Measurement And Analysis Of Mandibular Structure Related To Dental Implantation In68Chinese, Assessed By Spiral Computed Tomography

Objective:In this study, the mandibles of68Chinese patients were reconstructed by64-slice spiral CT. We measured and analyzed the anatomic structures of the mandible for dental implantation, and explored the height of the mandible, the width of the mandible, the course of mandibluar canal, mandible morphology, prevalence of the anterior loop and length of the anterior loop of the inferior alveolar nerve. These indicators were also compared in genders and age groups. We wanted to reveal the basic characteristics of the anatomical structures of the Chinese mandible, which could provide clinical guidance for mandible dental implantation surgery and help to reduce mandible surgery complications.Methods:CT data of the mandibles of68Chinese patients was collected from the department of radiology in general hospital of Guangzhou military command of PLA. The patients underwent CT examination from January2008through April2011, which concluded34male and34female (mean age40years). The age of17male and17female ranged19～40years, and that of17male and17female ranged41-61.51cases (75%) had complete dentition,11cases (16%) missed one tooth, and6cases missed two teeth which were discontinuity. The missing teeth were located in the mandibular posterior area (91%in the mandiblular first or second molar area).Samples complied with the following conditions:①The edentulous area did not affect the positioning of the mental foramen;②The mandibular teeth did not have severe periodontal disease:③The mandible did not have fracture;④the mandible did not have tumors and cysts;⑤The teeth did not have PFMAll CT images were similarly obtained using64-slice Siemens (Siemens Medical Systems, Erlangen, Germany) according to the same following protocol:0.6mm of slice thickness,0.7pitch,120kV,64～200mA,512x512matrix. All patients underwent mandible axial scanning. Scan data from CT hosts was sent into imaging workstation. Reconstruction thickness image was lmm, and reconstruction interval image was0.7mm, which was saved to a CD-ROM in DICOM format. The DICOM format data was imported to Simplant software, and three-dimensional reconstruction of the mandible was carried out. In the three-dimensional image reconstruction model, the reference plane of the axial image was adjusted so that it was parallel to the lower edge of the mandible. After the axial image of the mandible was adjusted, arch curve was marked in the plane of mental foramen. The software would automatically generate the cross-sectional image and the panoramic image. After three-dimensional reconstruction, four images were shown that were the cross-sectional image and the panoramic image, and three-dimensional image. The cross-sectional image was perpendicular to the arch curve, and its interval was lmm. The cross-sectional image in which the mental foramen was recognized was defined as section2, and the image6mm anterior to section2was defined as section1, corresponding to the area around the canine. The images from6,12, and18mm posterior to section2were defined as sections3(around the second premolar),4(around the first molar), and5(around the second molar), respectively. Other orientations image was used as a supplementary observation image.Measurement:The height of mandible H (Height):The vertical distance from the alveolar crest to the bottom of the mandible. The width of mandible W (Width):The widths A, B, C, and D were measured at heights of5,10,15, and20mm, respectively, above the inferior border of the mandible toward the alveolar crest.The shapes of the mandibles were classified into three types using the cross-sectional images Type A was round on the buccal side and concave on the lingual side, type B was concave on the buccal side and round on the lingual side, and type C was round shaped on both sides.The height of mandibular canal (SAC):the distance from the superior border of the canal to the alveolar crest. In the cross-sectional of mental foramen, the distance from the superior border of mental foramen and the superior border of the canal to the alveolar crest was measured, respectively. In the original cross-sectional of the anterior loop, the distance from the superior border of anterior loop to’the alveolar crest was measured (MF-S).The distance from the inferior border of the canal to the bottom of the mandible (IBM):in the cross-sectional of mental foramen, the