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The endothelial cell-specific vascular endothelial growth factor (VEGF) and its cellular receptors Flt-1 and Flk-1 have been implicated in the formation of the embryonic vasculature. This is suggested by their colocalized expression during embryogenesis and the impaired vessel formation in Flk-1 and Flt-1 deficient embryos. However, because Flt-1 also binds placental growth factor, a VEGF homologue, the precise role of VEGF was unknown. Here we report that formation of blood vessels was abnormal, but not abolished, in heterozygous VEGF-deficient (VEGF+/-) embryos, generated by aggregation of embryonic stem (ES) cells with tetraploid embryos (T-ES) and even more impaired in homozygous VEGF-deficient (VEGF-/-) T-ES embryos, resulting in death at mid-gestation. Similar phenotypes were observed in F1-VEGF+/- embryos, generated by germline transmission. We believe that this heterozygous lethal phenotype, which differs from the homozygous lethality in VEGF-receptor-deficient embryos, is unprecedented for a targeted autosomal gene inactivation, and is indicative of a tight dose-dependent regulation of embryonic vessel development by VEGF.

Aluminium industry discharges fluoride into the atmosphere and several studies have shown a slight but significant contribution to the intake of fluoride by children living around aluminium smelters. A monitoring system was set up in 1991, just before a new aluminium smelter came into operation in Loon-Plage, on the North Sea coast, to study the evolution of the urinary fluoride excretion in children around the plant. Every year, 250 children under 14 are sampled in infant clinics, nursery schools and a secondary school. Urinary fluoride excretion was assessed by a potentiometric method on a spot morning urine sample and information on exposure factors was obtained by questionnaire. Urinary fluoride levels decreased with age (r = 0.31) and were higher in children drinking a local bottled water rich in fluoride (geometric mean in mg per gram of creatinine: 0.69 vs 0.52) or taking fluoride tablets (0.82 vs 0.52). The mean urinary fluoride excretion in children did not vary significantly between 1991 (geometric mean: 0.70 mg per gram of creatinine, 95% CI: [0.64-0.77]), 1992 (0.68 [0.62-0.75]) and 1993 (0.68 [0.61-0.76]), even after adjustment for potential confounding factors and despite a moderate increase in atmospheric fluoride levels.

The records of 152 consecutive patients who underwent orthognathic surgery in the Division of Maxillofacial Surgery A.Z. St.-Jan, Brugge, between 1/10/90 and 1/10/91 were evaluated for pre- and postoperative temporo-mandibular joint (TMJ) symptoms. Fewer TMJ symptoms were found postoperatively, than preoperatively (14.4% versus 19.7%). In the mandibular retrognathism group there were twice as much TMJ symptoms preoperatively in the low and normal mandibular angle patient group than in the high mandibular angle group (26% versus 13%). After surgery, there was a decrease of TMJ symptoms in the low and normal angle patient group (83% improvement). In the high angle absolute mandibular retrognathism group however, more new TMJ symptoms were seen postoperatively (21%). Bimaxillary surgical correction of a high angle absolute mandibular retrognathism case may provoke condylar resorption. Advice for follow-up and suggestions to reduce this annoying complication are given.

A radiological technique, using a new CT software program for the evaluation of alveolar process height and width, is presented. Irradiation is kept within acceptable limits when this technique is used. Measurements obtained with this technique were compared with those obtained on panoramic radiographs in 40 "half-jaws" (21 maxillar and 19 mandibular). We found that new indications for implantation emerge in the mandibular region because 'Denta Scan' can sometimes show possibilities to place implants on the buccal side of the canal (2 of 19 mandibular cases) when no possibilities are present above the canal on both the panoramic radiographs and Denta Scan images. In the maxillar region Denta Scan avoids unnecessary interventions by demonstrating the insufficient width of the alveolar ridge, often missed on panoramic radiographs (4 of 21 maxillar cases). Moreover the use of Denta Scan allows the use of implants with optimal length and diameter (23 of the 40 cases), giving better long-term results.

A radiological technique, using a new CT software program for the evaluation of alveolar process height and width is presented. Our experience with this technique is described.

Internal derangements or disk dysfunctions represent the most frequent pathology of the temporomandibular joint (TMJ). The radiological study of TMJ dysfunction was, for a long time, restricted to arthrography. More and more MR is used to study the TMJ, because MR, allows non-invasive visualisation of without the use of X-rays. Moreover a "dynamic" MR technique can be used to study disk movements during mouth opening. A lot of the internal derangement problems can be solved with this technique and arthrography can often be avoided. This dynamic MR technique is described and some cases are discussed.

During the last five years (1970-1974) 42 cases of pseudotuberculosis were diagnosed among the Antwerp Zoo animals. The prevalence of disease, and the distribution frequency of gross lesions in the visceral organs were studied. The susceptibility of different animals and the influence of some factors to the disease are discussed. It demonstrates that Y. pseudotuberculosis, and particularly its two serotypes I and II, constitutes the principal causative agent. Pseudotuberculosis is found to be highly prevalent in cold season.