Root Canal Filling Materials and Techniques

6
Root Canal Filling Materials and Techniques

Bun San Chong1 and Nicholas Chandler2

1 Institute of Dentistry, Barts and The London School of Medicine and Dentistry, Queen Mary University of London, London, UK

2 Sir John Walsh Research Institute, University of Otago, Dunedin, New Zealand

6.1 Introduction

According to the American Association of Endodontists (AAE), ‘The ultimate goal of endodontic treatment is the long‐term retention in function of teeth with pulpal or periapical pathosis’ [1]. Following chemomechanical cleaning and shaping of the root canal system, a root canal filling is meant to provide a permanent, biocompatible, microbial‐, and fluid‐tight seal.

Root fillings consisting of gutta‐percha cones as a core material combined with a root canal sealer have been standard practice for many years. However, variations in obturation materials include [1]:

  • A sealer (cement/paste/resin) only.
  • A sealer and a single cone of a rigid or semirigid core material.
  • A sealer coating combined with cold compaction of core materials.
  • A sealer coating combined with warm compaction of core materials.
  • A sealer coating combined with carrier‐based core materials.

Newer materials focus on the deficiencies of the key groups of sealers and of gutta‐percha, whilst improved placement techniques have provided time and cost savings. Some improvements are aimed at replacing gutta‐percha, often accompanied by newer sealers. Newer cores are produced from materials designed to match the size and taper of the canal preparation instruments, such that single‐cone obturation is now considered acceptable.

Following its success in the treatment of the ‘open’ apices of immature teeth, mineral trioxide aggregate (MTA) may now be used as a root filling material on its own in selected cases. In addition, MTA and related hydraulic calcium silicate cements (HCSCs) have an increasing role as root canal sealers. Despite these developments, some root canal shapes – especially oval ones – remain challenging to fill.

Root canal obturation aims to:

  1. Seal the pulp chamber and canal system from coronal microleakage.
  2. Prevent remaining microorganisms from proliferating.
  3. Stop microorganisms entering the pulp space through the apical foramen and other pathways (lateral/furcation canals opening into the gingival sulcus, exposed and open dentinal tubules around the tooth).

Both a quality canal obturation and a well‐sealing coronal restoration are critical to long‐term success [2, 3]. Although canals can be filled immediately following preparation, in cases of infection the use of intracanal medicaments reduces the microbial population and the presence of endotoxins and may provide an improved prognosis [4]. Regardless, it is a requirement that canals be dried appropriately prior to obturation.

The smear layer influences sealer adaptation, tubular penetration, and leakage; the greatest potential for leakage is at the interface between the sealer and canal wall [5]. Removal of the smear layer and irrigation protocols is discussed in Chapter 5. Although the sealing ability and methods used to measure leakage are now considered outdated [6], they will be covered in this chapter as they have been employed for a number of years specifically in order to evaluate sealer performance and compare obturation methods.

6.2 Root Canal Obturation Materials

6.2.1 Sealers

Sealers play a critical role in sealing the root canal system by filling areas that are not occupied by the core filling material and through the entombment of remaining microorganisms after chemomechanical preparation [7]. They also act as lubricants and antimicrobial agents [8]. A dense appearance of obturated canals on radiographs is desirable, but some voids are likely with all root fillings [9]. Currently, no sealer is available that completely prevents leakage [10]. In general, conventional root canal sealers tend to shrink on setting, and many are hydrophobic; therefore, moisture in the apical region of the root canal system can prevent the formation of an effective seal. All sealers are soluble to an extent, and all differ in their setting times and their release of leachates [11]. These leachates can migrate through dentinal tubules and the apical foramina, creating porosities within the materials. Most conventional root canal sealers do not possess any biological activity, and some have been found to be cytotoxic to the periapical tissues when freshly mixed, causing cellular degeneration and delayed wound healing [12].

Sealer flow may be affected by root canal morphology, the core root filling material, dentine tubules, and the smear layer [13]. Increasing the rate of sealer insertion may increase volumetric flow and reduce the viscosity of the sealer. However, with a reduced internal canal width, there is reduced volumetric flow and increased viscosity. In addition, increasing the rate of insertion does not necessarily improve sealer flow; this depends on the sealer used and the width of a root canal. Similarly, reducing the powder–liquid ratio of a sealer may not improve flow, as it has been shown that flow may be reduced at a higher rate of insertion [13]. Furthermore, the flow of root canal sealers is temperature‐ and shear‐dependent, and varies between sealers [14].