distance from the inferior border of mental foramen and the inferior border of the canal to the alveolar crest was measured, respectively. In the original cross-sectional of the anterior loop, the distance from the interior border of anterior loop to the alveolar crest was measured (MF-I).Thickness from SAC to the buccal surface (TSB):The horizontal distance was from the outer edge of mandibular canal to the mandibular buccal bone plate. In the area of mental foramen, mental foramen opened on the buccal bone plate, which was counted as a distance of0mm.Thickness from SAC to the lingual surface (TSL):The horizontal distance was from the inner edge of mandibular canal to the mandibular lingual bone plate.The position of mental foramen:the position of the mental foramen was relative to the mandibular premolar or molar relationship.Prevalence of the anterior loop:The proportion of anterior loop in front of mental foramen.The length of anterior loop (ALL):The horizontal distance from the leading edge of mental foramen to the original cross-sectional of the anterior loop (mandibular incisive canal).The identification of the anterior loop was based on signs such as the existence of two separate canals beyond the anterior border, an oval or elongated shape of the same canal and finally on its size. However, not every case is so obvious. We devised a cut-off point of3mm for the maximum diameter of the incisive canal. That is, a canal of more than3mm was always considered part of the mandibular canal (anterior loop) and never of the mandibular incisive canal. We use this method to determine the original cross-sectional of the anterior loop (mandibular incisive canal), measured the length of anterior loop in the paranomic image.Results:The mandibular height was the greatest in section1and gradually decreased to section5. The means and SD of the heights ranged from27.6±2.7mm to32.3±2.7mm. The heights in male and female patients ranged from28.8mm±2.3mm to33.5±2.6mm and from26.3±2.5mm to31.0±2.3mm. There was a significant difference in height between genders. The height in male subjects was2.2to2.7mm higher than that in female subjects. The height in young and middle-aged patients ranged from27.5±2.9mm to32.0±2.7mm and from27.7±2.5mm to32.5±2.7mm. There was no difference in height between age group.The means and SD of the widths ranged from10.5±1.0mm to17.0±1.6mm. The widths at heights of5mm above the inferior border of the mandible toward the alveolar crest were almost the same about11mm from anterior to posterior. The widths at heights of10mm、15mm、20mm above the inferior border of the mandible toward the alveolar crest tended to increase from anterior to posterior. The widths in male and female patients ranged from10.7±1.0mm to17.2±1.6mm and from10.4±1.0mm to16.8±1.7mm. The widths in male at heights of15mm,20mm above the inferior border of the mandible toward the alveolar crest was the greatest, but that in female at height of15mm above the inferior border of the mandible toward the alveolar crest was the greatest. The width in male patients was slightly greater than that in female patients. The widths in young and middle-aged patients ranged from 10.5±1.1mm to17.3±1.7mm and from10.6±0.8mm to16.7±1.5mm. The widths of the anterior region in young age at heights of15mm,20mm above the inferior border of the mandible were the greatest. The widths of the posterior region at heights of15mm above the inferior border of the mandible were the greatest. The widths in middle-aged at heights of15mm above the inferior border of the mandible was the greatest. The width of the posterior region in young patients was slightly greater than that in middle-aged patients.Type C (round)(62%-76%) was the most common in the posterior region, followed by type A (lingual concavity)(14%-37%), whereas type B (buccal concavity)(35%-73%) and type C (23%-55%) were the most common types in the anterior region. The shapes were not affected by side.The SAC value was the greatest in section2and gradually decreased toward section5. The means and SD of the SAC ranged froml5.9±2.5mm to18.4±2.3mm. The SAC in male and female patients ranged from16.7±2.1mm to19.3±2.1mm and from15.1±2.6mm to17.5±2.1mm. There was a significantly difference in SAC between genders. The SAC in male subjects was2.2to2.7mm higher, than that in female subjects. The SAC in young and middle-age patients ranged from15.9±2.6mm to18.3±2.4mm and from15.8±2.4mm to18.5±2.3mm.There was no difference in SAC between age