Olivocochlear innervation of inner and outer hair cells during postnatal maturation: evidence for a waiting period

Reconstructions of the efferent innervation of the hamster (Mesocricetus auratus) cochlea were done during postnatal development. Efferent neurons were labeled via injections of biocytin and horseradish peroxidase into the crossed olivocochlear (OC) bundles using an in vitro brainstem technique. Such injections retrogradely labeled cell bodies in ventral periolivary regions of the superior olive consistent with their being medial OC neurons. Anterogradely labeled axons were traced to the cochlea, where they terminated on or below inner hair cells (IHCs) prior to postnatal day 5 (P5). After P5, labeled axons terminated on IHCs and outer hair cells (OHCs) and after P10, the majority of labeled axons terminated on the OHCs. In the electron microscope, small labeled terminals containing densely packed synaptic vesicles were found both adjacent to IHCs (axosomatic) as well as apposed to afferent and efferent fibers below IHCs prior to P5. By P10, large labeled terminals were axosomatic to OHCs and no longer found on IHCs. Consistent with previous reports, these data suggest that medial OC axons form part of an early primary innervation on and below IHCs before terminating on OHCs. This raises the possibility that OC neurons demonstrate a period of waiting below an intermediate target similar to that described in the development of thalamocortical projections.     

The use of bitewing radiographs in the management of dental caries: scientific and practical considerations

The objective of this paper is to synthesize published research on the use of radiographs in caries diagnosis in order to produce recommendations for guidelines that are clinically oriented but scientifically based. The options available include the use of various types of radiographic examination alone or in conjunction with other diagnostic aids. The outcomes should facilitate the optimal management of lesions as either preventive care advised (PCA) or operative care advised (OCA). Small initial lesions (PCA) require prompt detection, the application of appropriate preventive care and subsequent monitoring to maintain the most favourable tooth state achievable in the long term. Larger dentinal lesions (OCA) also require prompt detection so that appropriate high-quality operative care can be provided before further loss of tooth substance. Evidence was collected from the literature by updating several recent reviews by the author. The values employed were broadly analogous to those of the Canadian Task Force on the Periodic Health Examination. The use of ionizing radiation is always associated with a degree of risk: therefore all exposures must be kept as low as is reasonably achievable. Present evidence on the balance of risk and benefit indicates that the diagnostic yield for caries diagnosis is high enough to justify individualized examinations, particularly as changes in the morphology of caries have rendered clinical diagnosis of dentinal lesions less sensitive. This issue must be kept under review as alternative diagnostic technologies develop. There is good evidence that initial posterior bitewing radiographs are required for all new dentate patients over five years of age with posterior teeth. This procedure is required as an adjunct to clinical examination for the detection of caries on both the approximal and occlusal surfaces of the teeth. Although a 'blanket' regimen of routine radiographic examination at fixed intervals cannot be advocated, individualized bitewing examinations at varying frequencies determined on the basis of caries risk are supported. At the initial visit, an assessment of caries risk of the individual patient should be made. Varying intervals of first radiographic recall can then be suggested on the basis of differing degrees of risk. At present, risk assessment is imprecise, and risk status may change over time. Therefore, intervals between subsequent radiographic examinations must be re-assessed for each period. The purpose of detecting individual lesions should be to facilitate the planning of appropriate preventive treatment decisions based on lesion severity, caries risk and the patient. Different treatment should be employed for lesions in the PCA and OCA categories. Further rigorous studies are required to evaluate diagnostic methods appropriate for use in individual patient care, epidemiology and clinical research, and to increase the understanding of how findings from these applications inter-relate. Development and validation of reliable methods of caries risk assessment which are usable in general practice is a priority. Investigations of the processes involved in, and the outcomes of, dental decision-making are required to ensure that existing and new methods are used appropriately. Further work should develop and evaluate effective mechanisms of disseminating and implementing research findings by information transfer to dental educators and clinicians.