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Featured researches published by J. van Aken.


Oral Surgery, Oral Medicine, Oral Pathology | 1966

The integral absorbed dose in conventional and panoramic complete-mouth examinations

J. van Aken; L.W.J. van der Linden

Conventional and panoramic complete-mouth x-ray examinations differ in so many respects that a comparison of the amount of radiation administered to the patient cannot be made with the use of exposure measurements in roentgens. The integral absorbed dose, being the total amount of energy absorbed by the patient and expressed in gram rads or ergs, is more suitable for this purpose. This dose was determined by measuring the amount of energy passing through a cross section of the x-ray beam before entering the patient. The integral absorbed dose for a complete-mouth examination with the conventional technique was, for two different techniques, 700 and 1,300 gram rads. It can be shown that, for the conventional technique, an increase in KVP reduces the amount of radiation which the patient receives, but not as dramatically as the skin exposure suggests. Examination by the panoramic technique with the Orthopantomograph delivers 110 gram rads to the patient, whereas 19 gram rads is administered during examination with the Panoramix. These findings constitute an argument in favor of the new techniques and emphasize the need to consider them when selecting a technique for a complete-mouth examination.


Oral Surgery, Oral Medicine, Oral Pathology | 1969

Optimum conditions for intraoral roentgenograms

J. van Aken

D ifferent methods for making intraoral roentgenograms have been pub lished.lm3 In these publications, three geometric variables in the technique can be found: 1. Length of the c,one---distance from the focal spot to the object. The distance can be short or long as represented by the short-cone and longcone techniques. 2. Film placement. The film can be placed in contact with the teeth and the soft tissues and fixed in position by the patient’s fingers, or it can be placed in a position not completely determined by the contour of the soft tissues with the aid of a film holder. 3. Angulation of the x-raay beam. Different angulations of the x-ray beam are used, depending on the principles of the technique used. The beam may be directed at right angles to the tooth when the film is parallel with the tooth, or the beam may be at right angles to the plane bisecting the angle between the tooth and the film (bisecting-the-angle technique). The technique utilizing the beam at right angles to the tooth is most frequently described in connection with the utilization of a long cone, whereas the bisecting-the-angle procedure is most frequently applied with a short cone. In Part I of the present article the image formation will be studied as influenced by (a) the length of the cone, (b) the film placement, and (e) the angulation of the x-ray beam. Anatomic or other practical limitations will not be considered. In Part II the anatomic and practical limitations will be studied, and a search will be made for the best possible compromise. Part III will describe an attempt to standardize a technique that is in close agreement with the conclusion drawn from Part II.


Cellular and Molecular Life Sciences | 1992

Photon emission in tumor biology.

R. van Wijk; J. van Aken

Photon emission from mammalian cells has been subject of study for many years. Growing research activity is directed on the photon emission within the field of tumor biology. These studies, applying high-sensitivity photon counting methods, have paid attention to several aspects, including photon emission from serum of tumor-bearing animals, photon emission of tumors and of isolated tumor cells. In addition, research activity is increased with respect to the photon emission by white light from cultured tumor cells. In this review we report on the different aspects of spontaneous and induced photon emission of tumor cells as compared to normal cells. Throughout these studies the question of a functional biological role of this spontaneous and light-induced photon emission has been raised and some different points of view will be discussed.


Oral Surgery, Oral Medicine, Oral Pathology | 1973

The origin of localized increased radiopacity in the dentin

L.W.J. van der Linden; J. van Aken

Abstract It has been shown by electron probe studies that the radiopaque dentin under restorations is the result of the presence of tin or zinc. In carious areas the reduced absorption of x-rays by decalcification may be overcompensated by the effect of tin or zinc present in this soft material. The concentrations found were for both zinc and tin approximately 1 to 10 per cent. Phantom experiments proved that the recorded concentrations can produce the observed increase in absorption of x-rays. Some extracted carious teeth which were filled and incubated for 2 to 3 years showed an increased radiopacity of the dentin similar to the radiopacity seen in radiographs of patients.


Environmental Management and Health | 1994

A Molecular Basis for Understanding the Benefits from Subharmful Doses of Toxicants

R. van Wijk; H. Ooms; F. A. C. Wiegant; J. E. M. Souren; J.H. Ovelgönne; J. van Aken; A. W. J. M. Bol

In the past many scientists have published papers on hormesis, on molecular stress responses, and on the similia principle in homoeopathy. Very few, however, have stressed a common base of interdependence of these fields. Reviews the most important of these studies to demonstrate their evolution and their mutual importance. Furthermore, a multidisciplinary approach is chosen to demonstrate research into the beneficial effects of subharmful doses of toxicants administered in suboptimal conditions (such as in stressed or injured organisms and cells).


Oral Surgery, Oral Medicine, Oral Pathology | 1979

Factors influencing the design of aiming devices for intraoral radiography and their practical application

J. van Aken; J.W. Verhoeven

Intraoral roentgenograms can be made according to the long-tube paralleling technique utilizing aiming devices. These instruments consist of a bite block, an indicator rod, and a collimator plate. For the position of the film in relation to the bite block surface, the following data are decisive and therefore studied: the length of the teeth to be radiographed, the enlargement as a result of the divergence of the x-ray beam, and the periapical area necessary for the interpretation and mounting of the roentgenograms. As a result, the bite blocks of the instruments were provided with three vertical steps to permit different film positions needed for the specific situation in the different regions of the mouth. The use of the correct film positions results in roentgenograms with a high diagnostic value. In order to reduce the patients radiation dose the aiming devices include a collimator plate. A description is given of the data used for the design of the plate.


