Introduction:


Mineral trioxide aggregate (MTA) has been extensively studied as a material to seal the communication pathways between the root canal system and the periradicular tissues. MTA and its properties have been extensively evaluated in vitro and in vivo in the literature, but there are still no studies or long-term results. In the short term, this material is very promising for certain indications. MTA is a powder consisting of fine hydrophilic particles that set in the presence of moisture. Hydration of the powder generates a colloidal gel that forms a hard structure. MTA material is mainly composed of particles of tricalcium silicate, tricalcium aluminate, dicalcium silicate, tetracalcium ferric aluminate, bismuth oxide, and calcium sulfate dihydrate. The setting time of the material is between three and four hours. MTA is a highly alkaline cement, with a pH of 12.5. This pH is very similar to that of Calcium Hydroxide, and may enable antibacterial effects. The material has a low compressive strength, which means that it cannot be used in functional areas. Other characteristics of MTA are its low solubility and a greater radiopacity than dentin. In addition, MTA has shown good biocompatibility, excellent sealing against microleakage, good marginal adaptation and it seems to reduce bacterial microleakage.


 


MTA Preparation


MTA is marketed by Maillefer-Dentsply (Ballaigues, Switzerland) under the name ProRoot MTA®  and is presented in hermetically sealed sachets containing the MTA powder. The ProRoot attaches a few pipettes with sterile water. The MTA must be prepared immediately before use. The powder is mixed with sterile water in a 3:1 ratio on a glass slide to a workable consistency. Some authors use anesthetic solution instead of sterile water. Once the material has reached a suitable consistency, it can be applied using a transporter or small amalgam holder. MTA requires the presence of moisture for its setting. It can be compacted by means of a damp cotton ball, a paper point or a small tamper. After opening an MTA sachet, the unused powder can be stored in a resealable container for future use in other treatments. The main drawback of the MTA is its difficult handling, so practice is required.


 


Clinical indications for MTA


 


Pulp capping and pulpotomies


Pulp capping and pulpotomy are only indicated in teeth with immature apices when the pulp is exposed and it is desired to maintain its vitality. These treatments are contraindicated if there are symptoms of irreversible pulpitis. MTA has been shown to stimulate dentin bridge formation adjacent to the dental pulp. This dentin formation may be due to the sealing ability, alkalinity and biocompatibility or possibly other properties of MTA.


 


Apical barrier with MTA: apical formations


The creation of an apical barrier with MTA is indicated in teeth with necrotic pulps and open apices. Various materials (calcium hydroxide, tricalcium phosphate, collagen, calcium phosphate, etc.) have previously been used as an apical barrier, so that gutta-percha can condense, thus preventing possible extrusion of material during apex treatment of teeth. open. After a first appointment in which we clean and shape the canal, we place calcium hydroxide for 7 to 14 days to help disinfect and clean. At the second appointment, we removed the calcium hydroxide, and blotted the canal with paper points. If we consider it necessary, a matrix can be placed to avoid overfilling of the MTA. For this, biocompatible materials can be used such as: absorbable collagen (CollaCote, Calcitek, Plainsboro, NJ, USA), hydroxyapatite, calcium hydroxide powder, etc. The MTA is transported into the canal via an amalgam holder, and gently condensed to create a 3-4 mm apical barrier. The barrier is checked radiographically. If we do not achieve the expected result, it is advisable to wash with sterile water to remove the MTA, and try the procedure again. If the MTA apical barrier seems appropriate, we place a moist cotton ball in the canal next to the MTA, and seal the opening with a temporary filling. In a third appointment, the provisional is removed (at least three or four hours later), the rest of the canal is filled with gutta-percha or composite, and the permanent filling material is placed. MTA can therefore be used as an apical barrier in teeth with immature apices and necrotic pulp. This material stimulates the formation of hard tissue without producing inflammation in the area adjacent to the apex of immature roots.


