Unit three 2.pptx

UNIT 3 PARALLELING TECHNIQUE OBJ. 1 DESCRIBE THE BASIC PRINCIPLES OF THE PARALLELING RADIOGRAPHIC TECHNIQUE  BASIC PRINCIPLES The film is placed parallel to the long axis of the teeth being radiographed Central ray is directed at right angles to both the long axis of...

UNIT 3 PARALLELING TECHNIQUE OBJ. 1 DESCRIBE THE BASIC PRINCIPLES OF THE PARALLELING RADIOGRAPHIC TECHNIQUE  BASIC PRINCIPLES The film is placed parallel to the long axis of the teeth being radiographed Central ray is directed at right angles to both the long axis of the tooth and the film Film holding device must be used to keep the film parallel with the long axis of the tooth 1 TO ACHIEVE PARALLELISM: Film must be placed away from the tooth, toward the middle of the oral cavity Shape of the oral cavity (i.e. curvature of the palate) means that the object film distance must be increased in order to keep the film and tooth parallel. 1  MAGNIFICATION ↑ OFD = ↑ ↑ TFD = ↓ Magnification Magnification 1  OBJECT-FILM-BEAM ALIGNMENT Film parallel to Beam at 90º = tooth = ↓ ↓ distortion distortion 1 FILM HOLDING DEVICE  XCP (Extension Cone Paralleling)  Most common type  Developed specifically for the paralleling technique FILM HOLDING DEVICE  Precision Film Holder  Include metal collimating shields that restrict the size of the beam to the size of the film 2  FILM HOLDING  EEZEE Grip Film Holder DEVICE  Formally known as the Snap-A-Ray 2 FILM HOLDING DEVICE  Stabe Bite Block  Disposable styrofoam 2  FILM HOLDING DEVICE  Hemostat – used with a rubber bite block  Client bites on bite block 2 RINN - include: Plastic bite blocks, plastic aiming rings, and arm positioning system OBJ. 3. IDENTIFY AND DESCRIBE THE USE OF XCP INSTRUMENTS Most common type Developed to simplify paralleling procedures and minimize distortion Simple to position – adaptable and client can be in any position.  PARALLELING : ANTERIOR SIZE 1, RECEPTOR SIZE FOR PLACEMENT HIGH IN THE PALATE OR FLOOR OF THE MOUTH FOR THE ANTERIOR TEETH PARALLELING POSTERIOR  posterior uses a size 2 receptor in a horizontal position  film must be placed to cover the prescribed area of teeth to be examined and parallel film must be away from the teeth and towards the midline Central ray is perpendicular to film and long axis horizontal angulation – the central ray is directed through the contacts of the teeth PID must be centered to cover entire film and avoid cone cut AKA collimator cut off RULES FOR USING XCP INSTRUMENTS 1. Two points of contact - palate/floor of mouth and teeth – client should bite down after two points of contact have been established 2. Use length of bite block to get film parallel 3. align PID  See page 157-158 for setting up the XCP device for anterior and posterior placements  Establish an exposure sequence to follow to best utilize time and avoid errors. SETTING UP…. Always start with anteriors! Anterior set up – arm has two bends in it, straight aiming ring and vertical bite block  Posterior set up – arm has two bends, off-set aiming ring must align with bite block centred, horizontal bite block  OBJ. 4 COMPARE THE ADVANTAGES AND DISADVANTAGES OF THE PARALLELING TECHNIQUE Advantages: Direction of vertical angle – no x-rays are directed towards the thyroid gland or the lens of the eye Accuracy – produces an image with minimal dimensional distortion and maximum detail Simplicity – simple to learn and easy to do when using XCP instruments Comparison – when a series of radiographs