Registration accuracy of three-dimensional surface and cone beam computed tomography data for virtual implant planning

Objective: Virtual wax‐ups based on three‐dimensional (3D) surface models can be matched (i.e. registered) to cone beam computed tomography (CBCT) data of the same patient for dental implant planning. Thereby, implant planning software can visualize anatomical and prosthetic information simultaneously. The aim of this study is to assess the accuracy of a newly developed registration process. Material and methods: Data pairs of CBCT and 3D surface data of 16 patients for dental implant planning were registered and the discrepancy between the visualized 3D surface data and the corresponding CBCT data were measured on 64 teeth at seven points by two investigators in two iterations with a total of 1792 measurements. Results: All data pairs were matched successfully and mean distances between CBCT and 3D surface data were between 0.03(±0.33) and 0.14(±0.18) mm. At two of seven measuring points, statistically significant correlations were determined between the measured error and the presence and type of restorations. Registration errors in maxilla and mandible were not statistically significantly different. Conclusion: According to the results of this study, registration of 3D surface data and CBCT data works reliably and is sufficiently accurate for dental implant planning. Thereby, barium‐sulfate scanning templates can be avoided and dental implant planning can be accomplished fully virtual. To cite this article:
Ritter L, Reiz SD, Rothamel D, Dreiseidler T, Karapetian V, Scheer M, Zöller JE. Registration accuracy of three‐dimensional surface and cone beam computed tomography data for virtual implant planning.
Clin. Oral Impl. Res. 23 , 2012 447–452.
doi: 10.1111/j.1600‐0501.2011.02159.x     

应用3D打印熔融沉积技术制作个性化种植修复体的精确度研究

目的 应用3D打印熔融沉积（FDM）技术制作个性化种植修复体,评估其与天然牙的误差。方法 通过Mimics 15.0软件提取锥形束CT（CBCT）扫描的6颗因正畸减数而需拔除牙（体内牙）的数据模型并制作个性化种植修复体。在相同参数下重新扫描拔除后的正畸减数牙（体外牙）及个性化种植修复体获取数据模型,利用Geomagicstudio软件比较3种数据模型之间的三维偏差大小。结果 个性化种植修复体与体内牙数据模型整体模型间的高低区域偏差的平均值为0.19 mm和-0.16 mm,体内牙与体外牙数据模型整体模型间的高低区域偏差的平均值为0.14 mm和-0.07 mm;两组数据经独立样本t检验,差异均无统计学意义（P>0.05）。结论 1）应用3D打印FDM技术制作的个性化种植修复体精密度良好。2）基于相同参数CBCT扫描数据获得的体内牙与体外牙的数据模型仍存在一定误差。     

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口腔颌面锥形束CT可以提供矢状位、冠状位、水平位三个轴面的诊断信息,并且可以通过三维重建直观地显示立体图像,从而能够精确地确定埋伏阻生牙的形状、位置、数目、阻生方向及其与邻近结构的关系。     

Influence of scanning and reconstruction parameters on quality of three-dimensional surface models of the dental arches from cone beam computed tomography

The study aim is to investigate the influence of scan field, mouth opening, voxel size, and segmentation threshold selections on the quality of the three-dimensional (3D) surface models of the dental arches from cone beam computed tomography (CBCT). 3D models of 25 patients scanned with one image intensifier CBCT system (NewTom 3G, QR SLR, Verona, Italy) using three field sizes in open- and closed-mouth positions were created at different voxel size resolutions. Two observers assessed the quality of the models independently on a five-point scale using specified criteria. The results indicate that large-field selection reduced the visibility of the teeth and the interproximal space. Also, large voxel size reduced the visibility of the occlusal surfaces and bone in the anterior region in both maxilla and mandible. Segmentation threshold was more variable in the maxilla than in the mandible. Closed-mouth scan complicated separating the jaws and reduced teeth surfaces visibility. The preliminary results from this image-intensifier system indicate that the use of medium or small scan fields in an open-mouth position with a small voxel is recommended to optimize quality of the 3D surface model reconstructions of the dental arches from CBCT. More research is needed to validate the results with other flat-panel detector-based CBCT systems.     

Cone beam computed tomography in Endodontics – a review

Cone beam computed tomography (CBCT) produces undistorted three‐dimensional information of the maxillofacial skeleton, including the teeth and their surrounding tissues with a lower effective radiation dose than computed tomography. The aim of this paper is to: (i) review the current literature on the applications and limitations of CBCT; (ii) make recommendations for the use of CBCT in Endodontics; (iii) highlight areas of further research of CBCT in Endodontics.     

