Radiology is used in implant dentistry to supplement and confirm clinical findings. Radiographs can assist with diagnosis and treatment planning and in reviewing restored dental implants at regular maintenance visits. The 3D volume-rendered image shown here demonstrates the level of detail that can be obtained. However, all radiation - including x-rays - carries risk of tissue damage and long-term effects. Therefore, where radiography is planned, consideration must be given to the risks associated with the investigation, which must be balanced against the expected benefits that will result. Equally, consideration must be given to an assessment of the diagnostic and planning needs of the case. Selection of the correct radiographic technique should be based on this balance between diagnostic needs and risk.

After completing this ITI Academy Module, you should be able to list the radiographic techniques that can be used to gather data to assist in the treatment planning and follow-up of dental implants; describe the radiation dose from various imaging techniques; discuss radiation protection principles to reduce levels of dose-associated risk; and describe the indications for two-dimensional and three-dimensional radiographic investigations.

As part of a structured assessment where implant treatment is being considered, radiographs assist in detecting both healthy tissue and pathology. The normal anatomy of the site can be visualized and anatomic boundaries defined. The position and extent of any pathology can also be described. Radiographs can play a role in treatment planning for implant placement as well, detailing the shape and dimensions of available bone for implant placement and directing the position and angulation of these implants. It is important to ensure that any images taken of implant sites are assessed for diagnostic as well as treatment planning purposes. Although a radiograph might be intended for use in treatment planning, we must be ready for any signs of pathology that might present in the image. Diagnosis of pathology, even if unexpected, is a principle role of such investigations. It is important to note that, because implant treatment is an elective therapy, any pathology found during treatment planning investigations must be addressed prior to commencement of implant therapy.

Virtually every modern dental practice has the capability to take accurate intraoral images. These two-dimensional images form the mainstay of radiographic investigations in dentistry. Periapical views taken using a long-cone paralleling technique typically have sufficient accuracy to determine the amount of bone available for implant placement and the positions and anatomy of adjacent structures. Nearby pathology can also be visualized. In the clinical case on screen, the space available for placing an implant-supported fixed prosthesis to replace the upper right first premolar tooth can be seen. These images also indicate that there is sufficient bone height for implant placement between the crest of the alveolar ridge and the floor of the maxillary sinus in this area. A suboptimal root canal filling and periapical radiolucency associated with the upper right second premolar can also be seen. Periapical images can also be captured during implant placement to confirm the correct alignment of the osteotomy or the position of the implant, as seen in this image of an intrasurgical marker placed into the initial osteotomy in an upper right lateral incisor site.

Panoramic films, also known as orthopantomograms (or OPGs), offer an opportunity to assess all of the dental and paradental hard tissues in a single, relatively low-dose investigation. The panoramic view seen here is a typical example of this technique performed in a patient referred for implant treatment planning in the right mandible and maxilla. Although this imaging modality does not obtain high-resolution images, they are sufficiently detailed to detect most bony pathologies and to provide an indication of bone height in an edentulous region. Panoramic radiography may seem easy to perform, but it is a technique where many mistakes are made, not least in patient positioning. Both anterior and posterior regions can become distorted and thus misrepresent the jaw dimensions. Additionally, the method used to obtain the image can result in artifacts such as ghost images that can complicate interpretation of the radiograph. The magnification varies between different types of panoramic machines and the resulting images are not dimensionally accurate. It is thus important to make certain of the actual magnification in the image being evaluated - especially when choosing the dimensions of a dental implant to be inserted. In summary, a panoramic view is a very good imaging modality that provides an overview of the jaws and neighboring structures.

Another two-dimensional radiographic imaging modality that may be slightly less known and also less frequently performed in dental practices is lateral profile radiography, also known as cephalometric imaging. In implant dentistry, this technique is most useful for providing an assessment of the relationship between the upper and lower jaws, and for obtaining estimates of the angulation of the anterior jaws and the widths of the jawbones in their mid-sagittal regions. As such, lateral profile radiography is mostly used in orthodontic assessment, and its benefit in implant therapy is uncertain. However, in some circumstances it can be useful in radiographic assessment for implant placement in the anterior parts of the jaws. The advent of three-dimensional cone beam CT techniques has superseded this application in most dental practices. The lateral profile radiograph on the screen shows a patient referred for implant treatment planning in the maxilla and mandible. The bony anatomy of the jaws in the midline can be seen. These are the only sites for which this technique can be used for implant treatment planning.

