CURSO DE ANÁLISE DE VIBRAÇÕES - FUPAI
(Parte 1 de 6)
dental materials 24 (2008) 149–164 available at w.sciencedirect.com
journal homepage: w.intl.elsevierhealth.com/journals/dema
Mineral trioxide aggregate material use in endodontic treatment: A review of the literature
Howard W. Robertsa,∗, Jeffrey M. Tothb, David W. Berzinsc, David G. Charltond a USAF Dental Evaluation and Consultation Service, Dental Biomaterials Evaluation, Great Lakes, IL, United States b Medical College of Wisconsin, Department of Orthopedics; Marquette University School of Dentistry, Graduate Dental Biomaterials; Milwaukee WI, USA c Marquette University School of Dentistry, Graduate Dental Biomaterials; Milwaukee WI, USA d US Navy Institute for Dental and Biomedical Research, Great Lakes IL, USA article info
Article history: Received 26 July 2005 Received in revised form 23 April 2007 Accepted 30 April 2007
Keywords: Hydroxyapatite Portland cement Biocompatibility Pulp-capping Apexiﬁcation Root-end ﬁlling Pulpotomy Endodontics GMTA WMTA MTA Mineral trioxide aggregate abstract
Objective. The purpose of this paper was to review the composition, properties, biocompatibility, and the clinical results involving the use of mineral trioxide aggregate (MTA) materials in endodontic treatment. Methods. Electronic search of scientiﬁc papers from January 1990 to August 2006 was accomplished using PubMed and Scopus search engines (search terms: MTA, GMTA, WMTA, mineral AND trioxide AND aggregate). Results.Selectedexclusioncriteriaresultedin156citationsfromthescientiﬁc,peer-reviewed dental literature. MTA materials are derived from a Portland cement parent compound and have been demonstrated to be biocompatible endodontic repair materials, with its biocompatible nature strongly suggested by its ability to form hydroxyappatite when exposed to physiologic solutions. With some exceptions, MTA materials provide better microleakage protection than traditional endodontic repair materials using dye, ﬂuid ﬁltration, and bacterial penetration leakage models. In both animal and human studies, MTA materials have been shown to have excellent potential as pulp-capping and pulpotomy medicaments but studieswithlong-termfollow-uparelimited.PreliminarystudiessuggestedafavorableMTA material use as apical and furcation restorative materials as well as medicaments for apexogenesis and apexiﬁcation treatments; however, long-term clinical studies are needed in these areas. Conclusion. MTA materials have been shown to have a biocompatible nature and have excellent potential in endodontic use. MTA materials are a reﬁned Portland cement material and the substitution of Portland cement for MTA products is presently discouraged. Existing human studies involving MTA materials are very promising, however, insufﬁcient randomized, double-blind clinical studies of sufﬁcient duration exist involving MTA for all of its clinical indications. Further clinical studies are needed in these areas. © 2007 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.
None of the authors have any ﬁnancial interests in any of the products mentioned in this manuscript. The opinions stated in this manuscript are solely those of the authors and do not represent the opinion of the United States Air Force, the United States Navy, the Department of Defense, or the United States Government. ∗ Corresponding author. Present address: 310C B Street, Building 1H, Great Lakes, IL 60088, USA. Tel.: +1 847 688 7670; fax: +1 847 688 7667.
E-mail address: Howard.email@example.com (H.W. Roberts). 0109-5641/$ – see front matter © 2007 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.
|2. Chemical, physical, and mechanical properties||150|
|3. Microleakage studies||153|
|3.1. In vitro dye/ﬂuid ﬁltration method leakage studies||153|
|3.2. In vitro bacterial leakage studies||153|
|3.3. Biocompatibility studies||154|
|3.3.1. In vitro studies||154|
|3.3.2. In vivo studies||155|
|3.4. Characterization of MTA biocompatibility||156|
|4. Clinical applications of mineral trioxide aggregate materials||157|
|4.1.1. Animal models||157|
|4.2. Human studies||157|
|4.2.2. Pulpotomy dressing||157|
|4.2.3. Other MTA material use||159|
It is estimated that over 24 million endodontic procedures are performed on an annual basis, with up to 5.5% of those procedures involving endodontic apical surgery, perforation repair, and apexiﬁcation treatment . Endodontic surgery is performed to resolve inﬂammatory processes that cannot be successfully treated by conventional techniques, which may be due to complex canal and/or apical anatomy and external inﬂammatory processes . Surgical procedures may also be indicated for the resolution of procedural misadventures, to include root perforation that may occur either during canal instrumentation or post-space preparation [2,3]. Surgical treatment usually involves the placement of a material designed to seal the root canal contents from the periradicular tissues and repair root defects . Understandably, this material should demonstrate the ability to form a seal withdentaltissueswhilealsoexhibitingbiocompatiblebehavior with the periodontal tissues .
