paralleling technique

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  • 1. The following slides describe the Paralleling Technique.0 Paralleling Technique In navigating through the slides, you should click on the left mouse button when you see the mouse holding an x-ray tubehead or you are done reading a slide. Hitting Enter or Page Down will also work. To go back to the previous slide, hit backspace or page up.

2. Patient Preparation Prior to starting to take films, the patient must be positioned properly.Seat the patientand ask them toremovetheirglasses and any removable appliances .Adjust the headrestto support the head while taking films.Raise or lower the chairto a comfortable height for the operator.Place the lead apron and thyroid collaron the patient. You are now ready to begin taking films. It is a good idea toinform the patientabout the number of films you will be taking so they know what to expect. 3. Film/tooth/ring all parallel X-ray beam perpendicular to tooth/film X-ray beam In theparalleling technique , the film is placed in the mouth so that the long axis of the film is parallel with the long axis of the teeth being radiographed. A paralleling instrument with an aiming ring is normally used to orient the film, teeth and ring in a parallel relationship. When the x-ray beam is aligned with the ring, the x-ray beam will be perpendicular (right angle) to the teeth and the film. 4. Paralleling Technique (Advantages) There are two techniques for taking periapical films, the paralleling and the bisecting angle techniques. When comparing the two techniques, the advantages of the paralleling technique are: 1.Better dimensional accuracy : the parallelingtechnique results in less distortion of the image ofthe teeth. (The shape of the teeth and therelationship of the teeth to surrounding structuresis more accurate).2. When using the paralleling instrument with theaiming ring, thealignment of the x-ray beam issimplified . (continued next slide) 5. Paralleling Technique (Advantages) 3. It iseasier to standardize films . Because you areusing the positioning instrument, it is easier toposition the film in approximately the sameposition at different appointments. This can behelpful if you are trying to compare theappearance of a periapical lesion from one visitto the next. 4.Head position is not as critical . Because of theparalleling instrument, with its aiming ring, it iseasy to properly align the x-ray beam no matterhow the head is positioned. 6. When the long axis of the film is parallel with the long axis of the tooth, the image of the tooth on the film looks the same as the tooth itself (no distortion). The image will be slightly larger than the actual tooth (magnification), but the shape is the same. 0 7. Paralleling Technique (Disadvantages) When comparing the paralleling and bisecting angle techniques, the paralleling technique is: 1.Less comfortable . Because the film isusually more upright when using theparalleling technique, it impinges more onthe palate or floor of the mouth, thus makingit more uncomfortable. 2.More limitedby the anatomy of the patientsmouth. A shallow palate or floor of the mouthmakes it harder to position the film using theparalleling technique. 8. correct incorrect 0 Paralleling Film Placement As mentioned previously, the film is placed in the mouth so that thelong axis of the film is parallel with the long axis of the teeth . Since all teeth are inclined toward the middle of the head (not straight up and down), the film will be slightly angled in the mouth (see below left). If the film is maintained in an upright position (below right), the patient will not be able to close on the biteblock and the film will not be parallel. 9. To facilitate film placement, the film may be tipped up to 20 degrees beyond parallel. 0 Paralleling Film Placement 10. As a result, the film must be positioned away from the teeth (farther back in the mouth) to achieve parallelism. Because the palate and floor of the mouth are shallower as you approach the lingual of the teeth, the film often cannot be positioned properly close to the teeth. 0 Paralleling Film Placement 11. Because the film is farther from the teeth, there will be increased magnification (larger size) and decreased sharpness (less detail). To compensate for this, the target-film distance should be increased (the target is where the x-rays are produced). 0 Target 16 Target 8 size of image at 8 target-film distance size of image at 16 target-film distance 12. Long PIDShort PID Recessed target Medium PID Recessed target 0 The target-film distance is increased by using a longer PID, using a machine with a recessed target (opposite side of the tubehead from the PID) or a combination. The medium PID with a recessed target is a good compromise. The disadvantage to increasing the PID length is that the exposure time must be increased. If you change from an 8 target-film distance to a 16 target-film distance (double the distance) the exposure time will be four times as much (see Inverse Square Law). 