Bisecting technique Flashcards
basic concepts of bisecting technique
- another method than can be used to expose periapical films
- NO RINN KIT
- only use film holder
- must limit distortion of film
- use bisecting angles b/w film and tooth to direct the central ray
why do we use the bisecting technique?
- must use technique when film can not be held parallel to the tooth
- if no RINN kit available
- if film extremely uncomfortable and/or causing gagging with RINN kit
terminology for bisecting technique
- angle
- bisect
- triangle
- triangle, equilateral
- triangle, right
- triangles, congruent
- hypotenuse
- isometry
- long axis of the tooth
what is the rule of isometry?
- two triangles are equal if they have 2 equal angles and share a common side
how is the rule of isometry applied to the bisecting technique?
- the central ray is not perpendicular with the film, but the angle between the film and the tooth is bisected (imaginary)
- two resultant triangles are right angles and congruent
why is the rule of isometry so important in the bisecting technique?
- the radiographic image will turn out accurate and diagnostic
- when done properly, a tooth and its radiographic image will be equal in length when 2 equal triangles are formed that share a common side (imaginary bisector)
what is a film holder?
- a device used to position an intraoral film in the mouth
- recommended because they eliminate the need for the patient to stabilize the film
- film holder reduce the patient exposure to radiation
what is the finger-holding technique?
- patient’s finger or thumb is used to stabilize the periapical film
NOT RECOMMENDED - film holders reduce the patient’s exposure to radiation
common film holders:
A - Rinn BAI
B - Stabe bite blocks
C - Eezee Grip (Snap-A-Ray)
D - Foam Tabs
what size films are used for the bisecting technique and what part of the mouth are they used for?
size 1 and 2 film
- anterior: size 1, vertical placement
- posterior: size 2, horizontal placement
what is angulation?
- describes the alignment of the central ray of the x-ray beam in the horizontal and vertical planes
- angulation can be varied by moving the PID in either a horizontal or a vertical direction
what is horizontal angulation? what is correct and incorrect horizontal angulation?
- the positioning of the tubehead and direction of the horizontal or side to side plane
- correct horizontal angulation: the central ray is directed perpendicular to the curvature of the arch and through the contact areas of teeth
- incorrect horizontal angulation: overlapped contact areas (cannot be used to examine the interproximal areas of the teeth)
what is vertical angulation?
- the positioning of the PID in a vertical or up and down plane
- in paralleling: directed at film at 90 degrees
- in bisecting: directed at imaginary bisecting angle (not the film). the central ray is directed perpendicular to the imaginary bisector (90 degrees). is measured in degrees and is registered on the outside of the tubehead
- correct vertical angulation results in image that is the same length as the tooth
what is positive vertical angulation?
when the tubehead is too high up
what is negative angulation?
when the tubehead is too low
what will result from incorrect vertical angulation in the positive. angulation?
foreshortened images
- teeth appear shortened
- results from excessive vertical angulation
what will result from incorrect vertical angulation in the negative angulation?
elongated images
- teeth appear too long
- results from insufficient vertical angulation
rules for bisecting technique: film placement and film position
- film placement: same as parallel
- film position: along the lingual of the tooth - as close as possible. Dot - 1/8 inch beyond occlusal plane
- vertical angulation: central beam perpendicular to bisecting angle
- horizontal angulation: open contacts - central ray of the x-ray beam must be directed through the contact areas between the teeth
step-by-step procedures
- patient preparation
- equipment preparation
- exposure sequence for film placements
- film placement
patient preparation
- infection control procedures
- preparation of treatment area and supplies
- patient is seated
- patient is prepared
patient preparation for bisecting technique:
- explain the radiographic procedure
- position the patient in the cair
- adjust the headrest
- place and secure the lead apron with thyroid collar
- remove all objects from the patient’s mouth
equipment preparation
- set exposure factors
- open the sterilized package containing the film holder if film holders are used
exposure sequence for film placements in anterior teeth
anterior exposure sequence:
- begin with mx right canine tooth, expose all mx anterior teeth, end w mx left canine
- move to mn arch, begin w mn left canine, expose all the mn anterior teeth, end w mn right canine
exposure sequence for film placements in posterior teeth
posterior exposure sequence
- begin w mx right quadrant
- move to mn right quadrant
- move to mx left quadrant
- finish w mn left quadrant
- in each quadrant, expose the premolar film first then the molar film
what is film placement?
the specific area where the film must be positioned before exposure
- dictated by the teeth and surrounding structures that must be included on the resultant radiograph
advantages of the bisecting technique:
- can be used without a film holder
- reduce gagging and discomfort
disadvantages of the bisecting technique:
- image distortion
- angulation problems
- unnecessary exposure (if pt finger is used, also increase retakes)
