1. Periapical radiography

2. Main indications Detection of periapical infection
Assessment of the periodontal status
After trauma to the teeth and associated alveolar bone
Assessment of the presence and position of unerupted teeth

3. During endodontics
Preoperative assessment and postoperative appraisal of apical surgery
Detailed evaluation of bone lesions
Implant evaluation

4. Ideal positioning requirements
The tooth under investigation and the film packet should be in contact or ,if not feasible, as close as possible
The tooth and the film packet should be parallel to one another

5. The film packet should be positioned with its long axis vertically for incisors and canines, and horizontally for premolars and molars with sufficient film beyond the apices to record the apical tissues
The positioning should be reproducible

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

8. Positioning of the instrument

10. Theoretical basis of the bisected angle technique

17. Advantages of the paralleling technique
Geometrically accurate images are produced with little magnification, foreshortening or elongation
The shadow of the zygomatic buttress appears above the apices of the molar teeth

18. The horizontal and vertical angulations of the X-ray tubehead are automatically determined by the positioning device
There is no cone cutting
The radiographs are reproducible
The technique is useful for some patients with disabilities

19. Disadvantages of the paralleling technique
Positioning of the film packet for the posterior teeth can cause gagging
The anatomy of the mouth sometimes makes the technique imposible, e.g a shallow, flat palate
The apices of the teeth can sometimes appear very near the edge of the film

20. The technique cannot be performed satisfactory using a short focal spot to skin distance because of the resultant magnification
The holders need to be autoclavable
Positioning the holders in the lower third molar region can be very difficult

21. Advantages of the bisected angle technique
Positioning of the film packet is relatively simple and comfortable for the patient
If the angulations are assessed correctly the image should be diagnosticable

22. Disadvantages
Incorrect vertical angulation results in foreshortening or elongation of the image
The shadow of the zygomatic buttress overlies the roots of the upper molars
Incorrect horizontal angulation results in overlapping of the crowns or cone cutting

23. The periodontal bone levels are poorly shown
It is not possible to obtain reproducible views
The buccal roots of the maxillary premolars and molars are foreshortened