MINERAL TRIOXIDE AGGREGATE

INTRODUCTION TO MINERAL TRI-OXIDE AGGREGATE (MTA)

DR SYED SOHAIB GILANI

Mineral trioxide aggregate is a new biocompatible material with numerous exciting clinical application in endodontics. MTA was introduced by Torabinejad et Al at Loma Linda university in 1993 as a root-end filling material and for repair of lateral perforation .It has been patented and has received approval of FDA and is commercially available as Pro-Root MTA by Dentsply International .Several in vitro and in vivo studies have shown that MTA prevents microleakage, is biocompatible and promotes regeneration of original tissues when placed in contact with periradicular tissues or dental pulp.

Initially Gray MTA was introduced in market. It has been shown that after periradicular surgery and GMTA as root end filling periapical lesion heals to almost normal conditions over past 10-12 years. More than 125 articles have been published on properties and application of MTA. White MTA has recently been introduced to endodontics .One of the main reason for introducing WMTA as a substitute for GMTA was to provide a hue matched more closely to that of the colour of teeth as opposed to contrasting Gray colour of GMTA.

A Brazilian version of MTA was developed to improve handling and setting properties. The product is MTA Angelius and is claimed by manufacturer to have an initial setting time of 10 minutes. Sealing ability , marginal adaptation and cytotoxicity of MTA Angelus was found to be similar to Pro-Root MTA. Further attempts to improve the handling properties of MTA includes the formation of an experimental endodontic cement which handles like a gel ,Viscosity Enhanced Root Repair Material (VERRM). It has composition similar to MTA with handling characteristics and consistency similar to commercially available material such as IRM and Super EBA.

COMPOSITIONCOMPOSITION

MTA consists of fine hydrophilic particles. The material is primarily derived from calcium oxide ,silicon dioxide , and aluminium oxide . These raw materials are grind and clinkered in a kiln to produce•Dicalcium silicate •Tricalcium silicate•Tricalcium aluminate•Tetracalcium aluminate It also contains trace amount of silicon dioxide ,calcium oxide, magnesium oxide, potassium sulphate and sodium sulphate. These oxides are almost 75% of MTA .

In the 75% content of oxides the various oxides are distributed as :

•SiO2-21%

•Al2O3 -4%

•Fe2O3 -5%

•Ca O -65%

•Mg O -2%

•Alkalies (Na2O,K2O)- 0.5%

Bismuth oxide (20%) is also added for radio opacity. Calcium sulphate dihydrate (gypsum) (5%) is also present. Predominant oxides in MTA are lime (Cao),silica (Sio2), and bismuth oxide . According to Torabinejad et al main constituents of GMTA were calcium and phosphorus, but , Saeed Asgary et al showed by electron probe analysis that phosphorus is close to limit of detection. Material safety data sheet supplied by Denysply company also does not report phosphorus as a significant element in MTA. White MTA has significantly lower concentration of Al2O3, MgO, and FeO than GMTA .

Differences in FeO concentration is thought to be primarily responsible for variation in colour of WMTA (off white )in comparison to Gray MTA

GMTA was un aesthetic in cervical area of anterior tooth . Manufacturer’s claims that there are no changes in physical properties but mixing it tends to be more technique sensitive. White MTA is creamier when mixed and a little more difficult to manipulate but sets as hard as original grey MTA. A study by Gary et al concluded that grey MTA demonstrated significantly less apical dye leakage than white MTA. He hypothesised that slight volumetric shrinkage that occurred with WMTA may account for increased leakage.

