Drs. Mehmet Baybora Kayahan, Noyan Başal, and Esra Pamukçu Güven present a novel retrograde root canal shaping technique in which a combination of NiTi files and specially designed tubes are used



The success of endodontic treatment is described as the absence of symptoms and clinical signs of infection in a root-filled tooth that has also no radiographic evidence of periodontal involvement (Hoen and Pink, 2002; Wu and Wesselink, 2005). Nevertheless, it has been reported in some studies that a significant percentage of endodontically treated teeth is associated with periapical pathosis and poor treatment quality (Abramovitz et al, 2002; Gesi et al, 2003).

When failure occurs, nonsurgical retreatment via an orthograde approach is the treatment of choice, if the canals are accessible (Abramovitz et al, 2002; Kim and Kratchman, 2006). However, in some cases—such as teeth with an altered root canal morphology or teeth restored with posts, particularly zirconia—it can be impossible to solve the problems nonsurgically (Wu and Wesselink, 2005; Kim and Kratchman, 2006; Wagnild and Mueller, 2006). In these cases, surgical endodontics is indicated.
Although periapical surgery is an important method in contemporary endodontics, conflicting results have been reported for the success rate of this treatment (Boykin et al, 2003).

Kvist and Reit (1999) followed 45 cases for 4 years and reported 60% healing. In contrast, recent reports showed a success rate of over 90% (Rubenstein and Kim, 2002; Maddelone and Gagliani, 2003). It was reported that the high success rate in surgical endodontics could be attributed to the introduction of magnification through the use of microscopes, new concepts in soft and hard tissue management, and biologically acceptable root-end filling materials (Kim and Kratchman, 2006).

There is no doubt that the outcome of periapical surgery mainly depends on the retrograde cavity preparation and root-end filling, which isolates the root canal system from the periapical tissues (von Arx et al, 1998; Navarre and Steiman, 2002; Plotino et al, 2007). However, in some cases, the root-end cavity preparation and retrofilling procedure is not enough to fill the entire root canal. As the main purpose of root canal treatment is to clean, shape, and fill the root canal system, this aim must also be considered during periapical surgery. Otherwise, surgery can isolate but not eliminate the bacteria from root canals (Friedman, 2002).

It is not uncommon to detect a tooth with a resorbed root canal filling that has been restored with a cast post. In such cases, it is not feasible to perform a nonsurgical retreatment; therefore, it may be recommended to shape the root canal in a retrograde manner, from apical to coronal. This technique was first introduced by Reit and Hirsch (1986) and was described as retrograde root canal treatment, which was presented later in some case reports. This method was also tested in vitro by Wu et al (1990), who concluded that teeth shaped in a retrograde manner and filled 7-mm deep leaked significantly less compared to teeth filled with the traditional retrograde fillings.

Several methods are described in the literature to access these unprepared parts of the root canal system that conventional tips cannot reach. While some clinicians prefer to retroshape the root canal with a file held with a hemostat, others bend hand files for the retrograde preparation (Friedman, 2005; Jonasson et al, 2008). Despite a number of satisfying reports, this approach has not gained popularity likely because of the difficulties in retrograde shaping. It is not practical and may be time consuming to shape the root canal with a bent file or a file held with a hemostat (Jonasson et al, 2008).

The width of the bony crypt can also be a problem during the upward and downward movement of the file. It is clear that a novel approach is required to shape the root canal in retrograde root canal treatment. Hand and rotary files made of nickel titanium (NiTi), which is a flexible memory metal that revolutionized root canal shaping, are available today (Deplazes et al, 2001). Thus, it should be possible to benefit from NiTi files in retrograde root canal treatment. The aim of this article is to present a novel retrograde root canal shaping technique in which a combination of NiTi files and specially designed tubes were used.

Case report

A 25-year-old woman presented with pain in the region of the anterior teeth. During clinical examination, it was observed that the teeth were restored with crown restorations, and the patient had undergone orthodontic treatment (Figure 1). It was also detected that the maxillary right central incisor was sensitive to periapical palpation. Radiographic evaluation revealed that both the maxillary right and left central incisor teeth were restored with post restorations.

However, there was no root canal filling beyond the posts (Figure 2). Because the patient was happy with her restorations, and removing the post-and-crown restoration could result in serious clinical complications (such as root fracture and strip perforation), periapical surgery was indicated.

After it was confirmed that the medical history was also noncontributory, it was decided that periapical surgery should be performed both in the maxillary right and left central incisor teeth. The patient was informed about the treatment in detail. After the anterior region was anesthetized with 4% articaine hydrochloride with 1:100000 epinephrine (Ultracain® D-S Forte, Sanofi-aventis), a full-thickness mucoperiostal flap was reflected from tooth No. 12 to tooth No. 22 (Figure 3). Bone covering the periapical area was removed with round burs in a low-speed handpiece under continuous saline irrigation. Approximately 2 mm was removed from the tips of the roots without beveling. After preparing the bony crypt, bleeding was controlled by a hemostatic agent (ViscoStat®, Ultradent Products, Inc.) (Figure 4).



Retrograde root canal treatment procedure

The canals were identified with a Micro-Opener (Dentsply Maillefer, USA). To perform identification, the tip of the Micro-Opener was bent according to the shape of the bony crypt. After locating the root canals, it was decided that the root canal of the maxillary right central incisor would be shaped with the aid of tubes bent to facilitate the retroshaping. The tubes were made of stainless steel and were sterilized prior to use. Hero 642® (Micro-Mega) NiTi rotary files were used to shape the root canal (Figure 5).
With the guidance of the tube, which was held with a hemostat, the root canal was prepared with 2% tapered #20, 2% tapered #25, and 2% tapered #30 NiTi rotary files (Figure 6). During the shaping procedure, the root canal was copiously irrigated with 0.5% sodium hypochlorite.

