Products and Distinctions

Abstract

A summary is given of the known compositions and properties for MTA-type products, both commercial and experimental. Comparisons are made of the phases, particle sizes, and other attributes such as setting time or radiopacity. MTA-type materials used for root canal sealers are included.

These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

8.1 Introduction

This chapter describes the dental products that contain or are based on tri- or dicalcium silicates. Resin-based products that contain these powders are included. For simplicity, these products are denoted at MTA-type materials because they rely on the hydration reactions in Eqs. 8.1 and 8.2.

Tricalcium silicate:

$$ \begin{array}{c}2{\mathrm{Ca}}_3{\mathrm{SiO}}_5+7{\mathrm{H}}_2\mathrm{O}=3{\mathrm{Ca}\mathrm{O}}_2{\mathrm{SiO}}_2\cdot 4{\mathrm{H}}_2\mathrm{O}\\ {}+3\mathrm{Ca}{\left(\mathrm{OH}\right)}_2\end{array} $$

(8.1)

Dicalcium silicate:

$$ \begin{array}{c}2{\mathrm{Ca}}_2{\mathrm{SiO}}_4+5{\mathrm{H}}_2\mathrm{O}=3\mathrm{CaO}\cdot 2{\mathrm{SiO}}_2\cdot 4{\mathrm{H}}_2\mathrm{O}\\ {}+\mathrm{Ca}{\left(\mathrm{OH}\right)}_2\end{array} $$

(8.2)

Secondary or lesser hydration reactions occur involving the minor phases, but the strength and the release of calcium hydroxide for bioactivity arise from these two reactions. The key to the bioactivity of MTA-type products is the precipitation of hydroxyapatite when the calcium hydroxide reacts with phosphate ions in body fluids, as shown in Eq. 8.3.

$$ \begin{array}{c}7\mathrm{Ca}{\left(\mathrm{OH}\right)}_2+3\mathrm{Ca}\left({\mathrm{H}}_2{\mathrm{PO}}_4\right){}_2\\ {}\to {\mathrm{Ca}}_{10}\left({\mathrm{PO}}_4\right)6\left(\mathrm{OH}\right){}_2+12{\mathrm{H}}_2\mathrm{O}\end{array} $$

(8.3)

Calcium silicate, CaSiO₃ (wollastonite), is not part of this discussion because this compound does not react with water and hydrate. However, this distinction is not always clear in the literature. Calcium silicate was used in another experimental magnesium phosphate dental product [32, 79, 93]. The calcium silicate was not a hydraulic phase but a phase that reacted in situ contributing to bioactivity.

8.2 Commercial Products

From 1993 to 1998, Dr. Torabinejad of Loma Linda University (Loma Linda, CA, USA) distributed experimental samples of MTA from his laboratory to endodontists. Commercial introduction of MTA products began in 1998 by the Tulsa Dental Specialties division of Dentsply International with ProRoot® MTA. This product was introduced after two applications to the US Food and Drug Administration (FDA) for clearance of these indications: repair of pulpal exposures, apexification, root perforation, root-end filling, and management of internal resorption. A picture of this gray MTA product is shown in Fig. 8.1a. In 2008, the US FDA cleared additional indications of cavity liner, pulpotomies, obturation, and root canal sealer, for MTA-type products from Dentsply. In Korea, MTA-type products are used for replantation [36, 72], transplantation, file separation, and vertical cracks. MTA-type products are generally suitable for dental procedures that contact with pulpal or periapical tissues, as described in this chapter and others. The performance and the convenience of products for a procedure have varied, as can be gleaned in the following discussion.

Fig. 8.1

(a) Packet of ProRoot MTA powder, ampoule of water and powder, introduced in 1998. (b) Packet of tooth-colored (white) ProRoot MTA powder, ampoule of water and powder, introduced in 2002

Since the introduction of ProRoot MTA, a shorter setting time has been desired, so that the clinician can feel confident that the product has set before the procedure is finished, as is conventional for dental materials. Several products and many researchers have sought to achieve this goal, often by the addition of calcium chloride, a known accelerant for Portland cement setting even though calcium chloride is not necessarily the most effective salt for accelerating the set. The elimination of calcium sulfate is known to reduce setting time for Portland cement [68], and this approach has also been used by several manufacturers. Calcium sulfate is necessary in construction concrete pouring to avoid flash or “false” setting, as described in Chap. 1. In dentistry, flash setting is unimportant and may be beneficial as noted below.

Researchers and clinicians have reported that the ProRoot MTA product had poor handling characteristics and “looses consistency in the presence of excess liquid, even at the proportion recommended by the manufacturer,” creating a low viscosity, “soupy mix” [62]. Since 1998, many investigators and companies have developed alternatives that were less “sandy”, faster setting and less expensive.

The key characteristics for comparisons of MTA products are crystalline phases, particle-size distribution, setting time, handling adjuvants, radiopacifier, and resistance to washout. All of these characteristics contribute to the clinician’s ability to satisfactorily prepare and mix the material. Washout resistance is important for stable placement of the material, particularly for the products that have a long setting time. The evolution of the available products and supporting research is described here.