MANIPULATIONMANIPULATION

ProRoot MTA has been marketed by Dentsply Tulsa company. Each pack of MTA comes with pre measured unit dose of water for convenience in mixing. To use MTA simply pour the powder onto pad supplied ,add water and mix to working consistency. Water powder ratio should be 3:1 according to manufacturer. Variation on part of water powder ratio could account for increased solubility and porosity of material. Manufacturer also recommend not to reuse one sachet of powder to prevent contamination and cross contamination

MIXING OF MTAMIXING OF MTA

SETTING REACTIONSETTING REACTIONOn addition of water compound in MTA react to produce calcium silicate hydrate gel that is calcium hydroxide contained in a silicate matrix. The dissolution of anhydrous phase of MTA occurs followed by the crystallization of the hydrate in a interlocking mass which consists of cubic and needle like crystal. In the crystal kinetics point of view the complexity of MTA resulted in different nucleation rates and some parts move rapidly than others to construct the epitaxillary growth. According to patent of MTA C3S is a predominant phase and play an important role in its hydration behaviour.

The hydration of C3S is follows chemical process and produces calcium silicate hydrate and calcium hydroxide. The set MTA exhibits both crystalline and amorphous phases. The crystalline material is essentially calcium oxide and amorphous phase is calcium phosphate. MTA consists of hydrophilic particles and sets in presence of moisture. In clinical setting a moist cotton pellet need to be placed over MTA to help in setting reaction.

PROPERTIESPROPERTIESPHYSICAL STATE- solid (powder)

COLOR -grey/white

ODOR -no specific odor

BOILING POINT ->1000ºC

SETTING TIME : 2 hours 45 min – 4 hours

COMPRESSIVE STRENGTH: immediately after setting 40 Mpa 21 days after setting 70 Mpa

pH :10.2 at start of mix rises to 12.5 after 3 hours. In experimental setting MTA is capable of maintaining high ph for long time. The high pH of MTA could be of clinical significance when used in apical barrier technique since alkalinity creates a favourable environment for cell division and matrix formation. Due to high ph MTA shows antibacterial action similar to calcium hydroxide.

SOLUBILITYSOLUBILITYMTA is capable of partially releasing its soluble fraction to an aqueous environment over a period of time with decreasing rate. Solubility of MTA in water is about 0.1% -1.0%. The soluble fraction released by MTA in aqueous environment is mainly composed of calcium hydroxide. It has been proposed that calcium oxide present in MTA reacts with water to form calcium hydroxide. It has been shown that set MTA’s solubility is a function of water powder ratio (for optimum properties recommended w/p ratio is 3:1) MTA is mainly composed of a insoluble matrix of silica gel that maintains its integrity even in contact with water.

For this reason operators should not be concerned with complete solubilization in contact with periradicular tissues .

SEALING ABILITY/MARGINAL ADAPTATIONSEALING ABILITY/MARGINAL ADAPTATION

The sealing ability and marginal adaptation of MTA outperforms other material compared (amalgam, Super EBA IRM e.t.c. ). A stable barrier to bacterial and fluid leakage is one of the key factors in creating clinical success of root repair material. The sealing ability of MTA was investigated using florescent dye and confocal microscopy, methylene blue dye and bacterial marker. Its marginal adaptation was assessed using scanning electron microscopy.

The long tern seal was measured over a 12 week and 12 month period using different fluid transport methods. MTA’s sealing ability is probably due to its hydrophilic nature, long setting time ,and slight expansion when it is cured in moist environment. In dye leakage study conducted by Torabinejad et al the sealing ability and marginal adaptation of ProRoot MTA , amalgam and super EBA cement were compared. The results showed that MTA allow significantly less dye leakage and had better adaptation than other test material.

Clinically a barrier of 3-5 mm should be considered if root end surgery is a treatment option. Recent evidence has shown that teeth obturated with orthograde MTA and followed by root end resection showed periradicular healing similar to teeth with fresh MTA placed as a root end filling material (Torabimejad et al ). If a 3mm root end resection had to be performed after placement of 5mm apical barrier then no root end filling would have to be placed at the time of surgery. This thickness of MTA is sufficient to prevent marginal leakage and showed better sealing than other root end filling material.

