oral radio lec 3 final.docx

7/30/2019 oral radio lec 3 final.docx

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Periapical radiograph (Bisecting angle technique)

-Periapical radiograph is done by parallel technique or bisecting angle

technique.

*Parallel technique is that putting the film parallel to the tooth.

*HOW can that be done?

the middle of thetowardfrom the tooth andfar awayYou put the film-

palate or opposite to the mid surface of the tongue.

* Bisecting angle technique:-- Bisecting angle means that there must be an angle and I want to bisect it(divide it into two equal triangles)

- The ideal position requirement is that we need parallelism between the

tooth and the film. We need close contact as possible, minimum film totooth distance, and maximum targetfilm distance.

* In parallel technique we could not put the film in close contact to the

tooth. So we lost this requirement. While now in bisecting angle

technique we want to put the film in close contact to the tooth

* * Bisecting angle technique

1. It is the point where the film contactthe tooth, the plane of the film and thelong axis of the tooth form an angle.

2. The central ray of the x-ray beamperpendicular to the imaginary bisector.

3. The film must be placed in the lingualsurface of the tooth.

4. Imaginary bisector: the dentalradiographer must visualize a plane that

division half or bisects, the angle formedby the film and the long axis of the tooth.


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5. The two imaginary triangles that result are right triangle andcongruent , the hypotenuse of one imaginarytriangle is represented by the long axis of the tooth and the

other hypotenuse is represented by the plane of the film

*Isomitry: equality of measurements

Rule of isometry: states that two triangles are equal if they have two

equal angles and share a common side.

-when the rule of isomitry is followed strictly, the radiographic image of

the tooth is accurateWe depend on this rule to detect the real dimension

of the tooth.because when the x-ray beam is directed at right angle to

an imaginary bisector, the actual tooth and the image of the tooth on the

film are the same length.

-We assumed that the length (the real dimension of the tooth) of the tooth

on the film is accurate but it is not.

-As in parallel technique we have several film holders, as parallel

technique you set the patient in correct position and the film too. The

vertical angulation should be central to the beam.

*Film holders: is a device used to position an intraoral film in the mouth

and return the film in position during exposure. With the bisecting

technique, film holders are recommended because the need for the patient

to stabilize the film with their finger is eliminated.. This will reduce the

patient exposure to radiation.

*Examples of commercially available film holders:- Rinn BAI instruments.

- Stabe bite-block (Rinn).- EEZEE-Grip film holder (Rinn).


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*Finger-holding Method is the least desirable method for exposing films

using the bisecting technique.

-Disadvantages of this method:

1. The patient's finger is in the path of primary beam, resulting in

unnecessary radiation exposure.

2. The patient may use excessive force to stabilize the film, causing thefilm to bend and resulting in image distortion.

3. The patient may allow the film to slip from its position, resulting in

inadequate exposure of the prescribed area.

4. Without the use of a film holder with aiming ring, the dental

radiographer may align the PID incorrectly, causing a partial image or

cone-cut.

Vertical angulation: refer to the position of the PID in a vertical

plane (up or down). vertical angulation is measured in degrees and isregistration on the outside of the tube head.


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-5 degrees is added to the vertical angulation because of teeth inclination.

*The vertical angulation differs according to the radiograph technique

used as follows:

1. With the paralleling technique, the vertical angulation of the central ray

is directed perpendicular to the film and the long axis of tooth.

2. With the bisecting technique, the vertical angulation is determined by

imaginary bisector; the central ray is directed perpendicular to the

imaginary bisector.

-When using film holders no need to remember the vertical angulation

because it is already correct while when using finger-holding methodsyou have to remember it.

*Incorrect vertical angulation results in a radiographic image that is not

the same length as the tooth; instead, the image appears longer or shorter.

Elongated orforeshortened image are not diagnostic(distortion).Distortion:means abnormal shape, especially withfinger holding method

In the bisecting technique, the long axis of the tooth is

not parallel with the long axis of the film. This results in a

distortion of the image produced using this technique. In

the left radiograph below, the buccal roots appear much

shorter than the palatal root, even though in the actual

tooth the lengths are not that much different. In the other

radiograph taken with the paralleling technique, the

lengths are projected in their proper relationship(minimal distortion).

Distortion

bisecting paralleling


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Foreshortened image.results from excessive vertical angulation(too steep).

Elongated image..Results from insufficient vertical angulation(too flat).

>90 = foreshortening

90 the apex will

be imaged lower on the film, shortening the overall image.

Remember, a 90 angle between the x-ray beam and the

bisecting line is the ideal alignment.

image lengths


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Horizontal angulation refers to the positioning of the tube head anddirection of the central ray in a horizontal (side-to-side) plane.

