Length determination

It is essential that care is taken over identification of the correct canal length. Clinically, the aim is to identify the apical constriction that is the narrowest point of the root canal. Apical to this the canal space widens to form the apical foramen. The most common way of determining canal length is the working length radiograph. A file is placed in each canal at what is estimated to be the working length. This 'questimate' of length is obtained by studying the preoperative

radiograph (after adjustment for elongation or foreshortening) and using knowledge of the average lengths of teeth. Allowances obviously need to be made for fractured teeth and incisal wear. Tactile feel may also help in establishing the approximate working length provided pre-enlargement has been performed. A bisecting angle radiograph may be taken; alternatively

the film may be held using a pair of Spencer Wells artery forceps or an Endo Ray film holder (the latter two techniques allow for radiographs more resembling a paralleling technique to be performed). The file position is checked on the radiograph and adjusted as necessary. It

is recommended that a repeat radiograph should be exposed with the file reset if it is more than 2 mm from the desired position. Recently, electronic apex locators have been developed

that greatly assist in the placement of the first length determination file. These devices have a lip clip and a probe, which is touched against the file shaft. As the file approaches the foramen, the resistance or impedance changes and a visual display indicates when the file has touched the periapical tissues. It is usual to recheck the reading with different file sizes (08, 10, 15, 20 depending on canal size) to check for the accuracy of the reading. The file position is then

checked by exposing a radiograph and adjusted as necessary. The combination of electronic apex locators and radiographs is a reliable way of determining canal length. Care must be taken to ensure that the pulp chamber is dry and that there is minimal fluid in the root canals. Otherwise the fluid may short circuit the apex locator through the gingival tissues and cause a false reading. This is a particular problem in heavily restored or crowned teeth.

Ideally, a sealer should:

• satisfy the above requirements of a root filling material

• provide good adhesion to the canal wall

• have fine powder particles to allow easy mixing or be a two paste system

• set slowly.

Types of root filling material available

Solid and semisolid materials include gutta-percha and silver points. Silver points are not recommended as they do not seal the canal laterally or coronally and may

cause tooth or gingival staining.

Sealers and cements include Tubliseal, AH Plus, Pulp

Canal Sealer, Roths Sealer, AH 26.

Medicated pastes include N2, Endomethosone, Spad, Kri and are not recommended as they may contain paraformaldehyde, which is cytotoxic.