Veterinary Dental Radiography


Part 1: Conventionally Readying Veterinary Dental Radiographs for Short-term and Long-term Interpretation Using the Casa Loma Mnemonic

Author: LEE JANE HUFFMAN, DVM, DAVDC (Diplomate of the American Veterinary Dental College), Veterinary Dentist, Owner and Head of the MOVEH Dentistry Department, Mississauga Oakville Veterinary Emergency Hospital and Referral Services

Before learning how to interpret veterinary dental x-rays and even how to take them, knowing how to ready or prepare them for interpretation is necessary. A systematic approach to presenting veterinary dental radiographs reinforces a systematic approach to viewing and interpreting them, just as for conventional body films. Such an approach also serves to remind us what is necessary technique-wise to aid the clinician’s diagnosis whether they are in the same room or a different country.

“Casa Loma” (Spanish for Hill House) is a Gothic Revival style house and gardens turned museum, landmark, and event facility in midtown Toronto, Ontario, Canada. Wikipedia CASA LOMA (house on the hill/ mount) will serve as a mnemonic for helping us to remember how to conventionally prepare veterinary dental radiographs for interpretation and housing/archiving. We’ll use CASA as a verb as in to house or store. L will stand for LABEL/LOG, O for ORIENT, M for MOUNT, and A for ANNOTATE.

CASA reminds us that we will be ultimately storing our x-rays as part of the patient’s medical record. Hardcopy printouts or conventional film duplicates sent with the client and/or to a referring veterinarian backup and maintain the patient’s medical record for future treatments or follow-up and documentation of current or past clinician decisions (treatment(s), “watch”, no treatment(s)) in addition to the originals kept within a computer data base or hard copies within the patient file.

The first step in readying veterinary dental radiographs for interpretation is to properly LABEL them to attribute them to the correct patient and owner. Mislabelling and so misattribution can lead to misdiagnosis, missed treatments or mistreatments. Always label veterinary dental x-rays with the patient name, signalment, owner name, as well as your practice and ID number (patient practice ID or dental x-ray sequence ID). Labeling with signalment allows comparison of normals and abnormals according to age, breed, and sex and aids accurate identification of the patient. Labeling with names in addition to numbers allows for alternate means of retrieval of x-rays when needed in the future if names are misspelled or numbers improperly transcribed. Print labels to apply to your veterinary dental radiography LOG and enter the information into your digital x-ray system at or before patient premedication and/or apply them to the envelope +/- film mount(s) for conventional film storage. Assigning a sequential number prior to premedication in this way saves time and only risks easily remedied number assignment without use (if the procedure is aborted) or change (with patient order).

The next step in readying veterinary dental radiographs for interpretation is to conventionally ORIENT them. Conventional orientation of dental x-rays should be performed during initial screening of the x-ray for accuracy (a diagnostic x-ray has been obtained), between x-ray exposures, or after obtaining all of the desired x-rays. It is helpful to think about how the x-rays will be ultimately mounted during the ORIENT step. Conventional orientation of dental x-rays is such that when you are looking at conventionally oriented images it is as if you are on the outside, vestibular (previously termed facial) side of the patient, looking in (vs standing on the patient’s tongue which is impossible and so should not be attempted!). Conventional orientation is easy since it is what you already do when looking at the patient in the exam room lips-to-lips, moving to your right to view their left, or to your left to view their right. When lips-to-lips your right is the patient’s left (opposite) BUT when viewing the patient’s left side the left side of their lips is also the left side of your lips (same) and when you are viewing the patient’s right side the right side of their lips is to the right side of your lips. Also, when you are viewing your patient in the exam room or from the outside, up is up for both of you and down is down for both.

Conventional orientation dictates that up is up and down is down ie the upper jaw is up such that maxillary teeth are positioned at the top of the x-ray with their root apices facing upwards, and the lower jaw is down such that the mandibular teeth are positioned at the bottom of the x-ray with their root apices facing downwards. Anatomy helps to delineate maxillary from mandibular films. The maxilla has sinuses, nasal passages and palatine fissures and is the only jaw to contain three rooted teeth (108/208, dog 109/209, 110/210) barring aberrance.

The radiopacity of the dorsal and ventral cortices of the body of the mandible and ability to capture these both on smaller film sizes, the relative radiolucency of the mandibular canal, the absence of three-rooted teeth (unless aberrant), and the large mandibular 1st molar (309/409) which in cats is definitively whale-tail shaped coronally, with a more diminuitive distal root, allows one to easily recognize mandibular films. Further details of normal radiographic anatomy and the recognition of maxilla vs mandible will be discussed in Part 2: Interpreting Veterinary Dental Radiographs.

