Indications for 3-D diagnostics and navigation in dental implantology with the focus on radiation exposure: a systematic review

Dental implants are a well-established method of prosthetic oral rehabilitation. High-quality imaging of the bone and surrounding anatomical structures is necessary for proper diagnosis, implant-planning, and implant placement. In many cases, two-dimensional (2-D) radiographic images are sufficient; however, if all relevant anatomical structures cannot be evaluated, or if further information is needed [1, 2], three-dimensional (3-D) imaging might be helpful [3].

Throughout their history, many dental implants were placed using the freehand method. Although an experienced surgeon can achieve good results with this method, the use of static or dynamic navigation is well established and seems to improve the outcome in terms of placement accuracy, while protecting vulnerable adjacent structures [4].

The present review was conducted to evaluate the advantages and disadvantages of 2-D versus 3-D imaging techniques, as well as those of different navigation methods. This review aimed to provide a more detailed view of guidance techniques for implant placement.

The present systematic review was based on the Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) statement, with two focused research questions:

The basis for safe implant placement is a good understanding of the patient’s anatomy. A 2-D image, in combination with a clinical examination, is sufficient in many cases. A panoramic X-ray with a reference body should be used when possible. While 3-D images are superior in terms of image quality [13], they also have a higher radiation dose and cost. Higher accuracy can be achieved with static or dynamic navigation guidance, when compared with freehand implant placement, although more preoperative planning is necessary [14]. The radiation exposure from 3-D imaging is generally higher than that of 2-D imaging; however, there is a wide range, based on the scanning protocol [26, 32, 62]. Comparing the radiation exposure of conventional CT scans with CBCT, conventional scans generally have higher doses, despite an overlapping range of some indications [34, 63]. For implantology, CBCT should be the first choice for 3-D imaging in most cases [14, 64]. Furthermore, radiation exposure is highly dependent on the equipment and settings utilized. A reduction in exposure can be achieved by shielding vulnerable tissues such as the thyroid gland [26], by reducing the field of view [65], the acquisition time(s), the tube voltage, or by increasing the voxel size [8, 32]. Many CBCT scanners have programmed these settings as low-dose protocols, which are typically sufficient to provide the information required for dental implantology [8, 14, 35, 37, 66].

In complex cases, 3-D images may be preferable [13, 67]. Examples of these instances are as follows: anatomical variations of the bone [68], insufficient visibility of vital structures on 2-D imaging, pathological changes visualized on 2-D imaging, pre-existing conditions, previous surgery in the maxillary sinus [14], for certain guided implantological methods [14], and for detecting possible complications after augmentation or implantation [13, 32, 69].

To achieve high accuracy with navigational-guidance, the workflow must be well established, since inaccuracies in each individual step can compound on each other [70]. For example, the positioning of the drilling template must be secured. To ensure a safe and correct implant placement, a 2-mm [21] safety margin adjacent to vital structures, such as the mandibular nerve, should be utilized during the planning process [13].

The use of navigation should be considered in the following situations: for special prosthetic techniques like immediate implant placement, as support for minimally invasive techniques, or after complex jaw reconstructions [71]. There were no studies found that indicated a reduction of adverse events, such as nerve damage, when using 3-D imaging or navigational-guidance. This is most likely due to the fact that adverse events occur very infrequently, and the number requiring treatment that is needed to show a significant difference is prohibitively high for a limited study population. Additionally, it is likely that more support tools were used at difficult implant sites, which may be another reason for the absence of comparative studies. Future studies evaluating these differences would be beneficial. No studies were present investigating whether a higher accuracy in the implants placed with navigational guidance leads to a higher long-term survival of the prosthetic. Further research in this regard would also be beneficial. The limitations of the present study were primarily due to the heterogeneity of the included studies. Furthermore, many of the described outcome parameters depend on the personal skills and experience of the surgeon.

Although the availability of 3-D imaging is rapidly increasing, the temptation to utilize 3-D imaging in every implant placement has to be resisted. Despite the higher accuracy achieved in implants placed with the help of navigation, a difference in the survival of the implants has not been proven. In order to achieve the best possible outcome for the patient, the potential harm caused by radiation exposure also should be considered. Decisions regarding the imaging technique and the scanning protocols should be made on a case-by-case basis.