Decision making in restorative dentistry: intuition or knowledge based?
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Decision Making↗
Biomedical subjects
A J Plasschaert
Publications and source records attributed to A J Plasschaert.
Research directions and output in European dental schools.
Information pertaining to the research directions and output of dental schools in different countries is of importance in understanding intra- and inter- national differences amongst groups of dental practitioners. The research output of European dental schools has been assessed quantitatively and qualitatively on the basis of published abstracts of research presentations at IADR-meetings during 1993. These data are compared with comparable data for 1990/91. The results indicate that European dental schools are substantially different in terms of research output relative to total population, with the UK at one extreme and Italy at the other. The UK, Denmark, The Netherlands, Sweden and Norway are highly ranked while Portugal, Spain, Italy, Germany and France have low rankings, according to the method used. Periodontology, plaque, dental materials, and restorative dentistry would appear to be the principal foci of research. Possible ways of strengthening the coordination and the efficiency and effectiveness of dental research at the European level are discussed. It is suggested that the creation of centres of excellence and research networks are approaches to be considered. An unresolved problem will be the contradictory requirements from educational and research perspectives in relation to the training of dental practitioners.
Dental Materials↗
Failure behaviour of fatigue-tested post and cores.
Evaluation of the long-term behaviour of restorations in clinical trials can be time-consuming. A partial alternative to the clinical trial can be found in mechanical fatigue testing. The aim of this study was to evaluate the failure behaviour of post and core restored teeth when subjected to cyclic mechanical loading and to compare it with quasistatic failure. Eighty seven premolar teeth were restored with a titanium alloy post and an amalgam or composite core. Five to 21 days after restoration, the specimens were subjected to cyclic loading (frequency 5 Hz), at an angle of 45 degrees to the long axis of the tooth. The load levels were 50, 60, 65 and 70% of mean quasistatic failure loads. The specimens were divided into three groups according to their survival time: short (S) (< 10(4) cycles), intermediate (I) (10(4) < or = life < 10(5) cycles) and long (L) (> or = 10(5) cycles). For both core materials failure behaviour changed after approximately 10(5) cycles, and the change was most marked for the composite group. Catastrophic fatigue failure consisted of core fracture in the amalgam group (three times) and of post fracture in the composite L group (four times). Three post fractures occurred at a site theoretically predisposed to fatigue failure. It was concluded that fatigue failure characteristics of post and core restorations may be very different from those of quasistatic failure. Therefore, in addition to quasistatic tests, fatigue tests are necessary, covering at least 10(5) load cycles.
Bicuspid↗
The Weibull distribution applied to post and core failure.
In this study, data on initial failure loads of direct post and core-restored premolar teeth were analyzed using the Weibull distribution. Restorations consisted of a prefabricated titanium alloy post, and an amalgam, composite or glass cermet core buildup in human upper premolar teeth. The specimens were subjected to compressive forces until failure at angles of 10, 45 and 90 degrees to their long axis. The two- and three-parameter Weibull distributions were compared for applicability to the failure load data. For estimation of the parameters of the two-parameter distribution: sigma 0 (reference stress) and m (Weibull modulus), linear regression was used. In this distribution, it is assumed that the third parameter, sigma u (cut-off stress), equals 0. The Maximum Likelihood (MLH) method was used to estimate all three parameters. It was found that the choice of distribution has a strong influence on the estimated values and that the three-parameter distribution is best fitted for the failure loads in this study. Comparisons were made between the failure probability curves as found by MLH estimation for the different core materials and loading angles. The results indicated that the influence of loading angle on the failure mechanism was stronger than that of core material.
Bicuspid↗
Failure characteristics of endodontically treated premolars restored with a post and direct restorative material.
Ninety-one extracted maxillary premolar teeth were restored with a prefabricated post and amalgam, composite resin or glass-cermet core. Each group was again divided into three groups of 9-13 teeth to be subjected to an increasing load in one of three standardized directions (10, 45 and 90 degrees to the long axis of the tooth). Failure load and characteristics of failure were recorded. The glass-cermet-restored teeth had a lower strength than the other groups for every load direction (Student's t-test: P less than 0.01). Amalgam and composite resin groups showed a significant difference only for the 10 degrees loading condition (Student's t-test: P less than 0.02). Teeth restored with amalgam cores displayed a higher mean failure load, in combination with a 46% occurrence of root fracture.
Analysis of Variance↗
Fatigue behavior of direct post-and-core-restored premolars.