No sealer is ideal, but many work well in clinical practice. Some are initially toxic and many may be absorbed to some degree after setting, so that their volume is decreased; a low solubility and a film thickness <50 μm are requirements [15]. Sealers penetrate into dentinal tubules (Figure 6.1), which can be facilitated by methods such as ultrasonic obturation. This also improves the incidence of filled accessory channels [16]. However, all sealers must be regarded as implantable materials, and so caution is necessary during the development of novel sealer types and delivery methods.

Whilst their characteristics differ, there is only limited evidence that different types of sealers influence treatment outcome [4]. Nonetheless, the choice is important when considering the obturation technique employed [17]. Commonly used sealers can be divided into six groups based on their constituents:

  1. Zinc oxide‐eugenol (ZOE) sealers: e.g. Tubli‐Seal and Pulp Canal Sealer (Kerr Endodontics, Brea, CA, USA) and Roth’s Sealer (Roth International, Chicago, IL, USA).
  2. Calcium hydroxide sealers: e.g. Sealapex (Kerr Endodontics) and Apexit and Apexit Plus (Ivoclar Vivadent, Liechtenstein, Germany).
  3. Glass ionomer sealers: e.g. Ketac Endo (3M ESPE, Seefeld, Germany).
  4. Resin sealers: e.g. AH 26, AH Plus (Dentsply De Trey GmbH, Konstanz, Germany), SimpliSeal (Kerr Endodontics), 2Seal (VDW GmbH, Munich, Germany), and Obturys (Itena, Paris, France).
  5. Silicone‐based sealers: e.g. Roekoseal (Coltène/Whaledent, Langenau, Germany).
  6. HCSC sealers: e.g. BioRoot RCS (Septodont, Saint‐Maur‐des Fosses, France), EndoSequence BC Sealer (Brasseler, Savannah, GA, USA), and Totalfill BC sealer (FKG Dentaire, La Chaux‐de‐Fonds, Switzerland).

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.

Photos depict penetration of a sealer, dyed with Sudan Black B, at different levels of filled roots: absent (top left), inner third (top right), middle third (lower left), and outer third (lower right).

Figure 6.1 Penetration of a sealer, dyed with Sudan Black B, at different levels of filled roots: absent (top left), inner third (top right), middle third (lower left), and outer third (lower right).

Source: Humza Ahmed.

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 [3841]. 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].

Photo depicts confocal microscope image of penetration of AH Plus into dentinal tubules.

Figure 6.2 Confocal microscope image (×10) of penetration of AH Plus (Dentsply De Trey GmbH) into dentinal tubules.

Source: Assil Russell.

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].

6.2.1.6.1 Type 2 HCSC Sealers

Endo CPM Sealer is based on MTA but has additives to improve its performance. These include silicon dioxide, calcium carbonate, propyleneglycol alginate, sodium citrate, and calcium chloride [60]. It also contains bismuth trioxide and barium sulphate, which give it a radiopacity equivalent to 6 mm of aluminium [60]. The material sets within an hour [74]. Endo CPM Sealer has been found to be dimensionally stable, but it exhibits significantly more leakage when compared with MTA Fillapex and a conventional calcium hydroxide‐based sealer [75, 76]. It has been found to have a significantly higher bond strength to root dentine compared to MTA Fillapex and AH Plus [77]. It displays antibacterial activity against Staphylococcus aureus and Streptococcus mutans when freshly mixed, although less than that displayed by AH Plus [78]. It also displays biocompatibility [74, 79].

ProRoot Endo Sealer (Dentsply Tulsa Dental Specialties, Tulsa, OK, USA) was developed from ProRoot MTA root repair material (Dentsply Tulsa Dental Specialties) and introduced in 2016. The major powder components are tricalcium silicate and dicalcium silicate, with calcium sulphate included as the setting retardant, bismuth oxide as a radiopacifier, and a small amount of tricalcium aluminate; these are the same components found in ProRoot MTA, but ProRoot Endo Sealer is claimed to be enhanced, and it has thus been grouped with the Type 2 HCSCs. It is available as a predosed powder and liquid, and is designed for use with all obturation techniques. It has been indicated for use as a sealer in both cold and warm root canal filling techniques with a working time of 65 minutes and a setting time of 12 hours. It demonstrates superior sealing to a conventional ZOE sealer and exhibits bioactivity when in contact with physiological fluids [80, 81].

MTA Obtura (Angelus), from the same manufacturer as MTA Fillapex, is similar to grey MTA (Angelus) in composition. It exhibits a flow rate similar to AH Plus [82]. When used as a root canal sealing material, it has been found to demonstrate higher leakage than AH Plus [83].

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 [9196]. 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.

Photo depicts confocal microscope image of penetration of MTA Fillapex sealer into dentinal tubules.