The first patented MTA was a blend of a particular Portland cement composition, which included about 5 % iron oxide, and was believed to be unique in its ability to “work” (private communication about US Patents 5,415,547 and 5,769,638). Dentsply fabricated the patented cement formula under controlled environmental conditions and created a finer powder than the original samples, with better bismuth oxide distribution. This product became ProRoot MTA. The color of the powder was dark gray, as shown in Fig. 8.1a. The powder was packaged in foil pouches and supplied with ampoules of water in the kit (Fig. 8.1a). In 2002, a “tooth-colored” (white) ProRoot MTA (US Patent 7,892,342) product superseded the gray ProRoot MTA. This product was very similar but contained less than 0.5 % iron, so that the cement was yellowish white in color. The bismuth oxide contributed the yellow cast. In many articles, the tooth-colored ProRoot MTA product is denoted as white ProRoot MTA (Fig. 8.1b). Market demand required the original gray-colored ProRoot MTA to be reintroduced, and it has been sporadically available since then. Some papers have proposed greater biocompatibility for the gray version [37, 78].

The Angelus company in Londrina, Brazil, founded by Dr. Roberto Q. M. Alcântara, commercialized a more affordable MTA product in 2001. This product was available in Brazil and now is available through Henry Schein distributors. The format of their gray and white Angelus products is bottles of powder and water in a vial, different from ProRoot MTA powder in 1 g pouches with water ampoules. Originally, commercial Portland cement was used to create MTA Angelus, a gray-colored powder with bismuth oxide, which was followed by MTA Bianco, a white Portland cement with bismuth oxide.

When evaluating products, researchers have often repeated the term “sandy” feel of MTA [64]. Coarse particles give this sensation and scratchy sound when a powder is mixed with water on a glass slab. Therefore, the particle-size distributions have been compared for several powders. The particle-size distribution of the experimental samples of MTA from Loma Linda University is shown in Fig. 8.2a, and this powder has a significant portion of particles coarser than 40 μm, hence the “sandy feel.” The material was coarser than ProRoot MTA [65] and had incompletely dispersed bismuth oxide which appeared as bright spots in radiographs. The particle-size distributions in Fig. 8.2b, c are for the Angelus company’s white and gray MTA powders. The median particle sizes are below 10 μm, but each powder contains many particles which are coarser than 40 μm, up to 100 μm. The line at 20 μm allows a comparison of the number of particles that are coarse. Figure 8.2d–f show the distributions of particle sizes in ProRoot (gray and white) and DiaRoot powders (DiaDent Group International, Burnaby, British Columbia, Canada), which have significantly fewer coarse particles than the original MTA or the Angelus materials. Figure 8.3 has particle-size distributions for three newer materials, which are remarkably finer: Biodentine, EndoSequence sealer, and RetroMTA powders. None of these powders is “nano-sized.” Nano-sized particles are 1/1,000 of a micron and none of these materials is even submicron (1/10 of a micron).

Fig. 8.2

(a) Original, pre-commercial MTA powder particle-size distribution. (b) MTA Bianco from Angelus Corporation powder particle-size distribution. (c) MTA Angelus (gray) from Angelus Corporation powder particle-size distribution. (d) Early version of (gray) ProRoot MTA powder particle-size distribution. (e) Tooth-colored (white) ProRoot MTA powder particle-size distribution. (f) DiaRoot powder particle-size distribution

Fig. 8.3

(a) Biodentine powder particle-size distribution. (b)EndoSequence sealer powder particle-size distribution. (c) RetroMTA powder particle-size distribution

Nano-sized particles are of interest because of the high surface-to-volume ratio versus micron-sized particles. The surface-to-volume ratio changes from less than 10 % for micron-sized particles to more than 50 % for nanoparticles, which is important because a higher surface-to-volume ratio can dramatically increase reactivity, such as hydration. Fumed or colloidal silica are nano-sized particles that are commonly added to many dental products. Such silica products may be a minor addition to some MTA products; however, no MTA product has been identified that is primarily composed of nanoparticles.

Calcium sulfate is used in construction uses of Portland cement to delay setting. Without calcium sulfate, the calcium aluminate phase of Portland cement quickly hydrates and causes initial setting by stiffening the cement, which is undesirable for bulk pouring of concrete. For MTA indications, faster setting is desired. The Angelus company has integrated the manufacture of the tricalcium silicate powders into their operations so that their MTA products are now made with fewer trace metal oxides and without calcium sulfate (private communication, 2013). The initial setting time of their products is reported to be only 10 min, by allowing the tricalcium aluminate phase to quickly hydrate [54]. Later, the Angelus Corporation developed a sealer containing MTA powder (MTA Fillapex®), which is described in the ensuing sealer section.

DiaRoot® from DiaDent® was introduced by 2007, and this material was manufactured without tricalcium aluminate; therefore, no calcium sulfate phase is needed to control the rapid hydration of the tricalcium silicate. Tantalite (Ta₂O₅) is used as the radiopaque powder, making this material very white, by comparisons to gray ProRoot MTA or tooth-colored (white) ProRoot MTA that contain bismuth oxide. DiaRoot was advertised as containing calcium phosphate monobasic, but no phosphate phase was detected with XRD (Table 8.1), indicating that the phosphate was either amorphous or was present at less than 1 %. The format of this product is very similar to ProRoot MTA with one gm sachets of powder and water ampoules shown in Fig. 8.4. Currently, this product is sold through Verio Dental Co. (Vancouver, Canada) from Innovative BioCeramix Inc. (IBC) (Vancouver, Canada).