For radiographic 3D imaging, tomographic techniques can be used. The three different tomographic modalities used in implant dentistry are conventional tomography, computed tomography (or CT), and cone beam computed tomography (or CBCT). Although now largely superseded by CBCT, conventional tomography is still available. CBCT and CT both suffer from acquisition artifacts such as cupping, beam hardening, and scatter in the presence of radiopaque restorations and implants. Cupping results in distortion of metallic objects. Beam hardening results in streaks of dark bands that can appear between two dense objects. Scatter is seen as white streaks in CBCT slices. Long exposure times from CBCT and older CT scanners contribute to motion artifacts (also called patient-related artifacts), especially in children and elderly patients.

Both CT and CBCT collect radiographic data in volume elements, or voxels, that record the radiopacity of a small volume of space in the field of view. These voxels can then be formatted into any number of two-dimensional views that display this three-dimensional information in usable ways. These views represent the multiplanar information for a site, or a series of orthogonally distinct images of the region of interest. These images are dimensionally accurate and can be used to plan implant placement. In some situations this data can be formatted as volume-rendered images that appear three-dimensional to the viewer. The clinical images on screen show different orthogonal CBCT projections of a patient's upper left central incisor site, and a volume rendering of the same site. These images can be measured to obtain the dimensions of bone available for implant placement and to visualize the bony defect that may need to be managed. It should be noted that CBCT imaging often involves lower radiation doses than conventional CT scans. However, CBCT is less capable than CT for imaging soft tissues and is somewhat more prone to beam hardening and scatter artifacts.

CBCT plays a critical role in the digital implant workflow, offering advantages over traditional medical CT, particularly in terms of cost-effectiveness, reduced radiation exposure, and equipment that is more compact. When considering accuracy, it is important to note that CBCT's deviation is at least one voxel, equivalent to 0.3 cubic millimeters, as highlighted in the ITI Consensus Conference 2018. Several factors can impact CBCT accuracy, including changes in the angulation of the patient’s head, movement artifacts, scatter, the employed reconstruction algorithm, voxel size, and radiation exposure, among others. Understanding these factors is essential for optimizing the accuracy and reliability of CBCT in implantology.

The 6th ITI Consensus Report from 2018 provides essential recommendations and guidelines for clinical practice. First, CBCTs are recommended as the imaging tool of choice for three-dimensional dental implant site assessments. This allows for precise planning and evaluation, crucial for successful implant placement. Second, a safety margin of 2 mm to relevant anatomic structures is advised, ensuring adequate space to avoid complications with adjacent anatomy. Lastly, it's important to note that smaller voxel sizes do not necessarily increase accuracy in linear measurements on CBCT scans. For preoperative implant treatment planning, using a voxel size of 0.3 - 0.4 cubic millimeters, the smallest field of view, and partial rotations can significantly reduce radiation exposure without compromising image quality.

Available Techniques, Key Learning Points: Radiographic imaging is used to assess potential implant sites and to detect existing pathology. Periapical radiography is a fundamental technique with sufficient accuracy to estimate ridge height and detect pathology. Panoramic radiographs are good for overall assessment but are not dimensionally accurate for implant selection. CT and CBCT are three-dimensional imaging techniques useful in implant dentistry. They create various dimensionally accurate views of the bone available for implant placement.

The biologic effects of ionizing radiation may be divided into two categories: tissue reactions (previously called 'deterministic effects') and stochastic effects. Tissue reactions are proportional to the dose and occur in all individuals when the dose is large enough. They result in cell death or cell malfunction, and the severity of the effects increases with the dose. In contrast, stochastic effects are believed not to have dose thresholds. As such, there is no safe dose of radiation. The first step in assessing the risk for a group of patients or medical/dental staff is to estimate the effective dose. In this calculation, the relative risk of a specific type of radiation and the type of tissues or organs that have been irradiated are taken into account by radiation weighting factors. The tissue weighting factors are published by the International Commission on Radiological Protection. There is a range of radiation dosages for each imaging modality, and sometimes these ranges are broad. This reflects the equipment and materials used along with specific details of the research methodologies.

Patient risk from radiation has been a continuing concern in oral and maxillofacial imaging due to the frequency of radiographic examinations in dental practice. At least to some degree, these risks are dose related. Therefore, limiting exposure is a key part of limiting risk. ALARA is the acronym for 'As Low As Reasonably Achievable' and is a fundamental principle for diagnostic radiology. With the increased use of CBCT imaging in dental practice, clinicians must be made aware that patient radiation doses associated with CBCT imaging are higher than those of conventional, two-dimensional radiographic techniques. Therefore, routine replacement of current radiographic techniques must be considered with great care - especially when treating children.

