Chapter 22 Vet Diagnostic Imaging: Dental Radiography
The dental formula for the permanent teeth in the cat is:
(3131/3121) = 30
A dog has the following 3 rooted teeth:
108, 109, 110, 208, 209, 210
Feline dental formula
2(I (3/3) C (1/1) P (3/2) M (1/1)) = 30 total
Canine dental formula
2(I (3/3) C (1/1) P (4/4) M (2/3)) = 42 total
CR PSP plates are available in the following size, which is not available in film:
3
When x-raying a maxillary canine tooth, what is the angle in which the tube head is moved up vertically to prevent superimposition of the canine tooth over the premolars distal to it?
30
The bisecting angle technique in a dog is used on all of the following areas except:
409
You are using the extraoral technique for a mandible of the Lhasa Apso. To isolate the maxillary premolars, you will need to angle the mandible:
45 degrees
Maxillary incisors
> Bisecting angle technique > Sternal recumbency with the neck extended and the head level with the table > Place the film in the mouth so that the upper canines are resting on it and a small amount of the film is in front of the incisors > Center the tube head directly in front of the patient's head, and angle it about 80 degrees to the film in the rostrocaudal plane, which is the approximate bisecting angle for the distally curved roots
Maxillary canines
> Bisecting angle technique - focus on the root rather than the tooth > Each maxillary canine must be imaged on a separate film b/c the root lies over the maxillary first and second premolars in dogs and over the maxillary second premolar in cats > If the canines are imaged by using one rostral view only, they will overlap with the premolars on the image > Remember the apex of the canine root is near the mesial root of the second premolar - so to image the entire root, place the film distal to the second premolar
Film placement
> Can be challenging b/c of the anatomy of the tooth roots and the inability to see the roots > Correct film placement minimizes retakes! > The roots are usually much longer than the crowns in veterinary patients - especially with canine teeth, which has roots that are at least 2x as long as the visible crown > Always have the film too far in the mouth to ensure you capture the complete root structure > Place the film as close as possible to the tooth or teeth of interest (generally touching the tooth and gingiva) to minimize distortion
Dental x-ray unit
> Consists of a generator, extension arm (B), scissor arm (A), control panel (C) and x-ray tube, which has the collimator cone > Most units are preset with a kV of 70 or 80 and an mA of either 7 or 8, so the only variable is seconds > The x-ray tube is a stationary anode tube that is encased in the housing at the end of the scissor arm and will rotate around that stem
Why are dental radiographs the most important diagnostic tools available to a veterinary dentist?
> Detailed examination of the internal anatomy of the teeth - tooth roots and bone that surrounds the roots > Help diagnose many conditions such as fractured or broken roots, cysts, tooth resorption (especially in cats), early tumors, unerupted teeth, teeth that may look healthy but be compromised on the inside, and periodontal disease can be staged and addressed by examining the dental rads for bone loss around tooth roots
Setting the exposure
> Determine the amount of radiation that will be used to expose the image > Exposure settings in dental radiography differ from those in standard radiography in that the kVp and mA are held constant - only the time is adjusted > Technique chart is similar to the one used for a standard radiography machine, except for only one variable - exposure time - needs to be adjusted
Exposing the radiograph
> It is strongly recommended that everyone leave the room before exposing the radiograph to reduce x-ray exposure - not in front or behind it - at a 90-130-degree angle to the primary beam - wear PPE! > Regardless of the type of unit used, regular inspections and radiographic monitoring should be performed > Most dental radiography units have a hand-held switch; when exposing, if you release finger pressure on the switch during exposure, the production of x-rays will stop > On a manually adjusted dental radiography unit, this will result in an underexposed/light radiograph and on a computer-controlled unit, an error message will pop up and you'll have to restart the process > Make sure to press the button until the machine stops beeping - when using a digital system, this will be a short time
Dental x-ray imaging
> Non-screen dental film > Computed radiography (CR) - photostimulable plates > Direct digital receptors (DDR or DR)
Maxillary molars and premolars
> Precise bisecting angle technique must be used to achieve a high-quality radiograph of these teeth as these are the most challenging of the veterinary dental radiographs > Sternal recumbency wit the neck extended > The cusp tips of the teeth to be imaged should be resting on the film, which is relatively flat against the palate > Center the tube head over the tooth to be imaged, and place it at about a 45-degree angle to the film > Proper technique will produce an excellent image of the premolars and an acceptable image of the molars, but this technique does cause superimposition of the mesial and palatal roots of the fourth premolar > In cats, this will give an excellent view of the second premolar and part of the third premolar, but the zygomatic arch interferes with the maxillary fourth premolar, third premolar, and first molar
Patient positioning for dental radiography
> Sand bags, V-troughs or holders, and other implements will aid in stability and patient placement > Make sure the area of interest is appropriately positioned in the radiographic beam > Tooth to be radiographed is positioned on the up side
How does computed radiography work?
