0 Films ScreensThe following slides describe the compositionand uses of intraoral and extraoral films andintensifying screens.In navigating through the slides, you should clickon the left mouse button when you see themouse holding an x-ray tubehead or you aredone reading a slide. Hitting “Enter” or “PageDown” will also work. To go back to the previousslide, hit “backspace” or “page up”.
Intraoral FilmIntraoral film is used for (1) bitewing films(named for the tab that sticks out from the sideof the film which resembles a wing and onwhich the patient bites); this film shows thecrowns of both maxillary and mandibular teethon one film; (2) periapical films, which showthe entire length of the teeth in either themaxillary or mandibular arch and (3) occlusalfilms, which are usually exposed atapproximately right angles (perpendicular) tothe occlusal plane and show broad areas of theteeth and bone.
Bitewing FilmThe bitewing film is used to identify interproximalcaries (where the teeth contact each other; blackarrows) and the appearance of the alveolar bone(red arrows). The white areas on the film areamalgam restorations.
Periapical FilmPeriapical means “around periapical pathologythe apex”. This film isintended to show the areaaround the root of the tooth.Normally, the entire tooth isseen, allowing the internal resorptionidentification of rootproblems, interproximalcaries, and the condition ofthe bone surrounding theteeth. This film is also usedin endodontic treatment of a cariestooth.
Occlusal FilmThe occlusal film is usedto identify the extent oflarger pathologicalconditions, to locate anobject in the buccolingualdirection, to show thedeveloping dentition in Impacted maxillary caninechildren and to imagepatients with trismus(inability to open themouth). Anterior dentition - Child
Extraoral FilmExtraoral films used in Dentistry include thePanoramic, Lateral oblique jaw film, Skull film,Cepahalometric and TMJ (temporomandibularjoint). These will be discussed briefly in thefollowing slides.
The panoramic film is the most common extraoralfilm used in dentistry. It does not provide the detailthat intraoral films do but it gives an overall viewof the entire dentition, both maxillary andmandibular. It is very helpful for third molarextractions
The lateral oblique jaw film can be used to imagethe third molar region in adults and to show thedeveloping posterior dentition in children. It isonly used if a panoramic x-ray machine is notavailable. The panoramic film is preferred.
Skull films, such as thisPA (postero-anterior)view, are used to evaluatetrauma anddevelopmental problems.This patient had externalfixation appliancesplaced to help expand thebone.
Ortho-surg. patient – jaw realignment Surgery patient- mandibular implant Cephalometric films, such as the lateral cephs above, are used to identify both the bone and the soft tissue outline on the same film. This film is used routinely by orthodontists in developing treatment plans for their patients. It is also used by oral surgeons for evaluating trauma and conditions requiring surgical correction.
Transcranial film TomogramTemporomandibular joint (TMJ) films provideinformation on the components of this joint,including the head of the condyle, the glenoidfossa and the articular eminence.
Film CompositionAn x-ray film is composed of a plastic (polyester)base covered on both sides with an emulsion;this is called a double-emulsion film. Theemulsion contains silver halide crystals whichare surrounded by gelatin. The silver halidecrystals are affected by the x-rays and eventuallyform the image during film processing. Thegelatin, similar to that used in desserts, isporous, allowing processing chemicals to reachthe silver halide crystals, and is also clear,allowing light to readily pass through whenviewing films. (continued on next slide)
Film Composition (continued) 0 The emulsion (gray lines below) is attached to the base with a very thin layer of adhesive (green lines below). The base has a slight bluish tint which makes viewing the films easier on the eye. The emulsion is covered with a thin layer of gelatin, a “supercoat,” which helps to protect the film (yellow lines below). Double emulsion blue-tinted base adhesive(emusion on both sides) supercoat emulsion with silver halide crystals and gelatin
Silver Halide CrystalsThere are two types of silver halide crystals. Tabular(flat) crystals are used in F-speed (Insight) film and in T-Mat and Ektavision film. The crystals are placed in theemulsion so that the flat surface (top view below) isparallel with the surface of the film. Globular (rounded)crystals are used in D-speed (Ultraspeed) film; thesecrystals are like small pebbles. tabular globular top view side view tabular
Film TypesThere are two types of film used in Dentistry. Thefirst of these, Direct Exposure Film, is usedintraorally. It is exposed when x-rays come incontact with it. The film is sealed in a light-tightpacket because visible light, a type ofelectromagnetic radiation along with x-rays, willalso expose the film. There are two types ofdirect exposure film: D-speed, also calledUltraspeed, and F-speed, which is called Insight.