Table 8.1 X-ray diffraction results for some MTA products (weight percent)

Fig. 8.4

DiaRoot BioAggregate product showing powder sachet, water ampoule, and mixing tools

The Brasseler Co. (Savannah, GA, USA) offers MTA-type products, under the trade name EndoSequence BC or Bioceramic. These products appear to be related to the DiaRoot and iRoot products, and IBC is believed to be the supplier/manufacturer. The Brasseler products are based on fine tricalcium silicate powders that do not contain alumina. The products are offered in four formats: powder for mixing with water, a paste, a putty, and a sealer (Fig. 8.5). The EndoSequence BC putty, paste, and sealer have the powder mixed with various carrier liquids that do not cause setting; hence, the liquid must be anhydrous. These paste/putty forms of the EndoSequence BC material do not require mixing before placement and they allow a clinician to choose a viscosity suitable for the indication or case. When placed, water must diffuse from the tissues into the paste, putty, or sealer to displace the carrier liquid and cause hydration/setting of the tricalcium silicate powder. The percentage of the ceramic powder in any of the products is not known, but is estimated as 60–80 % MTA-type powder. The fine powders and convenience as putty or paste are solutions to the criticisms of MTA being coarse and hard to place. The time for diffusion of water to cause setting will vary with the indication and location. Brasseler EndoSequence putty sets more slowly than ProRoot MTA [28], but the setting times for these materials are more than 24 h, therefore irrelevant for the procedure. In vitro testing shows that setting of the sealer takes more than 1 week [71]. However, the ability to place the putty and complete the procedure may outweigh other concerns.

Fig. 8.5

Two of Brasseler’s EndoSequence products, putty (a) and sealer (b), are shown

Brasseler and IBC companies use the terms bioaggregate and bioceramic for their products. Bioaggregate has no technical meaning, but does imply the bioactivity that occurs when tri- and dicalcium silicates are placed in contact with tissue fluid. Bioceramic is a term used to refer any ceramic (nonmetallic and inorganic) material, including glass, in the body of suitable biocompatibility. Bioceramics are not limited to the Brasseler products, but include resorbable ceramics and inert ceramics such as alumina or zirconia used in dentistry and other medical devices.

Brasseler also manufactures EndoSequence BC gutta-percha points that contain the same tricalcium silicate powder used in their other tricalcium silicate products. This product is their approach to bonding the sealer to the gutta-percha and the dentin as a “monoblock” [94]. The use of MTA powder in gutta-percha has been patented (US 7,838,573).

Biodentine® (Septodont, Saint-Maur-des-Fossés, France) is a fast-setting tricalcium silicate product, which has the same indications as ProRoot MTA. The company has emphasized using the material to replace dentine lost to caries. Its use as a dentine replacement may not prevent leakage [22]. A composite resin should be placed over the Biodentine as the material will not be sufficiently stable when exposed to the oral cavity. Biodentine powder is packaged in unit doses of 0.75 g, more than is usually used for endodontic or vital pulp therapy indications (Fig. 8.6). The user manually adds the liquid to the powder’s capsule and the mixture is triturated. The water-based liquid, supplied in ampoules, contains a “plasticizer” (polycarboxylate) and calcium chloride to enhance the properties and speed the setting. Although advertised as “dentin in a capsule,” the Biodentine powder contains mostly tricalcium silicate (83 %) with 14 % calcium carbonate and 4 % zirconia (Table 8.1) and does not contain hydroxyapatite and collagen. Biodentine does not contain dentine and should not be confused with bone grafting material, which is hydroxyapatite. However, its fine powder and faster setting are improvements over the original MTA. The low amount of zirconia in Biodentine makes the material only as radiopaque as dentin. High radiopaque contrast is desired for dental materials, such as composite resins, which are also dentin replacements, for X-ray visibility. However, this product was stable to discoloration [95], unlike ProRoot MTA [9, 12, 59, 67, 70].

Fig. 8.6

Biodentine by Septodont, showing the triturator capsule and its foil packaging, liquid for addition to the capsule

TheraCal™ LC (Bisco Inc. Schaumburg, IL, USA) is the only commercial light-curing version of MTA to date and is indicated for pulpal tissue contact. This material contains less than 20 % MTA powder, a radiopacifier of barium zirconate (BaZrO₃), and dimethacrylate resins. The product literature describes the MTA component as Type III Portland cement, which denotes a finer powder than Type I Portland cement. The particle size is less important for a premixed material that needs no spatulation prior to light curing. TheraCal has been tested and shown to release more calcium ions than Dycal® (Dentsply International, York, Pennsylvania, USA), a calcium hydroxide-based pulp-capping material [44]. Also the TheraCal product has higher radiopacity, lower solubility, and better bonding than Dycal, the current “gold standard” for pulp capping. TheraCal is not indicated for the endodontic indications for which MTA has become known and may not be suitable for such indications based on cytotoxicity studies [55].

New endodontic cement (NEC, AKA calcium-enriched mixture or CEM) has been introduced (BioniqueDent, Tehran, Iran) and contains calcium compounds not found in ProRoot MTA. The NEC material contains more calcia than MTA does by the addition of [8] calcium oxide, calcium phosphate, calcium carbonate, calcium silicate, calcium sulfate, calcium hydroxide, and calcium chloride. Over time, calcium oxide powder will form hydroxide and then carbonate in the container, to create more calcium carbonate. Asgary has not disclosed the presence of tri- or dicalcium silicates, nor a radiopaque agent in the literature; however, the material’s similar performance to MTA makes this material likely to be based on the familiar MTA phases of tri- and dicalcium silicate phases. NEC has been reported to be bioactive and have good handling and sealing [6] as a root-end filling material. Its film thickness was lower than ProRoot MTA’s and its flow was higher, indicative of a finer particle size than the ProRoot MTA, which has the same indications. A study with pulp capping in canines has shown equivalent results of MTA and NEC, and NEC’s superiority to calcium hydroxide-based IRM® [91]. A root-end filling study in canines was successful (after 60 days) versus MTA when apical lesions were induced [5]. Pulpotomies in humans showed similar success (about 75 %) for NEC and MTA [76] for apical development for as long as a 1-year follow-up. A second study in humans compared conventional root canal therapy to pulpotomies (with NEC) for postoperative pain and 6-month radiographic outcome. Significantly less pain occured in the first 7 days for pain and radiographic superiority [4].

