The Good, The Bad, and The Ugly: Correcting Issues in Dental Radiography
In an earlier issue, we discussed the fundamentals of dental imaging. Practicing these rules and skills are critical to feeling confident with dental radiographs.
I would like to say when positioning of the patient and the sensor are perfect, all the radiographs will also be perfect; sadly that is just not the case. Troubleshooting is a critical part of dental radiography; both understanding when troubleshooting is required and how to do it. A good knowledge of the fundamentals and an ability to quickly troubleshoot the challenging images will make full mouth dental radiographs a realistic goal for all dental patients!
Let’s take some time to quickly review the basics and then we will spend some time talking about how to identify and correct radiographic issues.
There are two techniques we use in dental imaging: Parallel technique and bisecting angle.
Parallel technique is essentially conventional radiography. We line up the plate, the tooth, and the beam and take the image. Troubleshooting is straight forward with this technique and something most people do not struggle with at all. As a reminder, where we can use this technique is limited. We can only use it on the caudal mandibular premolars and molars in dogs.
Bisecting angle is by far the more challenging technique and where the most troubleshooting is required. Bisecting angle is a critical technique and is used entirely in cats and in dogs across the entire maxilla and the rostral portion of the mandible. As a review, bisecting angle theory can be summed up with the analogy of how the sun casts a shadow. If you had a pole standing alone in a fi eld at high noon, the pole would cast a very small shadow, as the sun drops lower in the sky, the pole will cast a longer and longer shadow.
Think of the tooth/tooth root as your pole, the sensor as the ground where the shadow is being cast, and the x-ray generator as the sun.
For us to understand how to troubleshoot, we must make sure we remember the basics of positioning.
For ideal images of the maxillary series of teeth, the patient should be in sternal with the patient’s maxilla as parallel to the table as possible. The sensor should be kept flat in the mouth with the teeth to be radiographed on the very buccal, or rostral edge of the sensor.
For ideal images of the mandibular series of teeth, the patient should be in dorsal with the patient’s mandible as parallel to the table as possible. The sensor should be kept flat in the mouth with the teeth to be radiographed on the very buccal, or rostral edge of the sensor. This rule does not apply to the caudal mandibular premolars and molars in dogs. Set these images up with parallel technique rules.
Before we delve into troubleshooting, let’s quickly review the standards that need to be met for a diagnostic image. These are important criteria for both veterinarians and technicians to be able to evaluate. Very often technicians are doing radiographs without veterinarians right there. We need to be able to determine if an image is diagnostic, and be able to troubleshoot them as needed. We need to be able to visualize the following:
• The apex of the root
• 2 – 3 mm of surrounding alveolar bone
• The crown, if possible
These images should be reflective of what we see in the mouth (roots not too long or too short).
We are going to spend some time going through some common issues seen, and how to work toward correcting them. We will also cover some challenging views where typical bisecting angle rules may not apply.
Bisecting angle rarely goes exactly as expected. The most common issues that require troubleshooting are the roots looking too long or too short.
These issues occur from the beam (the sun) either being too high or too low ‘in the sky’. When the beam is too high this results in root foreshortening, and when the beam is too low this results in root elongation. To be able to visualize where the beam is in relation to the sensor to result in these images I like to think of it this way; For root elongation the beam is too parallel to the sensor and root foreshortenin the beam is too perpendicular to the sensor.
Minor root foreshortening or elongation is not something I would stress over much, but if either of these are significant, you must take the time to correct them. When either of these issues are major, it results in challenges for veterinarians evaluating the images. The periodontal ligament space is harder to evaluate, and structures are no longer representative of what is in the mouth.
When attempting correction of these issues, it is imperative that you re-evaluate positioning basics first. Ensure that the patient’s mouth is parallel to the table, ensure the sensor is as fl at as possible, and that the teeth to be radiographed are on the very buccal, or rostral edge of the sensor.
If all these criteria are met, correction of root foreshortening should simply be a matter of dropping the beam a bit lower (lessen the angle), and correction of root elongation should simply be a matter of bringing the beam a bit higher up (increase the angle).
When we are doing dental radiography, we must remember that the tooth we can see (the crown) is only one third of what is there. A common difficulty seen (especially with larger teeth in dogs) is missing the very apex of the root. This results in a non-diagnostic image.
When doing all dental radiography, ensure you are aiming at the root and not at the crown. If we aim the beam at the crown, we will miss the apex of the root every time.
Cone cut is another commonly seen issue that is easily corrected. This is simply a sensor and beam issue. If you cut the tooth off at the edge of the beam, simply move the beam toward the area you cut off. This takes knowledge of anatomy and being able to interpret the image properly to know which way to move the beam. Similarly, but related to the sensor, if you cut the tooth off at edge off at the edge of sensor simply reposition the sensor to ensure it is in relation to the tooth you want the image of.
A diagnostic view of the maxillary canine in dogs is notoriously challenging. I struggled with it for a long time until I started following some simple rules. With the dog in sternal, place the sensor on the hard palate immediately behind the maxillary canine.
Bring the beam high up (probably 60 – 70 degrees) over where you can feel the canine root. This does not look like typical bisecting angle technique, but it will ensure that you capture that apex of that canine root every time!
The maxillary 4th premolar, otherwise known as the carnassial, in dogs is another tough image to achieve. It is a very large, three rooted – tooth.
Typical bisecting rules do apply here. The tooth should be on the most buccal edge of the sensor and the beam should be aimed at the apex of the root at approximately a 50 – degree angle. This should result in a decent image of this tooth. The area of issue becomes the rostral and palatal roots. After obtaining this image you will frequently notice that those two roots are superimposed. This is indeed an issue for diagnostics. Veterinarians must be able to visualize all three roots. If this image gives you separation of the rostral and palatal roots, great! There is no need to oblique in that case.
There are two different techniques that can be used to separate out those roots. Both are oblique techniques. One additional comment, before we talk about the techniques specifically; before doing an oblique view, ensure you can achieve a basic image of the carnassial (as above) first and then oblique from there.
The first oblique technique is the distolateral oblique projection. This is likely the more common of the two. From the proper positioning above the x-ray generator is shifted back so the tube is angled toward the mesial aspect of the tooth (a rostral direction).
The other technique is the mesiolateral oblique projection. This technique is less common, but could still be necessary in dogs where the distolateral oblique technique just will not separate those two roots. The set – up of this projection is very similar to the distolateral oblique projection, only the tube is angled mesial to distal (a caudal direction).
Either of these techniques will separate out those rostral and palatal roots. Between the first image we described of the carnassial and the oblique image, you will have excellent images for veterinarians to truly assess that tooth.
Dental radiography is challenging and necessary. It is a skill that takes practice to do well. Practicing troubleshooting is part of that. In my experience, it is a rare patient that I don’t have to troubleshoot at least an image or two.
The issues above are some of the more common troubleshooting I do on a day to day basis.
Hopefully, by following these simple rules, you will be able to manage some of these challenging areas quickly and easily; making full mouth radiographs for all our dental patients a realistic goal!