Anatomic Characteristics Of Distal Lingual Root Of Mandibular First Molar And Its Influence On Periodontal Tissue

Objective: The distal lingual root is a kind of anatomic variation of the root of the mandibular first molar and its detection rate is high in China population.There are many studies on the effect of distal lingual root on root canal therapy,but few studies on its effect on periodontal tissue.This study intends to measure the anatomical characteristics of mandibular first molars with distal lingual roots by screening subjects with distal lingual roots,and explore the influence of distal lingual roots on periodontal tissues.Methods: In this study,patients with CBCT shot in the imaging department of Stomatology Hospital Affiliated to China Medical University were selected,and the CBCT images were observed and measured by Invivo image analysis software.The detection rate of distal lingual root of mandibular first molar was calculated.The root trunk and root furcation angle of the mandibular first molar with the distal lingual root was measured and detected.The periodontitis patients of stage Ⅲ and Ⅳ and mandibular first molars with distal lingual roots were screened.The root trunk and root furcation were measured and compared with the corresponding indexes of all subjects.The patients with stage Ⅲ andⅣ periodontitis of mandibular first molars with unilateral distal lingual root were screened,and the radiographic bone resorption of this tooth was measured to analyze the relationship between distal lingual root and alveolar bone resorption of periodontitis patients.Descriptive analysis,chi-square test and t-test were carried out by SPSS23.0 statistical software.Results: The detection rate of distal lingual root of mandibular first molar at the patient level was 29.28%,and that of mandibular first molar at the tooth level was 25.83%.There was no difference between male and female,and the detection rate of the right distal lingual root was higher than that of the left.The average length of buccal root trunk,lingual root trunk and distal root trunk of mandibular first molar with distal lingual root were2.99±0.57 mm,3.65±0.65 mm and 4.53±0.93 mm,respectively.The length of distal root trunk of mandibular first molar with distal lingual root was longer than that of lingual root trunk,and lingual root trunk was longer than that of buccal root trunk.The average buccal,lingual and distal root furcation angles were 37.17±9.13°,41.41±9.10° and 67.52±14.73°,respectively.The distal root furcation angle was greater than that of lingual root,and the lingual root furcation Angle was greater than that of buccal root.There was no significant difference in the length of root trunk and the angle of root furcation between patients with periodontitis Ⅲ/Ⅳ and all subjects.There was no significant difference in radiographic bone loss at each site between the mandibular first molars with and without distal lingual root.Conclusions: The detection rate of the distal lingual root of the mandibular first molar is high in China,and the detection rate of the right distal lingual root was higher than that of the left.The distal root furcation of mandibular first molar with distal lingual root is the longest,and it is more difficult to expose root furcation.However,the distal root furcation is not easy to clean,and the root furcation angle is the largest,and the furcation involvement progresses faster.This study did not find that the distal lingual root of mandibular first molar had a promoting effect on the destruction of periodontal tissue.