Anidealendodonticrepairmaterialideallywouldadhereto tooth structure, maintain a sufﬁcient seal, be insoluble in tissue ﬂuids, dimensionally stable, non-resorbable, radiopaque, andexhibitbiocompatibilityifnotbioactivity[2,4,5].Anumber of materials have historically been used for retrograde ﬁllings and perforation repair, such as amalgam, zinc-oxide-eugenol cements, composite resin, and glass-ionomer cements [4,6]. Unfortunately, none of these materials have been able to satisfy the total requirements of an ideal material [4,5].
Mineral trioxide aggregate (MTA) is a biomaterial that has been investigated for endodontic applications since the early 1990s. MTA was ﬁrst described in the dental scientiﬁc literature in 1993  and was given approval for endodontic use by the U.S. Food and Drug Administration in 1998 .A si t will soon follow, MTA materials are derived from a Portland cementparentcompound:itisinterestingthatnoinformation has been published regarding to any investigations that led to the precise delineation of the present MTA materials. The aim of this article is to present a systematic review of the physical properties, biocompatibility testing, and pertinent clinical studies involving MTA materials.
A structured literature review was performed for articles published between January 1990 and August 2006. The Internet database PubMed (w.ncbi.nlm.nih.gov/entrez) and Scopus (w.scopus.com) was used to search for the keywords MTA, GMTA, WMTA, and mineral AND trioxide AND aggregate. For further reﬁnement, the following exclusion criteria were deﬁned: Publications were limited to those of English language and from the scientiﬁc, peer-reviewed literature. Furthermore, publications possessing a questionable peer-review process (e.g., manufacturer-supported) were excluded for consideration. Although clinical case reports were included, only clinical studies involving appropriate number, sufﬁcient controls and analysis were given serious consideration . Using the search keywords limited to dental publications produced a total of 245 results, of which application of inclusion criteria produced the 156 citations that forms the basis for this review (Fig. 1).
2. Chemical, physical, and mechanical properties
MTA materials are a mixture of a reﬁned Portland cement and bismuth oxide, and are reported to contain trace amounts icate, tricalcium silicate, tricalcium aluminate, gypsum, and tetracalcium aluminoferrite [10–12]. Gypsum is an important determinantofsettingtime,asistetracalciumaluminoferrate, although to a lesser extent . MTA products may contain approximatelyhalfthegypsumcontentofPortlandcement,as wellassmalleramountsofaluminumspecies,whichprovides a longer working time than Portland cement. Although it may be inferred that Portland cement could serve as a MTA substi-
Fig. 1 – Literature search criteria.
tute, it is important to emphasize Portland cement and MTA are not identical materials. MTA products have been reported tohaveasmallermeanparticlesize,containfewertoxicheavy metals,hasalongerworkingtime,andappearstohaveundergone additional processing/puriﬁcation than regular Portland cements [13,14].
The ﬁrst MTA material was described as a ﬁne hydrophilic powder composed predominantly of calcium and phosphorus ions, with added bismuth oxide to provide radiopacity greater thandentin.However,laterinvestigations[10,1,16]found phosphorus levels in MTA products to be very low, near electron probe microanalysis detection limit, which correlates with the manufacturer’s material safety data sheet . Since it is unlikely that a signiﬁcant compositional change in MTA materials occurred from the time of the ﬁrst report and given that Portland cement is primarily composed of silicate and aluminate materials [10,13,18,19] earlier reports  of MTA product phosphorus content are most likely in error .
The MTA product powder is mixed with supplied sterile water in a 3:1 powder/liquid ratio and it is recommended that a moist cotton pellet be temporarily placed in direct contact withthematerialandleftuntilafollow-upappointment.Upon hydration, MTA materials form a colloidal gel that solidiﬁes to a hard structure in approximately 3–4h [12,15], with moisture from the surrounding tissues purportedly assisting the set- ting reaction . Hydrated MTA products have an initial pH of 10.2, which rises to 12.5 three hours after mixing [1,15]. The setting process is described as a hydration reaction of trical- cium silicate (3CaO·SiO2) and dicalcium silicate (2CaO·SiO2), which the latter is said to be responsible for the development of material strength . Although weaker than other materials used for similar purposes, MTA compressive strength has been reported to increase in the presence of moisture for up to 21 days , while MTA product microhardness and hydration behavior has been reported to be adversely affected with exposure to the pH range of inﬂammatory environments (pH 5) as compared to physiologic conditions (pH 7) .
MTA materials have been reported to solidify similar to other mineral cements, in which the anhydrous material dissolves, followed by the crystallization of hydrates in an interlocking mass . The basic framework of the hydrated mass is formed by the interlocking of cubic and needle-like crystals in which the needle-like crystals form in sharply delineatedthickbundlesthatﬁlltheinter-grainspacebetween the cubic crystals . The effect of mixing MTA powder with different liquids and additives has shown that the choice of preparationliquidcanhaveaneffectonsettingtimeandcompressive strength . Three and ﬁve percent calcium chloride solutions, a water-based lubricant, and sodium hypochlorite gels decreased setting time; however ﬁnal compressive strength was signiﬁcantly lower than that obtained prepared with sterile water. Preparation with saline and 2% lidocaine anesthetic solution increased setting time; but compressive strength was not signiﬁcantly affected. Interestingly, a MTA product prepared with chlorhexidine gluconate gel did not set . It seems to reason that the setting reaction of MTA products,likeitsPortlandcementparentcompound,isahydration reaction;sufﬁcientwaterinpotentialpreparationliquidsmust be present for reaction . Furthermore, it should also be intuitive that the chosen preparation liquid must also possess water with the necessary diffusion ability to be available for the hydration reaction. Clinicians may consider different solutions instead of sterile water in the preparation of MTA materials; however, clinicians should consider the potential therapeutic gain versus the loss of MTA material physical properties in these situations.
