| Background and purposeIn recent years,domestic and foreign scholars have generally reached a consensus that endodontic treatment is the most effective treatment for pulpitis and periapical diseases.The criteria for success in root canal therapy include root canal preparation,chemical disinfection of root canal during root canal therapy,and final dense root canal filling.In the field of root canal preparation,the root canal system usually has complexity and variability,which often leads to the failure of root canal therapy.Therefore,mastering and grasping the physiological and anatomical morphology of the root canal system is an important factor determining the success of root canal therapy.The incidence of dental pulp disease and periapical disease in the first molar of the group is high,and the root canal therapy should be perfected whenever the root canal is found.However,the complex degree of root canal therapy is increased because of the complex diversity of the root canal physiological anatomy and the number of root canal.Since the beginning of 80s,many domestic and foreign scholars have done a lot of research on the middle mesial canals of mandibular first molairs.In 1981,American scientist Pomeranz H first discovered middle mesial canals of mandibular first molars,and studied 61 mandibular first molars.In 1984,another American scholar,Vertucci,also observed and analyzed the root canal system of the middle mesial canals of the first molar of the mandible,and proposed a Vertucci root canal taxonomy named after it was named.A large number of scholars,such as H,Kim,Banode A,Sharma P,Martins J N,Jabali A,have studied the middle mesial canals of mandibular first molars.However,most of them reported clinical cases,and the methods of transparent specimen and dental microscope were used to study the morphology of the root canal.Until recently,MMC has been a research trend both at home and abroad.Clinically,the omission of MMC can lead to failure of root canal therapy.Its appearance has increased the difficulty of root canal therapy for mandibular first molars.It is of great importance to identify and understand nearly third root canals in order to improve the success rate of root canal therapy for mandibular first molars.As an auxiliary equipment which has been widely used at home and abroad in recent years and has developed rapidly in clinical auxiliary examination,the conical beam CT(cone-beam computed tomography,CBCT)has a great advantage in the research of root canal system and morphological thinning.Imaging examination is closely related to the diagnosis and treatment of dental pulp disease.The commonly used dental root apex and oral surface tomography have low resolution,overlay of anatomical structure,and artifacts resulting in distortion and distortion,but CBCT has many advantages,such as low radiation dose,clear image resolution,three-dimensional reconstruction and more rapid and convenient transportation..Through the comprehensive analysis of computing software,many planes,such as the sagittal,coronal and axial planes,are clearly displayed at the same time,and they have the characteristics that are more in line with the needs of the oral cavity.The conical beam CT is widely used clinically.In the imaging study of the third canal(MMC)morphology and medullary direction in the proximal mandibular molar,the CBCT can be found in the axial,coronal,sagittal and 3D images to stereoscopic,clear and intuitively the MMC dissection physiology.One of the concepts advocated by modern root canal therapy is the three-dimensional preparation and three-dimensional filling of the root canal.It is an indispensable key step to complete the three-dimensional preparation and three-dimensional filling of the root canal system,and complete cleaning,disinfection,preparation and filling.Most of the location and detection of MMC depend on the two dimensional image of the X-ray film before the three-dimensional image of the tooth can be taken.The preoperative observation and analysis of the root canal system by using CBCT images can be used clinically to obtain a more accurate preoperative assessment of the root canal,which can make the clinician better master the treatment of the anatomical morphology related to the third canals in the first molar and the possible high incidence of the mandibular first molar.The success rate of clinical treatment of root canal.The group selected the MMC with a certain incidence,but easy to be ignored by clinicians and researchers.The goal was to calculate the incidence of the middle mesial canals of the mandibular first molar,and to determine whether it had the age correlation,the measurement of the curvature of the root canal,the position of the bend,and the observation of the morphology of middle mesial canals in the mandibular first molar,so as to observe the shape of the middle mesial canals in the mandibular first molar.The fine study of the middle mesial canals in the mandibular first molar has been done to guide the clinicians to better grasp the difference between the third canal forms of the first molar in the mandible,and to improve the effect of the root canal treatment of the first molar of the mandible,and to show that CBCT has an important role in the clinic.Materials and methods1.since January 2016,a total of 1600 CBCT images of 1600 patients(46.5 +14.8 years old)were collected from 1600 patients(46.5 + 14.8 years old)in the oral Imaging Department of the Southern Hospital of Southern Medical University,which were collected for oral examination,pre repair examination,pre dental extraction,pre orthodontic oral examination and so on.Image as the object of study,CBCT images of mandibular first molars(including 168 cases)with nearly third root canals were selected.The images were included in the following criteria:1 without periapical lesions of the teeth;2 teeth had not been treated with dental pulp and root excision;3 teeth were well developed,without root resorption;4.of the teeth were scanned by CBCT,and the images were clear without artifact;Planmeca Romexis Viewer soft pieces were used to reconstruct the images.The appropriate location was selected to intercept the image of the teeth in the buccal,lingual and near far directions.Schneider method was used to measure and analyze related parameters such as anatomy,physiology,morphology