MINERAL TRIOXIDE AGGREGATE Seminar by Guide: Dr. C. Ram Mohan Dr. T. Manisha Choudary
Introduction It was introduced by Mahmoud Torabinejad and colleagues at Lomalinda University in 1993. Has been used on experimental basis by endodontists for several years with anecdotally reported successes, some of it quite impressive. It was approved for the human usage by the FDA in 1998. The material appears to be an improvement over other materials for some endodontic procedures that involve root repair and bone healing.
MTA has been used in both surgical and non-surgical applications including;
1. Root end fillings
2. Direct pulp capping
3. Perforation repairs in roots or furcation
4. Apexification, etc.
It’s also useful for the troublesome problems of strip perforations and perforating resorptive defects.
Though there are many indications for MTA applications in the field of endodontics, nonetheless the material has got few contraindications.
The material is not recommended for obturation of primary teeth that are expected to exfoliate since the material is slowly absorbed, if at all.
MTA may be ideal material for use against bone, because it’s the only material that consistently allows for the overgrowth of cementum and formation of bone and may facilitate the regeneration of periodontal ligament
MTA is a mechanical mixture of three powder ingredients.
Portland cement (75%), Bismuth oxide (20%), and gypsum (5%). It also contains trace amounts of SiO2, CaO,MgO,K2SO4 and Na2SO4.
The major component, Portland cement, is a mixture of dicalcium silicate, tricalcium silicate, tricalcium aluminate, and tetra calcium alluminoferrite.
Since 2002, tooth colored MTA has been marketed to substitute for gray MTA, which was marketed earlier.
It is off white in color to provide a hue matched more closely to that of the color of teeth.
In a comparative study of white MTA and gray MTA, the biggest changes of all, infact occur in the concentrations of FeO (black), MgO (white), and Al2O3.
It therefore seems reasonable to suspect that the absence of significant FeO in white MTA is most likely cause the change in color from gray to white.
MTA when hydrated becomes a colloidal gel that solidifies to form a strong and impermeable barrier.
Setting time – 3 to 4 hours.
Initial pH (when hydrated) 10.2.
Set pH -12.5(comparable to Ca(OH)2).
Working time - 5 minutes
Set compressive strength -70 MPa. (Approx equal to IRM but much less than amalgam (311 MPa)).
Radio opacity slightly greater than dentin.
Excellent sealing properties
Sets in the presence of moisture
Least cytotoxic compared to other materials
Has dentinogenic, osteogenic potential
Induces cementum apposition
Facilitates regeneration of periodontal ligament.
Technique sensitive requires operator expertise
Delayed setting time.
ROOT END FILLING MATERIAL
An ideal root end filling material should
adhere and adapt to the dentinal walls of the root end preparation
prevent leakage of microorganisms and their byproducts in to the periradicular tissues
In addition it should be insoluble in tissue fluids,
dimensionally stable and unsusceptible to the presence of moisture.
According to Regan et al 2002 a DOUBLE SEAL consisting of
Physical barrier – provided by root end filling material and
Biological seal – formed by regeneration of periodontal apparatus over resected root face is the ideal outcome.
This has been shown to be achievable with rootend filling available today such as Diaket and MTA.
After raising the soft tissue flap, ostectomy, root end resection and root end preparation, periradicular hemorrhage should be controlled.
A lack of moisture control and presence of excessive bleeding during placement of MTA in the root end cavity makes it very soft and unmanageable.
MTA should be prepared immediately before its use. MTA powder should be kept in container with tight lids and away from moisture. The powder should be mixed with sterile water at a ratio of 3:1 on a glass or paper slab with the aid of a metal or plastic spatula, the mixture can be carried in a metal or plastic carrier to its intended site of the operation.
After complete filling of the root end cavity, the surface of the resected root and MTA mixture is cleaned with a wet piece of gauze or telfa.
Because MTA sets in the presence of moisture some hemorrhage is created from the periodontal ligament and bone and blood is brought over the resected root end and MTA. The field of operation is not rinsed. Soft tissue flap is sutured and the healing is assessed periodically.
Mechanism of action
Koh et al in 1997 used set MTA in their study of biological response of human osteoblasts to the material. They found that MTA caused an increase in the production of interlukin (IL)-1 , IL -1 , IL-6 and osteocalcin.
IL-1 and IL -1 interact with receptors on osteoblasts, which in turn activate osteclasts. Second only to collagen, osteocalcin is an abundant protein, which is present in bone and may be an indicator of bone matrix production
Mitchell etal (1999) found that set MTA was biocompatible when tested with a culture of human osteosarcoma cells.
They further reported that MTA induced the production of IL-6, IL-8 and the macrophage colony-stimulating factor.
IL-6 is a powerful factor produced by osteoblasts to induce bone resorption.
