INTRODUCTION TO MINERAL TRI-OXIDE AGGREGATE (MTA) DR SYED SOHAIB GILANI
Mineral trioxide aggregate is a newbiocompatible material with numerous excitingclinical application in endodontics. MTA wasintroduced by Torabinejad et Al at Loma Lindauniversity in 1993 as a root-end filling materialand for repair of lateral perforation .It hasbeen patented and has received approval ofFDA and is commercially available as Pro-RootMTA by Dentsply International .Several in vitroand in vivo studies have shown that MTAprevents microleakage, is biocompatible andpromotes regeneration of original tissues whenplaced in contact with periradicular tissues ordental pulp.
Initially Gray MTA was introduced inmarket. It has been shown that afterperiradicular surgery and GMTA as rootend filling periapical lesion heals to almostnormal conditions over past 10-12 years.More than 125 articles have beenpublished on properties and application ofMTA. White MTA has recently beenintroduced to endodontics .One of themain reason for introducing WMTA as asubstitute for GMTA was to provide ahue matched more closely to that of thecolour of teeth as opposed to contrastingGray colour of GMTA.
A Brazilian version of MTA was developed toimprove handling and setting properties. Theproduct is MTA Angelius and is claimed bymanufacturer to have an initial setting time of 10minutes. Sealing ability , marginal adaptation andcytotoxicity of MTA Angelus was found to besimilar to Pro-Root MTA. Further attempts toimprove the handling properties of MTA includesthe formation of an experimental endodonticcement which handles like a gel ,Viscosity EnhancedRoot Repair Material (VERRM). It has compositionsimilar to MTA with handling characteristics andconsistency similar to commercially availablematerial such as IRM and Super EBA.
COMPOSITIONMTA consists of fine hydrophilic particles. Thematerial is primarily derived from calcium oxide,silicon dioxide , and aluminium oxide . These rawmaterials are grind and clinkered in a kiln toproduce•Dicalcium silicate•Tricalcium silicate•Tricalcium aluminate•Tetracalcium aluminate It also contains trace amount of silicondioxide ,calcium oxide, magnesium oxide,potassium sulphate and sodium sulphate. Theseoxides are almost 75% of MTA .
In the 75% content of oxides the various oxides aredistributed 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 radioopacity. Calcium sulphate dihydrate (gypsum)(5%) is also present. Predominant oxides inMTA are lime (Cao),silica (Sio2), and bismuthoxide . According to Torabinejad et al mainconstituents of GMTA were calcium andphosphorus, but , Saeed Asgary et al showedby electron probe analysis that phosphorus isclose to limit of detection. Material safetydata sheet supplied by Denysply companyalso does not report phosphorus as asignificant element in MTA. White MTA hassignificantly lower concentration of Al2O3,MgO, and FeO than GMTA .
Differences in FeO concentration is thought tobe primarily responsible for variation in colour ofWMTA (off white )in comparison to Gray MTA GMTA was un aesthetic incervical area of anterior tooth . Manufacturer’sclaims that there are no changes in physicalproperties but mixing it tends to be moretechnique sensitive. White MTA is creamier whenmixed and a little more difficult to manipulatebut sets as hard as original grey MTA. A study byGary et al concluded that grey MTAdemonstrated significantly less apical dye leakagethan white MTA. He hypothesised that slightvolumetric shrinkage that occurred with WMTAmay account for increased leakage.
MANIPULATIONProRoot MTA has been marketed by Dentsply Tulsacompany. Each pack of MTA comes with premeasured unit dose of water for convenience inmixing. To use MTA simply pour the powder ontopad supplied ,add water and mix to workingconsistency. Water powder ratio should be 3:1according to manufacturer. Variation on part ofwater powder ratio could account for increasedsolubility and porosity of material. Manufactureralso recommend not to reuse one sachet of powderto prevent contamination and cross contamination
SETTING REACTIONOn addition of water compound in MTA react toproduce calcium silicate hydrate gel that iscalcium hydroxide contained in a silicate matrix.The dissolution of anhydrous phase of MTAoccurs followed by the crystallization of thehydrate in a interlocking mass which consists ofcubic and needle like crystal. In the crystalkinetics point of view the complexity of MTAresulted in different nucleation rates and someparts move rapidly than others to construct theepitaxillary growth. According to patent of MTAC3S is a predominant phase and play an importantrole in its hydration behaviour.
