The Scanora X‐ray unit permits linear and rotational narrow beam radiography as well as spiral tomography, making it well suited for implant planning radiography. The purpose of this study was to evaluate the reliability of measurements made in spiral lower jaw tomograms of patients examined with the Scanora® technique. Six observers measured the distance between the alveolar crest and the mandibular canal in spiral tomographic images taken on 40 consecutive patients before implant surgery. In one randomly chosen image from each patient, the observers marked the measuring points at the two locations. The measurements were repeated 2 months later. Three of the observers, all radiologists. excluded in total 11 sets of images considered to improve if retaken. Analysis of variance showed an average standard deviation between observers of 1.67 mm. This was mainly due to the intraobserver variation, 1.07 mm. The variation between plots was significantly larger at the alveolar crest. Confidence intervals showed that reliability improves with multiple readings, either made independently by one observer or separately by several. The inter‐ and intraobserver variation decreased to 1.42 mm and 0.86 mm, respectively. without the images of inferior quality. Compared with a similar study based on hypocycloidal images, the variability was less due to the intraobserver variation and was affected positively by an optimized image quality.
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Ekestubbe et al. (1993) studied this question.