100例下颌骨下颌管形态及其至牙槽嵴距离的观测研究

目的:观测下颌管形态结构及其周围的关系,为临床下颌骨手术、种植牙手术的进路、深度提供参考数据。方法:采用100个人体下颌骨,对其下颌管上缘至各牙槽嵴顶的间距和颏孔至下颌孔的间距进行观察与测量,根据吴汝康《人类骨学测量方法》规定的年龄估计及性别的标准加以分析。结果:下颌管均值长男性62.30mm,女性57.69mm;下颌管上缘至第二前磨牙牙槽嵴距离:男性14.79mm,女性15.14mm;下颌管上缘至第一磨牙牙槽嵴距离男性14.69mm,女性14.23mm;下颌管上缘至第二磨牙牙槽嵴距离男性14.68mm,女性14.21mm;下颌管呈圆形68例,卵圆形32例。结论:男女牙槽嵴至下颌管距离无显著性差异,P>0.05,但男女下颌管长度有显著性差异,男性大于女性,P<0.01。提示,在进行种植牙手术和下颌骨手术时,应留意下颌管与周围组织的关系。     

Spiral tomography for measuring bone width at different levels from the crest to the inferior border of the mandible in vitro

Introduction Tomography images provide sufficient detail for estimating the vertical and horizontal dimensions of alveolar bone and reducing surgical injuries. This study evaluated the role of spiral tomography in measuring mandibular alveolar bone width. Methods Cross-sectional tomography slices were taken using a Cranex Tome unit at three or four different locations on each side of three chosen mandibles, such that all the locations were distal to the mental foramen. In addition, artificial soft tissues were reconstructed using Play-Doh modeling clay. On the tomography image, a line was drawn from the crest to the inferior border of the mandible (MC), and the bone height to the mandibular canal and bone width were measured at one-third, two-thirds, and one-half MC, and the mandibular canal levels. Then, the mandibles were sectioned at the same sites, and the bone sections were measured. For statistical analysis, the sign test analysis was used. Results There was a statistically significant difference between the tomographic and real anatomical bone width at one-half and one-third MC, and the canal level (P < 0.05), while the difference between tomography and bone section measurements were not significant at two-thirds MC, or, the bone height to the mandibular canal (P > 0.05). Conclusions The bone width on tomographic images was overestimated by between 2.3 and 0.1 mm. Therefore, caution should be exercised when evaluating bone width measured from tomography images. In most locations, the measured height to the canal was underestimated by between 0.1 and 2.7 mm, which confirmed the safety of spiral tomography for estimating the distance related to the mandibular canal.     

Reliability of spiral tomography with the Scanora® technique for dental implant planning

The Scanora X‐ray unit permits linear and rotational narrow beam radiography as well as spiral tomography, making it well suited for implant planning radiography. The purpose of this study was to evaluate the reliability of measurements made in spiral lower jaw tomograms of patients examined with the Scanora® technique. Six observers measured the distance between the alveolar crest and the mandibular canal in spiral tomographic images taken on 40 consecutive patients before implant surgery. In one randomly chosen image from each patient, the observers marked the measuring points at the two locations. The measurements were repeated 2 months later. Three of the observers, all radiologists. excluded in total 11 sets of images considered to improve if retaken. Analysis of variance showed an average standard deviation between observers of 1.67 mm. This was mainly due to the intraobserver variation, 1.07 mm. The variation between plots was significantly larger at the alveolar crest. Confidence intervals showed that reliability improves with multiple readings, either made independently by one observer or separately by several. The inter‐ and intraobserver variation decreased to 1.42 mm and 0.86 mm, respectively. without the images of inferior quality. Compared with a similar study based on hypocycloidal images, the variability was less due to the intraobserver variation and was affected positively by an optimized image quality.     

