6.2.1.1 Zinc Oxide‐Eugenol Sealers

ZOE sealers have a long history of use in endodontics, and have commonly been considered the standard sealer for many decades. The original formulation took the form of a powder/liquid with silver particles to provide radiopacity [18]. Unfortunately, the presence of these particles caused this sealer to stain the teeth.

Rickert’s formula is commercially marketed as Pulp Canal Sealer, in both a standard and an extended working time (EWT) version. According to the manufacturer, it is a non‐irritating, radiopaque sealer. The EWT version has a setting time in excess of 6 hours, compared to 20–40 minutes for the basic formulation. Grossman modified Rickert’s formula, introducing a nonstaining ZOE sealer in 1958. This formulation is marketed as Roth’s Sealer and Tubli‐Seal; the latter is a catalyst/base sealer, which means that it has a faster setting time when compared to the earlier powder/liquid versions. These sealers also exhibit antimicrobial activity [19]. Proco‐Sol (Star Dental, Lancaster, PA, USA) is a nonstaining modification of Rickert’s original sealer with the silver particles removed. Another ZOE sealer, Wach’s Paste, has Canada balsam added, which makes it more viscous.

As a group, ZOE sealers require water in their setting process, are cytotoxic to the periapical tissues, shrink on setting, are soluble, and can stain tooth structures [20]. Since gutta‐percha soaked in eugenol shows an increase in volumetric expansion, and eugenol may exist in fresh mixes where it is not crystallized fully as zinc eugenolate, this combination of root filling materials may counteract the shrinkage sustained by any sealer [21].

6.2.1.2 Calcium Hydroxide Sealers

Calcium hydroxide sealers were initially developed to take advantage of the antimicrobial properties of calcium hydroxide, with the idea that they would display bioactive potential [22]. However, they have not shown bioactivity [20]. Sealapex, Apexit, and Apexit Plus are popular commercially available versions.

Calcium hydroxide sealers have been reported to be both soluble and cytotoxic [23]. The seal achieved is similar to that produced by ZOE sealers [24]. Dentalis (Neo Dental, Federal Way, WA, USA) is a calcium hydroxide sealer with iodoform, which gained US Food and Drug Administration (FDA) approval in 1997; this material exhibits excellent radiopacity but must be avoided in patients with an allergy to iodine.

6.2.1.3 Glass Ionomer Sealers

Glass ionomer cement (GIC) sealers were developed as restorative materials in the early 1970s [25]. They offered the potential to bond to dentine, suggesting a leak‐free root filling might be achievable. Initial research [26] on their endodontic use showed greater dye leakage compared to AH 26. The first GIC sealer set too rapidly to allow the use of the lateral condensation filling technique. For endodontic application, radiopacifiers were required, and modifications had to be made to the powder to increase its setting time. Prototype materials had similar leakage to Pulp Canal Sealer [26].

A commercial GIC sealer, Ketac Endo, was formulated in the early 1990s. The manufacturer’s data of the time stated particle sizes from less than 1 μm to a maximum of 25 μm and a working time of 40 minutes. It was claimed that the adhesion to dentine would cause treated teeth to be strengthened. Initial research reported a snap set, leaving a working time of just 60 seconds. Considering the time needed to transport the sealer to the root canal system, this resulted in radiographically detectable voids in the resultant root filling [27].

A single‐cone gutta‐percha technique is necessary with GIC sealers in order to allow retreatment; this way, space can be created to reinstrument the canal following gutta‐percha removal. Later work investigated Vitrebond (3M ESPE), a resin‐modified GIC, as a sealer; it was found that the bond to gutta‐percha was not better than that with a ZOE sealer, but there was good adaptation to the root canal wall and it penetrated into dentinal tubules [28]. Vitrebond has a mean particle size of 25 μm and a range 8–40 μm; its fluoride release may have a caries inhibitory effect.

The seal of Ketac Endo sealer was compared with AH 26 [29] and showed a higher leakage, which was attributed to its fast setting, higher volumetric shrinkage, and adhesive failure during setting. Support for the clinical use of Ketac Endo is derived from a 1995 study of 486 teeth treated by three operators [30]; the authors observed that any extruded material was not absorbed by the tissues in their 6–18‐month observation period.