> The active side of the PSP plate is light blue with the rear side of the plate containing the writing; it is easily viewed through the window of the barrier envelope > Once exposed, the PSP plate is removed from the barrier envelope and put through the scanner, which converts it into an image viewed on the computer > As the plate is scanned, the plate is erased and is ready to use again once the scanning is complete
How does Direct Digital imaging (DR) work?
> The sensor is attached directly to the computer's USB port > Once the sensor is exposed, the software program immediately converts the info into an image > The sensor should always be protected from fluids by using a barrier sleeve - a thin layer of Vet Rap can be placed once covered with a plastic sleeve - which enables the sensor to stay in place without slipping
Why at dental radiographs used?
> They provide your veterinarian with a tremendous amount of information > Increases the quality of dental care in your patients > Used as a tool for evaluating patients - routine dental care, dental problems > Full-mouth dental radiographs are an essential step in dental cleaning > Necessary for accurate oral evaluation and diagnosis > AAHA Dental Care Guidelines for Dogs & Cats state that preoperative and postoperative dental rads are mandated
Mandibular premolars and molars
> Typically use the parallel technique > exception may be the first and second premolars in dogs and the third premolars in cats b/c in certain breeds the interference of the mandibular symphysis makes exposing the apices of these teeth impossible with the parallel technique > Lateral recumbency with the arcade to be imaged up > Place the film parallel to the teeth on the lingual surface of the teeth or mandible, and position the tube head perpendicular to both the teeth and the film
Mandibular incisors and canines
> use the angle of the root for your bisecting angle calculation - keep in mind the roots curve backward to nearly a 45-degree angle in many cases > Place the distal edge of the film behind the second premolar > Dorsal recumbency with the neck fully extended > Place the film parallel to the plane of the mandible as possible to the film covers the entire extended area > Center tube head on the patient's head - perpendicular to the film > Then rotate the tube head in the same vertical plane to an angle about 75 degrees to the film - this should be an accurate bisecting angle for the roots
Your clinic has ordered a dental radiography unit, and the vet wishes you to investigate what extra electricity is required. You report that the dental unit requires:
A 110-volt line with no special wiring
Collimator cone
A projection from the tube housing; also called positioning indicator device (PID); cones are not interchangeable and are available in variable lengths and diameters; most presets on the unit are based on a distance of 2 inches or 5 cm from the tooth; there is no collimator light so the operator must view the cone from different perspectives to best estimate the center of the beam
Supragingival
Above the gums
Foreshortening
Artifact that results when the x-ray beam is aimed too directly at the film instead of at the bisecting angle; the tooth will appear to have the crown overlapping the root
Elongation
Artifact that results when the x-ray beam is aimed too directly at the long axis of the tooth instead of at the bisecting angle; the image will appear "stretched out" and the entire tooth may not have been captured on the film
If one used conventional unit to image a mandible, the kV is likely 45 to 50, yet when using the dental unit for mandibular teeth, the settings are generally preset at 70 or 80. More exposure is required:
Because there are no intensifying screens in dental film
Subgingival
Below the gums
The area on the periphery of the tooth where the crown and root meet is the:
Cementoenamel junction
The tips of the teeth should be situated on this size 4 film on the:
Convex side of the film
Do we have CR or DR at OTC?
DR
Computed Radiography (CR)
Digital radiographic imaging using a cassette containing an imaging plate; photostimulable phosphor (PSP) plates are used as the image receptor - they are thin and flexible and available in sizes 0-4, light sensitive, and are sealed in a barrier envelope for patient use
Which teeth are used for the parallel technique in dental rads?
Distal to and including the mandibular third premolars
Mandibular canine and incisor teeth - positioning
Dorsal recumbency
When should dental radiographs be performed?
Every 6 months
Extension arm
Extends from the generator, swings 180 degrees, and is available in variable lengths; at the end of this is the scissor arm, which also allows the dental x-ray machine to allow ease of positioning
Which part of your new dental x-ray machine can swing 180 degrees?
