0 Bisecting Angle Technique Occlusal TechniqueThe following slides describe the bisectingangle technique and occlusal techniquefor taking intraoral films.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”.
Patient PreparationPrior to starting to take films, the patient mustbe positioned properly. Seat the patient and askthem to remove their glasses and any removableappliances. Adjust the headrest to support thehead while taking films. Raise or lower the chairto a comfortable height for the operator. Placethe 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 thenumber of films you will be taking so they knowwhat to expect.
The Bisecting Angle Technique is an alternativeto the paralleling technique for taking periapicalfilms. The paralleling technique is recommendedfor routine periapical radiography, but there aresome instances when it is very difficult due topatient anatomy or lack of cooperation. In thesesituations, the bisecting angle technique may beused. The film can be held in the mouth with thethumb or index finger or a bisecting instrumentmay be used. During this discussion, fingerretention will be stressed; patient acceptance ofthe bisecting instrument is not much better thanfor the paralleling instrument.
In the Bisecting Angle Technique, the x-ray beamis directed perpendicular to an imaginary linewhich bisects (divides in half) the angle formedby the long axis of the tooth and the long axis ofthe film (see diagram below). Long axis of tooth Bisecting line X-ray beam Long axis of film
Bisecting Angle Technique (Advantages)When comparing the two periapical techniques, theadvantages 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 doesn’t 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
Anatomical VariationsAnatomical situations which might require usingthe bisecting angle technique are:• a shallow palate• a large palatal torus• a shallow or tender floor of the mouth• a short lingual frenum (tongue-tie)
Bisecting Angle Technique (Disadvantages)When comparing the two periapical techniques, thedisadvantages 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
DistortionIn the bisecting technique, the long axis of the tooth isnot parallel with the long axis of the film. This results in adistortion of the image produced using this technique. Inthe left radiograph below, the buccal roots appear muchshorter than the palatal root, even though in the actualtooth the lengths are not that much different. In the otherradiograph taken with the paralleling technique, thelengths are projected in their proper relationship(minimal distortion). bisecting paralleling
Head PositionWhen using a bisecting instrument, head position is notcritical. However, when using finger retention, headposition is important. When radiographing the maxillaryarch, the head should be positioned so that the maxillaryarch is parallel to the floor. For mandibular films, thehead is tipped back slightly so that the mandible isparallel to the floor when the mouth is open (The mouthis always open when using finger retention). Make surehead is supported by headrest. Maxilla Mandibleheadrest (head tipped back)
Head PositionWhen viewed from the front of the patient, theMidsagittal Plane (which divides the head intoright and left halves) is perpendicular to the floor. MSP floor
Bisecting Angle Technique Film Selection for AdultsThe # 2 size film is routinely used for all periapicalfilms using the bisecting angle technique. The longaxis of the film is vertical for anterior films andhorizontal for posterior films. #2 #2 anterior posterior
Bisecting Angle Technique Film Selection for ChildrenFor children with small mouths, the # 0 size film isused for both anterior and posterior periapicalfilms. However, if the child’s mouth is largeenough to reasonably accommodate the largersize films, and the child is cooperative, theyshould be used. #0 #0 anterior posterior
Anterior PeriapicalThe # 2 (or # 0) size film is positioned vertically with theall-white side of the film facing the teeth. The identifyingdot is placed at the incisal edge of the teeth. The thumb orfinger is applied to the back (colored) side of the film atapproximately the junction of the tooth with the gingiva;this provides good support for the film and avoids filmbending. The film should extend ¼” beyond the incisaledges of the teeth.
Posterior PeriapicalThe # 2 (or # 0) size film is positioned horizontally withthe all-white side of the film facing the teeth. Theidentifying dot is placed at the occlusal surface of theteeth. The finger is applied to the back (colored) side ofthe film at approximately the junction of the tooth withthe gingiva; this provides good support for the film andavoids film bending. The film should extend ¼” beyondthe occlusal surface of the teeth.
Bisecting InstrumentThe Bisecting Angle Instrument is shown below.Notice that the biteblock support, against which thefilm will be aligned, is not parallel with the ring; it isslightly angled to accommodate the bisectingtechnique. This slight tilt of the film does little tomake film placement more comfortable for the patientover the paralleling technique; that is why fingerplacement is recommended if the bisecting techniqueis indicated.
Snap-A-RayAnother instrument that may be used for posteriorperiapical films is the Snap-A-Ray shown below. Thealligator jaws hold the film tightly and, since there is nosupport behind the film, the film can flex as the patientcloses. This makes it more comfortable for the patient.
