Patient PreparationPrior to starting to take films, the patient must be positioned properly. Seat the patient and ask them to remove their glasses and any removable appliances. Adjust the headrest to support the head while taking films. Raise or lower the chair to a comfortable height for the operator. Place the lead apron and thyroid collar on the patient. You are now ready to begin taking films.

It is a good idea to inform the patient about the number of films you will be taking so they know what to expect.

Bisecting Angle Technique

The Bisecting Angle Technique is an alternative to the paralleling technique for taking periapical films. The paralleling technique is recommended for routine periapical radiography, but there are some instances when it is very difficult due to patient anatomy or lack of cooperation. In these situations, the bisecting angle technique may be used. The film can be held in the mouth with the thumb or index finger or a bisecting instrument may be used.

In the Bisecting Angle Technique, the x-ray beam is directed perpendicular to an imaginary line which bisects (divides in half) the angle formed by the long axis of the tooth and the long axis of the film (see diagram below).X-ray beamLong axis of toothBisecting lineLong axis of film

Bisecting Angle Technique (Advantages)When comparing the two periapical techniques, the advantages of the bisecting angle technique are: 1. More comfortable: because the film is placed in the mouth at an angle to the long axis of the teeth, the film doesnt impinge on the tissues as much. 2. A film holder, although available, is not needed. Patients can hold the film in position using a finger. 3. No anatomical restrictions: the film can be angled to accommodate different anatomical situations using this technique

Bisecting Angle Technique (Disadvantages)When comparing the two periapical techniques, the disadvantages of the bisecting angle technique are: 1. More distortion: because the film and teeth are at an angle to each other (not parallel) the images will be distorted (see next slide). 2. Harder to position x-ray beam: as mentioned previously, because a film holder is often not used it is difficult to visualize where the x-ray beam should be directed. 3. Film less stable: using finger retention, the film has more chance of moving during placement

In the bisecting technique, the long axis of the tooth is not parallel with the long axis of the film. This results in a distortion of the image produced using this technique. In the left radiograph below, the buccal roots appear much shorter than the palatal root, even though in the actual tooth the lengths are not that much different. In the other radiograph taken with the paralleling technique, the lengths are projected in their proper relationship (minimal distortion).Distortionbisectingparalleling

(head tipped back)Maxilla Mandible Head PositionWhen using a bisecting instrument, head position is not critical. However, when using finger retention, head position is important. When radiographing the maxillary arch, the head should be positioned so that the maxillary arch is parallel to the floor. For mandibular films, the head is tipped back slightly so that the mandible is parallel to the floor when the mouth is open . Make sure head is supported by headrest. headrest

MSPfloorHead PositionWhen viewed from the front of the patient, the Midsagittal Plane (which divides the head into right and left halves) is perpendicular to the floor.

anteriorposteriorBisecting Angle TechniqueFilm Selection for AdultsThe # 2 size film is routinely used for all periapical films using the bisecting angle technique. The long axis of the film is vertical for anterior films and horizontal for posterior films.#2

#0#0anteriorposteriorBisecting Angle TechniqueFilm Selection for ChildrenFor children with small mouths, the # 0 size film is used for both anterior and posterior periapical films.

Anterior PeriapicalThe # 2 (or # 0) size film is positioned vertically with the all-white side of the film facing the teeth. The identifying dot is placed at the incisal edge of the teeth. The thumb or finger is applied to the back (colored) side of the film . The film should extend beyond the incisal edges of the teeth.

Posterior Periapical

Bisecting InstrumentThe Bisecting Angle Instrument is shown below. Notice that the biteblock support, against which the film will be aligned, is not parallel with the ring; it is slightly angled to accommodate the bisecting technique. This slight tilt of the film does little to make film placement more comfortable for the patient over the paralleling technique; that is why finger placement is recommended if the bisecting technique is indicated.

Snap-A-RayAnother instrument that may be used for posterior periapical films is the Snap-A-Ray shown below. The alligator jaws hold the film tightly and, since there is no support behind the film, the film can flex as the patient closes. This makes it more comfortable for the patient.

When using finger placement, always use the hand opposite to the side of the mouth being radiographed. (e.g., use the left index finger when taking the right maxillary premolar film). Use either thumb for the max. incisor film, the thumb or index finger (opposite hand) for the maxillary canines, and the index finger for all mandibular films and for the maxillary posterior films (opposite hand). Help the patient by positioning their thumb or finger where you want them to apply pressure.Finger Retention

Bisecting Angle Film PlacementThe film placements below are appropriate for both maxillary and mandibular arches.