The various techniques used in maxillofacial radiology are associated with ranges in the effective doses that are given to patients. These ranges can vary considerably. Dose variations associated with a certain technique are related to the methods used to measure and estimate effective doses, as well as to variations between radiographic imaging machines. This graph demonstrates the effective dose ranges from different radiographic imaging modalities and devices as published by Harris and co-workers 2012. It is evident that CBCT devices using either dento-alveolar fields of view, which are small to medium, or craniofacial fields of view exhibit a wide range of effective doses that overlap and even surpass some CT devices.

Radiation surrounds us. From eating a banana to flying on a plane, many activities expose each and every one of us to radiation. When considering the use of radiographic investigations in patient assessment for any dental treatment, we need to ensure that the benefits derived from the investigation warrant the risks incurred by increasing our patients' exposure to radiation. Even still, each of these investigations incurs a radiation exposure equivalent to additional days or weeks of background radiation. The aim should be to avoid adding unnecessarily to this background dose. This aim is achieved by selecting the imaging modality that provides the necessary data at the lowest dose. 2D investigations such as intraoral and panoramic films have the lowest dose - in the order of days of additional radiation exposure. 3D investigations have much more exposure - in the order of approximately one week of background exposure for a CBCT to several weeks of background exposure for a conventional CT scan.

Assessing Radiation Exposure, Key Learning Points: There is no safe dose of radiation. Radiation risk is dose related. The effective dose of radiation received by patient or staff depends on the tissues being irradiated as well as the imaging modality. The dose range for a given imaging modality can vary. A fundamental principle of diagnostic imaging is ALARA, or doses that are As Low As Reasonably Achievable. This is achieved by selecting the imaging modality that provides the necessary information at the lowest dose.

Any radiation exposure entails a risk to the patient. Under normal circumstances, however, the risk from dental radiography is very low. Nonetheless, it is essential that every radiographic examination should show a benefit to the patient. The use of radiation is acceptable when it is expected to do more good than harm, weighing the total potential diagnostic benefits it produces against the individual detriment that the exposure might cause. The efficacy, benefits, and risks of available alternative techniques having the same objective, but involving more or less exposure to radiation, should be taken into consideration. It is essential to select an appropriate radiographic technique based on the individual patient history and the clinical examination. This forms the basis of the justification process. When choosing the radiographic technique, the prevalence of a disease or condition, its progression rate, and the diagnostic accuracy of the imaging technique in question all have to be considered. The criteria for radiographic imaging should be reviewed from time to time as more information becomes available about the risks and effectiveness of both new and existing imaging procedures. Some dentists may have to refer their patients to hospitals or dental colleagues for a radiographic examination when they lack the adequate equipment in their own offices. When acting as a referrer, the dentist should ensure that adequate clinical information about the patient is provided to the person taking responsibility for the radiographic examination. It should be noted that any clinician who performs a radiographic investigation is also responsible for describing the findings of that investigation in the patient's clinical record. Finally, CBCT imaging should be used only when necessary, specifically when 2D imaging does not provide sufficient diagnostic information. This is particularly important in elective procedures in dentistry.

Optimization of radiographic procedures to ensure high quality images involves consideration of many factors. These include selecting appropriate equipment, and then ensuring that it is well maintained. Additionally, exposures should be calculated for each patient to ensure that image quality is sufficient to be diagnostic. A quality assurance program is also needed to ensure appropriate diagnostic outcomes through regular testing and calibration of equipment, auditing of patient dosages, and assessing image quality outcomes.

Several strategies can be used to reduce the radiation dose. These include adjustment of exposure factors such as the quantity of x-rays, which is controlled by a combination of milliamperage and exposure time. The energy of the x-ray beam is controlled through the kilovolt setting and filtration. Other strategies include avoiding unnecessary exposure of radiosensitive organs and tissues outside the area of interest by limiting the exposed area or field of view. Recent findings suggest that the use of lead aprons and thyroid collars is not necessary for dental X-rays and can sometimes obstruct the primary beam, necessitating additional exposures. Modern digital X-ray equipment and beam collimation techniques are sufficient to protect against unnecessary radiation. Exposure protocols that are individualized for pediatric, adolescent, and adult patients should be employed. Staff and other patients in the office must also be protected. Good radiation hygiene practices, exposure monitoring, and the use of appropriate shielding in walls should be employed.

