Hydraulic cements for various applications in endodontics: Part 2

Material chemistry

Totalfill BC sealer (FKG) and BioRoot RCS (Septodont) are classed as different material types since the latter needs to be mixed with water for hydration while the former is ready-mixed and will hydrate after contact with the environmental liquids. Both sealers are composed primarily of tricalcium silicate and zirconium oxide as the radiopacifier. The liquid in BioRoot RCS (Septodont) is composed of water, calcium chloride and a hydro-soluble polymer.³ In addition to the tricalcium silicate and zirconium oxide, Totalfill BC sealer (FKG) also includes calcium phosphate and a non-aqueous vehicle.⁴

Material properties

BioRoot RCS (Septodont) is mixed with water and thus, its setting time of 324 (±1) minutes is controlled.⁵ Totalfill BC sealer (FKG) does not have a fixed setting time because it depends on the environmental moisture.³ Both hydraulic sealers have been reported to have high solubility,^5,6 which increases with time, but has been attributed to improper in vitro testing of the materials.^7,8

The calcium ion release also varies between the different sealers. The water-based sealer BioRoot RCS (Septodont) exhibits a higher calcium ion release compared to Totalfill BC sealer (FKG), which depends on the diffusion of ions through a non-aqueous matrix that delays, or restricts, the calcium ion formation and release.⁴ Furthermore, the presence of calcium phosphate monobasic in Totalfill BC sealer (FKG) also modifies the hydration reaction.⁹

The biological characteristics of sealers are important since they are in contact with the periodontal ligament and the bone in the apical region. Thus, both the biological properties of the sealer itself and that of any elutions are important. Elutions and even direct seeding of cells over the materials showed a high degree of cell proliferation.^{10,11,12,13,14} The cytotoxicity was dose dependent.¹² Comparison of different pre-mixed materials shows that the material chemistry influences the cell viability, cell attachment and cell migration rates and this was higher for materials releasing higher levels of calcium.^15,16 The hydraulic sealers also have an osteogenic^17,18 and an anti-inflammatory effect.¹⁹ Both Totalfill BC sealer (FKG) and BioRoot RCS (Septodont) have been shown to be antimicrobial.^19,20,21,22 There is a synergistic antimicrobial effect when sodium hypochlorite solution and hydraulic sealers are used in combination.²³ Prior dentine disinfection is necessary as the use of sodium hypochlorite over the dentine enhances the effect of the hydraulic sealers.

The Type 4 hydraulic calcium silicate-based sealers (such as BioRoot RCS, Septodont) are recommended for use in cold condensation techniques, such as the laterally condensed technique or single cone obturation. These sealers are water based, and the heat generated during warm vertical compaction will evaporate the water in the sealer leading to irreversible changes in the chemical and physical properties.³ Totalfill BC sealer (FKG) is not affected by the rise in temperature^24,25 as both the inorganic components (tricalcium silicate and zirconium oxide) and the organic vehicle are impervious to the heat generated during the obturation procedure; thus this sealer can be used for warm vertical compaction of gutta-percha techniques.

The hydraulic cement sealers have not been shown to bond to gutta-percha. Interaction of hydraulic sealers with root dentine results in the mobilization of silicon from the sealer to the tooth structure.²⁶ As the sealer comes in contact with pre-treated dentine, the irrigation protocol for optimal sealer interaction is thus important. The reported bioactivity when hydraulic cements interact with phosphate-containing solutions, such as tissue fluids, has led to a drive to use phosphate-buffered saline as the final irrigating solution. However, this will lower the surface pH of the sealer and will lead to a reduction in its antimicrobial action.²² Sodium hypochlorite solution potentiates the antimicrobial effect of hydraulic sealers.²³ EDTA is effective in removing the smear layer, but since it is a calcium chelator, it will cause chemical alterations to the sealers upon contact.²⁷ The pushout bond strength of hydraulic sealers was also reduced in the presence of EDTA.²⁸

Presentation of root canal sealers

BioRoot RCS (Septodont) is supplied as a powder and a liquid form that must be mixed by hand for 1 minute. The master apical gutta-percha point may then be coated sparingly with the root canal sealer before being inserted to length in the root canal (Figure 1a). Totalfill BC sealer (FKG) is supplied as a single syringe, and it is delivered through a plastic cannula that enables deep penetration inside the root canal (Figure 1b).

Clinical cases

Endodontic sealer

An 18-year-old patient with a history of trauma was referred with asymptomatic chronic peri-radicular periodontitis in UL1. The tooth was discoloured and had been previously root canal-treated with a screw post-retained composite resin to restore the missing tooth structure. The screw post was removed, and the tooth was root canal re-treated. A GP cone matched to the master apical file was used to obturate the root canal using a single cone obturation technique with Totalfill BC sealer (FKG) (Figure 2).