Conventional orientation of dental radiographs also dictates that the mesial aspect (towards midline) is always at the edge of the film such that the lips are at or just off the edge of the film. The lips or mesial aspect of the radiograph can be determined by anatomic features included on the film (teeth themselves, foramina....).

Conventional orientation is accomplished within digital dental x-ray programs with rotation of the image or horizontal or vertical flipping if necessary. Conventional orientation is accomplished with conventional x-rays by handling the film on the edge with clean dry fingers and rotating or flipping while ensuring that the film blip always faces out up towards you and centrally (because it is always at the lips end of the patient unless incorrectly positioned in the patient’s mouth during exposure – see Part 3

Veterinary Dental Radiograph Techniques). Some digital x-ray programs have a radiopaque marker akin to the film blip to aid orientation and sidedness if certain anatomical landmarks are not captured.

A radiopaque marker such as a needle or piece of gutta percha (rubberized material used to obturate root canals) placed within the patient’s mouth during exposure aids the identification of the sides of the radiograph (especially if the digital radiography system requires that the films be flipped post-exposure for conventional mounting); pathology localization such as retained roots or instrument pieces in need of retrieval; or the measurement of pathology and/or margins if a notched periodontal probe is used.

MOUNTING may occur during digital imaging by following a systematic order in taking x-rays or by selecting a position on the mounting view screen. Alternatively, some systems facilitate this by having one select a tooth immediately prior to exposure. The first rule of mounting (besides maintaining a diagnostic x-ray while mounting) is that the lips/mesial aspect (film blip/marker) is always positioned towards the centre of the screen/ page or mount at or beyond the edge of the radiograph.

ANNOTATION or more detailed explanation or comments may be added to the x-ray mount by hand, or within the digital x-ray report to further delineate what has been taken and/or why. Annotation of what has been taken might include labeling of specific teeth as text below or on the xray. Annotation of why the radiograph was taken might include “to better delineate the mesiopalatal root of tooth 108 re: questionable resorption, endodontic stenosis....”. If you are taking the x-rays but are not the one who will ultimately interpret and diagnose, annotation assists the person who will.

The use of digital dental x-ray enables minimization of steps eg one-time patient label entry and automatic application to all exposed x-rays, original image retrieval, rapid signalment comparison... such that there is overlap between readying/ preparing and technique. Digital dental x-ray systems allow one to mount x-rays chronologically or anatomically and alternate between single image and mounted screens during or between exposures. Moving x-rays within the mounting screen or later in reports is also possible. Some systems conventionally mount the x-rays left and right (eg scil DDX-R, scil ScanX Duo CR, Schick CDR Dicom) and by tooth during exposure-processing while others require that the images be flipped horizontally (eg iM3 CR7) between exposures.

In summary, the CASA LOMA mnemonic ensures the conventional preparation of veterinary dental radiographs for interpretation and housing/archiving. Knowing how to prepare dental radiographs for interpretation allows the person taking these x-rays to systematically prepare what they are looking for in the final product to be presented for viewing and interpretation.

To review: Casa (to house) is the end goal of archiving and recording Label patient logs and enter patient signalment and the assigned patient number into the digital x-ray system or apply to film mounts (plastic/cardboard) or storage envelopes. Orient images so that they are presented as if you are outside the mouth looking in as during a physical examination. Mount with Mesial or the lips towards the centre of the page, the upper jaw up with roots pointing up, and the mandible below with roots pointing down. Annotate ie label the x-rays in detail as to what and why they were taken, and/or the method and sensor used to take them with.

Easy Rules of Conventional Orientation and Mounting:

Film Blip (raised dot) raised out/up towards you (helps orient rostral vs caudal and so L vs R)

Film Blip/Lips positioned centrally (mesially)

Maxilla is up with maxillary tooth root apices pointing up towards the top of the film; maxilla identifiers:
• 3-rooted teeth (unless aberrant) only occur in upper jaw
• Nasal passages, sinuses
• Palatine fissures

Ventrum of the Mandibular body is down with mandibular tooth root apices pointing downwards; mandible identifiers:
• Body of Mandible (radiolucent mandibular canal),
• Mandibular (horizontal) Ramus is very radiopaque

From the front (lips-to-lips incisors and cuspids) patient’s right is your left, patient’s left is your right.
L = R
R = L

From side, film blip/lips pointing to your left is left and right is right
L = L
R = R