Comparison of three radiographic methods used to locate the mandibular canal in the buccolingual direction before bilateral sagittal split osteotomy

OBJECTIVE: Panoramic radiographs, computerized tomography (CT), and conventional spiral tomographic (Scanora, Soredex, Helsinki, Finland) radiographs were compared for their ability to locate the mandibular canal in the buccolingual direction. Furthermore, the relationship between the cortication of the mandibular canal in panoramic radiographs and the location of the canal in both computerized and conventional tomographic radiographs was assessed. STUDY DESIGN: The buccolingual location of the mandibular canal was determined bilaterally in twenty consecutive patients scheduled for bilateral sagittal split osteotomy. The position of the mandibular canal was evaluated by means of panoramic radiography, Scanora, and CT. The three imaging methods were compared for their ability to locate the mandibular canal in the buccolingual direction. The subjective neurosensory deficit of the lower lip and chin on both sides was registered preoperatively and at 4 days, 3 weeks, and 3 months after surgery, and the operative outcome was analyzed in relation to the distance from the mandibular canal to the buccal cortex of the mandible. RESULTS: CT gave better visualization of the mandibular canal than Scanora imaging. Cortication of the mandibular canal on the panoramic radiograph did not serve as a predictor of the proximity of the mandibular canal to the cortices of the mandible. At 3-month follow-up, there were only eight operated sides with abnormal sensation of the lower lip and chin. In seven of these sides, the distance from the mandibular canal to the buccal cortex was less than 2 mm. CONCLUSION: The buccolingual location of the mandibular canal is visualized better with CT than with Scanora or panoramic radiographs.     

Quality of preimplant low-dose tomography

OBJECTIVES: The aim of this study was to test the influence of radiation dose on image quality in mandibular preimplant computed tomographic examinations and to compare the quality of computed and conventional spiral tomographic images. STUDY DESIGN: Cross-sectional images were obtained on 17 patients with conventional spiral tomography (Scanora technique) and reformatted computed tomography at 40 and 80 mAs. Observers graded the acceptability of images for implant planning and traced the contour of the mandibular body and canal. RESULTS: Conventional spiral tomographic images scored significantly higher than computed tomographic images whereas mean score differences between computed tomographic techniques were not statistically significant. Anatomic structures, in particular the mandibular canal, were more frequently untraceable in high-dose than in low-dose computed tomography but always traceable in conventional tomograms. CONCLUSION: Conventional spiral tomograms were subjectively preferred over computed tomographic images. For mandibular implant planning, computed tomography examinations can be performed with lower-than-standard mAs. Quantum noise seems to contribute to the visibility of anatomic structures in reformatted computed tomographic images.     

Precision,reproducibility, and accuracy of bone crest level measurements of CBCT cross sections using different resolutions

Objective:To evaluate the precision, reproducibility, and accuracy of alveolar crest level measurements on CBCT images obtained with different voxel sizes.Materials and Methods:CBCT exams were made of 12 dried human mandibles with voxel dimensions of 0.2, 0.3, and 0.4 mm. Bone crest level was measured directly on the mandibles with a digital caliper and on CBCT images. Images were measured twice by two examiners. Intra- and interexaminer precision and reproducibility were assessed using paired and t-tests, respectively. Accuracy was evaluated using t-tests.Results:Precision and reproducibility of bone crest level tomographic measurements was good for all voxel sizes evaluated. The images with 0.2-mm voxel size showed a decreased number of intraexaminer errors. A high accuracy for measurements of bone crest level was observed for all CBCT definitions, except for the mandibular incisors using the 0.4-mm voxel size.Conclusions:Precision and reproducibility of alveolar bone level measurements were good for various voxel sizes. CBCT images demonstrated good accuracy for 0.2-mm and 0.3-mm voxel sizes. The mandibular incisor region needs better resolution than that provided by 0.4-mm voxel size for bone crest level measurements.     

Localisation of the mandibular canal using conventional spiral tomography: a human cadaver study

For certain surgical procedures (e.g. placement of implants), an accurate localisation of the mandibular canal is of utmost importance to avoid injuries to the neurovascular bundle. The aim of the present study was to evaluate, on human fresh cadavers (n = 6), the accuracy of conventional spiral tomography for the localisation of the mandibular canal. By means of the Cranex TOME multifunctional unit (Orion Corporation Soredex, Helsinki, Finland), tomographic slices were taken at 3 different locations in the left posterior mandible (distal to the mental foramen). The mandibles were then sectioned at these 3 sites with a microtome. With a digital sliding caliper, the following 3 measurements were performed both on the tomograms and the bone sections at the three sites: 1) distance from the crest to mandibular canal, 2) overall bone height and 3) bone width. Overestimations of the distance to the mandibular canal (8/18) ranged from 1.05 to 0.10 mm and underestimations from 0.30 to 1.36 mm. The same number of over- and underestimations occurred for the bone height (1.14 to 0.14 mm and 0.15 to 1.40 mm, respectively). The bone width scored more overestimations (10/18), ranging from 1.40 to 0.12 mm, while underestimations ranged from 0.25 to 1.35 mm. From the present results, it is concluded that spiral tomography using the Cranex TOME multifunctional X-ray unit provides accurate information and sufficient detail for preoperative planning of implant placement in the posterior mandible.     