 


Root perforations


Root perforations can occur during the preparation and shaping of root canals, in the placement of posts, in retreatments, and also as a result of internal perforating resorption of the periradicular tissues. Perforation repair can be attempted surgically or non-surgically. Factors that affect prognosis are the size of the perforation, bone and ligament damage, the time between perforation and repair, the ability to achieve a tight seal, and whether the perforation is supraosseous or subosseous. Many materials have been used to repair perforations such as gutta-percha, silver amalgam, glass ionomer, composite, Super EBA® (Harry J. Bosworth, USA), Cavit® (ESPE, Seefeld, Germany) or calcium hydroxide. When we seal a perforation, it is necessary to avoid the extrusion of material to the periradicular tissues. An internal matrix provides us with biocompatibility and control of the restorative material, avoiding over or under filling of the MTA in the perforation. Biocompatible materials such as: absorbable collagen (CollaCote, Calcitek, Plainsboro, NJ, USA), hydroxyapatite, calcium hydroxide powder, etc., can be used for this purpose. The matrix will be used in perforations larger than one millimeter. The clinical procedure depends on the location of the perforation:











 


– In the case of a perforation in the furcation:


First, we clean the area with NaOCl or saline. The ducts and perforation are located. First, the instrumentation and obturation are carried out, to later repair the perforation; or the perforation can be repaired first and then the canals can be instrumented and obturated. If necessary, an internal matrix is ​​placed before the MTA. We mix the MTA with the sterile water and place it in the perforation with a small amalgam holder. After the repair, a moist cotton ball is placed next to the MTA, and the opening is sealed with a temporary filling. Then, the provisional is removed (at least three to four hours later) at the next appointment to place the permanent filling material.


 


– In the case of a lateral perforation (stripping) in the middle third of the root:


Instrumentation and obturation of the ducts is always carried out first, to later repair the perforation in the manner described above.


 


– In the case of a perforation in the apical third of the root:


The MTA should be placed to form a three to five millimeter apical plug. It is placed with a very small amalgam holder. A moist cotton ball is then placed, and the opening is sealed with a provisional. At the next appointment (at least three or four hours later) the rest of the canal is filled with gutta-percha and sealing cement. Finally, a permanent filling material is placed.


 











– In the repair of internal perforating resorption:


First we proceed to clean and shape the canal. NaOCl is used during preparation, and calcium hydroxide between appointments, to help us clean the defect and at the same time reduce bleeding. At the next appointment, we removed the calcium hydroxide, and filled the canal with gutta-percha and cement, except for the defect, in which we placed the MTA. For the MTA to set, we put a damp cotton ball on top. At the next appointment, we remove the cotton ball and proceed with the permanent filling.


To achieve a good seal, it is important to always check the hardness of the MTA before placing the permanent filling material. 


Several in vitro and in vivo studies have shown that MTA is a suitable material for the repair of lateral or furcal root perforations.


 


Retro fillings in endodontic surgery


The performance of an apicoectomy and a retro cavity, and the subsequent obturation of the same with an apical obturation material is indicated to achieve a good apical seal, and thus prevent the penetration of irritants from the canal to the periradicular tissues, and vice versa. Several materials (amalgam, MRI, Super EBA…) have been used as retro-filling materials. Through in vivo studies, it has been shown that MTA is associated with less inflammation of adjacent tissues, cement formation adjacent to MTA, and good regeneration of periradicular tissues.


 


Other indications


MTA can also be used as a coronary barrier material, after canal obturation, and before internal bleaching. Avoid using MTA on the tooth above the gingival margin, as it may cause discoloration of the tooth. A white MTA formula is currently being studied to avoid this type of situation. Another indication may be the repair of vertical fractures. The repair of vertical fractures usually has an unfavorable evolution. The prognosis of treatment with MTA in a case with a vertical fracture, in which there is direct communication with the oral cavity for a long period of time, is unpredictable. This is because MTA dissolves in an acidic pH7.  Despite this, clinical cases have been described in the literature on the repair of vertical fractures.


 


Conclusion


MTA and its properties have been extensively evaluated in numerous studies in the literature, but there are still no studies or long-term results.











In the short term this material is very promising. It has been shown that it is a biocompatible material, with adequate sealing capacity and low solubility, with antimicrobial effects, and that it induces the formation of hard tissue and at the same time facilitates the regeneration of the periodontal ligament. 


All these treatments must be evaluated with periodic controls of at least six months to a year, or longer. 


To perform many of the treatments with this material, it is advisable to use magnification, either through a dental microscope, endoscope, or magnifying lenses to help visualize the field. 


Recent research has shown that the composition of MTA and Portland cement is similar. Some in vivo studies have found very similar results and biological reactions between the two materials19. Portland cement may become a very promising material for Endodontics in the near future. 


It is also important to assess the prognosis of the tooth and its importance to the patient before starting a procedure that is not going to have a predictable result. Another aspect to evaluate is the possibility of referring to an endodontist the most difficult patients or cases that are beyond our means, time, or specialty.


Author: Miñana-Gómez, Miguel


Dentist. Master of Endodontics, University of Texas Health Science Center (San Antonio, USA). Exclusive practice of Endodontics, Madrid