Periapical radiography describes intraoral tech-niques designed to show individual teeth and thetissues around the apices. Each film usually showstwo to four teeth and provides detailed informationabout the teeth and the surrounding alveolar bone.

Main indications

The main clinical indications for periapical radiography include:

• Detection of apical infection/inflammation• Assessment of the periodontal status• After trauma to the teeth and associated

alveolar bone• Assessment of the presence and position of

unerupted teeth• Assessment of root morphology before

extractions• During endodontics• Preoperative assessment and postoperative

appraisal of apical surgery• Detailed evaluation of apical cysts and other

lesions within the alveolar bone• Evaluation of implants postoperatively.

Ideal positioning requirements

The ideal requirements for the position of the filmpacket and the X-ray beam, relative to a tooth, areshown in Figure 8.1. They include:

• The tooth under investigation and the filmpacket should be in contact or, if not feasible,as close together as possible

• The tooth and the film packet should beparallel to one another

• The film packet should be positioned with itslong axis vertically for incisors and canines,and horizontally for premolars and molarswith sufficient film beyond the apices to recordthe apical tissues

• The X-ray tubehead should be positioned sothat the beam meets the tooth and the film atright angles in both the vertical and thehorizontal planes

• The positioning should be reproducible.

Radiographic techniques

The anatomy of the oral cavity does not alwaysallow all these ideal positioning requirements tobe satisfied. In an attempt to overcome the prob-lems, two techniques for periapical radiographyhave been developed:

• The paralleling technique• The bisected angle technique.

Periapical radiography8

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Fig. 8.1 Diagram illustrating the ideal geometricalrelationship between film, tooth and X-ray beam.

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Paralleling technique

Theory

1. The film packet is placed in a holder andpositioned in the mouth parallel to the long axisof the tooth under investigation.

2. The X-ray tubehead is then aimed at rightangles (vertically and horizontally) to both thetooth and the film packet.

3. By using a film holder with fixed film packetand X-ray tubehead positions, the technique isreproducible.

This positioning has the potential to satisfy fourof the five ideal requirements mentioned earlier.

However, the anatomy of the palate and the shapeof the arches mean that the tooth and the filmpacket cannot be both parallel and in contact. Asshown in Figure 8.2, the film packet has to bepositioned some distance from the tooth.

To prevent the magnification of the image thatthis separation would cause, a parallel, non-diverging, X-ray beam is required (see Fig. 8.3).As explained in Chapter 5, this is achieved usuallyby having a large focal spot to skin distance, byhaving a long spacer cone or beam-indicatingdevice (BID) on the X-ray set.

Film packet holders

A variety of holders has been developed for thistechnique.The choice of holder is a matter of per-sonal preference — the Rinn XCP® holders,shown in Figure 8.4, being favoured by the author.The different holders vary in cost and design butessentially consist of three basic components:

• A mechanism for holding the film packetparallel to the teeth that also prevents bendingof the packet

• A bite block or platform• An X-ray beam-aiming device.This may or may

not provide additional collimation of the beam.

Positioning techniques

The radiographic techniques for the permanentdentition can be summarized as follows:

76 Radiography and radiology for dental nurses

Fig. 8.2 Diagram showing the position the film packet hasto occupy in the mouth to be parallel to the long axis of thetooth, because of the slope of the palate.

Fig. 8.3 Diagrams showing the magnification of the image that results from using A a short cone and a diverging X-ray beamand B a long cone and a near-parallel X-ray beam.

A

B

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1. The appropriate holder and size of filmpacket are selected. For incisors and canines (max-illary and mandibular) an anterior holder shouldbe used and a small film packet (22 × 35 mm)with its long axis vertical. For premolars and molars(maxillary and mandibular) use a posterior holder(right or left as required) and a large film packet(31 × 41 mm) with its long axis horizontal, inaddition:

a. The smooth, white surface of the film packetmust face towards the X-ray tubehead.b. The end of the film packet with theembossed orientation dot is placed opposite thecrowns of the teeth (to avoid subsequentsuperimposition of the dot over an apex).2. The patient is positioned with the head sup-

ported and with the occlusal plane horizontal.3. The holder and film packet are placed in the

mouth as follows:a. Maxillary incisors and canines — the film

packet is positioned sufficiently posteriorlyto enable its height to be accommodated inthe vault of the palate

b. Mandibular incisors and canines — the filmpacket is positioned in the floor of the

mouth, approximately in line with the lowercanines or first premolars

c. Maxillary premolars and molars — the filmpacket is placed in the midline of thepalate, again to accommodate its height inthe vault of the palate

d. Mandibular premolars and molars — the filmpacket is placed in the lingual sulcus nextto the appropriate teeth.

4. The holder is rotated so that the teeth underinvestigation are touching the bite block.

5. A cottonwool roll is placed on the reverseside of the bite block.This often helps to keep thetooth and film packet parallel and may make theholder less uncomfortable.

6. The patient is requested to bite gentlytogether, to stabilize the holder in position.

7. The locator ring is moved down the indicatorrod until it is just in contact with the patient’s face.This ensures the correct focal spot to film distance.

8. The spacer cone or BID is aligned with thelocator ring. This automatically sets the verticaland horizontal angles and centres the X-ray beamon the film packet.

9. The exposure is made (see Figs 8.5–8.12).

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Fig. 8.4 (i) A selection of film packet holders designed for the paralleling technique. A Hawe–Neos Superbite posterior holder (colour coded red). B Hawe–Neos Superbite anterior holder (colour coded green). C Rinn XCP posterior holder (colour coded yellow). D Rinn XCP anterior holder (colour coded blue) with film packet inserted. E Unibite® posterior holder.(ii) Rectangular collimation provided by A the Masel Precision all-in-one metal holder and B the Rinn XCP holder with itsadditional metal collimator attached to the white locator ring.

B E

C

D

(i)

A

B

(ii)

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78 Radiography and radiology for dental nurses

Fig. 8.5A Patient positioning (Maxillary central incisor). B Diagram of the positioning. C Plan view of the positioning.D Resultant radiograph with the main radiographic features indicated.

Maxillary incisors

A

B C

D

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