Contributors: Alex Smithson

 Species: Feline   |   Classification: Techniques

Introduction Requirements Preparation Procedure Aftercare Outcomes Further Reading

Introduction

  • See dental radiography overview Dental radiography: overview.
  • Positioning X-ray film inside mouth minimizes superimposition of irrelevant structures.

Uses

  • Parallel technique: if angle between tooth and film <15° mandibular, ie molars and pre-molars Dental radiography: parallel technique 01 - for mandibular premolar and molar teeth  Dental radiography: parallel technique 02 - for mandibular molar and pre molar teeth .
  • Target teeth situated parallel to x-ray film with x-ray beam at 90° to film.
  • Bisecting angle technique: to give an image the same length as the object: if angle between tooth and film = >15° (maxillary molars/premolars, mandibular and maxillary incisors/canines) Dental radiography: bisecting angle technique 01 - left maxillary canine  Dental radiography: bisecting angle technique 02 - right mandibular canine .

Advantages

  • Parallel: simple.
  • Bisecting angle: minimizes superimposition of other structures.

Disadvantages

  • Parallel: limited to mandibular molars and pre-molars.
  • Bisecting angle: more technical to obtain; inaccuracies with flawed technique; good at casting the 'shadow' if superimposition of other structures occurs.

Technical Problems

  • Accuracy in obtaining bisecting angle line.
  • Head positioning if using standard x-ray machine.

Alternative Techniques

Procedure

  • 15-30 min depending on skill of radiographer.

Decision Taking

Criteria for choosing test

  • Whether angle between tooth and film = < or >15°.
  • Whether one technique will minimize superimposition best.

Requirements

Materials Required

Minimum equipment

Ideal equipment

  • Film holders/bite blocks Dental radiography: multiple chip dental x-ray film holder . 
  • Radiograph magnifier block/tube viewer.
  • Dental film.
  • Dental film developer Dental radiography: chair-side developing system  Dental radiography: light proof chair-side developing box . 
  • Dental film viewer.
  • Radiograph marking pen.
  • Dental non-screen film:
    • Use dental film sizes:
      • Occlusal (54 x 70 mm) - for large teeth in dogs.
      • Periapical size 2/adult  (30 x 40 mm) - for most teeth in dogs and cats.
      • Periapical size 0-1/child (20 mm x 30 mm) - for cats (especially good for mandibular cheek teeth).
    • Dental film of speed D is optimal for wet processing.
      Practice with cadavers using paper clip to detect distortions (radiograph paper clip on tooth then place paper clip on developed radiograph for size comparison).

Minimum consumables

  • Non-screen film.
  • Radiographic processing chemicals.
  • Dental radiograph envelopes; many different types including some self-developing (use intra-envelope developing, eg squeeze developer bubble into film envelope, massage envelope, pull tab   →   release film.

Technical values

  • Using dental non-screen film + dental xray unit:
  • Film focal distance set by cone (20-30 cm), place end of cone onto area of interest.
  • Dental x-ray machines have fixed mA and kV, only the time setting alters.
  • Usual fixed settings are around 50-70 kV and 8-15 mA.
  • Time settings may be adjusted by a dial or digitally either purely by observing the time reading or by use of pictorial aids.
  • The pictorial aids are manufacturer's suggested settings: machines intended for humans show different sized people and a choice of tooth types/positions while veterinary dental x-ray machines show different sized dogs (sometimes also cat, if not use small dog setting) and their teeth.
  • To use the pictorial settings simply select the size and tooth type/position which best matches your patient! Remember to allow for anticipated skull tichnesses/density!
  • Since all methods alter only time setting, the suggested settings below are equally applicable to each.
  • Suggested machine settings:
    • Small dog/cat:
      • Maxillary incisors - 0.25-0.32s    Mandibular incisors - 0.25-0.32s
      • Maxillary canines - 0.32-0.40s    Mandibular canines - 0.32s
      • Maxillary pre-molars & molars - 0.32-0.40s   Mandibular pre-molars & molars - 0.20-0.32s.
  • Using veterinary x-ray machine + non=screen film:
    • Film focal distance = 30-50 cm.
    • Suggested machine settings:
      • Small dog/cat: 65 kV, 20 mAS.

Ideal consumables

  • Dental film.
  • Dental (rapid) radiographic processing chemicals.

Preparation

Dietary Preparation

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

Restraint

Procedure

Approach

Step 1 - Set up

  • Similar to conventional skull radiography Radiography: skull (basic).
  • Position animal in lateral recumbency with side to be radiographed uppermost.

Step 2 -

  • Parallel: place dental intra-oral film lingual (medial) to relevant tooth Dental radiography: intra-oral placement of dental film .

Step 3 -

  • Push film ventrally into the mouth so that its edge is level with ventral border of mandible (to ensure whole tooth root will be radiographed).
    Edge of film can be palpated externally.

Step 4 -

  • Bisecting angle: press film as close to teeth as possible without bending it (any bending will distort image).
  • Hold film in place with, eg cotton wool, swab, foam wedge, crumpled paper towel, rubber mouth prop.
  • Bisecting angle - the x-ray beam is directed perpendicular to an imaginary line that bisects the angle between the long axis of the tooth and the film.

Aftercare

Outcomes

Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Smithson A (2006) Oral radiology Part 2: Image interpretationUK Vet 11 (1), 40-44 ResearchGate.
  • Smithson A (2005) Oral radiology Part 1. UK Vet 10 (8), 57.

Other sources of information

  • Veterinary Dentistry for the General Practitioner (2004) Dr Cecilia Gorrel,  Saunders.
  • Mulligan, Aller, Williams (1998) Atlas of canine and feline dental radiography. In: Veterinary Learning Systems. Trenton, NJ, USA (Excellent reference for dental radiography).