A Study Of Root Canal Taper And Cross-section Morphology Of The Permanent First Molar

Obejective:The aim of this anatomy study was to investigate the root canal diameters, original tapers and configuration of root canal cross-sections in permanent first molar of Chinese population by means of CBCT, so as to reveal the characteristics of the root canal morphology in permanent first molars and to provide useful information for root canal therapy. Simultaneously, we can obtain the original taper value of permanent first molars for clinical selection of suitable root canal instruments.Methods:40 maxillary and 40 madibular extracted human permanent first molars were collected for subsequent scanning by CBCT, and then the morphology of cross-sections of root canals were determined Bucco-lingual(BL) and Mesio-distal(MD) diameter of each canal were measured at cervical, middle and apical third of the canals. Finally, the taper were calculated and analyzed.Results:① The root canal diameter of maxillary first molar in buccal-lingual direction was greater than in mesial-distal direction except the Palatal root canal, and in both directions root canal diameter decreased apically (P<0.05). The root canal diameter of mandibular first molar in buccal-lingual direction was greater than in mesial-distal direction, and in both directions root canal diameter decreased apically (P<0.05).② The Palatal root canal taper of maxillary first molar in mesial-distal direction was greater than that in buccal-lingual direction (P<0.05).Root canal taper in mesial-distal direction decreased apically, and there were differences between cervical third and either of middle and apical thirds (P<0.05).while other root canals there were no differences among the tapers within the 3 levels of the root canal in both directions. The Distal-Lingual root canal taper of mandibular first molar in buccal-lingual direction increased apically, and there were differences between apical third and either of cervical and middle thirds (P<0.05).However, other root canals taper of mandibular first molar in buccal-lingual direction were greater than that in mesial-distal direction, but there were no differences among the tapers within the 3 levels of the root canal in both directions.③ Distribution of cross-section configuration in permanent first molar canals is different. In maxillary first molars, oval canals, flattened canals dominated in cervical and middle thirds. The cross section of the apical thirds is oval and round shapes. The distribution of cross section configuration in mandibular first molar canals is similar with maxillary first molar canals. Just flattened shapes dominated in Distal-Lingual root canals.Conclusion: ①The root canal physical morphology in permanent first molar is complicated. The results showed that the oval canal is common in permanent first molar.②The buccal-lingual diameter of root canals was greater than the mesial-distal diameter, while the buccal-lingual taper was also greater than mesial-distal taper (except the Palatal root canal of maxillary first molar). We should use the mesial-distal diameter and taper as the reference for choice instrument in root canal therapy.③The root canal is not a continuous taper, the buccal-lingual taper changed significantly (except the Palatal root canal of maxillary first molar). The result indicate that canal taper and configuration of the first molar is complicated, the chemical irrigation, ultrasonic vibration and warm gutta-percha obturation techniques are recommended to use in the root canal therapy in first molars to increase the quality of treatment.