Using finger retention of the film, there is no external guide to help you align the x-ray beam, as there is when using the paralleling instrument. You have to imagine where the bisecting line is and align the beam perpendicular to this line. This makes the technique much more difficult, but with practice it can be a beneficial adjunct to your radiographic technique.

When using this technique, keep in mind that all teeth incline slightly toward the middle of the head; they are not straight up-and-down. This will influence your visualization of the long axis of the tooth and the angle it forms with the film.Vertical Angulation

The x-ray beam is directed perpendicular to the bisecting line shown below. You can see the film long axis, but you have to visualize the inclination of the long axis of the tooth. Once you determine the angle, imagine the bisecting line and direct the x-ray beam at a 90-degree angle (perpendicular) to this line. This is the vertical angulation. X-ray beamLong axis of toothBisecting lineLong axis of film Vertical Angulation

In the diagram below, the tooth is imagined to be more upright than it really is. As the tooth is rotated into its correct inclination (click to rotate), the angle changes and the bisecting line (green dotted line) is less steep, requiring an increased vertical angulation (green arrow). Because most people imagine the tooth to be more upright than it really is, it is recommended that 5 degrees be added to the vertical angulation you have chosen.Vertical Angulation0

The horizontal angulation is adjusted so that a line connecting the front and back edge of the PID (yellow line below) is parallel with a line connecting the buccal surfaces of the premolars and molars (green line below). The x-rays will then be perpendicular to the film. Horizontal Angulation

For the anterior periapicals it is easy to see the sides of the film and makes it easy to center the beam on the film side-to-side. You then need to make sure the PID extends below the visible (incisal) edge of the film (maxillary arch) or above the visible edge (mandible). In the posterior region, the front edge of the PID should be anterior to the front edge of the film and the PID should extend beyond the visible (occlusal) edge of the film (above or below, depending on which arch is being radiographed). These steps will help to insure that the film is completely covered by the x-ray beam, avoiding cone-cuts.Centering the Beam

Maxillary IncisorsThe film is held in place using the thumb of either hand. The x-ray beam is directed perpendicular to the bisecting line vertically and the horizontal angulation aligns the x-ray beam perpendicular to the film. The x-ray beam is centered on the film. The film shows both central incisors and most of the lateral incisorstt (tube angle 60 cauded).

Maxillary CanineThe film is held in place using the thumb or index finger of the opposite hand. (Right hand for maxillary left canine pictured below). The x-ray beam is directed perpendicular to the bisecting line vertically and the horizontal angulation should open the contact between the canine and first premolar (see next slide). The x-ray beam is centered on the film. . (tube angle 50 degree cauded).

Canine Horizontal AngulationIf you direct the beam perpendicular to the canine, there will normally be overlap between the canine and first premolar. In order to open this contact, the horizontal angulation must be rotated posteriorly. Try to imagine the mesial surface of the first premolar and align the beam parallel with this surface. (see diagram below right). Incorrect Correct

diagonal placement (narrow arch)0Maxillary CanineIn many patients, especially ones with narrow maxillary arch widths, it is difficult to align the film ideally because the top edge of the film contacts the palate on the opposite side and doesnt allow enough film to register the apex of the canine. By rotating the film into a diagonal placement, this wont be a problem.Film cant be placed far enough into the mouth

Maxillary PremolarUsing the index finger of the opposite hand, position the film properly and align the beam vertically and horizontally. Center the x-ray beam on the film(tube angle 40degree cauded)..

Maxillary MolarUsing the index finger of the opposite hand, position the film properly and align the beam vertically and horizontally. Center the x-ray beam on the film. (tube angle 30 degree cauded).

Sometimes it is difficult to get the film far enough back to cover the third molar region due to gagging or anatomy, and all of the third molar will not be seen on the film (see diagram at left). By rotating the tubehead so that the beam is directed more anteriorly (diagram at right), the third molar is projected on to the film, giving us the needed information. Note, however, the increase in overlap that results.

Mandibular IncisorsUsing the index finger of either hand, position the film properly and align the PID as discussed earlier. All four incisors appear on the film.(tube angle 30 cevalic)..

Mandibular CanineUsing the index finger of the opposite hand, position the film properly and align the beam vertically and horizontally. Center the x-ray beam on the film. # 22 is shown on the film below(tube angle 20 degree caviled )..