Apical plug

A 45-year-old female patient was referred for specialist treatment on UL1. The tooth had been asymptomatic, but on pre-operative investigation prior to replacement of the unsightly crown, an open apex and associated peri-radicular radiolucency were discovered. The root canal was accessed and chemo-mechanically prepared using sodium hypochlorite and manual canal preparation at the first visit. An apical plug of Biodentine (Septodont) was placed and backfilled with thermo-plasticized gutta-percha (Gutta Percha Obturator, DiaDent, Chungcheongbuk-do, Korea) at the second visit. Although the Biodentine is not as radiopaque as gutta-percha and mineral trioxide aggregate (MTA), it is the most suitable material to use, particularly in anterior teeth owing to the risk of tooth discolouration with MTA.^29,30 The patient was recalled after 6 months and a peri-apical radiograph was taken that clearly showed a partial resolution of the lesion with the onset of bony infill (Figure 3). The use of hydraulic cements as apical plugs has enabled the endodontic management of immature teeth with non-vital pulps to be performed in one to two visits, with the single visit showing a slightly higher success rate when compared to the two visits³¹ as opposed to long-term calcium hydroxide therapy.

Section summary

Hydraulic cements may be used successfully in the root canal system, namely as a root canal sealing material and placed as an apical plug. The requirements for the materials in these two situations are very different. The sealers need to have an adequate flow and film thickness, while apical plugs are used in bulk and need to be compactable. The antimicrobial properties are important for both material types with the biological properties and the mineralizing ability being more important for apical plugs.

Presentation of materials used for extra-radicular procedures

Some formulations of MTA, such as ProRoot MTA (Dentsply-Sirona) and MTA Angelus (Angelus, Londrina, Brazil) are provided as a powder and a liquid to be mixed together on a glass slab. The powder to liquid dosage provided by the manufacturer should be maintained, and the use of smaller amounts than that provided in the sachet with undetermined quantities of liquid is discouraged. The addition of more water than instructed by the manufacturer will lead to deterioration in the physical properties of the material.^33,34,35 These formulations contrast with TotalFill BC RRM (FKG), which is pre-mixed and is applied directly at the site. This product is available in three formats, namely putty, fast-set putty and a paste supplied in a syringe with a narrow-bore, tipped plastic cannula for ease of application. Delivery to the surgical site is usually made using an MTA carrier (Figure 4a), which can be used with a number of angled tips or the use of a MTA pellet block (Figure 4b), which makes a pellet of the material to be carried to the surgical site on the tip of an endodontic plugger.

Material chemistry

Materials that are used for surgical procedures can be Type 1–5.¹ ProRoot MTA (Dentsply-Sirona) is a Type 1 material composed of Portland cement and bismuth oxide as the radiopacifier, which is mixed with water to form calcium silicate hydrate, calcium hydroxide and ettringite/monosulphate.^36,37,38 The hydration proceeds by the formation of calcium silicate hydrate that coats the cement particles, and calcium hydroxide is deposited in the cement matrix and leached in solution (Figure 5).

MTA Angelus (Angelus) is also composed of cement and radiopacifier. The material is different from ProRoot MTA (Dentsply-Sirona) in that the radiopacifier is calcium tungstate and is not associated with the tooth discolouration seen with bismuth oxide.^{29,30,39,40,41,42,43,44,45} Furthermore, MTA Angelus (Angelus) also contains calcium oxide, which modifies the hydration reaction. This is not added by the manufacturer, but results from the burning process during the cement manufacturing.⁴⁶

The TotalFill BC root repair materials (RRM) (FKG) are composed of tricalcium silicate, zirconium oxide, tantalum oxide, calcium phosphate monobasic and a non-aqueous vehicle.^47,48 The hydration of the tricalcium silicate results in the formation of calcium silicate hydrate and calcium hydroxide. Zirconium oxide and tantalum oxide are included as radiopacifiers, and calcium phosphate monobasic is a source of phosphate ions to enable biomineralization. This can lead to a reduction in the calcium ion release by the materials.⁹

Material properties

An adequate radiopacifier is important in surgical procedures to enable radiographic visualization on recall. Thus, materials that show a high radiopacity are preferred. These include ProRoot MTA (Dentsply-Sirona),⁴⁹ which has bismuth oxide as the radiopacifier, and TotalFill BC root repair materials (RRM) (FKG),⁵⁰ which also has sufficient radiopacity. Setting time is not a main consideration for root-end fillers, but rather the ease of delivery and handling, which has been addressed by the pre-mixed Type 5 materials that can be syringed to the surgical site.

