9: Implant Imaging

Chapter 9

Implant Imaging

Aim

Implantology is a major growth area in dentistry and uses a greater range of imaging techniques than other aspects of the profession. The aim of this chapter is to provide information about implant imaging.

Outcome

After reading this chapter, the reader should be able to:

  • give the indications for imaging in implantology

  • list the advantages and disadvantages of the imaging techniques used in implant imaging

  • state the doses of the common radiographic techniques used in implantology

  • appreciate the concept of tomography and be familiar with the tomographic techniques that may be used in implantology.

Indications for Imaging

Imaging is essential in implantology. It is required at the following stages:

  • preoperative

  • intraoperative

  • post-operative.

Table 9-1 summarises the indications for imaging and suggests appropriate views at these stages.

Table 9-1 Indications for imaging during implantology, and the appropriate views at each stage
Stage Indication Appropriate radiographic views Additional notes

Pre-operative

  • To establish the optimum position for the proposed implants

  • To identify important anatomical structures within the jaws, so they can be avoided during surgery

  • To assess the morphology of the bone, since a minimum height, width and volume of bone is required

  • To identify undercuts within the bone

  • To examine the quality of the bone, since implants placed in poor quality bone are more likely to fail

  • To exclude the presence of occult disease

  • Periapical radiograph

  • Dental panoramic tomograph

  • Occlusal radiograph (mandible)

  • Lateral cephalometric radiograph

  • Cross-sectional imaging

  • Radiographs need to be geometrically accurate

  • In uncomplicated single implant cases, cross-sectional imaging not normally necessary

Intra-operative

  • In difficult cases to facilitate precise positioning of the implant

  • Periapical radiograph

  • Radiographs need to be geometrically accurate

  • Digital radiography useful as images are displayed more quickly than with conventional radiography

Post-operative

  • To assess osseointegration

  • To assess long-term bony support

  • Periapical radiograph

  • Dental panoramic tomograph

  • Rarely other specialised techniques

  • Radiography essential if symptomatic

  • Radiographs need to be geometrically accurate so that the threads on the fixtures can be visualised

  • Digital subtraction radiography may be used to assess osseointegration

  • Rate of vertical bone loss should be less than 0.2 mm annually following the first year of placement

  • Radiographic review every 1-3 years until there is no evidence of continued bone loss

  • Computed tomography should not normally be used as the fixtures can cause significant artefacts

Imaging Techniques

The following investigations are frequently used in implant imaging:

  • periapical radiographs

  • occlusal radiographs (mandible)

  • dental panoramic tomographs

  • lateral cephalometric views

  • cross-sectional imaging (tomography and computed tomography).

The advantages and disadvantages of these techniques are shown in Table 9-2 (pages 143 and 144) and typical doses are shown in Table 9-3 (page 146).

Table 9-2 Advantages and disadvantages of the various radiographic techniques used in implantology
(Adapted from Radiation Protection 136: European Guidelines on Radiation Protection in Dental Radiology: the safe use of radiographs in dental practice)
Technique Advantages Disadvantages

Periapical radiography

  • Excellent resolution

  • Inexpensive

  • Low dose

  • Gives a vertical and horizontal measurement of bone available

  • Reproducible images obtained if the paralleling technique is used

  • Difficult to obtain reproducible images in edentulous patients

  • No cross-sectional information

Occlusal radiography

  • Excellent resolution

  • Inexpensive

  • Low dose

  • Shows width of the mandible

  • May show the course of the inferior dental canal and mental foramen

  • May be used as a planning view in tomography

  • No cross-sectional information

  • Only helpful in the mandible

Dental panoramic tomography

  • Low cost

  • Relatively low dose

  • Whole of mandible/maxilla can be seen on one film

  • Gives a vertical and horizontal measurement of bone available

  • Low resolution

  • No cross-sectional information

  • High inherent magnification

  • Magnification in vertical and horizontal planes not necessarily equal

  • Technique errors can lead to further geometric distortion

Lateral cephalo-metric radiography

  • Reproducible and accurate technique

  • Provides some cross-sectional information on the midline structures of the jaws

  • Low resolution

  • Because of superimposition, can only be used to assess the anterior region

  • Cephalometric equipment not necessarily available to the general dental practitioner

Cross-sectional tomography (spiral/ hypocycloidal)

  • Provides cross-sectional information

  • Accurate measurements

  • Imaging limited to sites of interest

  • Long acquisition time

  • Tomographic blur present on image

  • Technically difficult to perform

  • Tomographic blurring can make interpretation difficult

  • Limited availability

  • Relatively high dose

  • Moderately expensive

  • Bone density measurements not possible

Computed tomography (conventional)

  • Provides cross-sectional information

  • Accurate

  • Short acquisition time

  • No superimposed tomographic blurring

  • Multiplanar views and 3-D reconstruction possible

  • Uniform magnification

  • Bone density measurements possible

  • High dose

  • Imaging of entire jaw rather than site of interest

  • Amalgam can cause significant artefacts on image

  • Limited availability

  • Expensive

Cone beam computed tomography

  • Provides cross-sectional information

  • Accurate

  • Short acquisition time

  • No superimposed tomographic blurring

  • Multiplanar views and 3-D reconstruction possible

  • Uniform magnification

  • Technically straightforward to perform

  • Lower dose than conventional CT

  • PC based software

  • Imaging of entire jaw rather than site of interest

  • Limited availability

  • Relatively expensive

  • Amalgam can cause artefacts on image

  • Limited bone density information provided

Magnetic resonance imaging

  • No radiation dose

  • Provides cross-sectional information

  • Measurements accurate

  • No amalgam artefacts

  • Excellent contrast resolution

  • No specific software programmes available to help with planning

  • Difficult to interpret for the inexperienced

  • Very limited availability

  • Expensive

 

Table 9-3 Typical effective doses from common radiographic investigations used in implantology
* Estimate not based on published figures ** Wide variation in dose partly due to differences in scanning parameters utilised. Using modern scanning protocols, the expected doses would be at the lower end of this range.
Imaging technique Effective dose μSv Equivalent natural background radiation dose in the UK
Periapical radiograph 1–8 4–32 hours
Lower occlusal radiograph* 2–8 8–32 hours
Dental panoramic tomograph (if salivary glands included in the calculations) 16–26 2.6–4.3 days
Cephalometric lateral skull 3–5 12–20 hours
Cross-sectional slice on a panoramic machine (molar region) 9 36 hours
Single cross-sectional slice using spiral tomography 1–30 4 hours–5 days
CT mandible** 480–3324 80 days–1.5 years
CT maxilla** 240–1200 40 days–6.7 months
Cone beam CT mandible (if salivary glands included in the calculations) 75 12.5 days
Cone beam CT maxilla (if salivary glands included in the calculations) 42 7 days

Cross-sectional Imaging

Concept of Tomography

With conventional radiography, structures that lie along the same path as the emerging x-ray beam are superimposed on each other in the final image. As a result, overlying tissues may obscure those structures under investigation. Tomographic techniques can be used to produce a “slice”, or focal layer, to allow the required structures to be seen.

The simplest form of tomography is linear tomography. The x-ray tube and cassette are linked together and move in opposite directions about a fulcrum. A broad x-ray beam is used and the radiographic exposure is continuous throughout the movement. Three points, A, B and C, are shown in Fig 9-1 (page 145). If a conventional radiograph is taken, these objects become superimposed and little information can be gained. In this example, we shall assume information is r/>

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Jan 12, 2015 | Posted by in Oral and Maxillofacial Radiology | Comments Off on 9: Implant Imaging
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