Mandibular PremolarUsing the index finger of the opposite hand, position the film properly and align the beam vertically and horizontally. Center the x-ray beam on the film. (tube angle 10 caviled).

Mandibular MolarUsing the index finger of the opposite hand, position the film properly and align the beam vertically and horizontally. Center the x-ray beam on the film. This film clearly shows all of the third molar roots . (tube centre at right angle zero degree.

Adult full-mouth series, BisectingTechniqueUsing all # 2 size film, an adult full-mouth series of films consists of 14 periapical films; 6 anterior (from canine to canine, 3 maxillary and 3 mandibular) and 8 posterior (premolar and molar films in each quadrant). RLAll # 2 films0

Anterior FirstWhen taking films on a patient, you should always start with the anterior films. If you are doing a full series, start with the maxillary canine film and then finish all the anterior films, both maxillary and mandible. Then complete the posterior films, starting with the premolar, then molar, in each quadrant. When doing only a few films on a patient, start with the most anterior film and work your way back in the mouth. This sequence of taking films allows the patient to get used to the procedure with a minimum of discomfort and helps to avoid stimulation of the gag reflex.

Bisecting Angle TechniqueErrorsThe following slides identify some of the most common errors seen when using the bisecting angle technique.

Elongation If you have too little vertical angulation, as in the diagram below, the image will be elongated or stretched out on the film. The angle the x-ray beam forms with the bisecting line is less than 90. The red lines on the film represent the actual length of tooth # 9; the black arrow points to the end of the image of the tooth.long axis of toothbisecting linefilmbisecting linex-ray beam

Foreshortening long axis of toothbisecting linefilmIf you have too much vertical angulation, as in the diagram below, the image will be foreshortened or reduced in length. The angle the x-ray beam forms with the bisecting line is greater than 90. The red lines on the film represent the actual length of tooth # 9; the black arrow points to the end of the image of the tooth.

>90 = foreshortening90 the apex will be imaged lower on the film, shortening the overall image. Remember, a 90 angle between the x-ray beam and the bisecting line is the ideal alignment.image lengths

Improper Film PlacementAs with the paralleling technique, improper film placement is one of the most common errors seen in the bisecting angle technique. In the molar film below, the film was placed too far forward, cutting off the distal root of the second molar and failing to image the third molar region.Mandibular molar periapical

Film PlacementWith finger retention, it may be hard to keep the film from rotating around the end of the finger as it presses the film against the teeth. This may result in a tipped film as seen below. Notice the tip of the second molar is not visible, resulting in the need for a retake. (The teeth are also elongated; is this too little or too much vertical angulation?)Too little (not enough) vertical angulation0

0Film PlacementIt is important to place the film so that of film extends beyond the incisal edge (anterior) or occlusal surface (posterior). However, if too much film extends beyond, the roots of the teeth will usually not appear on the film, as seen below.

Film PlacementWhen placing the film using finger retention, it is important to make sure that finger pressure is applied where the film is supported by tooth structure, ideally at the junction of the crown of the tooth with the gingiva. If the film is not supported, film bending will result. In the canine film below, the canine root bends off of the film. What other error is seen on this film? Film not centered on canineCanine periapical0

Reversed filmIf the colored portion of the film faces the teeth being radiographed, the lead foil in the film packet will be between the teeth and the film. This results in the pattern stamped on the lead foil appearing on the film (see right side of film below). The film will also be lighter than the other films taken at the same time. What other situations could result in a film that is too light?Underexposure or processing error (e.g., developer solution too cold)0

Cone-cutting If the x-ray tubehead is not positioned properly, the x-ray beam may not cover the entire film. This is known as conecutting, which results in a clear (white) area on the film where the silver halide crystals were not exposed to x-rays (see film below). In the diagram below left, the dotted circle represents where the x-ray beam should have been positioned; the solid circle shows the actual position of the x-ray beam (too posterior).

Overlap (incorrect horizontal angulation) Overlap is the superimposition of part of one tooth with part of the adjacent tooth (dotted circles below left). The red arrow represents the direction of the x-ray beam; the x-ray beam should be perpendicular to the dotted line below. (See discussion of horizontal angulation on earlier slide).