The physical properties that are crucial for materials used during surgery are their solubility, dimensional stability and washout. The solubility of MTA has been shown to range from negligible⁴⁹ to high (22–31%),^51,52 dependent on the water–powder ratio. The addition of more water to MTA increases its solubility.^51,52 The dimensional stability of root-end filling and perforation repair materials is important as any shrinkage can lead to a gap between the material and the tooth, with the risk of microbial recolonization, while expansion may lead to root fracture. MTA was shown to be dimensionally stable even when the water–powder ratio was varied.⁵³ This contrasts with other data that show cement shrinkage, particularly in the early stages of setting, and that physiological-based solutions affected the setting of the materials.⁵⁴

Washout is also an important characteristic for root-end filling and perforation repair materials. This can be short term, which happens when the area where the material is placed is irrigated prior to flap closure or a restoration is placed, or long term by the action of the body fluids on the materials. The washout resistance of MTA was shown to be low.^54,55,56,57 A number of products include an anti-washout gel as a mixing liquid, replacing water (Neo MTA Plus, NuSmile, Houston, TX, USA), which increases the washout resistance of the cements.

The biological properties of extra-radicular materials are very important, and these are very well investigated for MTA. MTA in contact with peri-radicular tissues resulted in the expression of inflammatory mediators and cytokines at certain times,⁵⁸ which is similar to Biodentine (Septodont)⁵⁹ and worse than TotalFill BC RRM (FKG).⁶⁰ MTA used as a root-end filling material caused less peri-radicular inflammation fibrous capsule formation. In addition, the presence of cementum on the surface of MTA was a frequent finding.^61,62 The presence of infection and bacteria led to compromised healing in cases of root perforation.⁶³

The Type 5 pre-mixed materials also exhibited good cell viability comparable to MTA,^64,65 but showed reduced cell viability in the early ages when compared to MTA Angelus (Angelus).⁶⁶ This could be attributed to the time taken for the environmental moisture needed for hydration of pre-mixed materials to hydrate the tricalcium silicate. Perforation repair materials need to be more antimicrobial as they are in contact with contaminated dentine. MTA exhibits antimicrobial properties.^67,68 The presence of blood contamination has a buffering effect on the MTA, and ProRoot MTA (Dentsply Sirona) was shown to be less antimicrobial when in contact with blood.⁶⁹ Interaction of MTA with blood results in the deposition of calcium carbonate on the material surface.⁷⁰ Similar findings were shown for TotalFill BC RRM (FKG) when used as a root-end filling material.⁴⁷ The presumed bioactivity, where calcium phosphate crystals are precipitated on the material surface,⁷¹ is an in vitro phenomenon only, and has never been demonstrated clinically.

When MTA is used to repair perforations in the crown of the tooth, it will subsequently come into contact with other materials required to provide the definitive restoration. If a zinc oxide eugenol-based (ZOE) cement or glass polyalkenoate cements (GIC) are used to layer over MTA, detrimental microstructural changes occur in the latter material. With ZOE, zinc inhibits cement hydration and thus a layer of unset MTA is present at the material interface. With GIC, the acidity disrupts the microstructure of MTA.⁷² When placing composite resin over MTA, the use of a bonding agent is important to avoid changes at the material interface.⁷³ The placement of bonding agent over partially set MTA allows for immediate tooth restoration with composite resin. Other literature suggested that the placement of a restoration should be delayed until the MTA is fully set.⁷⁴ The placement of a wet cotton pellet to cover the MTA surface until material reaches the final set is thus recommended.

Section summary

Hydraulic cements used in extra-radicular situations are placed in contact with the peri-radicular tissues. The physical and biological properties of such cements are conducive in these indications, and their use has contributed to the improved prognosis of such procedures seen in recent years.

Clinical cases

Perforation repair

A 58-year-old male patient was referred by his GDP who could not locate two of the three root canals, and had perforated into the furcation of UR7. This tooth was important because it was the distal abutment of the three-unit conventional bridge in the upper right quadrant. The previously undiscovered root canals were located using an operating microscope, and following thorough chemo-mechanical preparation of the root canal system, the root canals were obturated using GP and BioRoot RCS (Septodont). The perforation was repaired with Biodentine (Septodont) at the same appointment as the obturation of the root canals. A coronal seal was established using Vitrebond Plus (3M) and the access cavity restored with resin composite (Figure 6).

Root-end filling

A 47-year-old female patient presented with pain localized to UL6. She had had extensive endodontics and fixed prosthodontics performed in Russia some years earlier. Radiographically, there was a peri-apical radiolucency associated with the mesio-buccal root of UL6 and a diagnosis of acute on chronic peri-radicular periodontitis was made (Figure 7a). Peri-radicular microsurgery was identified as the treatment of choice given the presence of the extensive restoration and risks of dismantling the tooth to attempt an orthograde approach. ProRoot MTA (Dentsply Sirona) was chosen as the root-end material (Figure 7b). Radiographic monitoring at appropriate intervals continues, and there is evidence of peri-radicular healing (Figure 7c,d).

Clinical performance

There is very limited information on the clinical performance of MTA used to repair root perforations. MTA used as a root-end filling material using a microsurgical approach is associated with high success rates.⁷⁵ However, regardless of the hydraulic nature and claimed superior properties, MTA used for this indication exhibits similar clinical outcomes as IRM (Dentsply)^76,77 and Super-EBA cement (Bosworth, Skokie, IL, USA),⁷⁸ even in the long term.⁷⁹