Bond strengths of GIC sealers to root canal walls were investigated [31], and it was found that phosphoric and citric acid were preferable for smear layer removal to ethylene diamine tetracetic acid (EDTA) when using Ketac Endo. Bonding without prior removal of the smear layer could not be measured. The bond strength of Ketac Endo and AH Plus to gutta‐percha was better than that to tooth structures [32]. It was speculated that the GIC would chelate with zinc components in the gutta‐percha cones. This work draws attention to apical leakage at different interfaces. The disadvantages of GIC as a sealer include its poor antibacterial activity [19] and the difficulties it presents during retreatment, as there is no known solvent.

GICs exhibit some antimicrobial properties due to fluoride release, low pH values when setting, and the presence of cations such as strontium and zinc [33]. An experimental GIC‐based root canal sealer, ZUT, was developed at the University of Toronto, with an emphasis on enhancing antimicrobial properties. This consisted of a GIC base combined with antimicrobial zeolites: porous ceramic (aluminosilicate) structures that can enclose a core material, which may be either an alkali earth metal ion or an organic molecule (e.g. pharmaceutical). The proportion of the zeolite in the GIC powder can vary depending on the desired physical properties of the material and the antimicrobial dose required. A study was conducted to compare the antimicrobial effects of ZUT with Ketac Endo, using Enterococcus faecalis as the test organism [34]. Ketac Endo suppressed E. faecalis effectively 24 hours after preparation, but failed to do so one week later. ZUT formulations showed a strong antimicrobial effect that was sustained for long periods. They had better or similar cytotoxicity to Ketac Endo and two AH 26 formulations (with and without silver) [35].

6.2.1.4 Resin Sealers

There are two main categories of resin sealers: epoxy resin sealers and methacrylate resin sealers. Epoxy resin sealers have repeatedly demonstrated excellent physicochemical properties and are considered the gold standard in many experiments. AH Plus, for example, has been widely used for over two decades [36]. It superseded the original AH 26, which became unpopular due to its release of formaldehyde, which reacted with the bismuth oxide in the preparation, leading to tooth and material discolouration [37]. AH Plus contains zirconium oxide and calcium tungstate instead of bismuth oxide. It is less cytotoxic than AH 26, can be used in a thinner film (Figure 6.2), has a lower solubility, and releases only a minimal amount of formaldehyde. It is now one of the most commonly used sealers as it forms a strong bond with dentine and has a low solubility and satisfactory dimensional stability [38–41]. Its disadvantage is that it does not display any bioactivity or osteogenic potential [42, 43]; however, this means that it is more stable. An excellent literature review is available [44].

Complex canal systems require considerable time to obturate and thus need sealers with extended working times. Furthermore, if heat is used during obturation then sealer setting time will become even more extended. When AH Plus is used with warm gutta‐percha techniques, the chemical changes involved will adversely affect its physical properties [45, 46]; its setting time will be reduced and its film thickness increased [17]. The choice of irrigant should be carefully considered when selecting resin‐based sealers, as the final rinse can have a positive influence on adhesion to dentine. The use of EDTA and sodium hypochlorite increases the bond strength of AH Plus to dentine; neither solution affects the bond strength of resin‐based root canal sealers, whilst both have a negative effect on HCSC sealers [47].

Methacrylate resin root canal sealers first appeared in the 1970s. As existing root canal filling materials did not bond to root canal dentine, methacrylate resin sealers were promoted as being adaptable and bondable, creating a ‘monoblock’ system. Many generations of these sealers have since been developed. A fourth‐generation one is marketed as Epiphany/RealSeal (SybronEndo, Kerr Endodontics); the manufacturer claims that it bonds to the Resilon (Pentron, Wallingford, CT, USA) core (see later) and attaches to the etched root surface, resulting in a gap‐free, solid mass in the root canal. It has been concluded, however, that methacrylate resin sealers do not create a monoblock root filling and fail to prevent leakage [48].

