We all strive to capture that ‘perfect’ radiograph, the one that is taken at the precise angle to beautifully show all necessary structures without distortion. To help achieve this goal, sensor manufacturers have had to balance the size and shape of the sensor to allow for greater positioning ease.
Many sensors also utilize holders that employ the paralleling technique first developed by DENTSPLY Rinn (Fig. 1). The principle behind this technique is to place the sensor (a) parallel to the long axis of the teeth to avoid foreshortening or elongation; (b) perpendicular to the inter-dental spaces to avoid overlapping; and (c) in the deeper areas of the mouth, at the midline, to allow for true parallelism and greater patient comfort.
Figure 1: Sensor employed in paralleling technique.
Once the sensor is placed into the appropriate holder, follow the paralleling steps above. For example, on an exposure for the maxillary canine (Fig. 2), the sensor is positioned so the canine is in the center and so it sits parallel to the root of the canine. The face of the sensor is positioned perpendicular to the interdental space between the canine and the lateral. Picture a line going through the contact. The sensor is then gently guided toward the midline where typically there is more room. The patient then closes on the biteblock and the X-ray is taken.
Figure 2: Sensor placement for maxillary canine.
Figure 3: Sensor placement for lower premolars.
The same technique is used for posterior exposures. In the case of the lower premolar exposure (Fig. 3), the sensor is parallel to the premolars’ roots and captures the distal of the canine. It is perpendicular to the interdental spaces so the contacts of the premolars are open, instead of overlapped, on the image. With the sensor placed at the midline, as the patient closes, there is greater comfort than if the sensor were next to the teeth.
Whether taking vertical or horizontal bitewing radiographs (Fig.4), use the paralleling steps. Since interproximal caries detection is the primary use for bitewing exposures, it is especially important that the face of the sensor is at a right angle to the interdental contact spaces. Again, to provide for the patient’s comfort, move the sensor toward the midline.
Figure 4: Sensor placement for bitewing radiographs.
Figure 5: Sensor bisecting angle technique.
Paralleling is always the preferred technique to use when taking radiographs. However, challenging situations where paralleling cannot be achieved such as the presence of tori or a lack of patient cooperation can present. In these cases, the clinician may adopt the bisecting angle technique (Fig. 5).
In this technique, the face of the cone (a) is positioned so it is at the bisected angle (b) of the long axis of the tooth (c) and the face of the sensor (d). Please Note: For clarity, sensor is shown without a barrier.