J J ten Bosch’s research while affiliated with University of Groningen and other places

There is no consensus about the definition and progression of outer and wall lesions in secondary caries. In this study we investigated whether lesion progression is influenced by an adjacent composite restoration and whether wall lesions develop at the composite-tooth interface. In order to study the appearance and progression of approximal primary caries lesions and lesions next to composite restorations, 16 samples were placed in a full denture of each of 8 subjects. Each denture housed 4 restored and 4 unrestored enamel samples and similarly 8 dentin samples. All samples were distributed over 2 sample holders, in each of which 4 approximal spaces were simulated. Every 4 weeks the sample holders were microradiographed using transversal wavelength independent microradiography and lesion depth was measured. At the end of the study, after 20 weeks, the lesion depth of the outer lesions was 0-350 microm for enamel and 0-750 microm for dentin. The estimated difference in progression between secondary and primary lesions (1.1 microm/4 weeks, 95% CI: -9.2 to 11.4 microm) was not statistically significant (p = 0.83). Secondary outer lesions appeared and progressed as primary caries lesions. No clear wall lesions were found next to composite, but they were observed next to acrylic resin.

This paper describes a microradiographic method for measuring mineral concentration in a transversal geometry with thick (< or =3.2 mm) sections: transversal wavelength-independent microradiography (T-WIM). It was tested on bovine enamel and dentin samples in vitro, and the results were validated with those of transversal microradiography (TMR). 48 enamel and 48 dentin samples (3.2 x 3.2 x 1.5 mm) were embedded in acrylic resin, randomly divided into six groups of 8 dentin or 8 enamel samples, and demineralized for 0 (sound control), 1, 2, 3, 4, or 5 weeks. For T-WIM, samples were imaged on film with polychromatic 40-kV Cu X-rays with an Al (0.25 mm)/Ni (0.02 mm) filter together with an aluminium/zinc step wedge. TMR slices (about 80 mum for enamel and about 130 mum for dentine) were subsequently cut from the centre of the samples and subjected to TMR. Microradiographs from both methods were digitized and image analysis software was used to calculate lesion depth and mineral loss. The relations between T-WIM and TMR results for mineral loss (DeltaZ) and lesion depth were nearly linear (r > or = 0.96) for both enamel and dentin. The slopes of the regression lines were between 0.99 and 1.02 except for DeltaZ in dentine, which was 0.89. It was concluded that T-WIM is a suitable method for TMR on thick samples.

The currently available instrument for electrical detection of occlusal caries lesions [Electronic Caries Monitor (ECM)] uses a site-specific measurement with co-axial air drying. The reproducibility of this method has been reported to be fair to good. It was noticed that the measurement variation of this technique appeared to be non-random. It was the aim of this study to analyse how such a non-random reproducibility pattern arises and whether it could be observed for other operators and ECM models. Analysis of hypothetical measurement pairs showed that the pattern was related to measurements at the high and low end of the measurement range for the instrument. Data sets supplied by other researchers to a varying degree showed signs of a similar non-random pattern. These data sets were acquired at different locations, by different operators and using 3 different ECM models. The frequency distribution of measurements in all cases showed a single or double end-peaked distribution shape. It was concluded that the pattern was a general feature of the measurement method. It was tentatively attributed to several characteristics such as a high value censoring, insufficient probe contact and unpredictable probe contact. A different measurement technique, with an improved probe contact, appears to be advisable.

Drying effects in 14 natural lesions were studied with quantitative light-induced fluorescence and optical pathlength spectroscopy. Results were compared with clinical judgments of the lesion surface and microradiographical characterizations of the lesions. Relative fluorescence and average pathlength decreased as a function of drying time with a decay time ranging from 35.5 to <1 min. Depth and mineral loss correlated with average pathlength total changes (r = -0.79/-0.60, respectively) and poorly with total fluorescence changes (r approximately = 0.3). The decay time of the drying process for the relative fluorescence correlated well with a theoretical model based on water diffusion in lesion and surface layer, but only for large decay times. Clinical judgments could not be related to the surface layer properties or the changes in the average pathlength, but were weakly related to the changes in the relative fluorescence. We conclude that (i) fluorescence effects are mostly due to the screening by the lesion of the fluorescence from the dentin and enamel-dentin junction; (ii) water evaporation in lesions conforms to the diffusion laws only in large lesions with low surface layer penetrability; (iii) the evaporation process is controlled by the surface layer only for small surface penetrabilities (approximately 0.1 vol% microm(-1)).

He was supposed to retire in 1999, and the abovementioned international symposium was to be held under the name "Dental research into gear". This title was derived from a wooden sign that used to decorate his office: "Put brain into gear, before mouth is opened." Those who knew him would agree that this admonition provides a snapshot of Arends' character—he liked to put things "into gear" without too much ado. A citation analysis revealed that Arends authored/co- authored over 350 peer-reviewed publications and had been cited over 3000 times (through 1998). Scientifically, his most productive period was in the mid-1980s, and more than 70 of his papers (over 20%) were the result of international collaborations. Citation analyses of his most-cited work helped us to confirm our colleague's primary influence in the field and allows us to memorialize some of these here.

Laser use in the dental clinic requires scientifically demonstrated improvement for patient and/or dentist, easily obtainable equipment, adequate training and safety. These aspects are summarized for all laser applications. Improvement has not been shown for all applications. In the Netherlands manufacturer-independent training is little available. Safety requires care, but not a large investment. Economical aspects include an adequate compensation for the necessary investment. For only a few applications laser treatment leads to decreased cost or time of treatment. However, also increased compensation by insurers or patients may be possible; some patients will be willing to pay more when laser treatment is less unpleasant than traditional treatment or, in the case of diagnosis, leads to better information.

A soft laser is a low-power laser emitting in the red and near-infrared part of the spectrum. Studies with cell cultures have shown that radiation from a soft laser, when used under proper conditions, promotes cell function and cell proliferation. However, wavelength and dose should be carefully adjusted to an optimum value: too low a dose does not work and neither does a high dose. The dose should be adjusted within an interval of about 10%. In a few animal studies a positive effect on wound healing has been demonstrated, although other studies did not show such an effect. Of the human studies done in the dental field, many do not meet scientific standards because there was no control group or the study was not double-blind. A few studies showed a positive effect but most did not. Perhaps the large variation in results may be explained by the required accuracy of adjustment of the dose, combined with the complicated processes that relate the incident dose to the dose to cells lying on or in tissue. More research, in particular studies in which the dose and wave length are varied systematically, are needed before responsible clinical use can be recommended.

© 2002 Optical Society of America

Diagnosis and treatment with lasers is becoming widely spread in dentistry. This article is an introduction to a series of articles that deal with the many dental applications of lasers. The article contains a summary of presently used lasers. It also describes the pertinent features of laser radiation: parallelism of the beam and narrow line shape in the spectrum of electromagnetic radiation. Finally, it summarizes the relevant processes of interaction of laser radiation with tissue: scattering, absorption, fluorescence and frequency-doubling.