Up to 2002, only one MTA material consisting of graycolored powder was available, and in that year white mineral trioxide aggregate (WMTA) was introduced as ProRoot MTA (Dentsply Endodontics, Tulsa, OK, USA) to address esthetic concerns . After that time, two forms of MTA materials were categorized: the traditional gray MTA (GMTA) and WMTA. Scanning electron microscopy (SEM) and electron probe microanalysis characterized the differences between GMTA and WMTA and found that the major difference between GMTA and WMTA is in the concentrations of Al2O3, MgO,andFeO[12,16](Table1).WMTAwasfoundtohave54.9% less Al2O3, 56.5% less MgO, and 90.8% less FeO, which leads to the conclusion that the FeO reduction is most likely the cause for the color change . WMTA was also reported to possess an overall smaller particle size than GMTA  while it was also suggested the reduction in magnesium could also contribute to the lighter color of WMTA . A reported elemental analysis comparing a commercial form of WMTA, a Portland cement,andthestatedMTApatentcanbeobservedinTable2.
Table 1 – Chemical compositions of GMTA and WMTA (wt%)
Chemical WMTA GMTA
Adapted from Asgary et al. .
X-ray photoelectron spectroscopy (XPS) that reported surface sulfur and potassium species increase 3-fold during the setting reaction. This suggested that MTA material setting time could be prolonged by the formation of a passivating trisulfate species layer, which may serve to prevent further hydration and reaction . This trisulfate species may serve a protective function, as it was reported that that WMTA ﬂexural strength was signiﬁcantly reduced when 2-m thick layers wereexposedtosterilesalinemoistureformorethan24h. Calcium release from MTA materials diminishes slightly with time  while MTA materials were reported to form a porous matrix characterized by internal capillaries and water channels in which increased liquid/powder ratio produced more porosity and increased solubility . GMTA solubility levels have been reported to be stable over time, but the usuallyreported pH of between 1 or 12 may slightly decrease . The high pH level of MTA materials has led some to theorize that the biologic activity is due to the formation of calcium hydroxide [2–25]. WMTA solubility, hardness, and radiopacity has been compared to two Portland cements reporting that WMTAwassigniﬁcantlylesssoluble,exhibitedgreaterVickers hardness, and was more radiopaque .
There are some evidence that MTA materials possess a prolonged maturation process that continues past the stated setting time of 3–4h, as GMTA retention strength for furcation repairshasbeenreportedtoresistsigniﬁcantlymoredislodge-
Table 2 – Elemental analysis comparison portland cement and ProRoot WMTA (wt%)
Element Portland cement WMTA Patent
Adapted from Dammaschke et al. .
ment at 72h as compared to 24h . This was corroborated by one study that reported increase push-out strength up to7d ays  with an additional study reporting maximum GMTA push-out strength observed at 21 days . Interestingly, GMTA that has not reached full maturity has been suggested to possess an ability to re-establish dislodgement resistance after partial displacement; but the re-established resistancestrengthdecreasedasdislodgementtimeincreased after placement .
Different intracanal irrigant/oxidizing agents have been found to affect the push-out strength of GMTA as it was susceptibletosodiumhypochlorite,sodiumperboratemixedwith saline, 30% hydrogen peroxide, sodium perborate mixed with 30% hydrogen peroxide, and saline at 7 days . GMTA pushout strength was also reported to be similar to Super-EBA and IRM when exposed to saline or sodium hypochlorite, but GMTA was more susceptible to oxidizing agents , which was reinforced by a report that a hydrogen peroxide-based canal preparatory agent signiﬁcantly reduced the push-out strength of GMTA to dentin, whereas 2% chlorhexidine and 5.25% sodium hypochlorite did not . Another report found thatperforationretentionstrengthwasnotaffectedbypreparing GMTA with either saline, sterile water, or lidocaine, but the bond strength to blood-contaminated root dentin was signiﬁcantly less than that observed to uncontaminated dentin . Any adhesion that may be formed between GMTA and dentin may be stronger than the cohesive strength of the GMTA material, as it was reported that GMTA–dentin bond failures was usually cohesive within the MTA material . Furthermore, total GMTA–dentin bond strength is also heightened by increased surface area, as one report states that 4mm of GMTA has been reported to afford more resistance to displacementthan1-mmthickapplications,andwasnotaffected by previous calcium hydroxide placement .
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