IL-8 promotes the development of new blood vessels and activates the precursors of osteoclasts.
Macrophage stimulating factor may have a significant function in osteoblasts development and maturation.
Numerous materials have been suggested as root end filling materials; Guttaparcha, Zinc oxide-eugenol cement, Cavit, Composite resin, Gold foil, and Glass ionomer cement, Amalgam etc.,
Amalgam has been used as a root end filling material for many years. Its potential disadvantages however include
Mercury and tin contamination.
Need for an undercut in the cavity preparation.
Super EBA was very popular in the 1990’s and was slowly replacing amalgam as “the” material in the endodontic practice. MTA is relatively a new material that became available in the late 1990’s.This material appears to be the most promising to date, as it comes closest to being the ideal material for retrofilling and the results of reported are indeed impressive.
Because of these disadvantages, Zinc oxide eugenol based such as Super EBA and IRM have been advocated as root end filling materials. The potential disadvantages however, of Zinc oxide eugenol based cements include:
Irritation of vital tissue.
Difficulty in clinical handling of material.
Inability to promote regeneration of the periradicular tissues to their prediseased state and normalcy.
In two separate investigations, Torabinejad etal; compared the efficacy of MTA with amalgam as a root end filling material in dogs and monkeys. The results of these investigations showed significant differences between the two materials.
The use of MTA as root end material was associated with significantly less inflammation, cementum formation over MTA, and regeneration of the periradicular tissues to almost normal pre experimental status.
Torabinejad et al compared the sealing ability of MTA with SuperEBA and amalgam and found that MTA leaked significantly less than amalgam and SuperEBA.
Keiser et al used the human periodontal ligament fibroblasts to evaluate the cytotoxicity of MTA and compared with amalgam and SuperEBA and found that in both freshly mixed as well as set state, the MTA was less toxic.
Apaydin ES et al compared the effect of fresh MTA with set MTA on hard tissue healing after periradicular surgery, the results indicated that
there was no significant difference in the quantity of cementum or osseous healing associated with freshly placed or set MTA.
It has been found that resecting a root end containing the set material does not significantly alter the biocompatibility of MTA, which seems to support the production of hard tissue.
The process of placing MTA in an orthograde manner and then resecting the set material with a high-speed handpiece apparently does not significantly disturb the apical seal of MTA and has no significant bearing on the subsequent apical tissue regeneration.
The ultimate success of the surgery depends on the regeneration of a functional periodontal attachment apparatus, including cementum overlying the resected root end surface, periodontal attachment and alveolar bone
PERFORATION REPAIRS IN ROOTS OR FURCATIONS
Caries Resorptive processes Iatrogenically induced like misdirected bur during access preparation and during preparation of post space. Excessive flaring of cervical portion of curved roots in molars can cause lateral root perforations Strip perforations during preparation of curved canals
According to Washington study (1961), root perforations result in endodontic failures accounting for approximately 10% of all failed cases.
Difficulties encountered when repairing furcation perforations include
Inadequate sealing of the defect
Extrusion of the repair material
Inadequate material biocompatibility.
Historically, materials used to repair root perforations have been associated with the formation of a fibrous connective tissue capsule a contact with the adjacent bone at best.
In fact, formation of a periodontal defect has been a more common finding adjacent to the majority of previously used materials.
A characteristic that differentiates MTA from other materials is its ability to promote regeneration of cementum, despite its extrusion in to the periradicular tissues, thus facilitating regeneration of periodontal apparatus.
Perforation repair can be achieved
external surgical approach.
Non surgical intracoronal approach usually precedes surgical repair.
This can be affected by the
1. location and size of the perforation,
3. availability of modern equipments like endodontic microscopes, and
4. by the physical and chemical characteristics of the repair material.
For successful treatment of such defect, the root surface should be reconstructed in order to allow reattachment of periodontal ligament. Success of such treatment obviously depends on elimination of bacteria from the root canal system and the perforation site.
In some cases granulation tissue may have grown in to the perforation. This granulation tissue must be displaced from the perforation to allow exact reconstruction of the root surface.
. Lemon et al (1992) introduced the “internal matrix concept” for treatment of root perforations. He recommended the use of amalgam for sealing the perforation, which would be condensed against an external matrix of hydroxyapatite, carefully pushed through the perforation thus serving as an external barrier of matrix.
MODIFIED MATRIX CONCEPT
It is described by C.Bargholz for perforation repair with MTA in an article published in 2005.
For application of MTA, no such pressure resistant support is necessary. Freshly mixed MTA has a soft consistency and may be applied without pressure. Small pieces of Collagen (Kollagen-Resorb; Resorba, Nuremberg, Germany.) are used to push the granulation tissue out of the perforation and keep it in place outside the root.
