Processing is the general term used to describe the sequence of events required to convert the invisible latent image, contained in the sensitized film emulsion or in the solid-state or phosphor layer of the digital sensors, into the visible black and white radiographic film or digital image. This chapter summarizes the two methods involved, namely:
It is CRUCIAL that the stages involved in chemical processing are performed under controlled, standardized conditions with careful attention to detail. Strict quality assurance procedures must be applied (see Ch. 17). Unfortunately, all too often in dental practice poor chemical processing is the cause of radiographic films being of inadequate diagnostic quality, irrespective of how reliable and expensive the X-ray equipment or how accurate the operator’s radiographic techniques.
A detailed knowledge of the chemistry involved in processing is not essential. However, a working knowledge and understanding of the theory of processing is necessary so that processing faults can be identified and corrected. A simplified approach to the stages involved in converting the green film emulsion into the black/white/grey radiograph is shown in Fig. 5.1 and outlined below:
|Phenidone||Helps bring out the image|
|Sodium sulphite||Preservative – reduces oxidation|
|Potassium carbonate||Activator – governs the activity of the developing agents|
|Benzotriazole||Restrainer – prevents fog and controls the activity of the developing agents|
|Glutaraldehyde||Hardens the emulsion|
|Fungicide||Prevents fungal growth|
|Buffer||Maintains pH (7+)|
|Ammonium thiosulphate||Removes unsensitized silver halide crystals|
|Sodium sulphite||Preservative – prevents deterioration of the fixing agent|
|Acetic acid||Acidifier – maintains pH|
• If the development process is allowed to continue for too long, more silver will be deposited than was intended and the radiograph will be too dark. Conversely, if there is too short a development time the radiograph will be too light.