Bitewing radiographs take their name from the original technique which required the patient to bite on a small wing attached to an intraoral film packet (see Fig. 8.1). Modern film holders, as shown later, have eliminated the need for the wing (now termed a tab), and digital image receptors (solid-state or phosphor plate) can be used instead of film, but the terminology and clinical indications have remained the same. An individual image is designed to show the crowns of the premolar and molar teeth on one side of the jaws.
• The posterior teeth and the image receptor should be parallel – the shape of the dental arch may necessitate two separate image receptor positions to achieve this requirement for the premolars and the molars (Fig. 8.3).
• The beam-aiming device should ensure that in the horizontal plane the X-ray tubehead is aimed so that the beam meets the teeth and the image receptor at right angles, and passes directly through all the contact areas (Fig. 8.3).
• The beam-aiming device should ensure that in the vertical plane the X-ray tubehead is aimed downwards (approximately 5°–8° to the horizontal) to compensate for the upwardly rising curve of Monson (Fig. 8.4).
Fig. 8.4 Diagram showing the ideal image receptor position and the approximate 5°–8° downward vertical angulation of the X-ray beam (determined by the beam-aiming device) compensating for the curve of Monson.
It is sometimes not possible to use an image receptor holder (with beam-aiming device) and achieve these ideal technical requirements – particularly in children. Dental care professionals therefore still need to be aware of the original technique of using a tab attached to the film packet or phosphor plate and aligning the X-ray tubehead by eye.
Several image receptor holders with different beam-aiming devices have been produced for use with film packets or digital phosphor plates and with digital solid-state sensors, held either horizontally or vertically. A selection of different holders is shown in Fig. 8.5. As in periapical radiography, the choice of holder is a matter of personal preference and dependent upon the type of image receptors being employed. The various holders vary in cost and design but essentially consist of the same three basic components that make up periapical holders (see Ch. 7), namely:
Fig. 8.5 Bitewing image receptor holders with beam-aiming devices. A A selection of horizontal bitewing holders set-up using a film packet as the image receptor – note the red colour coding for the Rinn XCP System. B The Hawe–Neos Kwikbite horizontal holder set-up using a digital phosphor plate. C Vertical bitewing holders – the red Rinn XCP holder and the yellow Hawe–Neos Parobite holder set-up using film packets. D The red Rinn XCP-DS horizontal bitewing solid-state digital sensor holder. E The Planmeca horizontal bitewing holder designed specifically for use with their dixi2 solid-state digital sensors. (See colour plates section)
4. The anterior edge of the image receptor should be positioned opposite the distal aspect of the lower canine – in this position the image receptor extends usually just beyond the mesial aspect of the lower third molar (see Fig. 8.6).