This article focuses on radiographic imaging with regard to planning, treating, and maintaining partially and completely edentulous prosthodontic patients with dental implants. Cone-beam computed tomography (CBCT) is the preferred imaging method for pretreatment dental implant treatment planning. Radiographic guides containing radiopaque materials and/or fiducial markers transfer both the proposed prosthesis design and desired implant location for appropriate radiographic evaluation. The three-dimensional CBCT analysis provides information on the adjacent relevant anatomy, bone volume of the edentulous sites, and restorative space assessment.
Key points
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Prosthetically driven implant planning enables and ensures esthetic, functional, and long-lasting restorative outcomes.
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Cone-beam computed tomography is the preferred imaging method for pretreatment dental implant treatment planning.
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The prosthodontically driven implant planning includes evaluation of adjacent anatomy, three-dimensional measurements of the edentulous sites, anterior-posterior spread considerations, and restorative space assessment.
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Restorative space assessment is necessary to ensure adequate space for optimum physical and mechanical properties of all components/materials required in the prosthesis.
Implant imaging for the rehabilitation of the partially and completely edentulous patient.
Introduction
Prosthodontics is the dental specialty pertaining to the diagnosis, treatment planning, rehabilitation, and maintenance of the oral function and esthetics of patients with missing or deficient teeth by using prosthetic substitutes. Prosthodontic patients may be completely dentate and interested in improving the esthetics and/or function of their existing dentition. They could also be missing 1 or more teeth (partially edentulous) or all of their teeth (completely edentulous) and seeking to replace their missing dentition. The prosthetic substitutes that prosthodontists use to restore and/or replace the deficient tissues may be divided into 4 categories depending on the type of support that is used:
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Fixed prostheses supported on remaining teeth, which cannot be removed by the patient, such as veneers, onlays, inlays, full-coverage crowns, and fixed dental prostheses (FDPs).
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Removable prostheses supported mainly on soft tissues, which can be removed by the patient, such as complete or partial dental prostheses (dentures) and overdentures.
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Fixed or removable prostheses that are supported mainly by dental implants.
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Maxillofacial prostheses, intraoral or extraoral, and are supported on hard and/or soft tissues and/or dental implants.
The evolution of implant dentistry has expanded the prosthetic rehabilitation options for completely and partially edentulous patients and those dentate patients with indications for tooth extraction. The patient selection criteria along with thorough clinical and radiographic evaluation of areas indicated for implant therapy play a major role in the planning process that greatly affects the prosthetic result. Therefore, it is of paramount importance to begin the planning process with the end in mind. Prosthetically driven implant planning enables and ensures esthetic, functional, and long-lasting prosthodontic outcomes. This article focuses on the radiographic evaluation with regard to planning, treating, and maintaining partially and completely edentulous prosthodontic patients with dental implants.
Background
Cone-Beam Computed Tomography
Sir Godfrey Hounsfield introduced a technology that used image reconstruction developed by Alan Cormack in the 1960s. This discovery became known as computed tomography (CT) and its three-dimensional (3D) capabilities revolutionized medicine; it is now the standard of care for diagnostic imaging in medicine. Similarly, the advent of implant dentistry fueled a desire for a 3D imaging system that had lower radiation dose than medical CT as well as lower cost to the patient. Cone-beam CT (CBCT) was introduced in 1998 by Mozzo and colleagues when they described the NewTom-9000 as a low-dose alternative to medical CT for implant planning purposes. CBCT units can be dedicated machines for only 1 field of view (FOV) or may be able to image a variety of FOVs within the same unit. Example of the various FOVs associated with corresponding diagnostic tasks are as follows:
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FOV 4 to 10 cm (2”–4″): adequate for imaging the dentoalveolar region for a more local or endodontic purpose.
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FOV 10 to 15 cm (4”–6″): adequate for imaging the maxillary and mandibular region for implants and dentoalveolar concerns.
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FOV 15 to 23 cm (6”–9″): desirable for the maxillofacial and craniofacial regions for orthodontic and oral surgery, and evaluation of the temporomandibular joints.