Distilled water was the final irrrigant. The perforated irrigation needle (KerrHawe SA) was also positioned with the aid of the tube inside the root canal. To prevent spillage of the irrigant, a Surgitip aspirator tip attached to a Luer Vacuum Adapter (Ultradent Products) was used for aspiration.
After shaping and irrigation, the root canal was dried with paper points (DiaDent) (Figure 7).

The root canal was then obturated using a single-cone technique with an ISO #30 gutta percha cone. AHPlus® (Dentsply) was used as a sealer. The sealer was carried by a Pastinject lentulo (Micro-Mega) with the help of the tube. After obturation, the opening of the retrograde cavity was sealed with mineral trioxide aggregate (MTA) (ProRoot® MTA, Dentsply/Tulsa Dental) to isolate the root canal filling. The retrograde cavity of the maxillary left central incisor was prepared only with ultrasonics and was in a retrograde manner filled with mineral trioxide aggregate (Figure 8). At the end of the procedure, the flap was re-approximated and sutured with 4/0 silk suture.

The maxillary right central incisor was asymptomatic clinically and radiographically at the 6-month follow-up (Figures 9A and 9B). The maxillary left central incisor also showed no symptoms of infection at the same follow-up period (Figures 9A and 9B). The 12-month follow-up radiograph revealed healthy periapical tissues for both teeth (Figure 10).

Discussion

The purpose of the tube introduced in this report is to function as a guide in shaping the root canal from apical to coronal during apical resection in teeth that cannot be accessed coronally, such as those restored with cast posts or zirconia posts, or with altered root canal morphology from a previous root canal treatment.

This idea of using tubes for retrograde root canal shaping is an improvement on conventional retroshaping approaches performed with hand files. The tube is cylindrical in shape and curved to form an “A” angle. This “A” angle, which varies between 90 and 120 degrees, provides direction for more effective use of the root canal instrument. The long edge, on the upper side of the A angle, is 5 mm, and the short edge, which is on the lower part after the curvature, is 2 mm long (Figure 11).

During application, the long edge is held by any holder, such as a hemostat. Similar to ultrasonic surgical retrotips, the length of the edges and A angles of tubes may vary according to the location of the resected root. Because it is an advantage to perform retrograde preparation and filling more deeply (Wu et al, 1990), it seems that the guidance provided by the tube could fulfill this goal. Compared to other retrograde shaping methods, such as the application of bent stainless-steel files or Hedstrom files held with a hemostat, retroshaping with the guidance of a tube is faster and more effective because the width of the bony crypt is not a problem during the upward and downward movement of the file. One other advantage is that there is no need to remove additional bone to facilitate retrograde instrumentation. Particularly in cases where there is no periapical lesion, and the bony crypt is smaller in size, the tube provides easy access to the apical part of the root. Moreover, the root canal can be isolated from the surgical site by the application of the tube; thus, files are not contaminated while shaping the root canal.



In the case presented, the root canal was shaped with 2% tapered Hero 642® NiTi rotary files, which have a triple helix cross-section with a non-cutting passive tip. However, NiTi hand files can also easily be used with tubes.

Recent developments in the physical properties of NiTi, such as higher resistance to cyclic fatigue, support this approach (Plotino et al, 2009). The root canal was also irrigated by the guidance of the tube. In this case, a #30-gauge, stainless-steel, perforated irrigation needle was used for this purpose; however, NiTi irrigation needles could also be used. Sodium hypochlorite was the irrigant. Although there have been conflicting reports about the concentrations of sodium hypochlorite, 0.5% NaOCl was preferred to minimize irritation of hard and soft tissue. In addition, surgical tips designed for apical surgery can be used to avoid transferring the irrigation solution into the bony crypt.
The root canal was obturated using a single-cone technique, and the opening of the retrograde cavity was sealed with MTA to prevent leakage. The root canal could also be filled with theramoplasticized gutta percha techniques.



While there was short unprepared root canal space beyond the post in the maxillary left central incisor tooth, it was indicated to prepare the retrograde cavity only with ultrasonics. On the other hand, retrograde root canal preparation was indicated in the maxillary right incisor tooth because there was more unprepared root canal space, and deeper preparation was required. Follow-up radiographs revealed healthy periapical tissues in both teeth.

With the help of tubes, it will be easier to shape, irrigate and obturate the entire root canal system in a retrograde manner. Moreover, as presented in this case, this novel approach is not complicated for the clinician who is familiar with conventional apical surgery. The technique does not constitute an obstacle for today’s retrograde filling methods.

After shaping and filling the canal from the root apex, the retrograde cavity opening can be prepared with ultrasonic tips as in conventional methods, and a retrograde filling material such as mineral trioxide aggregate can be placed.

Conclusion

This article describes a novel approach in retrograde root canal treatment. The proposed technique to retroshape the root canals with the assistance of bent tubes might be a promising method. However, more clinical data are needed to verify the method.

Bios

Mehmet Baybora Kayahan, DDS, PhD, is associate professor in the department of endodontics, faculty of dentistry, Yeditepe University.

Noyan Başal, DDS, PhD, is in private practice limited to oral and maxillofacial surgery.

Esra Pamukçu Güven, DDS, PhD, works in the department of endodontics, faculty of dentistry, Yeditepe University in Istanbul, Turkey.

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