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Biomedical subjects

A J Plasschaert

Publications and source records attributed to A J Plasschaert.

At least 19 recordsLinked to original sources
PubMed2001

Substance use among Dutch dental students.

OBJECTIVES: The objectives were to assess the prevalence of substance use among Dutch dental students and to determine their attitudes about substance use and its consequences. METHODS: In association with a national study of drug use among US dental students, a questionnaire was translated from English into Dutch and administered to dental students at two dental schools in The Netherlands. Students received an anonymous 115-item questionnaire in the fall of 1996. RESULTS: Alcohol was the students' drug of choice for lifetime (95%), past year (94%) and past month (88%) use. No significant correlations were found between alcohol use and gender, schools, and years in dental education. In the past month, 58% of students reported drinking on 5 or more days; 53% had 5 or more drinks on the same occasion, 20% had 5 or more drinks on the same occasion on 5 or more days; and 17% reported getting drunk at least monthly. Prevalence rates for past month use of tobacco was 24% and marijuana, 4%. Male students smoked twice as much as females, with significant differences found for all three periods of use (X2>19.00, P<0.01). When asked whether their schools offered policies and education programs on alcohol and other drugs, 52% of students reported that these were not available. CONCLUSIONS: Dental schools should develop effective programmes to educate students about responsible use of alcohol and other licit and illicit drugs. Schools should also inform students about their susceptibilities to substance abuse and dependency.

Adult↗
PubMed2001

Effect of composite resin placement techniques on the microleakage of two self-etching dentin-bonding agents.

PURPOSE: To evaluate microleakage of Class V resin-based composites (RBC) bonded with two self-etching dentin adhesive systems. Class V cavities were restored with either one or three increments of RBC to determine whether the restorative method affected microleakage. MATERIALS AND METHODS: 60 extracted human premolars and molars were randomly assigned to 6 groups for bonding with Clearfil Liner Bond 2V or Etch & Prime 3.0 or Prime & Bond NT. The latter, using a total-etch technique, was used as a control. Cavities were cut in both the buccal and lingual surfaces. Half of each preparation was in enamel and half was in cementum/dentin. The teeth were thermocycled and the restorations examined microscopically for leakage using Procion Brilliant Red as a marker. SEM microphotographs were prepared from dye-labeled and non dye-labeled areas to illustrate the micromorphology of the systems. RESULTS: None of the groups showed microleakage at the enamel margins. All groups showed microleakage at the gingival margins. At the gingival margin, there was no significant difference between the groups irrespective of the bonding material (Kruskal-Wallis: ANOVA P=0.2113). No significant difference was observed with each material when the bulk filling (one increment) technique was compared with the three-increment technique. SEM showed that the self-etching materials produced a shallower depth of etch, and a less abundant resin tag complex than the material using a separate phosphoric acid gel. In dye-labeled areas, debonding was predominantly cohesive in resin. CLINICAL SIGNIFICANCE: Gingival margin microleakage is not prevented by either restoring cavities with self-etching materials of the control using a total-etch technique.

Acid Etching, Dental↗
PubMed2000

Marginal leakage of filled dentin adhesives used with wet and dry bonding techniques.

PURPOSE: To evaluate the effect of wet and dry bonding on microleakage of Class V restorations bonded with three filled bonding agents. MATERIALS AND METHODS: Sixty extracted human premolar and molar teeth were randomly assigned to five groups for bonding with OptiBond Solo, PermaQuick PQI, Prime & Bond NT (one coat), Prime & Bond NT (two coats) and Prime & Bond 2.1, as a control material. Cavities were cut in both the buccal and lingual surfaces. Half of each preparation was in enamel and the other was in cementum/dentin. The cavities were restored with resin-based composite after the application of dentin bonding agents using a wet and dry technique for each material. The teeth were stored in distilled water for 6 days at 37 degrees C, thermocycled, and the restorations examined microscopically for leakage using Procion Brilliant Red as a marker. RESULTS: All groups showed microleakage at both the enamel and dentin margins. At the gingival margin, there was a significant difference between the groups for wet bonding (P = 0.0349) but not for dry bonding (P = 0.9983) (Kruskal-Wallis test). There was no significant difference between the groups at the enamel margin (wet bonding: P = 0.9999, dry-bonding: P = 0.9304) (Kruskal-Wallis test). The wet-bonding technique was compared with the dry-bonding technique for each material at both the gingival and enamel margins and no significant differences were observed (in all cases P > 0.5) (Mann-Whitney U-test).

Analysis of Variance↗
PubMed1997

The effect of a multimedia interactive tutorial on learning endodontic problem-solving.

New technology may create additional opportunities for learning in dental education. One of these new features is a multimedia approach, courseware combining sound, text, stills and video with interactive learning. A multimedia program was developed to train dental students and dental practitioners in decision making and problem solving in endodontics. This study compared the effects of the multimedia program with a more traditional approach consisting of written information, without interaction. 28, 4th-year dental students at the University of Kentucky in Lexington, KY, USA were randomly assigned to the multimedia or the text-based groups. They were given a written pre-test using 2 cases of dental pain and were instructed to study independently using either the multimedia program (group A) or the written information (group B). No restrictions were imposed on the amount of time to be invested, and the total study time was recorded for each student. 3 weeks after the pre-test, the students completed the post-test. A total of 18 students completed both the pre-test and the post-test and their scores were included in the final data. Statistical analysis of the average scores using paired t-tests revealed no significant difference between the performance of the students in either group, indicating that the multimedia approach to learning endodontic problem solving may successfully replace traditional learning strategies.

CD-I↗
PubMed1995

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↗
PubMed1995

Opinions and experiences of dental students and faculty concerning computer-assisted learning.

This study assessed the opinions and attitudes of faculty and students concerning the use of computer-assisted learning (CAL) at three different dental schools on two continents (Manchester, U.K.; Nijmegen, The Netherlands; and Lexington, Kentucky, U.S.A.). In each school students and faculty received a questionnaire; faculty by internal mail, students at the end of a lecture. Response rates for students were 76 percent in Manchester, 64 percent in Nijmegen, and 91 percent in Lexington. The respective figures for faculty were: 42 percent, 47 percent, and 39 percent. In all three schools approximately 50 percent of students had a computer at home. Students in Lexington and Manchester seemed to be more advanced in the use of computers for self-instructional learning. Students and faculty in Lexington had more experience with interactive multimedia than did those in Manchester and Nijmegen. In general, Lexington students were somewhat more familiar with computers and CAL than Manchester students, with Nijmegen showing the lowest percentages. Few CAL programs were available at any school, with small numbers of dental students having been exposed to programs involving animation (vision, sound). The majority of students are of the opinion that the use of computers for learning is not impersonal, nor difficult, but challenging and motivating. There is good agreement that if a program is to be bought or developed, it should be a combination of text, images, and sound. It is postulated that concerted action by dental schools is required to realize the potential of CAL in dental education, and that international organizations should give consideration to coordinating this action.

Adult↗
PubMed1993

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↗
PubMed1992

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↗
PubMed1992

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↗
PubMed1992

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↗
PubMed1991

[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↗
PubMed1991

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↗
PubMed1991

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↗
PubMed1991

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↗
PubMed1991

[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↗
PubMed1991

[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↗