Introduction
The development of dental implant-related treatments has led to the establishment of computerized tomography (CT) as an important tool for the 3-dimensional (3D) presurgical assessment of the dimensions of the available alveolar bone, and for locating important anatomic structures, such as the mandibular canal.1 Standard panoramic and periapical radiographs do not provide cross-sectional information and have therefore been considered insufficient for implant site evaluation.2
Studies on oral implantology have described the advent of CT methods to allow the professional to perform image-guided surgical planning and to fabricate a stereolithographic surgical guide.3 Cone-beam computerized tomography (CBCT) units were developed for use in the maxillofacial area. Compared with other CT methods, CBCT offers advantages such as reduced effective radiation doses, shorter acquisition scan time, easier imaging, and lower costs.4
The use of CBCT devices provides high-quality 3D diagnostic reconstructed images of the maxillofacial region from the acquired data. It offers the advantage of analyzing the images by using multiplanar (MPR-CBCT, ie, cross-sectional and panoramic CBCT images) and 3D reconstructed (3D CBCT) images by volume rendering technique. These 3D CBCT images can be rotated in any spatial plane without superposition of the anatomic structures5 and have proven to offer complementary information for improving the implant placement surgical plan, commonly evaluated using only cross-sectional and panoramic CBCT views.1 However, we did not find any article in the literature review on the use of 3D CBCT images to evaluate the status of grafts and dental implants previously placed in jaws, in order to assess the tomographic follow-up of implant rehabilitation treatments and to perform a 3D evaluation of the sinus grafted area prior to implant placement in the posterior maxilla.
Thus, this technical note is aimed at presenting a simple and accessible technique of editing 3D CBCT reconstructed images using an advanced open-source software, in a retrospective case series, to assess follow-up information on grafts and implant placement.
Materials and Methods
The study population consisted of 15 patients, who previously underwent 21 multiple implant placements. In all cases, endosseous dental implants (either XiVE plus, DENTSPLY-Friadent, Mannheim, Germany, or Straumann SLA, Institut Straumann AG, Basel, Switzerland) were used to rehabilitate edentulous sites. Five patients had previously undergone sinus lifting procedures (3 cases of bilateral procedure and 2 cases of unilateral procedure).
After surgery, all patients were submitted to a routine CBCT exam, taken after different follow-up periods (minimum of 3 months after grafting surgery or implant placement). All cases demonstrated clear indications for taking CBCT exams (ie, planning future oral surgeries, diagnosing an unrelated pathologic condition, and assessing 3D information on sinus grafted areas or on alveolar bone defects). A CBCT scan unit (i-CAT Classic, Image Sciences International, Hatfield, Pa) was used and configured with a diagnostic protocol used for dental implants (0.25-mm voxel, 120kVp, 8mA, field of view of 16-cm in diameter and 6-cm in height), from which 3D reconstructed images were rendered by using the OsiriX imaging software (open-source, DICOM viewer OsiriX 3.9.4 version, Pixmeo, Geneva, Switzerland; http://www.osirix-viewer.com) installed on a MacOS 10.7 Apple Computer.
The CBCT images were provided from files of DICOM (Digital Imaging Communication in Medicine) format, and manipulated in order to obtain and use 3D reconstructed images for evaluating the postoperative and follow-up conditions of grafts and implants placed in the analyzed cases. In 5 cases including sinus lifting procedures, additional CBCT grafting postoperative images obtained before implant placement were also evaluated by using 3D reconstructed images.
In all cases, a thresholding tool named “16-bit CLUT (color look-up table) editor” available with the OsiriX software was used to evidence the images of grafts and implants in the 3D reconstructions to evaluate the rehabilitation treatment conditions. Cross-sectional and panoramic CBCT views of each case were also analyzed and compared to the 3D reconstructed images to confirm whether advantages were evidenced by 3D reconstructed images.
Results
In all cases, it was possible to use the OsiriX “16-bit CLUT editor” to evidence grafts and implants placed with the colors yellow and white, respectively. Bone tissue was depicted in red. Foramens, oral and maxillofacial spaces, and beam-hardening artifacts were shown in black (Figures 1 through 3).
Figure 1. Three-dimensional cone-beam computerized tomography (3D CBCT) reconstructed image of maxilla, before (a) and after (b) thresholding colors edition. Figure 2. 3D CBCT reconstructed image of mandible, before (a) and after (b) thresholding colors edition. Figure 3. Three-dimensional cone-beam computerized tomography (3D CBCT) reconstructed image of maxilla in a case of full-implant rehabilitation. Anterior (a) and lateral view (b).
Figure 1. Three-dimensional cone-beam computerized tomography (3D CBCT) reconstructed image of maxilla, before (a) and after (b) thresholding colors edition. Figure 2. 3D CBCT reconstructed image of mandible, before (a) and after (b) thresholding colors edition. Figure 3. Three-dimensional cone-beam computerized tomography (3D CBCT) reconstructed image of maxilla in a case of full-implant rehabilitation. Anterior (a) and lateral view (b).