Figure 6.3 Confocal microscope image (×10) of penetration of MTA Fillapex (Angelus) sealer into dentinal tubules.

Source: Assil Russell.

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 [99101].

6.2.1.6.3 Type 4 and Type 5 HCSC Sealers

The tricalcium silicate‐based sealers were developed to avoid the trace element contamination of Portland cement. The water‐based ones include BioRoot RCS, a powder/liquid hydraulic tricalcium silicate‐based cement which has been on the market since early 2015. This Type 4 HCSC is recommended for single‐cone or cold lateral condensation techniques. Heating results in evaporation of the water component, a reduction in setting time and flow, and an increase in film thickness [17]. The manufacturer claims it has a minimum working time of over 10 minutes and a maximum setting time of 4 hours [102], although studies have found the actual final setting time to be 300 ± 5 min [86]. The powder contains tricalcium silicate, povidone, and zirconium oxide, whilst the liquid component is an aqueous solution of calcium chloride and polycarboxylate. BioRoot RCS is formulated so that it does not stain teeth and has great flowability, and retreatment is simple to carry out [86, 102]. Obturations have shown higher void volumes compared with AH Plus [103]. Although the material is radiopaque, this property is significantly less than that of conventional sealers such as AH Plus and Pulp Canal Sealer [86]. A recent in vitro study reported that BioRoot RCS was bioactive and biocompatible [104]. Unfortunately, it has also exhibited some degree of cytotoxicity, although lower than that of conventional root canal sealers [105, 106]. It shows exceptional antimicrobial properties [107] regardless of the irrigation protocol used [108].

EndoSequence BC Sealer, also known as iRoot SP (Innovative Bioceramix Inc., Vancouver, BC, Canada) or TotalFill BC Sealer depending on the region where it is sold, is a calcium silicate‐based, premixed, ready‐to‐use, injectable white hydraulic cement paste; the term ‘bioceramic’ was coined for this sealer type [109, 110]. It is composed of tricalcium silicate, dicalcium silicate, calcium phosphate monobasic, calcium hydroxide, and a thickening agent. The working time of the material is 30 minutes, and in normal conditions it sets within 4 hours [10]; if the dentine is very dry, it can take up to 10 hours. It has a radiopacity equivalent to 3.83 mm of aluminium, just above the minimum reference standard – although one study reports an equivalent of 6.09 mm of aluminium [111]. It has been found to increase the force to fracture of root‐filled premolar teeth [112]. Specifically developed for warm obturation techniques, EndoSequence BC Sealer HiFlow (Brasseler) and TotalFill BC Sealer HiFlow (FKG) exhibit a lower viscosity when heated and are more radiopaque [113]. Neither show any chemical changes when subjected to high temperatures [113, 114], with their nonaqueous vehicle preventing desiccation.

iRoot SP sealer has an initial antibacterial effect against E. faecalis in vitro, but this has been found to dramatically decrease just seven days after setting [64]. The manufacturer claims that there is no shrinkage on setting. In vitro studies have shown that it demonstrates some degree of cytotoxicity, although less than that of AH Plus [62, 115, 116]. A recent study found that it displayed a higher cytocompatibility when compared to MTA Fillapex and AH Plus [96]. It has antibacterial properties due to its high alkalinity during setting [64]. It also shows promising in vitro results in providing increased resistance to root fracture [117]. It has higher dentinal tubule penetration following various irrigation protocols when compared to AH Plus, GuttaFlow, and MTA Fillapex [118], and it produces a higher resistance to dislodgement from root dentine compared to AH Plus, Epiphany, and MTA Fillapex [119].

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 Core Materials

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.

Photo depicts mandibular left first molar root filled with silver points.

Figure 6.4 Mandibular left first molar root filled with silver points.

Source: Bun San Chong, Nicholas Chandler.

Photo depicts gutta-percha cones of different sizes and tapers.

Figure 6.5 Gutta‐percha cones of different sizes and tapers.

Source: Bun San Chong, Nicholas Chandler.

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 [126130]. 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].

Photo depicts suboptimal, poorly condensed gutta-percha root filling in a maxillary left central incisor.

Figure 6.6 Suboptimal, poorly condensed gutta‐percha root filling in a maxillary left central incisor.

Source: Bun San Chong, Nicholas Chandler.