Finger RetentionWhen using finger placement, always use thehand opposite to the side of the mouth beingradiographed. (e.g., use the left index fingerwhen taking the right maxillary premolar film).Use either thumb for the max. incisor film, thethumb or index finger (opposite hand) for themaxillary canines, and the index finger for allmandibular films and for the maxillaryposterior films (opposite hand). Help thepatient by positioning their thumb or fingerwhere you want them to apply pressure.
Bisecting Angle Film PlacementThe film placements below are appropriate forboth maxillary and mandibular arches.
Vertical AngulationUsing finger retention of the film, there is no externalguide to help you align the x-ray beam, as there iswhen using the paralleling instrument. You have to“imagine” where the bisecting line is and align thebeam perpendicular to this line. This makes thetechnique much more difficult, but with practice it canbe a beneficial adjunct to your radiographictechnique.When using this technique, keep in mind that all teethincline slightly toward the middle of the head; theyare not straight up-and-down. This will influence yourvisualization of the long axis of the tooth and theangle it forms with the film.
Vertical AngulationThe x-ray beam is directed perpendicular to thebisecting line shown below. You can see the film longaxis, but you have to “visualize” the inclination of thelong axis of the tooth. Once you determine the angle,imagine the bisecting line and direct the x-ray beamat a 90-degree angle (perpendicular) to this line. Thisis the vertical angulation. Bisecting line Long axis of tooth X-ray beam Long axis of film
Vertical Angulation 0In the diagram below, the tooth is imagined to bemore upright than it really is. As the tooth is rotatedinto its correct inclination (click to rotate), the anglechanges and the bisecting line (green dotted line) isless steep, requiring an increased vertical angulation(green arrow). Because most people imagine thetooth to be more upright than it really is, it isrecommended that 5 degrees be added to the verticalangulation you have chosen.
Horizontal AngulationThe horizontal angulation is adjusted so that a lineconnecting the front and back edge of the PID (yellowline below) is parallel with a line connecting the buccalsurfaces of the premolars and molars (green line below).The x-rays will then be perpendicular to the film. correct incorrect
Centering the BeamFor the anterior periapicals it is easy to see the sides ofthe film and makes it easy to center the beam on thefilm side-to-side. You then need to make sure the PIDextends ¼” 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 shouldbe ¼” anterior to the front edge of the film and the PIDshould extend ¼” beyond the visible (occlusal) edge ofthe film (above or below, depending on which arch isbeing radiographed). These steps will help to insurethat the film is completely covered by the x-ray beam,avoiding cone-cuts. ¼”
Maxillary IncisorsThe film is held in place using the thumb of either hand.The x-ray beam is directed perpendicular to the bisectingline vertically and the horizontal angulation aligns the x-ray beam perpendicular to the film. The x-ray beam iscentered on the film. The film shows both centralincisors and most of the lateral incisors.
Maxillary CanineThe film is held in place using the thumb or index fingerof the opposite hand. (Right hand for maxillary leftcanine pictured below). The x-ray beam is directedperpendicular to the bisecting line vertically and thehorizontal angulation should open the contact betweenthe canine and first premolar (see next slide). The x-raybeam is centered on the film. The film shows tooth # 11.
Canine Horizontal AngulationIf you direct the beam perpendicular to the canine,there will normally be overlap between the canine andfirst premolar. In order to open this contact, thehorizontal angulation must be rotated posteriorly. Tryto imagine the mesial surface of the first premolar andalign the beam parallel with this surface. (see diagrambelow right). Incorrect Correct
Maxillary Canine 0 In 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 doesn’t allow enough film to register the apex of the canine. By rotating the film into a diagonal placement, this won’t be a problem.Film can’t be placedfar enough into the diagonal placementmouth (narrow arch)
Maxillary PremolarUsing the index finger of the opposite hand,position the film properly and align the beamvertically and horizontally. Center the x-ray beamon the film.
Maxillary MolarUsing the index finger of the opposite hand,position the film properly and align the beamvertically and horizontally. Center the x-ray beamon the film.
Sometimes it is difficult toget the film far enoughback to cover the thirdmolar region due togagging or anatomy, andall of the third molar willnot be seen on the film(see diagram at left). Byrotating the tubehead sothat the beam is directedmore anteriorly (diagramat right), the third molar isprojected on to the film,giving us the neededinformation. Note,however, the increase inoverlap that results.
Mandibular IncisorsUsing the index finger of either hand, position thefilm properly and align the PID as discussed earlier.All four incisors appear on the film.
