Accuracy of linear tomography in comparison with computed tomography to assess bone quantity for dental implant treatment

    Background: Assessing bone quantity to restore missing teeth is necessary before implant placement.   Objective: The purpose of this study was to compare the accuracy of linear tomography and computed tomography (CT) in measuring linear distances on specified sites of dry mandible.   Methods: This analytical study was performed on 2 completely edentulous dry mandibles in 2011. 27 potential implant sites were marked using Gutta-Percha (No.60). Tomography images were obtained using a Planmeca® unit. 3 slices with image layer thickness of 3mm were obtained at each site. Computed tomography images were obtained using a Spiral CT (General Electronics®) unit and the axial slices with image layer thickness of 0.7 mm were provided. The overall height of the mandible, the distance between alveolar crest and superior border of the mandibular canal, and the mandibular width at half of the overall height, perpendicular to long axis of tomographic slices were measured by 2 oral and maxillofacial radiologists using a caliper. The mean value of 3 slices was recorded for every site. Similar measurements were performed for CT images. Then, the mandibles were cut at the marked sites and direct measurements were performed at each slice using a caliper. Data were analyzed using Wilcoxon-signed Rank test and Pearson’s correlation coefficient .   Findings: The correlation coefficients were found to be more than 0.9 between measurements of the two observers for most variables in both methods, except for overall height measurement by CT, which was about 0.6. The differences for the crest-to-canal distance and the mandibular width between CT measurements and direct measurements were statistically significant. The differences for the mandibular width were statistically significant comparing tomographic technique and direct measurements. Comparing two radiographic techniques, there was statistically significant difference in overall height measurement, while there were no significant differences in the mandibular width and crest-to-canal distance.   Conclusion: Linear tomography has an appropriate and comparable accuracy compared to CT images in measuring vertical distances on implant sites of mandible and therefore can be an alternative for CT images when the edentulous area is restricted to one site, in order to reduce the received radiation.