Q. 2. Name intraoral radiographic techniques.
What are the uses of occlusal X-ray? Describe the techniques of occlusal X-ray of maxillary palate.
What are indications for occlusal radiographs? Describe the radiographic techniques in taking maxillary and mandibular cross-sectional occlusal radiographs.
Ans. Classification of intraoral radiographic techniques is as follows:
I. Intraoral radiographic techniques
a) Bitewing radiography
b) Peri-apical radiography:
i. Bisecting angle technique/short cone technique.
ii. Paralleling technique/Long cone technique/right-angle technique.
c. Occlusal radiography
i. Maxillary occlusal views
ii. Mandibular occlusal views
Maxillary and mandibular occlusal views are further divided into:
i. Cross-sectional occlusal views
ii. Topographic occlusal views—anterior/posterior
iii. Paediatric occlusal views.
II. Intraoral localization radiographic techniques
b. Buccal object rule
c. Contrast radiography
d. Tube shift technique/Clark’s rule
e. Right angle technique/Miller’s technique.
• Occlusal films are used to show larger areas of the maxilla or mandible. The size of the film is 57 × 76 mm.
Indications of occlusal radiographs
• To examine the area of cleft palate.
• To precisely locate retained roots of extracted teeth, supernumerary teeth, unerupted and impacted teeth.
• This technique is especially useful for impacted canines and third molars and also to localize foreign bodies on the maxilla and mandible.
• To locate sialoliths in the ducts of sublingual and submandibular glands.
• To demonstrate and evaluate the integrity of the anterior, medial, and lateral outline of the maxillary sinus.
• To aid in the examination of patients with trismus, who can open their mouths only a few millimetres.
• To obtain information about the location, nature, extent, and displacement of fractures of the mandible and maxilla.
• To detect disease in the palate or floor of the mouth and determine the medial and lateral extent of disease (cysts, osteomyelitis, malignancies).
• To measure the changes in the size and shape of the maxilla and mandible.
• To study the expansion of the palatal arch during the orthodontic jaw expansion.
Maxillary occlusal projections
There are three different maxillary occlusal projections: i. Topographic ii. Lateral (right or left) iii. Paediatric.
i. Topographic projection: The maxillary topographic occlusal projection is used to examine the palate and the anterior teeth of the maxilla.
ii. Lateral (right or left) projection: The maxillary lateral occlusal projection is used to examine the palatal roots of the molar teeth. It may also be used to locate foreign bodies or lesions in the posterior maxilla.
iii. Paediatric projection: The maxillary paediatric occlusal projection is used to examine the anterior teeth of the maxilla and is recommended for use in children 5 years old or younger.
Technique of maxillary topographic occlusal projection
• Position the patient upright with the maxillary arch parallel to the floor so that the sagittal plane is perpendicular to the floor and occlusal plane is horizontal.
• Place a size-4 film with the white side facing the maxilla and the long edge in a side-to-side direction.
• Insert the film into the patient’s mouth, placing it as far posteriorly as the patient’s anatomy permits usually till it contacts the anterior border of mandibular rami.
• Ask the patient to bite gently on the film, retaining the position of the film in an end-to-end bite.
• Position the PID so that the central ray is directed through the midline of the arch toward the centre of the film at a vertical angulation of +65 degrees and a horizontal angulation of 0 degrees towards the midline of the film. The top edge of the PID is placed between the eyebrows on the bridge of the nose. In general, the central ray enters the patient’s face through the bridge of the nose.
Maxillary lateral occlusal projection
• Position the maxillary arch parallel with the floor.
• Position a size-4 film with the white side facing the maxilla and the long edge in a front-to-back direction. Insert the film into the patient’s mouth and place it as far posteriorly as the patient’s anatomy permits. Shift the film to the side (right or left) of intended interest. The long edge of the film should extend approximately ½ inch beyond the buccal surfaces of the posterior teeth.
• Instruct the patient to bite gently on the film, retaining the position of the film in an end-to-end bite.
• Position the PID so that the central ray is directed through the contact areas of intended interest.
• Position the PID so that the central ray is directed at +60 degrees toward the centre of the film. The top edge of the PID is placed above the corner of the eyebrow.
Maxillary paediatric occlusal projection
• Position the maxillary arch parallel with the floor.
• Position a size-2 periapical film with the white side facing the maxilla and the long edge in a side-to-side direction. Insert the film into the child’s mouth.
• Instruct the child to bite gently on the film, retaining the position of the film in an end-to-end bite.
• Position the PID so that the central ray is directed through the midline of the arch toward the centre of the film.
• Position the PID so that the central ray is directed at +60 degrees toward the centre of the film. The top edge of the PID is placed between the eyebrows on the bridge of the nose.
