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Biomedical subjects

R McFadzean

Publications and source records attributed to R McFadzean.

10 recordsLinked to original sources
PubMed1999

Laboratory evaluation of a compomer and a resin-modified glass ionomer cement for orthodontic bonding.

The mean shear debonding force of stainless steel orthodontic brackets with microetched bases bonded with either a compomer or a resin-modified glass ionomer cement was assessed. In addition, the amount of cement remaining on the enamel surface following bracket removal was evaluated. Finally, survival time of orthodontic brackets bonded with these materials was assessed following simulated mechanical stress in a ball mill. Debonding force and survival time data were compared with those obtained for brackets bonded with a chemically cured resin adhesive, a light-cured resin adhesive, and a conventional glass ionomer cement. There were no significant differences in mean shear debonding force of brackets bonded with the compomer, resin-modified glass ionomer, chemically cured resin adhesive, or the light-cured resin adhesive. Brackets bonded with a conventional glass ionomer cement had a significantly lower mean shear debonding force than that recorded for the other materials. The Adhesive Remnant Index (ARI) mode score indicated that significantly less cement remained on the enamel following debonding of brackets cemented with resin-modified or conventional glass ionomers compared with other adhesives. The median survival time for brackets cemented with the compomer, resin-modified glass ionomer, chemically cured resin, or light-cured resin were significantly longer than for brackets cemented with conventional glass ionomer. The compomer and the resin-modified glass ionomer adhesive appear to offer viable alternatives to the more commonly used resin adhesives for bracket bonding.

Acid Etching, Dental↗
PubMed1998

A 5-year clinical review of bond failure with a light-cured resin adhesive.

The purpose of this study was to investigate the time to first failure of stainless steel orthodontic brackets (Ormco Corp, Glendora, Calif) bonded with a light-cured resin adhesive (Transbond, 3M Unitek, Monrovia, Calif) and assess whether time to failure was related to the patient's age at the start of treatment or sex, the proficiency of the individual placing the brackets, or the presenting malocclusion. Data on 548 patients with 7118 bonded brackets were analyzed. Survival analysis was carried out on a single bracket per patient. In each patient, the first bracket to fail was studied. In cases where no brackets failed, the bracket with the shortest follow-up time was analyzed and handled as a censored observation in the formal analysis. Median time until first bracket failure was 442 days, and an overall failure rate of 6% was recorded. There were no significant differences in time to first failure of brackets with respect to the sex or age of the patient at the start of treatment (p = 0.168, and p = 0.261, respectively), operator proficiency in placing brackets (p = 0.189), or presenting malocclusion (p = 0.052). Performance of brackets bonded with Transbond does not appear to vary significantly according to the variables examined.

Adolescent↗
PubMed1998

Positional acuity in amblyopia: does a perceptual consequence of neural recruitment exist?

Animal models of amblyopia have shown that visual deprivation for even brief periods can result in dramatic changes in cortical architecture. Active neural recruitment mechanisms present the possibility that the non-deprived eye of amblyopes may show enhanced visual capacity. This idea was tested by measuring a form of positional acuity which we have termed alignment threshold. Three subject groups were examined, adults, visually normal children, and children with amblyopia in which the non-deprived eye was tested. Alignment thresholds in adults were significantly better (approximately 0.3 log unit) than the thresholds for visually normal children. No significant difference was found in thresholds between the visually normal children and the non-deprived eye of the amblyopic children. The results of this study suggest that subjects with unilateral amblyopia do not show enhanced visual alignment performance in their non-deprived eye.

Adult↗
PubMed1997

Habituation-like effects cause a significant decrease in response in MRI neuroactivation during visual stimulation.

A wide range of rest/stimulus cycle durations (40-360 sec) is reported to have been used by various groups for MRI neuroactivation studies of the visual cortex. In this paper we demonstrate a clear habituation-like response for longer cycle durations which results in a halving of apparent activation between cycle durations of 138 and 276 sec. This has important implications, not only in terms of optimizing the technique, but also in providing an insight into the underlying physiological mechanisms.

Adult↗
PubMed1996

Objective detection of hemifield and quadrantic field defects by visual evoked cortical potentials.

