Before the instrumentation of a previously opened pulp cavity to remove food particles and saliva.
At intervals during instrumentation, often after each size file is used.
At the completion of canal instrumentation, before placement of medication.
When using root canal preparation type.
Canal cleansing and shaping is the progressive elimination of organic and inorganic debris within the root canal by mechanical instruments. As part of the cleansing process, the canals are enlarged and shaped with
endodontic files and reamers. Filing shapes the walls of the root canal so that they are smooth with specific size and shape.
The filing procedure begins by first establishing the approximate or estimated length of the root canal. Accurately determining the length of the tooth is vital to successful endodontic treatment. Failure to determine an accurate length may lead to apical perforation and overextension, with increased postoperative pain or incomplete instrumentation and underfilling.
The estimated length is determined from an accurate, preoperative periapical radiograph of the tooth being treated. Multirooted teeth may require radiographs from various horizontal angulations to determine the exact number and alignment of each root. The length of the tooth is measured using either an endodont ic millimeter ruler (fig. 7-17) or a file held near the radiograph from a reference point on the crown portion of the tooth to the apex. Good reference points are the incisal edges of anterior teeth and cusps on posterior teeth. Files are measured on a millimeter ruler and marked accordingly with the placement of rubber stops. The estimated working length is recorded in the patient record for future reference and modification. If necessary, a more accurate length is established as the filing process continues. The working length is verified by exposing and measuring a periapical radiograph with a reamer or tile in the canal. Once the tooth length is established, you will use an endodont ic gauge to
adjust the position of the rubber stops on the appropriate sizes of reamers and the files the dentist selects. It is important that the rubber stops be placed at a right angle to the long axis of the instrument and not an oblique angle. When the file is inserted into the root canal, the rubber stop touches the reference point on the crown when the tip of the file is at the apex of the root. With the stops in place, arrange the reamers and files in order of their use. As the filing progresses, the file sizes are increased to enlarge the size of the canal. When teeth with more than one canal are filed, it is essential that each canal be filed to a predetermined length. Occasionally, an electronic apex locator may be used to help verify the working length. Each canal can be filed to different diameters, as well as, different lengths.
During the filing, the root canal is irrigated with solution to keep the dentin shavings from the canal walls from clogging the cutting edges of the file. After the filing is complete, the canal is thoroughly flushed simultaneously with irrigating solution and suction. The canal is dried with paper points held in locking forceps and inserted into the canal to absorb the solution. This is repeated with several paper points until the paper points are completely dry when withdrawn.
After the root canal is dried with paper points, medications are occasionally placed in the canal between appointments to aid in the control of microbial activity within the tooth. A small cotton pellet is moistened with medication and blotted dry with a cotton roll or gauze. The small dry medicated cotton pellet is placed on the floor of the pulp chamber (fig. 7-18) over the opening on the canal and covered with a larger, dry cotton pellet. More often, only a dry cotton pellet with no medication is placed, or a paste of calcium hydroxide is placed into the canals before the dry cotton pellet is placed. A temporary filling must be placed over the larger cotton pellet to prevent contaminating the root canal with saliva and food
Figure 7-17. - Estimated working distance using an endodontic millimeter ruler.Continue Reading