Mineral trioxide aggregate

Mineral trioxide aggregate (MTA) is a dental material used in vital pulp therapy and some endodontic root canal procedures. Originally developed for perforation repair and root end filling, MTA was a refined (reagented) Portland cement Type I with bismuth trioxide for radiopacity. MTA has expanded its uses to one-visit apexification, pulp capping and root canal obturation and so on. MTA is expanding the meaning from Portland cement to all kinds of mineral aggregate including limestone cement, calcium aluminate cement, magnesium silicate cement, lithium silicate cement as natural ceramic cements widely. MTA is the name of specific dental product material, of mineal aggregate and radiopacifier of bismuth trioxide.

Composition

MTA is composed of 1. tricalcium silicate, 2. dicalcium silicate, 3. tricalcium aluminate, 4. tetracalcium aluminoferrite, 5. calcium sulfate and 6. bismuth oxide. The later 4 phases vary among the commercial products available. Original ProRoot MTA is a refined Portland Cement with Bismuth Trioxide as radiopacifying agent. ProRoot MTA is especially made by Portland Cement Type I, 55% (C3S), 19% (C2S), 10% (C3A), 7% (C4AF), 2.8% MgO, 2.9% (SO3), 1.0% Ignition loss, and 1.0% free CaO. A limitation on the composition is that the (C3A) shall not exceed fifteen percent. Main constituents of MTA are tricalcium silicate and dicalcium silicate naturally composed. MTA contains innated tricalcium aluminate (C3A)and tetracalcium aluminoferrite(C4AF). These constituents are determined to Portland Cement Type (I to V). White MTA was developed for reducing of discoloration to tooth structure. It was eliminating C4AF (tetracalcium aluminoferrite) as iron (Fe)'s main discoloration induced element. The initial White MTA contained significantly lesser amount of aluminum oxide (Al2O3), magnesium oixde (MgO) and ferric oxide (Fe2O3) than grey MTA. The current White MTA was developed in 2008 with White Portland Cement. - White Portland Cement - Limestone Silica Compounding Cement, main consitituent is Calcium Carbonate Cement of Limestone.

Rawmix formulation

"The characteristic greenish-gray to brown color of ordinary Portland cement derives from a number of transitional elements in its chemical composition. These are, in descending order of coloring effect, chromium, manganese, iron, copper, vanadium, nickel and titanium. The amount of these in white cement is minimized as far as possible. Cr2O3 is kept below 0.003%, Mn2O3 is kept below 0.03%, and Fe2O3 is kept below 0.35% in the clinker. The other elements are usually not a significant problem. Portland cement is usually made from cheap, quarried raw materials, and these usually contain substantial amounts of Cr, Mn and Fe. For example, limestones used in cement manufacture usually contain 0.3-1% Fe2O3, whereas levels below 0.1% are sought in limestones for white manufacture. Typical clays used in gray cement rawmix may contain 5-15% Fe2O3. Levels below 0.5% are desirable, and conventional clays are usually replaced with kaolin. Kaolin is fairly low in SiO2, and so a large amount of sand is usually also included in the mix. Iron and manganese usually occur together in nature, so that selection of low-iron materials usually ensures that manganese content is also low, but chromium can arise from other sources, notably from the wear of chrome steel grinding equipment during the production of rawmix. See rawmill. This wear is exacerbated by the high sand-content of the mix, which makes it extremely abrasive. Furthermore, to make a combinable rawmix, the sand must be ground to below 45 μm particle diameter. Often this is achieved by grinding the sand separately, using ceramic grinding media to reduce contamination."

Also newly developed fast set MTAs were developed by Pozzolan Cement or Zeolite Cement. These were used by pozzolanic reaction. Pozzolan Cement is a mineral aggregate with watery calcium silicate hydration.

