Analysis Of The Relationship Between Crown And Root Anatomy In Maxillary Second Molar:A CBCT Study

AIM: To detect the relationship between the anatomical morphology of the maxillary second molar teeth and the number of root canals in a Chinese population by cone-beam CT images,and to analyze whether the distance between root canal orifices are related to the number of root canals,which would provide help for the root canal treatment of maxillary second molars in clinic.METHODS: CBCT images of 210 patients with maxillary second molars(410 teeth)were randomly selected.The number of root and root canals was observed and counted by Mimics 10.01 software.Three-dimensional reconstruction of maxillary second molars was performed.The buccolingual diameter and mesiodistal diameter were measured on three-dimensional reconstructed dental models,and the relationship between the measured results and root canal types was analyzed.At the same time,the occlusal morphology was observed and recorded,and the relationship between occlusal morphology and root number was explored.Adjust the long axis of the maxillary second molar,measure the distance between the root canal orifices to find the rule between the distance of orifices and the number of root canals in the axial view.RESULTS: Three roots with three canals were the most common form,and its incidence was 46.83%(192/410).The incidence of single root canal was the lowest,and its incidence was 0.98%(4/410),42.20%(173/410)of the maxillary second molars had root fusion.The buccolingual diameter and mesiodistal diameter of the maxillary second molars with different root canal types were single canal(10.21 ± 0.50,8.82 ± 0.17 mm),double canals(11.25 ± 0.55,9.47 ± 0.42 mm),three canals(11.68 ± 0.68,9.47 ± 0.54 mm),and four canals(12.01 ± 0.63,9.52 ± 0.57mm).The buccolingual diameters of different root canal types were different significantly(P < 0.05).Except for single root canal,there was no significant difference in the mesiodistal diameters between other root canal types(P > 0.05).The ratio of buccolingual diameter and mesiodistal diameter corresponding to three and four root canals were also different from the other two root canal types(P < 0.05)(single canal 1.16 ± 0.05,double canals1.19 ± 0.05,three canals 1.23 ± 0.06,four canals 1.26 ± 0.05).There were differences in occlusal morphology among different number of roots(P < 0.05).64.15%(263/410)of the occlusal surface morphology were oblique,11.95%(49/410)were square,13.17%(54/410)were round and10.73%(44/410)were oval.The round triangle occlusal morphology were mostly with single or double roots,the oval ones were mostly with double roots,and the square or oblique ones were mostly with three roots.There were significant statistical differences in the distance between root canal orifices of teeth with different number of root canals.The average distance between buccal to palatal canal orifices were more less than that of other root canal types,85.71%(24/28)of the two canal orifices were less than or equal to 4.41 mm,and only18.05%(61/338)、7.50%(3/40)of the distance between buccal to palatal canal orifices in the three and four canals were less than or equal to 4.41 mm.CONCLUSION: The anatomical shape of the maxillary second molar is complex,and there is a certain relationship between its anatomical shape and the number of root or root canals.The occurrence of root and root canals of maxillary second molar can be preliminarily judged by its tooth shape.Combined with the regularity of the distance between the root canal orifices to locate and find the root canal orifices,which will be helpful for root canal therapy in clinic.