COMPARATIVE STUDY OF SINGLE AND MULTISLICE COMPUTED TOMOGRAPHY FOR ASSESSMENT OF THE MANDIBULAR CANAL

Objective:

The purpose of this study was to evaluate the accuracy of relative measurements from the roof of the mandibular canal to the alveolar crest in multislice (multidetector) computed tomography (MDCT) and single-slice computed tomography (SSCT).

Material and Methods:

The sample consisted of 26 printed CT films (7 SSCT and 19 MDCT) from the files of the LABI-3D (3D Imaging Laboratory) of the School of Dentistry of the University of São Paulo (FOUSP), which had been acquired using different protocols. Two observers analyzed in a randomized and independent order a series of 22 oblique CT reconstructions of each patient. Each observer analyzed the CT scans twice. The length of the mandibular canal and the distance between the mandibular canal roof and the crest of the alveolar ridge were obtained. Dahlberg test was used for statistical analysis.

Results:

The mean error found for the mandibular canal length measurements obtained from SSCT was 0.53 mm in the interobserver analysis, and 0.38 mm for both observers. On MDCT images, the mean error was 0.0 mm in the interobserver analysis, and 0.0 and 0.23 mm in the intraobserver analysis. Regarding the distance between the mandibular canal roof and the alveolar bone crest, the SSCT images showed a mean error of 1.16 mm in the interobserver analysis and 0.66 and 0.59 mm in the intraobserver analysis. In the MDCT images, the mean error was 0.72 mm in the interobserver analysis and 0.50 and 0.54 mm in the intraobserver analysis.

Conclusion:

Multislice CT was demonstrated a more accurate method and demonstrated high reproducibility in the analysis of important anatomical landmarks for planning of mandibular dental implants, namely the mandibular canal pathway and alveolar crest height.     

Computed tomographic analysis of the position of the mandibular canal in unilateral temporomandibular joint ankylosis patients

The aim of this study was to investigate the position of the mandibular canal through the region of the mandibular angle and body using computed tomographic (CT) imaging, and to relate the findings to those in the molar region on the ankylosed temporomandibular joint (TMJ) and the normal side. The mandibles of 25 patients with unilateral ankylosis of the TMJ (14 women and 11 men) were recorded on coronal CT slices 2 mm thick. All patients included in the study had had ankylosis diagnosed before they were 16 years old. The position of the mandibular canal was studied from the region of the third molar to that of the first molar on ankylosed and normal mandibles. The following variables were measured: the distance between the external surface of the buccal cortical plate and the outer surface of the mandibular canal (B); the distance between the external surface of the lingual cortical plate and the outer surface of the mandibular canal (L), and the distance between the external surface of the inferior border of the mandible and the outer surface of the mandibular canal (I). Our results suggest that changes are more pronounced in the regions of the second and third molars. The mandibular canal is closest to the inferior border of the mandible in the region of the second molar and farthest in that of the third molar. The greatest distance between the outer surface of the mandibular canal to the external surface of the buccal cortex on the ankylosed and normal sides was found in the first and second molars, and it was greater on the normal side. To minimise the risk of injury to the inferior alveolar nerve, the measurements of B, L, and I should be considered separately on the ankylosed and normal sides when planning mandibular osteotomies for distraction osteogenesis and orthognathic surgery, and when using monocortical screws.     

