Abstract: The relationships between crown buccal-lingual diameter, proximal-distal mid-diameter and occlusal surface morphology and root and root canal types of maxillary second molars was studied by three-dimensional reconstruction of CBCT images. The CBCT images of 220 patients (410 maxillary second molars) were collected. The morphology of maxillary second molars was observed after enlarging the horizontal images to 400% on sagittal plane, and the number of root canals and fusion were recorded. Three-dimensional reconstruction of the CBCT images of the maxillary second molars was performed to observe and measure the morphology of the crown and occlusal surface, and to analyze the relationship between the buccal and lingual diameters, distal and distal diameters of the crown and occlusal surface morphology and root and root canal types. Of 200 subjects with maxillary second molars on both sides, 88% (176/200) had completely symmetrical root canal types. Of 410 maxillary second molars, 46.83% (192/410) had three root canals, 54.39% (223/410) had three independent root canals, 42.20% (173/410) had root fusion, and 82.44% (338/410) had three root canals. The buccal and lingual diameters of the crowns of the maxillary second molars with different root canal types were different (P<0.05). The proximal and distal diameters of the crowns of the maxillary second molars with single root canal were different (P<0.05). There was no significant difference in the proximal and distal diameters of the crowns of the other root canal types (P>0.05). Among 410 maxillary second molars, occlusal surface morphology was classified as oblique 64.15% (263/410), square 11.95% (49/410), circular triangle 13.17% (54/410), oval 10.73% (44/410). Among them, the root of the round triangle is mostly single and double, the oval is mostly double, and the square and oblique are mostly three. The occlusal morphology of maxillary second molars with different root numbers was different (P<0.05). In a word, the buccal and lingual diameters, distal and distal diameters and occlusal surfaces of maxillary second molars are related to root and root canal types. Three-dimensional reconstruction of CBCT images of maxillary second molars can be used to determine the root and root canal types of maxillary second molars by using the anatomical morphology of crowns, which can provide a reference for root canal therapy.

Key words: maxillary second molar, cone beam computed tomography, anatomical morphology of crown, root canal therapy