| BackgroundBecause of the complicacy of the canal system, the second mesiobuccal canals(MB2) of mesiobuccal root of the maxillary first molars are often omitted by clinicians during daily diagnosis and treatment. Chinese and overseas scholars have utilized many metheds to analyse the morphology of the MB2.The common used methods to research on extracted teeth are Clearing techniques, staining and dental operating microscope.CBCT technology, also known as Layer cone beam volume imaging technology, advent in the late1990s. CBCT, which is a noninvasion imaging test, has been use for Clinical diagnosis of oral diseases in recent years. It is a computer equipment with Tapered beam exposure and restructuring of tomographic images.The principle of CBCT is X-ray generator at a relatively low amount of ray (usually ball tube current is controlled in10ma or so) around the pitch do as body ring DR (Digital shot photos). And then it will move around the projection body many times collecting data to make a reconstruction. Finally, we will get a three-dimensional image. The study of MB2of mesiobuccal root of the maxillary first molars by using CBCT have found that CBCT can provides the first reliable image information for clinic. Because it can show a clear and stereoscopic visual of the morphology of MB2in coronal view, sagittal view and axial view. But the results are different from each other in various studies. These differences may be related to races diversity, observation methods and technology and whether the operators have detected the MB2carefully and consciously. Research results will also diverse under different setting of CBCT. At all events, CBCT, comparing with the conventional methds, is more accurate to help clinicians to know the complicacy and high incidence of MB2of mesiobuccal root of the maxillary molars.ObjectivesCBCT is a clinical auxiliary equipment which is developing rapidly these years. CBCT technology, compared with X-ray, panoramic radiograph and traditional spiral CT, has various distinct virtues like small dose of radiation, high resolution image, three-dimension reconstruction and user-friendly control. It can also show the image in coronal view, sagittal view, and axial view simultaneously and analyse it through the software on computer. These advantages are appropriate for the need of clinical therapy.CBCT has been used in field of endodontic diseases. As a auxiliary examination equipment, CBCT has been utilized for the research of MB2of mesiobuccal root of the maxillary first molars. However, the studies before have not focused on the aging of the maxillary first molars, except for the morphology and category of them. In our study, we attempt to utilize CBCT to investigate the relationship between aging and the morphology of the mesiobuccal root of maxillary first molars. So as to improve the curative effect of root canal therapy. Materials and methodsChapter One The stuty of the correlation between age and the mesiobuccal root of maxillary first molars by CBCT1. A total of153patients were enrolled in the study, including those suffering from wisdom tooth extraction, jaw trauma, maxillary sinusitis and those who required a pre-operative assessment for inplants or orthodontic treatment.262maxillary first molars of153patients were divided into two groups(Group A, Group B) by the age of40. All the enrolled teeth are based on the following criteria:(1) maxillary first molars without periapical lesions;(2) maxillary first molars had not been endodontically treated;(3) maxillary first molars have no root canals with open apices, absorption or calcification;(4) the CBCT images were of good quality.2. CBCT is a PROMAX3D imaging system manufactured by Finnish company Planmeca. Image resolution:401×401×401, voxel dimensions:200μmx200μm, voltage:84kv, current:14mA, gray scale:15bit, time of exposure:12s, time of reconstruction:30s-150s, minimum thick-layer:0.2mm, resolution of the detector:1024×1024, pixel size:127μm×127μm. Image acquisitions rotate200degrees at a time. Image domain:140×105×130mm. The Server of three dimension reconstruction use Feldkamp filtered back projection which the company have a patent on it. High contrast object compensation improved artifact removal (IAR). Image data use DICOM as the saving format.3. All the CBCT images were analysed by the native software within CBCT system. Software is running on a32-bit Windows7system. Display screen is manufactured by Lenovo Company with a resolution of1280×1024. Evaluation of all the images were carried out in a dark room by1clinician of oral image and1postgraduate majored in endodontics. Consensus were made when different opinions ture up. The following data were measured in all two groups:(1) detection rate of MB2;(2) length of the mesiobuccal root of maxillary first molars;(3) distance of canal orifices between MB and MB2.Chapter Two The study of canal curvature of the mesiobuccal root of maxillary first molars by CBCT1. CBCT images collection quantity, screening criteria, groups design, the type and software of CBCT are the same as Chapter One.2. The following data were measured in all two groups:(1) the curvature degree and position (value P, P=ab/bc) of mesiobuccal roots of the maxillary first molars in mesiodistal direction, and whether there is a second curvature.