How to get picture perfect dental radiographs in less time

You know the importance of full mouth dental radiographs for your patients. However, the time it takes to get a diagnostic full mouth study is making you second guess this step.

If you want to ensure all patients get full mouth dental radiographs in a reasonable timeframe, and the bisecting angle technique makes you anxious, this article is for you. The subtle changes to the bisecting angle technique that will feel like “cheater codes” as well as this author’s approach to “bad radiographs” will be addressed.

These 2 things will help you and your team get consistently better radiographs faster. However, before we get to the “cheater codes” and “bad radiographs” we will start with a general overview of the 2 main intraoral dental radiology techniques: Intraoral Parallel Technique (IPT) and Bisecting Angle Technique (BAT).

The IPT is the same technique used to acquire diagnostic images for the rest of the body. The plate or sensor—sensor will be used for both throughout the article—used to capture the image is positioned parallel to the target anatomy. The generator, also called the tube head, is positioned perpendicular to both the sensor and the patient.^1-3 (Figure 1a and Figure 1b)

All images courtesy of Amy Thomson, DVM, DAVDC

Figure 1a: A phosphor plate placed parallel to the right caudal teeth of a canine skull with the tube head postitioned perpendicular to the plate.

Figure 1b: A sensor placed parallel to a feline patient’s left mandibular teeth with the tube head positioned perpendicular to the sensor. Both show the Parallel Technique.

The IPT is preferred as it allows for the most accurate image of the target anatomy with minimal distortion.^1-3 If we could use this method for full mouth dental radiographs in our canine and feline patients it would be ideal. However, because of the absence of a vaulted palate and the presence of a mandibular symphysis, the sensor can only be placed parallel to the entire tooth for the mandibular molars and, in some patients, the most caudal mandibular premolars.^1-3

Figure 2: The Cieszynski rule of isometry; where side AB is the angle of the tooth root, BC is the angle of the sensor and BD is the bisecting angle and therefore the angle to which the tube head must be perpendicular to in order to obtain an accurate dental radiograph.

The anatomic differences between humans and veterinary patients means that the majority of our patient’steeth will require the BAT to obtain radiographs. The BAT is most commonly used in patients’mouths where the IPT cannot be used. However, it can be used for all teeth in patients’ mouths.¹ This is because the BAT is based on a geometric theorem: Cieszynski rule of isometry (Figure 2). This theory, coming from the geometric Law of Isometry, is applied to dental radiographs to obtain an accurate image when IPT cannot be used. The law has also been called the theory of equilateral triangles³, stating two triangles are equal if they have 2 equal angles and a shared side.

The reason for all this geometry is to ensure the image captured has the least amount of distortion. The other way to consider this is that BAT is a way to create an IPT when the sensor cannot be placed parallel to the entire tooth. Remember, the IPT has the tubehead directed perpendicular to BOTH the tooth and the sensor, which is not possible for most of our patient’s teeth. By bisecting the angle between the sensor and the tooth, this creates the angle to which the tubehead can be placed perpendicularly,similar to the IPT. While the BAT works for all teeth, the canine teeth given their curvature present a challenge. This article will first focus on the approach for imaging the majority of teeth and then will review the slight changes needed for imaging canine teeth.

Now that both intraoral dental radiography techniques have been reviewed, we can progress to the “cheater codes” to help improve your technique and speed.

Cheater codes

Simplify the angles

The first way to simplify the BAT is to simplify the angles involved. Although many authors^3-5 advise to place the sensor “as parallel as possible” to the tooth, it is this author’s recommendation and others⁴ that the sensor be placed perpendicular to the tooth. This small change in sensor positioning allows for a 90-degree angle between the tooth and sensor which is visually much simpler to bisect: 45 degrees. (Figure 3a and Figure 3b)

Figure 3a: The angles involved when using the “simplified’ bisecting angle to image the right mandibular premolars while the patient is in dorsal recumbency. The “sensor” (in this picture, it is a phosphor plate being used) is placed perpendicular, 90°, to the long axis of these premolars–blue line. The angle of the premolar teeth-dark purple line. This makes the bisecting angle 45°- light green line.

Figure 3b: The red arrow shows the angle of the tube head, perpendicular to the bisecting angle.

To ensure the sensor is perpendicular to the long axis of the maxillary teeth, the sensor should be placed parallel to the hard palate. For the mandibular teeth: using the patient’s tongue to fill the intermandibular space will give your sensor a flat surface to lay against that is perpendicular to the tooth roots. (Figure 4a and Figure 4b)

Figure 4a: The sensor placed parallel to the patient’s palate in order to create a 90° between the right maxillary fourth premolar (108) and the sensor.

Figure 4b: The sensor perpendicular to the left mandibular premolars by by placing it between the patient’s tongue and guaze.

