The 2010 Star of the North Meeting Table Clinic Winners

The 2010 Star of the North Meeting Table Clinic Winners

Jeffrey Wiswall, D.D.S.; and Brian Meade, D.D.S., University of Minnesota Division of Endodontics:

Editors' note: The following abstract is the third of the three table clinic winners from this year's Star of the North Meeting.


Indirect Ultrasonic Energy - The Peters Technique

Most clinicians have faced the challenge of treating root canal systems obstructed with separated instruments. Often, these blockages inhibit access to the apical terminus of these canal systems. Our ability to safely remove these obstructions may be critical to proper chemo-mechanical debridement of these systems. While studies have varied on the measureable effect of separated instruments on treatment outcomes, consensus exists that root canal systems devoid of bacteria heal more consistently than those with bacteria1-4.

Traditional methods to retrieve such obstructions often require the removal of greater amounts of tooth structure, potentially leading to perforation or eventual vertical root fracture. These risks can be minimized by employing the “Peters Technique”, introduced by a practicing endodontist in Mankato, Dr. Scott Peters. This technique utilizes ultrasonic energy transmitted through a specialized endodontic explorer, thereby converting it into an active, cutting tip and allowing precise and accurate removal of tooth structure.

The clinician’s decision tree for case selection with this technique is similar to other instrument retrieval methods. The clinician must weigh the risks against the benefits for each individual case. Consideration should be given to the stage of canal preparation achieved prior to when the instrument separated. Necrotic canals containing bacteria that have a separation early in the instrumentation and irrigation sequence should be treated more aggressively than those with vital contents, or those late in the chemo-mechanical debridement sequence. The clinician’s ability to bypass an obstruction may allow cleaning and shaping beyond the separated instrument without the need for removal. As with any technique, straight-line access to the obstruction is required. Lack of straight-line access typically limits retrieval of separations that occur in the apical third. Additionally, adequate visualization of the segment under a surgical microscope is required to utilize the technique.1 Understanding these principles aids in the precise removal of dentin around the obstruction, and helps the clinician to both conserve dentin and avoid danger zones in certain teeth.5,6

Prior to employing the Peters Technique, the clinician planes the walls of the canal to create a smooth surface and verifies straight-line access to the separated segment. A staging platform made with a modified Gates Glidden creates a flat surface that allows precise removal of dentin around the segment of file. The unique feature of the Peters Technique is the JW-17 endodontic explorer (CK Dental, USA). The JW-17 has several advantages over traditional endodontic explorers, such as the DG-16. First, the explorer has a thinner tip. This permits greater visualization around the head of the explorer, and at the same time conserves more tooth structure. Second, the specific metallurgy of the JW-17 resists fracture during the application of ultrasonic energy. The Peters Technique is four-handed. The auxiliary lightly applies ultrasonic energy to the JW-17 with an ultrasonic tip. Communication between the clinician and the auxiliary aids in finding a “sweet spot”, or a contact area, on the JW-17 that gives the best energy transmittal. This turns the normally passive end of the JW-17 into an ultrasonically activated cutting tip that can be used for precisely removing dentin around the separated instrument. Following the exposure of the separated instrument, one of two instrument removal techniques can be employed. Exposure of a portion of the segment and retrieval with a needle sleeve technique may be accomplished. Alternatively, the clinician may continue to apply energy to the segment laterally while removing dentin circumferentially. This transfers energy to the segment, loosening it and eventually causing it to “jump” from the location in which it was lodged.

The Peters Technique has several advantages over traditional instrument removal techniques. First, the decreased cost of the instrument is considerable when compared to manufactured ultrasonic tips. Additionally, the JW-17 has a much lower fracture rate than these manufactured tips. Visualization is greatly enhanced due to the narrow working tip of the JW-17. Because the tip of this explorer is so narrow, it allows minimal removal of dentin and very precise cutting around the offending segment. Furthermore, a greater dislodging force can be applied to the obstruction because of the JW-17’s increased fracture resistance.

While instrument fracture rates are generally reported as low, the most sure-fire method of instrument retrieval is prevention.7,8 As with many dental procedures, case selection in endodontics is paramount for success. Identifying curvatures pre-operatively with multiple angled radiographs can help to minimize separations. Considerable attention must also be given to achieving straight-line access, as well as establishing and maintaining a glide path throughout the procedure. When indicated, instrument retrieval may be a valuable service to our patients. While no method completely eliminates the risks associated with retrieval, the Peters Technique has many advantages that other methods may lack.



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            2.         Kakehashi S, Stanley HR, Fitzgerald RJ. The Effects of Surgical Exposures of Dental Pulps in Germ-Free and Conventional Laboratory Rats. Oral Surg. Oral Med. Oral Pathol. 1965;20:340-349.

            3.         Möller AJ, Fabricius L, Dahlén G, Ohman AE, Heyden G. Influence on periapical tissues of indigenous oral bacteria and necrotic pulp tissue in monkeys. Scand J Dent Res. 1981;89(6):475-484.

            4.         Lin LM, Di Fiore PM, Lin J, Rosenberg PA. Histological study of periradicular tissue responses to uninfected and infected devitalized pulps in dogs. J Endod. 2006;32(1):34-38.

            5.         Degerness RA, Bowles WR. Dimension, Anatomy and Morphology of the Mesiobuccal Root Canal System in Maxillary Molars. Journal of Endodontics. 2010;36(6):985-989.

            6.         Berutti E, Fedon G. Thickness of cementum/dentin in mesial roots of mandibular first molars. J Endod. 1992;18(11):545-548.

            7.         Wolcott S, Wolcott J, Ishley D, et al. Separation incidence of protaper rotary instruments: a large cohort clinical evaluation. J Endod. 2006;32(12):1139-1141.

            8.         Shen Y, Haapasalo M, Cheung GS, Peng B. Defects in nickel-titanium instruments after clinical use. Part 1: Relationship between observed imperfections and factors leading to such defects in a cohort study. J Endod. 2009;35(1):129-132.