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Biomedical subjects

D A Crossley

Publications and source records attributed to D A Crossley.

At least 19 recordsLinked to original sources
PubMed2005

In vitro comparison of three materials as apical sealants of equine premolar and molar teeth.

REASONS FOR PERFORMING STUDY: Surgical endodontic therapy is a conservative dental technique used in horses with some degree of clinical success. Failure of this procedure can partially be explained by inadequate sealing of the root apices with resultant microleakage in the periapical area. OBJECTIVES: To assess and compare in vitro sealing ability of 3 different dental restorative materials used as apical sealants during equine surgical endodontics. METHODS: Thirty extracted equine cheek teeth were divided randomly into 3 groups and subjected to apicoectomy and apical sealing using 3 materials: reinforced zinc oxide-eugenol cement; intermediate restorative material (IRM); a resin-modified glass ionomer; and amalgam. After apical sealing, the teeth were submerged in a solution of Procion Brilliant Cresyl Blue stain for a period of 7 days. The teeth were then washed, embedded in resin, sectioned and assessed microscopically for dye leakage around the apical restorations. RESULTS: Although the materials proved effective as apical sealants, some dye leakage was encountered in all 3 groups with no statistical difference (P = 0.114). CONCLUSIONS AND POTENTIAL RELEVANCE: IRM, a resin-modified glass ionomer and amalgam all showed comparative features as apical sealants when used in vitro in equine teeth. IRM is currently regarded as the superior material in clinical situations due to its ease of handling and lesser sensitivity to environmental moisture during placement compared to the other 2 materials.

Animals↗
PubMed2001

Skull size and cheek-tooth length in wild-caught and captive-bred chinchillas.

Chinchillas are herbivorous rodents with teeth that all grow continuously. In captivity, they are commonly affected by dental disease. As the range of dental disease occurring in wild chinchillas is unknown, the dentition of museum specimens originally obtained from the wild was assessed and compared with specimens prepared from captive-bred animals. Skulls from wild-caught chinchillas showed minimal evidence of dental disease and the teeth were all short, cheek-tooth lengths averaging 5.9 mm. Cheek-tooth lengths in zoo specimens (average 6.6 mm), clinically normal (average 7.4 mm) and captive-bred animals with dental disease (average 10 mm) were significantly elongated by comparison (P<0.0001). Captive-bred specimens showed a wide range of tooth-related lesions. These results suggest that some aspect of captivity is responsible for the development of dental disease in chinchillas. It is suggested that the diet (its physical form and composition) is the main aetiological factor, and that provision of a diet closely matching that of wild chinchillas should significantly reduce the incidence of dental disease in captive animals.

Animal Feed↗
PubMed2001

Dental disease in chinchillas in the UK.

Dental abnormalities are common in chinchillas, although knowledge of the lesions responsible for the clinical signs is incomplete. Animals bred in the UK were examined to gain further knowledge of dental disease in this chinchilla population. Dental abnormalities, particularly those related to tooth elongation, were detected on careful external examination of 35 per cent of apparently healthy chinchillas. Incisor abnormalities were seen on clinical examination in 55 per cent of chinchillas presented because of clinical illness. In all but one case, this occurred secondarily to crown elongation of the cheek teeth or to the absence of opposing teeth, rather than being a primary skeletal problem. Clinical signs commonly attributed to malocclusion, such as ventral mandibular swelling, weight loss, dysphagia, altered chewing pattern and changed food preferences, were not specific to malocclusion, being seen associated with coronal spike formation, root elongation and advanced periodontal lesions. Caries and resorptive lesions rarely caused clinical signs in this population, but were identified during 37 per cent of postmortem examinations. Congenital absence of teeth, skeletal malocclusion and pathological loss of teeth all resulted in significant clinical signs, but were rare. It is concluded that provision of a diet with physical properties more closely matching that of wild chinchillas should improve the dental health of captive animals.

Animal Husbandry↗
PubMed2000

Role of nitric oxide in the systemic and pulmonary circulation of anesthetized turtles (Trachemys scripta).

