Dental radiography: overview

• Essential for viewing the largest part of the teeth/roots and supporting structures which are hidden below gum line.
• The roots and periodontium form the biggest portion of each tooth and can only be fully visualized by means of intra-oral radiographs.
• The roots and periodontium are where much pathology will form.
• As result up to 70% of the pathology in the mouth may go undetected without the use of intra-oral radiography.
• Some lesions may be detected clinically but the full extent of the lesion or disease can only be accurately assessed with radiographs, eg feline odontoclastic resorptive lesions ('neck'/resorptive' lesions) Odontoclastic tooth resorption (resorptive lesions).
• With the high incidence of feline odontoclastic resorptive lesions, feline dentistry should not be performed without the use of radiography.
• Approximately 70% of cats over 3 years of age have some form of dental disease.

Technique

• Intra-oral radiography Radiography: intra-oral parallel and bisecting angle (film inside mouth) allows an accurate representation of each tooth providing fine detail that would otherwise be missed.
• Using an extra-oral technique Radiography: dental extra-oral parallel results in superimposition of structures and lower resolution images.
• Two techniques are used:
  • Parallel technique: the film is placed parallel to the tooth structure to be radiographed  . This is only possible for mandibular premolars and molars. The x-ray beam is then directed at 90º to the x-ray film. 
  • Bisecting angle technique    : when the film cannot be placed parallel to the tooth strucutre to be radiographed (ie all incisors, canines, maxillary premolars/molars) an imaginary line is drawn dividing in half the angle between the tooth and the film. The x-ray beam is then directed at 90º to this 'bisecting angle' line.

• Endodontics:
  • To assess loss of attachment, receding bone height relative to cemento-enamel junction, and bony pockets.
  • Assess suitability, eg absence of long axis fracture.
  • Planning the technique (endodontics).
  • Intra-operatively and post-operatively to assess pulp canal length, width and complications.
  • Check whether the pulp cavity has been breached.
• Extractions Dental extraction:
  • Diagnosis and treatment planning of fractured teeth Dental fracture and surrounding tissues.
  • Post-extraction of teeth to check that all root tissue is extracted.
• Detection of missing permanent teeth.
• To differentiate permanent from temporary teeth.
• Diagnosis of neoplasia, dentigerous cysts.

Advantages

• Relatively standard procedure.
• Equipment available in most practices.

Procedure

• 15-30 min depending on skill of radiographer and views required.

Criteria for choosing test

• Apical rarefaction (or 'halo') suggests endodontic lesion, periodontal lesion or both.

Minimum equipment

• Standard X-ray machine.
• Suggested settings for standard x-ray machine:
  • Cat: 65 KV, 20 mAs.
• Film: focal distance = 20 cm (dental x-ray machine); 30-50 cm (standard x-ray machine).
• Viewer.
• Magnifying glass.
• Bright spot illumination.

Ideal equipment

• Dental X-ray machine (alows patient's head to remain in position while cone of machine is moved into correct position).
• Film holders/bite blocks  .
• Speed D dental film (non-screen, supplied in small pre-wrapped envelopes) to give high definition images.
• Dental film    .
• Film clips and hanger if wet processing.
• Dental film viewer, magnifier +/or tube viewer (card tube!).
• Dental radiograph envelopes/mounting system.
• Radiograph marking pen.

Minimum consumables

• Non-screen film size 2.
• Radiographic processing chemicals.
• Dental radiograph envelopes.
• Dental radiographs: many different types exist,  including some which use intra-envelope developing (squeeze bubble of chemicals into film area envelope, massage 1 min,  pull tab on film envelope   →   release film.
  These are relatively expensive per film.

Ideal consumables

• Dental film (child and adult apical film, size 1 and 2, for cats: adult apical and occlusal film). Speed D best for wet processing.
• Dental (rapid) radiographic processing chemicals.

• Fast animal for 12 hours before routine anesthesia to prevent reflux esophagitis.

• General anesthetic - essential because any movement causes loss of film detail.
• Bite block.
• Mouth gag.
• Ties.

Step 1 - Choose technique

• Parallel techniques Radiography: dental extra-oral parallel  Radiography: intra-oral parallel and bisecting angle  : target teeth situated parallel to film with x-ray beam at 90° to film.
• Limited to mandibular premolars and molars.
• Bisecting angle technique Radiography: intra-oral parallel and bisecting angle : if angle between tooth and film >15°.
• Prevents foreshortened or elongated images.
• Radiographic settings depend on technique used. Standard vs dental unit, intra- vs extra-oral, etc.
• Options for film processing:
  • Automatic processors, expensive.
  • Hand/wet processing.
• 'Chair-side' hand/wet developers (= mini dark room).
• Radiographic views:
  • Multiple views (6-10) are required to assess the full dentition.
  • Maxillary premolars and molar extra-oral and intra-oral.
  • Canines:
    • Occlusal view of canines and incisors.
    • Lateral view for evaluating periapical region - bisecting angle.

Step 1 - Processing

• Manual processing using rapid access developer or fixer. Standard x-ray processing chemical can be used but is slower and gives poorer results.
• Set out 4 cups in the darkroom for developer, water, and fixer and water.

Step 2 - Interpretation

• Use magnification or tube viewer.
• Good contrast between hard tissues (enamel, dentine, bone) and air.
• The lamina dura is a thin white line around the root. It represents dense cortical bone and is not a structure in its own right. A complete lamina dura is suggestive of good periodontal health.
• The lamina dura is separated from the tooth by the periodontal ligament which is relatively radiolucent. The majority of jaw bone is trabecular in pattern and varies in density with age and location.
• If in doubt, radiograph the contralateral tooth for comparison.
  Temporary teeth may have a less distinct root morphology - if in doubt do not extract, seek clarification from dental experts.
• See Radiology: dental for more detail Radiology: dental .

Refereed papers

• Recent references from PubMed and VetMedResource.

Other sources of information

• Smithson A (2006) Oral radiology Part 2. UK Vet 11 (1), 40-44.
• Smithson A (2005) Oral radiology Part 1. UK Vet 10 (8), 57.
• Gorrel C (2004) Veterinary Dentistry for the General Practitioner. Saunders.
• Mulligan, Allen, Williams (1998) Atlas of canine and feline dental radiography. In: Veterinary Learning Systems. Trenton, NJ, USA (Excellent reference for dental radiography).