AIMS/BACKGROUND: An objective method for detecting hemifield and quadrantic visual field defects has been developed using steady state visual evoked cortical potentials (VECPs), an adaptive noise canceller (ANC), and Hotelling's t2 statistic. The purpose of this study was to determine the sensitivity and specificity of the technique. METHODS: Nine subjects (mean age 44 years) were investigated with field loss due to a variety of causes including both anterior and posterior visual pathway lesions. Dynamic perimetry was performed by means of a Goldmann or Tübingen perimeter. VECP recordings were made from each visual field quadrant (23 degrees X 23 degrees) by means of a steady state reversing checkerboard (7.7 rev/s). The central 5 degrees of the visual field and the vertical and horizontal meridians were masked during these measurements. Recordings were made from three electrode sites, positioned over the visual cortex, relative to a mid frontal electrode. Each recording lasted 2 minutes, during which time fixation was monitored. The data from each recording were divided into 4 second segments, and the amplitude and phase of the VECP signal measured using the ANC. Hotelling's t2 statistic was applied to determine the probability of signal detection. Receiver operating characteristic curves were used to find the optimum signal detection threshold for identification of the visual field defects. RESULTS: The results of the study confirmed patterns of subjective visual field loss. The technique had a sensitivity and a specificity of 81% and 85%, respectively, for detecting 'non-seeing' areas in the inferior visual field, and 82% and 89%, respectively, for detecting 'non-seeing' areas in the superior visual field. CONCLUSION: These results demonstrate that the technique is of potential clinical value to ophthalmologists and neurologists when subjective perimetry is not possible.

Adolescent↗
PubMed1994

Representation of the visual field in the occipital striate cortex.

The representation of the field of vision in the human striate cortex is based on the Holmes map in which about 25% of the surface area of the striate cortex is allocated to the central 15 degrees of vision. Following the introduction of computed tomography of the brain, the accuracy of the Holmes map was apparently confirmed by clinical/radiological correlation, but a revision has been proposed by Horton and Hoyt based on a magnetic resonance imaging study of three patients with visual field defects due to striate lesions. They propose that the central cortical representation of vision occupies a much larger area. This study reviews the perimetric and imaging findings in a larger series of patients with striate cortical disease and provides support for the revised representation. The clinical phenomenon of macular sparing and its relation to representation of the macula at the occipital pole is also discussed.

Adult↗
PubMed1994

Fibrous dysplasia of the orbit.

Twelve patients with fibrous dysplasia of the orbit are reviewed and the ophthalmic findings described. Three case histories are presented in detail. Six patients were managed conservatively; four have shown radiological progression of the disease. Six patients underwent surgery. A conservative procedure, comprising debulking dysplastic bone, was carried out in four--all required further surgery including radical excision in two patients. Two subjects had primary radical operations. No recurrence was encountered in the four patients who had undergone radical surgery. It would appear that fibrous dysplasia is not a disease confined to adolescence but may continue into adulthood, and even middle age. Patients may never require surgery, but require follow up for late progression. If surgical intervention is deemed necessary, an attempt should be made to excise all dysplastic bone, since progression of the disease after conservative surgery is relatively common.

Adolescent↗
PubMed1994

A diagnostic quartet in leptomeningeal infiltration of the optic nerve sheath.

A rare case of optic leptomeningeal carcinomatosis secondary to a rectal adenocarcinoma is recorded. The presentation of rectal disease with blindness is unique. A diagnostic quartet of symptoms and signs of leptomeningeal infiltration of the optic nerve sheath is proposed and its value emphasized by the inability of further investigation to confirm the clinical diagnosis. The investigation and treatment of leptomeningeal carcinomatosis is reviewed.

Adenocarcinoma↗
PubMed1992

Indications for and accuracy of magnetic resonance imaging and computed tomography in orbital disease.

All patients referred for orbital imaging to the neuroradiology department of the Institute of Neurological Sciences in Glasgow over a three year period were enrolled in the study and were scheduled to undergo both magnetic resonance imaging and computed tomography. A total of 101 of the 110 referred patients were deemed suitable for analysis. Details of key presenting symptoms, signs, and a pre-imaging diagnosis were recorded prospectively. A final diagnosis was obtained by histology in 65% of cases with an orbital abnormality, by a minimum of one year of clinical review in 19.5%, by response to antibiotic or steroid therapy in 8.5%, or by conclusive investigations such as carotid angiography in in 7% of patients, 29% of the patients had no detectable orbital disease despite a minimum one years' follow-up, and so were regarded as a "normal" group. The images were interpreted prospectively by separate masked observers. The diagnostic accuracies of the two techniques were compared to the final diagnosis. The two imaging methods were shown to be comparable in overall diagnostic accuracy, with a small and statistically non-significant advantage held by magnetic resonance imaging. Interpretation of the two investigations gave more accurate information in different types of disease.

Academies and Institutes↗