Two manufacturers from Korea have introduced MTA products to the USA and elsewhere: OrthoMTA and RetroMTA (BioMTA, Daejeon, Korea), and Endocem MTA (Maruchi, Gangwon-do, Korea) shown in Fig. 8.7. OrthoMTA and RetroMTA products are fine powders, advertised as having an average particle size of 2.6 μm, although independent testing has shown that the powders have a median particle size of about 10 μm (Fig. 8.3c). The indications for OrthoMTA and RetroMTA overlap, although RetroMTA has more vital pulp indications. OrthoMTA is sold in (centrifuge vials) containing 0.2 g of powder. The user adds his/her own water to the powder in the vial and places the vial in a battery-powered centrifuge to spin for 20 s. Then the excess water is decanted and the retained powder is considered hydrated for dispensing. Special instruments are used for dispensing. Initial setting time is 3 min. and the final setting is about 6 h. The phases present are said to include tri- and dicalcium silicate, tricalcium aluminate, tetracalcium aluminoferrite, less than 1 % free calcia, and 3 % of amorphous phase. Its radiopaque component is bismuth oxide. The material is indicated for orthograde use.

Fig. 8.7

(a) RetroMTA shown in sachet, packaged with water ampoule. (b) OrthoMTA shown in vial placed in centrifuge (Image courtesy of Dr. Yoojin Shin, BioMTA.) (c) Endocem shown in vial, having a gray color

RetroMTA has a different format from OrthoMTA. Sachets of 0.3 g of powder are packaged in a flat plastic container disk with separate ampoules of water, which are manually mixed by the user. This light gray tri- and dicalcium silicate powder has about 25 % zirconia, some tricalcium aluminate phase, calcium chloride, and silica (Table 8.1). It is advertised as containing calcium aluminozirconate for radiopacity, but this was not detected by X-ray diffraction. The RetroMTA brochure lists “lack of discoloration” as an attribute; discoloration has been attributed to bismuth oxide [23]. RetroMTA does not contain bismuth oxide, so the discoloration claim seems valid. The initial setting time of RetroMTA is said to be 1.5 min, which is likely caused by the calcium chloride.

Endocem MTA shown in Fig. 8.7c is advertised as setting in 3:15 min. Like the OrthoMTA, the powder is sold in a flip-top vial of the kind that is often used in centrifuging biological samples. The Endocem product literature states that zirconia is present, but bismuth oxide was identified in X-ray diffraction (Table 8.1). Endocem was the only product tested that contained only dicalcium silicate, with no tricalcium silicate for the hydraulic reaction. The setting was not tested independently; however, dicalcium silicate is slower setting than tricalcium silicate. About 40 % calcium carbonate was also identified, with minor amounts of calcium phosphate, crystalline silica, and magnesia. This excess calcium carbonate indicates that the material is pozzolanic.

Cerkamed PPH (Wojciech Pawlowski, Nisko, Poland) has introduced an MTA +  product (Fig. 8.8), which is distinct from the product MTA Plus® described below. The MTA +  product is distributed in small polymer bottles containing 0.3 g of powder with a separate vial of water. This white powder contained primarily tricalcium silicate (63 %) with silica, and about 9 % each of bismuth oxide and zirconia, and a small amount of an aluminate phase (Table 8.1) in X-ray diffraction.

Fig. 8.8

MTA + material from Cerkamed, shown in vial, having a white color

Medcem GmbH (Weinfelden, CH) offers a Portland cement powder for use instead of formocresol [83]. However, this powder has no radiopaque material; therefore, its radiopacity is similar to dentin.

Two MTA Plus® products are available and both are tri/dicalcium silicate powders with bismuth oxide. The white version is sold outside the USA, and is manufactured by Prevest Denpro (Jammu, India); its phase composition is substantially identical to that of tooth-colored ProRoot MTA (Table 8.1). Grey MTA Plus is manufactured in the USA by Avalon Biomed Inc. (Bradenton, FL, USA). Both products include a powder and gel for mixing.

Both MTA Plus products are indicated for pulp and periapical tissue contact. This is the only MTA product that is indicated for the additional indication of a root canal sealer. The variety of indications from pulp-capping to root-end filling can be satisfied by varying the ratio of powder to gel to the desired consistency for the procedure. The benefit of the gel is the washout resistance, versus other MTA products mixed with water. The MTA Plus powders are finer than ProRoot MTA powder, as can be seen in the scanning electron micrographs of Fig. 8.9. The coarse particles of ProRoot MTA create the “sandy” feeling when mixing with water. The MTA Plus powder is packaged in a desiccant-lined bottle, which is more protective and convenient than sachets of other manufacturers against water absorption by the cement, and permits the clinician to use any amount of powder without waste. Several articles have been written about the properties of MTA Plus including remineralization, anti-washout, and use as a root canal sealer [25, 40, 69, 75, 84]. A product similar in appearance to the white-version of MTA Plus is marketed by Dentonics (Charlotte, NC, USA) as Masterdent® MTA.

