Wednesday, December 14, 2011

Coronal preparation or radicular access

Coronal preparation or radicular access, First, the pulp chamber is copiously irrigated with sodium hypochlorite. Gates Glidden burs are next introduced into the canal, directed apically and laterally away from the furcation. The larger sizes are introduced first, working sequentially further down the canal with smaller sizes. Some canals will accept a size 6 bur, but normally a size 4 would be used first, followed by a size 3. Each bur will penetrate 2 3 mm further than the previous one. EDTA paste should be used with each bur, and the canal should be irrigated between each entry. Eventually, in a relatively straight canal, the No. 2 bur is inserted 10 12 mm into the canal from the occlusal reference point. In a curved canal the pre-operative radiograph should be checked for the maximum straight line penetration of the bur.
Gates Glidden burs should be rotated with constant medium drill speed from the time they enter the canal until removed. Gates-Glidden burs must not be taken into a curve, or they will almost certainly fracture. If the shank of a bur does break, it usually does so near the handpiece head and may be retrieved easily from the tooth, as seen in Figure 11. However, if the head does become separated from the shank within the canal, removal may be extremely difficult.
The bur may be flexed against the canal wall slightly on withdrawal to ensure that the natural shape of the canal is maintained. Thus a round canal will remain round, but an oval canal will be prepared to a smooth oval funnel. A wide oval or  figure-of-eight  shape may need preparing at both extremities to produce a wide flare. Instrumentation with the stepdown technique in the radicular access is accomplished using only light pressure directed apically and away from the furcation, or perforation may result.
An alternative to Gates Glidden burs is the use of standard flexible K-type files with safe tips, used with the balanced force technique. Following initial widening of the mouth of the canal only with a Gates Glidden bur, the largest hand file which will enter the canal is selected and worked apically, using
EDTA paste as a lubricant.  Once penetration proves difficult the file should not be forced further, or fracture may result.  The next size smaller file is selected, and sequentially smaller files used until the coronal preparation is complete.