Should Cone Beam Computed Tomography Be Routinely Obtained in Implant Planning?

Clinical assessment and conventional 2-D radiographs often provide inadequate diagnostic data for proper implant placement. Cone beam CT (CBCT) enables 3-D visualization of the alveolar ridge, aiding clinicians with identification of anatomic structures and pathologies. CBCT provides accurate linear measurements at low radiation dose compared with conventional CT scan, which helps in diagnosis and treatment planning, particularly in complex implant cases. Even though straightforward implant surgery can be performed with careful clinical and 2-D radiographic assessment, CBCT should be considered. It provides the unparalleled benefit of computer-aided implant planning, leading to improved clinical outcomes and reduced complications.

Key points

  • Cone beam CT (CBCT) offers high-quality 3-D images at relatively low radiation doses and costs.

  • CBCT should only be used when the question for which the imaging is required cannot be answered adequately by conventional, lower dose dental radiography, applying the As Low As Diagnostically Acceptable (ALADA) principle.

  • CBCT imaging allows for 3-D morphometric analysis of the potential implant sites with submillimetric accuracy.

  • CBCT allows for identification of anatomic landmarks and pathologies.

  • Specialized software can be used for the virtual planning and the fabrication of surgical guides for precise implant placement.

Introduction

The advent of cone beam CT (CBCT) as a relatively low-dose 3-D dental imaging technology has improved both diagnostic accuracy and implant planning. The 3-D visualization of the alveolar ridge enables clinicians to easily identify anatomic structures and anomalies. CBCT is essential to assess alveolar ridge deficiencies and bone augmentation outcomes. A 3-D evaluation is key in particular techniques, such as zygomatic implants, pterygoid implants, and osteogenic distraction.

CBCT images enable clinicians to discuss the patient-specific clinical scenario while presenting an individualized treatment plan. In this review, the authors discuss the added value of CBCT in implant dentistry and investigate the question of whether CBCT should be routinely obtained for preoperative implant planning.

Cone beam CT radiation doses

The effective radiation dose associated with CBCT imaging in implant dentistry is varied, ranging from 10 μSv to 271 μSv, depending on the model of CBCT scanner and field of view (FOV) selected. CBCT provides an equivalent patient radiation dose of 3 days to 48 days of background radiation or 5 times to 74 times that of a conventional panoramic radiograph ( Table 1 ). The use of additional personal protection (thyroid collar) and patient positioning modifications (tilting the chin) can substantially reduce the dose by up to 40%. Other methods of reducing patient exposure include decreasing scan time or scan arc and increasing voxel size, which decreases the image resolution but does not affect measurement accuracy. Based on a systematic review, it has been suggested that a voxel size of 0.3 to 0.4 mm was adequate to provide CBCT images of acceptable diagnostic quality for implant treatment planning. Many CBCT systems offer ultra–low-dose imaging that has radiation doses comparable to conventional panoramic images, without significant reduction in image quality.

Table 1
Effective dose estimates for common dental radiographic examination, cone beam CT, and multidetector CT imaging (estimates for adult patients)
Examination Effective Dose (μSv)
Four-image posterior bitewings with phosphor storage plate or F-speed film and rectangular collimation 5.0
Panoramic radiograph with digital sensor (charge-coupled device) 3.0–24.3
Cephalometric radiograph with phosphor storage plate 5.1–5.6
Full-mouth radiographs with phosphor storage plate or F-speed film and rectangular collimation 34.9
Full-mouth radiographs with phosphor storage plate or F-speed film and round collimation 170.7
CBCT small FOV 60
CBCT medium FOV 107
CBCT large FOV 151
MDCT mandible 427
MDCT jaws 697
MDCT head 1088

Clinicians should apply the As Low As Diagnostically Acceptable (ALADA) principle in reducing patient exposure during the acquisition of CBCT images. This includes appropriate justification of CBCT use, optimizing exposure parameters, using the smallest FOV necessary for the diagnostic task, and using appropriate personal protective shielding.

Cone beam CT versus multidetector CT

In a CBCT machine, the x-ray beam emerges as a divergent cone-shaped or pyramidal beam. Data are acquired as a series of sequential planar projection images (basis images) made with angular differences as the beam rotates around a patient’s head. Projection data are reconstructed through software algorithms, producing a volumetric data set used to generate primary reconstruction images in 3 orthogonal planes (axial, sagittal, and coronal).

In contrast, the x-ray beam in a multidetector CT (MDCT) scanner emerges as a flat fan beam. Data are acquired as a series of consecutive axial slices of a patient’s head obtained from multiple rotations of the x-ray source around the patient. In MDCT, the average density of each voxel is measured in a Hounsfield unit (also known as a CT number); this unit represents the average attenuation coefficient in that voxel. The Hounsfield units that are derived from various CBCT systems, however, are not consistently representative of the actual density values, sometimes even within the same system.

