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.     

Evaluation of odontogenic maxillary sinusitis using cone-beam computed tomography: three case reports

Introduction

Ten to twelve percent of all cases of maxillary sinusitis derive from odontogenic origin. The purpose of this study was to report the use of cone-beam computed tomography (CBCT) scanning in elucidating dental pathology as an etiology of maxillary sinusitis.

Methods

Intraoral periapical radiographs and CBCT scanning were performed in the evaluation of three patients presenting with pain, sinus congestion, or respiratory complaints. In the first case, extractions of impacted third molar and adjacent nonrestorable tooth were performed. In the second two cases, endodontic therapy was done. Radiologic follow-up with CBCT scanning or medical computed tomography scanning was performed 6 to 12 months after dental procedures were performed.

Results

All three patients presented with severe sinusitis that resolved after appropriate dental treatment. The first patient also showed marked improvement of chronic bronchitis after completion of dental treatment. In all patients, complete or near total resolution of sinusitis, including eradication of mucous retention cyst, was confirmed by post-treatment CBCT or computed tomography scanning.

Conclusions

These cases show the utility of CBCT scanning in evaluating patients presenting with concurrent sinus and dental complaints. In these three patients, maxillary sinusitis of odontogenic origin responded well to the eradication of dental etiology.     

Prevention of enamel demineralization after tooth bleaching by bioactive glass incorporated into toothpaste

Background: The aim of this study was to determine the effects of bleaching on the structure of the enamel layer of teeth and the potential of the commercial bioactive glass NovaMin® in two different toothpastes to remineralize such regions of the enamel. Three aspects were considered: the extent and nature of the alterations in the enamel after application of the bleaching agents; the extent of remineralization after application of two commercial toothpastes containing bioactive glass; and whether or not there were differences between the toothpastes in terms of their effectiveness in promoting remineralization. Methods: Bleaching agent based on 16% carbamide peroxide was applied to the enamel surface of freshly extracted human molars for 8 minutes, once a day for 7 days. After the bleaching cycles, the enamel surface was analysed by SEM and EDX. Results: The results obtained in the study lead to the conclusion that application of 16% carbamide peroxide causes distinct morphological changes to the enamel surface which vary from mild to severe. Subsequent treatment with either of the toothpastes containing the bioactive glass NovaMin® resulted in the formation of a protective layer on the enamel surface, consisting of bioactive glass deposits, with only slight differences between the two brands. Application of these dentifrices also caused increases in the Ca and P content of the enamel layer, returning it to that of undamaged enamel. Conclusions: Remineralizing toothpastes should be used after bleaching, in order to repair any damage to the mineral tissue caused by these procedures.     

In vitro study of the inactivation by dentine of some endodontic medicaments and their bases

Background: The aim of this study was to investigate the antimicrobial effect of endodontic medicaments and their bases in the presence of dentine powder. Methods: The medicaments tested were Ledermix paste, Pulpdent paste, a 50:50 combination of the Pulpdent:Ledermix and their bases. The test organism was Enterococcus faecalis ATCC 29212. The presence or absence of dentine was examined as well as the effect of autoclaving dentine. Serial dilutions of samples at 1 hour, 1 day and 3 days were used for colony counting. The effects of dentine powder on pH for saturated Ca(OH)₂ solution and Pulpdent paste at 1 hour and 24 hours were also measured. Results: Pulpdent and the 50:50 combination of Pulpdent:Ledermix completely inhibited the growth of E. faecalis from 1 hour onwards, and these results were not affected by the presence/absence of dentine powder, pre‐incubation period, timing of autoclaving, or exposure time. Saturated solutions of Ca(OH)₂ are prone to inactivation by dentine powder unlike Pulpdent paste. Ledermix paste took 3 days to exert a significant effect on the growth of E. faecalis. Conclusions: In this laboratory study, both Pulpdent and the 50:50 mixture of Pulpdent with Ledermix were effective medicaments against E. faecalis in the presence of dentine powder.     

Comparison of the instructional efficacy of an internet-based temporomandibular joint (TMJ) tutorial with a traditional seminar

There has been growing interest in the use of virtual learning environments (VLEs) by universities over the past decade to supplement traditional teaching methods. In this study a tutorial providing information about the temporomandibular joint (TMJ), temporomandibular disorders and teaching of a thorough TMJ examination was developed on a VLE platform to enable students to enhance their examination and diagnostic skills. The success of this VLE tutorial was compared with conventional teaching by a cross-over trial. Thirty students were initially randomly allocated to one of two groups; Group 1 completed the VLE tutorial and Group 2 attended the face-to-face seminar in the first instance. The groups then crossed over and had the other method of teaching provided. The findings from the cross-over trial and the students' feedback indicated that no differences were found between either teaching modes, and both are equally effective at delivering information to students. In addition, the order in which the students received the teaching did not make a difference, but giving the teaching twice reinforced their knowledge. There is a strong case to be made for introducing clinical lectures on a VLE platform, and this form of e-learning is, in general, well perceived by new generations of students.