Film Types (continued)The other type of film is Screen Film. Screen filmsare used for extraoral radiographs. Screen film ismade to be especially sensitive to the effects oflight from an intensifying screen. When thesescreens, on either side of the film in a cassette, areexposed to x-rays, they emit light which in turnexposes the film. (The x-rays contribute a verysmall percentage of the actual exposure of thefilm). Using the screen-film combination allows avery large reduction in the amount of radiationneeded to expose the film (30-60 times lessradiation than that required by direct exposurefilm).
Intensifying Screen FunctionOne of the properties of x-rays is that they causecertain materials to fluoresce (emit light); thephosphor crystals found in intensifying screensare one of these materials. The light emission isusually green or blue, depending on the type ofphosphor crystal used. The composition of thefilms used with these screens is adjusted by themanufacturer to be sensitive to either blue light orgreen light. It is important to make sure that thecorrect film is used with whichever type screen isselected. (Blue-sensitive film with blue light-emitting screen, etc.)
0 Intensifying Screen Composition (this side toward film)The base of the screen (yellow line above) is made ofplastic and provides support. A reflecting layer(silver line) reflects light emitted by the phosphorback toward the film. The phosphor layer (green line)contains the phosphor crystals that emit the light.The surface of the phosphor layer is covered with aprotecting coat (white line) , which is a thin layer ofplastic that protects the phosphor layer fromdamage when the screens are handled.
0 Rare Earth PhosphorThe most common type of phosphors being usedare the rare earth phosphors, which emit blue orgreen light depending on the type of rare earthmaterial being used. (Click to show interaction ofx-rays with phosphor crystals) film = phosphor crystal
Intensifying Screen Speed 0The speed of the screen depends on crystal size andthe thickness of the phosphor layer (larger crystalsand thicker layer increase speed). Image qualitydecreases as the screen speed increases. The threespeeds are:• Fast (Rapid): requires the least exposure but the images are less sharp• Medium (Par): medium speed, medium sharpness• Detail (Slow): produces the sharpest images but requires the most exposure
Cassette A cassette holds two intensifying screens (one on each side) in tight contact with the film. The cassette isRigid metal cassette either rigid (metal) or soft (vinyl), depending on the type of panoramic machine. The rigid cassette has a layer of foam padding under each screen to assure tight contact with the film.Flexible vinyl cassette (See next slide)
Cassette/Screens/Film x-rays cassette front foam (rigid cassettes) screen support phosphor/coating film phosphor/coating screen support foam (rigid cassettes) cassette back
0The surface of thescreens must be keptvery clean. Any debrisin the cassette(between the screenand film) will result ina white spot on thefilm (red arrow). Theother white spots(green arrows)represent tonsillarcalcifications.
0 Screen Film (continued)The two types of screen film used with rare earthscreens are T-Mat and Ektavision. These films areavailable in three styles: G, which is used toprovide the best contrast; L, which has the widestlatitude (long-scale contrast) and is good for softtissue visualization and H, which is used to providean extra film for referral purposes (two films areplaced in the cassette at the same time).The advantage of Ektavision film over T-Mat film isthat it has anti-crossover layers incorporated intothe film. This prevents light from one screenaffecting both emulsion layers; this produces asharper image on the film. (See following slides).