DELIVERY TECHNIQUEDELIVERY TECHNIQUE

The method of placement of MTA in apical barrier technique is still controversial. Aminoshariae et al obtained a more accurate adaptation of MTA by hand compaction compared with ultrasonic condensation, whereas Lawley et al and Matt et al showed that ultrasonic condensation of MTA results in hardest and most impervious barrier. Barriers placed with ultrasonic activation demonstrated fewer voids than barriers placed without ultrasonic energy. The ultrasonic energy helped move the MTA apically and more completely condense the material without dislodging.

STUDIES ON ADAPTATION/MICROLEAKAGESTUDIES ON ADAPTATION/MICROLEAKAGE

• Fluid transport models comparing microleakage of MTA and amalgam or EBA, amalgam and MTA showed less microleakage with MTA (Yasshushiri et al )

•Torabinejad et Al evaluated marginal adaptation using SEM revealed that MTA had better adaptation than other material.• •Endotoxin studies by Torabinejad et Al also confirms superior sealing ability of MTA using E.Faecalis to test sealing property.

•Study by Lawley et Al using PCR followed by reverse blot confirms superior sealing and adaptation of MTA.

•Schress found that MTA did not allow passage of strict anaerobes for duration of 47 days. MTA also gives seal against S.Epidermidis,F.nucleatum,S.Marcesences

MECHANISMMECHANISM

MTA’ s sealing ability and better marginal adaptation is probably due to its hydrophilic nature, longer setting time and slight expansion when it is cured in moist environment. MTA contains 5% gypsum that expands during setting contributing to better adaptation .

BIOCOMPATIBILITY/RESPONSE OF BIOCOMPATIBILITY/RESPONSE OF PERIRADICULAR TISSUESPERIRADICULAR TISSUES

Biocompatibility is the ability of the material to perform with an appropriate host response in a specific application. This means that the tissue of patient comes in contact with the material does not suffer from any toxic , irritating, inflammatory, allergenic and carcinogenic action. The biocompatibility assessment of MTA encompassed in vitro cell culture technique using established cell lines, primary cell culture of various combination. Apart from variation in sensitivity of cell types used the result showed MTA to be biocompatible.

Tissue response evaluated in vivo by intra osseous and subcutaneous implantation experiment found MTA to be well tolerated. MTA was also shown not to have an adverse effect on connective tissue microcirculation when assessed using an improved rabbit ear chamber . In vivo usage tests revealed less inflammation with MTA root end filling material compared to amalgam in addition to presence of new cementum formed over and adjacent to MTA

The major difference among periapical tissue’s response to amalgam EBA and MTA as root end filling material are degree of inflammation, type of infiltrated inflammatory cells, frequency of fibrous capsule .formation and cementum formation. MTA was best material overall. Torabinejad et al compared cytotoxicity of MTA, amalgam, EBA ,IRM using radiochromium release method, MTA was least cytotoxic.

REGENERATIVE CAPABILITIESREGENERATIVE CAPABILITIES

Regeneration has been defined as the replacement of tissue components in the appropriate location, in the correct amount and the correct relationship to each other. This means reformation of the bone in the surgical site, adjacent to fully reconstituted PDL, attached to newly formed cementum, over resected root end and root end filling material.

MTA has the ability to encourage hard tissue disposition and the mechanism of action may have same similarity to that of calcium hydroxide. Although hard tissue formation occurs early with MTA, there was no significant difference in the quantity of cementum or osseous healing associated with freshly mixed or set MTA

STUDIESSTUDIESInvestigation of why MTA appears to induce cementogenesis found that material seemed to offer a biologically active substrate for osteoblasts, allowing good adherence of the bone cells to the material while also stimulating production of cytokines. Koh et Al found that MTA causes an increase in production of interleukin IL-1α, IL-1β, IL-6 an ostoecalcin. Osteoclacin is an abundant protein and may be an indicator or bone matrix production. Mitchell et Al found that set MTA induced production of IL-6, IL-8, and macrophage colony stimulating factor

IL-8 promotes the development of new blood vessels and activate precursor of osteoblasts. Macrophage stimulating factor may have a significant function in osteoclast development and maturation.

