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Successful Single-Cone Obturation
Tricalcium silicate sealer facilitates a simplified technique with long-term stability
Randall G. Cohen, DDS
Gutta-percha, a compressible, relatively inert material, is employed when obturating canals to minimize the quantity of endodontic sealer needed, thereby limiting the impact of the undesirable qualities exhibited by many of them. Deficiencies such as dissolution, microleakage,1 shrinkage,2 and cytotoxicity3 in sealers have made it necessary to use the least amount possible when sealing the canals. To accomplish this, different methods of compacting gutta-percha have been developed, including cold lateral condensation with spreaders, warm vertical compaction with pluggers, and delivery of warm gutta-percha on a carrier. Each of these methods has advantages and drawbacks. This article will discuss a simplified technique using a single, well-fitting master cone to seal the canal-a technique made possible by incorporating a tricalcium silicate sealer.4
Canal Debridement and Disinfection
Together, biochemical preparation, microbial control, and canal obturation form the basis for endodontic therapy.5 The advances in canal instrumentation technology have been extraordinary, improving NiTi rotary instrumentation in a way that even curved canals can be prepared for simplified debridement and shaping. Generally, proper canal debridement does not require more than minimal canal enlargement, particularly if facilitated with good irrigation techniques. It has been documented that a size 35/.04 preparation to the apex is all that is needed in most canals.6After the canals are debrided mechanically and disinfected chemically, the case is ready for obturation.
The Endodontic Seal
Gutta-percha forms the bulk of the endodontic fill. It is compressible, dimensionally stable, non-resorbable, minimally reactive with periapical tissues, and easily dissolvable with chloroform should retreatment be required.
The other component to the fill is the endodontic sealer, which functions with the gutta-percha to isolate the canal in all directions. Grossman listed a number of properties centered on handling, dimensional stability, biocompatibility, and insolubility in oral fluids that make for an ideal sealer.7 However, the endodontic sealers that have been used until very recently, including his own formulation, did not fully meet Grossman's stated requirements. The inadequacies of available sealers led to the development of obturation techniques using gutta-percha to fill the bulk of the canal, which minimizes the thickness of the sealer.
Compacting gutta-percha into canals is necessary in part because the cone shape of the material does not fully fill the ovoid shape of the canals. In addition, the "step back" method of canal shaping, historically performed with hand instruments of increasing size and decreasing length, widens the coronal third of the canal, leaving voids around the master cone.
Cold lateral condensation involves fitting a master cone to length and then using a spreader to condense additional accessory cones into the space until the operator believes that the canal is obturated. Vertical compaction, originally developed by Schilder, involves fitting a sealer-coated gutta-percha cone to length, pressing a hot plugger into the mass, and then compacting the softened gutta-percha with pluggers into the apical 3 to 4 mm space.8 The apical plug remains, and the coronal part of the canal is backfilled, usually with an extrusion mechanism.
The cold lateral condensation method can result in issues that affect the long-term success of endodontic treatment, such as voids between the cones, poor adaptation to the canal walls, a lack of homogeneity, and in many cases, the presence of hydrophobic sealer at the apex where it can degrade and lead to microleakage.9
Vertical compaction presents another set of problems. One is the need to get the hot plugger within 4 mm of the apex, which can necessitate the removal of too much radicular dentin. Other issues are similar to those associated with lateral condensation: lack of homogeneity, a large proportion of endodontic sealer at the apex, poor adaption to the canal walls, and apical extrusion of gutta-percha.10
A concern with both the lateral condensation and vertical compaction methods is "how hard to push" during obturation. Excessive pressure increases the risk of root fracture.
Maintaining Coronal Dentin
The dentin within the canal is important to the long-term survivability of the tooth. Therefore, the operator must avoid over-tapering the canal, which often occurs during lateral condensation and vertical compaction cases, to reduce the chance for fracture.
Historically, the idea of using a single gutta-percha point to obturate canals was rejected because this method would depend too heavily on sealers that were subject to dissolution and shrinkage to fill the voids that surround the master point, especially in ovoid canals.11
However, there has been renewed interest in single-point obturation, driven by a new class of "bioceramic" sealers that create a tight, 3-dimensional seal all along the canal, penetrate the inaccessible portions of the canal, and set well in the presence of moisture due to their hydrophilic nature.12
This method does not require accessory points, cold lateral condensation, or warm vertical compaction. Instead, the canals are shaped using rotary NiTi files, disinfected, dried, and filled using bioceramic sealer on a single gutta-percha cone that matches the size of the last instrument taken to length. The single cone is coated with sealer and inserted to the apex, resulting in a uniform mass that eliminates the type of failures that are associated with the use of multiple cones. This simplified technique is more efficient and less time-consuming than any of the traditional methods of compacting gutta-percha. From a clinical perspective, operator and patient fatigue are reduced, preservation of coronal dentin is increased, and lateral pressure on the root is eliminated.
An elderly, male patient presented to the office with an asymptomatic lesion on tooth No. 27. He was treated with an endodontic technique that used a combination of hand files (Hedstrom files) and rotary instrumentation (Edge Endo) to debride and shape the canal. Following this canal preparation, a gutta-percha point (Edge Endo) matching the size of the last NiTi file used (ie, 40/.04) was placed, and the fit was verified. A tricalcium silicate endodontic sealer (BioRoot™ RCS, Septodont) was chosen, which provides advantages over other sealers due to its dimensional stability, biocompatibility, alkaline pH, calcium ion release, radiopacity, and flow characteristics. After mixing the sealer according to the manufacturer's directions, the gutta-percha point was rolled in the sealer mix and inserted into the canal to length. In this manner, the cone is used to coat the canal walls with sealer. The cone was then withdrawn, recoated, and inserted snugly to length. Next, the gutta-percha was finished at the level of the chamber with a hot plugger, and the seal was further refined using a round No. 2 bur (Figure 1 through Figure 3). The 1-year follow-up radiograph shows good bone replacement of the periapical lucency, indicating healing and a successful outcome.
Earlier endodontic sealers exhibited degradation, shrinkage, and some degree of toxicity to the tissues, which lead to the need to compact gutta-percha into the canal space to displace as much of the sealer as possible. Unfortunately, obturation methods involving gutta-percha are difficult to perform properly, can be time consuming, and cause patient and operator fatigue. Furthermore, they typically result in the excessive removal of coronal dentin and put the patient at risk of root fracture due to the pressure exerted by spreaders or pluggers. Additional disadvantages include potential microleakage and bacterial regrowth within the canal.
The use of a single gutta-percha point in conjunction with a tricalcium silicate sealer overcomes the problems that were associated with earlier materials. Once the operator has properly shaped the canals with NiTi endodontic instruments, sliding a single point to length is simple to accomplish. Because there is no lateral or vertical force needed, obturation is unlikely to result in a root fracture. In addition, avoiding excessive taper in the preparation maintains the coronal dentin, strengthening the tooth.
When combined with proper chemomechanical debridement, this simplified method of canal obturation meets the objectives of good endodontics. It creates a stable, bacteriostatic seal; avoids accidental fracturing of teeth during the fill procedure; and preserves radicular dentin. This approach will enable the practitioner to preserve teeth longer, especially when combined with a rational, conservative approach to restorative dentistry.
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