Applications of cone beam computed tomography in dental and oral medicine

Cone beam computed tomography (CBCT) is a radiological technique available since 1998 in dental and oral medicine in which a cylindrical volume is acquired with a conical x-ray beam during one rotation around the head of the patient (cone beam computed tomography, cone beam CT). This technique is increasingly replacing conventional radiological procedures due to the possibility of arbitrary reconstructions and views free of superimposition. CBCT focuses on the display of the bones of the jaw, so that its use concentrates on problems in implantology, before surgical removal of impacted and displaced teeth, in traumatology, and in craniofacial malformations. The objective of this overview was to emphasize the advantages of cone beam computed tomography in the individual disciplines. However, schematization of examinations should be avoided for reasons of radiation protection and for avoiding forensic pressure. The limits of CBCT and thus an indication for computed tomography exist where there is suspicion of bone tumors with soft tissue participation as well as in extensive fractures with suspicion of craniocerebral trauma. In the case of tumors in the soft tissues and of functional temporomandibular joint symptoms, magnetic resonance tomography is preferable to CBCT.     

Cone beam computed tomography for diagnosis and treatment planning of supernumerary teeth

Conventional radiographic images are frequently used to detect supernumerary teeth. However, recent developments in 3D imaging systems have enabled dentists to better visualize supernumerary teeth, with better contrast and more details. Cone beam computed tomography (CBCT) has improved diagnosis and treatment planning of patients with supernumerary teeth. The decision to use CBCT should be based on the diagnostic information required. This article presents three case reports of patients with supernumerary teeth to demonstrate the need for accurate diagnosis and treatment planning based on a comprehensive evaluation using CBCT.     

Accuracy and surgical feasibility of a CBCT‐based stereolithographic surgical guide aiding autotransplantation of teeth: in vitro validation

Summary The aims of this study were to determine the accuracy of a 3D computer model and stereolithographic (STL) replica when compared to the real tooth and to develop a cone beam computed tomography (CBCT)‐based planning technique including surgical guide fabrication. A STL surgical guide and a tooth replica were fabricated using SimPlant Pro 12.1. To validate this process, tooth segmentation and replica design were prepared for comparison to an optical scan of the corresponding tooth. For surgical intervention, a dry dentate mandible was scanned using a Scanora CBCT and the donor tooth was segmented. The donor tooth was repositioned, and two guides were designed. These tooth replica and guides were used in socket preparation of the dry mandible. The 3D computer model of the segmented teeth and related STL models showed satisfactory results with an acceptable accuracy. The surfaces were within 0·25 mm distance, but in some areas up to 2·5 mm deviation were seen. The results showed that 79% of the points was between 0·25 and ?0·25 mm, 3% was overestimated (>0·25 mm) and 18% was underestimated (in vivo planning of CBCT‐based autotransplantation.     

Accuracy of 3D reconstructions based on cone beam computed tomography

Three-dimensional imaging of teeth will increase its impact in clinical practice if reconstructions are metrically accurate. We hypothesized that, with cone beam computed tomography (CBCT) data, three-dimensional images of teeth can be reconstructed with the same accuracy and precision as with in vitro micro-computed tomography (micro-CT) data acquisition, the current reference standard. We used a sample of CBCT and micro-CT data taken of tooth germs. Volumes obtained with CBCT and micro-CT devices were statistically similar (n = 120, Passing-Bablok regression). Geometric deviations between CBCT and micro-CT three-dimensional surface reconstructions did not show any areas of important and systematic errors. Future investigations with the use of larger samples may also demonstrate that CBCT data will be helpful for a more in-depth study of other aspects of dental morphology--for example, assessing tooth development. With sufficient accuracy for clinical situations, potential future medical applications of such measurements with CBCT are envisaged.     

锥形束CT在治疗上颌前牙区埋伏牙中的应用

目的:探讨锥形束CT(CBCT)在治疗上颌前牙区埋伏牙中的临床应用价值。方法:收集我院2009—2010年经普通X线片确定有埋伏牙,但不易具体定位的患者11例,进行CBCT扫描和三维重建,确定埋伏牙在颌骨内的具体位置。结果:经CBCT扫描、三维重建后,所有患者均可直观再现埋伏牙的形态、数目、在颌骨中的具体位置和发育情况。11例患者共16颗埋伏牙,其中既有埋伏阻生牙又有埋伏多生牙,3例(4颗)为埋伏多生牙,1例有2颗埋伏牙;2例为倒置埋伏,2例为水平埋伏,3例为垂直埋伏,4例为斜位埋伏。根据CBCT结果制订治疗方案,获得满意的治疗效果。结论:CBCT三维重建对于上颌前牙区埋伏牙治疗方案的设计及实施具有重要意义。     

Detection accuracy of proximal caries by phosphor plate and cone-beam computerized tomography images scanned with different resolutions

