| Background and objectiveRoot canal therapy is the basical treatment method and also the best choice for pulpand periapical disease. Meanwhile, thorough understanding of the root canal anatomy is animportant factor for the root canal therapy. At present, the root canal morphology isobserved mainly by X-ray examination. However, the morphological variations of the rootsurfaces, such as invagination, groove cracking, bifurcation, may affect the imageobservation of root canal morphology; and the root canal is likely to be mis-diagnosed dueto image overlaping of root canals; also, the root canal system of mandibular first molar iscomplicated and diversed. Therefore, it is critical to gain a thorough understanding of themorphology of the root canal system and its variations so as to achieve successful therapy.In this study, Micro CT was mainly applied to perform mandibular first premolarscanning and three-dimensional reconstruction to observe and analyze the root canalanatomical characteristics, so as to more throughly study the relationship between thedental anatomy and structure (both inside and outside) of dental root tissue, and to providereference for dental treatment and repair in clinic.Materials and Methods:1. Totally115human mandibular first premolars collected from January2009to June2010in the southwest China were selected,15of which had no age information. All thespecimen were reserved in a numbered bottle after debriding periodontal tissue andcalculus.2. The100mandibular first premolars with age information were selected to observethe existence of root groove. Then digital X-ray film(RVG) was radiographed in buccolingual and mesiodistal directions and was recorded. Based on the classification ofVertucci root canal morphology, the specimens that didn’t fit Vertucci classification weredefined as additional type (Ⅸ type). The information about the root canal type of each toothwas obtained by reading RVG image result by a dentist who has experienced training infilm reading.3. The100above-mentioned teeth specimens were embedded and placed in a fixer.Micro-CT scanning was performed from apex cuspid to apical root and then inserted thescanning data into the computer software. Mimics10.01software was applied to devideeach tooth specimen and reconstruct three-dimensional image. Micro-CT scanning resultswere evaluated by a dentist to obtain the information of root canal type of each tooth, whichwas also compared with the RVG image results. Finally, the consistency checking wasconducted between the two imaging results.4. Fifteen teeth specimens were also collected and performed three-dimensionalreconstruction of micro-CT image. Therefore, totally115three-dimensional micro-CTimages were obtained. Mimics10.01software was used to open the three-dimensionalimage of each tooth specimen,so as to systematically study the anatomical structure ofcanals, and to observe the morphology of the root canal orifice, position and number of theroot foramen, minute structure of accessory canal, intercanal communications and apicaldelta. The three-dimensional image of each tooth specimen was observed from differentdirections and classified based on the Vertucci root canal morphology classification method,while the rest types that didn’t fit Vertucci were defined as the additional type. Furthermore,the additional types were further subdivided into1-2-3,1-3,1-3-2based on the experimentalresults. Then the type of each canal was obtained by reading Micro-CT images.5. From the X-ray image radiographyed in buccolingual and mesiodistal directions,two X-ray film results all indicated mandibular first premolars with a single root canal.Then digital imaging system software was used to exclude the tooth specimens withcurvature degree larger than20°. Finally,58specimens of mandibular first premolars wereobtained.6. The58mandibular first premolars were divided into three groups: young age group (33), middle age group (15) and elderly age group (10). Each tooth root was divided into3parts:apical root, middle root and cervical root. Mimics10.01Software was applied tomeasure the buccolingual and mesiodistal diameter in the cross-sectional images, and thencalculated the canal taper in the buccolingual and mesiodistal directions. In addition, thedifferences in the canal diameter and canal taper were compared among the3groups.7. Samples of26mandibular first premolars(type Ⅴ,1-2) were extracted. Thefull-length of teeth was measured using a vernier caliper, then the Mimics10.01softwarewas used to save the three-dimensional perspective view of the26teeth as the BMP formatof lingual surface and mesial surface, then the Image-Pro Plus6.0software was used tomeasure the full length of teeth, the distance between apical root and the location of thelingual canal orifice, the distance between apical root and enamelo-cemental junction in theperspective view which was saved as BMP format. Also, the differences of root canalorifice observed from the buccolingual and mesiodistal direction were analyzed.AndImage-Pro Plus6.0software was used to measure the angle between lingual root canal andbuccal root cana, the curvature degree of lingual root canal in the three-dimensionalperspective view measured from buccolingual and mesiodistal direction. Also, thedifferences of lingual root canal angle observed from the buccolingual and mesiodistaldirection were analyzed.Results:1. Both of the Micro-CT scanning and digital imaging system indicated that theoccurrence rate of single root canal was63%, but the occurrence rate of multiple canalswas25%. Consistent checking was performed between Micro-CT and RVG images resultsof the root canal, indicating moderate consistency between the two methods (Kappa value0.541). By observing the dental canal of the100mandibular first molars,29teeth werefound root groove, which was mainly distributed in mesial root; Micro-CT imaging findingsshowed that24teeth with root groove had two or two more root canals (82.8%), whilecombined with the Miicro-CT dimentional image and dimentional perspective view, itindicated that three teeth were mis-diagnozed mesial root as root canal by RVG imaging. 