Originally, MTA was formulated from commercial Portland cement combined with bismuth oxide powder for radiopacity , to make the material visible on a dental x-ray. However, dental materials are required to have high purity and be lead and arsenic-free, unlike portland cement, and dental companies have created materials to meet the dental standards (ISO 9917) for purity and performance (ISO 6876 and ADA 57). The original MTA was dark gray in color, but white versions have been on the market since 2002. ProRoot® MTA and MTA Angelus® brands are based on the original formulas for white and gray MTA, contain roughly 20% bismuth oxide, and are available as white or gray.^[1] Current tooth-colored MTA was marketed in 2008 by US Patent 7,892,342. Original MTA was formulated form Ordinary Portland Cement as Calcium Silicates, but current White MTA was developed by White Ordinary Portland Cement as different manufacturing process and different raw material of Calcium Carbonate (Limestone). Though chemical compositions are similar, the properties and activities are different by the raw materials' compounding technology. Oridnary Portland Cement is made by long-term natural process of heat and compression. But limestone silica compounding cement is artificially compounded by decarbonation and mixturing process of Lime (CaO) and Silica (SiO2) with Alumina (Al2O3).

Aluminum-containing phases, and calcium sulfate are minor phases present in some MTA products. Although some studies have shown an increased risk of developing Alzheimer's disease with environmental factors such the intake of metals, particularly aluminium; the neurotoxicity of calcium aluminate compounds has not been demonstrated. ^{[2] [3] [4]}

Characteristics and products

1. Biocompatible with periradicular tissues
2. Non cytotoxic to cells, but antimicrobial to bacteria
3. Non-resorbable
4. Minimal leakage around the margins.
5. Very basic AKA alkaline (high pH when mixed with water).
6. As a root-end filling material MTA shows less leakage than other root-end filling materials, which means bacterial migration to the apex is diminished.
7. Treated area needs to be infection free when applying MTA, because an acidic environment will prevent MTA from setting.
8. Compressive strength develops over a period of 28 days, similar to Portland cement. Strengths of more than 50 MPa are achieved when mixed in a powder-to-liquid ratio of more than 3 to 1.^{[citation needed]}

Originally, MTA products required a few hours for the initial and final setting, which is uncommon in dental materials. The first patented products were either gray or white ProRoot MTA from Dentsply. http://www.tulsadentalspecialties.com/default/endodontics/Ultrasonics/rootrepair.aspx Newer materials are available that set more quickly and have added characteristics. For instance, Angelus company has made MTA products similar to ProRoot MTA, but added a salicylate based sealer, have less than 20% MTA powder.

MTA Plus is washout resistant.^[5] MTA Plus may be used for 10 indications.

MTA Products: Original ProRoot MTA Grey: Calcium Alumino-Silicate Cement (C3S, C2S with C3A)- Portland Cement Type I with Bismuth Trioxide. (ex. MTA Angelus Grey) ProRoot MTA White : Calcium Carbonate alumino-silicate Cement (CaCO3 + SiO2 with Al2O3). Final phase is similare to Portland Cement. (Limestone Portland Cement) -ex. MTA Angelus Blanc, EndoCem/Zr, MM MTA, Tech BioSeal MTA, Trioxident, most white MTAs.

Setting Time: Original ProRoot MTA is set by water. But for faster/quicker setting, there are hydration accelerants. Also Alumina more containing MTA can be set faster than less alumina containing MTA. GIC solution is polyacrylic acid. GIC is alumino-silicate (glass) bioceramic cement. As MTA is mainly composed of calcium-alumino-silicate, PAA (polyacrylic acid) is an accelerant for MTA. PAA set MTA within 15–18 minutes. More aluminate, faster set. Also high concentrated calcium chloride (CaCl2, 70% more) is well known as accelerator of Portland cement. So high concentrated -over 70%- Calcium Chloride solution sets MTA within 12 minutes. Or Pozzolanic reaction is also faster set chemical reation of calcium silicate hydrate. By this pozzolanic reaction, MTA Agelus, MM MTA and EndoCem MTA are pozzolan-calcium carbonate with fumed silica hydration for fast set. But pozzolanic reacted cement has lower compressive strength at 15 MPa maximum. Easy broken and easily removable property of pozzolanic MTA.

