Dental Radiography of the Maxillary 4th Premolar, Simplified

Dental radiography is rapidly gaining popularity as veterinarians recognize the diagnostic potential, value to clients, and relative ease of use. As with any piece of new equipment, however, there are some trepidation and hurdles to overcome on the way to achieving proper techniques. One of the more challenging concepts for veterinary personnel starting to use dental radiography is the positioning for intraoral radio­graphy of the maxillary carnassial tooth (the maxillary 4th premolar).

• Most veterinarians are taught radiography using large cassettes to radiograph the abdomen, chest, and extremities using the parallel technique. This positioning implies that the object to be radiographed is parallel to the film, and the beam of x-radiation is aimed perpendicular to the film and object. This approach works in most cases, but the space available for intraoral radiography is limited. With intraoral radiography, the film (or digital sensor) is placed in the mouth and the x-radiation beam is passed across the tooth/bone to the film-basically casting a shadow of the tooth and bone onto the film. This technique works well in the mandibular premolar and molar regions, but does not work for maxillary dentition because the film cannot be placed exactly parallel to the teeth to be radiographed due to the presence of the hard palate and mucosa.

A common geometric principle incorporated to allow radiography of the maxillary teeth is the bisecting angle technique. Sometimes just the phrase "bisecting angle technique" creates unsettling flashbacks to high school geometry in both veterinarians and technicians. Fortunately, there is an easier way to understand the basic principle of this technique. This series of photographs is intended to provide a visual illustration of positioning the maxillary 4th premolar-one of the most likely candidates for problems when dental radiographs are being taken.

Indications for Dental Radiographs

• Periodontal disease: Use to show bone loss around tooth roots
• Broken teeth: Look for signs of root tip infection
• Discolored teeth: Look at pulp chamber and for signs of root tip infection
• Suborbital swellings: Look for root tip infection or cystic teeth

• Resorptive lesions: Use to determine if type I or type II resorption has occurred

• Oral tumors: Look for bone involvement

• Pre- and postextraction: Check to be sure all roots are gone

• Missing teeth: Check to be sure there are no missing teeth below the gingiva

• Oral surgery: Use to diagnose oral fractures or to determine margins for oral tumor surgery

• Full-mouth series: Make sure all teeth, roots, and bone appear healthy-offer this as an elective service for your clients if you are not already doing so

Step by Step How to Take Radiographs of the Maxillary 4th Premolar

Step 3. Positioning of the x-ray machine tubehead perpendicular to the plane of the dental x-ray film (A, B) would create a foreshortened image of the tooth or roots (B). This image would probably not be diagnostic, but the apex of the palatal root can be seen.

Procedure Pearl: Consider dental radiography technique as being the same as casting a shadow of the tooth and roots onto a film, using the tubehead as your flashlight.

Step 4. Proper positioning of the x-ray machine tubehead (A). Again, it is not directed perpendicular to the long axis of the tooth or perpendicular to the plane of the film, but is instead placed halfway between these two reference alignments (B). This creates a good diagnostic image of the maxillary 4th premolar crown, roots, alveolar bone, and apexes of the roots (C). One limitation is the superimposition of the mesial roots on each other. The clinical significance of this superimposition is arguable.

Procedure Pearl: When positioning for the bisecting angle technique, remember not to position the tubehead either directly perpendicular to the long axis of the tooth to be radiographed or directly perpendicular to the film, but halfway in between.

Procedure Pearl: A rostral or caudal shift of the tubehead helps to separate the two mesial roots, if such separation is needed.

DENTAL RADIOGRAPHY OF THE MAXILLARY 4TH PREMOLAR, SIMPLIFIED • R. Michael Peak

Suggested Reading

An Atlas of Veterinary Dental Radiology. DeForge DH, Colmery BH-Ames, IA: Iowa State University Press, 2000.
Atlas of Canine and Feline Dental Radiography. Mulligan TW, Aller MS, Williams CA-Trenton, NJ: Veterinary Learning Systems, 1998.
The Veterinarian's Companion for Common Dental Procedures. Lobprise HB, Wiggs RB-Lakewood, CO: AAHA Press, 2000.
Veterinary Dentistry Principles and Practice. Wiggs RB, Lobprise HB-Philadelphia:
Lippincott-Raven, 1997.