groups.The distance from the inferior border of the canal to the bottom of the mandible in anterior mandible was significantly greater than that in posterior mandible. There was no difference in the distance from the inferior border of the canal to the bottom of the mandible between posterior mandible areas. The IBM in male and female patients ranged from9.1±1.4mm to11.2±1.5mm and from8.3±1.3mm to10.6±1.0mm. There was a significant difference in IBM between genders. The IBM in male subjects was0.5to0.8mm higher than that in female subjects. The IBM in young and middle-aged patients ranged from8.6±1.6mm to10.8±1.4mm and from8.8±1.3mm to11.1±1.2mm. There was no difference in IBM between age groups.The MF-S was13.0±1.8mm. The MF-S in male and female patients was13.2±1.7mm and12.8±1.9mm, respectively. The MF-S in young and middle-aged was12.8±1.9mm and13.2±1.7mm, respectively. There was no difference in MF-S between genders (P=0.11) and age groups (P=0.31).The MF-I was15.5±1.5mm. The MF-I in male and female patients were16.3±1.5mm and14.8±1.0mm, respectively. The MF-I in young and middle-aged were15.4±1.4mm and15.6±1.5mm, respectively. There was no difference in MF-I between age groups, whereas there was a significant difference in MF-I between genders. The MF-I in male subjects was1.5mm higher than that in female subjects.The means and SD of TSB ranged from0mm to7.8±1.3mm. The TSB was greatest (7.8±1.3mm) in18mm posterior to the mental foramen (section5) and shortest (0mm) in mental foramen area (section2). The means and SD of TSL ranged from3.6±1.1mm to5.6±1.6mm. The TSL was greatest (5.6±1.6mm) in6mm anterior to the mental foramen (section1) and shortest (3.6±1.2mm and3.6±1.1mm) in12mm and18mm posterior to mental foramen (section4and section5).The mental foramen was situated below the second premolar tooth in64%of cases, between the first and second premolar tooth in22%of cases, between the second premolar and first molar tooth in12%of cases, in the first premolar tooth in1%of cases, and in the mesial root of the first molar tooth in1%of cases.An anterior loop was present in113of136mandible sides from68patients (prevalence83.1%). There was no difference in the prevalence of the anterior loop between the left and right sides of the mandibles (P=0.493), between genders (P=0.253), or between different age groups (P±0.118). The ALL of the entire population under study ranged from0mm to5.31mm. with a mean value of2.09±1.34mm. The ALL in male and female was2.42±1.38mm and1.77±1.22mm, respectively. The ALL in males was significantly longer than in females (P=0.005). There was no significant difference in ALL between sides (P=0.260). Spearman’s rank correlation coefficient revealed no relationship between ALL and age (r=-0.039, P=0.656).Conclusions:The mean height of the mandible and the mean SAC gradually increased from posterior to anterior, the mean height and the mean SAC in male patients was significantly larger than that in females. The width of the mandible in male patients was slightly greater than that in female patients. The width of the posterior mandible in young patients was slightly greater than that in middle-aged patients. Type A (lingual concavity) was14%-37%in the posterior region. The risk of lingual cortical bone perforation is greater with type A for dental implantation, whereas type B (buccal concavity) was35%-73%in the anterior region. The risk of buccal cortical bone perforation is greater with type B. The risk of perforation with type C is lower than that with the other types because of the sufficient lateral bone in the posterior regions.In the posterior region of mental foramen, the distance from mandibular canal to the inferior border of mandible was almost constant. In the anterior region of mental foramen, the distance gradually increased. The anterior loop runs upwards and backwards to the mental foramen. Because large variations in measurements were observed, for the position of metal foramen, the length of the anterior loop, and prevalence of the anterior loop, no fixed distance mesially from the mental foramen should be considered safe. The preoperative MSCT/CBCT measurement yields important information for each case.Spiral CT (or cone-beam CT) through a three-dimensional reconstruction can be a good indication for the cause of mandibular canal and the shape of the mandible, and can accurately measure the position of the mandibular canal. This is a great of importance for dental implant surgery in the mandible.