Characteristic curves of dental x-ray film.

The characteristic curves of the dental x-ray films Ultra-Speed, Ekta-Speed, Defilux, Dentus, and Phil-X30, all of which are used in Finland, and the absorption of radiation in the films with their protective wrappers were determined at the x-ray laboratory of the Institute of Radiation Protection. The most sensitive film (Ekta-Speed) was found to be almost three times more sensitive than the least sensitive film (Defilux). In the usable optical density range, the gradient of the characteristic curve obtained with the three most sensitive film types--Ekta-Speed, Dentus and Ultra-Speed--was roughly the same, whereas Phil-X30 was far more gentle. All film types gave a resolution better than 10 lp/mm. The grain size used in the most sensitive film was slightly larger than that used in the less sensitive films. The films provided with lead backing foil transmitted 10% to 20% of the radiation, whereas the film type without lead backing foil (Phil-X30) transmitted 70% to 80%.