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Biomedical subjects

M M Vrijhoef

Publications and source records attributed to M M Vrijhoef.

At least 55 records · Page 3Linked to original sources
PubMed1986

Facial injuries sustained during sports and games.

This study is an investigation into the number and type of facial injuries due to sports and games, because no detailed information on these dental misfortunes could be found in the literature. The group investigated consisted of 319 patients, treated at the Department of Oral and Maxillo-Facial Surgery, Nijmegen in the period January 1, 1971-December 31, 1978. Facial injuries were classified into different types of fractures according to site as also were further series of associated injuries. Males were shown to be more prone to facial injuries than females (2.4:1). In the age group 15-40 years, males proved to be more prone to such injuries than the age group under 15 years. The major part of the injuries is due to fractures of the alveolar process and/or luxation of teeth (59.6%), the zygomatic bone and arch (24.2%) and the mandible (15.3%). Fractures of the maxilla and the nose were rarely seen.

Adolescent↗
PubMed1986

Creep versus marginal fracture of amalgam restorations.

In the literature there is controversy over the existence of a correlation between creep and marginal deterioration of amalgam restorations. It was the aim of this study to re-investigate this correlation. In five clinical trials, 2068 amalgam restorations were made of six conventional alloys and ten high copper systems. The results show a correlation between creep and marginal fracture in the conventional, low copper amalgams. No correlation could be found for the group of high copper, non-gamma-2, amalgams. It is emphasized that dental practitioners should not buy their amalgam alloy on the basis of creep data, because wrong decisions might be taken. Evidence from a controlled clinical study is a more reliable criterion.

Chemical Phenomena↗
PubMed1986

A modified technique to determine the tear energy of impression materials.

A modified method to determine tear energy of impression materials is described. Trousers-shaped specimens were prepared between two platens. They are different from those used before in that a V-shaped line is created so as to guide tear growth, and the thickness gradually increases, then remains constant and, ultimately, decreases instantaneously. The specimens were tested at ten different rates between 0.2 and 50 cm/min. lambda can be computed from the force-time diagram. Six different materials were tested: two condensation silicones, Xantopren regular (Bayer, FRG) and Xantopren light; a polyvinylsiloxane, Reprosil regular (DeTrey, Switzerland); a polysulphide Coeflex regular (Coe, USA); a polyether, Impregum (Espe, FRG); and an alginate, Cavex, Fast Set, Dust Free (Keur & Sneltjes, The Netherlands). Tear strength (in kJ/m2) variations at rates between 0.2 and 50 cm/min are as follows: Xantopren regular, 0.37-0.64; Xantopren light, 0.29-0.46; Coeflex, 1.10-5.29; Reprosil, 0.66-1.07; Impregum, 0.62-1.04; Cavex, 0.22-0.37. These values are consistent with those reported before. It might be concluded that the new test method gives reliable tear energy values.

Alginates↗
PubMed1986

Composite versus amalgam restorations. A three-year clinical evaluation.

In a clinical study the behaviour of posterior composite restorations was evaluated. For the study, 232 Class I or II restorations in premolars and molars were made by three operators in a group of forty-nine adult patients. Each patient underwent one or two series of four restorations. The materials within a series were a strontium glass filled composite (Profile), a microfilled composite (Estic MF), a macrofilled composite (Adaptic Radiopaque) and a high copper amalgam (Dispersalloy). The last two materials served as a negative and positive controls respectively. For a period of 3 years the clinical behaviour was evaluated yearly with the USPHS criteria (anatomic form, marginal adaptation, colour match, marginal staining and caries). Differences in the ratings of the criteria between materials, tooth type and evaluation year were tested statistically for significance. The number of restorations replaced after 3 years in clinical service was eight (= 3.6%). The results showed that the material, tooth type and evaluation year all have an influence on the anatomic form and the colour match of the restoration. The behaviour of the three composites with respect to colour match, marginal adaptation and marginal staining was acceptable. For anatomic form, however, only the behaviour of the microfilled composite Estic MF was still acceptable after 3 years.

Adult↗
PubMed1985

A method to determine the loss of substance of dental restorations.