Fig. 8.9

Particle-size comparison of ProRoot MTA (a) versus MTA Plus with (b)

In 2013, several European companies introduced MTA products that have 0.3 g “unit doses” in triturator capsules containing powder. When the capsules are squeezed to activate (like an amalgam capsule), a separate compartment with water is opened and the powder and water are triturated. Harvard Dental International’s (Hoppegarten, Germany) MTA, Micro-Mega (Besancon, France) MM-MTA™, S&C Polymer Silicon’s (Elmshorn, Schleswig-Holstein, Germany) MTA cement, and MTA Caps by Acteon (Merignac, France) all have unit-dose triturator capsules (Fig. 8.10). These capsules are sold in foil pouches, to protect the powder in the capsule from humidity. Ironically, the capsules also contain water for mixing. The water must be sufficiently segregated to avoid harming the powder during storage, or the shelf life will be impaired.

Fig. 8.10

MTA Caps by Acteon showing the triturator capsule and foil pouch

The MTA Caps powder was analyzed (Table 8.1) and found to contain tricalcium and dicalcium silicate, tricalcium aluminate, about 18 % calcium carbonate, and 31 % calcium tungstate (for radiopacity). A small amount of silica and calcium chloride hydrate is included, which presumably enhance handling and accelerate initial setting. MM-MTA is also said to have a “faster set time” (20 min), achieved by the addition of calcium carbonate.

Other products are close to marketing such as Trioxident (VladMiVa, Belgorod, Russia)’s NEX MTA (Tokyo, Japan) cement or Endo–Eze MTA by Ultradent (South Jordan, UT, USA). The Trioxident product is a powder–water system, with the powder sold in sachets. The powder has some coarse particle but appears to be a conventional MTA formula with bismuth oxide. The NEX MTA is a powder–liquid system and the powder is provided in sachets. The format of the Endo–Eze MTA is unknown.

The spectrum of formulas, packaging, properties, and colors is widening. Undoubtedly, more calcium silicate products will enter the marketplace in the coming years.

8.3 Experimental Products

In 2005–2010, experimental products from Dentsply were described in the literature: ProRoot MTA Advanced [79, 97] and ProRoot MTA sealer (AKA Generex A and B, respectively). The former had the usual periapical and pulpal contact indications; the latter was indicated only for root canal sealing. Although the results were favorable for sealing [57, 99] and bioactivity [99], these powder/gel products have not been commercially introduced. The experimental Dentsply products were disclosed as being more radiopaque and having improved handling compared to ProRoot MTA. Each product had a unique liquid for use for its indications.

Another experimental product was Viscosity Enhanced Root Repair Material (VERRM) [30] which contained Portland cement, bismuth oxide, and “other compounds” such as polyvinyl alcohol, polyethylene oxide, natural gums, cellulose, or clay dispersions to improve the handling versus MTA. Cellulose and calcium chloride have also been tested by others [10] for mixing with MTA products.

Camilleri has been a forerunner in experimental materials by testing gray and white Portland cements, with the addition of an industrial plasticizer. The plasticizer improved the handling (workability) and did not reduce biocompatibility [26]. The absence of calcium sulfate in a tricalcium silicate accelerated setting [18]. She did pioneering work [19] in investigating the suitability of MTA products for use as a sealer, when MTA-type materials were mixed with Glenium® (Degussa, Manchester, UK), a polycarboxylic ether polymer, to attempt to meet the requirements of ISO 6876 for root canal sealers.

Ding has researched sol–gel–processed dicalcium silicate cement for endodontics and possibly bone cement. He used mixtures of the cement with sodium phosphate dibasic (Na₂HPO₄) as an accelerant [34]. Recently he reported on ß-Ca₂SiO₄ powder, combined with gelatin and chitosan oligosaccharide (COS) solution in a liquid phase [29]. Research has also been performed by his group regarding incorporating zinc oxide, magnesia, and iron oxide additions to tricalcium silicate powders [63] for improved properties.

Gandolfi and Prati have tested Portland cement-based materials (denoted as TC materials) using variations that include montmorillonite (a type of inorganic clay that is a layered phyllosilicate), calcium chloride, and fluoride, sometimes mixed with Articaine®. Their MTA formulas were as biocompatible as the ProRoot MTA product and more biocompatible than AH Plus® (Dentsply, Konstanz, Germany) root canal sealer [42]. Other experimental formulas, also denoted as TC, used another white Portland cement and showed the bioactivity of the experimental materials [48], although the pushout strengths of their experimental formulas were not as high as for ProRoot MTA [61]. A promising light-curable formula has also been reported [47].

An experimental material containing barium sulfate, Portland cement, and undisclosed emulsifiers has been investigated. Like other Portland cement products, implantation was equal to MTA (Angelus) [51].

Asgary, the inventor of NEC, mentioned other materials that were being developed for MTA-type applications, but information on these experimental materials was not available: Root MTA (Salamifar in Iran) ([41]), Abyek cement (Abyek company in Iran), Melcann cement or Melcann white cement (Melcann cement in Australia), and Saveh white cement (Saveh company in Iran) [7]. However, the latter three cements seem to reference cement brands, not dental companies or brands.

An experimental root canal sealer has been reported in the literature, MTAS [96], having a composition of 80 % white Portland cement with zirconia for radiopacity. Its liquid contains water, calcium chloride, and a “resinous vehicle” [81].