Mandibular CanineUsing the index finger of the opposite hand,position the film properly and align the beamvertically and horizontally. Center the x-ray beamon the film. # 22 is shown on the film below.
Mandibular PremolarUsing the index finger of the opposite hand,position the film properly and align the beamvertically and horizontally. Center the x-ray beamon the film.
Mandibular MolarUsing the index finger of the opposite hand,position the film properly and align the beamvertically and horizontally. Center the x-ray beamon the film. This film clearly shows all of the thirdmolar roots (# 17).
Adult full-mouth series, BisectingTechnique0 Using 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). All # 2 filmsR L
Anterior FirstWhen taking films on a patient, you should alwaysstart with the anterior films. If you are doing a fullseries, start with the maxillary canine film andthen finish all the anterior films, both maxillaryand mandibular. Then complete the posteriorfilms, starting with the premolar, then molar, ineach quadrant. When doing only a few films on apatient, start with the most anterior film and workyour way back in the mouth. This sequence oftaking films allows the patient to get used to theprocedure with a minimum of discomfort andhelps to avoid stimulation of the gag reflex.
Bisecting Angle Technique ErrorsThe following slides identify some of the mostcommon errors seen when using the bisectingangle technique.
ElongationIf you have too little vertical angulation, as in thediagram below, the image will be elongated orstretched out on the film. The angle the x-ray beamforms with the bisecting line is less than 90°. The redlines on the film represent the actual length of tooth #9; the black arrow points to the end of the “image” ofthe tooth. long axis of tooth bisecting line x-ray beam film bisecting line
ForeshorteningIf you have too much vertical angulation, as in thediagram below, the image will be foreshortened orreduced in length. The angle the x-ray beam formswith the bisecting line is greater than 90°. The red lineson the film represent the actual length of tooth # 9; theblack arrow points to the end of the “image” of thetooth. long axis of tooth bisecting line film
When using the bisecting angle technique with finger retention,the incisal edge /occlusal surface will always be in contact withthe film. This part of the tooth will always appear at the samespot on the film no matter what the angulation is. However, theapex of the teeth, being farther away from the film, will beimaged at different positions depending on the verticalangulation. The arrows in the diagram below identify where theapex of the tooth will be at different angulations; e. g., at >90°the apex will be imaged lower on the film, shortening the overallimage. Remember, a 90° angle between the x-ray beam and thebisecting line is the ideal alignment. >90º = foreshortening <90º = elongation image lengths
Improper Film PlacementAs with the paralleling technique, improper filmplacement is one of the most common errorsseen in the bisecting angle technique. In themolar film below, the film was placed too farforward, cutting off the distal root of the secondmolar and failing to image the third molar region. AP Mandibular molar periapical
Film Placement 0With finger retention, it may be hard to keep thefilm from rotating around the end of the finger asit presses the film against the teeth. This mayresult in a tipped film as seen below. Notice thetip of the second molar is not visible, resulting inthe need for a retake. (The teeth are alsoelongated; is this too little or too much verticalangulation?) Too little (not enough) vertical angulation
Film Placement 0It is important to place the film so that ¼” of filmextends beyond the incisal edge (anterior) orocclusal surface (posterior). However, if toomuch film extends beyond, the roots of theteeth will usually not appear on the film, as seenbelow.
Film Placement 0When placing the film using finger retention, it isimportant to make sure that finger pressure is appliedwhere the film is supported by tooth structure, ideallyat the junction of the crown of the tooth with thegingiva. If the film is not supported, film bending willresult. In the canine film below, the canine root“bends” off of the film. What other error is seen onthis film?Film not centeredon canine Canine periapical
Reversed film 0If the colored portion of the film faces the teethbeing radiographed, the lead foil in the film packetwill be between the teeth and the film. This resultsin the pattern stamped on the lead foil appearingon the film (see right side of film below). The filmwill also be lighter than the other films taken at thesame time. What other situations could result in afilm that is too light? Underexposure or processing error (e.g., developer solution too cold)
Cone-cuttingIf the x-ray tubehead is not positioned properly, the x-raybeam may not cover the entire film. This is known asconecutting, which results in a clear (white) area on thefilm where the silver halide crystals were not exposed tox-rays (see film below). In the diagram below left, thedotted circle represents where the x-ray beam shouldhave been positioned; the solid circle shows the actualposition of the x-ray beam (too posterior).