MTA may be layered against the collagen until the perforation is repaired. For this process no pressure is required at any time due to the consistency of the material.
Direct observation of the material site through the operating microscope is very helpful to avoid inadvertent blockage of the still empty root canal space with MTA to confirm correct placement of the repair material.
Following application of the collagen the sealed perforation and the newly accomplished reconstruction of the root surface are monitored radiographically.
Different leakage models have been used in the past to assess the ability of materials to seal furcation perforations. These include the fluid filtration model, dye leakage model and bacterial leakage model.
Nakata et al(1998) used an anaerobic, bacterial leakage model to assess the sealing ability of MTA and amalgam.
The investigators found that teeth with furcation perforations repaired using MTA allowed the passage of Fusobacterium nucleatum significantly less than teeth repaired with amalgam.
A search of the literature revealed two short term studies that evaluated the clinical efficacy of MTA as a perforation repair material.
Arens and Torabinejad (1996) reported on two cases in which MTA had been used to repair furcal perforations. The first case showed bone regeneration after 3 months. Continued healing was observed radiographically at 6 and 12 months. The second case had similar findings, with radiographic evidence of resolution of a lesion in the furcation region at 9 and 12 months. In a similar case report using MTA to repair perforations,
Schwartz et al 2 (1999) found radiographic evidence resolution of a furcal perforation lesion and absence of any clinical symptoms 6 months after the repair procedure.
Jong lee S, Monsef M and Torabinejad M (1993) tested the sealing ability of amalgam, IRM and MTA for repair of experimentally created root perforations. They found that MTA had significantly less leakage than IRM or amalgam.
The MTA also showed the least overfilling tendency while IRM showed least underfilling tendency.
Daoudi and Saunders (2002) studied the use of MTA and resin modified glass ionomer cement to seal furcation perforations using a dye leakage model.
The authors found that perforations repaired with MTA leaked significantly less to the dye tracer than ‘VitreBond’.
Ferris D M and Baumgartner (2004) evaluated the two types of MTA to seal furcal perforations in extracted human molars using an anaerobic bacterial leakage model and found no significant difference between the two types of MTA in preventing leakage of Fusobacterium nucleatum past furcal perforation repairs.
To date no controlled, clinical trials have been published documenting the use of MTA as a material suitable to repair furcation perforations.
However two case reports published by Arens et al demonstrated that MTA may be a suitable material for closing the communication between the pulp chamber and the underlying periodontal tissues
In teeth with incomplete root end and necrotic pulps, the root canals must be completely debrided. Because of a lack of apical seal and the presence of thin and fragile walls in these teeth, it is imperative to perform apexification to obtain an adequate apical seal.
After rubberdam isolation, pulp is extirpated and root canal system cleaned with endodontic instruments and 5.25% Sodium hypochlorite irrigation.
Calcium hydroxide is then placed in the root canal system for one week to fully disinfect the root canal system.
Calcium hydroxide paste is removed from the root canal system with Sodium hypochlorite irrigation and dried with paper points.
MTA is mixed and placed in the canals and condensed to apical end of the root to create a 3-4 mm of apical plug.
The patient can return in one week for obturation of the rest of the canal or final obturation is delayed until healing is completed.
The canal can be obturated with thermoplastic gutta-percha and sealer or with composite in thin walled teeth.
A more expensive, but an effective canal obturation technique in posterior teeth is to fill the entire canal with MTA
Although MTA and Calcium hydroxide both similar alkaline pH levels,
MTA also shows
excellent marginal adaptability and
is non resorbable.
These important physical characteristics of MTA allow apexification cases to be restored after approximately two weeks as opposed to Calcium hydroxide therapy, where apexification may require months.
Another distinct advantage as noted by Schmitt D et al (2001) is that follow up radiographs may indicate continual apexogenesis of immature root apices.
. Calcium hydroxide has become the material of choice for apexification. Despite its popularity for the apexification procedure, calcium hydroxide therapy has some inherent disadvantages that include
variability of treatment time,
unpredictability of apical closure,
difficulty in patient follow up, and
Therefore, the search continues for procedures and materials that may allow for the continued apical closure in teeth with immature apices.
An alternative treatment to long-term apexification procedure is the use of an artificial apical barrier that allows immediate obturation of the root canal.
In 1993, Schumacher and Rutledge used calcium hydroxide powder to form an apical barrier before root canal obturation with gutta-percha.
Schwartz R S et al (1999) used MTA for apexification of right maxillary central incisor with two step apical barrier technique.
In the first visit MTA was placed in the canal and condensed to a minimal thickness of 2mm. Rest of the canal space was filled with Ca(OH)2 paste and the tooth was temporized to allow the MTA to set overnight.