2. Systematic study on micro CT imaging of root canals of115mandibular firstpremolars demonstrated that the occurrence rate of oval-shaped root canal orifice was84.3%(97/115),flattened-ribbon-shaped7%(8/115),8-shaped7%(8/115), triangule-shaped1.7%(2/115). Most root foramen located at the lateral side of root (77%,89/115), of whichsingle root foramen (50.4%,58/115), double apical foramens (28.7%,33/115), threeapical foramens (14.8%,17/115), four apical foramens(6.1%,7/115). There were41mandibular first premolars with accessory canals (35.7%,41/115), and92.7%of accessorycanals were located in the apical third of the root (38/41). The remaining three teethspecimens were found accessory canals in the middle third of the root, including oneaccessory canal(87.8%,36/41), two accessory canals(9.8%,4/41), four accessorycanals(2.4%,1/41). Meanwhile,apical delta only accounted for6.1%(7/115). Intercanalcommunications were observed in3.5%(4/115) of the specimens. One was located in themiddle third of the root and three in apical third of the root. Loops were present in7.0%(8/115) of specimens. Three were located in the middle third of the root and five in apicalthird of the root. An isthmus was identified in only two specimens. These were located inthe middle and apical third of the root of these specimens.3. Based on the Vertucci root canal classification, the115mandibular first premolarswere divided according to the type of micro-CT system as following:65.2%(75/115) wereidentified as Type Ⅰ(1-1),2.6%(3/115) Type Ⅲ (1-2-1),22.6%(26/115) Type Ⅴ (1-2) and0.9%(1/115) Type Ⅶ (1-2-1-2). Additional types identified included:2.6%(3/115) Type1-3-2,5.2%(6/115) Type1-3and0.9%(1/115) Type1-2-3.4. In the four cross-sections from buccolingual direction, despite of root foramen,there were statistical differences in root canal diameter in3age groups((P<0.05), and themaximum diameter was observed in young age group; however, the difference was mainlyexisted between young age group and elderly age group in mesiodistal direction(P<0.05).There was difference in root canal taper between the young age group and the middle andelderly age group(P<0.05), but no statistical difference between middle age group andelderly age group; in mesiodistal direction, there was difference between the young agegroup and elderly age group (P <0.05). 5. In type Ⅴ(1-2) mandibular first premolars, there was no significant difference in thelingual root canal orifice in the lateral and mesiodistal direction (P>0.05). About81%(21/26) were positioned in the middle third of teeth in the lateral direction, and theremaining (19%,5/26) in the apical third of the teeth,38%(10/26) in the apical third of theroot,62%(16/26) in the middle third of the root. And69%(18/26) were positioned in themiddle third of teeth in the mesiodistal direction, and the remaining (31%,8/26) in theapical third of the teeth,27%(7/26) in the apical third of the root,73%(19/26)in the middlethird of the root.6. There was statistical difference in the angle between lingual root canal and buccalroot canal in the lateral and mesiodistal direction (P<0.01). The average value was8.31°inthe lateral direction, but33.54°in the mesiodistal direction;92%lingual root canal wasfound straight or slightly curve(24/26), but77%severe curve in mesiodistal direction(20/26). The average value in the lateral direction was11.31°,26.66°in mesiodistal direction.Also, there was statistical difference in lingual root canal curve by comparing the resultsobserved from the two directions.Conclusions1. Micro-CT images could clearly show the morphology of root canal; RVG imagesobserved in the buccolingual and mesiodistal direction could distinguish the root canal typeof mandibular first premolar, but poor accuracy in distinguishing complex root canal,resluting in mis-diagnosing mesial invagination as root canal.2. In southwest China, the root canal morphology of mandibular first molar is complex,and the incidence of collateral accessory canal, intercanal communication, multi-root canalis high. Complex root canal and C-shaped canal may relate to sample of root groove.3. Micro-CT cross-section of mandibular first premolars with single root canalindicates that the shape of root canal is complex and diversed. With age increases, the rootcanal diameter in the same cross-section gradually narrows, the diameter of the root canalin the middle root shows great change, but little change in apical foramen. In buccolingualdirection, the original root canl taper is different among the three age group, but almost the same in the mesiodistal direction. In clinic, the original canal taper should be chosen basedon the mesiodistal direction. In the mesiodistal direction, the taper of3-segment canal in theyoung and middle age group (13-45age) nearing0.075, and it is recommended to choose0.07for perservation.4. Lingual root canal orifice of typeⅤ (1-2) mandibular first premolar mainly locates5-12mm from the apical canal; meanwhile, because of large angle between lingual canaland the buccal root canal, the lingual root canal of type Ⅴ mandibularfirst premolar islikely to be neglected, which should be paid more attention in clinic. |
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