Overlap (incorrect horizontal angulation)Overlap is the superimposition of part of one toothwith part of the adjacent tooth (dotted circles belowleft). The red arrow represents the direction of the x-ray beam; the x-ray beam should be perpendicular tothe dotted line below. (See discussion of horizontalangulation on earlier slide).
Film “Softening”If you try to make the film more comfortable for thepatient by “softening” the corners or edges, theemulsion of the film will be affected, resulting inblack lines (see film below). With finger retention,film placement is usually not very uncomfortable;therefore, film softening is not needed.
Double exposureWhen taking films, you should always place each film ina container or paper bag immediately after it is exposed.Exposed films should never be placed in the same areawhere unexposed films are located. If you inadvertentlypick up an exposed film and use it for another exposure,the result is a double exposure. Two different areas ofthe mouth are superimposed, making the imagesworthless. This is the worst error because two films haveto be retaken. 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 0 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 filmwas extending above theocclusal surface on thispremolar periapical film,cutting off the top part ofthe crowns of the teeth.
Thyroid collarWith finger retention of films in the mandibular arch, thetubehead may be positioned so that the x-ray beampasses through part of the thyroid collar (see photobelow). This lead in the thyroid collar prevents x-raysfrom passing through, resulting in an unexposed, cleararea on the film as seen below right. PI D
Incorrect Exposure FactorsThe standard exposure settings on your x-ray machinewill be acceptable for the majority of your patients.However, if you are taking radiographs on a child youwould need to decrease the settings. If your patient isvery large, you would need to increase the settings.Underexposure results when the exposure factors areset too low for the patient size. Overexposure resultswhen the exposure factors are set too high. underexposure correct exposure overexposure
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 Technique Head PositionMaxillary film: the maxillary arch is parallel to thefloor; the midsagittal plane is perpendicular tothe floor.Mandibular film: the head is tipped back so thatthe mandibular arch is as close to perpendicularto the floor as possible.
Occlusal Technique Film positionThe film is placed so that the all-white side ofthe film (# 4 for adults, # 2 for children) faces thearch being radiographed. The film is usuallyplaced with the long axis side-to-side, but this isnot critical. The film is large enough to normallycover the entire arch, but make sure it coversthe area of interest. Position the film as far backin the mouth as possible and the patient gentlybites on it to keep it in place.
Occlusal Technique X-ray Beam PositionThere are three types of occlusal films (to bediscussed on the following slides): “Normal” Maxillary “True” Maxillary MandibularFor all three of these, the x-ray beam is centered onthe area of interest. Because of the curved beam,the corners of the film that sticks out of the mouthare often not exposed, resulting in slight conecuts.This is not an error, since these areas contain noneeded information.
Normal Maxillary OcclusalThe Normal Maxillary Occlusal film is the mostcommon occlusal film taken in the maxillary arch.The vertical angulation is set at 65 degrees.Because of this angle, structures located towardthe back of the mouth may be projected off theback edge of the film and not be imaged. 65 degrees
True Maxillary OcclusalThe True Maxillary Occlusal film is not often usedbecause of the much higher exposure time needed toproperly expose the film. (Because the verticalangulation is 90 degrees, the x-ray beam passesthrough the very dense frontal bone; this is the reasonfor the increased exposure). Structures located fartherback in the mouth are more likely to be imaged on thisfilm. 90 degrees
Mandibular OcclusalWith the head tipped back as much as possible,the x-ray beam is directed at a 90 degree angle tothe film. Bony expansions of the mandible as wellas abnormalities or pathology in the floor of themouth can be imaged with this film. 90 degrees
Occlusal Technique Exposure SettingsThe exposure times for the “normal” maxillary andmandibular occlusal films are the same as for aperiapical or bitewing film of comparable filmspeed. For the “true” maxillary occlusal film, theexposure time is four times as long, allowingenough x-rays to pass through the frontal boneand properly expose the film.
Normal Maxillary OcclusalImpacted canine Supernumerary tooth Pedo anterior
Modified Bisecting OcclusalIf a patient has difficulty opening the mouth due totrismus, an occlusal film can be used to provide areasonable image of the teeth. The film is centered onthe side of interest with the long axis front to back. Thebeam is aligned using the Bisecting Angle technique.The images will be greatly distorted, but may providethe necessary information.
0This concludes the section on BisectingAngle and Occlusal Techniques.Additional self-study modules are availableat: http://dent.osu.edu/radiology/resources.htmIf you have any questions, you may e-mailme at email@example.com.Robert M. Jaynes, DDS, MSDirector, Radiology GroupCollege of DentistryOhio State University