while the proportions of streptococci and yeasts did not differ significantly; the proportions of mutants streptococci were similar in both samples. These data indicate that the microflora overlying primary root caries lesions is significantly different from that associated with the infected root dentine. The method of sampling and culturing the microflora of root caries lesions must, therefore, discriminate between the microflora of the superficial supragingival plaque and the microflora associated with destruction of the infected underlying dentine.

Actinomyces↗
PubMed1995

Bond strengths of ceramic brackets using different bonding techniques.

A series of laboratory investigations was carried out to compare the shear-type bond strengths and site of bond failure of ceramic orthodontic brackets bonded to etched enamel. When light-cured composite resin was used as the luting agent, there was no reduction in bond strength when using 2.5 per cent nitric acid to etch the enamel, compared to 37 per cent phosphoric acid. The use of the two resin modified glass ionomer cements were found to give rise to significantly lower bond strengths than composite resin when used for placing ceramic brackets. Significantly less composite resin remained on the enamel surface following bracket removal in those samples etched with nitric acid.

Acid Etching, Dental↗
PubMed1995

Chemomechanical caries removal.

A system for the removal of caries by Chemomechanical means is reviewed. Its development, mode of action, safety, efficacy, advantages and disadvantages are considered.

Aminobutyrates↗
PubMed1995

Molecular mechanisms of the bleaching actions associated with commercially-available whitening oral health care products.

An increased public awareness in dental aesthetics has resulted in the wide availability of techniques of tooth bleaching, both in the dental chair and at home. This article reviews the aetiology of tooth discolouration both at the clinical and the molecular level, together with methods of alleviating such discolouration. Much of the therapeutic and aesthetic actions of commercially-available tooth whiteners, gels, oral rinses and other dentifrices are predominantly dependent on their ability to act as oxidants. A novel method of evaluating these aspects of dentifrice activity is also described: high resolution proton nuclear magnetic resonance (NMR) spectroscopy is a virtually non-invasive, multi component bioanalytical technique that can be employed to study oxidation/reduction reactions at the molecular level and is utilised here to investigate the mechanisms of action of a newly developed dentifrice (Ultrawhite Opal, Janina International). Such methodology also offers much potential for studies concerning the numerous chemical reactions occurring within the oral environment.

Dentifrices↗
PubMed1994

Glass polyalkenoate bond strength to dentine after chemomechanical caries removal.

The bond strength of a glass polyalkenoate cement after chemomechanical caries removal of dentine with or without the use of a conditioning agent and the mode of bond failure using scanning electron microscopy was examined. Forty extracted carious human teeth were divided into four groups of ten. Conventional caries removal was carried out on two groups and chemomechanical caries removal on the other two groups. Surface conditioner was applied to the dentine in one conventionally treated and one chemomechanically treated group. Glass polyalkenoate cement was applied via a metal holder to the dentine. The samples were stored for 7 days in a moist environment at 37 degrees C. The samples were subjected to a shearing-type stress at a cross-head speed of 0.5 mm min-1. The mean bond strength for each group, in MPa (standard deviation), was: conventional caries removal alone 1.32 (0.51), conventional caries removal and conditioner application 2.43 (0.47), chemomechanical caries removal alone 2.47 (0.99) and chemomechanical caries removal and conditioner application 2.76 (0.96). Mean bond strengths for both the chemomechanically treated groups and the conventionally treated group, coupled with the use of the conditioning agent, were significantly greater than for the conventionally treated groups alone at the 0.05 level. There was no significant difference between the chemomechanically treated groups or the group conventionally treated with conditioner application. SEM examination revealed a combination of cohesive and adhesive bond failure. Different morphologies between the conventionally and chemomechanically treated surfaces were also evident.

Acrylic Resins↗
PubMed1994

Sleep hypoxia in myotonic dystrophy and its correlation with awake respiratory function.

BACKGROUND: Tiredness and daytime respiratory failure occur frequently in myotonic dystrophy. Sleep hypoxaemia was studied in 12 patients with myotonic dystrophy and correlations were sought with their daytime lung and respiratory muscle function. METHODS: All patients underwent overnight sleep studies, clinical assessment, measurement of flow-volume loops and carbon monoxide transfer factor, arterial blood gas analysis, and physiological assessment of both thoracic muscle function and upper airways obstruction. RESULTS: The mean nadir of oxygen saturation during sleep was 75% (95% confidence interval 69% to 81%). A mean of 3.4% of total sleep duration was spent at an oxygen saturation level below 85%. Five of the 12 patients had an apnoea index of > 5, the group mean apnoea/hypopnoea index being 15.8 events/sleep hour. The mean awake arterial oxygen tension (PaO2) was 10.7 kPa. There was a trend to hypercapnoea with a mean awake arterial carbon dioxide tension of 6.1 kPa; carbon dioxide retention worsened during sleep. Respiratory muscle dysfunction was mainly evident as a low maximum expiratory mouth pressure. Upper airway obstruction assessed by physiological criteria was found in four of the 12 patients. The proportion of total sleep duration with oxygen saturation levels below 85% was directly related to body mass index (weight/height2) and inversely related to the awake PaO2. Body mass index was inversely related to the overnight nadir of oxygen saturation. CONCLUSIONS: Patients with myotonic dystrophy are often hypoxic during sleep and the subgroup that are obese, or have symptoms of sleep apnoea, or both, are particularly at risk. Sleep studies should be considered in this subgroup of patients with myotonic dystrophy.

Adult↗
PubMed1994

A comparison of primary root caries lesions classified according to colour.

Three hundred and ninety-five primary root caries lesions in 117 patients were included in this study. Each lesion was clinically characterised (colour, dimensions, distance from gingival margin and texture) and a sample of infected or altered dentine was taken using a standardised sampling procedure. The relationships between the colour and the microflora, texture, physical dimensions and distance from the gingival margin of the lesions were investigated. Lesions in each colour group (light brown, yellow, dark brown and black) were identified in each texture category (soft, leathery and hard), except for black lesions which were recorded as only soft or leathery. Black soft and black leathery lesions had a significantly greater area and harboured more lactobacilli than all other types of lesions while black leathery lesions also harboured significantly more yeasts. There were no significant differences in the number of bacteria or mutans streptococci isolated from soft or leathery lesions irrespective of lesion colour. Overall, these data indicate that the colour of primary root caries lesions is not a reliable indicator of primary root caries activity. Assessment of the clinical severity of primary root caries lesions requires consideration of lesion texture and the distance of the lesion from the gingival margin rather than the colour of the lesion.

Actinomyces↗