Pre-enlargement and straight-line radicular access

Pre-enlargement is achieved by watchwinding file sizes 10-35 in series, gradually opening up narrow canal orifices to a size sufficient to take a Gates-Glidden bur. The pre-enlargement can then be developed further to produce straight-line radicular access taking care to work

the drill away from furcal regions of roots. A file should stand upright in the tooth and pass undeflected deep into the canal once adequate straight-line radicular access has been achieved.

Gates-Glidden burs may be used to relocate a canal away from the danger zone; however, care should be taken to avoid overenlargement. Gates-Glidden No. 6 and 5 should only be used on the walls of the access cavity, and No. 4 no deeper than the canal orifice. The No. 3 may be used to the mid-canal region and the No. 2 to the beginning of the canal curvature, or to near full length in a straight canal. The No. 1 is quite fragile, but may be used at ultraslow speeds provided it is loose in the canal.

Advantages of pre-enlargement and establishment of straight-line access There are a number of advantages from achieving a straight-line access:

• it creates sufficient space to introduce files and irrigating needles / solutions deeper in the canal

• the bacterial count in the more coronal aspects of the canal is reduced

• a reservoir of irrigant is created that files pass through as they move apically

• the increased space allows files to fit passively in the canal, making inoculation of infected material into the periapical tissues less likely

• pressure on the coronal flutes of the file is decreased thereby increasing tactile sense and control when using files in the apical third

• precurved files remain curved, can be easily inserted and freely pass down the canal

• a greater volume of irrigant is present enhancing pulp digestion

• the bulk of pulpal and related irritants are removed reducing debris accumulation apically

• working length is more accurate because there is a more direct path to the canal terminus.

• larger files may be used for the working length radiograph. It is important to ensure that the apical region of the canal is not blocked with dentine debris or pulp tissue when using a crown-down technique. For this reason it is important that small files +/- chelating agents are

used to prevent blockage and ensure canal patency. Although apical preparation develops throughout canal enlargement, it is not completed until the end of the procedure

when greater control is possible over the files in this most delicate region of the root canal.