Cure performance of light-activated composites by differential thermal analysis (DTA)

A technique which utilizes differential thermal analysis and a divided fibre optic system is a valuable aid to the study of the curing behaviour of lightactivated composites. Degree of cure and temperature rise can readily be evaluated as a function of irradiation time. Shade of material, thickness, sample temperature and the presence of porosity all have a significant effect on cure behaviour. The temperature rise for a 60 mm³ sample of material varies between 20°C and 40°C for the materials tested.     

Salivary concentrations of steroid hormones in males and in cycling and postmenopausal females with and without periodontitis

Concentrations of testosterone, dehydroepiandrosterone, eslradiol, progesterone, 17α-hydroxyprogesterone, and cortisol were measured in the saliva by radioimmunoassay. Saliva from male and cycling and postmenopausal female patients with and without periodontitis was studied.
It was found that salivary concentration of progesterone was increased in all patients with periodontitis. While testosterone was significantly increased in the female diabetic and non-diabetic patients with periodontitis, no difference in its concentration was found in the saliva of non-diabetic males with and without periodontitis. Salivary dehydroepiandrosterone was also increased in postmenopausal females with periodontitis. In contrast, estradiol was significantly decreased or not measurable in all patient groups with periodontitis. The concentration of cortisol and 17α-hydroxyprogesterone showed no significant differences in postmenopausal patients with and without periodontitis. In addition, the salivary concentration of all hormones in postmenopausal females showed circadian variation. Moreover, results obtained in postmenopausal and ovariectomized females provided evidence for extragonadal production of sex steroid hormones in postmenopausal females.
The present results suggest that there is a relationship between the altered production of sex steroid hormones and the incidence of periodontal pathology.     

Perturbation of cobalt 60 radiation doses by metal objects implanted during oral and maxillofacial surgery

The influence on cobalt 60 dose distributions of typical metal parts used in oral and maxillofacial surgery was studied. Relative doses were determined by exposing x-ray films in a polystyrene phantom set-up containing samples of Vitallium, titanium, and stainless steel. Optical densities were converted to doses with the aid of sensitometric curves. The results show that for normal incidence there is a 25% to 40% increase in dose at the entrance side of the metal and a 20% to 25% decrease in dose at the exit side. The enhancement effect falls off rapidly and becomes negligible at about 1 mm from the interface. The reduction effect decreases more gradually and is still evident at distances of a few centimeters. These dose perturbations should be taken into account in the planning of radiation therapy for patients in whom metal objects have been implanted.     

Radiology instruction and use of ionizing radiation in U.S. dental schools

In fall 1980, the Commission on Dental Accreditation of the American Dental Association conducted a comprehensive survey of radiology instruction and the use of ionizing radiation in dental education. All 60 dental schools in the United States responded to the survey. Data were collected on course objectives, course content, clock hours of instruction, radiology content in other clinical courses, the number, educational background, and years of teaching experience of radiology faculty, clinical requirements in radiology and the measures used to assess student competency, and the use of radiographs in providing patient care. Attention was directed to practices used in monitoring radiation protection and hygiene. These data provide a frame of reference for evaluating the status of radiology instruction at the respective schools. More important, they provide faculty with a baseline for determining what changes, if any, are needed in the current radiology curriculum.     

Application of analytical stress solutions to bi-axially loaded dental ceramic–dental cement bilayers

OBJECTIVE: Increased consideration of dental ceramics and dental cements as a singular structural unit for in-vitro mechanical testing has resulted in the reporting of a wide range of analytical methods to calculate the failure stresses. Therefore a comparison of observations between studies is complicated by the use of dissimilar stress solutions despite the employment of a similar testing methodology and specimen geometry. MATERIALS AND METHODS: Three analytical solutions to calculate failure stresses in bi-axially loaded dental ceramic-dental cement bilayers were appraised for a commonly utilized testing geometry (ball-on-ring). Clinically relevant datasets were generated from the bi-axial flexure testing of uncoated and dental cement coated aluminous core ceramic exposed to differing ceramic surface preparations. A Weibull statistical approach was utilized in order to provide insight into the impact of the analytical method on both the scale (sigma(0)) and distribution (m) of the failure stress data. RESULTS: Calculation of the bi-axial flexure stress utilizing Timoshenko's analysis resulted in an increase in sigma(0) for the uncoated (6%) and dental cement coated (11-12%) aluminous core ceramic, when compared with the bilayered solutions reported by Rosenstiel and Hsueh. However, the shape of the failure distributions illustrated by the consistency of m and associated 95% confidence intervals was not influenced by the analytical stress solution employed. SIGNIFICANCE: The choice of the analytical method chosen to calculate failure stresses in bi-axially loaded dental ceramic-dental cement bilayers will impact on the magnitude of the reported strength. Comparison between the failure stresses of uncoated and cement coated dental ceramics is more accurately represented by bilayer solutions, which account for the mismatch between the elastic constants of dissimilar materials. However, within the context of dental cement coated dental ceramics of clinically relevant dimensions, the choice of solution is unlikely to impact on the interpretation of the observations previously reported in the dental literature.     

Analysis of the degradation of a model dental composite

Dental composites undergo material property changes during exposure to the oral environment and may release compounds of potential toxicity, such as bisphenol A. Degradation of dental composites was studied in a simplified overlayer model in which bisphenol A diglycidyl methacrylate (BisGMA) was covalently bound to a porous silicon oxide surface. It was hypothesized that the chemical structure of this overlayer would allow release of bisphenol A, BisGMA, and the decomposition products thereof, upon exposure to water for an extended period. Liquid chromatography mass spectrometry found leaching of intact BisGMA and several degradation products that contained the bisphenol A moiety from the overlayer into distilled water after 2 wks of aging. The absence of bisphenol A release from the overlayer reduces concerns regarding its potential health risk in dental composites. Nevertheless, health concerns might arise with respect to BisGMA and the leached degradation products, since they all contain the bisphenol A moiety. Abbreviations: BisGMA, bisphenol A diglycidyl methacrylate; HPLC, high-performance liquid chromatography; LCMS, liquid chromatography mass spectrometry; MA, methacrylic acid; MPS, 3-(trimethoxysilyl) propyl methacrylate; m/z, mass-to-charge ratio; and TIC, total ion chromatogram.     

A cost-efficiency analysis of a mobile dental clinic in the public services.

During 1997, the Gauteng Oral Health Services implemented a Mobile Oral Health Care System (MOHCS) in the province. For the first year (1997/98) one mobile dental clinic was utilised in the West Rand region of the province and services were provided by dentists, dental therapists and oral hygienists. The purpose of the MOHCS is to provide an accessible and affordable comprehensive oral health care service of high quality and standard. The aim of this study was to determine the cost-efficiency of the mobile dental clinic utilised in the West Rand region over the first year of implementation. After consultation with all stakeholders, an operational plan was finalised. The plan included a traveling schedule, clinicians available for service delivery, and a management information system (MIS). Statistics on dental materials, consumables, treatment provided, etc. were collected and analysed. During the study period 2072 patients received dental treatment at 38 different sites in the region. At an average cost of R56.50 (+/- US$11) per patient, services to the value of R92.45 (+/- US$18) per patient were delivered during 104 working days. Of the 1477 patients treated by a dentist or dental therapist, 53% were treated by extracting 1026 teeth, and 27% by restoring 570 teeth. For oral hygiene patients, 67% received an oral hygiene procedure and 13% received fissure sealants. With a net margin ratio of 0,39 and a breakeven point of 1173,46 patients and 58,90 days, an accessible and cost-efficient service was provided to health districts in the West Rand region.