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Biomedical subjects

J C Hamilton

Publications and source records attributed to J C Hamilton.

At least 19 recordsLinked to original sources
PubMed2001

A clinical evaluation of air-abrasion treatment of questionable carious lesions. A 12-month report.

BACKGROUND: The efficacy of treating questionable incipient lesions early with air abrasion, a modality used by many practitioners, has not been adequately demonstrated. METHODS: The authors enrolled 223 teeth, each with a questionable incipient pit-and-fissure carious lesion, from 93 dental patients in a projected five-year randomized clinical trial. Caries was defined as softness, decalcification or cavitation at the base of a pit or fissure or radiographic evidence of caries. Each tooth was randomly assigned to either a treatment group (n = 113 teeth) or a control group (n = 110 teeth) (which was observed but left untreated until the definition of caries was met). Each tooth in the treatment group was air-abraded and restored with a flowable resin-based composite. The authors re-examined teeth in both groups every six months; they evaluated the restorations using a modified set of Ryge criteria and inspected teeth for caries using radiographs, mirrors and standardized explorers. RESULTS: Of the 113 teeth with questionable incipient carious lesions air-abraded in the treatment group, 50 had caries extending into dentin. After 12 months of clinical service, there were three sealants that exhibited a partial loss of sealant which did not require any re-treatment. Two restorations with penetrating staining were re-treated. In the control group at the end of 12 months, only nine of the 86 recalled teeth were diagnosed with pit-and-fissure caries and were treated with air abrasion and restored with flowable resin-based composite. There was no statistically significant difference between the volume of the treatment and control preparations. CONCLUSION: After 12 months of clinical service, two preventive resin-based composite restorations in the treatment group required re-treatment. Fewer teeth than expected in the control group were diagnosed as having caries and were treated. CLINICAL IMPLICATIONS: The merit of treating questionable incipient pit-and-fissure carious lesions early with air abrasion has not been demonstrated after 12 months in this clinical study.

Adolescent↗
PubMed2000

Effect of variable light intensity on composite shrinkage.

STATEMENT OF PROBLEM: Polymerization shrinkage is a critical limitation of dental composites and may contribute to postoperative pain, tooth fracture, microleakage, and secondary caries. Polymerization with high-intensity light sources has been related to increased depth of cure and improved mechanical properties. However, high-intensity light initiation has also been associated with greater polymerization shrinkage. PURPOSE: The purpose of this study was to investigate the effect of sequentially increasing light intensity on the polymerization shrinkage of 2 composites, a hybrid and a microfil. A Knoop hardness test was used to evaluate effectiveness of the cure with each intensity increase. MATERIAL AND METHODS: Four groups of 12 samples were measured for polymerization shrinkage by using a linometer. Light intensity curing sequences were as follows: full-intensity control (100% intensity for 40 seconds), low-intensity control (25% intensity for 40 seconds), test group 1 (25% intensity for 20 seconds, 50% for 10 seconds, 100% for 10 seconds), and test group 2 (25% intensity for 10 seconds, 50% for 10 seconds, 100% for 20 seconds). Statistical comparisons were made using a 1-factor ANOVA and a Tukey multiple comparisons test within each material. RESULTS: Results showed a significant difference (P<. 05) in mean linear shrinkage between the full-intensity control group and the other 3 sequences for both composites. No difference existed within the other 3 groups for either composite. Knoop hardness was similar for the full-intensity control and test group 2. The low-intensity control group and test group 1 were also similar but significantly lower. CONCLUSION: Curing composites for 10 seconds at 25% intensity, 10 seconds at 50%, and 20 seconds at 100% significantly reduced polymerization shrinkage while not compromising depth of cure.

Analysis of Variance↗
PubMed1998

"The Flemish Giant", reflections on the defense against endometriosis, inspired by Professor Emeritus Ivo A. Brosens.

Reproductive research benefits from combining animal and clinical studies. In Leuven, rabbits have constituted an animal model for many reproductive disorders, especially for those that involved surgical treatment. Much of what has been learned from animal experiments has been applied to human clinical reproductive research soon after. In this manuscript we wish to address the problem of the constant intra-abdominal battle between the menstrual aggressor and the peritoneal defense. From all published evidence we may conclude that endometriosis appears to be a dynamic disease, especially in the early phase, with subtle, atypical lesions emerging and vanishing again. In the end however the peritoneal defense system will prevail and the disease will be contained in the majority of patients. When doing repeat laparoscopies in young patients one should be prepared to encounter more advanced histological types of lesions, which not necessarily do have to indicate more advanced stages of the disease: the classical, blue and black powderburn spots and blueberry lesions reflect the extinguishing phase of the dynamic endometriotic process, and herald its inactivated histological end-stage. The dynamic phase of the disease may involve a varying interval of each patient's life, and medical suppression of the activity of the implants during this interval may lead one to conclude erroneously that treatment has been effective. If subsequently (after the end of medical suppression of the activity of the lesions) ovarian activity resumes and the lesions are stimulated again by ovarian steroids, their productive activity returns. Recurrence of disease may be diagnosed if at that stage a laparoscopy would be performed, whereas in reality only reactivation of temporarily obscured lesions did occur. The suppressed, dormant (but never absent) lesions produce mucus again, desquamation occurs, and reaction by the surrounding tissue. The inflammatory response, the local hyperemia and the neogenesis of vessels accentuate the presence of previously invisible endometriosis lesions and make them visible again. Endometriosis resumes its temporarily halted natural course of development, tissue remodeling occurs again, the battle between the aggressor and the defense resumes and waxing and waning of the several types of lesions, red, white and black, can be found again.