Alternative to MTAs - BioA, Bioceramic Aggregate

Mineral is ceramic in nature. MTA was used by mineral aggregates from natural resources. Instead of mineral aggregate, sythetic artificial pure calcium silicate is used for dental and medical products. It is named as Bioceramic (chemically bonded cermic) cement. Recently medical graded calcium silicate based materials were developed. It is the replacement of MTA. So it is classified as bio-aggregates (BA or BioA). Hydraulic calcium silicate cements are integrated name of calcium silicate based materials. The examples are BioDentine and BioAggregate (DiaRoot). Silicate based bioceramic is a glass ionomer cement (GIC) as restorative material. Calcium based bioceramics are calcium phosphate, calcium carbonate, calcium aluminate, calcium sulfate, calcium silicate, etc. However, as calcium phosphate, calcium sulfate and calcium carbonate are biodegradable materials, these are used for bone grafting material. As root canal filling material and root repair material is non-biodegradable material permanently, so calcium aluminate cement and calcium silicate bioceramic materials have been used for endodontic materials and restorative materials. Calcium alumino-silicate cement is a potential material. In root canal sealing/filling material, calcium based material with bioactivity is commonly used rather than alumina-based material of calcium aluminate cement because alumina is bioinert bioceramic.

BioAggregate was marketed after FDA approval in 2006, 2 years faster than White Portland Cement MTA in 2008. BioAggregate is newly pure medical graded calcium silicates (tricalcium silicate and dicalcium silicate) by 65% and calcium phosphate as admixture by 6% and tantalum pentoxide by 25% as radiopcifier. This is the artificial name of bioceramic aggregate in opposition of mineral aggregate. Mineral is ceramic in nature, bioceramic is chemically bonded ceramic, artificial sythetic pure calcium silicates. So there is no toxic heavy metals and unnecessary heavy metals of iron, manganese, nickel, copper, zinc. Also BioA is not used by bismuth trioxide, but by tantalum pentoxide, zirconia, or calcium tungstate as radiopaque material. It is a differentiation from MTA, trioxide. Before MTA was developed, calcium phosphate bioceramic materials were developed as root-end filling material. But calcium silicate bioceramic materials have been used only as bone cement or admixture. After MTA is nothing but Portland cement (calcium-alumino-silicate cement), pure calcium silicate bioceramic materials were developed for root-end and root canal filling material. After researching, BioAggregate (DiaRoot) was approved by FDA and then marketed. It is an alternative to MTA.

Biodentine material is a newer tri/dicalcium silicate powder (aluminum-free) that is made radiopaque with zirconia, and has salt and other additives for quicker setting.^[6] Biodentine is pure tricalcium silicate and dicalcium silicate with calcium carbonate by 20% and high concentrated calcium chloride solution as hydration accelerant. It is called as tricalcium biosilicate technology. Biodentine is also an alternative to MTA. - aluminum-free (non-tricalcium aluminate) and zirconia (ZrO2) instead of bismuth trioxide.

Brasseler offers paste and putty versions of tri/dicalcium silicate, including sealer, which set in vivo.^[7] The Brasseler products are based on the same free-tricalcium aluminate containing powders as Diaroot BioAggregate, Bioceramic Aggregate. These powders are very white, non-discoloration and are made radiopaque by tantalum pentoxide and zirconia or any other radiopacifying agents except bismuth trioxide. Brasseler's bioceramic sealers (BC sealer, RRM and RRM putty) are different from powderic bioceramic materials. The compositions are similar to bio-Aggregate, but the material is in paste-form of bioceramic gel formation. BioAggregate is an alternative to MTA. Bioceramic pastes are higher technologies of Bio Tech, Ceramic Tech and Nano Tech integrated technology based advanced bioMaterial (esp. Bioceramic Science) for dental and medical purpose.