The radiation dose of the CBCT is less than that for an MDCT examination (the dose reduction is between 76.2% and 98.5%). Most CBCT systems use x-ray tubes similar to those in panoramic x-ray machines, operating in the range of 2 mA to 14 mA, whereas for MDCT, the tube current may be in excess of 250 mA. CBCT is more reliable for linear measurements than MDCT and less affected by metal artifacts.

Patient selection criteria

In addition to a thorough clinical examination, a radiographic assessment is essential to evaluate the potential implant sites. Various conventional and tomographic (cross-sectional) imaging techniques are available for evaluation of the implant site and related anatomical structures. Intraoral periapical images are a valuable tool to estimate the mesiodistal and vertical dimensions of an implant site. Panoramic radiographs are less suited because of inherent distortion. Unlike cross-sectional techniques, however, neither panoramic nor periapical radiographs provide information on the buccolingual width or angulation of the alveolar ridge.

The selection of an appropriate radiograph should be based on the needed diagnostic information while balancing the potential benefits and risks. Evidence-based guidelines for patient selection criteria were published in an American Academy of Oral and Maxillofacial Radiology (AAOMR) position paper. In their guidelines, the initial assessment of a potential dental implant site should be completed using intraoral periapical and/or panoramic radiographs. CBCT is recommended as the imaging modality of choice for presurgical implant planning ( Table 2 ).

Table 2
Summary of the position statement of the American Academy of Oral and Maxillofacial Radiology on selection criteria of imaging modalities in implant dentistry
Clinical Situation Specific Indication(s) Imaging Modality
Initial phase
  • Panoramic ± periapical radiography

  • Presurgical phase

    • Clinical doubt of alveolar bone height, width, and/or shape

    • Bone density

    • Anterior esthetic zone

  • Anterior maxilla (nasal floor, incisive fossa)

  • Posterior maxilla (maxillary sinus, posterior superior alveolar canal)

  • Anterior mandible (lingual foramen, genial tubercles, incisive canal)

  • CBCT + radiographic guide

  • Specific anatomic sites

  • Posterior mandible (inferior alveolar nerve canal, mental foramen, anterior loop, lingual undercut, retromolar foramen)

  • Zygomatic region (orbital floor, infraorbital foramen, zygomatic bone)

  • Site development

  • Sinus floor elevation

  • Block or particulate bone grafting

  • Ramus or symphysis grafting

  • Pathology/impacted in the area of interest

  • Prior traumatic injury

  • Computer-assisted treatment planning

  • Follow manufacturer recommendations

  • Postsurgical phase

    • Postoperative implant integration

  • Marginal peri-implant bone height

  • Bone-implant interface

  • Postaugmentation assessment

  • Implant mobility

  • Periapical + bitewing radiography

  • Panoramic radiography in extensive implant therapy

  • Postoperative complications

  • Altered sensation

  • Infection (sinusitis)

  • CBCT

The use of CBCT for presurgical implant planning provides a morphometric and skeletal analysis of the alveolar ridge, highlighting the proximity to vital anatomic structures. When the clinical examination and conventional radiograph reveals the need for bone augmentation or site development procedure, CBCT should be considered for preoperative and postoperative evaluation ( Figs. 1–3 ). In addition, CBCT can be used for an accurate, prosthetically driven implant planning. Intraoral periapical and panoramic radiographs are indicated for postoperative assessment. CBCT imaging, however, may be indicated postoperatively if the implant placement is complicated by local infection or nerve injury ( Fig. 4 ).

Fig. 1
Comparative sets of axial, reformatted panoramic, and sequential 1-mm–thick cross-sectional CBCT images show consolidation of the graft material to the right mandibular posterior edentulous region. This graft increases the alveolar bone width necessary for implant placement.

Fig. 2
Parasagittal CBCT image of a partially edentulous maxilla showing homogenous hyperdense sinus-lift graft material with minimal mucosal thickening.

Fig. 3
( A ) Comparative sets of cross-sectional CBCT images in the anterior maxillary edentulous region show labial cortical concavity. ( B ) Postoperative images show the width gain and bone graft consolidation.

Fig. 4
Comparative sets of axial, reformatted panoramic, and consecutive 1-mm–thick cross-sectional CBCT images of the right mandibular posterior edentulous region demonstrate embarrassment and compression of the mandibular canal by a dental implant. The patient reported postoperative paresthesia of the right lip.

Anatomic considerations

Alveolar Bone Quality

Assessment of alveolar bone quality takes into consideration overall bone volume and morphology. The cortical thickness, trabecular bone pattern, and bone density ( Figs. 5–7 ) are positively correlated with implant primary stability.

Fig. 5
Comparative sets of axial, reformatted panoramic, and serial 1-mm–thick cross-sectional CBCT images of a completely edentulous mandible. The alveolar ridge in the posterior region shows a constriction between the alveolar process and the basal bone resulting from both a buccal and a lingual concavity, resulting in an hourglass configuration.
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Apr 27, 2020 | Posted by in General Dentistry | Comments Off on Should Cone Beam Computed Tomography Be Routinely Obtained in Implant Planning?
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