This study was carried out to assess whether the spatial resolution has an impact on the detection accuracy of proximal caries in flat panel CBCT (cone beam computerized tomography) images and if the detection accuracy can be improved by flat panel CBCT images scanned with high spatial resolution when compared to digital intraoral images. The CBCT test images of 45 non-restored human permanent teeth were respectively scanned with the ProMax 3D and the DCT Pro scanners at different resolutions. Digital images were obtained with a phosphor plate imaging system Digora Optime. Eight observers evaluated all the test images for carious lesion within the 90 proximal surfaces. With the histological examination serving as the reference standard, observer performances were evaluated by receiver operating characteristic (ROC) curves. The areas under the ROC curves were analyzed with two-way analysis of variance. No significant differences were found among the CBCT images and between CBCT and digital images when only proximal enamel caries was detected (p = 0.989). With respect to the detection of proximal dentinal caries, significant difference was found between CBCT and digital images (p < 0.001) but not among CBCT images. The spatial resolution did not have an impact on the detection accuracy of proximal caries in flat panel CBCT images. The flat panel CBCT images scanned with high spatial resolution did not improve the detection accuracy of proximal enamel caries compared to digital intraoral images. CBCT images scanned with high spatial resolutions could not be used for proximal caries detection.     

Guided endodontic access of calcified root canal by laser melting templates

目的 利用激光熔融数字化导板技术获得钙化根管治疗的新方法,并评估其准确性。方法 采用激光熔融数字化导板技术辅助2例前牙钙化根管的治疗。术前使用锥形束CT（CBCT）扫描患者上颌牙,建立三维牙体硬组织根管系统模型;制取患者上颌印模,三维扫描仪扫描模型,整合CBCT及三维扫描数据,通过Mimics 19.0及3-matic 11.0软件设计开髓路径,使用钴铬合金激光熔融法打印导板,在根管导板引导下开髓及打通钙化段根管,完成根管治疗。测量术前开髓设计路径和术后实际路径的位置和角度偏差。结果 2例患牙均获得较好的治疗效果。病例1的开髓角度偏差为1.77°,钻基底偏差为0.403~0.497 mm,钻尖端偏差为0.433~0.537 mm。病例2的角度偏差为3.26°,钻基底偏差为0.183~0.347 mm,钻尖端偏差为0.310~0.463 mm。结论 钴铬合金激光熔融根管导板辅助建立根管通道是治疗钙化根管的有效方法,可作为钙化根管治疗的新策略。     

A comparison between two-dimensional and three-dimensional cephalometry on frontal radiographs and on cone beam computed tomography scans of human skulls

The aim of this study was to evaluate whether measurements performed on conventional frontal radiographs are comparable to measurements performed on three-dimensional (3D) models of human skulls derived from cone beam computed tomography (CBCT) scans and if the latter can be used in longitudinal studies. Cone beam computed tomography scans and conventional frontal cephalometric radiographs were made of 40 dry human skulls. From the CBCT scan a 3D model was constructed. Standard cephalometric software was used to identify landmarks and to calculate ratios and angles. The same operator identified 10 landmarks on both types of cephalometric radiographs, and on all images, five times with a time interval of 1 wk. Intra-observer reliability was acceptable for all measurements. There was a statistically significant and clinically relevant difference between measurements performed on conventional frontal radiographs and on 3D CBCT-derived models of the same skull. There was a clinically relevant difference between angular measurements performed on conventional frontal cephalometric radiographs, compared with measurements performed on 3D models constructed from CBCT scans. We therefore recommend that 3D models should not be used for longitudinal research in cases where there are only two-dimensional (2D) records from the past.     

Accuracy and validity of stitching sectional cone beam computed tomographic images

To determine whether three-dimensionally reconstructed images of skulls created by stitching multiple cone beam computed tomographic (CBCT) images are as accurate as single images obtained using multidetector computed tomography (MDCT), 10 skull models were scanned using an optical three-dimensional scanner, MDCT, and CBCT. Cone beam CT images at 3 different levels of the skull were manually superimposed and stitched. The reconstructed CBCT images at each level were aligned and fused using computer software and then compared to the nominal reference image obtained from the optical three-dimensional scanner by determining positional errors. The reconstructed MDCT images were also compared, and the differences in the mean errors for the 3 image types compared with the nominal reference image data were evaluated. There were no significant differences between the MDCT images and the manually merged CBCT images (Wilcoxon signed rank test, P = 0.017). In contrast, there were significant differences between the MDCT images and the software-aligned CBCT images (P = 0.005). Manual stitching of CBCT sectional images at different levels can provide accurate anatomic details of the oral and maxillofacial regions.     