- It does not differ according to the radiographic technique used.

Correct horizontal angulation: thecentral ray directed perpendicular to the

curvature of the arch all through the

contact areas of the teeth.

Incorrect horizontalangulationresults in overlapped

contact areas.

intraoral film is used with the bisecting2Size*

size 1 forandhposterior teettechnique for

.hanterior teet

*Notes:

-Vertical angulation of the film for

anterior teeth

-Horizontal angulation of the film for

posterior teeth

*There are:

- 5 films forupper anterior

- 3 films forlower anterior

- 8 films forposterior teeth

- 4 bitewing films

*There's no need to memorize angulation unless you use finger

technique (especially vertical angulation).

*Bisecting technique advantages:1. Close contact between tooth and film (one of the ideal requirements of

ideal image).

2. Decreased exposure time when a short PIDis used with the bisectingtechnique, a shorter exposure time is recommended.


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*But in parallel technique we use long cone to compensate for

magnification

3. It can be use without a film holder when the anatomy of the patient isdifficult (shallow palate, bony growths, sensitive mandibular premolar

areas).

4. In edentulous patient because the muscle tense when he open his

mouth and an area in partially edentulous patients when the holder is notstable we can use cotton.

*In the bisecting technique we lose two ideal requirements:

1. Parallelism2. The central ray of the x-ray beam must be directed perpendicular to the

film and the long axis of the tooth.

-Some students in the clinic use the same holder of the parallel technique

in the bisecting technique but they put the film perpendicular to the tooth

which is wrong of course we have to use special holder in bisecting

technique.

*Bisecting technique disadvantages:

1. Image distortion.2. Angulation problems.

3. Excess radiation exposure to patients hands.

- If a film holder is not used, as result of using

finger holding method we may end with

phalangioma on radiograph


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*Note: We have intra oral radiograph:

-Periapical radiograph..

Parallel techniquebisecting technique

*Bite-wing technique-It is an intraoral radiographic technique that is used to examinethe inter-proximal surfaces of teeth.

-A bite-wing radiograph shows the crowns of the maxillary and

mandibular teeth and the areas of crestal bone on the same film.

*The main advantageof the bitewing technique is to detect inter-

proximal caries that are not clinically evident.

- Bitewing radiograph are also useful in examining the crestal bone levels

between teeth.

The indication of bitewing technique:-

1. Indicate caries (inter-proximal examination).2. Assessment of restorations and overhanging.

3. Assessment of periodontal status.

4. Detection of inter-proximal calculus.

5. Pulp chamber examination

6. Examining crestal bone levels between teeth.

7. Overlapped contact: where the contact area of one tooth is super-imposed over the contact area of the adjacent tooth.

8. Open contact: open contacts appear as thin radiolucent line betweenadjacent tooth surfaces.

9. Alveolar bone: bone that support and encases the root of the teeth.

10. Crestal bone: coronal portion of alveolar bone found between the

teeth (alveolar crest).

11. Contact area: area of a tooth that touches an adjacent tooth, the areawhere adjacent tooth surfaces contact each other.


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*In bitewing we achieve some parallelism and in the same time it will be

inter-occlusal, so this point gives the Bitewings superiority in detecting

carious lesions.

Angulation of PID

Horizontal angulation:Positioning of the central ray in a

horizontal plane (side to side).

Correct horizontal angulation: the central ray directedperpendicular to the curvature of the arch all through the contact areas of

the teeth. As a result the contact area will appearopened and we can

examine the caries.


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Incorrect horizontal angulationresults in overlapped contact

areas.

-We use horizontal angulation to detect inter-proximal caries for

maxillary and mandibular together.

Vertical angulation: refer to the position of the PID in a vertical orup and down plane.

If the PID is positioned abovethe occlusal plane and the central ray

is directed downwardthen the vertical angulation is positive.

If the PID is belowthe occlusal plane and the central ray directed

upwardthen the vertical angulation is negative.

Incorrect vertical angulationresults in distorted image.

Vertical bitewing radiograph used to examine the level of alveolar

bone loss in the mouth. (Mild, moderate, severe). When the loss is more I

need to put the film vertically to cover more area

**Film for bitewing technique:-

Size 0 films:isused to examine the posterior teeth of

children with primary dentitions

-this film is always placed with the long portion of the

film in a horizontal (sideways) direction.


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Size 1 fi lm:is used to examine posterior teeth of children with

mixed dentition.

*Posterior region size 1 film -- > placed in horizontal direction.

*Anterior teeth size 1 film -- > placed in a vertical (up and down)direction.

