From Volume 43, Issue 2, March 2016 | Pages 114-129
Once cleaning and shaping is complete the clinician must obturate the canal. There are many different materials and techniques available each with their own discrete advantages and disadvantages. Whichever technique is used, the goal is to seal the entire prepared length of the root canal. This paper describes how best this may be achieved.
The purpose of obturation is to seal the cleaned, shaped and disinfected root canal system and to prevent re-infection. It is now well understood that teeth that are poorly obturated are often poorly prepared.1 When assessing obturated roots, it has been shown that obturation without voids and to within 2.0 mm of the apex has a significant positive influence on the outcome of treatment.2 It has been emphasized that good obturation should create a good seal; this includes apical and coronal seal as well as lateral seal. There have been several materials and techniques developed to achieve this; however, all the materials and techniques are believed to show evidence of leakage to some degree.3
Many materials and techniques are available to obturate the root canal system. Grossman et al have described the properties of an ideal obturation material (Table 1),4 however, no single material can currently satisfy all these requirements. As such, practitioners are dependent upon a combination of sealer and some type of core material to ensure optimal obturation.
| Easily introduced into the root canal system | Should seal the canal laterally as well as apically |
| Should not shrink after being inserted | Should be impervious to moisture |
| Should be bacteriostatic or at least not encourage bacterial growth | Should be radio-opaque |
| Should not stain tooth structure | Should not irritate periapical tissue |
| Should be sterile or easily and quickly sterilized immediately before insertion | Should be easily removed from the root canal if necessary |
Sealers are a necessary part of the obturation process. They fill in the gap between the dentinal wall and the core root filling material as well as the space between the core segments, if applicable. They are also able to fill in irregularities within the canal system and are able to occlude accessory canals as well as isthmi between canals. Grossman has described the properties of an ideal sealer material (Table 2). Again, no such material exists as yet but many forms of sealer are marketed, each with specific pros and cons (Table 3).
| Should exhibit tackiness when mixed to provide good adhesion to the canal wall when set | Should establish a hermetic seal |
| Should be radio-opaque | Should be prepared in very fine powder so it can mix with liquid easily |
| Should not shrink on setting | Should not stain tooth structure |
| Should be bacteriostatic or at least not encourage bacterial growth | Should exhibit a slow set |
| Should not be soluble in tissue fluids | Should not irritate periapical tissue |
| Should be soluble in a common solvent if it is necessary to remove it |
| Type of the sealer | Example | Pros | Cons |
|---|---|---|---|
| Zinc oxide and eugenol | Pulp Canal | Long history of use | Shrinkage on setting |
| Sealer | Will absorb if extruded | Soluble | |
| EWT | Slow setting time | Can stain tooth structure | |
| Roth’s Sealer | Antimicrobial effect | May negatively affect bonding of core materials | |
| Tubli-Seal | Radio-opaque | ||
| Wach’s Sealer | |||
| Calcium hydroxide | Apexit | Antimicrobial effect (unproven) | Soluble |
| Apexit Plus | Radio-opaque | May weaken dentine | |
| Sealapex | |||
| Glass ionomer | Activ GP | Dentine-bonding properties | Hard to remove in retreatment |
| Ketac-Endo | No antimicrobial properties | Minimal antimicrobial effect | |
| Resin | AH-26 | Long history of use | Some release formaldehyde when setting |
| AH Plus | Adhere to the wall | Chlorhexidine as an irrigant can reduce their bond strength | |
| Diaket | Some can adhere to the core | May not bond any more effectively than conventional sealers | |
| EndoREZ | Do not contain eugenol | ||
| Epiphany | Slow set | ||
| RealSeal | |||
| Silicone | GuttaFlow | Triturated | Expand slightly on setting |
| RoekoSeal | Long working time | Setting time is inconsistent | |
| Fills canal irregularities with consistency | Setting time gets delayed by sodium hypochlorite | ||
| Biocompatible | |||
| Bioceramic | SmartSeal | Hydrophilic | Minimal supporting clinical data |
| SmartPaste Bio | Does not shrink on setting | Questions raised over ease of removal for retreatment | |
| Biocompatible | |||
| Antimicrobial properties |
A variety of core materials exist which can be used in conjunction with a sealer or cement (Table 4).
