Load the film into the cassette – This must be performed in the darkroom. Because the panoramic film incorporates special dyes that make it more sensitive to the light emitted by the intensifying screen, this film (also called “indirect exposure” film) is more sensitive to the darkroom safelight. Therefore, after a film is removed from the container, the lid should be replaced immediately. The operator now has a reasonable time (approximately 2 min.) to place the film into the cassette without producing film fog.
Unlike rigid cassettes in which they are attached, intensifying screens are easily removed from flexible cassettes. Special care must therefore be taken when flexible cassettes are used as it is easy to insert the film between the intensifying screen and plastic holder.
Flexible cassettes are opened by removing one tab of the Velcro fastener whereas rigid cassettes have a mechanical “snap” lock device.
Load the cassette into the receptor assembly – If a flexible cassette is used this is loaded onto the receptor assembly by securing the Velcro end to the drum and carefully wrapping the cassette around the curved surface ensuring that the lower edge of the cassette is butted against the rim of the drum. The other end of the cassette is secured to the central shaft of the receptor assembly with a Velcro tab. Rigid cassettes are easier to load into the receptor assembly and are guided by rails and secured into position by locks. However, this does not prevent rigid cassettes from being inserted back to front or upside down. Therefore, rigid cassettes will often have some annotation on one side providing guidance as to their correct insertion.
Set the program mode on the panoramic unit – Even the simplest panoramic units can be used in a variety of modes. It is important that the operator ensure that the correct mode is selected prior to patient exposure.
Examples of the program mode controls on two panoramic units:
Set the exposure – For most panoramic units patient exposure is adjusted by alteration of the kilovoltage (kVp). This adjustment should be based on the physical stature of the patient. Basic guidelines follow that assist the clinician in this decision-making process. While the operator should follow the general guidelines recommended by the manufacturer, consideration needs to be given to the patient size, thickness of tissues, presence of teeth and bone density characteristics. Patients that are considered above the norm in each of these characteristics would require an increase in the kVp setting while patients below the norm would indicate a decrease. If the unit is manually adjusted an exposure chart is available in the user’s manual. For manually adjusted panoramic units it is necessary and mandated by law that an exposure chart be posted adjacent to the exposure control.
Assemble and insert bite block – Bite blocks can be either disposable or designed to be reused. Disposable bite blocks are usually made of a material that is unable to be autoclaved. Reusable bite blocks are either chemically sterilized or autoclavable. Often they will come as two components; a chin rest attachment and the bite block proper. Before they are inserted into the chin rest they are usually assembled and covered with a protective barrier.
Position machine slightly higher than patient’s chin – Prior to patient preparation the approximate height of the patient should be determined and the chin rest adjusted to be slightly higher than the patient’s chin. When the patient attempts to bite in the grooves of the bite block (see 2a. Patient Positioning and Exposure – a. Bite in bite block) they must therefore raise their head. It is easier to adjust the vertical position of the patient’s head downwards from this position than to force the head up with the action of the panoramic unit.