跨下牙槽神经种植相关解剖结构的影像学测量及分析研究

目的 通过锥形束CT影像数据测量下颌第二磨牙处下颌神经管位置,分析跨下牙槽神经种植术的理论植入范围,为临床上使用该方法解决下颌后牙区种植骨量不足问题提供理论依据。方法 选取80例下颌第二磨牙缺失且缺牙区垂直骨高度<9 mm的患者CBCT图像,测量该处下颌神经管到颊侧骨皮质、舌侧骨皮质、牙槽嵴顶距离,并模拟跨下牙槽神经种植,测量种植体颊舌向倾斜的角度范围。结果 下颌第二磨牙处下颌神经管到颊侧骨皮质、舌侧骨皮质、牙槽嵴顶的距离分别是(6.913±1.222)、(2.859±0.891)、(7.991±0.783)mm,下颌神经管到颊侧骨皮质距离明显大于到舌侧骨皮质距离。75%的患者可行跨下牙槽神经种植术,模拟植入种植体颊舌向倾斜最小角度为19.360°±7.086°,最大角度为39.462°±6.924°。结论 下颌第二磨牙处下颌神经管明显偏向舌侧,保障了颊侧足够的骨量,多数下颌第二磨牙处无法垂直植入短种植体的患者仍可通过跨下牙槽神经种植术植入常规长度种植体。     

Evaluation of accuracy of computer-aided intraoperative positioning of endosseous oral implants in the edentulous mandible

The overall accuracy of a novel surgical computer-aided navigation system for placement of endosseous implants was evaluated. Five dry cadaver mandibles were scanned using high resolution computed tomography (HRCT). The position of four interforaminal dental implants was planned on the computer screen and transferred to the cadaver mandibles using VISIT, a surgical navigation software developed at the Vienna General Hospital. The specimens were HRCT-scanned again to compare the position of the implants with the preoperative plan on reformatted slices after matching of the pre- and postoperative data sets using the mutual information technique. The overall accuracy was 0.96 +/- 0.72 mm (range 0.0-3.5 mm). No perforation of the mandibular cortex or damage to the mandibular canal occurred. We conclude that computer-aided implant surgery can reach a level of accuracy where further clinical developments are feasible.     

Evaluation of Dimensional Accuracy of Panoramic Cross‐Sectional Tomography,Its Ability to Identify the Inferior Alveolar Canal,and Its Impact on Estimation of Appropriate Implant Dimensions in the Mandibular Posterior Region

Objectives: To evaluate the dimensional accuracy of panoramic cross‐sectional tomography, its impact on implant size estimation and its ability in identifying the inferior alveolar canal in the mandibular posterior region. Material and Methods: Eight partially edentulous mandibles with 18 edentulous sites were obtained. Orthopantomograms and tomograms were made and the mandible's outline and the position of mandibular canals on tomograms were traced on a clear acetate paper. Horizontal and vertical magnification factors were calculated. The mandibular height, distance between mandibular canal and alveolar crest, maximum bucco‐lingual width, distance between buccal cortex and mandibular canal, and cortical thickness at the inferior border of the mandible were measured. Potential implant sites were identified and implant sizes were estimated. Location and visibility of mandibular canals were also evaluated. The mandibles were sectioned at each site and all the above mentioned parameters were assessed which served as gold standard. Results: Mean horizontal and vertical magnification factors were 1.47 ± 0.048 and 1.53 ± 0.038. Total height and maximum bucco‐lingual width were underestimated by 1.88% and 1.59%. Crest to canal distance, cortical thickness at the inferior border of the mandible and buccal cortex to mandibular canal were overestimated by 0.59%, 5.16%, and 3.64%. Implant sizes were estimated for 11 sites and changes were recorded at 2 sites between record 1 and record 2. However, there was no disagreement between record 2 and record 3. Of the canals, 61.11% were located lingually and the visibility of mandibular canals was poor in 44.44% of cases. Conclusions: The tomograms were found to be accurate for the measurements in both horizontal and vertical planes and reliable for implant size estimation, taking into consideration proper magnification factors. They were also found to be useful in assessing the location of mandibular canal but were not very effective in discerning it.     