The hydration of C3S is follows chemicalprocess and produces calcium silicate hydrateand calcium hydroxide. The set MTA exhibitsboth crystalline and amorphous phases. Thecrystalline material is essentially calciumoxide and amorphous phase is calciumphosphate. MTA consists of hydrophilicparticles and sets in presence of moisture. Inclinical setting a moist cotton pellet need tobe placed over MTA to help in settingreaction.
PROPERTIESPHYSICAL STATE- solid (powder)COLOR -grey/whiteODOR -no specific odorBOILING POINT ->1000ºC
SETTING TIME : 2 hours 45 min – 4 hoursCOMPRESSIVE STRENGTH: immediatelyafter setting 40 Mpa 21 days after setting 70 MpapH :10.2 at start of mix rises to 12.5 after 3hours. In experimental setting MTA is capableof maintaining high ph for long time. The highpH of MTA could be of clinical significancewhen used in apical barrier technique sincealkalinity creates a favourable environment forcell division and matrix formation. Due to highph MTA shows antibacterial action similar tocalcium hydroxide.
SOLUBILITYMTA is capable of partially releasing its solublefraction to an aqueous environment over a period oftime with decreasing rate. Solubility of MTA inwater is about 0.1% -1.0%. The soluble fractionreleased by MTA in aqueous environment is mainlycomposed of calcium hydroxide. It has beenproposed that calcium oxide present in MTA reactswith water to form calcium hydroxide. It has beenshown that set MTA’s solubility is a function ofwater powder ratio (for optimum propertiesrecommended w/p ratio is 3:1) MTA is mainlycomposed of a insoluble matrix of silica gel thatmaintains its integrity even in contact with water.
For this reason operators should not beconcerned with complete solubilization incontact with periradicular tissues .
SEALING ABILITY/MARGINAL ADAPTATION The sealing ability and marginal adaptation of MTAoutperforms other material compared (amalgam,Super EBA IRM e.t.c. ). A stable barrier tobacterial and fluid leakage is one of the key factorsin creating clinical success of root repair material. The sealing ability of MTAwas investigated using florescent dye and confocalmicroscopy, methylene blue dye and bacterialmarker. Its marginal adaptation was assessed usingscanning electron microscopy.
The long tern seal was measured over a 12week and 12 month period using differentfluid transport methods. MTA’s sealingability is probably due to its hydrophilicnature, long setting time ,and slightexpansion when it is cured in moistenvironment. In dye leakage studyconducted by Torabinejad et al the sealingability and marginal adaptation of ProRootMTA , amalgam and super EBA cement werecompared. The results showed that MTAallow significantly less dye leakage and hadbetter adaptation than other test material.
Clinically a barrier of 3-5 mm should beconsidered if root end surgery is a treatmentoption. Recent evidence has shown that teethobturated with orthograde MTA and followed byroot end resection showed periradicular healingsimilar to teeth with fresh MTA placed as a rootend filling material (Torabimejad et al ). If a 3mmroot end resection had to be performed afterplacement of 5mm apical barrier then no root endfilling would have to be placed at the time ofsurgery. This thickness of MTA is sufficient toprevent marginal leakage and showed bettersealing than other root end filling material.
DELIVERY TECHNIQUEThe method of placement of MTA in apical barriertechnique is still controversial. Aminoshariae et alobtained a more accurate adaptation of MTA by handcompaction compared with ultrasonic condensation,whereas Lawley et al and Matt et al showed thatultrasonic condensation of MTA results in hardest andmost impervious barrier. Barriers placed with ultrasonicactivation demonstrated fewer voids than barriers placedwithout ultrasonic energy. The ultrasonic energy helpedmove the MTA apically and more completely condense thematerial without dislodging.
STUDIES 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 PCRfollowed by reverse blot confirmssuperior sealing and adaptation ofMTA.•Schress found that MTA did not allowpassage of strict anaerobes forduration of 47 days. MTA also givesseal againstS.Epidermidis,F.nucleatum,S.Marcesences
MECHANISMMTA’ s sealing ability and better marginaladaptation is probably due to its hydrophilicnature, longer setting time and slightexpansion when it is cured in moistenvironment. MTA contains 5% gypsum thatexpands during setting contributing to betteradaptation .