These hydraulic Calcium Silicate based materials are alternatives to Mineral calcium silicate cements. Alumino-silicate bioceramic, Calcium Aluminate Bioceramic, Calcium Alumino-Silicate Bioceramics are developed for Root-end filling and root canal filling materials rather than mineral aggregate based materials.

Usage in some clinical cases

Root-end Filling after Apicoectomy

In root canal therapy where an apical infection is persistent, an apicoectomy may be required. Flap is raised over the tooth and the root tip is resected and a cavity created (3–4 mm) in the root tip removed. Retrograde application of MTA to the root tip cavity is completed.

MTA was originally developed for root-end filling. There were several different materials such as amalgam, reinforced zinc oxide eugenol cements (intrim restorative material - IRM, super ethoxy benzonic acid [EBA], glass ionomer cement and composite resin for root-end filling after apicoectomy. MTA, a refined "Portland cement" - calcium alumino-silicate cement-, was found to have less cytotoxic and better results in biocompatibility and micro-leakage sealing ability, giving it more success over root-end filling materials. But MTA is not acceptable as "ideal root-end filling material" because MTA has some drawbacks of toxic heavy metal presence, discoloration, difficult handling, short working time, long setting time, washout before setting and washout after set (calcium carbonate based MTA has solvent of carbonic acid).

For ideal Root-end filling, there are many new materials or improved materials developed. 1. Glass ionomer cement: It is based on alumino-silicate based bioceramic material. Most cytotoxicity is caused by polyacrylic acid. So current GIC as root-end filling material is reducing the cytotoxic acclerator's concentration. - calcium alumino-silicate - MTA (calcium alumino-silicate) + GIC (alumino-silicate), calcium reinforced glass ionomer cement is developed. It's a promising material.

2. Calcium phosphate cement (hydroxyapatite) bioceramic material: CPC has been studied since 1985 in the US. Bone grafting material, artificial bioceramic CPC is developed for Root-end filling or pilot material in root-end filling and root repair material.

3. Calcium silicate based material - bioceramic material: It was known as bioceramic sealers. But actual bioceramic aggregates are composed of pure medical graded calcium silicate based material. BioAggregate, Biodentine, EndoSequence RRM and RRM Putty are based on calcium silicate bioceramic material.

4. Calcium aluminate bioceramic material - (alumina cement in minerals, calcium aluminate cements in bioceramics) Alumina is an initial fast setting element and high compressive strength. It has been used as dental products as luting agent. Calcium aluminate cement (bioceramic) has been developed for dental products and root-end filling material.

These newly developed root-end filling materials are based on bioceramic, chemically bonded ceramic, not by mineral (ceramic in nature) like MTA. Even if mineral shows higher biocompatibility, minerals have potential toxic heavy metals in material. Bioceramic or bioMaterial is used for medical and dental products. BioMaterials can reduce the issues on discoloration and toxic heavy metals' presence initially.

Internal & external root resorption & obturation

In internal resorption… root canal therapy is performed, putty mixture of MTA is inserted in the canal using pluggers to the level of the defect. Gutta percha and root canal sealer are placed above the defect to complete the root canal treatment. In direct cases, the canal may be completely obturated with MTA. The MTA will provide structure and strength to the tooth by replacing the resorbed tooth structure. In external resorption… after root canal therapy is performed. Flap is raised over the tooth and the defect removed from the root surface with a round bur. Retrograde application of MTA to the root surface is then completed.

Lateral or furcation perforation

Lateral perforation occurs when an instrument has perforated the root during cleaning & shaping of the canal by the dentist. If it happens, one should finish cleaning & shaping of the canal , irrigate the canal with sodium hypochlorite to disinfect it and dry it with a paper point. The perforation can be sealed with a thick mixture of an MTA-type product, preventing bacterial ingress. Make sure that you can locate the canal while the MTA has not set and remove the excess material from the area.