Dorsal recumbency and head rotation

Positioning your patients in dorsal recumbency allows you and your team to complete the entire Comprehensive Oral Health Assessment and Treatment (COHAT) , including full mouth dental radiographs, without moving the patient or disconnecting any monitoring equipment. With the patient in dorsal recumbency, rotate their head 45°. By rotating their head and using the above simplification the bisecting angle will now be a vertical line which results in the tubehead angle being 0° or horizontally positioned. (Figure 5)

Figure 5: A patient in dorsal recumbency has their head titled at a 45° with the sensor place parallel to plate (90° to the maxillary fourth premolar)—blue line. The angle of the teeth is shown by the purple line. This results in the bisecting angle being a vertical line, shown in light green. This requires the tube head, red arrow, to sit horizontally or parallel to the table in order to be perpendicular to the Bisecting angle.

Work smarter

Once you get the correct angle for the first radiograph in the quadrant, do not change the angle of the patient, sensor or the tubehead. The only change to be made is to the move the sensor and tubehead either mesial or distal along that quadrant. This will save time by not rechecking any of the angles.

The curvature of canine teeth

The biggest challenge to the bisecting angle simplification are the canine teeth. This is because while the rest of our patient’s dentition have similar angles between the crowns and roots, the canine teeth do not.

Instead of using the angle of the crown for the canine tooth, the angle of the rostral mandible should be used. This is because the root of the canine tooth follows that curvature. Canine teeth are a bit of an anatomical exception, given their crowns and roots do not have the same angle, you need to use the root angle to get the correct bisecting angle.

What to do with a 'bad' radiograph

Often a nondiagnostic radiograph, missing part of the tooth or inappropriate angle, is called bad. The radiograph is only bad if you do not then use it to help you get the diagnostic radiographs you want.

In this author's experience teaching dental radiography, most participants are quick to be critical of nondiagnostic radiographs. They often change patient, sensor and tubehead positioning or angle all at once.

Instead, it is important to focus on the positives of the nondiagnostic radiograph, to determine what should not be changed. The main 2 things to focus on are whether the angle is correct and whether the teeth of interest are in the radiograph in their entirety.

The dental radiograph in Figure 6 is a nondiagnostic image. It is nondiagnostic because the apex of the roots are not included in the image, however, the angle of the image is correct. Therefore, the only change that should be made is a sensor movement.

Figure 7a: The sensor placement that resulted in the dental radiograph shown in Figure 6.

Figure 7b: The change in sensor placement that is reflected in the dental radiograph shown in Figure 7c.

Figure 7c: The diagnostic radiograph that resulted from the change in sensor placement.

Once the sensor was moved further into the mouth, in a palatal direction, the entire root structure of right maxillary molars (109/110) are included in the image as well as the distal root of the maxillary fourth premolar (108). (Figure 7a, Figure 7b and Figure 7c) The part of the sensor that could be seen outside of the mouth or beyond the teeth in image (a) corresponds to the black space in the dental radiograph in previous figure. It is important to line up the long side of the sensor with the cusp of the tooth/teeth to ensure the entire senor is used. This sensor placement is similar to collimating full body radiographs: ensuring all the target anatomy is within the radiograph.

Other times a “bad” radiograph may be caused by angles and not sensor placement. In those instances, the angle of the tube head may need to be corrected.

Takeaway

Evaluating the 'good' parts of your nondiagnostic dental radiographs will help you get to a diagnostic radiograph faster than focusing on what is 'bad' about it. This, other tips or 'cheater codes' will help decrease the time needed to take full mouth radiographs. As with any skill, this will take time and practice to learn this new way of obtaining and evaluating your dental radiographs.

Amy Thomson, DVM, DAVDC, is a specialist in small animal dentistry and oral surgery. She began her career in small animal general practice and, although challenging at times, she gained a great deal of dentistry education. The more she learned, the more her passion for dentistry grew as well as a desire to become a specialist. While Thomson enjoys all aspects of clinical practice, she also very much enjoys providing continuing education for all veterinary professionals in small animal general practice. There is a huge demand for veterinary dentistry and oral care, and she wants to support general practice teams to provide the best care to their patients.

References

1. Altier B. Tips for mastering veterinary dental radiology. dvm360, January 19, 2021. Accessed February 27, 2025. https://www.dvm360.com/view/tips-for-mastering-veterinary-dental-radiography
2. Mulherin BL. Veterinary Oral Diagnostic Imaging. John Wiley & Sons Inc. 2024
3. Lobprise HB, Dodd JR. Wigg’s Veterinary Dentistry: Principles and Practice. 2^nd edition. John Wiley & Sons Inc. 2019
4. Altier B. The ABCs of dental radiology: dental radiology demystified (Proceedings). dvm360. September 1, 2019. Accessed February 27, 2025. https://www.dvm360.com/view/abc-s-dental-radiology-dental-radiology-demystified-proceedings-pdf
5. Niemiec BA. Dental Radiology Series: Techniques for Intraoral Radiology. Today’s Veterinary Practice. August 14, 2015. Accessed February 27, 2025. https://todaysveterinarypractice.com/dentistry/practical-dentistry-dental-radiology-series-techniques-for-intraoral-radiology/