Evaluation of long-term mechanical behavior of new types of restorations in clinical trials is time-consuming. A partial alternative can be found in experimental fatigue-testing, which simulates accelerated mechanical deterioration. The aim of this study was to determine the feasibility of using fatigue-testing of a complex dental restoration and to evaluate the mechanical fatigue behavior of premolar teeth restored with a titanium alloy post and an amalgam or composite core. Eighty-seven human upper premolar teeth were decoronated, embedded, and restored with a prefabricated post of 1 mm diameter. The teeth were randomly assigned to one of two groups corresponding with a core build-up of amalgam or chemically-cured core composite, respectively. Five to 21 days after restoration, the specimens were subjected to cyclic loading (frequency, 5 Hz), at an angle of 45 degrees to the long axis of the tooth. The boundary technique was used for determination of the mean fatigue strengths of the restorations at 10(4), 10(5), and 10(6) cycles, simulating up to 1-3 years of clinical functioning. Mean fatigue strength was expressed in percentage of initial strength: For 10(4), 10(5), and 10(6) cycles, the results were 66%, 58%, and 52%, respectively, for the amalgam and 62%, 62%, and 53% for the composite group. It is concluded that fatigue-testing of more complex systems is possible, if a suitable testing method is selected. The restorations showed a comparable strength reduction after 10(6) cycles of about 50% of their initial strength. The composite core build-up showed a behavior less predictable than that of the amalgam, which might be attributed to handling parameters.
Alloys↗
[Veterinary dentistry in dogs and cats; a survey among veterinarians].
To gain an insight into the prevalence of dental disease in dogs and cats and forms of dental treatment, a postal survey was conducted among veterinarians in the Netherlands. Seventy per cent of the veterinarians replied that they made routine oral examinations of dogs and cats. Of dental diseases observed in dogs and cats periodontal diseases were stated to be the most common dental problem. Dental treatments, such as removal of calculus and extractions, were performed by nearly all veterinarians. Fifty per cent of the veterinarians asked for assistance of a dentist when a dental treatment could not be carried out by themselves. More education in veterinary dentistry to veterinary students and veterinarians is required.
Animals↗
Estimation of the mechanical lifetime of dental restorations: method and preliminary results.
To assess the clinical performance of restorative materials with respect to mechanical failure, the shape of the restoration, the strength and fatigue properties and the loading history are important. This study deals with the feasibility of a method to estimate the mechanical lifetime of dental restorations. The method takes into account that the mechanical lifetime is a stochastic quantity determined by shape, strength and fatigue properties and by the cyclic nature of the mastication forces. The general outline of the method is described and the necessary experimental data are discussed. Preliminary estimates of the lifetime of a composite and an amalgam restoration are made. The method is found to be feasible and the estimated lifetimes of the restoration are of the same order of magnitude as found clinically.
Bicuspid↗
Applicability of an image analysis system in alveolar bone loss measurement.
Clinical and epidemiological studies in the field of periodontics and endodontics often utilize radiographs to monitor or measure the changes in bone structure and density. Periodontal bone loss or gain can be quantified on a radiograph by measurement of the distance between the bottom of the bony pocket and the apical contour of the involved tooth. The objective of this investigation was to study the accuracy of an image analysis system (IAS) to measure changes in height of the interproximal crest on radiographs. Artificial bone lesions were introduced in a dissectioned part of a human mandible. The distances between crest and apices were measured with a micrometer (MM). Radiographs were produced with horizontal and vertical deviations of 10 degrees. The radiographs were digitized and processed by computer. The landmarks in the digital image were enhanced mathematically and by histogram-based thresholding. The depth of the introduced defect was increased 6 times, followed by the measurement procedure. The IAS produced measurements of crown-apex distances with an accuracy of 0.066 to 0.358 mm. Repeated crest height measurements were recorded with an accuracy of 0.112 to 0.184 mm. Both the histogram-based binarization and the ellipse-fitting type of contour detection could be applied precisely. Misangulation errors during radiographic exposure of 10 horizontal or vertical did not statistically significant influence the IAS-measurements. The IAS can be applied in clinical trials and follow-up studies.
Alveolar Bone Loss↗
Trends in caries prevalence in 5-, 7- and 11-year-old schoolchildren in The Hague between 1969 and 1989.
Starting in 1969, periodic cross-sectional examinations of schoolchildren have been carried out in the city of The Hague. In 1989 the periodic examinations were continued and, in general, caries prevalence was found to be very low; D3MFS values ranged between 1.5 and 2.2 at age 11.8 years. Compared to 1984, 5-year-old-children of low and medium socio-economic levels (SES) in 1989 had significantly higher d3mfs values (p less than 0.01), mainly due to a marked increase in decayed surfaces per child; a significant increase in caries experience of the deciduous dentition amongst 7-year-olds of low social level was found (p less than 0.01). A further reduction of D3MFS values for 7-year-old children of low and medium SES could be observed in 1989 compared to 1984. Between 1978 and 1989 a marked D3MFS reductions amongst 11-year-olds in the three social levels was found. Possible explanations for the observed differences in caries experience between 1984 and 1989 are discussed.
Child↗
[Veterinary dentistry in dogs and cats. Results of a postal inquiry in The Netherlands].