BIOCOMPATIBILITY/RESPONSE OF PERIRADICULAR TISSUESBiocompatibility is the ability of the material toperform with an appropriate host response in aspecific application. This means that the tissue ofpatient comes in contact with the material doesnot suffer from any toxic , irritating,inflammatory, allergenic and carcinogenic action. The biocompatibilityassessment of MTA encompassed in vitro cellculture technique using established cell lines,primary cell culture of various combination. Apartfrom variation in sensitivity of cell types usedthe result showed MTA to be biocompatible.
Tissue response evaluated in vivo by intra osseousand subcutaneous implantation experiment foundMTA to be well tolerated. MTA was also shown notto have an adverse effect on connective tissuemicrocirculation when assessed using an improvedrabbit ear chamber . In vivo usage tests revealedless inflammation with MTA root end fillingmaterial compared to amalgam in addition topresence of new cementum formed over andadjacent to MTA
The major difference among periapical tissue’sresponse to amalgam EBA and MTA as root endfilling material are degree of inflammation, typeof infiltrated inflammatory cells, frequency offibrous capsule .formation and cementumformation. MTA was best material overall.Torabinejad et al compared cytotoxicity of MTA,amalgam, EBA ,IRM using radiochromium releasemethod, MTA was least cytotoxic.
REGENERATIVE CAPABILITIESRegeneration has been defined as thereplacement of tissue components in theappropriate location, in the correct amountand the correct relationship to each other.This means reformation of the bone in thesurgical site, adjacent to fullyreconstituted PDL, attached to newlyformed cementum, over resected root endand root end filling material.
MTA has the ability to encourage hard tissuedisposition and the mechanism of action mayhave same similarity to that of calciumhydroxide. Although hard tissue formationoccurs early with MTA, there was no significantdifference in the quantity of cementum orosseous healing associated with freshly mixedor set MTA
STUDIESInvestigation of why MTA appears to inducecementogenesis found that material seemed tooffer a biologically active substrate forosteoblasts, allowing good adherence of thebone cells to the material while also stimulatingproduction of cytokines. Koh et Al found thatMTA causes an increase in production ofinterleukin IL-1α, IL-1β, IL-6 an ostoecalcin. Osteoclacin is anabundant protein and may be an indicator orbone matrix production. Mitchell et Al foundthat set MTA induced production of IL-6, IL-8, and macrophage colony stimulating factor
IL-8 promotes the development of new bloodvessels and activate precursor of osteoblasts.Macrophage stimulating factor may have asignificant function in osteoclast developmentand maturation. The source or origin of newcementum is not clearly understood, Twopossibilities exists, one derived form remainingPDL or one from growing connective tissue frombone.
MTA was found to stimulate extra cellularregulated kinases, members of mitogen activatedprotein kinase pathway which are involved with bonecell proliferation, differentiation and apoptosis.MTA also induces fibroblasts to express geneassociated with cementum formation of anosteogenic phenotype.Sarkar et Al investigate thephysiochemical basis of biological properties ofMTA. They concluded that calciumions releasedform MTA reacts with tissue phosphates yieldinghydroxyappetite matrix at dentin MTA interface. 10 Ca2+ + 6(PO4) -3 + 2(OH) -1 Ca10(PO4)6(OH) 2
authors concluded that MTA is not aninert material in a simulated oralenvironment, it is “BIOACTIVE”. Thesuccess of MTA in terms of sealingability, biocompatibility anddentinogenic activity is believed to bein these physicochemical reaction.
DENTINOGENIC ACTIVITY MTA is used for pulp capping / pulpotomy andshown to have dentinogenic effect. Pulp capping ismainly indicated for reversible pulp tissue injuryafter physical or mechanical trauma on developingor mature tooth. The ultimate goal of pulp cappingmaterial is to induce the dentinogenic potential ofpulpal cells. The dentinogenic potential can beinduced directly as a specific biological effect ofthe capping material on pulpal cells or indirectly as apart of stereotypic wound healing mechanism intraumatised pulp.
Experiments showed that pulp capping withMTA induces cytological and functionalchanges in pulpal cells resulting in formationof fibrodentin and reparative dentin at thesurface of mechanically exposed pulp. MTAoffers a biologically active substrate forpulpal cells and is able to regulatedentinogenic events.
Reparative dentinogenesis wasclearly observed three weeks aftercapping of exposed pulp with MTA.Odontoblasts like cells elaboratingtubular matrix in predentin likestructure is seen. These data’sconfirmed similar mechanism forinitiation of reparativedentinogenesis in capping with MTAand calcium hydroxide basedmaterial.