The next day the MTA was found to be hard and the root canal space was obturated with ZOE sealer and vertical condensation of injectable gutta-percha.
At nine and twenty month recall visits the tooth was asymptomatic and normal periapical bony architecture was present.
Matt G D et al (2004) investigated the use of MTA as an apical barrier by comparing the sealing ability of white and gray MTA.
Apical barriers of white and gray MTA were placed to a thickness of 2mm or 5 mm. The samples were obturated immediately (one step) or after the MTA set for 24 hrs (two steps). After placement in methylene blue dye for 48 hrs the samples were sectioned for leakage analysis and microhardness testing of the barrier.
Gray MTA demonstrated significantly less leakage than white MTA and the two step technique showed significantly less leakage than one step. The 5 mm thick barrier was significantly harder than 2 mm barrier, regardless of the MTA types or no. of steps.
Leimburg M L et al (2004) used polymerase chain reaction (PCR) followed by reverse dot blot to detect Enterococcus faecalis leakage through MTA apical obturation of pulpless teeth with open apices and reported MTA provides adequate seal even in cases of orthograde apical obturation.
Al Kahatani et al (2005) evaluated the seal created by varying depths of MTA plugs placed in an orthograde fashion in five groups and results showed a statistically significant difference in only 5mm apical plug which completely prevented bacterial leakage.
Al Hezaimi et al (2005) assessed in-vitro leakage of orthograde placed grey MTA white MTA and vertically condensed gutta-percha with sealer and found both MTA preparations were more resistant to human saliva leakage than vertically condensed gutta percha.
DIRECT PULP CAPPING
A major difficulty in obtaining successful results with pulp therapy is the prevention of recontamination by bacteria after treatment has been completed. . The inability of the Ca(OH)2 to provide a permanent seal and the porous nature of bridge allows the ingress of bacteria and inflammatory byproducts. These irritants can compromise pulpal vitality, often leading to dystrophic calcification, root canal therapy or potential extraction.
Once MTA has been placed, no further irrigation can be accomplished, since the unset MTA can be easily washed off.
1-1.5 mm thick layer of freshly mixed MTA is placed over the exposed pulp; a wet thinned, flattened cotton pellet is placed over it. The cotton pellet provides the moisture for a proper set. Due to its hygroscopic nature, Cavit absorbs water and can be inflammatory to the vital pulp and therefore should not be used as a temporary filling material in vital teeth. Light cured photocore, IRM, or other suitable material is used for temporization.
The patient should return one week later for final restoration. At that time, the temporary and cotton pellet should be removed and vitality reassured.
With relation to the studies that have evaluated the pulpal response to the MTA, Pittford etal, capped the teeth of monkeys and verified the formation of a mineralized tissue bridge in all specimens; in only one case pulp inflammation was reported.
Junn etal has demonstrated that pulps capped with MTA exhibited less inflammation and higher dentin bridge formation than in the group of teeth treated with Ca(OH)2.
Holland etal compared the dogs pulp responses on capping with either MTA or Ca(OH)2 In teeth treated with MTA, all bridges were tubular morphologically. In the superficial portion of these bridges, the presence of a slight layer of necrotic pulp tissue was observed suggesting that material, similar to Ca(OH)2, initially causes necrosis by coagulation in contact with pulp connective tissue. This reaction may occur because of the product’s high alkalinity, whose pH is 10.2 during manipulation and 12.5 after 3 hours. The results were similar to the findings of Pittford etal.
In another study Holland etal; observed granulation bifringent to polarized light nearest to the opening of dentin tubules filled with MTA.
They reported that these structures are similar to the calcite crystals observed with Ca(OH)2.
MTA does not contain Ca(OH)2 but after its hardening, it contains CaO that could react with tissue fluids to form Ca(OH)2.
According to Seax etal those calcite crystals attract fibronectin, which is responsible for cellular adhesion and differentiation. Therefore it is believed that MTA mechanism of action is similar to that of Ca(OH)2 .
Jafari SM indicated that tooth colored PROROOT MTA induced proliferation and not apoptosis of pulpal cells in vitro and these findings suggests a potential mechanism to explain the regenerative effect observed in the dentin pulp complex when MTA was used for direct pulp capping.
Hollan G etal assessed the effect of MTA as pulp dressing material following pulpotomy in primary molars with carious pulp exposure and compared them to those of Formocresol and obtained a success rate of 97% for MTA and 83% for Formocresol.
Aeinehchi compared the MTA with Ca(OH)2 as pulp capping agent and on histological evaluation there was less inflammation,hyperaemia and necrosis plus thicker dentinal bridge formation and more frequent odontoblastic layer formation with MTA than Ca(OH)2.
MTA is one of the most promising material to enter the dominion of endodontics in last few years.
Clinical case reports have been published to corroborate its potential value in many instances.