| Core material | Pros | Cons |
|---|---|---|
| Gutta-percha | Plasticity | Lack of adhesion to dentine |
| Ease of manipulation | Shrinkage on cooling when heated | |
| Minimal toxicity | ||
| Radio-opacity | ||
| Ease of removal with heat or solvent | ||
| Coated cones | Similar to gutta-percha | Adhesion is not complete and leakage has been demonstrated |
| Adhesion to canal wall | ||
| Resilon | Similar to gutta-percha | Formation of monoblock is controversial |
| May form a monoblock | ||
| Pro-Points | Expand to fill voids and lateral canals | Limited evidence on effectiveness |
| Used with bio-active sealer |
Gutta-percha (GP) is the most common core material used for obturation. GP cones are available in standardized and non-standardized (conventional) sizes. The non-standard nomenclature refers to the dimension of the tip and body; for example a fine medium (F-M) cone has a fine tip and a medium body. The standardized cones match the taper of the nickel-titanium and stainless steel instruments; for example, a size 30/06 cone has a tip of 0.3 mm and a taper of 0.06mm per millimetre. Any method of heating GP will result in 1–2% shrinkage of the core material. Exposure to air and light over time can result in the GP becoming brittle. Storage in the fridge extends the shelf-life of the material (Figure 1).
These core materials consist of GP coated with resin (EndoREZ), chlorhexidine or glass ionomer (Activ GP Plus). A single cone is used with the matching sealer with an aim to form a bond between the core material and the canal wall to reduce microleakage.
Resilon is a high-performance industrial polycaprolactone polyester that has been adapted for dental use to replace GP. Epiphany, RealSeal and Resinate claim that their resin-based sealer systems bond to the canal wall as well as the Resilon core to form a monoblock (see below). Resilon resembles GP and is available in standardized (2% taper) and non-standardized cones, as well as in pellet form for use in an ‘Obtura’ gun (a thermal injection technique). It can be placed using lateral compaction, warm lateral or vertical compaction or thermoplastic injection techniques. Sodium hypochlorite can adversely affect the bond strength of the primer; therefore, EDTA should be the last irrigant used before rinsing the canal with sterile water, saline or chlorhexidine. Once the canal is dried, the self-etching primer is applied and the excess is removed. The resin sealer is then mixed and applied to the working length (WL) before the canal is obturated with Resilon. It is recommended to light-cure the coronal section for 40 seconds as the sealer takes 25 minutes to set (Figure 2). The evidence supporting the use of Resilon is inconclusive. Laboratory-based tests comparing Resilon to conventional GP for lateral canal sealing, bond strength to root canals and sealing ability are equivocal.5
Pro-Points (EndoTechnologies, LLC, Shrewsbury, MA) are a new ‘smart sealing’ system. They consist of a nylon polymer core with a hydrophilic polymer coating. They are used in conjunction with a hydrophilic MTA-based sealer (SmartPasteBio, EndoTechnologies, LLC, Shrewsbury, MA). The points undergo hygroscopic expansion within the canal to fill voids. The polymer and sealer are theoretically expressed into dentinal tubules and form a seal that is resistant to micro leakage.6 There is as yet minimal laboratory or clinical evidence to substantiate these claims.
This concept is borne from the desire to place a root-filling material that bonds to dentine and forms a homogeneous mass or ‘monoblock’ within the canal. Different types of monoblock have been described based upon the number of interfaces between core materials, sealers and the root canal walls. A primary monoblock has one interface: that with the canal wall. A canal filled with MTA may be said to have a primary monoblock. A secondary has two interfaces, such as the use of a sealer and core material. A tertiary monoblock has three interfaces; classically a bonded post:
Though conceptually appealing, the concept of bonding to the root canal structure is fraught with difficulty and as yet an ideal material to achieve this does not exist.7
Several obturation techniques exist with little difference in their long-term outcome results and there is no technique that prevents leakage.8,9 There is some evidence to suggest that warm vertical compaction is superior to lateral compaction.10,11
This refers to the use of a size-matched greater taper cone to fit the preparation of the canal precisely. Such an approach is often used in conjunction with specific filing systems. This technique is often reliant upon sealer and may not adequately obturate the canal in 3 dimensions. Nonetheless, the apical portion should be well fitting. Up to 49% of dentists favour this technique and laboratory evidence suggests that this is comparable to lateral compaction12,13 (Figure 4).