One of the well-known advantages of CBCT is its ability to provide isotropic voxels (a cuboidal volume element that is geometrically equal in the x, y, and z planes). Therefore, it provides geometric accuracy, minimal distortion, as well as a 1:1 measurement ratio of objects within the volumetric images. However, it is not able to differentiate between soft tissue densities such as fluid and soft tissue disorders because of its lack of gray-scale sensitivity, but it is able to clearly and accurately visualize high-contrast osseous structures in the maxillofacial region. , The advantages and disadvantages of various imaging modalities used in the evaluation and treatment planning for potential implant sites, such as panoramic radiography and CBCT, are compared in Table 1 . ,
| Imaging Modalities | Advantages | Disadvantages |
|---|---|---|
| Panoramic radiography |
|
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| CBCT |
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Cone-Beam Computed Tomography Dosimetry
Low-level ionizing radiation is used with CBCT. Dental practitioners are taught to observe the principle of as low as reasonably achievable as well as selection criteria in the use of ionizing radiation. However, a discussion of dosimetry is important when deciding whether an image is justified for a particular diagnostic purpose. The effective dose is used to calculate radiation dose and represented in microsieverts (μSv). This method can give a broad indication of the level of detriment to health from radiation exposure by expressing the risk to the whole body. The effective dose takes into consideration both the volume as well as the sensitivity of the tissues involved. It is estimated that the population in the United States receives approximately 3100 μSv of ubiquitous background radiation a year, which equates to approximately 8.5 μSv/d. An additional average annual dose from medical sources of approximately 3100 μSV to the population has been cited, bringing the total average yearly dose from both background radiation and medical sources to 6200 μSv/y. Table 2 shows the various FOVs and effective doses of CBCT units with a comparison with digital panoramic units as well as days of per capita background radiation in the United States. Medical CT radiation dose is also observed for comparison purposes.
| Effective Doses from CBCT and Medical CT Compared with Digital Panoramic Equivalent and Days of Per Capita Background Radiation | |||
|---|---|---|---|
| CBCT/CT | Effective Dose (μSv) c | Digital Panoramic Equivalent d | Annual Per Capita Background Radiation (d) e |
| CBCT examination (average dose for small-FOV protocols) b | 84 | 6 | 10 |
| CBCT examination (average dose for medium-FOV protocols) b | 177 | 13 | 21 |
| CBCT examination (average dose for large-FOV protocols) b | 212 | 15 | 25 |
| Medical CT maxillomandibular: skull a | 2100 | 150 | 247 |
| Comparison with Somatom Sensation32 row/64 slice MultiDetector CT a | 860 | 61 | 101 |
| Comparison with Somatom 32-row/64-slice multidetector CT with CARE dose 4 D a | 534 | 38 | 63 |
a Ludlow and colleagues, , Ludlow and Ivanovic.
c Effective dose calculated with International Commission on Radiological Protection 2007 tissue weights.
d Median of published effective dose for digital dental panoramic radiography = 14 μSv.
e Annual per capita = 3.1 mSv (3100 μSv) per annum or approximately 8.5 μSv/din the United States.
Discussion
The American Academy of Oral and Maxillofacial Radiology (AAOMR) recommends cross-sectional imaging for dental implant treatment planning and that CBCT is the preferred imaging method for obtaining the pretreatment images. In addition, it is advised that a panoramic radiograph with supplemented intraoral images should be taken for the initial pretreatment evaluation to determine whether the patient is a candidate for implants before taking a CBCT scan ( Fig. 1 ).
Diagnosis and Treatment Planning for Prosthodontic Patients
Anatomy
The anatomy surrounding the potential implant site should be thoroughly evaluated. Before focusing on the height and width of the residual alveolar bone to measure the dimensions for implant placement, the entire volume should be reviewed to rule out pathologic entities. Sinus augmentation procedure recommendations using the residual alveolar bone height classification is used as a reference for predictable implant treatment planning ( Fig. 2 ). , The following localized anatomy should be evaluated in the pretreatment assessment of the CBCT based on the position of the desired implant :
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Maxilla ( Figs. 3–5 )
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Maxillary tuberosity
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Maxillary sinuses
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Thickness and angle of the lateral cortical borders
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Topography of the sinus floor and bony septations
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The height and width of the maxillary sinus
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Location of the maxillary sinus ostium to ensure that sinus augmentation will not result in blockage of the sinus drainage pathway
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Vascularization along the floor of the maxillary sinus: posterior superior alveolar artery, infraorbital artery, and the anastomosis between the 2 arteries known as the alveolar antral artery
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Posterior superior alveolar nerve canal
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Common incidental findings that may complicate sinus augmentation, such as mucosal thickenings/sinus disease, mucus retention pseudocysts, and antroliths
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Nasopalatine canal
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Anterior superior alveolar nerve canal
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Pathologic findings such as tumor or cysts
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