An experimental resin sealer composed of 70 wt% vinylidene fluoride/hexafluoropropylene copolymer, methyl methacrylate, zirconia, and tributylborane catalyst has been developed, called Endoresin [49]. Its dentine bonding and sealing ability were evaluated, and good adhesion to both dentine and gutta‐percha was demonstrated in comparison to controls (Pulp Canal Sealer EWT and Sealapex). Endoresin‐2, a modified version, was subsequently developed to overcome the problem of supply of the fluoropolymer, which was a key component of the initial formulation. This fluoropolymer is substituted with polymethylmethacrylate. The new material has been found to have good sealing ability, high adhesiveness to dentine, and easy removability [50].

6.2.1.5 Silicone Sealers

RoekoSeal is a polydimethylsiloxane‐based sealer which expands slightly on setting (0.2%) and is very radiopaque; the claimed advantages include good sealing ability [51], excellent biocompatibility [52], and very low cytotoxicity [53].

GuttaFlow (Coltène/Whaledent) is a modified version containing particles of gutta‐percha <30 μm in size. It expands similarly on curing and is considered almost insoluble. It is used with a single master gutta‐percha cone, without mechanical compaction, although lateral or vertical condensation is acceptable. Its flow into lateral grooves and depressions in the apical regions of root canals is significantly better than the lateral condensation or warm compaction of gutta‐percha combined with AH 26 sealer [54]. It is also effective in filling oval‐shaped canals [55]. Its sealing qualities are similar to obturations obtained by lateral compaction or the System B technique with AH 26 [56]. All traces of irrigants must be thoroughly removed by rinsing the canal with water or isopropyl alcohol prior to its introduction. GuttaFlow has a working time of 15 minutes and a setting time of about 30 minutes, whilst GuttaFlow FAST has a working time of 5 minutes and a setting time of 10 minutes. A potential concern is extrusion of material beyond the apex [54], although its cytotoxicity is lower than that of some other sealers.

GuttaFlow and GuttaFlow2 (Coltène/Whaledent) consist of a small amount of gutta‐percha in RoekoSeal in a capsulated form. The material is injected into a canal, and then a single gutta‐percha master cone is then placed.

6.2.1.6 HCSC Sealers

HCSC sealers feature a hydration setting reaction and have a hydraulic nature, representing a major shift in the chemistry of sealer types. They are mostly based on tricalcium or dicalcium silicate, and their main characteristic is the formation of calcium hydroxide when setting in contact with water [57, 58]. Unlike other sealer types, HCSC sealers interact with the clinical environment, leading their chemistry to change accordingly; this characteristic has been termed ‘bioactivity’. They do not conform to the ISO 6876;2012 standard for sealer ideal properties [15], which was developed for materials that are stable and whose chemistry does not change in use [59].

Based on the classification proposed in Chapter 1, there are five types of HCSCs. Most are composed of a cement and a radiopacifer, and are either mixed with water or delivered in a nonaqueous vehicle. They set when in contact with the surrounding tissues. Endo CPM Sealer (Egeo, Buenos Aires, Argentina) is composed of Portland cement and a radiopacifer and is mixed with water and an accelerator [60]. It is a good example of a Type 2 HCSC, since it is a Portland cement type with additives and mixed with water. MTA Fillapex (Angelus, Londrina, Brazil) has a salicylate‐resin matrix and thus can be classed with the calcium hydroxide sealers. However, Type 3 HCSCs are Portland cement‐based with additives and a nonaqueous carrier, so it could fit in this category as well. Furthermore, MTA Fillapex only sets in a moist environment [59], another typical property of the Type 3 HCSCs. Endoseal (Maruchi, Wonju, Korea) is another premixed Type 3 HCSC. Type 4 HCSCs include those that are tricalcium silicate‐based with additives and mixed with water, such as BioRoot RCS. Type 5 HCSCs are all premixed sealers based on tricalcium silicate, such as the Totalfill BC sealer.