is needed, comparison radiographs are more reliable 4 DISADVANTAGES Film placement – film holding device must be used and this can be challenging for some clients Discomfort – film holding device or edge of film may impinge on oral tissues (Long PID – must be used to compensate for OFD) 4  OBJ. 5 DESCRIBE FILM SIZES AND PLACEMENT OF THE Most commonly size #1 film is used for PARALLELING TECHNIQUE the anterior PA’s and size #2 is used for FOR the posterior PA’s INDIVIDUAL RADIOGRAPHS AND FMS 5 FMS Anterior-8 (4 max and 4 mand) Posterior (premolars then molars) For the premolar exposure, this must include the distal of the canine and the molar film must show the distal contact of the second premolar MAXILLARY CENTRAL AND LATERAL MAXILLARY CANINE MAXILLARY PREMOLAR MAXILLARY MOLAR MANDIBULAR CENTRAL AND LATERAL MANDIBULAR CANINE MANDIBULAR PREMOLAR MANDIBULAR MOLAR OBJ. 6 Most problems are a result of poor film SUMMARIZE placement (too close=increase vertical angulation=foreshortening) THE MOST CRITICAL Remember ‘dot goes in the slot’ PARALLELING For PA’s, crowns, roots including apices, RADIOGRAPH contact areas and surrounding bone must be IC ERRORS in view AND HOW TO White side of the film must face the teeth CORRECT THEM. Make sure the bite block is stabilized by the teeth and not the lips PRINCIPLES BEHIND PARALLELING TECHNIQUE 2. 1. Advantages Relationship and of PID, film Disadvanta and tooth ges  A LITTLE REVIEW BEFORE FINISHING UNIT THREE! WHAT CAUSED THIS?  FILM PACKET REVERSAL 6 WHAT CAUSED THIS? 6 FAULTY FILM PLACEMENT 6 WHAT IS WRONG WITH THIS RADIOGRAPH ? 6 MISSING APICES 6 WHAT IS WRONG WITH THIS FILM? 6 FAULTY DOT PLACEMENT 6 WHAT IS WRONG WITH THIS FILM? 6 DOUBLE EXPOSURE 6 WHAT HAPPENED HERE? 6 CLIENT MOVEMENT – BLURRED IMAGE 6 WHAT IS WRONG WITH THIS RADIOGRAPH? 6  FORESHORTENING 6 WHAT IS WRONG WITH THIS RADIOGRAPH 6 ELONGATION 6  WHAT CAUSED THIS? 6 BENT FILM - DISTORTION 6  EYE GLASSES 6 6  PARTIAL DENTURE 6 6 FULL UPPER DENTURE 6  What happens to the radiographic image when the object- film distance is increased?  Image magnification, loss of definition  How does the paralleling technique offset this problem?  Increase the target film distance. Longer cone or more inset tungsten target in the tube head.  What piece of equipment is required to hold the film parallel to the long axis of the tooth in the paralleling technique?  Use of a film holder.  What do the letters X, C, and P stand for?  X = extension; C = cone (PID); P = paralleling OBJ. 7  Shallow palate (low palatal vault) MODIFICATIONS IN  Lack of parallelism occurs due to THE PARALLELING the tilting of the bite block TECHNIQUE THAT  Generally acceptable if it doesn’t MAY BE USED TO exceed 20 degrees but if it does you need to modify by using: ACCOMMODATE VARIATIONS IN ANATOMIC CONDITIONS SHALLOW PALATE  May be difficult to get the film parallel to the long axis of the tooth  May use cotton rolls, but this will reduce periapical coverage 7 SHALLOW PALATE  Increasing vertical angulation to increase periapical coverage for clients with a shallow palate  Increase vertical angle by 5- 15º 7 BONY GROWTHS MAXILLARY TORUS – FILM PLACED ON THE FAR SIDE OF THE TORUS BONY GROWTHS  Mandibular tori – film placed between torus and the tongue 7 NEXT CLASS – NOT NEXT WEEK AS IT’S A HOLIDAY! 1 2 3 Review Chapter Complete Quiz Study for test #1!! 17 #2: Will open Test #1 will take place in today at 4pm class in Week 5 and be open until May 23rd Review posted on DC connect