Purpose: To know whether there would be a difference among spiral tomograms of different slice thicknesses in the measurement of distances which are used for dental implant planning. Materials and Methods: 10 dry mandibules and 40 metal balls were used to take total 120 Scanorailll tomograms with the slice thickness of 2 mm, 4 mm and 8 mm. 3 oral radiologists interpreted each tomogram to measure the distances from the mandibular canal to the alveoalr crest and buccal. lingual and inferior borders of mandible. 3 observers recorded grades of 0, 1 or 2 to evaluate the perceptibility of alveolar crest and the superior border of mandibular canal. ANOVA with repeated measure. Chi-square tests and intrac!ass correlation coefficient(R₂, α) were used For statistical analysis. Results: There was not a statistically significant difference among spiral tomograms with different slice thicknesses in the measurement of the distances and in the perceptibility of alveolar crest and mandibular canal(p>0.05). All of them showed a good relationship in the reliability analysis. The perceptibility of alveolar crest and mandibular canal was almost similar and an excellent relationship was seen on all of them. Conclusions: There would be no significant difference. no matter which spiral tomogram of any slice thickness may be used in dental implant planning. considering the thickness of dental implant fixture.