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PRODUCT PROFILE: Mineral Trioxide Aggregate (MTA): An Updated Review

December 1, 2000
by Ioana Cirstescu, DDS and Maria-Lilliana Rodriguez, DDS


ABSTRACT: Mineral Trioxide Aggregate (MTA)* is a special purpose dental material developed at Loma Linda University. Studies to evaluate its properties and explore possible applications have yielded promising results. Ease of manipulation as well as the unique ability to stimulate osteogenesis and cementogenesis make this biocompatible material a perfect choice for endodontic repair. Excellent results were observed when used as a root end filling material, a direct pulp capping agent and for root perforation repair. Continuing research and long term clinical studies are needed to confirm and consolidate present findings.

Pulpal and periradicular pathosis result from exposure of dental pulp and periradicular tissues to microorganisms. Maintaining pulp vitality and/or sealing the pathways of contamination between the root canal system, the periradicular tissues and the oral cavity are the main objectives for an adequate treatment. MTA was developed as a repair material that does not irritate the surrounding tissues and has good sealing properties. Sealing ability, non-inflammatory reaction, ease of manipulation and the property of stimulating hard tissue formation make MTA a valuable repair material in endodontics. It is currently used as a root end filler, root perforation sealer, apical barrier for open apex and a pulp capping material.

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This paper is intended to review MTA’s properties, related techniques and applications, as well as its present and future potentials.

COMPOSITION

MTA is a powder that consists of fine hydrophilic particles that sets in the presence of moisture. The ingredients are tricalcium silicate, bismuth oxide, dicalcium silicate, tricalcium silicate, tetracalcium, aluminoferrite and calcium sulfate dihydrate (gypsum). Hydration of the powder results in a colloidal gel that solidifies to a hard structure.

PHYSICAL PROPERTIES

MTA must be prepared immediately before its use. Preparation and placement must be done under controlled moisture, which acts as an activator for the chemical reaction.

The slow setting time of MTA in a moist environment provides the adequate conditions for dimensional stability and a good seal.

Ph

The initial ph is 10.2 changing gradually to 12.5 (similar to Calcium Hydroxide) in 3 hours.

Marginal Adaptability

MTA has a significantly better adaptation to dentinal walls at the root apex than amalgam, Super EBA and IRM..

Sealability

Compared to amalgam, Super EBA and IRM, leakage is significantly lower even under moisture contamination. The presence of blood does not affect its performance. MTA’s sealing ability has been attributed to its hydrophilic nature and slight expansion when set in a moist environment.

Solubility

MTA shows no signs of solubility in water, like amalgam and Super EBA, but dissolves in acid ph.

Compressive Strength

Comparable to IRM, the compressive strength is increased in the presence of limited moisture. Over time it will change from 40 MPA (in 24 hours) to 70 MPA (after 21 days).

Resistance to Displacement/ Dislodgement, Retention

MTA has the ability to reestablish resistance to dislodgement from the dentinal walls when the initial displacement has occurred within 24 hours.

Setting Time

Average setting time is 3 hours, depending on the size of the particles, powder to water ratio, temperature, presence of water, entrapped air. This value may explain the better than average sealing properties. A longer setting time allows less shrinkage and less bacterial leakage providing dimensional stability.

Radiopacity

More radiopaque than IRM and Super EBA, gutta percha and dentin. Easily distinguishable.

BIOCOMPATIBILITY

The antimicrobial property of MTA is comparable to that of other materials used in endodontic repair (amalgam, Super EBA and IRM). Its anitibacterial effect on some facultative bacteria has been attributed to its sealing ability.

Cellular Reaction

MTA is less cytotoxic than IRM, Super EBA and amalgam.

Mutagenicity

MTA is not mutagenic.

Tissue Reaction

In vitro studies have shown that MTA may actively promote hard tissue formation: direct bone apposition (osteogenesis) and inductive effect on cementoblasts (cementogenesis). When compared to other restorative materials, studies have demonstrated that this healing process is achieved without inflammation.

INDICATIONS

Root End Filling Material

Several studies have confirmed MTA as a potential root-end filling material. The periradicular tissue response in dogs to MTA showed less periradicular inflammation and apical hard tissue formation (cementum) on the surface of MTA. Tests on periradicular tissue in monkeys and guinea pigs have led to similar results.

The results of these investigations showed that MTA as root-end filling material is associated with significantly less inflammation, better sealing property, periapical regeneration and even cementum formation.