Root canal sealer

Several MTA products are available as sealer. MTA Plus has the highest percentage of MTA in its formula.^[8] As calcium based materials have washout property in dam, the antiwashout agents are used. The examples are chitosan and gelatin, which has been used with injectable bone grafting paste. MTA Plus is used with gelatin complex as antiwashout agent. MTA Angelus Fillapex sealer contains less than 20% tri/dicalcium silicate powder in a salicylate carrier medium. By element analysis, there is no bismuth oxide of MTA. Instead, MTA Fillapex is composed of calcium oxide and silica in salicylate resin like Sealapex. EndoSeal MTA, Tech BioSeal MTA are also MTA root canal sealer. MTA is used as filler in the resin like MTA Fillapex. In epoxy resin based sealer, MTA is mixed with fillers. But it is not MTA based root canal sealer, but resin modified root canal sealer.

Newly non-MTA (Bioceramic, BioA) Root Canal Sealers: BioAggregate, BC Sealer, RRM, Biobinder, calcium aluminate bioceramic root canal sealer, calcium phosphate injectable Root canal sealers were developed and are devloped for root canal sealer. They are not a kind of MTA Sealer, but a BioA or Bioceramic based Sealer.

Brasseler Endosequence offers a pre-mixed sealer with a non-reactive carrier medium and the product only sets in vivo. Brasseler's EndoSequence bioceramic sealers are not MTA, but calcium silicate based material. Its medium is used with inorganic bioceramic gel type (non-biodegradable), which is different from organic agents of chitosan or gelatin (biodegradable). By bioceramic high technology, it is set by the water/moisture in the root canal and body. 100% hydraulic bioceramic without mixing of hardener before using. Root Canal Sealer is required by non-discoloration and non-toxic heavy metals and easy handling and higher biocompatibility, bioactivity and bacteria-tight sealing. These ideal requirements need more biomaterial than minerals.

Apexification (Necrotic pulp)

When the root is not completely formed in adolescents, but an infection occurs nd the pulp is not vital, apexification can be performed to maintain the tooth in position as the roots develop. In case of non-vital pulp: 1. Isolate the tooth with a rubber dam 2. perform root canal treatment. 3. Mix the MTA and insert it to the apex of the tooth, creating a 3 mm thickness of plug. 5. Fill the canal with sealer and gutta percha.

Apexogenesis (Vital pulp)

The process of maintaining pulp vitality during pulpal treatment to allow continued development of the entire root (apical closure occurs approximately 3 years after eruption). 1. Isolate the tooth with a rubber dam 2. Perform a pulpotomy procedure. 3. Place the MTA material over the pulp and close the tooth with temporary cement until the apex is completely formed.

Pulp capping

In case of mechanical exposure that occurs during cavity preparation and not a pathological exposure due to caries. Proper isolation should be completed using a rubber dam and cotton pellet.Disinfection of the cavity with sodium hypochlorite. then application of MTA over the exposure area. restoration of the cavity with amalgam or composite is done. MTA provides a higher incidence and faster rate of reparative dentin formation without the pulpal inflammation.

MTA Plus material is also indicated for base and liner in vital pulp therapy. In root-end filling after apicoetomy, the anti-washout agent (chitosan or gelatin) is useful to prevent from MTA washout. But in vital pulp therapy, anti-washout gel doesn't increase bioactivity or bacterial tight sealing ability of MTA. Instead, hydraulic (100% pure water) MTA shows the higher success rate than anti-washout gel or resin medium. Resin Modified MTA or Calcium Silicate Cement was marketed already. TheraCal LC is HEMA-free resin modified calcium silicate cement (MTA-like, Portland cement Type III) light-curable for base and liner in vital pulp therapy.

See also

• Calcium hydroxide
• Internal resorption
• External resorption
• Endodontic therapy

References