Quality of root-end preparations using ultrasonic and rotary instrumentation in cadavers.

Prior investigations have demonstrated dentinal cracking and chipping during ultrasonic preparation of the root-end. This study compared the frequency of cracking and chipping in two groups, cadaver and extracted teeth, using an indirect resin technique. Preparations were performed using either a 33 1/2 inverted cone bur in a high-speed handpiece, or with ultrasonics using a CT-2 tip at either high or low intensity. After replication of the root-end in epoxy resin, all teeth were evaluated for cracking and chipping under scanning electron microscopy. Statistical analysis using a general contingency table or ANOVA with Scheffé post-hoc analysis (p = 0.05) revealed no significant difference between all groups in terms of root-end cracking. In extracted teeth (n = 15), rotary instrumentation produced less chipping than either ultrasonic technique. Varying the intensity was not significant. There was no significant difference between any instrumentation group in cadaver teeth (n = 10) related to the amount of chipping.

Medication errors during hospital drug rounds.

Objective--To determine the nature and rate of drug administration errors in one National Health Service hospital. Design--Covert observational survey be tween January and April 1993 of drug rounds with intervention to stop drug administration errors reaching the patient. Setting--Two medical, two surgical, and two medicine for the elderly wards in a former district general hospital, now a NHS trust hospital. Subjects--37 Nurses performing routine single nurse drug rounds. Main measures--Drug administration errors recorded by trained observers. Results--Seventy four drug rounds were observed in which 115 errors occurred during 3312 drug administrations. The overall error rate was 3.5% (95% confidence interval 2.9% to 4.1%). Errors owing to omissions, because the drug had not been supplied or located or the prescription had not been seen, accounted for most (68%, 78) of the errors. Wrong doses accounted for 15% (17) errors, four of which were greater than the prescribed dose. The dose was given within two hours of the time indicated by the prescriber in 98.2% of cases. Conclusion--The observed rate of drug administration errors is too high. It might be reduced by a multidisciplinary review of practices in prescribing, supply, and administration of drugs.

A method for teaching the classical inferior alveolar nerve block.

A teaching method was developed to improve the ability of dental students to understand and perform their first inferior alveolar nerve block. Lectures, demonstrations, and laboratory sessions were utilized to provide correlation of anatomical and clinical information. The use of cadavers for injection demonstration and practice was an integral part of this teaching approach. Cadavers were dissected so that the oral cavity remained intact. Laterally the skin and masseter muscle were reflected, and the superior portion of the ramus of the mandible was removed. This procedure permitted exposure of the medial pterygoid muscle and the inferior alveolar and lingual nerves and, therefore, permitted observation of a syringe needle during the practice of inferior alveolar nerve blocks. In addition, the supraorbital, infraorbital, and mental nerves were exposed. This combined anatomical-clinical experience provided reinforcement of the relevance of anatomy in clinical practice, provided instruction and practice sessions before the first patient injection, and aided in relieving some of the anxiety often associated with the initial injection.

The isolation and primary culture of putative human root odontoblasts.

The use of procedures adapted from a routinely successful method of culturing bovine bone has led to the first system for the study of dentinogenesis in vitro. Two types of cells have been grown from pulp obtained from the growing root tips of impacted third molars extracted from 14- to 19-years olds: (1) epithelial-like cells that are probably derived from fragments of the epithelial root sheath and (2) odontoblast-like cells. The cultured epithelial-like cells grow out in distinctive rounded plaques while the odontoblast-like cells are tethered to and/or grow on top of the epithelial-like cells. The odontoblast-like cells produce mineralized matrix by 10 days when cultured on a defined mineralization formula containing conditioned medium obtained from fetal bovine bone cell cultures. Growth factors in this conditioned medium are important to cell proliferation and growth and to the synthesis of mineralized matrix. Sequential enzyme digestion in dispase and dispase/collagenase in serum-free Dulbecco's Modified Eagle's Medium is essential to obtaining adequate cell yields from the apical 3-5 mm of the developing root. Reduction of the number of fibroblasts by treating cultures with dispase in Tyrode's solution midway through the initial growth period enhances the purity of these cell cultures.

Immunocytochemical localization of contractile and contraction associated proteins in the spiral ligament of the cochlea.

Most of the extracellular fibers of the spiral ligament are associated with a distinct band of 'anchoring' cells which occur at the boundary between the spiral ligament and the otic capsule. These cells are characterized by parallel arrays of intracellular filaments which, along with the extracellular fibers, insert into electron dense, conical adhesion plaques. The intracellular filaments show a close morphological resemblance to the 'stress fibers' of cultured fibroblasts (Henson et al., 1984). In the present study we have demonstrated by immunofluorescence techniques that the anchoring cells, unlike adjacent cells of the spiral ligament, contain a complement of proteins that is typically associated with stress fibers and with contractile systems. In addition to actin, the cells contain myosin, tropomyosin, alpha-actinin and talin. These results lend further support to the hypothesis that the anchoring cells have the capacity to create and/or maintain tension on the spiral ligament-basilar membrane complex and to influence the mechanical properties of the basilar membrane.

The attachment of the spiral ligament to the cochlear wall: anchoring cells and the creation of tension.