Size 2 fi lm:used to examine the posterior teeth in adults and may be

placed horizontally or vertically.

* * * Size 2 fi lm i s usuall y placed in hori zontal dir ection, it is used for

most bi tewing exposur es.

Size 3 fi lm:is not recommended because overlapped contacts result,

because of the difference in the curvature of the arch between the

premolar and molar areas.

-In addition, the crestal bone areas may not be adequately seen on the

radiograph.

Film holder and bitewing tab:-

-In the bitewing technique either we use a film holder or bite-wing tab.

1) F ilm holders:is a device used to position an intraoral film in the

mouth and retain the film in position during exposure (They are color

codedred one use for bitewing).


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-Rinn XCP bitewing instrument: include plastic

bite-blocks, plastic aiming rings, and metal

indicator arms to reduce the amount of radiation

the patient receives.

-A snapon ring collimator can be added to theplastic aiming ring. These film holders are

reusable and must be sterilized after each use.

2) BITE-WING TAB:readymade or can you made

by yourself.

-it is used as an alternative to a filmholding device,

a film can be fitted with a bite wing tab.

*The bitewing tab: is a heavy paper-board tab or loop fitted around a

periapical film and used to stabilize the film during the exposure. The

periapical film is oriented in the bite loop so that the tab portion extends

from the white side (tube side) of the film.

-Bite loops are available in various sizes;

adhesive bite tabs are also available.

Ideal exposure factors

1. Assessment of caries and restoration-high kVp which ensures good

contrast to allow differentiation between enamel, dentin and allow EDJ tobe seen

2. Assessment of periodontal status- low kVp to avoid burn-out of the

thin alveolar crestal bone

3. In the X-ray machines with fixed kVp and mA these results are

achieved through exposure time


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*Rules for bite-wing technique:-

1. F ilm placement:the bitewing film must be positioned to cover theprescribed area of teeth to be examined .specific film placements aredetailed in the following procedures.

2. F ilm position:the bitewing film must be positionedparallelto thecrowns of the both the upper and the lower teeth .the film must be

stabilized when the patient bites on the bitewing tab or bitewing holder.

3. Vertical angulation:the central ray of the x-ray beam must be

directed at +10 degrees.

4. Horizontal angulation:the central ray of the x-ray beam must bedirected through the contact areas between the teeth. (Perpendicular to the

curvature of the arch).

5. F ilm exposure:the x-ray beam must be centered on the film toensure that all areas of the film are exposed .failure to center the x ray

beam results in a partial image on the bitewing film or a cone-cut.

*Note: We have anterior bitewing and posterior bitewings, posterior

bitewing we have two films one for the premolar and one for molar

because of the difference in the curvature of the arch.

Premolar bitewingyou have to put the anterior edge of the film in

the distal part of the canine and the premolar have to be in the middle of

the film.

Molar bitewingyou have to see all the molars than you put the

anterior edge of the film in the distal part of the second premolar.

I n the bitewing fi lm the maxill ary and the mandibular teeth equall y

detect on the f i lm and the occlusal plane must divide the fi lm into half.

We put the vertical angulation in +10 degrees is used to

compensate for the sli ght bend of the upper portion * * * * curve of

wilson***


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Advantages of Bitewing technique:

1. Simple

2. Inexpensive

3. The tabs are disposable, so no extra cross- infection control proceduresrequired

4. Can be used easily in children

Disadvantage of the bitewing technique:

1. Operator-dependent assessment of horizontal and vertical angulation ofthe X-ray tube head

2. Radiographs are not reproducible

3. Cone cutting is common4. The tongue can easily displace the film packet

5. Difficulty in vertical and horizontal angulation when you use loop or

tab.

Patient preparation for bitewing technique:

1. Briefly explain the radiographic procedure to the patient before theprocedure begins.

2. Position the patient upright in the chair; adjust the level of the chair to

a comfortable working height for the dental radiographer.

3. Adjust the headrest to support and position the patients head.

-The patients head must be positioned so that the upper arch is parallel tothe floor and the mid-sagittal (midline) plane is perpendicular to the floor.


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MSP

floor

Head Position

When viewed from the front of the patient, the

Midsagittal Plane (which divides the head into

right and left halves) is perpendicular to the floor.

4. Place and secure the lead apron with the thyroid collar on the patient.

5. Remove all the object from the mouth (denture retainers, chewinggum) that may interfere with film exposure, eyeglasses must also remove.

*I n the clinic most of the time the student make gag refl ex to the patient

why??? Because they slowly remove the fi lm.

*The patient must be watched during the exposure because you have

leaded glass window in the door because the patient or the cone maybe

move and this result incorrect radiograph.

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oral radio lec 3 final.docx