In reptiles the influence of local vascular factors on blood flow regulation is vaguely understood. The aim of this study was to investigate the role of nitric oxide (NO) on vascular function in anesthetized Trachemys scripta. The experimental protocol consisted of serial injections of sodium nitroprusside (SNP; 25 microg. kg(-1)), L-arginine (185 mg. kg(-1)) and L-NAME (50 mg. kg(-1)). SNP induced a systemic vasodilation (0.05 to 0.02 kPa. min. kg. mL(-1), P = 0.015), with no change in pulmonary vascular resistance (0.07 versus 0.08 kPa. min. kg. mL(-1), P > 0.05). L-Arg had no effect on resistances but increased cardiac output by 17%. L-NAME increased systemic resistance (33% increase; P = 0.01) while pulmonary resistance was unchanged. These effects are consistent with in vivo and in vitro studies on the systemic vasculature of different reptilian species, suggesting that NO has an important role in maintaining systemic vascular tone. The pulmonary vasculature did not respond to NO due to either a lack of an endogenous NO tone or a relaxed state of the pulmonary vasculature. The importance of NO-based mechanisms versus other neuro-humoral modulators in the reptilian circulation remains uncertain. However, as established in prior studies, cholinergic control of the proximal pulmonary artery is the main regulator of pulmonary resistance while systemic resistance depends on a more complex suite of neural, humoral and local effectors that include NO.

Anesthesia, General↗
PubMed2000

Control of blood pressure mediated by baroreflex changes of heart rate in the chicken embryo (Gallus gallus).

Pharmacological manipulation of peripheral resistance via sodium nitroprusside and phenylephrine was used to study baroreflex function over the latter two-thirds of incubation in embryonic chickens. From day 9 to day 19 of incubation, there is a positive linear relation between heart rate and blood pressure, indicating the feedforward action of arterial pressure on heart rate. A reciprocal relationship between blood pressure and heart rate became pronounced during the last 3 days of incubation. For the purpose of the study, gain of the baroreflex was calculated as maximal gain (only those embryos that demonstrated the response) or average gain (all embryos). Maximal gain increased progressively from 13 +/- 7 beats. min(-1). kPa(-1) at 18 days to 105 +/- 83 beats. min(-1). kPa(-1) in 2-day-old hatchlings. The percentage of embryos older than 18 days with baroreflex responses increased from 33% on day 19 to 56% on day 21, indicating that baroreflex regulation begins late in incubation ( approximately 90% incubation time), and the gain of this reflex exhibits a maturation over the final 3 days of incubation.

Animals↗
PubMed2000

Physiological variability in neonatal armadillo quadruplets: within- and between-litter differences.

The role of genetics on neonatal physiological variability was examined in the nine-banded armadillo (Dasypus novemcinctus). Since armadillos give birth to only monozygous quadruplets, the genetic variation within litters is essentially zero. Quadruplets born in captivity were isolated and weighed within 8 h of birth. Oxygen consumption (V.(O2)) was measured in resting neonates by flow-through respirometry, heart rate obtained from an electrocardiogram and ventilation was measured by impedance techniques. Following the measurements, neonates were returned to the mother. Measurements were repeated at 4 and 8 days after birth. Mean heart rate significantly increased from 132 beats min(-1) on the day of birth to 169 beats min(-1) on day 8. Mean ventilation rate significantly decreased from 81 breaths min(-1) on the day of birth to 54 breaths min(-1) on day 8. During this same developmental period, mean mass significantly increased from 100 g to 129 g, and mean mass-specific oxygen consumption significantly decreased from 32.2 ml O(2)kg(-1)min(-1) to 28.6 ml O(2)kg(-1) min(-1). For all variables measured, within-litter variability was always significantly less than between-litter variability, confirming a 'sibling effect' that we attribute to the genetic components determining physiological characters.

Aging↗
PubMed1998

Use of computed tomography to investigate cheek tooth abnormalities in chinchillas (Chinchilla laniger)

Computerised tomographic scanning was used to investigate tooth structure in chinchillas (Chinchilla laniger), both cheek tooth crown and root abnormalities being common in this species. This paper describes a common form of dental disease affecting species with continuously growing teeth, with particular reference to the chinchilla, and confirms the potential role of computed tomography (CT) in its early diagnosis. CT imaging is compared with previously available methods of investigation which frequently fail to detect early pathological changes.

Animals↗
PubMed1995

Grasshopper crop and midgut extract effects on plants: an example of reward feedback.

Acid extracts and a resultant fraction from solid-phase extraction (SPE) of Romalea guttata crop and midgut tissues induce sorghum (Sorghum bicolor var. Rio) coleoptile growth in 24-h incubations an average of 49% above untreated controls. When combined with plant auxin, indole-3-acetic acid (IAA), the SPE fraction shows a synergistic reaction, yielding increases in coleoptile growth that average 295% above untreated controls and 8% above IAA standards. The interaction lowered the point of maximum sensitivity of IAA 3 orders of magnitude, resulting in a new IAA physiological set point at 10(-7) g/ml. This synergism suggests that contents in animal regurgitants making their way into plant tissue during feeding may produce a positive feedback in plant growth and development following herbivory. Such a process, also known as reward feedback, may exert major controls on ecosystem-level relationships in nature.

Journal Article↗