Abstract: 【Abstract】 Objective:To assess the value of CBCT in observing the positional relationship bewteen mandibular third molar and mandibular canal. Methods:Totally 104 aduted patients (Stomatological Hospital of Tianjin Medical University, from 2012.1 to 2012.5) with 191 mandibular third molars were assessed with CBCT. All the images were classed and measured by CBCT Image processing software (Examvision).The results were processed statistically with SPSS software package.Results:There were 85 mandibular third molars contacting with mandibular canals.The positional relationship bewteen mandibular third molar and mandibular canal and the probability of mandibular third molar contacted with mandibular canal were independent of gender（P＞0.05）.The Correlation existed between their positional relationship and the probability of mandibular third molar contacted with mandibular canal.And when mandibular canal locates at the lingual side of mandibular third molar or between the roots of mandibular third molar, it has the largest probability of contacting with mandibular third molar. Conclusion:CBCT can predict exactly the positional relationship bewteen mandibular third molar and mandibular canal.

Key words: CBCT, mandibular third molar, mandibular canal.