锥形束CT在诊治牙体根尖周病中的应用进展

锥形束CT（CBCT）具有高空间分辨率、相对较低的辐射剂量,从三维角度显示复杂的口腔颌面部影像,获得无失真的颌面部骨及牙体组织信息,是口腔颌面部疾病的重要影像检查工具。本文就CBCT在诊治牙体根尖周病中的应用进展进行综述。     

New dimensions in endodontic imaging: Part 2. Cone beam computed tomography

Cone beam computed tomography (CBCT) has been specifically designed to produce undistorted three-dimensional information of the maxillofacial skeleton, including the teeth and their surrounding tissues with a significantly lower effective radiation dose compared with conventional computed tomography (CT). Periapical disease may be detected sooner using CBCT compared with periapical views and the true size, extent, nature and position of periapical and resorptive lesions can be assessed. Root fractures, root canal anatomy and the nature of the alveolar bone topography around teeth may be assessed. The aim of this paper is to review current literature on the applications and limitations of CBCT in the management of endodontic problems.     

Volumetric analysis of extraction sockets using cone beam computed tomography: a pilot study on ex vivo jaw bone

Aim: The aim of this study was to determine the accuracy of volumetric analysis of extraction sockets using cone beam computed tomography (CBCT). Material and Methods: The volume of 40 dental alveoli in nine dry skull specimens (four mandibles and five maxillae) was determined by measuring the volume of the tooth socket impression using the water displacement technique. This was considered as the gold standard. Then, the tooth socket was scanned with CBCT and data were uploaded in the semi‐automated Livewire^® segmentation software. The software segments the tooth socket in consecutive 1 mm‐thick two‐dimensional slices. After segmentation, the total volume of the delineated socket was computed. The statistical difference between direct volumetric measurements and those obtained with CBCT imaging was assessed using the Student paired t‐test. Result: The mean socket volume of the skull specimens was 227±91 mm³ when obtained by direct measurement and 225±90 mm³ when obtained by CBCT imaging. Student paired t‐test showed no significant differences between both volume measurements (p>0.1). Conclusions: CBCT permits imaging of anatomical structures in three planes and allows for reliable volume estimates. The results should be verified in clinical circumstances and might have potential applicability for evaluation of extraction socket healing under different conditions.     

Head positioning in a cone beam computed tomography unit and the effect on accuracy of the three‐dimensional surface mode

Head position during cone beam computed tomography (CBCT) examination can easily deviate from the ideal, which may affect the accuracy of the segmented three‐dimensional (3D) model. The aim of this study was to determine the effect of head positioning on the accuracy of the 3D model. A human dry skull was positioned at predetermined orientations in a CBCT scanner and scanned in multiple orientations and voxel sizes. The resulting 3D surface models were superimposed over those derived from the reproducible centered positioned skull with 0° inclination. Color mapping and analysis of the differences expressed by the root mean square error (RMSE) were performed. The RMSE for each orientation using the 0.3 mm voxel ranged from 0.31 to 0.87 mm for the whole maxillofacial region, from 0.44 to 0.91 mm in the maxilla, and from 0.31 to 0.72 mm in the mandible. For the 0.4 mm voxel, the RMSE ranged from 0.47 to 0.86 mm for the whole maxillofacial region, from 0.60 to 0.96 mm in the maxilla, and from 0.56 to 0.86 mm in the mandible. The maxilla showed a slightly higher deviation than the mandible in both voxel groups. It can be concluded that the head position affects the accuracy of the segmented 3D model, but the inaccuracy does not exceed clinically relevant levels.     

The use of cone beam computed tomography to predetermine root canal lengths in molar teeth: a comparison between two-dimensional and three-dimensional measurements

Objectives

The aim of this study was to evaluate the accuracy of two-dimensional (2D) and three-dimensional (3D) root canal length measurements in molar teeth using cone beam computed tomography (CBCT).

Materials and methods

Root canal lengths of twenty molar teeth were measured with two different CBCT approaches. After adjusting the CBCT images, 2D measurements were performed within the sagittal plane between the apical foramen and the coronal reference (cusp). The 3D approach measured centrically in axial planes. A linear mixed model with random intercepts was fitted to compare differences between methods (2D and 3D). The correlation between CBCT measurements and the actual root canal length was evaluated using the Pearson correlation coefficient.

Results

Differences between 3D measurements and the actual root canal lengths were significantly smaller compared to the 2D approach (p?<?0.001). Mean differences were 0.32 and 0.58 mm, respectively. A high correlation was found between the actual root canal length and 3D measurements (Pearson correlation coefficient?=?0.97). Compared to the actual root canal length, 80 % of the 3D measurements were within the limits of ±0.5 mm.

Conclusions

3D measurements of root canals in molar teeth are more accurate than simple 2D measurements and show a high correlation to the actual lengths.

Clinical relevance

In cases where a CBCT is already available, root canal lengths in molar teeth can be accurately predetermined using a standardized 3D approach.