Intraoral dental X-ray film is available in two speed groups: D and E/F. Clinically, film of speed group E/F is approximately twice as fast (sensitive) as film of group D and thus requires only half the exposure. Fast films are desirable from the standpoint of exposure reduction. Multiple studies have found that E/F-speed film is preferred, because it has the same useful density range, latitude, contrast, and image quality as D-speed films and can be used in routine intraoral radiographic examinations without sacrifice of diagnostic information.  Current digital sensors offer equal or greater dose savings than E/F-speed film and comparable diagnostic utility. Reference: White and Pharoah's Oral Radiology Principles and Interpretation 7th edition page no 33