Endodontic hydraulic sealers are hydrophilic, setting by reaction with water. They are dimensionally sound, expand on setting, and have excellent properties for root canal sealing [61, 62]. However, their dimensional stability is dependent on the environment, as drying out will lead to shrinkage [63]. The pH of unset hydraulic sealers is above 12, due to the formation of calcium hydroxide and subsequent dissociation into calcium and hydroxyl ions [64, 65]. When mixed with water, a matrix of calcium silicate hydrates and calcium hydroxide is formed, which hardens with time. The calcium hydroxide is then released, which has been linked to bioactivity [66]. It has been shown in vitro that it reacts with phosphate ions in physiologic fluid, resulting in the precipitation of hydroxyapatite [67, 68]. This is a similar interaction to that of bioactive glass [69]. It is enhanced by the availability of phosphates in the canal, such as with a final phosphate‐rich irrigating solution [70]. This has been shown for a number of sealers when in contact with dentine [71]. The hydroxyapatite coprecipitates with the calcium silicate hydrate, reinforcing the set material. These properties improve the tissue attachment of bioactive materials [72]. HCSC sealers demonstrate radiopacity, which is enhanced with a radiopacifier, and they flow in accordance with ISO 6876/2012 [15], with a minimum radiopacity equivalent to 3 mm of aluminium [73].

6.2.1.6.2 Type 3 HCSC Sealers

MTA Fillapex (Angelus) sealer is an HCSC‐based, salicylate resin root canal sealer. It was created in an attempt to combine the biocompatibility and bioactive potential of MTA with a synthetic resin, which demonstrates sound physical properties. It consists of a yellow‐coloured base paste and white catalyst paste. It is indicated for use in cold and warm root canal filling techniques [84]. It has a high pH and therefore displays antimicrobial activity. It was found to produce a greater zone of inhibition against E. faecalis in an agar diffusion test when compared to Endo CPM Sealer; however, neither sealer material was able to sustain this antibacterial effect seven days after mixing [85].

MTA Fillapex is more radiopaque than BioRoot RCS, a tricalcium silicate root canal sealer, but less so than the conventional sealers, such as AH Plus and Pulp Canal Sealer [86]. It has a radiopacity equivalent to 7 mm of aluminium, due to the presence of bismuth trioxide [87]. Other researchers report a lower radiopacity value [84]. According to the manufacturer, its composition after mixing is essentially MTA, salicylate resin, natural resin, bismuth, and silica, and it has a setting time of less than 240 minutes. It has a high flow rate (Figure 6.3) and can fill lateral and accessory canals. It has been reported to have higher solubility, dimensional and volumetric change, and porosity compared to AH Plus [88], as well as significantly less leakage [89]. When compared to a ZOE sealer, depending on whether there is bismuth oxide in its formulation, discolouration is minimal on placement in the pulp chambers of molar teeth [90]. Recent studies have demonstrated contradictory results regarding cytotoxicity and genotoxicity, with MTA Fillapex displaying no biocompatibility or bone tissue repair and instead inducing an irritating effect on tissues [91–96]. Other recent studies have concluded that it is cytotoxic [97, 98]. Therefore, despite the presence of MTA, this formulation may not have the intended biological advantages.

Other sealers based on Portland cement and using nonaqueous vehicles have been introduced. One is Bio‐C Sealer (Angelus, Londrina, Brazil), which is based on Portland cement, a radiopacifier, and additives and is delivered in a propylene glycol nonaqueous matrix [99–101].

6.2.1.7 Other Sealer Types

Use of chloroform‐based sealers such as Rosin‐chloroform, Chloropercha (Tanrac Ltd, Gavle, Sweden), and Kloropercha has declined due to concerns about their toxicity. Formaldehyde‐containing sealers are no longer recommended because they contain substantial amounts of paraformaldehyde and are considered unsafe.

Calcium phosphate‐based sealers such as Capseal I and II and Sankin Apatite Root Canal Sealer (Sankin Kogyo, Tokyo, Japan) are available. The presence of iodoform and polyacrylic acids in these formulations is said to cause cytotoxicity [120], and questionable results have been found with regard to their biocompatibility [121].

Almost all endodontic materials can discolour teeth, so it is unlikely that any sealer will guarantee colour stability in a root‐filled tooth [122]. This emphasizes the need to terminate the root filling well clear of the clinical crown, protect it with an orifice barrier, and carefully clean the access cavity before placement of the final coronal restoration.