Cellular and Molecular Life Sciences | 1999

The effect of temperature and protein synthesis on the renaturation of firefly luciferase in intact H9c2 cells

J. E. M. Souren; F. A. C. Wiegant; P. van Hof; J. van Aken; R. van Wijk

A mild increase in temperature that does not exert an effect on tolerance development or synthesis of heat shock proteins (Hsps) in control cells can stimulate these processes when applied to cells that have previously been heat shocked. To study the underlying mechanism of this effect, H9c2 cells were stably transfected with the gene encoding firefly luciferase (Luc). Heat-shock-induced inactivation of Luc and its subsequent reactivation is frequently used as a model for cellular protein denaturation and renaturation. Luc reactivation was determined following a damaging heat shock (43 or 44 °C for 30 min) in cells that were subsequently exposed to either control temperatures (37 °C) or various mild hyperthermic conditions (from 38.5 to 41.5 °C for 1 h). To prevent changes in Luc activity consequent to new synthesis of Luc, Luc reactivation was monitored in the presence of cycloheximide, an inhibitor of protein synthesis. The results showed that reactivation of Luc was inhibited when heat-treated cells were post-treated under mild hyperthermic conditions. The observed increase in Hsp synthesis under mild hyperthermic post-heat shock conditions therefore appears to be the result of an increase in the period during which denatured proteins are present. In addition, we studied Luc reactivation in the absence of protein synthesis inhibitors. This condition led to much higher Luc activity. By estimating half-life times of Luc, the contribution of new Luc synthesis in this recovery could be determined, and only partially explained the observed increase in Luc reactivation after heat shock. Thus the synthesis of other proteins must be important for the renaturation of heat-damaged proteins.


Cell Biology International Reports | 1979

Induction of tyrosine aminotransferase by dibutyryl cyclic-AMP in synchronized hepatoma cells

K. W. van de Poll; J. van Aken; R. van Wijk

In Hepatoma Tissue Culture (HTC) cells induction of tyrosine aminotransferase (TAT) by dibutyryl cAMP (DBcAMP) is regulated at some posttranscriptional step. In synchronized HTC cells TAT can be induced by DBcAMP in late G1 and in the S phase of the cell cycle only.


Oral Surgery, Oral Medicine, Oral Pathology | 1982

The optimum circular field size for dental radiography with intraoral films

F.J. van Straaten; J. van Aken

Intraoral radiographs are often made with circular fields to irradiate the film, and in many instances these fields are much larger than the film. The feasibility of reducing a circular radiation field without increasing the probability of excessive cone cutting was evaluated clinically, and an optimum field size was determined. A circular radiation field 4.5 cm. at the tube end was found to minimize cone cutting and reduce the area of tissue irradiated by at least 44 percent. Findings suggest that current I.C.R.P. recommendations for a 6 to 7.5 cm. diameter circular field may be too liberal.


The Holocene | 2016

Centennial-scale lake-level lowstand at Lake Uddelermeer (The Netherlands) indicates changes in moisture source region prior to the 2.8-kyr event

Stefan Engels; M.A.J. Bakker; S.J.P. Bohncke; C. Cerli; Wim Z. Hoek; Boris Jansen; T. Peters; H. Renssen; Dirk Sachse; J. van Aken; V. van den Bos; B. van Geel; R. van Oostrom; Tim Winkels; M. Wolma

The Uddelermeer is a unique lake for The Netherlands, containing a sediment record that continuously registered environmental and climatic change from the late Pleistocene on to the present. A 15.6-m-long sediment record was retrieved from the deepest part of the sedimentary basin and an age–depth model was developed using radiocarbon dating, 210Pb dating, and Bayesian modeling. Lake-level change was reconstructed using a novel combination of high-resolution palaeoecological proxies (e.g. pollen, non-pollen palynomorphs, chironomids), quantitative determinations of lake-level change (ground-penetrating radar), and estimates of changes in precipitation (lipid biomarker stable isotopes). We conclude that lake levels were at least as high as present-day water levels from the late glacial to 3150 cal. yr BP, with the exception of at least one lake-level lowstand during the Preboreal period. Lake levels were ca. 2.5 m lower than at present between 3150 and 2800 cal. yr BP, which might have been the result of a change in moisture source region prior to the so-called 2.8-kyr event. Increasing precipitation amounts around 2800 cal. yr BP resulted in a lake-level rise of about 3.5–4 m to levels that were 1–1.5 m higher than at present, in line with increased precipitation levels as inferred for the 2.8-kyr event from nearby raised bog areas as well as with reconstructions of higher lake levels in the French Alps, all of which have been previously attributed to a phase of decreased solar activity. Lake levels decreased to their present level only during recent times, although the exact timing of the drop in lake levels is unclear.

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Boris Jansen

University of Amsterdam

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P.F. van der Stelt

Academic Center for Dentistry Amsterdam

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X.L. Velders

Academic Center for Dentistry Amsterdam

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