The source or origin of new cementum is not clearly understood, Two possibilities exists, one derived form remaining PDL or one from growing connective tissue from bone.

MTA was found to stimulate extra cellular regulated kinases, members of mitogen activated protein kinase pathway which are involved with bone cell proliferation, differentiation and apoptosis. MTA also induces fibroblasts to express gene associated with cementum formation of an osteogenic phenotype.Sarkar et Al investigate the physiochemical basis of biological properties of MTA. They concluded that calciumions released form MTA reacts with tissue phosphates yielding hydroxyappetite matrix at dentin MTA interface. 10 Ca2+ + 6(PO4) -3 + 2(OH) -1

Ca10(PO4)6(OH) 2

authors concluded that MTA is not an inert material in a simulated oral environment, it is “BIOACTIVE”. The success of MTA in terms of sealing ability, biocompatibility and dentinogenic activity is believed to be in these physicochemical reaction.

DENTINOGENIC ACTIVITYDENTINOGENIC ACTIVITY MTA is used for pulp capping / pulpotomy and shown to have dentinogenic effect. Pulp capping is mainly indicated for reversible pulp tissue injury after physical or mechanical trauma on developing or mature tooth. The ultimate goal of pulp capping material is to induce the dentinogenic potential of pulpal cells. The dentinogenic potential can be induced directly as a specific biological effect of the capping material on pulpal cells or indirectly as a part of stereotypic wound healing mechanism in traumatised pulp.

Experiments showed that pulp capping with MTA induces cytological and functional changes in pulpal cells resulting in formation of fibrodentin and reparative dentin at the surface of mechanically exposed pulp. MTA offers a biologically active substrate for pulpal cells and is able to regulate dentinogenic events.

Reparative dentinogenesis was clearly observed three weeks after capping of exposed pulp with MTA. Odontoblasts like cells elaborating tubular matrix in predentin like structure is seen. These data’s confirmed similar mechanism for initiation of reparative dentinogenesis in capping with MTA and calcium hydroxide based material.

Regulatory effect of MTA and production of osteocalcin or alkaline phosphatase or intereleukin 6 or 8 might be further related to stimulation of dentinogenic activity. In addition the importance of fibronectin rich zone which formed on to crystalline structures along pulpal side of MTA and possible effect of alkaline environment in the solution of growth factors from surrounding dentin as has been suggested for calcium hydroxide may not be excluded

DISADVANTAGES OF CALCIUM HYDROXIDEDISADVANTAGES OF CALCIUM HYDROXIDE

Calcium hydroxide remains the standard of pulp capping. Subsequent to pulp capping with calcium hydroxide the adjacent pulp tissue is usually completely deranged and distorted forming a zone of obliteration. A weaker chemical effect on subjacent more apical tissue results in a zone of coagulation necrosis. The superiority of calcium hydroxide is questioned because of degradation over time ,tunnel defects through dentinal bridges under it and poor sealing properties.

CALCIUM HYDROXIDE SHOWING GRANULATION TISSUE

ADVANTAGES OF MTAADVANTAGES OF MTA

With MTA thicker dentinal bridges are formed and the presence of an odontoblastic layer was a frequent finding. Hyperaemia of pulp is a less frequent finding with MTA while hyperaemia is seen in almost every case with calcium hydroxide. MTA has sufficient compressive strength to allow condensation of amalgam in contrast to calcium hydroxide which has limited strength

DENTINOGENIC ACTIVITY WITH MTA

ANTIBACTERIAL EFFECTANTIBACTERIAL EFFECT

In addition to having good sealing ability and biocompatibility root end filling material should ideally have some antibacterial properties to prevent bacterial growth. A study by Torabinejad et Al concluded that MTA has no antibacterial against anaerobes but causes effects on facultative bacteria. The antibacterial effect of MTA could be due to its high ph or release of diffusible substances.

White MTA in concentration of 50 mg/ml may exert an antifungal effect against C.albicans a period of up to 30 days. Recently it has been suggested to mix chlorhexidine to MTA to enhance its antibacterial properties ,however its not clear what effect chlorhexidine has on physical and chemical properties of MTA.

