Simplifying Dental Radiography: Getting You What You Need
During my career as a veterinary technician, nothing has been more frustrating for me than learning how to take diagnostic dental radiographs. It did not come naturally to me. No matter how many times I heard the description of the sun and shadows, it just did not sink in. Every radiograph I took only showed the crown, and often it was elongated, slanted, and just generally awful. This lead to long COHATs, frustrated Veterinarians, and one very frustrated me.
About 10 years into my career, I found myself primarily teaching dentistry. I was now in a position where I had to figure this out. The system I am going to sum up for you in this article is the system that has worked most consistently for myself and for individuals that I am teaching to produce their first dental radiographs. Hopefully, by applying the following guidelines, you can get what you need exactly as stated in the starting quote.
You can’t always get what you want,
but if you try sometimes, well, you might find you get what you need.”
Keith Richards/Mick Jagger
The Diagnostic Image
Let us start by determining what elements we want to see on the image before we send them to our Veterinarians for evaluation.
Ideally we want to see the entirety of the crown, the apex of the root, and 3-5 mm of surrounding alveolar bone, with the apex of the root being the most essential. This is a realistic goal with proper positioning and a size 2 DR or CR sensor.
There are some teeth where this will not be possible; for example, the canines on large breed dogs. For most situations in general veterinary practice, focusing on getting the apex of the root of those teeth is adequate. If you are in a speciality situation where the entirety of the crown of those teeth is needed along with the apex of root, then you will need to divide the images into a series.
When you are assessing these images, make sure you see the apex of the root, the crown (if possible), and 3-5 mm of surrounding alveolar bone. If you do not see these things, a retake is required.
We know that patient positioning is critical when performing conventional radiography. The same is true of dental radiography.
The best results are achieved when the animals are placed in sternal recumbency for the maxillary series, and in ventral recumbency for the mandibular series.
In both those positions, ensure to place some support under the neck so the maxilla and the mandible are as parallel to the table as possible. I prefer to use a pool noodle that has been cut in small pieces and then cut again in half for this purpose. I find the pool noodle does not hold on to water quite the same way as a towel roll. Because it doesn’t get as soaked, it does not tend to cool the patients quite as quickly as a really wet towel will. They are also fairly easy to clean or replace.
These positions will be best when starting out with dental radiography. I am often asked the question about the time lost from having to place the patients into sternal or ventral. The time loss is minimal, if you structure your dentistry in a such a way that these positions become advantageous. When I am inducing anesthesia in a dental patient, they are in sternal, they are intubated in sternal. Once they are intubated I ensure they are stable under general anesthesia, then I immediately take the maxillary series of images. I then disconnect them from the anesthesia, place them onto their back, and take the mandibular series. I then gently lay them in lateral and start the cleaning. The radiographs can be sent to the Veterinarian for assessment, and they can decide on their treatment plan while I am cleaning. It is a very efficient use of time.
There are many technicians that prefer to do dental radiographs with the patient in lateral positioning. That is 100% acceptable, provided you are comfortable seeing the angles required. When people start out, sternal and ventral body positioning are most certainly easiest, and produce the most consistent diagnostic results.
Bisecting Angle & Parallel Techniques
There are two techniques we use to produce dental radiographs; Bisecting angle, and parallel technique.
Parallel technique is, by far, the easiest and what most technicians feel most comfortable with. It uses the same theory as conventional radiography; line up the sensor, the tooth, and the beam. The beam will be at a 90-degree angle and the image is produced. Where we can use parallel technique is very limited however. In dogs we can only use this technique on the caudal, mandibular premolars and molars. In cats, parallel technique should not be used at all. Their mouths are simply too small.
Bisecting angle will produce superior imaging in cats, always. Bisecting angle is the technique that tends to strike fear in the hearts of most technicians and it can certainly be challenging. We need bisecting angle because the mouth is a very limited space. We simply cannot use anything else. 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 field 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.
Proper sensor placement is a very important element of achieving a diagnostic dental image. I often explain it this way: If the pole out in the field was on a slope the sun at high noon would not produce a predictably minimal shadow. The angles are different. We can only reliably predict how the sun (X-ray generator) will produce an image on flat ground (surface).
When placing the sensor, place the teeth to be radiographed on the very buccal or labial edge of the sensor. This leaves you with as much ‘ground’ as possible to cast a shadow on. “Think of the tooth/tooth root as your pole, the sensor as the ground where the shadow is being cast…” Ensure the sensor is as fl at as possible. You can use a small gauze role to assist with this, especially on teeth like the maxillary 4th premolar in dogs and maxillary molars in dogs.
In cats, maintaining a flat sensor is very easy to achieve. You simply place the sensor as far back in the mouth as possible and it tends to stay there with no assistance.
The Variables We Know We Can Control
In dental radiography, there are variables we know we can control. I like variables I know I can control. It lessens my anxiety and makes my results more consistent.
The two elements we have talked about that can be easily controlled by us are patient positioning and sensor placement/positioning.
I would encourage you to take control of those elements. If we know those are correct, we have one element to troubleshoot, and that is the beam. It does seem much simpler to worry about only one thing in an already complex process!
The x-ray generator can be the most unpredictable element of dental radiography. Sometimes we set it up and everything looks perfect and we end up with something we did not expect.
First and foremost, as started above, if you are having difficulty, go back and look at patient positioning and sensor placement.
When those pieces are confirmed correct, then step back before taking the image and ask yourself if the positioning makes sense as it relates to the analogy of how the sun casts a shadow.
An x-ray generator can also help us more than we think it can. If we look at the rotator cuff on the generator, there are typically numbers. These numbers are the angles around a circle.
One of the ways I help people just starting out with dental radiography is to provide them with expected numbers to see on the x-ray generator when the image is properly setup.
What I would encourage you to do as you take your radiographs is when you have an ideal image, quickly note exactly what number the x-ray generator angle was set at. After you have numbers for each image of a full mouth series, build a technique chart of sorts.
This numerical information will really help take some anxiety out of setting up bisecting angle and will result in more consistent results.
One of the things that helped me the most with dental imaging was going back to the basics. Review patient positioning and sensor placement. When things go wrong so frequently, something has happened in either or both of those areas.
We need to ask ourselves a few questions as it relates to dental radiography. Is dental radiography necessary? Is dental radiography challenging? Is dental radiography gold standard medicine for all COHATs? The answer to all of these questions is resounding yes!
As technicians we must take the time to practice dental radiography skills. If you have skulls in your clinic take 30 minutes on a quieter day to practice a full mouth series. Having these skills will significantly benefit you, your Veterinarians, and your patients.
Trust me when I say, if I can do this, so can you!