Extension arm
You are getting a patient file for the vet to review about a month after dental films were processed. You notice that the films, which were perfectly diagnostic at the time, now appear foggy and have a coffee color appearance with poor density and contrast. You realize that you:
Fixed the film for 15 seconds and dabbed the film in the water jar
As you are setting up for tooth 104 you notice that the central ray is angled more on the film instead of the bisecting angle. you alter the angle because otherwise you will have:
Foreshortening
Periodontal ligament
Forms the attachment of the cementum to the alveolar bone; it appears as a thin gray line surrounding the roots
Direct digital dental radiography in dentistry:
Generally utilizes a smaller sensor
The beam for this modified x-ray technique of the maxillary premolar should be aimed:
In a near-parallel technique with a 20- to 25-degree tilt to bypass the opposite arcade
Parallel technique
Involves placing the dental film directly behind and parallel to the tooth and then directing the x-ray beam perpendicular to the film; the anatomy of dog and cat mouths allow this technique to be used in only one area - distal to and including the mandibular third premolars; produces the most accurate image
Size 3
Known as the "bite wing" and is rarely used in veterinary dentistry
Modified Triadan System
Labels each tooth with a code of 3 numbers, starting at the midpoint of the arch in each quadrant; the first number delegates the quadrant; upper right quadrant is 1, upper left is 2, lower left is 3, and lower right is 4 and deciduous teeth use 5-8 for the quadrants; the second 2 numbers are determined by tooth position - incisors are numbers 01, 02, 03; the canine tooth is 04; premolars are 05, 06, 07; molars are 09, 10, 11
Mandibular premolar and molar teeth - positioning
Lateral recumbency with the side to be imaged up
Maxillary teeth - positioning
Lateral recumbency with the side to be imaged up
The vet suspects damage of tooth 104 in a Border Collie. You are best to position the patient in:
Left lateral recumbency
Normal adult mandibular premolars and molars
Look for dark black areas above and below the mandible
Normal adult mandibular incisors
Look for dark black line distal to incisors that separates mandibular rami (mandibular symphysis)
Normal adult maxillary premolars and molars
Look for the fine white line representing the maxillary recess apical to the roots
Normal adult maxillary incisors
Look for white space distal to incisors with 2 dark oval spaces, which are the palatine fissures
If the x-ray cone is directed form the distal aspect of tooth 108, toe root that will appear in the middle on the radiograph is:
Mesial-palatal root
Size 0-1
Occasionally used for small and pediatric patients
Enamel
Outer covering of the crown of the tooth
Crown
Part of the tooth above the gum
Logging dental radiographs
Patient, client, date, area imaged, mA, kV, mAs
You should utilize the bisecting angle with the long axis of the maxillary canine tooth. this is best visualized from the:
Side of the patient with a 30-degree tilt of the x-ray cone
Canine teeth (C)
Single-rooted teeth used for grasping and holding prey; the structure of feline canine teeth supports that cats are true carnivores; there are shallow longitudinal grooves on the buccal surfaces of these teeth - these grooves "wick" away blood from held prey
What are the most common sizes of film used in veterinary medicine?
Size 4 and size 2
Apical delta
Small openings at the tip of the root that allow the blood supply and nerves to enter the tooth
Premolar teeth (P)
Teeth designed for cutting and shearing meat; have prominent sharp cusps and have 1-3 roots
Molar teeth (M)
Teeth that generally have flattened occlusal surfaces with the exception of the mandibular first molar tooth in dogs, which does have a cutting edge on the mesial cusp; the first mandibular tooth in cats has no flattened occlusal table - instead it has 2 cutting edges; molar teeth have 2 or 3 roots, but some roots appear to be fused together to give the appearance of being single roots (feline maxillary first molar); molar teeth in dogs are used for grinding food
Incisors (I)
Teeth used for grooming, grasping, and cutting; single-rooted
Dentin
The bulk of the tooth; appears lighter than the pulp chamber on a radiograph
Cementoenamel Junction (CEJ)
The junction line between the enamel layer and the cementum layer of the tooth
Cementum
The outer covering of the root
Root canal
The root portion of the pulp chamber; on a radiograph the pulp chamber is the darker inner concent of the tooth extending throughout the crown and the root
Lamina dura
The wall of the alveolar socket that surrounds the tooth; appears as a dense white line adjacent to the periodontal ligament space
Bisecting angle technique
This technique is used on all maxillary teeth, all incisors and canines, and mandibular premolars 1 and 2; formed by the intersection of the plane of the film and the long axis of the tooth; if the central ray is perpendicular to a line that bisects this angle, the resulting image is as accurate as possible; most common one in veterinary dentistry
Apex
Tip of the root
The extraoral x-ray technique for a feline's patient tooth 208 (left maxillary premolar) that is preferred is with the patient lying in lateral recumbency and the DR sensor placed:
Under the left side of the patient because it is in left lateral recumbency
Size 2
Used for individual teeth or for smaller patients
Size 4
Used for large patients, whole quadrants, or exposing full mouth radiograph sets
Angle meter
Useful for setting up some dental x-ray views, depending on what technique is used; especially helpful for imaging canine teeth, as a "tilt" in the cone is required to prevent superimposition on the premolars distal to it
Is there a dentistry specialty for veterinary technicians?
Yes! The Academy of Veterinary Dental Technicians (ADVT)
How do you accurately visualize the long axis of the tooth?
You should stand at the patient's side (premolar teeth) or the patient's front (incisor and canine teeth) to find the bisecting angle
A modified x-ray technique is used to x-ray the maxillary premolars in a cat because of interference of which structure?
Zygomatic arch