(2) the curvature degree and position(value P, P=ab/bc) of mesiobuccal roots of the maxillary first molars in buccolingual direction, and whether there is a second curvature.Chapter Three The study of categories of the mesiobuccal root canals of maxillary first molars by CBCT1. CBCT images collection quantity, screening criteria, groups design, the type and software of CBCT are the same as Chapter One.2. The following data were measured in all two groups:(1)categories of the cannals of mesiobuccal roots of the maxillary first molars;(2)distance between canal orifices and the positions where canal furcation occurred;(3)root number of the maxillary first molars.Results1. The detection rate of MB2of mesiobuccal roots in262maxillary first molars are74.4%. The rate in Group A is80.4%, while the rate in Group B is67.2%. Difference was statistically significant(P<0.05). 2. The length of the mesiobuccal roots of maxillary first molars has a mean value of17.9±1.4mm in Group A and17.7±1.3mm in Group B, with no statistical significance(P>0.05).3. The distance of canal orifices between MB and MB2has a mean value of1.3±0.5mm in Group A and1.5±0.5mm in Group B, with statistical significance(P <0.05).4. The curvature degree of mesiobuccal roots of the maxillary first molars in mesiodistal direction has a mean value of28.5°±8.2°in Group A and26.2°±7.7°in Group B, with statistical significance(P<0.05). The curvature degree of mesiobuccal roots of the maxillary first molars in buccolingual direction has a mean value of16.2°±9.1°in Group A and17.0°±7.4°in Group B, with no statistical significance(P>0.05).5. The curvatures position of mesiobuccal roots of the maxillary first molars in mesiodistal and buccolingual direction of Group A are both occurred commonly in the middle third portion, with a percentage of88.8%and80.4%respectively. For the mesiobuccal roots of the maxillary first molars in Group B, the maximum curvatures were also mainly located in the middle third which account for94.1%, both in mesiodistal and buccolingual direction.6. Except for the Vertucci Type I, the Vertucci Type Ⅳ(37.1%)canal configuration was the most prevalent in the MB roots of maxillary first molars in Group A, following by Vertucci Type Ⅱ(27.9%) and Vertucci Type VI(1.4%). For the maxillary first molars in Group B, the most prevalent canal configuration was Vertucci Type Ⅳ(25.2%), following by Vertucci Type Ⅱ(21.8%) and Vertucci Type111(8.4%). A new type of canal was found in the present study which is configurate as2-3-2-1canal type.7. The distance between canal orifices and the positions where canal furcation occurred of maxillary first molars in Group A has a mean value of2.2±1.2mm and2.0±0.6mm in Group B, with no statistical significance(P>0.05).8. In total,260maxillary first molars (99.2%) had three separate roots. Only two of them have a fused root in buccal direction.Conclusions1. The detection rate of MB2canals decreased with age in maxillary first molars. Especially after the age of40, there had been a marked decline in the rate of MB2detection in maxillary first molars.2. In total,74.4%of the maxillary first molars were detected to have MB2canals by using CBCT. And99.2%of the maxillary first molars have three separate roots.3. The distance of canal orifices between MB and MB2will increase with age, while the length of the mesiobuccal root of maxillary first molars will not.4. The maximum curvatures are mainly located in the middle third of the mesiobuccal root of maxillary first molars in distal direction. The curvature degree of mesiobuccal roots of the maxillary first molars in mesiodistal direction will increase with age.5. The most prevalent canal configuration of mesiobuccal roots of the maxillary first molars was Vertucci Type IV (2-2) when MB2was present, following by Vertucci Type II (2-1). A new type of canal was found in the present study which is configurate as2-3-2-1canal type.6. The distance between canal orifices and the positions where canal furcation occurred will not increase with age. |
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