Technique in taking mandibular cross-sectional occlusal view
• This projection shows soft tissues of the floor of the mouth and delineates the lingual and buccal plates of the jaw and the teeth from second molar to second molar.
• The film is placed in the mouth with its long axis perpendicular to tile sagittal plane and the pebbled side towards the mandible.
• The anterior border of the film should be approximately ½ an inch anterior to the mandibular central incisors.
Projection of the central ray
• The central ray is directed at right angles to the centre of the film.
• The point of entry is in the middle through the floor of the mouth approximately 3 cm below the chin.
Q. 3. Compare paralleling and bisecting techniques.
• The paralleling and bisecting techniques will be compared from the standpoint of the basic principles (rules) for shadow casting mentioned below:
i. Focal spot should be as small as possible.
ii. Focal spot–object distance should be as long as possible.
iii. Object–film distance should be as small as possible.
iv. The long axis of the object and the film placed should be parallel.
v. X-ray beam should strike the object and film at right angles.
vi. There should be no movement of the tube, film or patient during exposure.
• Under given conditions, both procedures would use the same source of radiation. Hence factors affecting rule 1 would be the same in both techniques.
• The paralleling technique more adequately fulfills rule 2 for shadow casting. It ordinarily uses a long or extended cylinder, which at least doubles the target–object distance as compared to the short cone or cylinder bisecting technique.
• The bisecting technique can be used advantageously with either the short or extended distance.
• The tooth–film distance is somewhat greater in the paralleling technique, particularly in the coronal area of the tooth. This separation of the tooth and film is due to anatomic limitations such as palatal curvature and muscle attachments. Thus the bisecting technique more closely satisfies rule 3 of shadow casting. This inadequacy of the paralleling technique is compensated for by the increased target–object distance.
• The paralleling technique again excels in fulfilling rules 4 and 5. The paralleling technique is so named because the tooth and film are parallel.
• In the bisecting procedure, the film contacts the tooth at the occlusal or incisal surface and then diverges away from the long axis of the tooth. If the tooth and film are not parallel, it is impossible for the rays to strike both object and recording surface at right angles.
• When the bisecting technique is used, it is impossible to superimpose labial or buccal anatomic entities on their palatal or lingual counterparts; invariably, when viewed on the radiograph, the labial or buccal counter part of a similar joint on the palatal or lingual surface will lie closer to the occlusal or incisal edge. This situation is not necessarily bad, but the interpreter must view the resultant films with this phenomenon in mind.
In brief the bisecting angle technique and paralleling techniques are compared as follows:
|Bisecting Angle Technique
||Parallel Line Angle Technique
|Distortion of image occurs
||Sharpness is more as compared to bisecting technique
|Elongation and shortening of image is more
||It is less compared to bisecting technique
|Bending of film is common
||Bending of film is uncommon
|Shadow of alveolar bone tends to fill the interproximal spaces
||Alveolar crest is seen in true relationship with teeth
|Super imposition of zygomatic arch occurs on apices of molar teeth
||Superimposition of zygomatic arch occurs on apices of molar teeth
|Easier and less space required
||Need trained technician and more space
|Cone cut is common
||It is uncommon
|Distortion of film occurs due to bending by finger pressure.
||As film holder is used bending does not occur
Q. 4. Describe the indications/advantages, disadvantages and technique of bitewing radiographs.
• Bitewing radiography is an intraoral technique which allows the clinicians to evaluate initial lesions by passing the primary ray perpendicular to the long axis of the respective teeth.
• In this technique, the patient is asked to bite on the bite block provided by the special bitewing film holders.
• The exposed film is designed to show the crowns of the teeth and the alveolar crystal bone.
Indications of bitewing radiographs
• Screening for incipient proximal carious lesions.
• To check the health of the inter-dental alveolar bone in normal and periodontal diseases and detect calculus deposits in inter-dental areas.
• Detection of secondary caries under the restorations and to determine if restoration is fractured.
• To know relationship of deciduous to the permanent teeth in children during mixed dentition period.
• Routine annual evaluation of all patients who come to check up without any complaint.
Disadvantages of bitewing radiographs
• As many variables are involved in this technique, it often results in the image being badly distorted.
• Incorrect vertical angulation may result in foreshortening or elongation of the image.
• The periodontal bone levels are poorly shown.
• The shadow of the zygomatic buttress frequently overlies the roots of the upper molars.
• Considerable skill is required as the horizontal and vertical angles have to be assessed for every patient.
• It is not possible to obtain reproducible views.
• Coning off or cone cutting may result if the central ray is not aimed at the centre of the film, particularly if using rectangular collimation.
• Incorrect horizontal angulation will result in overlapping of the crowns and roots.
• The crowns of the teeth are often distorted, thus preventing the detection of proximal caries.
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