13. Best OK OK Paralleling Technique Head Position As mentioned previously, head position is not as important when using the paralleling technique. However, in general it is best to position the head in an upright position so that the maxillary arch is parallel to the floor. 14. #1 anterior posterior Paralleling Technique Film Selection for Adults The # 1 size film is used for anterior periapical films using the paralleling technique. The long axis of the film is vertical. For posterior films, # 2 size film is used with the long axis horizontal. #2 15. #0 #0 anterior posterior Paralleling Technique Film Selection for Children For children with small mouths, the # 0 size film is used for both anterior and posterior periapical films. However, if the childs mouth is large enough to reasonably accommodate the larger size films (# 1 anterior, # 2 posterior), and the child is cooperative, they should be used. 16. Rinn Paralleling Instruments ANTERIOR POSTERIOR The Rinn paralleling instruments are used at the Ohio State University College of Dentistry. They are color-coded, with yellow being the posterior instrument and blue being the anterior instrument. The metal bar connects to the side of the biteblock and the ring slides on the bar. 17. front back The film is placed in the biteblock so that the all-white side of the film packet faces the teeth and, by extension, the ring. (The colored portion of the film is against the back support of the biteblock). When you look down through the ring, you should see the all-white side of the film packet centered in the opening. opposite side toward tube 18. Anterior Periapical long axis vertical 0 slot For the anterior periapical, the # 1 size film is placed vertically in the biteblock. The film is rotated so the identifying black dot is down; this end of the film goes into the slot of the biteblock (dot-in-the-slot). Push the film back against the biteblock support and slide it down into the slot. colored side of film white side of film white side facing teeth/ringF E Speed 1-FilmINSIGHT Dental Film Kodak dot 19. Posterior Periapical long axis horizontal slot 0 For the posterior periapical, the # 2 size film is placed horizontally in the biteblock. The film is rotated so the identifying dot (faint embossed circle) is down; this side of the film goes into the slot of the biteblock (dot-in-the-slot). Push the film back against the biteblock support and slide it down into the slot. colored side of film white side of film white side facing teeth/ring OPPOSITE SIDE TOWARD TUBE KODAK INSIGHT 1- FILM F E dot 20. For all periapical films, the teeth being radiographed must be in contact with the biteblock to avoid not having the apices of the teeth on the film (see errors section of slide show). Make sure patient doesnt just close lips tight around biteblock; have them part their lips so you can confirm the contact. correct incorrect General Technique Guidelines 21. As shown above, cotton rolls may be used in any area of the mouth to help support the biteblock, especially if an edentulous region or uneven teeth oppose the teeth being radiographed. Using a cotton roll alsomakes it more comfortable for the patient to bite in some situations. The cotton roll should be placed against the arch opposite the one being radiographed. General Technique Guidelines 22. General Technique Guidelines If a patient has a partial denture or a complete denture in one of the arches, the appliance can be used to help support the biteblock when the patient closes. This is normally preferable to using cotton rolls. Make sure that thedenture is only used in the arch opposite to the one being radiographed . Partial dentures can not be left in the arch being radiographed because the metal framework will be superimposed over the images of the teeth (see Errors). 23. After the patient is biting on the biteblock, and before aligning the PID, the ring needs to be moved closer to the patients face. While supporting the bar with the fingers of one hand, slide the ring down close to the face with the other hand.0 General Technique Guidelines 24. Always make sure the head is supported by the headrest before aligning the PID and exposing the films. General Technique Guidelines 25. The PID should be aligned with the ring so that the end of the PID is equidistant from the ring and within of the ring. The PID doesnt have to touch the ring and the placement doesnt have to be perfect. Dont spend excessive time making adjustments when aligning the PID. (Remember: the paralleling technique is not very comfortable and the patient wont appreciate any delays in exposing the film). Incorrect Incorrect Correct PID PID PID (not equidistant) (not close enough) General Technique Guidelines 26. Maxillary Central-lateral The film iscentered on the contact between the central and lateral incisors . Make sure themesial edge of the film crosses the midline slightly(into t