6.2.2.3.1 Coated Cones

To enhance the bonding of GIC sealer to gutta‐percha, one product consists of gutta‐percha coated with 2 μm of GIC particles on its surface (ActiV GP Precision Obturation System, Brasseler, Savannah, GA, USA). This was compared with AH Plus and gutta‐percha in a bacterial leakage model and no significant difference was found [135]. Bioceramic‐coated/impregnated gutta‐percha cones are also available (TotalFill gutta‐percha cone, FKG); the gutta‐percha is impregnated and coated with calcium silicate nanoparticles and used as a single cone. When combined with TotalFill BC sealer (FKG), no difference was found in fracture load compared with teeth filled with gutta‐percha and AH Plus [136]; the bioceramic combination, however, demonstrated higher bond strength and greater sealer penetration at all root levels.

6.2.2.3.2 Chlorhexidine‐Impregnated Gutta‐Percha Points

Some studies have shown that E. faecalis is relatively resistant to calcium hydroxide [137, 138]. In order to take advantage of the antibacterial properties of chlorhexidine, especially to E. faecalis, a chlorhexidine‐impregnated gutta‐percha point, Activ point (Roeko), has been marketed. According to the manufacturer, it contains a gutta‐percha matrix embedded with 5% chlorhexidine diacetate. Studies have been undertaken to investigate the antimicrobial activity of Activ points, concluding that they do not possess an inhibitory activity strong enough to completely eliminate a moderately large number of E. faecalis organisms from infected human dentinal tubules [139, 140]. An in vitro study testing the cellular toxicity of medicated and nonmedicated gutta‐percha points found that chlorhexidine‐impregnated gutta‐percha points were more cytotoxic than either calcium hydroxide‐impregnated or nonmedicated gutta‐percha points [141].

6.2.2.3.3 Gutta‐Percha Points Impregnated with Metronidazole

According to the abstract of a study conducted at Shandong University in China [142], controlled‐release delivery gutta‐percha points (CDGMCs) containing metronidazole compounds were made and placed in prepared extracted teeth. A non‐drug CDGMC was used as the control. The absorbency of the drugs in normal saline (37 °C, pH 7.4) was determined, and the percentage of release and cumulated release of the drugs were calculated according to the concentrations in medium. The authors concluded that CDGMCs could continuously release effective drug concentrations for more than 10 days [142].

The introduction of antimicrobials into gutta‐percha points and their disinfection prior to clinical use has recently been reviewed [132].

6.2.2.3.4 Gutta‐Percha Allergy

Cases of allergy to gutta‐percha arise but are unusual. There has been speculation regarding potential cross‐reactivity between NRL and gutta‐percha allergens in latex‐allergic patients, as they are related materials from the same family of trees. In case reports [143, 144], lip and gingival swelling, throbbing sensation, diffuse urticaria, and tachycardia have been noticed following the placement of gutta‐percha root fillings; these symptoms resolved completely after removal of the fillings. In contrast, investigations of cross‐reactivity between different latex materials using the radioallergosorbent test (RAST) inhibition assay concluded that there was an absence of cross‐reactivity between raw or manufactured gutta‐percha and NRL antibodies. However, gutta‐balata (if added to gutta‐percha products) may cross‐react with latex‐specific immunoglobulin E (IgE) antibodies [145]. Similarly, a study using the enzyme‐linked immunosorbent assay (ELISA) reported no cross‐reactivity between gutta‐percha and NRL protein allergens; the authors speculated that additives in gutta‐percha cone manufacture, such as zinc oxide, barium sulphate, waxes, formaldehyde, and paraformaldehyde, might be responsible for eliciting allergic reactions in patients [146]. For these rare cases, consideration should be given to providing root fillings of MTA, as an example.

6.3 Root Filling Techniques

Since gutta‐percha remains the most commonly used core root filling material, the main focus of this section will be on techniques utilizing gutta‐percha.

During obturation, sealer may be extruded beyond the apex (Figure 6.7) or out of a lateral/accessory canal (Figure 6.8). A radiographic study of 92 overextension cases involving ZOE sealers (Procosol and Roth’s 801) in well‐obturated canals found that 96% showed evidence of periapical repair at recall and that the extruded material remained unchanged in only three cases (1.6%). Extruded materials disappeared over time and did not prevent healing [147].

Photo depicts extrusion of sealer from the mesiolingual canal of a mandibular right first molar.

Figure 6.7 Extrusion of sealer from the mesiolingual canal of a mandibular right first molar.

Source: David Yong.

Photo depicts root canal sealer extruded through to reveal a lateral canal in a maxillary right central incisor, explaining the adjacent bone loss.

Figure 6.8 Root canal sealer extruded through to reveal a lateral canal in a maxillary right central incisor, explaining the adjacent bone loss.

Source: Finn Gilroy.

6.3.1 Cold Gutta‐Percha Condensation Techniques

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]

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Mar 12, 2022 | Posted by in Endodontics | Comments Off on Root Canal Filling Materials and Techniques
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