A master cone corresponding to the final working length (FWL) and canal shape is chosen, coated in sealer and compacted laterally with finger spreaders. Accessory cones will be used until the obturation is complete (Figure 5). This technique does not produce a homogeneous mass and the core material and the accessory cones remain separated. As a result, sealers should be used to fill in the gaps. Excessive force whilst compacting GP may lead to root fracture.14
Tips for success include:
A master cone corresponding to the correct working length and canal size is chosen. The cone should resist displacement at this length. Once confirmed, the cone is coated with sealer and placed in the canal and compacted vertically using a heated plugger until the apical 3–4 mm segment of the canal is filled. The canal system is then backfilled using warm pieces of core material. It is important to check the apical fill radiographically before back filling, otherwise it is costly in terms of time to rectify apically inadequately fills.
A variation of this is the continuous wave compaction technique.17 It describes a method of warm vertical compaction when a commercial heating device, such as ‘System B’ or ‘Elements’, is used. After fitting an appropriated cone with sealer, the heated plugger is inserted to within 5–7 mm of the working length, either in a continuous ‘down-pack’ motion or ‘down-packing’ intermittently. After a 10-second pause, whilst the softened GP is cooling, a separation burst of heat is applied severing the apical GP. The warm GP apical to the point of severance is compacted with a flat-ended plugger and the canal is then ‘backfilled’ using an injection technique (Figures 7 and 8).
A master cone corresponding to the working length and canal shaper is coated with sealer and inserted. A warm spreader or Endotec II device is then used to compact the core material laterally. The process is then continued by using the accessory canals and the compaction is repeated. The heat results in adhesion of the accessories to the core material and a more homogeneous mass of GP is produced within the canal. An advantage of this technique over the vertical techniques is the ability to control the working length.
Warm GP or ‘Resilon’-coated plastic core carriers (more recently, guttapercha core carriers – Dentsply) are inserted into the canal to the working length. In practice a blank core must be inserted into the canal before obturation to verify length, taper and fit. Following this, the canal should be lightly coated with sealer and the point is placed in an oven to heat before being carefully but quickly inserted within the canal (Figures 9 and 10). This technique is fast and obturates the canal well, but true length control is lacking and there is a risk of extrusion of both sealer and GP. It is also easy for the GP to ‘strip’ off from the carrier before being fully inserted, leaving an inadequate fill with voids and contact of the carrier with the root wall rather than sealer and GP.
Removal of cores can be difficult in retreatment cases or when a post is intended. Though specific burs are available for removing the cores, these can be tricky to use. Plastic cores are being superseded by cross-linked GP cores (Figure 11GuttaCore, Dentsply, Tulsa, USA) and may negate some of the problems described, but as yet there is a paucity of clinical data to confirm or refute this.
A master cone coated with sealer is fitted to working length and is compacted by hand spreader and then with a rotary instrument running between 5,000 and 10,000 rpm. The rotary instrument is pre-coated with pre-warmed gutta-percha which, owing to its more fluid state, and also due to friction of the compactor and the canal wall, vectors the GP and sealer into the canal and all intricacies.
Plastic techniques have the theoretical benefit of improving obturation as the material can flow within the canal space. Injection techniques alone without a cold cone or plug of GP at the apical constriction are not advised due to difficulties in length control. Although GP is relatively biocompatible, the clinician should take care to prevent extrusions, especially into the sinus or ID canal.20
The core material is heated outside the mouth and injected into the canal system using the commercially available devices. A master cone is not usually used and the canal should be coated with sealer before injection (Figure 12).
Triturated GP is mixed with resin sealer (di-polyvinyl siloxane) in an amalgamator to form a cold flowable matrix. The matrix is injected into the canal and a single master cone is placed to the working length. The material provides a working time of 15 minutes and sets within 30 minutes. The use of a master cone within the GP sealer is advocated.
