Effect of root curvature on post length in the restoration of endodontically treated premolars

– Two hundred and eighteen bi-rooted maxillary premolars were examined radio graphically to determine the length from the apex at which root curvature occurred. The information may serve as a guide in determining post preparation length. The results of the study indicated that the lingual root was slightly straighter than the buccal root. The curvature of the root was on the average 6.47 mm from the apex on the buccal root and 5.18 mm from the apex on the lingual root.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75753/1/j.1600-9657.1985.tb00577.x.pd

Fast, automated measurement of nematode swimming (thrashing) without morphometry

Background: The "thrashing assay", in which nematodes are placed in liquid and the frequency of lateral swimming ("thrashing") movements estimated, is a well-established method for measuring motility in the genetic model organism Caenorhabditis elegans as well as in parasitic nematodes. It is used as an index of the effects of drugs, chemicals or mutations on motility and has proved useful in identifying mutants affecting behaviour. However, the method is laborious, subject to experimenter error, and therefore does not permit high-throughput applications. Existing automation methods usually involve analysis of worm shape, but this is computationally demanding and error-prone. Here we present a novel, robust and rapid method of automatically counting the thrashing frequency of worms that avoids morphometry but nonetheless gives a direct measure of thrashing frequency. Our method uses principal components analysis to remove the background, followed by computation of a covariance matrix of the remaining image frames from which the interval between statistically-similar frames is estimated. Results: We tested the performance of our covariance method in measuring thrashing rates of worms using mutations that affect motility and found that it accurately substituted for laborious, manual measurements over a wide range of thrashing rates. The algorithm used also enabled us to determine a dose-dependent inhibition of thrashing frequency by the anthelmintic drug, levamisole, illustrating the suitability of the system for assaying the effects of drugs and chemicals on motility. Furthermore, the algorithm successfully measured the actions of levamisole on a parasitic nematode, Haemonchus contortus, which undergoes complex contorted shapes whilst swimming, without alterations in the code or of any parameters, indicating that it is applicable to different nematode species, including parasitic nematodes. Our method is capable of analyzing a 30 s movie in less than 30 s and can therefore be deployed in rapid screens. Conclusion: We demonstrate that a covariance-based method yields a fast, reliable, automated measurement of C. elegans motility which can replace the far more time-consuming, manual method. The absence of a morphometry step means that the method can be applied to any nematode that swims in liquid and, together with its speed, this simplicity lends itself to deployment in large-scale chemical and genetic screens. </p

A survey of failed post-retained restorations

Survival of endodontically treated, post-restored teeth depends on a multitude of factors, all of which are practically impossible to include in a randomized, controlled clinical study. The purpose of this survey was to characterize and analyze reported failures of post-retained restorations to identify factors critical to failure and to type of failure. A questionnaire was mailed to private practitioners in Denmark with a request to complete the questionnaire whenever a patient presented with a failed post-retained restoration. Information was gathered on factors related to the patient, the tooth, the restorative materials, and the techniques. Two-hundred and sixty questionnaires were collected from 171 practitioners over a 3-year period. Functioning time until failure varied between 3 months and 38 years. Mean survival time until failure was 11 years. Of the failed restorations, 61% had functioned for 10 years or less. Fracture of the tooth was the most common type of failure reported, followed by loosening of the post and fracture of the post. Tapered posts implied an increased risk of tooth fracture compared to loosening or fracture of the post, and the relative risk of tooth fracture increased with the functioning time until failure. Fracture of the post was more common among male than female patients. On the basis of this survey of failed post-retained restorations, it was concluded that tapered posts were associated with a higher risk of tooth fracture than were parallel-sided posts