6.2.2.1 Silver Points

Due to the limitations of early root canal preparation instruments, curved root canals were difficult to enlarge adequately to accept semi‐rigid materials such as gutta‐percha cones. Rigid core materials such as silver points, first used in 1931 [123], which could be forced down narrow canals, offered easier placement to the correct depth. Since placement was easier, the silver point technique could sometimes lead to less care being taken during root canal preparation, with infected dentine and debris being left in the canals, resulting in treatment failure (Figure 6.4). Silver points could also corrode when exposed to tissue fluids or saliva [124], and their round cross‐section led to obturations with excessive sealer. Being made of 99.9% silver, they were initially thought to offer valuable antimicrobial properties, but in fact the corrosion products were toxic and could reach the periapical tissues and compound the problems caused by sealer dissolution [125]. Silver points are thus no longer recommended as a core root filling material.

6.2.2.2 Acrylic Points

‘PD’ Acrylic Points (Produits Dentaires SA, Vevey, Switzerland) are colour‐coded and radiopaque. They are made of a methyl methacrylate polymer, bismuth oxide, zinc oxide, and a cadmium‐free colouring agent. As a rigid core material, they are meant to offer all of the advantages and none of the disdavantages of silver points, and they are promoted as being removable with burs, solvents, or essential oils if retreatment is necessary.

6.2.2.3 Gutta‐Percha

Over 2000 plant species produce natural rubber latex (NRL), the main constituent of which is poly(cis‐1,4 isoprene). The main constituent of endodontic gutta‐percha, on the other hand, is 19–22% poly(trans‐1,4 isoprene); other constituents added to it for endodontic use include zinc oxide (59–75%) and various waxes, colouring agents, antioxidants, and metal salts as radiopacifiers. The proportions vary from brand to brand, so there are considerable variations in stiffness, brittleness, and tensile strength. To facilitate fit, gutta‐percha cones are available in different sizes and tapers (Figure 6.5).

Gutta‐percha has two crystalline forms. In its unheated β‐phase, the material is solid and compactable. When heated, it changes to the α‐phase, becoming more pliable and capable of being made to flow under pressure. The α‐phase shrinks as it cools and sets, which is a disadvantage clinically. The thermomechanical properties of gutta‐percha have been well reported [126–130]. Most of the changes in phase occur from room temperature to around 60 °C.

Gutta‐percha has many advantages, being:

1. inert;
2. dimensionally stable after treatment;
3. nonallergenic;
4. antibacterial;
5. nonstaining to dentine;
6. radiopaque;
7. compactable;
8. softenable by heat;
9. softenable by organic solvents; and
10. easily removable from the canal, when necessary.

It also has some disadvantages (Figure 6.6), being:

1. nonrigid;
2. nonadherent to dentine; and
3. capable of being stretched.

As early as 1961, Ingle commented that ‘There has been no serious attempt to replace the time‐honored plastic gutta‐percha with a modern plastic … with a strong possibility it will be replaced by a newer plastic’ [131]. Gutta‐percha may be disinfected prior to use at the chairside in solutions of sodium hypochlorite for one minute [132]. Its biggest drawback is that it does not adhere to dentine. This can lead to penetration of bacteria along the space between the gutta‐percha and the canal walls in the absence of an adequate coronal seal [133], resulting in treatment failure. Microbial degradation of rubber is a relatively new area of research; fortunately, there is currently no evidence of the poly(trans‐1,4 isoprene) in gutta‐percha being associated with biodegradation by microbial enzymes [134].

6.3.1.1 Lateral Condensation

Gutta‐percha may be used cold or softened by heat or solvents. Lateral condensation is the most popular cold obturation method (Figure 6.9). Today’s preparation techniques produce a flared canal which cannot be filled with just one 0.02 taper gutta‐percha cone, so standardized sizes with larger tapers (e.g. 0.04 or 0.06) are available. A laboratory study of curved canals found a single tapered cone method comparable to lateral condensation in terms of the quantity of gutta‐percha in the root canal space; the technique was also faster than lateral condensation [148].

It has been said that lateral condensation is ‘single cone filling with a conscience’, as the space that must be created can lead to overpreparation, weakening the tooth and leading to the risk of root fracture, given the forces involved [149]