Regulatory effect of MTA and production of osteocalcinor alkaline phosphatase or intereleukin 6 or 8 might befurther related to stimulation of dentinogenic activity. Inaddition the importance of fibronectin rich zone whichformed on to crystalline structures along pulpal side ofMTA and possible effect of alkaline environment in thesolution of growth factors from surrounding dentin as hasbeen suggested for calcium hydroxide may not beexcluded
DISADVANTAGES OF CALCIUM HYDROXIDE Calcium hydroxide remains the standard ofpulp capping. Subsequent to pulp capping withcalcium hydroxide the adjacent pulp tissue isusually completely deranged and distortedforming a zone of obliteration. A weakerchemical effect on subjacent more apicaltissue results in a zone of coagulationnecrosis. The superiority of calcium hydroxideis questioned because of degradation overtime ,tunnel defects through dentinal bridgesunder it and poor sealing properties.
ADVANTAGES OF MTAWith MTA thicker dentinal bridges are formedand the presence of an odontoblastic layer wasa frequent finding. Hyperaemia of pulp is a lessfrequent finding with MTA while hyperaemia isseen in almost every case with calciumhydroxide. MTA has sufficient compressivestrength to allow condensation of amalgam incontrast to calcium hydroxide which has limitedstrength
ANTIBACTERIAL EFFECTIn addition to having good sealing ability andbiocompatibility root end filling materialshould ideally have some antibacterialproperties to prevent bacterial growth. Astudy by Torabinejad et Al concluded thatMTA has no antibacterial against anaerobesbut causes effects on facultative bacteria.The antibacterial effect of MTA could be dueto its high ph or release of diffusiblesubstances.
White MTA in concentration of 50 mg/mlmay exert an antifungal effect againstC.albicans a period of up to 30 days.Recently it has been suggested to mixchlorhexidine to MTA to enhance itsantibacterial properties ,however its notclear what effect chlorhexidine has onphysical and chemical properties of MTA.
Bacteria inhibiting root canal is composedmainly of strict anaerobic bacteria, somefacultative anaerobes and usually noaerobes. In apical portion of root canal68% of bacteria are anaerobes. Therelative proportion of strict anaerobesbacteria to facultative bacteria increaseswith time. Although EBA, ZOE, and MTAare ineffective against a number ofbacteria MTA is superior to others due toits sealing ability preventing migration ofbacteria and some antibacterial activityagainst facultative anaerobes.
APEXIFICATION/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 calciumhydroxide pastes has been highly successful,an alternative treatment is the use of anartificial barrier that allows immediateobturation of the canal. Thus some of thedisadvantages of calcium hydroxide therapyincluding increased cost and patientcompliance with multiple appointments over6-24 months could be eliminated. Calciumhydroxide has also been shown to decreasethe fracture resistance of tooth. Dentinchips, freeze dried cortical bone , andcalcium phosphate also has been used, butthey do not provide well sealed environment.
ADVANTAGES OF MTAMTA is superior to all other material dueto its•Sealing ability•Biocompatibility• Ability to set in presence of moisture• Induces hard tissue formation
TECHNIQUEPrior to placement of MTA all necrotic debris should becleaned and canal bio mechanically prepared.Manufacturer recommend medication of canal withcalcium hydroxide for 1 week with subsequent removalusing sodium hypochlorite. They also recommend a 3-5thickness of MTA to be placed at apex. The delivery technique is controversial, someprefers hand condensation while others prefersultrasonic condensation.
Moisture from periapical area could besufficient for MTA to set but additionalmoisture from a cotton pellet is crucial for thematerial to establish its optimum properties. Itis recommended to place a most cotton pellet orpaper point in canal before temporising.
If after placement of orthograde MTAperiapical surgery can not be excluded thaneven after root end resection of 3 mmadditional root end filling need not be placed assimilar healing is shown with fresh MTA or setMTA. It is also recommended to follow twostep apexification procedure that is afterplacement of apical barrier a damp cottonpellet in canal, temporize and allow material toset for at least 4 hours or do obturation nextday.
ROOT-END FILLING Numerous materials have been used as a root-end filling material. The main disadvantage include their inability to prevent egress of irritants from infected root canal into periradicular tissues, lack of biocompatibility, and their inability to promote regeneration of periradicular tissues to their prede asesed status and normalcy. MTA is superior to other material as it provides “DOUBLE SEAL” that is physical seal due to its excellent sealing property and biological seal due to regeneration of cementum over it.