The advantages provided in cases of multiple implant placement analyzed by 3D CBCT reconstructed images include: 3D visualization of 2 or more implant inclinations in the same image, 3D evaluation of the relation between implant bodies and supported prostheses, 3D measurements of the extension of the sinus grafted volume (Figure 4), and 3D reevaluation of the prosthetic plan after implant placement.
Figure 4. 3D CBCT reconstructed image of maxilla in a case of bilateral sinus lifting. Note the grafted area depicted with the yellow color. Figure 5. CBCT assessment of case of implants placed in the right sinus grafted area (note the failure in the distal implant-prosthesis connection): (a) Panoramic CBCT cut showing beam-hardening artifact between the implants, preventing the evaluation of the sinus grafted area. (b) 3D CBCT reconstructed image showing the implants placed in the sinus grafted volume (note the presence of other implants placed in the left maxillary sinus).
Figure 4. 3D CBCT reconstructed image of maxilla in a case of bilateral sinus lifting. Note the grafted area depicted with the yellow color. Figure 5. CBCT assessment of case of implants placed in the right sinus grafted area (note the failure in the distal implant-prosthesis connection): (a) Panoramic CBCT cut showing beam-hardening artifact between the implants, preventing the evaluation of the sinus grafted area. (b) 3D CBCT reconstructed image showing the implants placed in the sinus grafted volume (note the presence of other implants placed in the left maxillary sinus).
All artifact images, observed between different implants in the cross-sectional and panoramic CBCT images, were minimized in the 3D CBCT images (Figure 5).
Discussion
The importance of imaging diagnosis of grafting and implant surgery with CT methods has already been described in the literature.3,4 Furthermore, recent articles have suggested that CBCT plays a definite role in the postoperative evaluation of these surgeries.6,7 CBCT is considered a standard imaging method indicated to assess treatment related to implant placement and reconstructive dentistry, since the sites of planned implants have to be reconstructed in terms of both height and width.4,6
Nevertheless, since dental implantology inherently deals with metallic bodies, CBCT images may show beam-hardening artifacts. They are caused by the backprojection of an intensity that is measured, but that does not correspond to the actual absorption, mainly because high-energetic X rays penetrate the relatively dense implant, commonly shown in CBCT axial slices of multiple implant placement cases.8 In the present study, the edited 3D CBCT follow-up images of multiple implant placement cases minimized the artifacts between the implant images, which prevented evaluation of the peri-implant bone between different implants on the cross-sectional and panoramic CBCT images. Therefore, the results from this technical note suggest that more studies on quantitative analyses of the bone and graft volumes rendered by OsiriX free software may be recommended in order to validate this method to precisely analyze the amount of peri-implant bone in cases of multiple implant placements.
Cavalcanti et al1 stated the role of 3D reconstructed images of a commercial software (Vitrea) using a volume rendering technique was as an important additional tool to perform measurements for the diagnosis of implant placement, using a specific 3D postprocessing protocol as an alternative to improve volumetric visualization for implant treatment planning. On the other hand the present technical note supports the additional role of 3D CBCT images to assess the follow-up of implants placed during rehabilitation treatment, by using a different 3D postprocessing protocols from the OsiriX free open-source software.
In the present article, the OsiriX imaging software was used. This is a free, open-source software that is not limited to implant dentistry and can be valuable in oral radiology research.9 However, a recent article has suggested an important role for this software in assessing dental-related treatments.10 The rendering algorithm of this software assigns a given color and opacity to the lowest level of intensity displayed. This allows setting the rendering of different tissue densities (skin, muscle, or bones). Then, the program assigns a color and opacity to each intensity level included in the tomography.
The 16-bit CLUT editor was used in all of these cases. It is a software tool for manipulating thresholding colors, which allows the professional to edit the colors and opacity associated with the contrast and intensity assigned to the images, 2 factors responsible for selecting the threshold density value used for rendering the opaque tissue level. The use of a threshold to accurately digitize radiographic guides has been described in a recent article, where a 3D model could be created using optimal threshold.11 As shown in the present technical note, high contrasts selected either metallic bodies or bone density and therefore removed soft tissue, while low contrasts would select soft tissue contours and spaces. Furthermore, 3D- reconstructed imaging evaluation, which is not offered by the commonly used 3D implant planning software, could be provided by the OsiriX free software, providing important additional information for cases regarding treatment evaluation.
In conclusion, the 3D CBCT images obtained by the OsiriX imaging software and rendered by using the thresholding colors edition can be indicated as a useful method in allowing the visualization of grafts and implants placed in the jaws. This imaging protocol also provides more detailed information for evaluating implant-related treatments.
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