Bisecting angle vs paralleling technique /orthodontic courses by Indian dental academy

Seminar

Bisecting angle versus Paralleling Bisecting angle versus Paralleling techniquetechnique

INDIAN DENTAL ACADEMYLeader in continuing Dental Education

www.indiandentalacademy.com

Learning ObjectivesLearning Objectives

At the end of the session the learners should be able to-

Enumerate the basic principles of projection geometry.

Describe the bisecting angle and paralleling technique.

Describe advantages and disadvantages of bisecting angle and paralleling technique.


Contents

Ideal positioning requirements Principles of projection geometry Comparison between paralleling and

bisecting angle technique Conclusion


Ideal positioning requirement The tooth under the investigation and the film packet

should be in contact or, if not feasible, as close together as possible.

The tooth and film packet should be parallel to one another The film should be positioned with its long axis vetically for

incisors and canines, and horizontally for premolars and molars with sufficent film beyond the apices to record the apical tissues.

The X-ray tubehead should be positioned so that the beam meets the tooth and film at right angles in both horizontal and vertical planes.

The positioning should be reproducible.


Radiographic techniques The anatomy of the oral cavity does not always

allows these ideal positioning requirements to be satisfied.

In an attempt to overcome the problems, two techniques for periapical radiography have been developed.

- The paralleling technique - The bisected angle technique


PRINCIPLES OF PROJECTION GEOMETRY (SHADOW CASTING)

BASIC PRINCIPLES:- The focal spot (Source of radiation) should

be as small as possible.



The focal spot – Object distance should be as long as possible.



The Object – Film distance should be as small as possible.



The long axis of the object & the film planes should be parallel.



The X-Ray beam should strike the object & the film planes at right angles.


There should be no movement of the tube, film or patient during exposure.(Given by Mason & Lincoln)

PRINCIPLE OF PROJECTION GEOMETRY (SHADOW CASTING)


BISECTING ANGLE PARALLELINGTECHNIQUE TECHNIQUESynonyms - Short cone

technique Finger holding

technique

Synonyms - Long cone

technique. Right angle

technique. Extension

paralleling technique


BISECTING ANGLE PARALLELINGTECHNIQUE TECHNIQUE Based on geometric

principle CIESZYNSKI’S Rule of isometry - Two triangles are equal if they have two equal angles and share a common side.

Based on the fact that x-ray film is supported parallel to the long axis of the tooth being radiographed.


BISECTING ANGLE PARALLELINGTECHNIQUE TECHNIQUE Central ray is

perpendicular to imaginary bisector of angle formed by film & long axis of tooth.

Central ray of the x-ray beam is directed at right angles to both the tooth and the film.


BISECTING ANGLE PARALLELINGTECHNIQUE TECHNIQUE

Satisfies Rule 1 & 3 of shadow casting.

Size 2 film preferred.

Satisfies Rule 1, 2, 4 & 5 of shadow casting.

Size 1 film preferred anteriors and size 2 film for posteriors.


BISECTING ANGLE PARALLELINGTECHNIQUE TECHNIQUE Target -Film Distance is 6” – 8”

Target – FilmDistance is 16” – 18”


BISECTING ANGLE PARALLELINGTECHNIQUE TECHNIQUE Use of film holder

is not mandatory Rinn BAI Stable bite block Snap-A-Ray

Use of film holder is mandatory Rinn XCP Precision film

holders Grip film holder Hemostat with bite

block



Film touches tooth at crown portion. Thus, the crown film distance is less than apex film distance.

Film is parallel & away from tooth.


BISECTING ANGLE PARALLELINGTECHNIQUE TECHNIQUE Requires less

exposure Hence kvP is

reduced Divergent rays

used for image formation.

Requires more exposure

Hence kvP is increased

Parallel rays used for image formation.



Film placement easier.

Film placement difficult, so discomfort to the patient.



Patient can hold the film.

Patient cannot hold the film. Film holder mandatory.


BISECTING ANGLE PARALLELINGTECHNIQUE TECHNIQUE Film holders not

routinely used so vertical and horizontal angulations have to be adjusted.

Use of film holder with a beam alignment device eliminates the need to device vertical and horizontal angulations so distortions eliminated.



used routinely. So chances are less for impingement and causing discomfort.

Film holders used may impinge on oral tissue causing discomfort & gagging to the patient.



Distortion of the image.

Image is more or less anatomically accurate.


BISECTING ANGLE PARALLELINGTECHNIQUE TECHNIQUE Increased

elongation or foreshortening of image.

Image has same size & shape as that of object.


BISECTING ANGLE PARALLELINGTECHNIQUE TECHNIQUE Distortion of image

due to oblique exposure & bending of film due to incorrect digital pressure.