Apical Plug

Tests conducted to observe the rat subcutaneous connective tissue reaction to the implanted dentin tubes filled with CaOH or MTA, showed that the mechanism of action of MTA has some similarity to that of CaOH.

In a case study on a 29-year-old female patient, MTA was used as an apical stop, in a non-vital tooth with an open apex. The root canal space was obturated with ZOE and vertical condensation of gutta percha was done. At a 20-month recall, the tooth was asymptomatic and normal periapical bone architecture was present.

The ability to induce apical hard tissue formation, associated with less inflammation compared to other materials (calcium hydroxide), makes MTA a good choice as an apical stop in teeth with immature apexes.

Repair of Root Perforations

Several studies were conducted on human maxillary and mandibular molars to evaluate MTA’s ability to seal furcal perforations. Its hydrophilic properties combined with a mineral composition similar to dentin makes MTA a good repair material (better than amalgam).

Perforation repair is more predictible with MTA than with amalgam and IRM, but only if these defects are repaired before bone destruction has occurred.

A four case report (age ranging from 13 to 72) recommends MTA as a good material for treating iatrogenic furcal perforations. Similar results were found in all cases. Follow up recalls at six and 12 months, showed that there were no signs, symptoms or pathology and the radiolucency of the furcation was resolved. Lack of adverse effects after extrusion of MTA into the furcation area confirms its biocompatibility.

Repair of Lateral Root Perforations

Several studies have been done to compare amalgam, IRM and MTA as a repair material for lateral root perforations. The results of a four-week trial period are based on staining of perforation sites with methylene blue. The study shows that MTA leaks significantly less than amalgam and IRM and has less overfilling tendency when compared to the other materials.

Coronal Plug

MTA’s sealing ability makes it a good choice as a coronal plug after complete obturation of the root canal system and before internal tooth whitening of discolored teeth. MTA should be placed with a 3-4 mm. thickness in the prepared cavity.

Pulp Capping Material.

Exposed dental pulp has the capacity to heal when microleakage and bacterial contamination are not present. Therefore, an effective pulp capping material should be biocompatible, provide a biological seal and prevent bacterial leakage.

Pulp capping has traditionally been performed with Calcium Hydroxide but MTA has now been shown to be more effective. The ideal situation is capping a young tooth with an incompletely formed root and an apical diameter of 1mm. or more. The tooth has to be free of irreversible inflammation.

A study in monkeys, which examined the dental pulp response to MTA and CaOH when used as pulp capping materials, showed that MTA stimulates dentin bridge formation. The bridge formed adjacent to the MTA was thick and continuous with the regional dentin. No bacteria were observed on the cavity walls when MTA was used. Although the dentin bridg
e presented some irregularities, no tunnel defects or soft tissue inclusions were noted.

Dentinogenesis induced by MTA, is explained by its sealing ability, biocompatibility, alkalinity or possibly other properties associated with this material.

CONCLUSIONS

MTA promotes regeneration and hard tissue formation, is biocompatible, has good sealing ability, dimensional stability and is easy to manipulate. It has been used with success as an apical sealer, perforation repair and pulp capping material. Continuing research and long term clinical studies are needed to confirm and consolidate present findings.

Oral Health welcomes this original article.

REFERENCES

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15.Bates C.F., Carnes D.L., Del Rio C.E.. Longitudinal Sealing Ability of Mineral Trioxide Aggregate as a Root-End Filling Material. J.Endodon. 1996; 22:575-8.

16.Pitt Ford T.R., Torabinejad M., Abedi H.R., Bakland L.K., Kariyawasam S.P. Using Mineral Trioxide Aggregate as a Pulp Capping Material. JADA. 1996; 127:1491-4.

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20.Torabinejad M., Smith P.W., Kettering,J.D., Pitt Ford T.R.. Comparative Investigation of Marginal Adaptation of Mineral Trioxide Aggregate and Other commonly Used Root End Filling Materials. J. Endodon. 1995; 21: 295-9.

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25.Kettering J. D., Torabinejad M. Investigation of Mutagenicity of Mineral Trioxide Aggregate and Other Commonly Used Root-End Filling Materials. J. Endodon. 1995; 21:537-9.

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28.Torabinejad M., Higa R.K., McKendry D.J., Pitt Ford T.R. Dye Leakage of Four Root-End Filling Materials: Effects of Blood Contamination. J. Endodon. 1994; 20:159-63.

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