T-Mat (crossover) 0Light produced by the phosphor crystal spreads outas it goes toward the film and with T-Mat film itaffects the emulsion on both sides. Since it hasspread out more when it reaches the emulsion onthe opposite side of the film (crossover), thesharpness (edge detail) of the image is decreased. film
Ektavision (anti-crossover) 0Ektavision film has a crossover control layer on eachside of the film base. These layers allow the light from aphosphor crystal to reach the emulsion on the sameside as the crystal but prevent the light from reachingthe emulsion on the opposite side of the film. X-rayseasily pass through this anticrossover layer. film
Film Sizes (Intraoral)# 0: Used in children for both periapical (PA) and bitewing (BW) films; used for small mouths.# 1: Used for adult anterior periapicals with the paralleling technique.# 2: Used for adult posterior periapicals and bitewings and for children with larger mouths; also used in anterior region of adults for periapicalfilms taken with bisecting-angle technique; may also be used for occlusal films in children.# 3: Used for extra-long bitewing films; one film covers all teeth on one side of the mouth.# 4: Used for occlusal films (primarily adults). (See next slide for comparative sizes)
Adult PA, BW Extra-long BW #2 #3Child occlusalAdult ant. PA #1 Occlusal in adults #4Child PA, BW #0
Film Sizes (Extraoral)5” x 12” and 6” x 12”: Both of these films are usedin panoramic radiography. Some machines use 5”x 12” and others use 6” x 12”.8” x 10”: This size is used for cephalometric films,skull films and tomograms (TMJ).5” x 7”: This size is not often used. It may be usedfor lateral oblique jaw films or for transcranial films(used for TMJ views).
Film Speed 0The speed of a film represents the amount ofradiation required to produce a radiograph ofacceptable density. (Density is the degree ofdarkening of the film; the middle film below hasacceptable density. The one on the left is too lightand the one on the right is too dark). As the speedof the film increases, the amount of radiationneeded to properly expose it decreases.
Intraoral Film SpeedD-speed (Ultraspeed): Once the most commonintraoral film speed used, it is now gradually beingreplaced by F-speed film. Technically, this slowerfilm produces sharper images, improving thediagnostic ability of the film. It has globularcrystals.F-speed (Insight): this film has larger silver halidecrystals; they are flat tabular crystals. Because ofthe larger size, less radiation is needed to exposethese crystals, resulting in a 60 % reduction inpatient exposure when compared to D-speed film.
Extraoral Film SpeedThe speed of extraoral film is increased with anincrease in the size of the silver halide crystals.In general, the faster the film, the less sharp theradiographic image will be.Extraoral film is always used with intensifyingscreens. Like films, screens have differentspeeds.The overall speed of an extraoral film system(film plus screen) is determined by thecombined speeds of the film and the screen.
Clinasept Barrier Packets 0Clinasept barriers are sealed plastic covers that protectintraoral film packets from saliva contamination. Afterexposing the film, the barrier is opened at the notch(see below) and dropped into a bag without touchingthe film (see next slide). front notch back
Removing the clinaseptbarrier from the filmpacket and dropping itinto the film bag. Thefilm packet must not betouched with the glovesthat have been in thepatient’s mouth. Thishelps to assure that thefilm packet is notcontaminated when it istaken to the darkroomfor processing.
Film PacketThe x-ray film packet is made of plastic or paper,depending on film size. The cover protects the filmfrom light and moisture. The back side identifies thetype of film (by color), the number of films in thepacket (also by color), and the location of theidentifying dot used for film mounting. dot # of films #2 #2 in packet #1 plastic plastic paper D-speed F-speed tab (Ultraspeed) (Insight)
Contents of Film Packet 0Black paper: surrounds film;protects emulsion.Film: one or two films;raised dot in one cornerused for film orientation.Lead foil: protects film frombackscatter (see next slide);reduces patient exposure;strengthens packet; patternon foil identifies when film isplaced backwards (back offilm faces teeth).
0Scatter (secondary) radiation is produced when theprimary x-rays from the x-ray tube interact with thepatient’s hard and soft tissues. Backscatter radiationrefers to those scattered x-rays that go “back”toward the film. Primary x-rays Scatter (secondary) x-rays
0 Film Storage• Films should be stored at 50–70 degrees F. Storage at high temperatures may result in film fogging.• Opened boxes of screen (extraoral) film need to be kept in light-tight area (darkroom); need to be cool.• Use film before expiration date to avoid film fogging.• Do not store film in room where radiographs are taken
0This concludes the section on Films andScreens.Additional self-study modules are availableat: http://dent.osu.edu/radiology/resources.htmIf you have any questions, you may e-mailme at: email@example.comRobert M. Jaynes, DDS, MSDirector, Radiology GroupCollege of DentistryOhio State University