Periapical Radiographs

Periapical radiographs offer great advantages to evaluate the implant patient.19,20 They provide an overall assessment of the quantity and quality of the edentulous alveolar ridge and the adjacent teeth. They are easy to obtain in the dental office, are inexpensive, and deliver low radiation to the patient (Table 73-2). Dentists are familiar with the depicted anatomy and possible pathology. Because these direct-exposure projections do not use intensifying screens, intraoral radiographs offer the highest detail and spatial resolution of all radiographic modalities (Figure 73-1). Thus, intraoral radiographs are the projection of choice when subtle pathology, such as a retained root tip, needs to be detected and evaluated.

The most significant disadvantage of periapical radiographs is their susceptibility to unpredictable magnification of anatomic structures, which does not allow reliable measurements.¹⁵ Foreshortening or elongation can be minimized by the use of paralleling technique. However, distortion is particularly accentuated in edentulous areas, where missing teeth and resorption of the alveolus necessitate receptor placement at significant angulation in relation to the long axis of the teeth and alveolar bone. Additionally, periapical radiographs are two-dimensional representations of three-dimensional objects and do not provide any information of the buccal–lingual dimension of the alveolar ridge. Structures that are distinctly separated in the buccal–lingual dimension appear to be overlapping. Also, the periapical image is limited by the size of film or sensor being used. Often, it is not possible to image the entire height of the remaining alveolar ridge, and when extensive mesial–distal areas need to be evaluated, multiple periapical radiographs are required.

In summary, periapical radiographs are useful screening images that offer a detailed view of a small area of the alveolar arch. Limitations that must be considered include the possibility of distortion and the two-dimensional representation of anatomic structures.

Occlusal Radiographs

Occlusal radiographs are intraoral projections that offer easy, economic, low-dose, and high-resolution images covering a larger area than periapical projections.²⁰ Depending on receptor placement and the angulation of the x-ray tube, occlusal radiographs can provide an image of the mandibular width or can depict an extended area of the edentulous ridge. Occlusal radiographs have the same limitations of distortion and overlapping anatomy as periapical radiographs.

In summary, occlusal radiographic projections are good screening images that can provide an overview of the mandibular width or can visualize larger areas of alveolar ridge compared with periapical radiographic projections.

Panoramic Radiographs

Panoramic radiographs are often used in the evaluation of the implant patient because they offer several advantages over other modalities.¹⁶ Panoramic radiographs deliver low radiation (see Table 73-2) to provide a broad picture of both arches and thus allow assessment of extensive edentulous areas, angulation of existing teeth and occlusal plane, and important anatomy in implant treatment planning such as the maxillary sinus, nasal cavity, mental foramen, and mandibular canal (Figure 73-2). Panoramic units are widely available and easy to operate, and dentists are familiar with the anatomy and pathology depicted by the images. Similar to intraoral projections, panoramic images are two-dimensional and thus do not offer diagnostic information for the buccal–lingual width of the alveolar arch.

Panoramic images appear intuitively familiar. However, they combine characteristic physical and radiographic principles that make them distinct from other intraoral and extraoral radiographs. Although outside the scope of this chapter, familiarity with the principles underlying panoramic radiography is central in understanding, and thus compensating for, the limitations and constraints of the images. The reader is referred to other textbooks for detailed discussion of this topic.7,10 Briefly, the existence of ghost shadows, unpredictable horizontal and vertical magnification, distortion of structures outside the focal trough, projection geometry generated by the negative vertical angulation of the x-ray beam, and propensity to patient-positioning errors do not allow consistently detailed and accurate measurements to be generated. As a result, panoramic radiographs do not provide the highly detailed images that are generated by intraoral radiographs.

Measurement distortion is more prevalent and varies across the radiographic image. On average, panoramic radiographs are 25% magnifications of actual size. Implant manufacturers often provide transparency sheets with implant size outlines of 25% magnification. However, it is important to appreciate that the 25% magnification is an estimate. The actual magnification may range from 10% to 30% in different areas within the same image, and depends greatly on patient positioning during panoramic radiography. For this reason, precise measurements on panoramic projections are not possible. Nonetheless, panoramic radiographs offer an overall view of the maxilla and mandible that can be used to estimate bone measurements and evaluate the approximate relationships between teeth and other anatomic structures. More precise diagnostic imaging should be used to measure proximity of critical anatomic structures, such as the maxillary sinus or the mandibular canal, to proposed implant positions.

In summary, panoramic projections are useful screening images of the jaws for approximations and relative spatial relationships. However, because of magnification and distortion errors, panoramic radiographs should not be used for detailed measurements of proposed implant sites.

Lateral Cephalometric Radiographs

Lateral cephalometric radiographs are occasionally used to evaluate potential implant patients.¹⁷ These projections provide useful information for the cortical thickness, height, and width of the alveolar ridge at the midline, as well as the skeletal relationship between maxilla and mandible and facial profile. Lateral cephalometric radiographs are low in cost, readily available, and easy to interpret, and have a predictable magnification of the depicted structures. However, their use for the implant patient is limited to structures at the midline, with minimal usefulness for other areas of the jaws.

In summary, lateral cephalometric radiographs have a limited use in implant treatment planning.

Multislice Computed Tomography

CT scanning is widely used in the evaluation of the implant patient.3,6 The detailed physics behind image acquisition during CT scanning are beyond the scope of this chapter.⁴ In general, a fan-beam of x-rays and an array of detectors rotate around the patient to generate axial slices of the area of interest (Figure 73-3, A). Multiple overlapping axial slices are obtained by several revolutions of the x-ray beam until the whole area of interest is covered. These slices are then used to generate, with the help of a computer and sophisticated algorithms, a digital volume of the imaged object. CT’s advantage during evaluation of the implant patient is the construction of this three-dimensional digital map of the jaws. Specialized software can be used to generate appropriate views that best depict the dimensions of the jaws and the location of important anatomic structures.

Typical dental views reconstructed from a CT scan include axial (see Figure 73-3, B), panoramic (see Figure 73-3, C), and cross-sectional (see Figure 73-3, D) views of the jaws. Appropriate axial slices through the alveolar ridge of interest are selected as scout views. The curvature of the maxillary or mandibular ridge is then drawn on the axial slices, and panoramic images along the drawn line are created. Finally, cross-sectional slices, every 1 to 2 mm and perpendicular to the drawn curvature, are created. In addition to these flat, two-dimensional views, complex, three-dimensional images with surface rendering can also be generated from the CT data (see Figure 73-3, E). These images can provide useful information about the alveolar ridge defects that are easy to comprehend. Images can be printed on photographic paper or tr/>