In order to get insight in the prevalence of dental diseases in dogs and cats and dental treatments, a postal survey amongst veterinarians in the Netherlands was carried out. 70% of the veterinarians answered to practice routine oral examinations of dogs and cats. Of dental diseases observed in dogs and cats periodontal diseases were most often mentioned. Dental treatments as calculus removal and extractions were performed by nearly all veterinarians. 50% of the veterinarians asked for assistance of a dentist in case a dental treatment could not be performed by themselves.
Animals↗
[Trends in dental caries among five- and seven-year-old school children in The Hague. Is the caries prevalence among the young changing?].
Starting in 1969 cohort examinations on schoolchildren are carried out in the city of The Hague. In 1989 the periodical examinations were continued. Compared to 1984, five-year-old children of low and medium SES had in 1989 significantly higher d3mfs values, mainly due to a marked increase in decayed surface per child; a significant increase in caries experience of the deciduous dentition amongst seven-year-olds of low social level was found. A further reduction of D3MFS values for seven-year-old children of low and medium SES could be observed in 1989 compared to 1984. Compared to children of Dutch origin, children of ethnic minorities (Turkey and Marokko) had a significantly higher caries experience.
Child↗
Prevention of dental caries in The Netherlands.
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Adolescent↗
Prevalence and need for replacement of amalgam and composite restorations in Dutch adults.
In 1986, the first nationwide epidemiological survey of adult oral health and attitudes to oral health care was carried out in The Netherlands. One of the aims of this study was to evaluate the prevalence and the quality (in terms of need for replacement) of amalgam and composite restorations in the Dutch adult population. A group of 600 dentate individuals, 20-44 years of age, was examined. Stratified cluster sampling included as factors age, gender, socio-economic status, and area of residence. Two additional parameters were studied: frequency of visiting a dentist and type of health insurance. Oral examinations consisted of direct (mirror and explorer) and indirect (color slides and bite-wing radiographs) observations with use of well-defined criteria. On average, 13.4 restorations per individual were present, of which 23.3% were classified as unsatisfactory. A great difference in prevalence and quality data was found among several types of restorations. Test results (ANOVA) for effects of age, gender, socio-economic status, area of residence, frequency of visiting a dentist, and insurance on the prevalence of (un)satisfactory restorations resulted nearly always in significant effects of only age and frequency of visits to a dentist. There was a tendency (p less than 0.05) for the prevalence of (un)satisfactory restorations to be higher with increasing age.(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
A computer-aided image analysis system for area measurement of tooth root surfaces.
The characteristics of a computer-aided Image Analysis System (IAS) to conduct linear and area measurements on tooth root surfaces were investigated. The borders of the features to be measured were extracted from a digitized video image by histogram-based thresholding and binarization. The lengths and square areas were expressed in the number of pixels. The reference-length and area of one pixel were obtained through measurement of the diameter of a metal ball of known diameter in the same digital image. The validity of the IAS was tested using radiographs of teeth containing round metal restorations of known diameter and area. The accuracy of the length measurements ranged from -2.0 to 2.1%, whereas the accuracy of area measurement was between -5.3 and 0.8%. The precision of the IAS to identify the borders of a tooth root surface and to reproducibly calculate its area, expressed in a coefficient of variation, ranges from 0.49 to 4.11%. The results indicate that imaging techniques can be applied to obtain very accurate measurements of tooth root surfaces.
Dental Enamel↗
[Restoration of endodontically treated elements. A literature review on the mechanical behavior of post and core structures].
Rapid developments in dental health and science have resulted in an increasing number of teeth receiving post and core restoration. The dentist can choose from a wide range of restoration-modalities. Success or failure of these restorations largely depends on their ability to meet functional demands. This article presents a review of the literature on the mechanical behaviour of post-core restorations, as it is determined by functional forces, shape of the tooth and restoration and properties of the materials the construction incorporates. Some attention is drawn to the importance of failure characteristics in view of re-restoration possibilities. As a conclusion some guidelines for the use of post and core restorations in the general dental practice are formulated.
Bicuspid↗
[Dental aspects of aging].
The oral cavity fulfils important functions also at an older age in life. In getting older the chances to loose quality in these functions will increase. The following three problem areas are relevant in this respect: teeth can decay by dental caries or by progressive wear; the gums and periodontal tissues may develop serious inflammation and degeneration; finally after extraction of teeth dentures can be provided, but may create new problems in turn. Dental life can be extended by preventive measures and restorative treatment. New developments in the areas of so-called adhesive dentistry and dental implantology may contribute to quality improvement. Based on recently published epidemiological data and on computer simulation studies it is expected that there will be no major changes in need and supply for dental care in the dutch population. However, care spent on children and adults will shift towards care for adults and elderly.
Adult↗
The thermal diffusivity of two replica resins.
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Diffusion↗