The major difference between MTA and other rootend filling material on periradicular response aredegree of inflammation, extent of inflammation,frequency of fibrous capsule and cementumformation over MTA. Formation of fibrousconnective tissue cementum and low level ofinflammation with MTA indicates its excellentbiocompatibility.
TECHNIQUEAfter careful debridement of apical lesion, rootend is sectioned and root end cavity prepared.Preparation of root end cavity with ultrasonicretro tips have shown better results than cavityprepared with a bur. MTA is mixed according tomanufacturer’s instruction and is carried to rootend preparation with modified amalgam carrier orother specially designed carrier. Once MTA ismicro ball burnisher and micro pluggers are usedto gently compact it. A damp cotton pellet is usedto remove any excess MTA from cavity. Thesurgical area should be kept dry and care shouldbe taken not to wash out the filling material byirrigation before closure.
REPAIR OF ROOT PERFORATIONPerforations are procedural accidents that can haveadverse effect on the outcome of endodontictreatment. The prognosis for the tooth with aperforation depends on location of perforation, thetime the perforation is open to contamination, thepossibility of sealing the perforation andaccessibility of main canal. MTA as a perforationrepair material has been shown to leak less thanamalgam and Super EBA and is less cytotoxicity.
TECHNIQUEBefore placing MTA over a perforation site the areashould be copiously irrigated with NaOcl (5% or 2.5%).After perforation site has been soaked with NaOcl forapproximately 5 minutes, haemostasis and a barrier mustbe now be achieved. Even though MTA sets in presenceof moisture the site should be kept as dry as possible,because MTA will be difficult to place and manipulate. Aphysical barrier must now be achieved at the perforationsite to prevent MTA from being packed into the bone orthrough pulpal floor into the furcation site. To achievehaemostasis and a physical barrier collagen type materialor calcium sulphate can be used.
REDUCED PROBING DEPTH AT 1-MONTH HEALED LESION AT 6-MONTH
These materials are resorbable and needed to helpcreate a dry field and a solid foundation against whichoperator packs MTA. The procedure is bestperformed under a surgical microscope that providesmagnification and illumination. After placement of calciumsulphate /collagen MTA is placed. WMTA should bepreferred in cervical area of anterior tooth as grayMTA not aesthetically pleasing. MTA is packed with acondenser. A moist cotton pellet should be placed ontop of MTA and cavity is restored temporarily. Innext appointment MTA sets and teeth can bepermanently restored.
REPAIR OF ROOT RESORPTIONMTA can be used and is promising in treatment ofexternal as well as internal root resorption .TECHNIQUEIn case of internal root resorption isolate the toothdo RCT in usual manner. Once the canal has beencleaned and shaped place a putty mixture of MTAand fill the canal with it using a plugger or Guttapercha cone. Next place a safe sider 25/.08 downthe canal to spread the cement laterally and createa new canal. Fill canal with sealer and obdurate withsingle Gutta percha cone. The set MTA will providestructure and strength to the teeth by replacingresorbed tooth structure.
In case of external root resorption ,doRCT first, next raise the flap to removethe defect and granulation tissue. MixMTA and apply it to root surface.Remove excess cement and conditionroot surface with doxycycline. Graft thedefect with bone grafting material andclose the site.
PULP CAPPING/PULPOTOMYDirect pulp capping is a well establishedmethod of treatment in which exposed dentalpulp is covered with a suitable material thatprotects pulp from additional injury andpermits healing and repair. Pulp capping ismainly recommended for reversible pulp injuryafter physical or mechanical trauma ondeveloping or mature tooth.
TECHNIQUEAfter proper isolation and achievinghaemostasis MTA is placed over exposuresite and light pressure has to applied with adamp cotton pellet. The cavity can berestored with amalgam / composite/ GIC.MTA has shown to induce reparative dentinformation in three weeks, earlier thancalcium hydroxide. The quality of calcificbridge formed is also better than thatformed with calcium hydroxide.
ADVANTAGES•Biocompatible•Non toxic•Non resorbable•Good marginal sealing•No irritation to surroundingtissues•Stimulates hard tissueformation•moisture insensitivity•Radio opaque
DISADVANTAGES•Difficult to manipulate•Longer setting time•Need two appointments