Mineral trioxide aggregate (MTA) is a calcium silicate–based dental material recognized for its outstanding biocompatibility, superior sealing ability, and capacity to induce the formation of a hard tissue barrier at pulp and periapical interfaces. Introduced in the early 1990s, it has become one of the most clinically significant materials in contemporary endodontics.

Composition and Setting Behavior

MTA consists primarily of tricalcium silicate, dicalcium silicate, and tricalcium aluminate, with bismuth oxide added to confer radiopacity for radiographic visualization. Upon mixing with water, the powder hydrates to form a colloidal gel that sets into a rigid structure. A defining advantage is its ability to set and maintain structural integrity in the presence of moisture — a property that distinguishes it from many conventional root canal sealers and restorative cements.

Clinical Applications

MTA is indicated across a range of procedures where biocompatibility, hermetic sealing, and tissue regeneration are priorities:

• Direct pulp capping: Placed over an exposed vital pulp to stimulate dentin bridge formation and preserve pulp vitality.
• Pulpotomy: Used as a coronal pulp dressing in both primary and immature permanent teeth to maintain radicular pulp health.
• Apexification: Creates a calcific apical barrier in teeth with open or incompletely formed apices, enabling subsequent root canal obturation.
• Perforation repair: Seals iatrogenic or pathological root perforations near the periodontal ligament, limiting bacterial ingress and supporting tissue healing.
• Root-end filling: Placed in retrograde cavities during apical microsurgery to prevent microleakage at the resected apex.

Biological Mechanism

MTA’s bioactivity is largely attributable to its alkaline pH and sustained release of calcium ions, which inhibit bacterial growth while stimulating cementum– and odontoblast-like cell activity. This promotes regeneration of periapical attachment tissues and deposition of a mineralized matrix at the material–dentin interface, supporting long-term healing rather than simple void filling.

Traditional gray MTA formulations carry a risk of tooth discoloration, particularly problematic in anterior cases where enamel translucency is esthetically critical. Newer white MTA and contemporary bioceramic-based alternatives address some of these handling and esthetic limitations while retaining comparable sealing and bioactive properties.

For clinicians managing complex endodontic scenarios — open apices, root perforations, or pulp exposures with uncertain prognosis — MTA’s decades-long evidence base and genuine tissue-inductive capacity make it a dependable material that often determines whether a tooth can be retained rather than extracted.