The technique involves softening the tip of the master GP cone using chloroform, eucalyptol or xylol and fitting it into the canal. The mass is then compacted using a lateral technique. Though this technique exhibits shrinkage and has been replaced by other techniques, these authors believe that there is still a place for customization of points to improve the apical fit of GP. The master point should be dipped in solvent (30 seconds for eucalyptus oil) and then inserted into the canal; it will form a custom impression of the apical region. The point is then removed, and sealer applied before being reseated with exactly the same path of entry and position.
The pastes are injected into the prepared canal as the final root-filling material, usually in the absence of a cone. Examples, such as Traitement SPAD and Endomethasone have been used in the past. These have fallen out of favour, principally because the agents are very toxic if extruded and also due to problems which include; porosities resulting in poor seal, inadvertent extrusion and difficulties presented for retreatment.
An apical barrier technique plays an important role when obturating teeth with open apices. Mineral trioxide aggregate (MTA) is the material of choice. MTA is compacted by hand to fill the apical 3–5 mm of the canal. Initially it is a good idea to create a 1–2 mm plug first at the apex and then check this radiographically. Once this has been placed satisfactorily, further MTA can be placed coronal to this. A total of 3–5 mm of MTA should be placed in increments with either hand instruments or micro pluggers. This is often only possible in wider, straighter canals. The remainder of the canal system can then be filled with an injection technique (Figures 13 and 14).
There are risks and benefits to all systems (Table 5). We recommend operators familiarize themselves with multiple systems: this affords the ability to adapt to the clinical scenario presented. Furthermore, it is possible to ‘pick and mix’ techniques. A classic example of such may be in the case of upper incisors, where the canal is wide and greater taper cones do not fit ‘snuggly’ following preparation. The operator may choose cold lateral compaction to obturate the apical 50% followed by a ‘continuous wave technique’, which can soften the laterally condensed GP, giving a more homogenized fill, before adding further GP more coronally.
| Method | Example | Pros | Cons |
|---|---|---|---|
| Single point | Matched greater taper preparation and GP point | Simple |
Inadequate fill |
| Cold lateral compaction | ISO GP and accessory points | Commonly taught Good for canals without standardized tapers |
Compaction of GP only |
| Warm vertical condensation | Schilder technique Continuous wave condensation | Good 3-dimensional obturation | Technique sensitive |
| Thermomechanical techniques | McSpadden technique | Good 3-dimensional obturation | Risk of apical extrusion |
| Carrier-based systems | Thermafil Guttacore | Single point technique |
GP may strip from carrier |
| Plastic techniques | Obtura Guttaflow | Good 3-dimensional obturation | Risk of apical extrusion |
| Apical barrier | MTA | Good apical control of material |
Expensive |
Recent evidence suggests that, for every mm a canal is underfilled, the success of the root treatment drops by 12%. If the GP is over extended, the success drops by 62%.23 This supports the adage that it is preferable to be short of the apex than long, but alerts the clinician to the importance of attempting to shape and obturate to within just 2 mm of the anatomical apex. Assuming apical patency and adequate working length was achieved, three possible scenarios may result that do not favour a good outcome. These are as follows16,24 (Figure 15).
This reflects both poor apical fit of the cone and poor obturation technique. These cases may fail and retrieval of overextended GP is not easy. A carefully rotated Hedstrom file into the GP may be sufficient to pull out the entire point during retreatment, but often these cases can only be managed surgically. If the working length (WL) measurement is 22 mm, and the GP fits snugly at 27 mm, the operator should be alerted to the possibility of an error somewhere!
This may be a reflection of overzealous apical preparation and loss of apical architecture but can occur when there is an immature apex or external inflammatory resorption.25 There is evidence that a more aggressive apical preparation may have a more favourable healing but the clinician must always aim to remain within the canal and preserve the apical constriction.26 If there is pre-operative radiographic evidence of changes in the periapical anatomy, or anticipated difficulty in controlling obturation, the clinician must consider an alternative technique, such as the use of MTA as described above.
This is indicative that the canal space has not been adequately shaped and/or cleaned, as such bacterial colonies may remain within the root canal system and disease can persist.
There is minimal evidence to support the use of one method of obturation over another. All techniques have advantages and disadvantages. Decision-making should be based upon the clinical scenario, not dogma. As such, having a broad knowledge of the options helps the clinician choose the optimal technique for the tooth being treated.
