Intra-oral radiography Flashcards
Peri-apical radiographs
Film shows 2-3 teeth
Detects abnormalities of the root and entire alveolar bone
There is the bisecting and paralleling technique
Ideal peri-apical positioning requirements
Receptor should be flat
Receptor must be parallel to the long axis of the tooth
Central ray (beam) must be perpendicular to the teeth and film
Positioning should be reproducible
Tooth and film should be in contact as much as possible
Indications of periapical radiographs
Detecting apical infection and inflammation
Assessment of periodontal status
After trauma to the teeth and associated alveolar bone
Assessment of position and prognosis of implants
Assessment of presence and position of unerupted teeth
Assessment of root morphology, before extractions
During endodontics
Detailed evaluation of apical cysts and other lesions within alveolar bone
Preoperative assessment and post operative appraisal of apical surgery
General guidlines to patient care
- Patient should be postioned comfortably with the occlusal plane horizontal and parallel to the floor
- Specs, dentures and orthodontic appliances should be removed
- Patient should wear a protective lead thyroid collar
- Intraoral film packets should be positioned carefully to avoid trauma to the soft tissues
Full Mouth Survey
An intraoral full mouth examination is composed of both periapical and bite-wing projections.
On the average adult, a full mouth series consists of 18 to 20 films.
An ideal full mouth set consists of 21 films
Not done on persons under 18 years of age.
Not done routinely in a training facility; only on request from supervisor.
Only be repeated after 2 years
The basic principles of optimal image geometry
In order to minimize distortion effects and achieve optimal image geometry, the following principles have been advocated for intra-oral radiography.
- 1.The focal spot should be as small as possible
- 2.The focal spot to object distance should be as long as possible (long cone)
- 3.The object to film distance (FOD) should be as small as possible (Except for when examining the lower mandibular molars)
- 4.The long axis of object and film should be parallel** (deviation less than 20 degrees)
- 5.The **central ray **should be perpendicular to both the object and the film
Packet film positioning
**Maxillary incisors and canines **
Positioned posteriorly to enable its height to be accommmodated in the vault of the palate
**Mandibular incisors and canines **
Positioned in the FOM approximately in line with lower canines or 1st premolars
Maxillary premolars and molars
Placed in the midline of the palate
**Mandibular molars and premolars **
Placed in the lingual sulcus
The Paralleling Technique
Position the film parallel to the long axis of the tooth.
The film in the film holder must be placed away from the teeth and toward the middle of the mouth… (except when examining the lower mandibular molars)
Since the films are placed at a distance to minimize magnification a large focal spot to skin distnace is indicated by using a long spacer cone or BID
Advantages of the paralleling technique
- Accuracy images are free of geometric distortion (magnification)
- Simplicity Horizontal and Vertical position of the x-ray tube head are auomatically determined if the positioning is right
- Reproducible radiographs are present
- Periodontal bone levels are well represented
- Images have better resolution
- Periapical tissues show minimal elongation
Crowns of the teeth show approximation of the caries
There is no cone cutting present
Disadvantages of the paralleling technique
Receptor placement may be difficult due to anatomy (shallow or flat palates)
Film packet may cause discomfort especially in posterior teeth which may result in gagging
Inexperienced operators may find positioning of the film holders in the mouth difficult
The holders need to be autocalved or disposable
Positioning the holders in the lower 3rd molars may be difficult
Technique cannot be accurate using a short focal spot to skin distance (short space coner) due to magnification
Tips for Film Placement
The white side of the film always faces the teeth.
The anterior films are always placed vertically.
The posterior films are always placed horizontally.
Always position the film holder away from the teeth and toward the middle of the mouth. (with the exception of the mandibular molars)
Always center the film over the areas to be examined.
Always place the film parallel to the long axis of the teeth.
Advantages of the bisecting angle technique
Positioning of the film packet is relatively comfortable
Postitioning is relatively simple and quick
Film holders are not needed
There are no anatomical restrictions
Vertical and Horizontal angulation
Vertical angulation
Line of the central ray is extended until it meets the occlusal plane. Direct the central ray of the x-ray beam perpendicular to the film and the long axis of the tooth.
When the X-ray beam is directed at the occlusal plane, the vertical angulation is said to be zero. Angulation in the downward direction is called positive vertical angulation. Angulation in the upward direction is called negative
Horizontal angulation
Direct the central ray of the x-ray beam through the contact areas between the teeth, this is to avoid overlapping (still perpendicular to the film).
- Central ray (CR): Center the x-ray beam on the center of the film to ensure that all areas of the film are exposed (i.e. no cone cutting).
Disadvantages of bisecting angle techniques
Image distortion
Periodontal bone levels are poorly displayed
Incorrect vertical angulations result in image elongation
Shadow of the zygomatic buttress often overlies the roots of the upper molars
Horizontal and vertical angulations need to be assessed for every patient and skills are required
Reproducible views cannot be obtained
Coning off or cone cutting can occur
Crowns of the teeth are often distorted hence preventing the detection of proximal caries
BISECTING ANGLE
The angle formed between the long axis of the tooth and the long axis of the film is assessed and mentally bisected
The x-ray tube head is positioned at right angles to the bisecting line and the x-ray beam aimed through the tooth apex
Based on the geometric principle of Cieszynski’s rule of isometry of similar triangles, the actual length of the toooth in the mouth will be equal to the image of the tooth on the film
Short (or long) cone is used. Film is in contact with the crown of tooth; protrudes 2 - 3mm beyond incisal edges/occlusal surfaces. It is usually held by patients finger
Bite tab
It is made up of paper loop.
**Advantages **
Simple.
Not expensive.
Disposable.
Can be used easily in children
