Film Types & Image Receptors

TYPES OF DENTAL FILM

According to sensitivity, there are two types of films :

    

    i.            Direct action or non-screen film

•   Also called wrapped or packet film.
•   This type of film sensitive primarily to to x-ray photons.

   ii.            Indirect action or screen film

• Used in combination with intensifying screen in a cassette.
• It is sensitive primarily to light photons, which are emitted by the adjacent   intensifying screen on  exposure to x-rays.
• Advantage- exposure to the patient is minimized.
• It is mainly of two types 

 -->Blue light sensitive : These films contain calcium tungstate in the screen. 

 -->Green light sensitive : These films contain rare earth elements.

INTRAORAL X-RAY FILM

   SENSITIVITY CLASS D

• Double-emulsion, non-screen film of medium speed.
• High contrast and fine grain, providing high image quality and outstanding detail definition.
• Good spatial resolution.
• Typical delivered dose : about 0.5mGy
• Typical exposure times : 0.3-0.7
• This general-purpose film is intended for direct-exposure routine intraoral radiographs.
•  For processing manually or in auto processors.
• Each film is provided with an embossed dot located near the edge of the film that serves as an identificator of the radiation side on the processed film. Its raised portion indicates the side facing the radiation source.

SENSITIVITY CLASS E

•  Double-emulsion, high speed non-screen film.  
•  High contrast and fine grain, providing high image quality and outstanding detail definition.
• The film is intended for direct-exposure routine intraoral radiographs.
•  The high speed of the film enables to reduce the X-ray dose to 30 % – 50 % in comparison with the dental films of D class.
• Good spatial resolution.
• Typical delivered dose : about 0.25mGy
• Typical exposure times : 0.1-0.3s
• For processing manually or in auto processors.

SENSITIVITY CLASS F

• Double-emulsion, non-screen film of extra high speed.
• High contrast and fine grain, provides high image quality and outstanding detail definition.
• The film is intended for direct-exposure routine intraoral radiographs.
• The higher speed of the film enables to reduce the X-ray dose to 50 % in comparison with the dental films of D class, and to 25 % in comparison with the dental film of the E class.

EXTRAORAL X-RAY FILM

Green light sensitive film

• Green-sensitive X-ray film of a high-quality, high-contrast and low-fog. 
• Designed for use with green-emitting intensifying screens.
• The film is suitable for all extra-oral radiographic techniques.

Blue light sensitive film

• Blue-sensitive X-ray film of a high-quality, high-contrast and low-fog. 
• Designed for use with blue-emitting intensifying screens.
• The film is suitable for all extra-oral radiographic techniques.

IMAGE RECEPTORS

There are several types of image receptors used in dentistry.  Radiographic film remains widely used image receptor.  The speed of radiographic film represents the sensitivity of the emulsion to x-rays.  The faster the film, the less radiation exposure that is required.  Letters of the alphabet denote film speed with D, E, E/F and F. F speed is the fastest film currently available and its use can significantly decrease the exposure (70% compared to D and 20% compared to E) to the patient while maintain quality image.

                          Image Receptor 

                             Radiographic Film

      

       Digital receptors are replacing film at an increasing rate.  Digital receptors include rigid wired or wireless sensors such as the charged-coupled device (CCD), complementary metal oxide semiconductor (CMOS) and photostimulable phosphor plate (PSP) or storage phosphor plate (SPP) receptors. Rigid digital receptors are composed of an array of x-ray or light sensitive pixels on a pure silicon chip.

     Digital receptors offer the further potential benefit of reduced exposure and improved work flow. The degree of dose reduction is dependent on the comparison to a particular film speed. It is estimated that digital radiography reduces patient radiation dose by 75% compared with D speed  film, 50% compared with E speed film and approximately 40% compared with F speed film. The actual amount of exposure reduction achieved with digital receptors is dependent on a number of factors including : 

      A)    speed

      B)    collimation

      C)    technique

      D)    retakes.