Bacteria inhibiting root canal is composed mainly of strict anaerobic bacteria, some facultative anaerobes and usually no aerobes. In apical portion of root canal 68% of bacteria are anaerobes. The relative proportion of strict anaerobes bacteria to facultative bacteria increases with time. Although EBA, ZOE, and MTA are ineffective against a number of bacteria MTA is superior to others due to its sealing ability preventing migration of bacteria and some antibacterial activity against facultative anaerobes.

CLINICAL APPLICATIONSCLINICAL APPLICATIONS

APEXIFICATION/APICAL BARRIERAPEXIFICATION/APICAL BARRIER

One of the principal objective of non -surgical root canal therapy is seal the canal system from apical and coronal leakage after cleaning and shaping. The absence of an adequate apical constriction is often found in cases of apical root resorption, apical perforation, and immature necrotic tooth. In these cases it is critical that either a stop be developed or an apical barrier be placed to limit extrusion of obturation material .

Although apexification with calcium hydroxide pastes has been highly successful, an alternative treatment is the use of an artificial barrier that allows immediate obturation of the canal. Thus some of the disadvantages of calcium hydroxide therapy including increased cost and patient compliance with multiple appointments over 6-24 months could be eliminated. Calcium hydroxide has also been shown to decrease the fracture resistance of tooth. Dentin chips, freeze dried cortical bone , and calcium phosphate also has been used, but they do not provide well sealed environment.

ADVANTAGES OF MTAADVANTAGES OF MTA

MTA is superior to all other material due to its •Sealing ability •Biocompatibility • Ability to set in presence of moisture • Induces hard tissue formation

TECHNIQUETECHNIQUEPrior to placement of MTA all necrotic debris should be cleaned and canal bio mechanically prepared. Manufacturer recommend medication of canal with calcium hydroxide for 1 week with subsequent removal using sodium hypochlorite. They also recommend a 3-5 thickness of MTA to be placed at apex. The delivery technique is controversial, some prefers hand condensation while others prefers ultrasonic condensation.

Moisture from periapical area could be sufficient for MTA to set but additional moisture from a cotton pellet is crucial for the material to establish its optimum properties. It is recommended to place a most cotton pellet or paper point in canal before temporising.

If after placement of orthograde MTA periapical surgery can not be excluded than even after root end resection of 3 mm additional root end filling need not be placed as similar healing is shown with fresh MTA or set MTA. It is also recommended to follow two step apexification procedure that is after placement of apical barrier a damp cotton pellet in canal, temporize and allow material to set for at least 4 hours or do obturation next day.

ROOT-END FILLINGROOT-END FILLING Numerous materials have been used as a root-Numerous materials have been used as a root-

end filling material. The main disadvantage end filling material. The main disadvantage include their inability to prevent egress of include their inability to prevent egress of irritants from infected root canal into periradicular irritants from infected root canal into periradicular tissues, lack of biocompatibility, and their inability tissues, lack of biocompatibility, and their inability to promote regeneration of periradicular tissues to promote regeneration of periradicular tissues to their prede asesed status and normalcy.to their prede asesed status and normalcy.

MTA is superior to MTA is superior to other material as it provides “other material as it provides “DOUBLE SEALDOUBLE SEAL” ” that is physical seal due to its excellent sealing that is physical seal due to its excellent sealing property and biological seal due to regeneration property and biological seal due to regeneration of cementum over it.of cementum over it.

The major difference between MTA and other root end filling material on periradicular response are degree of inflammation, extent of inflammation, frequency of fibrous capsule and cementum formation over MTA. Formation of fibrous connective tissue cementum and low level of inflammation with MTA indicates its excellent biocompatibility.