Film holders prevent such errors producing anatomically accurate image.



Incorrect horizontal angulations may lead to overlapping of the crowns and roots.

Less chances of incorrect horizontal angulations.


BISECTING ANGLE PARALLELINGTECHNIQUE TECHNIQUE More vertical

angulation. Less vertical

angulation.So maximum chances of overlapping of buccal and lingual cusps.


BISECTING ANGLE PARALLELINGTECHNIQUE TECHNIQUE Less tooth area

underneath the restoration is relevant due to more vertical angulation.

More tooth area underneath the restoration is relevant due to less vertical angulation.


BISECTING ANGLE PARALLELINGTECHNIQUE TECHNIQUE Difficult to visualize

the imaginary bisector and determine the vertical angulation and direct the central ray.

Central rays perpendicular to both film and long axis of tooth.


BISECTING ANGLE PARALLELINGTECHNIQUE TECHNIQUE Superimposition of

the shadow of the zygomatic arch on the teeth

Less vertical angulation causes minimum superimposition of zygomatic buttress of maxilla over the upper roots. Teeth apices & maxillary sinus better seen.



BISECTING ANGLE PARALLELINGTECHNIQUE TECHNIQUE Cone cut results

particularly if rectangular collimation used.

PID aims the X-ray beam accurately so there is no coning off or cone cutting.


BISECTING ANGLE PARALLELINGTECHNIQUE TECHNIQUE Shadows of the

alveolar bone tend to fill the interproximal spaces. The loss of bone or pathology is misinterpreted.

Alveolar crest seen in true relationship to the teeth.


BISECTING ANGLE PARALLELINGTECHNIQUE TECHNIQUE More effective

when palatal vault is deep or shallow, bony overgrowth or children with underdeveloped jaws.

Difficult in shallow palatal vault, small mouth, children, handicapped patients.



used making it comparatively easier to carry Endodontic work.

Use of film holder with a beam alignment device makes it difficult to carry Endodontic work.


BISECTING ANGLE PARALLELINGTECHNIQUE TECHNIQUE Sterilization of

holders not required as they are not used usually.

Unnecessary exposure because patient touches film.

Sterilization must. Holders need to be autoclaved or disposable holders (Styrofoam bite blocks) to be used.

Film holders are used - so no unnecessary exposure.


BISECTING ANGLE PARALLELINGTECHNIQUE TECHNIQUE Vertical

angulations may expose vital organs such as thyroid gland and the lens of the eye.

Lack of extreme vertical angulations cause less exposure to critical organs.


BISECTING ANGLE PARALLELINGTECHNIQUE TECHNIQUE Shifting may lead to

improper centering of the film- cone cutting and/or blurring.

Position indicating device used, so shifting of patients head may not affect much.


BISECTING ANGLE PARALLELINGTECHNIQUE TECHNIQUE Duplication of

technique is difficult.

Hence, comparison in serial radiographs not possible.

Technique is easy to standardize & can be accurately duplicated.

Hence serial radiography is possible.



BISECTING ANGLE PARALLELINGTECHNIQUE TECHNIQUE Positioning of the

film in third molar region comparatively easy

Positioning the film in the third molar region very difficult.


BISECTING ANGLE PARALLELINGTECHNIQUE TECHNIQUE Economic

Requires less time

Comparatively expensive because of need of higher KVP machine and film holders.

Requires more time


BISECTING ANGLE PARALLELINGTECHNIQUE TECHNIQUE Requires less

space. Adjustments can

be made easily.

Does not have any anatomical constraints.

Requires more space.

Adjustments cannot be made so easily.

Have anatomical constraints.


BISECTING ANGLE PARALLELINGTECHNIQUE TECHNIQUE Can be used when

tooth is longer than film.

More factors to be standardized.

Is difficult to use when the patient is in supine position.

Cannot be used when tooth is longer than film.

Less factors to be standardized.

Not difficult as PID’s are used.


Conclusion The diagnostic advantages of the accurate,

reproducible images produced by paralleling technique using film holders and beam-aiming device should be regarded technique of choice for periapical radiography.

Periapical radiography is not always as straightforward in practice as it appears in theory.

Although paralleling technique should be regarded as the technique of choice, it is not always possible.


However, a knowledge of the theoretical requirements of imaging enables the clinician to modify the available techniques to suit individual needs of patients.


ReferencesReferences

Oral Radiology – White & Pharoah Dental Radiography- Haring Jansen Textbook of Dental & Maxillofacial Radiology – Freny R.Karjodkar Essentials of Dental Radiography & Radiology

third edition – Eric Whaites,

