Flashcards in Other intraoral techniques Deck (14):
what is the bisecting angle technique
Central ray is projected perpendicular to imaginary line that bisects long axis of tooth and plane of image receptor.
This technique was the one first used in intraoral dental radiography. It has been superseded by the paralleling technique, but is still of some value in certain instances; e.g. for periapicals taken during endodontic treatment, for regions of the mouth where the patient is unable to tolerate the bite block. This technique is also often useful for periapical radiography in children.
In the bisecting angle method, the intraoral image sensor is placed as close as possible to the tooth being imaged. This often means that the long axis of the tooth does not correspond to the long axis of the image receptor because of the intraoral anatomy. Projecting the central ray perpendicular to either the long axis of the tooth or the image receptor will result in a distorted image. A "compromised" approach is therefore used wherein the central ray is directed perpendicular to a line which bisects the angle formed by the long axes of the tooth and image sensor.
what are the principles of the bisecting angle technique?
1. Shortest object-film distance is used.
2. Isometric triangles are formed when central ray is directed correctly.
The two triangles formed by the intersecting long axes of the tooth and the plane of the image receptor with the bisecting line are isometric -- this means that the length of the image on the image receptor will be the same length as that of the tooth if the central ray is directed perfectly perpendicularly to the bisecting line.
With bisecting angle technique, in many parts of the mouth, image receptor is touching the crown, but is some distance from the root and root apex.
Therefore, if central ray not directed optimally, dimensional distortion of coronal or radicular portions of image will occur (see “Errors and Pitfalls” lecture).
what are the advantages of the bisecting angle technique?
1. Can be used in almost any area of the mouth with minimal difficulty.
2. A special holder is not absolutely necessary to obtain a periapical using the bisecting angle technique.
In some cases, the image receptor can be held in place using forceps, a hemostat or other instruments, and if nothing suitable is available, the patient can also use his/her fingers. Whenever possible, though, a holder should be used, as it usually allows more stable and accurate positioning.
what are the disadvantages of the bisecting angle technique ?
1. Difficulty in determining position of “bisecting line”.
2. Distortion and non-uniform magnification (image receptor is not the same distance from all portions of tooth).
3. For maxillary molar periapicals, the
zygomatic process is almost always projected over root apices (although this sometimes occurs with paralleling technique, too).
what is long cone versus short cone?
1. Bisecting Angle Technique
- short OR long cone can be used
2. Paralleling Technique
- long cone (long source-receptor distance) is
- use of short cone will theoretically result in
slight magnification and reduced definition of image (see “Rule of Accurate Shadow Casting” in lecture 7)
Paralleling technique sometimes referred to as “long cone ” technique, and bisecting angle technique sometimes referred to as “short cone” technique.
"Long Cone" versus "Short Cone"
For the paralleling technique, a “long cone” (i.e. a 16 inch distance between the x ray source and the image receptor) must be used in order for the principles of accurate shadow casting to apply. Using a short cone (8 inch source-image receptor distance) with the paralleling technique is NOT RECOMMENDED.
The bisecting angle technique is sometimes referred to as the "short cone" method, but either a short or long cone can be used with it.
what about bitewing radiographs, and what are the 2 purposes?
The bitewing radiograph is arguably one of the most commonly taken, if not THE most commonly taken, radiographs taken in the world. Although there are such radiographic views as anterior bitewings, these are seldom used. The term “bitewing” usually refers to bitewing views of the posterior teeth.
The purpose of bitewing radiography is to image:
1) the interproximal areas of the teeth; and
2) the crests of the alveolar processes of the maxillae and mandible.
Therefore, the interproximal contacts of the teeth should be clearly seen and unobstructed by overlapping, and the crest of the alveolar process must be seen in its entirety.
For patients with substantial loss of bone as a result of periodontal disease, the image receptor may be re- oriented 90°, and a so-called, vertical bitewing radiograph can be made.
In our clinic, students routinely use Rinn XCP alignment devices for posterior bitewing images. These will be taught to you in the lab.
how do you do a bitewing?
Patient’s occlusal plane parallel to floor.
The central ray is directed at 0°, or slightly downwards, at the
middle of the bitewing tab (arrow).
“Front face” of cone/PID parallel to line drawn tangentially
￼across buccal surfaces of posterior teeth.
what are the purposes of occlusal radiographs?
1. To provide a more extensive view of the maxilla or mandible than periapicals or bitewings allow.
2. To obtain another perspective of the jawbone at 90° to periapical or panoramic projections.
a. To determine the effect of pathologic lesions on the buccal and lingual cortices of the mandible.
b. To determine the buccolingual extent of pathologic conditions where there is swelling of the jawbone.
c. Localization of foreign bodies, unerupted teeth, retained roots, salivary calculi, etc.
d. Investigation of a buccal or lingual periosteal response to inflammation or other pathoses
in the mandible.
what are the four occlusal projections used?
Maxillary Standard Occlusal
Mandibular Anterior Occlusal
Mandibular Standard Occlusal
how is the maxillary standard occlusal view carried out/
-Occlusal plane parallel to floor
-Active side of image receptor (e.g. phosphor side of size 4 phosphor plate) faces up (against maxillary teeth)
-Long axis of image receptor placed mediolaterally
-Vertical angulation of PID is 65-70°
-Central ray directed through bridge of nose towards centre of/sensor/imaging plate
how is the mandibular anterior occlusal carried out?
-Tube side of image receptor against mandibular teeth
-Occlusal plane tipped back 55°
-Vertical angulation of PID is 0°
-Central ray directed through point of chin towards centre of image receptor (note that this is basically a type of bisecting angle view)
mandibular standard and mandibular anterior occlusals are basically variations of what technique?
"bisecting angle" technique
how is thhe mandibular standard occlusal carried out?
-Tube side of image receptor against mandibular teeth
-Occlusal plane tipped back as far as possible and measured; negative angulation "added" to PID to yield total angulation of 100°
-Central ray directed approximately 1" lingual to point of chin towards centre of film/imaging plate (CR is approximately parallel to the long axes of the mandibular incisors)