TECHNIQUETECHNIQUEAfter careful debridement of apical lesion, root end is sectioned and root end cavity prepared. Preparation of root end cavity with ultrasonic retro tips have shown better results than cavity prepared with a bur. MTA is mixed according to manufacturer’s instruction and is carried to root end preparation with modified amalgam carrier or other specially designed carrier. Once MTA is micro ball burnisher and micro pluggers are used to gently compact it. A damp cotton pellet is used to remove any excess MTA from cavity. The surgical area should be kept dry and care should be taken not to wash out the filling material by irrigation before closure.

MTA CARRIER

MICRO BALL BURNISHER AND CONDENSER

REPAIR OF ROOT PERFORATIONREPAIR OF ROOT PERFORATION

Perforations are procedural accidents that can have adverse effect on the outcome of endodontic treatment. The prognosis for the tooth with a perforation depends on location of perforation, the time the perforation is open to contamination, the possibility of sealing the perforation and accessibility of main canal. MTA as a perforation repair material has been shown to leak less than amalgam and Super EBA and is less cytotoxicity.

TECHNIQUETECHNIQUEBefore placing MTA over a perforation site the area should be copiously irrigated with NaOcl (5% or 2.5%). After perforation site has been soaked with NaOcl for approximately 5 minutes, haemostasis and a barrier must be now be achieved. Even though MTA sets in presence of moisture the site should be kept as dry as possible, because MTA will be difficult to place and manipulate. A physical barrier must now be achieved at the perforation site to prevent MTA from being packed into the bone or through pulpal floor into the furcation site. To achieve haemostasis and a physical barrier collagen type material or calcium sulphate can be used.

PREOPERATIVE RADIOGRAPH

PLACEMENT OF MTA

REDUCED PROBING DEPTH AT 1-MONTH

HEALED LESION AT 6-MONTH

These materials are resorbable and needed to help create a dry field and a solid foundation against which operator packs MTA. The procedure is best performed under a surgical microscope that provides magnification and illumination. After placement of calcium sulphate /collagen MTA is placed. WMTA should be preferred in cervical area of anterior tooth as gray MTA not aesthetically pleasing. MTA is packed with a condenser. A moist cotton pellet should be placed on top of MTA and cavity is restored temporarily. In next appointment MTA sets and teeth can be permanently restored.

REPAIR OF ROOT RESORPTIONREPAIR OF ROOT RESORPTION

MTA can be used and is promising in treatment of external as well as internal root resorption .TECHNIQUEIn case of internal root resorption isolate the tooth do RCT in usual manner. Once the canal has been cleaned and shaped place a putty mixture of MTA and fill the canal with it using a plugger or Gutta percha cone. Next place a safe sider 25/.08 down the canal to spread the cement laterally and create a new canal. Fill canal with sealer and obdurate with single Gutta percha cone. The set MTA will provide structure and strength to the teeth by replacing resorbed tooth structure.

In case of external root resorption ,do RCT first, next raise the flap to remove the defect and granulation tissue. Mix MTA and apply it to root surface. Remove excess cement and condition root surface with doxycycline. Graft the defect with bone grafting material and close the site.

PULP CAPPING/PULPOTOMYPULP CAPPING/PULPOTOMY

Direct pulp capping is a well established method of treatment in which exposed dental pulp is covered with a suitable material that protects pulp from additional injury and permits healing and repair. Pulp capping is mainly recommended for reversible pulp injury after physical or mechanical trauma on developing or mature tooth.

TECHNIQUETECHNIQUE

After proper isolation and achieving haemostasis MTA is placed over exposure site and light pressure has to applied with a damp cotton pellet. The cavity can be restored with amalgam / composite/ GIC. MTA has shown to induce reparative dentin formation in three weeks, earlier than calcium hydroxide. The quality of calcific bridge formed is also better than that formed with calcium hydroxide.

ADVANTAGESADVANTAGES

•Biocompatible •Non toxic•Non resorbable•Good marginal sealing•No irritation to surrounding tissues•Stimulates hard tissue formation•moisture insensitivity •Radio opaque

DISADVANTAGESDISADVANTAGES

•Difficult to manipulate •Longer setting time•Need two appointments

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