Many studies have used commercial Portland cements as a substitute for MTA products on the market and as the basis for experimental products [3, 7, 13, 14, 24, 31, 33, 35, 43, 45, 50, 58, 60–62, 65, 66, 74, 82, 86–88, 90, 92, 100]. Often, the focus has been on biocompatibility of the Portland cements, usually cell culture studies, versus ProRoot MTA. Other studies have measured the arsenic or other trace metal oxides in Portland cements versus commercial products. The total arsenic oxide content of the noncommercial preproduction MTA powder was 5 ppm (unpublished data, 2007), determined by inductively coupled plasma technique (ICP), although the leachable content would be less. Researchers disagree on methods for arsenic determinations and the reports of the amounts in commercial cements or MTA products have varied, ranging from <1 ppm to over 50 ppm. The potential arsenic content has been discussed [80], as a possible contaminant in commercial Portland cements designed for construction, versus medical devices. The International Standards Organization (ISO) 9917 document limits the leachable arsenic content to 2 ppm for water-based dental cements. No researcher has reported a commercial construction grade Portland cement that meets all the important attributes of sealing, fine particle size, freedom from lead and arsenic, and conformance to ISO 6876 standards such as insolubility and radiopacity.

8.4 Alternative Formulas

Portland (calcium silicate) cement has been combined with calcium aluminate cement for some tests as a dental material. Monocalcium aluminate cements should not be confused with the tricalcium aluminate phase of Portland cements. The monocalcium aluminates, hereafter referred to as calcium aluminate cement, are commercially used for high-temperature linings of furnaces and as a coating in some sewer systems. The calcium aluminate cements have the advantages of higher early strength and greater resistance to acid than calcium silicate (Portland-type) cements; however, the calcium aluminate cements undergo “conversion,” a reversible hydration reaction at environmental temperatures, making them unsound for massive construction. The main setting reaction calcium aluminate cements at body temperature is given in Eq. 8.4, which is a dissolution–precipitation reaction.

$$ \begin{array}{c}6\left(\mathrm{CaO}\cdot {\mathrm{Al}}_2{\mathrm{O}}_3\right)+24{\mathrm{H}}_2\mathrm{O}\\ {}\to 2\left(\mathrm{CaO}\right)\cdot {\mathrm{Al}}_2{\mathrm{O}}_3\cdot 6{\mathrm{H}}_2\mathrm{O}+4\mathrm{Al}\left(\mathrm{OH}\right){}_3\end{array} $$

(8.4)

Calcium aluminate cements have higher strength than the minor phase of tricalcium aluminate, present in most Portland cements as described earlier. Furthermore, some reactivity of the monocalcium aluminate occurs with silica, which seems to contribute to the Quick-Set material described below.

Capasio, now known as Quick-Set, is an experimental material that has been investigated as an MTA improvement. The Quick-Set system includes a fine calcium aluminosilicate powder and a water-based gel. This material is quick-setting, washout resistant, and acid resistant [97]. Quick-Set is chemically distinct from MTA because it does not contain tri- or dicalcium silicate. This fine aluminosilicate powder has been shown to penetrate dentinal tubules [11] and to biocompatible [38, 98]. EndoBinder material (Binderware, São Carlos, SP, Brazil) is a calcium aluminate product, which does not contain silica but is a water-setting hydraulic material. EndoBinder has less MMP-2 activity than other hydraulic dental materials [89]. Other properties of Endobinder have been shown to be favorable [1, 2, 49]. The monocalcium aluminate in EndoBinder and in Quick-Set powders is known to be more acid resistant, which is beneficial for placing the cement in infected conditions or for the placement of a composite, which requires acid etching, over the cement.

Camilleri also tested combinations of calcium aluminate, calcium silicate cements, and fluoride-containing silicate cements with calcium sulfate additions reporting adequate in vitro properties [15, 17], acceptable biocompatibility [16], and successful reduction of the initial and final setting times. While some companies have removed calcium sulfate, Camilleri added about 8 % CaSO₄ and a plasticizer to achieve desirable test results. Dye leakage was noted with these experimental materials [20], but bacteria may be killed by the high pH of the interstitial liquid in the cement, preventing harm from leakage. Attack by acid on these predominantly tricalcium silicate materials did occur [21].

8.5 Root Canal Sealers

MTA-based root canal sealers are intriguing because of the biocompatibility of MTA and its osteogenic potential for accidental extrusion beyond the apex. The American Dental Association (ADA) 57 and ISO 6876 requirements for root canal sealers are useful for evaluating such root canal sealer products. These two documents’ requirements and methods are identical with two exceptions. The ISO 6876 standard uses a flow and working time sample of 0.05 ml versus 0.5 ml for the ADA 57 standard. The second difference is the ISO 6876 version has no requirement regarding dimensional stability, whereas the ADA 57 standard requires the linear dimensional stability over 30 days to be less than 1 % shrinkage and less than 0.1 % expansion (1 % <∆L <+ 0.1 %.). Data from the literature have been gathered in Table 8.2

Table 8.2 Properties tested per ADA 57, ISO 6876, and ISO 9917 tests (From Asgary et al. [8], Candeiro et al. [27] and Zhou et al. [101]; Otherwise measured by the author)

for several materials discussed above. The requirements provide a basis for comparisons; however, the standards are not designed to compare clinical handling, sealing of the canal, or clinical efficacy. The following discussion of MTA-containing sealers refers to the methods of these standards.

The EndoSequence BC sealer of Brasseler is a single paste sealer that contains a very fine tricalcium silicate powder and an unidentified liquid medium. The fill percentage of powder is also undisclosed. Within the tooth, water must interact with the powder, displace the medium, and cause hydration and setting of the tricalcium silicate around the gutta-percha. The sealer has been reported to meet the ISO 6876 requirements [27, 101], as shown in Table 8.2. When used with EndoSequence BC gutta-percha, some hydration and bonding of the tricalcium silicate in the gutta-percha can be expected with the sealer. However, the benefits of this interaction have not been published, such as, evidence that hydration does bond the sealer to the gutta-percha. The EndoSequence BC sealer’s setting time is quite long (>24 h), depending on the testing methodology, but zinc oxide eugenol (ZOE) sealers also have a long setting time.