If you try to make the film more comfortable for the patient by softening the edges, the emulsion of the film will be affected, resulting in black lines (see film below). With finger retention, film placement is usually not very uncomfortable; therefore, film softening is not needed. Film Softening

Double exposureWhen taking films, you should always place each film in a container or paper bag immediately after it is exposed. Exposed films should never be placed in the same area where unexposed films are located. The film at left shows images of mandibular posterior teeth , both upright and inverted. The film was used for both the premolar and molar films on the same side.

Patient Movement If the patient moves slightly during the exposure of the radiograph, the image will be blurred as in the film below. Always advise the patient to remain still for the very short time it takes to complete the exposure. What other error is evident on this film?Less than 1/4 of film was extending above the occlusal surface on this premolar periapical film, cutting off the top part of the crowns of the teeth.0

Thyroid collarWith finger retention of films in the mandibular arch, the tubehead may be positioned so that the x-ray beam passes through part of the thyroid collar (see photo below). This lead in the thyroid collar prevents x-rays from passing through, resulting in an unexposed, clear area on the film as seen below right.

overexposureunderexposureIncorrect Exposure Factors correct exposureThe standard exposure settings on your x-ray machine will be acceptable for the majority of your patients. However, if you are taking radiographs on a child you would need to decrease the settings. If your patient is very large, you would need to increase the settings. Underexposure results when the exposure factors are set too low for the patient size. Overexposure results when the exposure factors are set too high.

Occlusal Technique

Occlusal FilmThe occlusal film is used to: identify the extent of lesions in a buccolingual direction identify the buccolingual location of impacted teeth or other abnormalities show the location of developing teeth in children, using # 2 size film image patients with trismus that have limited mouth opening

Occlusal TechniqueHead PositionMaxillary film: the maxillary arch is parallel to the floor; the midsagittal plane is perpendicular to the floor.Mandibular film: the head is tipped back so that the mandibular arch is as close to perpendicular to the floor as possible.

Occlusal TechniqueFilm positionThe film is placed so that the all-white side of the film (# 4 for adults, # 2 for children) faces the arch being radiographed. The film is usually placed with the long axis side-to-side, but this is not critical. The film is large enough to normally cover the entire arch, but make sure it covers the area of interest. Position the film as far back in the mouth as possible and the patient gently bites on it to keep it in place.

Occlusal TechniqueX-ray Beam PositionThere are three types of occlusal films (to be discussed on the following slides): Normal Maxillary True Maxillary Mandibular

For all three of these, the x-ray beam is centered on the area of interest. Because of the curved beam, the corners of the film that sticks out of the mouth are often not exposed, resulting in slight conecuts. This is not an error, since these areas contain no needed information.

Normal Maxillary OcclusalThe Normal Maxillary Occlusal film is the most common occlusal film taken in the maxillary arch. The vertical angulation is set at 65 degrees. Because of this angle, structures located toward the back of the mouth may be projected off the back edge of the film and not be imaged.

True Maxillary OcclusalThe True Maxillary Occlusal film is not often used because of the much higher exposure time needed to properly expose the film. (Because the vertical angulation is 90 degrees, the x-ray beam passes through the very dense frontal bone; this is the reason for the increased exposure). Structures located farther back in the mouth are more likely to be imaged on this film.90 degrees

Mandibular OcclusalWith the head tipped back as much as possible, the x-ray beam is directed at a 90 degree angle to the film. Bony expansions of the mandible as well as abnormalities or pathology in the floor of the mouth can be imaged with this film.

Occlusal TechniqueExposure SettingsThe exposure times for the normal maxillary and mandibular occlusal films are the same as for a periapical or bitewing film of comparable film speed. For the true maxillary occlusal film, the exposure time is four times as long, allowing enough x-rays to pass through the frontal bone and properly expose the film.

Normal Maxillary OcclusalImpacted canineSupernumerary toothPedo anterior

Mandibular OcclusalPathology SialolithsPedo anterior

Modified Bisecting OcclusalIf a patient has difficulty opening the mouth due to trismus, an occlusal film can be used to provide a reasonable image of the teeth. The film is centered on the side of interest with the long axis front to back. The beam is aligned using the Bisecting Angle technique. The images will be greatly distorted, but may provide the necessary information.

This concludes the section on Bisecting Angle and Occlusal Techniques. Additional self-study modules are available at: http://dent.osu.edu/radiology/resources.htm

If you have any questions, you may e-mail me at jaynes.1@osu.edu.

Robert M. Jaynes, DDS, MSDirector, Radiology GroupCollege of DentistryOhio State University0