Radiology

Contrast on radiographs

• The more x-rays that reach the receptor, the darker the image in that area

• Denser structures such as bone, dentine and enamel appear white on radiographs as they absorb more x-rays and therefore fewer x-rays reach the receptor

• Thi sis radiopaque

• Less dense structures such as the PDL and pulp appear dark on radiographs as they absorb fewer x-rays and therefore a greater number of x-rays reach the receptor

• This is radiolucent

Normal Apex

• Rooth canal terminates at the apical foramen

• An adult with a fully formed tooth has a closed apex and the root canal tapers to a point to the apical foramen

Open Apex

• Immature teeth have an open apex where the root isn’t fully formed and there is a wide apical foramen

• Around the apex there is a small radiolucency which is called the apical papilla

Lamina Dura

• Radiopaque

• Socket is lined by a thin layer of dense cortical bone

• In a newly extracted tooth socket, the LD is still visible

In a healthy tooth, the PDL space should be at the same width all around the root. Widening of this space usually indicates inflammation but can be due to occlusal trauma

Healthy Patient

The normal alveolar crest lies 2-3mm below the CEJ and forms a sharp angle with the lamina dura. The crest is not always well corticated.

Periodontal disease results in a reduction of the alveolar bone levels

• On a radiograph, you can calculate the percentage of bone loss:

  (CEJ to bone crest) / (CEJ to root apex) x100

• Alternatively, you can use descriptors:

  Interproximal bone loss

  • Stage 1 (Early/Mild): <15% or 2mm attachment loss from CEJ

  • Stage 2 (Moderate): coronal third of root

  • Stage 3 (Severe): mid third of root

  • Stage 4 (Very severe): apical third of root

Interproximal caries

• 50% demineralisation is required for radiographic detection of a lesion

• Usually up to a 3rd larger clinically than radiographically

Factors affecting appearance of caries:

• Buccolingual thickness of tooth. The thicker the tooth, the more difficult it is to see the extent of the caries

• Two dimensional film. Cannot see the extent of carious involvement in a buccolingual direction

• The density of the enamel on either side is dense enough to obscure the small carious lesion (also due to the angle of the beam)

• X-ray beam angle (horizontal or vertical). Important when trying to identify recurrent caries, since changes in angulation may cause the superimposition of the existing restoration with the carious lesion.

• Exposure factors: caries detection is improved with a lower kVp setting, which provides a higher contrast. If the density of the film is too light or too dark, the diagnostic potential of the film is limited.

Caries Classification

I - Incipient (1)

M - Moderate (2)

A - Advanced (3)

S - Severe (4)

Incipient (Approximal caries)

• Outer 50% of enamel

• Usually not restored unless the patient has a high level of caries activity

• Treat with fluoride

Moderate (Approximal caries)

• Inner 50% of enamel (up to ADJ)

• Treat with fluoride and OHI

Advanced

• Reaches into dentine (<50%)

Severe

• More than 50% into dentine or into the pulp chamber

Cervical burnout

• Cervical burnout is an apparent radiolucency round just below the CEJ on the root

• It is an artificial phenomenon created by the anatomy of the teeth

• Mimics root caries

Mach band effect

The zone at the distal cervical margin directly beneath the white metallic restorationshadow, appears radiolucent

• It is the optical illusion of radiolucency next to a very dense restoration

• The trick is to black out the restoration

Apical Pathology

• Tooth develops caries (necrotic)

• Caries advances into the pulp

• Pulp becomes inflamed (irreversibly)

• Toxins are produced and excreted around the periapical region

• Causes inflammatory process at apex

When the pulp becomes necrotic, with time an apical periodontitis will develop. The inflammatory changes within the apical tissues manifest as an apical radiolucency

Inflammatory Process

• PDL widens

• Lamina dura gets destroyed

• Apical radiolucencies form

• Reform LD around radiolucencies

  • Sign of chronic and long-standing (avoid spreading)

Often around the margins of a loosened area, the margins are more dense due to new, more dense bone forming as part of the inflammatory process (condensing or focal sclerosing osteitis)

Radiolucency would be rarefying osteitis (less dense bone)

Fractures

When there is very severe periodontal bone loss and apical pathology and you see prio-endo lesions

When there is very focal bone loss in one area, especially with heavily restored teeth

→ consider root fractures

Justification

• A legal obligation and must be recorded in the patient’s notes

• Radiographs must follow a history and clinical examination

Assessment of radiographs

• Diagnostically acceptable or unacceptable

• It is a legal requirement that all radiographs undergo a clinical evaluation

• The report should be of the entire area image and not just the area of interest

Dental therapist radiographs must have a second opinion from a dentist for things that may fall outside their scope of practice.