and any potential associated pathology and disease in the local region; however, it is limited in the physical size of the film and being a single plane.
Occlusal radiographs: These provide an overall view of the patient's bony anatomy, but they provide limited information due to superimposition of structures and magnification.
Lateral cephalometric radiographs: These provide the mid‐sagittal jaw width as well as the maxillo‐mandibular jaw relationship.
Panoramic radiographs: These provide an overview of vital structures and quantity of bone. However, magnification and distortion are a major limitation, and the panoramic view provides no cross‐sectional information. It is still widely used during the diagnostic phase as an initial screening record.
3.1.1.1 Three‐Dimensional Imaging
Computed tomography (CT) has revolutionised treatment planning for dental implants. It provides a vast array of images in high resolution, such as panoramic, cross‐sectional, axial, and 3D. The major drawbacks are cost, accessibility, and higher radiation dosage. With radiation dosage in mind, the advent of cone beam computed tomography (CBCT) scanners in the late 1990s have been designed for the maxillofacial region. CBCT imaging reduces the radiation exposure to the patient and is also more accessible as many dental offices and radiology centres possess these machines. CBCT provides high‐resolution images allowing visualisation of anatomical structures and identification of local pathology, and provides multiplanar views of the tissue volume to be investigated. CBCT utilises a cone‐shaped X‐ray beam with both the source and detector rotating around the patient. It is currently the recommended comprehensive diagnostic method to obtain a comprehensive analysis for implant placement. The American Academy of Oral and Maxillofacial Radiology consider the CBCT as a standard of care examination for dental implant planning [2].
Radiographic imaging aims to follow the ALARA principle, which is to use a dose that is as low as reasonably achievable. Intra‐oral radiographs and orthopantomograms typically deliver dosage equivalent to days of background radiation, while the CBCT emits dosages of a week or more of additional background radiation. CT imaging is equivalent to several weeks of background radiation. The CBCT allows selection of smaller field of view (FOV) and by restricting it to the region of interest (ROI) there is a reduction in the effective dose of radiation (Table 3.1).
Table 3.1 Ionising radiation dosage chart: comparing background radiation to both dental, medical and the yearly Australian safety limit.
Sources: Ludlow, J.B., Davies‐Ludlow, L.E., Brooks, S.L. et al. (2006). Dosimetry of 3 CBCT devices for oral and maxillofacial radiology. Dentomaxillofac. Rad. 35: 219–226; White, S.C. and Pharaoh, M.J. (2009). Oral Radiology: Principles and Interpretation. St. Louis, MO: Mosby Elsevier; Australian Radiation Protection and Nuclear Safety Agency (2016). Radiation Protection in Planned Exposure Situations. ARPANSAR.
| Procedure | Effective dose (μSv) | Dose as days of equivalent background radiation |
|---|---|---|
| 1 day of background radiation (sea level) | 7–8 | 1 |
| 1 dental PA radiograph | 6 | 1 |
| Kodak CBCT focused field anterior | 4.7 | 0.71 |
| Kodak CBCT focused field maxillary posterior | 9.8 | 1.4 |
| Kodak CBCT focused field mandibular posterior | 38.3 | 5.47 |
| Chest X‐ray | 170 | 25 |
| Medical CT (head) | 2000 | 1515 |
| Federal occupational safety limit per year (Australia) | The current legal limit of radiation exposure for Australian workers is 20 000 μSv/y averaged over 5 years, and not more than 50 000 μSv received in any 1 year for effective (whole‐body) dose | |
The limitation with CBCT is in assessment of soft tissue volume and the use of CT imaging is preferred if an assessment of soft tissue volumes is needed. A further limitation for both CT and CBCT is artefacts from the presence of radiopaque restorations and implants. This can be seen as cupping (distortion of metallic objects), beam hardening (dark streaks between dense objects), scatter, and motion artefacts (longer exposure times are vulnerable to patient movement).
3.1.1.2 Templates
Radiographic templates can be used in diagnostic imaging, and these are based on desired tooth positions, and accordingly planned with correct spacing and biomechanical principles. These guides are used to determine if the desired implant prosthesis is possible and can assist the surgeon in determining if augmentation is required at the surgical site. They must replicate the desired final tooth position and must be stable during the process of taking the CBCT. There are various methods for creating radiographic guides including conventional analogue and more recent digital techniques:
The analogue technique traditionally starts from waxing up the desired teeth on articulated study models, creating a vacuum‐formed retainer or acrylic template, then filling the desired positions with a radiopaque material (Figure 3.1).
Digital techniques begin with intra‐oral scans and the desired tooth position is planned. The radiographic guide can then be milled or 3D printed.
Figure 3.1 Analogue/traditional radiographic template.
Templates (guides/stents) have various functions:
They simulate prescribed teeth in the intended implant sites. These are positioned according to prosthodontic planning with the numbers of implants as well as the position of the teeth for best aesthetics, function, and phonetics. The implants are positioned so that they are 1.5 mm away from teeth and 3 mm from adjacent implants.
They indicate any need to replace soft and/or hard tissues.
They are used in surgical site assessment, radiographic assessment, and surgical placement of implants. This may also allow visualisation to see whether screw retention is possible.
Radiographic templates constructed during the initial prosthetic work‐up may be used in conjunction with the CBCT, allowing the clinician to determine whether bone grafting will be needed and also to guide the clinician in choosing an appropriate prosthesis [3].
Various methods have been used to allow imaging with the use of gutta percha markers, radiopaque teeth, or barium sulfate in acrylic. The use of radiopaque gutta percha markers have been used to simulate the alignment
