Objective·To analyze the root canal diameter and taper of mandibular first molars using cone-beam CT(CBCT),investigate age-related changes in these parameters,and propose optimized clinical protocols for root canal preparation.Methods·From October 2022 to October 2023,CBCT images of 240 healthy mandibular first molars(120 three-canal type cases and 120 four-canal type cases)were collected from patients aged 20?59 years at the Stomatology Center,Haikou Affiliated Hospital of Central South University Xiangya School of Medicine.The three-canal type and the four-canal type samples were respectively divided into four age groups(20?29,30?39,40?49,and 50?59 years),with 30 cases in each group.Root canal length was measured,and buccolingual and mesiodistal diameters were recorded at four levels(coronal,middle,apical,and foramen).The tapers of the coronal 1/3,middle 1/3,and apical 1/3 segments were calculated in both buccolingual and mesiodistal directions.Differences among the age groups were compared.Results·The buccolingual diameters of all root canals exceeded the corresponding mesiodistal diameters.At several levels of most root canals,the diameters in the<50-year-old groups were significantly larger than those in the 50?59-year-old group(P<0.05).The buccolingual tapers exceeded the corresponding mesiodistal tapers in all root canals of mandibular first molars.The mean mesiodistal tapers in different age groups ranged from 0.07 to 0.34 in the coronal 1/3 segment,0.03 to 0.09 in the middle 1/3 segment,and 0.05 to 0.11 in the apical 1/3 segment.At several levels of most root canals,the tapers in the<50-year-old groups were significantly larger than those in the 50?59-year-old group(P<0.05).Conclusion·Mandibular first molars exhibit age-related narrowing of root canal diameter and reduced taper in individuals aged≥50 years.For initial apical file selection,#15 files are recommended for the distal canals in the three-canal type,while#10 files are advised for all other canals in the three-canal type and all canals in the four-canal type.For patients aged 50 years or older,the files for the distal canals in the three-canal type can be adjusted to#10,and the files for the mesiobuccal and distallingual canals in the four-canal type to#8.Regarding preparation taper,a 0.08-taper orifice opener is recommended for the coronal 1/3 segment.During mid-lower segment preparation,0.04-taper master apical files are suggested for the mesiobuccal and mesiolingual canals in the three-canal type and the mesiolingual and distallingual canals in the four-canal type,0.06-taper files for the distal canals in the three-canal type and the mesiobuccal canals in the four-canal type,and 0.08-taper files for the distobuccal canals in the four-canal type.Root canal obturation is recommended to be performed using vertical compaction with large-taper gutta-percha cones combined with bioceramic sealer.

Objective·To analyze the root canal diameter and taper of mandibular first molars using cone-beam CT(CBCT),investigate age-related changes in these parameters,and propose optimized clinical protocols for root canal preparation.Methods·From October 2022 to October 2023,CBCT images of 240 healthy mandibular first molars(120 three-canal type cases and 120 four-canal type cases)were collected from patients aged 20?59 years at the Stomatology Center,Haikou Affiliated Hospital of Central South University Xiangya School of Medicine.The three-canal type and the four-canal type samples were respectively divided into four age groups(20?29,30?39,40?49,and 50?59 years),with 30 cases in each group.Root canal length was measured,and buccolingual and mesiodistal diameters were recorded at four levels(coronal,middle,apical,and foramen).The tapers of the coronal 1/3,middle 1/3,and apical 1/3 segments were calculated in both buccolingual and mesiodistal directions.Differences among the age groups were compared.Results·The buccolingual diameters of all root canals exceeded the corresponding mesiodistal diameters.At several levels of most root canals,the diameters in the<50-year-old groups were significantly larger than those in the 50?59-year-old group(P<0.05).The buccolingual tapers exceeded the corresponding mesiodistal tapers in all root canals of mandibular first molars.The mean mesiodistal tapers in different age groups ranged from 0.07 to 0.34 in the coronal 1/3 segment,0.03 to 0.09 in the middle 1/3 segment,and 0.05 to 0.11 in the apical 1/3 segment.At several levels of most root canals,the tapers in the<50-year-old groups were significantly larger than those in the 50?59-year-old group(P<0.05).Conclusion·Mandibular first molars exhibit age-related narrowing of root canal diameter and reduced taper in individuals aged≥50 years.For initial apical file selection,#15 files are recommended for the distal canals in the three-canal type,while#10 files are advised for all other canals in the three-canal type and all canals in the four-canal type.For patients aged 50 years or older,the files for the distal canals in the three-canal type can be adjusted to#10,and the files for the mesiobuccal and distallingual canals in the four-canal type to#8.Regarding preparation taper,a 0.08-taper orifice opener is recommended for the coronal 1/3 segment.During mid-lower segment preparation,0.04-taper master apical files are suggested for the mesiobuccal and mesiolingual canals in the three-canal type and the mesiolingual and distallingual canals in the four-canal type,0.06-taper files for the distal canals in the three-canal type and the mesiobuccal canals in the four-canal type,and 0.08-taper files for the distobuccal canals in the four-canal type.Root canal obturation is recommended to be performed using vertical compaction with large-taper gutta-percha cones combined with bioceramic sealer.

BACKGROUND:The laser applied in the clinical oral medicine is mainly for early diagnosis of caries, removal of carious tissue, pulpotomy for pulp bleeding, dentin hypersensitivity treatment, disinfection of infected root canals, and periodontitis treatment. OBJECTIVE:To explore the changes of basic fibroblast growth factor in inflammatory pulp after laser treatment. METHODS:Five healthy adult beagle dogs were enroled, and six teeth were randomly selected from each dog. Then, these teeth were randomly divided into three groups, 10 teeth in a group, and they were treated with laser irradiation, saline and gentamicin irrigation respectively. At days 1, 2, 3 after operation, exudates from the pulp were colected for detection of basic fibroblast growth factor expression. Meanwhile, the dental pulp was detected by hematoxylin-eosin staining and immunohistochemistry method. RESULTS AND CONCLUSION:In the al three groups, the expression of basic fibroblast growth factor at day 3 was significantly higher than that at days 1 and 2, and there were no differences between days 1 and 2. Moreover, these three groups also showed no significant differences. Under hematoxylin-eosin and immunohistochemical staining, blood vessels in the pulp cavity were in good condition and the pulp arranged tightly. These findings suggest that the laser is safe, convenient and effective for oral clinical application, and has no injury to the inflammatory pulp.