MTA Plus products are indicated for use as a root canal sealer. The MTA Plus powders are very similar in composition to the original MTA, but the powder is finer and a gel is included, not water. The finer powder and gel allows the small film thickness to be achieved (<50 μm is required) for a root canal sealer, which was not possible with ProRoot MTA (Table 8.2), or in general, for construction grade Portland cements. Setting time is less than 10 h in vivo, using the ISO 6876 test method, when mixed to the consistency needed for a sealer.

MTA Fillapex (Angelus, Londrina, Brazil) is a two-paste root canal sealer that contains MTA powder in a salicylate resin (Fig. 8.11). The 1,2 butylene glycol disalicylate resin creates a 35 min working time and a 2:10 h setting time; however, the sealer contains only 13.2 % MTA powder. Studies are needed to find out if the MTA will hydrate within the resin and if bioactivity occurs in this format. If not, then the sealer’s resin carrier is more similar to the pulp-capping material called Dycal, without the calcium hydroxide. Studies have shown Fillapex to be antibacterial but also to be more soluble than AH Plus sealer [39].

Fig. 8.11

MTA Fillapex shown in its 2-tube format (a) and auto-mixing tip format (b)

Retreatability has been an issue regarding MTA-based sealers, because of the challenge of removing the old sealer before retreatment. Two studies have shown that complete removal of the EndoSequence sealer, Fillapex, and MTA Plus sealers is not possible [56, 75]. No study has shown that retreatment will be more or less important for these sealers.

Endoseal by Maruchi is an MTA powder that is mixed with water for use with gutta-percha cones. This material is provided in a plastic vial within a foil pouch for unit doses of 0.3 g. The material is said to contain zirconia and no heavy metals.

Endo CPM material (EGEO SRL, Buenos Aires, Argentina), shown in Fig. 8.12, is a powder–liquid system for use as a root canal sealer. The composition is reported to be 50 % MTA (SiO₂, K₂O, Al₂O₃, SO₃, CaO), 7 % SiO₂, 10 % CaCO₃, 10 % Bi₂O₃, and 10 % BaSO₄, with a liquid containing 1 % propylene glycol alginate, 1 % propylene glycol, 1 % sodium citrate, and 10 % calcium chloride in water [52]. Small differences from the stated formula were found by X-ray diffraction as presented in Table 8.2. Bacterial leakage for this sealer was reported to be worse [77] and antibacterial action was less than AH 26 sealer (Dentsply International, Konstanz, Germany) [73]. However, implantation studies show equivalence to MTA and superiority to AH Plus [85] and bioactivity [52].

Fig. 8.12

CPM root canal sealer kit by EGEO, containing a powder and a “physiological” liquid

Tech Biosealer products from Isasan SRL (Rovello Porro (CO; Italy)) seem to be based on the compositions of Gandolfi et al. [46, 53], where a phyllosilicate is added to improve handling of the tricalcium silicate powder. The powder is a mixture of white CEM (presumably Portland cement), CaSO₄, CaCl₂, Bi₂O₃, “water-swelling silicate” (montmorillonite), and NaF. The liquid contains Dulbecco’s phosphate-buffered saline (DPBS). The cement is milled and heat-treated before packaging into kits with capsules containing 0.27 g of powder, with one vial of liquid containing 5 cm³ of DPBS. The product is offered in three formats: root-end, pulp capping, endodontic, and apexification. The four product differentiations could not be discerned as to which was best for root canal sealing.

8.6 Summary

A wide variety of commercial MTA-type materials are now available for pulp-capping, endodontic treatment, and root canal sealing, many having improved characteristics and wider indications that the original MTA products. Several products have finer particles, less “sandy” handling, and faster initial or final setting. Adjuvants are incorporated in some products for faster setting achieved by the addition of fluoride, the elimination of calcium sulfate, or an increase in tricalcium aluminate phase. Additions to the mixing liquid to speed setting include calcium chloride, polycarboxylate, or various organic resins. Several new products have enhanced calcium content compared to the original MTA, although the biological benefits of excess calcium oxide or carbonate have not been substantiated. A gel system has been developed (MTA Plus) to reduce washout resistance and speed setting. Even a light-cured MTA-containing material is marketed. Depending on the product, the radiopacity and the radiopacity agent may vary. The product formats include bulk powder/liquid containers (1–8 g), unit doses as small as 0.27 g in triturator capsules, or unit doses in centrifuge tubes. All-purpose materials, for use for all endodontic and pulpal indications, including root canal sealer, are also available.

No studies have shown superior biocompatibility over the original MTA formula. Portland cements normally used for construction have not been shown to be biologically inferior, despite their slow setting, impurities, low radiopacity, and coarseness. The bioactivity of tri- and dicalcium silicate powders, by the release of calcium hydroxide during setting, dominate the biological response. The resulting layer of HA masks the underlying cement, reducing the opportunity for leaching of any impurity into the tissues.

Major advances have been made to create more convenient MTA products that have good handling, faster setting, good radiopacity, washout resistance, and resistance to discoloration. However, no product has definitively improved on the biocompatibility or bioactivity of the original formula.

Alumina :

Aluminum oxide Al₂O₃.

Amorphous :

Lacking a crystalline structure identifiable by x-ray diffraction.

Ceramic :

Inorganic, nonmetallic material, usually an oxide, but includes other compounds such as sulfates, carbonates, sulfides, or carbides.

