Radiography: dental extra-oral parallel

• See also dental radiography overview Dental radiography: overview.
• Extra-oral technique positions the X-ray film outside the mouth.
• Parallel technique positions the film parallel with the object (tooth).

• Maxillary pre-molars and molars.
  Less useful for mandibular molars/pre-molars because mandible narrower than maxilla → more superimposition of tooth images.
• Good for large lesions such as oral neoplasms.

Advantages

• Can use standard cassettes with intensifying screens.
• Can use non-screen film of varying sizes, eg dental film sizes 2 and 4.
• Reduces superimposition by the zygomatic arch.

Disadvantages

• Accurate interpretation difficult because of superimposition of other irrelevant images.
• Proper evaluation of other individual teeth is difficult.
• Teeth may appear magnified, poor detail.

• Head shape provides positioning difficulty.

• Intra-oral radiographic techniques Radiography: intra-oral parallel and bisecting angle - give much better results where zygomatic arch superimposition can be eliminated.

Procedure

• 15-30 min depending on the skill of radiographer.

Minimum equipment

• Standard veterinary X-ray machine.
• Viewer.

Ideal equipment

• Dental accessories.
• Mouth gag (soft ends to protect teeth).
• Foam pad to position head.
• Standard x-ray machine: 20 cm for non-screen and dental film; 75 cm for standard cassettes.
• Collimate as much as possible to limit X-ray beam and improve detail.
• Dental x-ray machine: already set by cone length (around 20 cm); simply place end of cone onto area of interest. Cone also collimates to within its circumference.

• Small dog: non-screen 60 kV/7 mAs; screened 60 kV/2 mAs.
• Medium dog: non-screen 65 kV/10 mAs; screened 65 kV/5 mAs.
• Large dog: non-screen 65-80 kV/10 mAs; screened 70 kV/6 mAs.

Suggested dental x-ray machine settings (with dental, non-screen film)

• Small dog/cat: 0.32-0.40s.
• Medium dog: 0.40-0.63s.
• Large dog: 0.63-1.00s.

Minimum consumables

• Standard cassettes with fast tungstate screens.
• Non-screen film (sizes 2 and 4).
• Radiographic processing chemicals.
• Dental radiograph film; many different types including some 'self-developing' which use intra-envelope developing, eg squeezing injects developer and massage envelope, pull tab on envelope → releases film.

Ideal consumables

• Dental non-screen film sizes 2 and 4 - can be used extra-orally.
• Dental (rapid) radiographic processing chemicals.

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

• See dental radiography overview Dental radiography: overview.
• Radiolucent gag to open mouth as wide as possible, eg cut-down hypodermic syringe case.
  Avoid excessive mouth gape, especially for prolonged periods. Relax gape adnd massage masseter muscles to prevent myositis!
• Foam pads to position the head.

Step 1 - Set up

• Place animal in lateral recumbency with the side of interest nearest the table.
• Use a radiolucent gag to open the mouth as wide as possible.
• Position the head with foam pads so that the long axis of the tooth of interest is parallel to the table.
• This will often require some rotation of the ehad about teh long axis, ie lateral oblique position created.

Step 2 - Position film

• Place film under the tooth and angle X-ray beam at 90° to film.
• With lateral oblique positioning the beam will pass through the palate then tooth area to film.

Potential complications

• Temporary teeth may have a less distinct root morphology while presence of adjacent adult dentition complicates interpretation - if in doubt do not extract - obtain the opinion of a referral colleague on the radiogaph.

Refereed papers

• Recent references from PubMed and VetMedResource.
• 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.

Other sources of information

• 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).