A method is described for quantitative in vivo wear measurements on Class I and II composite restorations. Class I gold inlays were made in an acrylic premolar and molar. Over the occlusal parts of the teeth cast silver caps were made after releasing the surface of the inlay with tinfoil. Wear on the restorations was simulated by grinding away some gold from the inlay. Silicon impressions of the teeth were made with the caps both before and after this simulation. The volume and the average thickness of the removed gold was measured from the weight of the enclosed impression material in the cap before and after the wear simulations, the density of the tinfoil and the impression material as well as thickness and the weight of the tinfoil-release. Values expected for the volume and the average thickness of the removed gold were calculated from the weight of the restored acrylic teeth before and after the wear simulation, the weight, the density and the thickness of the tinfoil and the density of the gold used for the inlays. Measured and expected values are linearly correlated (r = 0.97). An average wear thickness of the occlusal surface of a particular tooth of at least 30 micron can be detected. Because of its simplicity, inexpensiveness and accuracy the wear measurement method is highly productive and suitable for large scale and long-term clinical research on the wear behaviour of posterior composites.

Acrylic Resins↗
PubMed1985

Cost benefit analysis of direct posterior restorations.

A clinical study was conducted in which three operators made 232 Class I and Class II composite and amalgam restorations in a group of 49 adult patients. The time for different parts of the operative process was measured. The time periods were analysed as to the influence of the factors operator, tooth type and number of surfaces, by an analysis of variance (ANOVA). Results show that the various factors have a significant influence on the total treatment time. The treatment time for amalgam restorations is equal to the treatment time of composite restorations. The productivity of making restorations from the 'best' available amalgams, i.e. the amalgam with an extrapolated half-life time of more than 20 yr, turns out to be more than 3-4 times better than that of the 'worst' amalgams (half-life time 4 1/2-8 yr) and more than two times better than that of making restorations of the best composite material, used in this study (extrapolated half-life time of Estic MF is 10 yr).

Adult↗
PubMed1984

The influence of polishing on the marginal integrity of amalgam restorations.

The influence of the polishing procedure on the marginal integrity of amalgam restorations was investigated in a clinical study. In this study two operators each made 150 class I or II restorations in a group of forty-eight adult patients. The restorations were made in a series of six per patient. Within each series, two restorations were made of three different high copper amalgam alloys. Only one restoration of each pair was polished. From each restoration a black and white photograph was taken after finishing and after 0.5, 1.0 and 1.5 years. The marginal integrity of each restoration at the four time periods was quantified with a 6-point photo rating scale. The quantifications were analysed as to their variance for the factors alloy, polishing procedure, operator and patient. After finishing, all four factors had a significant influence on the marginal integrity. From 0.5 to 1.5 years, the influence of the factors alloy, polishing procedure and patient were very significant. The influence of the patient on marginal integrity was more or less equal to that of the alloy. The size of the polish influence was relatively small. Therefore, it was concluded that the contribution of the polishing procedure to the prevention of marginal deterioration was questionable.

Adult↗
PubMed1984

Long-term influences on marginal fracture of amalgam restorations.

A clinical study was conducted in which two operators made 180 class I or II amalgam restorations in a group of fifty-seven adult patients. The restorations were made in a series of six per patient. Each restoration was made of a different alloy (five conventional composition alloys and one high copper alloy). During a period of 5 years the marginal fracture formation of all restorations was yearly quantified with a 6-point photo rating scale. The quantifications were analysed as to their variance for the factors alloy, patient and operator. The relative importance of significant factors was calculated. The results show that for a period of 5 years the alloy, patient and operator all had a significant influence on the marginal fracture formation. The operator influence was stable in time. This factor was relatively small because the operator sample was highly selected. After 1 year the influence of the patient on marginal fracture was equal to that of the alloy. The patient influence in time was stable. However, the alloy influence increased considerably. The longer the service time of the amalgam restoration the more important becomes the influence of the alloy on the marginal fracture formation.

Adult↗
PubMed1983

Phenomenological model of creep of dental amalgam.

Earlier work revealed that creep of a particular dental amalgam can be described by the model F(t) = F0 exp (t/t0)m. Here F(t) is the creep compliance at time t, whereas F0, t0 and m are constants of the model. In the previous study only three alloys were used. It was the aim of this study to investigate the factor alloy more thoroughly. After specimen preparation, the nineteen different amalgams were aged at 37 degrees C for either one day or one week. Then creep was determined at a temperature of 22.5 degrees C and a compressive stress of 117 MN/m2. F0 turns out to depend upon both the ageing time as well as on the choice of the alloy. As expected, t0 shows up substantial differences between the respective amalgams, whereas the differences between the two ageing are absent or relatively small. The factor alloy significantly influences m. However, the ageing time exerts no significant influence upon m.

Chemical Phenomena↗