Bioceramic :

Any ceramic material that is used in the body; includes all MTA products.

Calcia :

Calcium oxide, usually created by calcining (heating) calcium carbonate (CaCO₃) to release carbon dioxide.

Calcium aluminate cement :

A high-temperature (refractory) cement based on hydration of CaO·Al₂O₃

Calcium hydroxide :

Portlandite, a reaction phase of hydrating tri- or dicalcium silicates; Ca(OH)₂ or CH in cement notation.

Calcium silicate :

CaSiO₃, AKA wollastonite, a non-hydraulic compound of calcium oxide and silica.

Calcium sulfate :

CaSO₄, which may be present as anhydrous, hemihydrate, and dihydrate.

Cement notation :

Abbreviations used for the phases of Portland cement for brevity and convenience.

Clinker :

The cement product, usually a particle larger than 1 cm, that exits from a rotary kiln.

Component :

(1) The materials that are used before firing a ceramic. For example, calcium carbonate is used to make Portland cement; or (2) the compound in a phase diagram to show the interrelations of several components usually over a range of temperatures.

Dicalcium silicate :

Belite, the second most common phase in Portland cement. Ca₂SiO₄, also written as 2CaO·SiO₂ or C₂S in cement chemist notation.

Ettringite :

A hydrated calcium aluminum sulfate mineral with formula (CaO)₆(Al₂O₃)(SO₃)₃·32H₂O or (CaO)₃(Al₂O₃)(CaSO₄)₃·32H₂O, formed by reaction of tricalcium aluminate with calcium sulfate.

Ferrite :

Tetracalcium aluminoferrite; 4CaO·Al₂O₃·Fe₂O_3, also shown in cement notation as C₄AF.

Glass :

An amorphous (noncrystalline) ceramic, usually based on silica but can also be based on boron oxide or phosphorous oxide as the main components.

Hydraulic material :

A powdered ceramic material that hardens (sets) when mixed with water.

Hydroxyapatite :

The mineral component of the bone having the formula Ca₁₀(PO₄)₆(OH)₂. Carbonated calcium-deficient hydroxyapatite is the main mineral of dental enamel and dentin.

Kiln/rotary kiln :

A furnace capable for high temperature (higher than 1,200 °C) for firing materials such as Portland cement. A rotary kiln rotates the feedstock (usually balls of 1–3 in. in diameter) to economically, uniformly, and continuously fire (react and sinter) Portland cement.

Minerals :

Compounds that are mined which may vary in purity depending on the source. Some deposits of minerals are one nearly pure phase, or they may be a combination of phases or purities. For instance, calcium carbonate sources can be very pure, white calcium carbonate, with less than 1 % or any other carbonate, such as strontium carbonate or magnesium carbonate. Other mines may have calcium carbonate mineral interspersed with iron oxide; such raw material sources will create a gray-colored Portland cement by the presence of iron.

Mineral trioxide aggregate (MTA) :

An inorganic powder composed primarily of tricalcium and dicalcium silicates, usually with a radiopacifier and other minor ceramic phases.

Nano-sized :

Particles that are close to a nanometer (nm) in size, which is 1/1,000 of a micron (μm).

Phase :

A chemical compound that is present in a material, uniquely identifiable by X-ray diffraction.

Pozzolan, pozzolanic :

(1) A Portland cement that has free silica added which reacts with calcium hydroxide released from the Portland cement during the hydration of its calcium silicate phases, or (2) Roman-era cement that relied on the reaction of calcium oxide, made by heating calcium carbonate, with silica to form calcium silicate hydrates, via the reaction below, which differs from the Portland cement hydration (Eq. 8.5):

$$ \begin{array}{c}\mathrm{Ca}{\left(\mathrm{OH}\right)}_2+{\mathrm{H}}_4{\mathrm{SiO}}_4\to {\mathrm{Ca}}^{2+}+{\mathrm{H}}_2{{\mathrm{SiO}}_4}^{2-}+2{\mathrm{H}}_2\mathrm{O}\\ {}\to {\mathrm{Ca}\mathrm{H}}_2{\mathrm{SiO}}_4\cdot 2{\mathrm{H}}_2\mathrm{O}\end{array} $$

(8.5)

Portland cement :

A range of compositions based on reacting calcia, silica, and alumina to form powders containing tricalcium silicate and dicalcium silicate, usually with some minor phases. Calcium sulfate is commonly added to the silicate powders to control and slow the setting time for use in large scale constructions. Type I and Type III are the common categories for construction uses of Portland cement. The properties are similar, but the Type III product is a finer powder.

Silica :

Silicon dioxide, SiO₂, usually amorphous, but the quartz form is crystalline.

Sintering :

A heating process for powders that reduces the overall surface area by various atomic movements, to cause a powder to form a solid mass, and usually reduces porosity. For Portland cement, the sintering process is concomitant with the reaction process to create the calcium silicate phases from the raw materials in the kiln.

Tricalcium aluminate :

Ca₃Al₂O₆, also written as 3CaO·Al₂O₃, or C₃A in cement notation. A minor phase in most Portland cements.

Tricalcium silicate :

Ca₃SiO₅, also written as 3CaO·SiO₂ or as C₃S in cement chemist notation. The main component of Portland cement.

Zirconia :

Zirconium oxide, ZrO_2.

Ziron :

Zirconium silicate, ZrSiO₃

Zirconates :

Compounds that combine another oxide with zirconia into a unique compound such as CaZrO₃.

Tungstate :

Compounds that combine another oxide with tungsten into a unique compound such as CaWO₄, which is commonly used for radiopacity in dental materials.