In 2014, the National Council on Radiation Protection and Measurements (or NCRP) proposed a shift from ALARA to ALADA (or "as low as diagnostically acceptable"), to emphasize the importance of dose optimization in medical diagnostic imaging. This is especially important in the use of CBCT in dentistry, where these investigations are being used for assessment and planning for what are essentially elective procedures. Thus, CBCT images should only be used where 2D imaging fails to give sufficient information, rather than being used for routine investigations. Limiting the field of view and exposure protocols to give adequate information at the lowest possible dose should be our goal.

Minimizing Radiation Risk, Key Learning Points: Radiation risk is minimized by justification of the investigation, optimization of the image acquisition process, and limitation of the dose. Justification means that a radiographic examination should be performed only when the diagnostic and clinical benefits outweigh potential radiation risk. Optimization means that the radiation dose to the patient is sufficient to create high-quality, useful images; this requires appropriate equipment and exposure settings. Radiation doses should be limited by controlling the exposure settings and field of view and by shielding the thyroid and salivary glands. The ALADA principle states that doses should be As Low As Diagnostically Acceptable without compromising image quality.

Diagnostic radiographs seek to assess areas for the presence of pathology and the boundaries of any such conditions that are discovered. The radiographic appearance of a lesion can be important in helping to develop a differential diagnosis. As for many dental situations, the initial investigation of a region is done with two-dimensional imaging techniques. Either intraoral films or panoramic radiographs can be used, and here the choice of techniques is predominantly based on the size of the area to be investigated. 3D techniques are not normally used in initial assessment, but can be very helpful in further investigation of issues that are detected in 2D images. In the clinical situation shown, this single intraoral film shows sufficient detail to determine that there is no significant pathology in the area of the upper left lateral incisor, where an implant-supported prosthesis is planned.

Treatment planning for implant-supported prostheses requires information regarding the anatomy of the edentulous bony ridge where implant placement is planned. This includes the dimensions and volume of the ridge. The location of adjacent anatomic structures that might impact on implant placement must also be visualized. Here again, 2D imaging techniques are likely to be ideal for initial assessment, supplemented by 3D images if there is a need for more information, especially in regard to nearby anatomic structures. 3D imaging techniques are indicated as the initial investigation technique in cases where guided surgery is desirable. In such cases, clear patient-centric benefits should justify the additional radiation risk. In the clinical case shown, initial 2D images showed an enlarged nasopalatine foramen near the site of a planned implant crown to replace the missing upper left central incisor. These CBCT views show the position of the foramen, but they also confirm that there is sufficient space for an implant, although some additional grafting may be needed at the time of implant placement.

Radiographs are often used when monitoring implant-supported prostheses after their insertion, both at the time of delivery, and later. In such situations, the clinician is seeking to confirm the stability of the bone crests surrounding the implant, and to assess the extent of any peri-implant pathology. 2D imaging is usually sufficient for these purposes. 3D imaging is normally not indicated, unless there is a need to visualize the extent of a significant lesion associated with, or near to, an existing implant. In such situations, artifacts associated with the radiopaque implant may limit the accuracy of these investigations. In this clinical case, an intraoral image was taken in 2014 at the time of delivery of the implant crown replacing the upper left central incisor. Comparison of this image with one taken in 2016 confirms the stability of the peri-implant tissues at that time.

Selecting Appropriate Imaging Modalities, Key Learning Points: For diagnosis, treatment planning, and post-treatment monitoring, the preferred initial investigation is 2D imaging. 3D imaging can be used for further investigation of pathology detected in 2D images. 3D imaging can be used to investigate adjacent teeth and anatomic structures that may impact on implant placement. If guided surgery is indicated, the initial investigation should be 3D imaging. 3D imaging is rarely indicated for assessment of bone crest levels and peri-implant pathology.

Introduction to Radiographic Assessment, Module Summary: 2D periapical and panoramic radiographs are sufficient for initial diagnosis and planning. 3D CT and CBCT imaging give dimensionally accurate views of the jaws at higher radiation doses than 2D techniques. All radiographic investigations should be justified by benefits that outweigh the potential harms. Radiation risk can be reduced by selecting the imaging modality and exposure protocols that limit the radiation dose without compromising image quality. Limiting the FOV and shielding radiosensitive tissues such as the thyroid further reduce radiation risk.