A proper implant position that allows an ideal final restoration is always desired by clinicians regardless if it is a single crown, an implant-supported fixed dental prosthesis, implant-retained overdenture, or implant-supported fixed removable hybrid prosthesis. In order to achieve a successful result, a thorough analysis of the anatomy of the residual ridge and evaluation of bone density is required. Typically, two-dimensional radiographic images — periapical and panoramic — have been used for the visualization of the edentulous area. Despite the high spatial resolution of the 2D images, the main disadvantage is that the buccolingual width of the alveolar bone and cortical plates cannot be accurately assessed which may lead to implant positioning errors and a compromised final outcome.3 CBCT technology provides accurate assessment of dimensions and contours of the residual ridge in a buccolingual dimension (Figure 11).
Figure 11. CBCT images for potential implant site assessment.
CBCT in implant planning utilizes multiplanar and 3D images to aid in determining the exact height, width and alveolar ridge anatomy of the alveolar bone, as well as the relationship of the edentulous sites with adjacent anatomical structures. These important structures include the mandibular canal, mental foramen, and the maxillary sinus and nasal fossa. Guided implant placement surgery can be performed with the aid of the CBCT data sets. With the 3D capability of the CBCT the clinician can determine if pre-prosthetic surgery such as bone grafting or sinus lift is needed prior to implant placement.
It is suggested that a well-fitting radiographic guide be used during the acquisition of the data volume.10 The radiographic guide is an appliance with radiopaque markers for the localization of ideal implant sites.3 The appliance is seated in the patient’s mouth prior to the scan. Various materials may be utilized for the fabrication of guides and for the markers; an ideal guide is non-flexible to avoid distorting the location of the marker during acquisition. With the use of barium/acrylic, foil or composite, not only the site and angle of the implant can be assessed, but also prosthetic information such as the shape of the final crown and the restorative margin can be visualized for better positioning of the desired implant. With the information gained, the clinician can determine the best surgical approach for each specific situation.
After the CBCT acquisition is complete, the data volume may be exported in a file format that is compatible with third-party software to create virtual 3D models for implant planning or to fabricate surgical guides; each CBCT file set created for the patient might be several hundred MB. The clinician can also select the shape, length, and platform size of the implant from various software programs.3
In 2012, the American Academy of Oral and Maxillofacial Radiology published a position statement on selection criteria for the use of radiology in dental implantology with emphasis on CBCT. It stated that the panoramic image should be used for initial implant evaluation along with periapical radiographs; CBCT imaging should not be used exclusively for an initial evaluation. However, in implant planning, cross-sectional images are important images for treatment planning in many cases and thus a CBCT scan may be appropriate imaging to acquire.12
To follow up previous implant surgery, a 2D image such as a periapical image is the most convenient imaging modality, especially if the implant is asymptomatic. However, if the implant is symptomatic and the 2D image suggests bone loss adjacent to an implant requiring further evaluation and treatment, a CBCT scan may be advised, although the beam hardening artifact generated by the implant may reduce the ability of the scan to detect fine details.12