1) Paralleling
2) Bisecting angle
Paralleling periapical technique is preferred because it produces images with:
- minimal distortion
- minimal discomfort
- minimal overlap of zygoma on maxillary molars
Periapical Radiographs: Paralleling Technique
- Horizontal angle alignment
Molars: 90-80 degrees. Position the tube head so the center of the PID is aligned with the outer canthus of the eye.
Premolars: 80-70 degrees. Horizontal angle is aligned perpendicular to buccal surface of first molar. Position tubehead so the center of the PID is lined up with the middle of the eye.
Canines: 60-75 degrees. Horizontal angle is aligned perpendicular to the facial surface of the canine, or embrasure between canine and lateral incisor. Position tubehead so the center of the PID is lined up with the ala of the nose.
Central-lateral incisor: For maxillary: Horizontal angle is aligned at the embrasure space between the central and lateral incisors. Position tubehead so the center of the PID is lined up with embrasure space between central and lateral incisors. For mandibular: Horizontal angle is aligned with the embrasure space between central incisors (0 degrees horizontal angle).
If horizontal angle is incorrect contact points are overlapped --can't see proximal surfaces
- Film placement
- Films are positioned in a biteblock for insertion into oral cavity
- Films are usually centered on the biteblock
- Several biteblocks are available:
-Dentsply Rinn XCP instruments (plastic with ring)
-Dentsply Rinn Stabe (disposable styrofoam)--more likely to lead to errors with novices
-Dentsply Rinn Snap-A-Ray (used with children) - When biteblock is placed in mouth, it must contact crowns of teeth in order to capture apices
- If biteblock is not in contact with crowns, apices will not be visible
- Film must be placed toward midline (away from teeth) to be parallel to the long axis of the teeth
- This also makes film positioning more comfortable
- This is true for all periapical radiographs taken with the paralleling technique
- The film must be positioned so it is parallel to the horizontal alignment of the PID
- Film should be parallel to the end of the PID from back to front
- When placing biteblock for maxillary periapical radiographs:
- Place film in the midline of the palate and at an angle
- Position biteblock on crowns of teeth
- Hold biteblock as patient bites
- The result is a film that is parallel to the long axes of the teeth and the horizontal alignment of the PID, positioned to capture the apices, and is comfortable
Maxillary molar: Rotate film posteriorly to align with the horizontal angle of the PID. Place biteblock on crown of 2nd molar and hold it against tooth as patient closes.
Maxillary premolar: Place biteblock on crown of 2nd premolar and hold it against tooth as patient closes.
Maxillary canine: Place biteblock on the cusp tip of canine and hold it against tooth as patient closes.
Maxillary central-lateral incisor: Place biteblock on embrasure between the central and lateral incisor, and hold it against tooth as patient closes.
- When placing biteblock for mandibular periapical radiographs:
- Have patient raise tongue
- Place film almost flat against floor of the mouth, towrad midline (away from arch)
- Position biteblock on crowns of teeth
- Hold biteblock as patient bites
- Film will rotate downward as patient closes
Mandibular premolar: Place biteblock on crown of 2nd premolar and hold it against tooth as patient closes. It is sometimes difficult to position the film anteriorly enough to capture distal half of canine. If this happens there are two options:
1) You can decrease the horizontal angle: this will project canine onto film and not cause too much overlapping.
2) OR you can slightly bend corner of film.
Mandibular canine-lateral incisor: Place biteblock on tembrasure between the canine and lateral incisor and hold it against tooth as patient closes.
Mandibular central incisor: Position biteblock on embrasure between the central incisors, and hold it against tooth as patient closes.
- Vertical angle alignment
- The vertical angle should be directed perpendicular to the film and long axes of the teeth
- To align the vertical angle, position the end of the PID so it is parallel to the film from apical to coronal (top to bottom)
- Operator must stnad where you can see the PID, tooth, and film in the same line of sight.
What happens if the vertical angle is too large?The apices of the teeth are projected toward the midline of the film and the croens may be projected off the film. This is called foreshortening. This also projects zygomatic process and zygoma over the roots of the maxillary molars. Foreshortening projects buccal cusps farther down than palatal cusps.
What happens if the vertical angle is too small?Apices are projected to edge of the film and crowns are projected toward middle of film. This is called elongation.
- Align PID with coronal aspect of film
- Must cover film with x-ray beam
- If beam is not aligned, part of the film is not exposed: a cone-cut
- To cover the film from apical to coronal (top to bottom):
- Maxillary periapicals: align the bottom of the PID with the bottom of the biteblock
- Mandibular periapicals: align the top of the PID with the top of the biteblock
- Align PID with anterior aspect of film
- Molar Periapicals:
- Align center of PID with outer canthus of eye
- If you are using a round PID, align anterior aspect of PID with corner of mouth
- If you are using a rectangular PID, align anterior aspect of PID with middle of second premolar
- Align center of PID with middle of eye
- If you are using a round PID, align anterior aspect of PID with ala of nose
- If you are using a rectangular PID, align anterior aspect of PID with anterior canine
- Align middle of PID with ala of nose
- If you are using a round PID align anterior aspect with tip of nose
- If you are using a rectangular PID, align anterior aspect of PID with central-lateral incisor embrasure
- Align PID directly over film
- You can't miss it!!
- Molar Periapicals:
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