Animals↗
PubMed1997

Resin restorations.

Explore the source record for details and available documents.

Composite Resins↗
PubMed1992

Generalized rank annihilation method using similarity transformations.

Recently several papers have described the generalized rank annihilation method; however, in some cases complex eigenvalues and eigenvectors may appear when the generalized eigenproblem is solved. When complex eigenvalues and eigenvectors are encountered, the results cannot be used to estimate pure component profiles (e.g. spectra or chromatograms). In this paper, a similarity transformation is used to transform complex eigenvalues and eigenvectors into real eigenvalues and eigenvectors, thereby permitting spectra and profiles of pure constituents to be estimated. The modified GRAM method is illustrated with simulated and real data.

Algorithms↗
PubMed1980

The effects of season and stage of pregnancy on plasma 25-hydroxy-vitamin D concentrations in pregnant women.

Plasma 25-OHD levels were measured in the same 26 Caucasian women before pregnancy and during the first, second and third trimesters of their pregnancy. This was done to assess whether pregnancy alters vitamin D status in healthy women. During most times of the year there was no association between the 25-OHD levels and the stage of pregnancy, but between January and March there was a progressive fall in 25-OHD levels with each trimester. When 25-OHD levels were related to hours of possible sunlight exposure a negative association between 25-OHD levels and stage of pregnancy was noted only in subjects with the lowest possible exposure to sunlight. These observations suggest that pregnancy has an effect on vitamin D metabolism, but that in healthy Caucasian women these effects only become manifest where there is a low level of exposure to sunlight.

England↗
PubMed1979

Plasma binding capacity for 25-hydroxy-vitamin D in the elderly.

Plasma 25-hydroxy-vitamin D (25-OHD) concentrations and 25-OHD binding capacities were measured in 14 elderly patients and in 14 young controls. Both 25-OHD concentrations and 25-OHD binding capacities were reduced in the elderly. In neither group, however, was there a significant correlation between 25-OHD binding capacities and 25-OHD concentrations. Thus, although 25-OHD binding capacities are reduced in sick old people this does not account for the low 25-OHD concentrations often found in this group.

Adult↗
PubMed1978

Ultra-violet irradiation and 25-hydroxy-vitamin D levels in sick old people.

Twelve elderly patients in a rehabilitation ward were given a four-week course of ultra-violet irradiation from a Vitalux lamp. They were compared with 12 controls selected from the same ward. Treatment produced a significant elevation in plasma 25-hydroxy-vitamin D (25OHD) by the end of the second week and concentrations continued to rise over the four-week period. Subject showing the greatest response were those starting with the lowest levels of plasma 25OHD. The findings suggest that ultra-violet irradiation is an effective means of treating vitamin D deficiency in old age and that patients with the greatest degree of deficiency show the greatest response.

Aged↗
PubMed1978

25-hydroxy-vitamin D, diet and sunlight exposure in patients admitted to a geriatric unit.

Dietary intake, sunlight exposure and 25-hydroxy-vitamin D levels were estimated in 62 patients admitted to a geriatric assessment unit. There was a significant correlation between vitamin D intake and 25-hydroxy-vitamin D levels but none between sunlight exposure and these. This suggests that in old age dietary deficiency may be a more important cause of metabolic bone disease than limited sunlight exposure.

Adolescent↗
PubMed1978

Adrenal function and ascorbic acid concentrations in elderly women.

Tetracosactrin (Synacthen) tests were performed on 19 elderly women who had leucocyte ascorbic acid (LAA) levels of less than 15 microgram/108 WBC. 9 were then given a daily dose of 200 mg ascorbic acid orally for 2 weeks while the other 10 were left untreated. Following this, tetracosactrin tests were repeated in both groups. All initial plasm cortisol responses to tetracosactrin were within normal limits. Treatment with ascorbic acid produced no changes in these. This suggests that the low LAA levels often found in old people do not result in adrenal insufficiency.

Adrenal Glands↗
PubMed1977

Vitamin D supplements and 25-hydroxy vitamin D concentrations in the elderly.

Serial 25-hydroxy vitamin D (25-OHD) concentrations were measured in long-stay geriatric patients treated with vitamin D. Comparison between a treatment and a control group showed that a daily dose of 500 IU vitamin D produced a significant increase in 25-OHD levels by two months. The supplement had a striking effect when the initial 25-OHD level was low and very little effect when it was high. 25-OHD levels in subjects on 2000 IU vitamin D daily were only marginally higher than those in subjects on 500 IU. A dose of 500 IU vitamin D daily should therefore produce adequate blood 25-OHD concentrations in most old people, and probably prevent most cases of osteomalacia in the elderly--though a large-scale study is needed to confirm this.

Aged↗