Bisecting Technique Flashcards
Bisection of the angle
Receptor is no longer parallel to the teeth as in PT
Based on the theory of the equilateral triangle (two triangles have a common side, but are equal triangles)
General rule of BAT
The CR is directed perpendicular to an imaginary line which bisects the long axis of the tooth and the receptor (angle bisector)
Advantages of BAT
More comfortable
use of short cone- less radiation
Disadvantages of BAT
More distortion
Difficult technique
Placement of the receptor tube head
Place receptor so it is centered over the area of interest or specific tooth
Vertical placement of the receptor is approx 1/8-1/4” above or below the occlusal line
Vertical angulation of tube head
Occlusal plane parallel to the floor Angulations above occlusal= + Angulations below occlusal= - Angulation will vary w/ eat patient If receptor holder is used, angulation will decrease
Angulation errors in BAT
Too little V. angulation= elongation
Too much V. angulation= foreshortening
Advantages of a bite block holder
Patients hand no exposed to radiation
When patient occludes on bite block, less of a chance of receptor movement
Vertical angulation decreases b/c there is less of an angle
Disadvantages of bite block holder
W/ some patients it is difficult to position
Increase in discomfort
What is the holder of choice for bisecting?
Snap-a-ray
Snap-a-ray technique
Place receptor in holder
Have patient occlude LIGHTLY
Anterior- have pt. hold holder w/ slight pressure up or down)
Posterior- Patient occludes on bite block
Minimum # of exposures in a FMS
14 to survey both arches
7max CCP=9max
7man CCP= 7man
Bite-wing should accompany PA (not included in 14)
Positioning for cuspid shots
Place CR btw the contact point of the cuspid and 1st bicuspid to prevent overlapping
Alternatives- oblique receptor placement/cross arch receptor placement
Oblique receptor placement reasons and positioning
Reason: difficulty placing receptor high enough due to low palate
Positioning: use diamond shape, positioning edge of receptor below the occlusal line not more than 1/8”
Cross arch receptor placement reason/positioning
Reason: Arch too narrow for standard or oblique receptor placement
Positioning: Pace receptor on the occlusal surface of teeth in vertical alignment with cuspid
Angulation will increase
Placement rules for occlusal expoures
For maxillary, occlusal plane parallel to floor
For mandibular, pt. is reclined
For topographical, rules of BAT followed
Cross sectional exposures
CR is directed toward area of interest and perpendicular to receptor
Result= circular or eliptical appearance of teeth
Steps for maxillary topographical
Anterior exposure of the maxillary arch
- max arch parallel to floor
- no.2 receptor or occlusal film in the mouth
- cone placed above the bridge of nose
- CR is directed in center
- Bisect the angle
Steps for mandibular topographical
Anterior exposure of mandibular arch
- Plane of occlusion, head tilted 45 degree angle to plane of floor
- No. 2 receptor
- center of cone placed at the tip of patients chin
- bisect the angle
Maxillary crossectional
- occlusal plane parallel to the floor
- CR perpendicular to film
Mandibular crossectional
- Pt. is totally reclined
- No. 2 receptor or occlusal film
- cone placed 1” posterior to tip of chin
- tube head angled at 0 degrees, CR at right angle to receptor
Indications for size 2 anterior occlusals in place of PA’s
to see unerupted toot position
Indication for size 2, 4 crossectional exposures
Impacted or supernumerary teeth Fractures Foreign bodies Cyst Odontomas Osteomyelitis Malignancies etc.
Panorex
Excellent supplement
View of overall jaw development and development of permanent teeth