The spiral ligament of the cochlea contains an array of criss-crossing extracellular fibers which are anchored to the bony wall of the cochlea and into the outer margin of the basilar membrane. In certain areas there is an accumulation of unusual sponge-shaped cells which are clearly involved in anchoring the extracellular fibers to the bony wall and possibly in maintaining or applying radial tension on the spiral ligament-basilar membrane complex. The latter is suggested by the occurrence of a large number of intracellular fibers which have many of the characteristics of the so-called 'stress fibers' of cultured fibroblasts. Where these cells occur the fibers of the spiral ligament bend sharply, presumably due to tension applied on them. This paper provides transmission and scanning electron micrographs of the 'anchoring' cells in the mouse and two species of bats. In the horseshoe bat, the anchoring cells provide the sole mode of attachment of most of the spiral ligament to the otic capsule. Marked differences occur not only among species but also in different regions of the spiral ligament. A diagram is provided to show how the system of cells and fibers might create or maintain tension on the basilar membrane.

Ultrastructure of the lining of the scala tympani of the bat, Pteronotus parnellii.

The cells lining the scala tympani of the cochlea of Pteronotus p. parnellii were studied in whole mount preparations and with light and scanning and transmission electron microscopy. On the basis of structure and location three different cell types were recognized: (1) those lying on the undersurface of the basilar membrane; (2) those covering the internal surface of most of the otic capsule; and (3) those associated with a thick layer of osmiophilic substance and restricted to a specific region in the basal turn. The cells associated with the osmiophilic substance were strikingly different from the other cells; they were relatively rich in organelles and had a Golgi complex which appeared to produce granules which coalesced both intracellularly and extracellularly to form the osmiophilic layer. The function and composition of the osmiophilic substance is unknown but it seems to be unique to Pteronotus parnellii and related subspecies known to have greatly enlarged perilymphatic scalae and unusual hearing capacities associated with Doppler shift compensation sonar.

Sustentacular cells of the organ of Corti--the tectal cells of the outer tunnel.

The cells which form the roof of the outer tunnel of the organ of Corti were studied by light microscopy and scanning and transmission electron microscopy. In the mustache bat, Pteronotus p. parnellii, the cells are characterized by: (1) a unique position in the roof and along the lateral wall of the outer tunnel; (2) no contact with the basilar membrane; (3) isolation of adjacent cell bodies; (4) an extensive endolymphatic surface with a sparse population of short microvilli; (5) a loose association with the adjacent mat of polypous surface projections on the outer tunnel surface of the first row of Hensen's cells; and (6) a darkly staining cytoplasm. These cells occur in certain other mammals (cats and mice) and have been classified previously as Hensen's or Deiters' cells, but since they lack the distinct morphological characteristics of either of these types of cells, it is suggested that they be recognized as a distinct cell type, the tectal cells of the outer tunnel.

The cells of Boettcher in the bat, Pteronotus p. parnellii.

The structural characteristics, distribution and intercellular relationships of the cells of Boettcher were studied in the mustache bat, Pteronotus P. parnellii. The cells of Boettcher have many structural features similar to those described in other mammals, but in Pteronotus they are distributed throughout the cochlea and are associated with relatively large amounts of secretory and/or absorptive material. Much of this material seems to be derived from or contribute to, a darkly staining upper layer of the basilar membrane. This material accumulates in elaborate microvillus-filled intercellular channels which are restricted to an area near the basilar membrane. The channels communicate with the basilar membrane surface through wide intercellular spaces and through small canals. The microvillus-filled channels are confluent with large extracellular spaces between Boettcher's cells and a single row of cells which form the floor of the outer tunnel. The latter have irregular shaped nuclei, contain many vacuoles and like Boettcher's cells, are associated with large amounts of basilar membrane-like material. Observations on Pteronotus, as well as other species of bats, do not support concepts relating Boettcher's cells to hair cell innervation patterns or to high frequency hearing.

A transmission and scanning electron microscopic study of the saccule in five species of catfishes.

The sacculi of five species of catfishes were studied by transmission and scanning electron microscopy. In four species, the sagitta exhibited a multifluted anterior part and a tapered posterior part; in Corydoras aeneus, however, the fluted part was absent, and a vertical component extended dorsally to terminate near the opening of the transverse canal. In all species, the otoliths had a laminar structure. An otolithic membrane was present, and hair cell bundles projected into cavities on the macular surface of the membrane. Attachments of the otolithic membrane to the neuroepithelium included short extensions of the membrane to the tallest components of the hair cell bundles of the peripheral cells and more delicate connections to the kinocilium and taller stereocilia of central cells; in addition, attachments to the microvilli of supporting cells were present. In both hair cells and supporting cells single microtubules and bundles of microtubules were present; the bundles had an orderly arrangement and were associated with cytoplasmic densities surrounding the desmosomes. The hair cells were innervated by both afferent and efferent nerve endings. Studies of the polarization of the hair cells in all species (except C. aeneus) showed that there was a single longitudinal axis that divided dorsally polarized cells from those oriented ventrally. In Doras spinosissimus and Bunocephalus bicolor, an additional line of polarization was evident in a small area in the anterior part of the macula; therefore, in these forms there was a double bipolar orientation.