and so on.The incidence of the middle mesial canals of the first permanent molar of the mandible,the curvature of the root canal of the first permanent molar of the mandible,the curvature of the root canal of the first permanent molar of the mandible,and the number of the middle mesial canals of the first permanent molar of the mandible were counted,and the corresponding analysis of the third canals of the first permanent molar of the mandible was made.2.in addition to the team,2 senior dental pulp specialists,qualified by the standard consistency test,evaluated the CBCT images at the same time and obtained more accurate results.The third assessor's dental pulp disease experts confirm the external anatomical morphology and internal anatomy of the root canal physiology.3.use Planmeca Romexis Viewer software to reconstruct 3D images.Then select the appropriate location to intercept the image of the teeth in the near far,middle and buccal and lingual directions.Schneider method was used to measure the morphology and other related parameters of the collected images.The CBCT images of the 2856 mandibular first permanent molars of 1600 patients(age 46.5+ 14.8 years old)were divided into group ABCDE five(group A:18-29 years old;B group:30-39 years;C group:40-49 years;D group:50-59 year old;E group:60-80 years old).The 5 groups measured the following data:the incidence of 1.MMC,the mesial and distal middle of the 2.mandibular first molar and the flexural and flexural position of the buccal tongue(P value,P = ab/bc);the improved detection rate of 3.vertucci;the number of the proximal middle teeth in the proximal third canals of the 4.mandibular first molar;and 5.of the middle of the first molar of the mandibular first molar.The distance between the middle buccal root and the mesial root canal of the middle tongue.The root canal classification method used in this study was the Vertucci root canal classification of American scholar Vertucci in 1984.After summarizing all the sample data,it was found that this method did not include all types of middle mesial canal of mandibular first molars.Therefore,we improved classification of Vertucci classification,clinical appending method and root canal type.Class I correspond to Type VIII in the new modified classification classification method;class ?corresponds to type 3-2 and MB fusion;class III corresponds to type 3-2 and ML fusion;type IV corresponds to 2-3-1;type V corresponds to 2-3-2;type VI corresponds to 2-3-2-1;? coirresponds to 1-2-3-2;type VIII corresponds to 1-3-4-1;type 3-1;3-2-1 It should be type 3-2-3-2;the XII class corresponds to the 3-4-3-2-1 type.Results? CBCT image of 2856 mandibular-first molars in 1600 outpatients.Among them,168 cases had middle mesial canals.In the first molar of the mandible,the middle mesial canals found in the A group was 37.50%,the B group was 17.80%,the C group was 14.88%,the D group was 19.64%,the E group was 10.12%,and the total discovery rate was 5.88%.?The mesial and distal curvature degree of the middle mesial canals in mandibular first molar was A group:28.67 + 7.14 degrees;the buccal tongue curvature A group:30.57 + 9.86 degrees;the mesial and distal curvature degree of B group was 27.44 + 10.76 degrees;the buccal tongue curvature degree was 29.96 +12.74 degrees;the mandibular submandibular mesial bend degree was 28.98 + 9.37 degrees;the buccal tongue bending degree:31.03 + 11.02 degrees;D group;D group The curvature degree of the near far middle direction:27.39 + 9.49 degrees;the buccal tongue bending degree:30.55 + 11.06 degrees;the mesial curvature degree of the E group was 29.33 + 10.14 degrees;the buccal tongue bending degree was 30.53+ 9.37 degrees.The difference was statistically significant(P<0.05).?The distribution of 1/3 in the third root canals of the mandibular first molar was higher than that in the root,with a maximum of 96.67%and a minimum of 73.01%.In the 5 groups,14 cases(22.22%)were found in the root crown 1/3 at most of the A group,and the middle of 1/3 in the root was 54(85.71%)in group A,and 3 cases(4.76%)appeared in the apical 1/3 as the mesial and distal direction of group A.?the improved classification of the third canals of the first molar of the southern Chinese population:the discovery rate of vertucci type I Type VIII:8.33%;class ?3-2 and MB fusion type;class ? type 3-2 and ML fusion type 2.98%;class IV 2-3-1 type 2.98%;class V 2-3-2 type 26.79%;class ? 2-3-2-1 type 2.38%;VII 1-3-4-1 type;VIII 1-3-4-1 type 1.79%;category IX 3-1 type 0.60%;category 3-2-1 2.38%;category 3-2-3-2 0.60%;? class 3-4-3-2-1 0.60%.The incidence of double roots in mandibular first molar with MMC was 12.5%,of which 3-2 cases had the highest number of bilateral roots.Conclusions? The discovery rate of the middle mesial canals in the first molar of the mandible decreased with age,especially after 30 years of age,and the rate of discovery was obviously decreased after 30 years of age.The middle mesial canals system in the first molar of the mandible was complicated and changeable.?The near and distal direction of the middle mesial canals in the first molar of the mandible and the buccal tongue curvature chart showed that both the mean and the buccal lingual curvature values fluctuated within the range of moderate and severe curvature degrees.The results also showed that the mesial and distal third canals in the first molar of the mandible increased with age,the bending degree decreased,and the five groups of mesial and distal root canal curvature 22 compared with the group A and C,D,E three,the difference was statistically significant,and there was no statistical difference in the other groups.? The firequency of MMC near,far,middle and buccal lingual flexion areas was 1/3>root cap 1/3>root tip 1/3.That is,the third root canal of mandibular first molar is mostly 1/3 in the root,but the bending part is located at the root cap 1/3 and root tip 1/3 to some extent.? The distance between MMC and MB and ML at the bottom of the pulp chamber was measured.The average distance between the above type MM and ML and MB was not statistically different,compared with the distance from the ML and the distance from MB.? CBCT can provide more guidance for clinical treatment,and can reduce the actual operative failure rate. |
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