The use of 3 different imaging methods for the localization of the mandibular canal in dental implant planning

PURPOSE: The purpose of this study was to investigate the efficiency of panoramic radiography, conventional (cross-sectional) tomography, and computerized tomography for location of the mandibular canal before implant placement in the posterior region of the mandible. MATERIALS AND METHODS: Edentulous mandibles from 6 dry adult human skulls were used in this study. Four measurements (D1, D2, D3, D4) were made of 12 areas, one on each side of each mandible. Panoramic radiographs, conventional tomograms, and computerized tomograms were obtained. On each image, measurements were made for localization of the mandibular canal by one researcher. All measurements were repeated 3 times within a period of 3 weeks. Upon completion of imaging, the mandibles were surgically sectioned to provide direct measurements. The measurements obtained from the images were compared with direct measurements. Pearson correlation coefficients were calculated to detect statistical correlations between repeated measurements. The Dunnett t test was performed for statistical comparison of measurements from images and direct measurements. RESULTS: Pearson correlation coefficients showed strong linear correlation for all measurements (P < .01). No statistically significant difference was observed between direct measurement and D1, D2, or D4 (P < .05), but a statistically significant difference for D3 (buccolingual width 5 mm under mandibular crest; Dunnett t test; P > .05) between measurements was obtained from the images and direct measurements. CONCLUSION: The measurements obtained from computerized tomographic images were more consistent with direct measurements than the measurements obtained from panoramic radiographic images or conventional tomographic images.     

Measurements of distances related to the mandibular canal in radiographs

Before implant surgery in the mandibular side segment, it is of utmost interest to locate the mandibular canal in radiographs to avoid interference with the neurovascular bundle during surgery. Six mandibular specimens were radiographically examined with 2 panoramic and 3 tomographic techniques. The distances between the superior border of the canal and the alveolar crest and between the mandibular base and the inferior border of the canal were measured. In addition, the height of the canal was measured. The measurements were performed by 3 or 4 observers and compared with measurements on contact radiographs of the same areas. Tomography gave more accurate values of the above distances than panoramic techniaues. The variation between observers in detecting the mandibular canal Aas large.     

Effect of mandibular positioning on preimplant site measurement of the mandible in reformatted CT

The purpose of this study was to evaluate the effect of mandibular positioning on measurement of the reformatted cross-sectional image of the mandible in computed tomography (CT) according to the area on the mandible. Five dried mandibles, partially edentulous in the premolar and molar areas, were selected. The inferior border of the mandible was placed at 0-, 5-, 10-, 15-, and 20-degree angles to the CT scanning plane, and CTs were taken. The marked area of the reformatted cross-sectional image taken at each angle was found, and the distance from the most superior border of the mandibular canal to the alveolar crest was measured. As the angle between the CT scanning plane and mandibular plane increased, the distance from the most superior border of the mandibular canal to the alveolar crest also increased. The degree of increase was more pronounced in the posterior portion of the mandible than in the anterior portion of the mandible. As mandibular positional change in the CT gantry can affect the vertical measurement of the reformatted cross-sectional image, a correct guiding plane is necessary to accurately position the jaw to the CT scanning plane.     

2-D and 3-D reconstructions of spiral computed tomography in localization of the inferior alveolar canal for dental implants

OBJECTIVE: The purpose of this study was to compare and validate the accuracy of measurements on 2-dimensional and 3-dimensional reconstructions from spiral computed tomography in localization of the inferior alveolar canal. STUDY DESIGN: Four edentulous human cadaver heads with intact mandibles were imaged in a spiral computed tomography scanner. The data were transferred to a networked computer workstation to generate 2-dimensional orthoradially reformatted and 3-dimensional volumetric images. Linear measurements of the images were made from the superior border of the inferior alveolar canal to the alveolar crest. The specimens were then dissected at corresponding locations, and physical measurements were made. RESULTS: There were no statistically significant differences between the 2-dimensional computed tomography measurements and the physical measurements or between the 3-dimensional computed tomography measurements and the physical measurements. However, we did find a statistically significant difference between the 2-dimensional and 3-dimensional computed tomography measurements. CONCLUSIONS: 2-dimensional and 3-dimensional computed tomography images allow accurate measurements for localization of the inferior alveolar canal.     

下颌管的走行及解剖结构的研究

目的　研究下颌管的位置及解剖结构 ,为种植牙提供解剖依据。方法　选 15具成人有牙下颌骨标本在特定截面上测量下颌管纵横径和四壁厚度 ,观察 4具动脉灌注新鲜标本的下颌管内血管神经之间的关系。结果　下颌管在下颌骨体部走行中偏舌侧 ,并近下颌骨下缘 ;管内血管位于神经之上。结论　牙种植术中按正常解剖方位钻孔 ,可避免损伤下牙槽神经。如术中下颌管内突然涌出大量新鲜血 ,则提示继续手术可能损伤下牙槽神经     

基于CBCT的下颌后牙区骨内重要解剖结构研究

目的利用锥形束CT（cone beam computed tomography,CBCT）软件分析系统NNTViewer对活体下颌骨三维影像重建测量,研究下颌神经管与邻近解剖结构之间的关系。方法选取100例CBCT影像资料,在下颌骨横截面上测量：①下颌第一前磨牙至同侧第二磨牙各牙牙根中点、根尖与颊舌侧骨壁的距离;②下颌神经管与每个后牙根尖之间及与之相对应的颊舌侧骨壁、牙槽嵴顶和下颌骨下缘的距离。结果下颌第一前磨牙至同侧第二磨牙各牙牙根与颊、舌侧骨壁之间的距离,在牙根中点处分别为1．26—5．02mm、3．74～4．45mm,在根尖处分别为3．85—9．23mm、5．43—7．94mm;下颌第二前磨牙至同侧第二磨牙各牙根尖与下颌神经管之间的距离为5．31～8．19mm。下颌第二前磨牙至同侧第二磨牙各牙根尖下方处的下颌神经管与颊、舌侧骨壁之间的距离分别为3．71～7．62mm、2．91～4．12mm,与牙槽嵴顶之间的距离为17．09-19．22mm,与下颌骨下缘之间的距离为8．22～9．28mm。结论下颌后牙（下颌第三磨牙除外）牙根及下颌神经管与颊侧骨壁之间的距离由前往后逐渐变大。下颌神经管距离第二磨牙远中根最近,距离第一磨牙两根最远;与牙槽嵴顶的距离,在第一磨牙处最大,第二磨牙处最小;与下颌骨下缘的距离,在第二磨牙处最大,第一磨牙近中根处最小。     

Measurement accuracy of reconstructed 2-D images obtained by multi-slice helical computed tomography

The present dental reconstructed computed tomography (CT) images consist of continuously piled-up axial CT images that are perpendicular to the axial CT plane. In the mandibular posterior region, the angles of designed implants frequently differ from the angles perpendicular to the axial CT plane and the measurement of mandibular height is inaccurate. This study was performed to clarify the measurement accuracy of double-oblique reconstructed images in multi-slice helical CT, using dried mandibles. The mandibular height was measured from the alveolar crest immediately below the aluminum tube to the superior border of the mandibular canal using the double-oblique reconstructed images and the micro-CT average images of three semi-lateral dried mandibles. The mean of the differences between the double-oblique reconstructed images with a table pitch of 1.5 in a helical scan and the micro-CT average images was 0.31 mm. It is concluded that the accuracy of the double-oblique reconstructed image measurements with helical scan is high. So this double-oblique program can be applied to the imaging diagnosis in dental implant treatment.     

成人下颌前行管的锥形束CT影像学研究

目的探讨成年人群下颌神经管影像学特征,为临床下颌骨手术提供参考。方法随机抽取2018年1月至2021年1月就诊于贵阳市口腔医院的成年患者锥形束CT(cone beam CT,CBCT)影像学资料1000例,观察其下颌前行管及其余分支,统计前行管在下颌升支区、磨牙后区、磨牙区的发生率以及到下颌骨各位点的距离。结果本研究最终观察患者901例(1802侧),有386例患者发现了下颌神经管分支,发生率为42.84%;有182例患者发现前行管(男性97例,女性85例),占总人数的20.20%(182/901),共发现225侧下颌骨有前行管,左侧下颌有101例,右侧有124例,性别和左右侧差异无统计学意义。前行管主要发生在磨牙区、磨牙后区和升支区,而前行管起点在升支区最好发,止点在磨牙区发生最多(P<0.05)。前行管平均长度(L1)为(10.364±3.833)mm;前行管到下颌神经管主干的平均高度(L2)为(3.623±2.035)mm;前行管到牙槽嵴顶的平均高度(L3)为(9.280±3.240)mm。结论下颌神经管分支普遍存在,男女及左右侧分布无差异;下颌前行管在磨牙区发生率最高。