Mineral Trioxide Aggregate

Mineral Trioxide Aggregate Excellent results have been reported 1-4 with the use of mineral trioxide aggregate (MTA) (ProRoot MTA, Dentsply-Tulsa Dental, Tulsa, OK, USA) as a pulp capping agent. When compared with calcium hydroxide, MTA produced significantly more dentinal bridging in a shorter period of time with significantly less inflammation. Dentin deposition also began earlier with MTA. MTA a biocompatible material has an antibacterial effect similar to that of calcium hydroxide, and has the property of providing a biologically active substrate for cell attachment. This feature makes it effective in preventing microleakage and improves treatment prognosis. MTA stimulated pulp healing with dentin bridge formation and minimal inflammatory reaction in exposed pulps in monkeys. 4 Its dentinogenetic effect in short-term capping experiments was demonstrated in dogs. 33 It was demonstrated 5 that after direct pulp capping in dogs, the underlying pulp tissue was consistently normal. After 2 weeks, the beginning of a hard-tissue barrier was observed, and reparative dentinogenesis was observed after 3 weeks, associated with a firm fibrodentin matrix. This material has been approved for use by the ADA. A preliminary study in human teeth reported better results with MTA than with calcium hydroxide. 6 In studies 7 of the effects of MTA on cementoblast growth and osteocalcin production in tissue cultures, the results showed MTA was cementoconductive with cementoblast attachment and growth as well as the production of mineralized matrix gene and protein expression. Sarkar and associates 8 reported the interactions of MTA with a synthetic tissue fluid composed of a neutral phosphate buffer saline solution and the dentin of extracted teeth. Endodontically prepared teeth filled with MTA and stored in this synthetic tissue fluid for 2 months produced an adherent precipitate interfaced with the dentin wall. This precipitate had the same composition and structure as hydroxyapatite. It was concluded that calcium, the dominant ion released from MTA, reacts with phosphate in tissue fluid, producing hydroxyapatite, and that the sealing ability, biocompatibility, and dentinogenic activity of the material occur because of these physiochemical reactions. In the pulp capping or pulpotomy procedure MTA is placed directly over the exposure site. Because MTA requires 3 to 4 hours to set, a hard-setting material must be placed over it before the final restoration is completed. Following application of the MTA, a thin layer (1/2 to 1 mm thick) of flowable light curable composite resin is flowed over the

material and light cured. The remaining tooth structure is etched and a bonded restoration is placed. Although the flowable composite directly over the MTA is not bonded, by careful placement of the material, most of the prepared dentin and enamel is available for bonding, thus not weakening the seal of the restoration. In the event of failure of direct pulp capping, the option of endodontic therapy usually exists. Pulp capping should not be considered for primary teeth with carious pulp exposures or for permanent teeth with a history of spontaneous toothache, radiographic evidence of pulpal or periapical pathosis, calcifications of the pulp chamber or root canals, excessive hemorrhage at the exposure site, or exposures with purulent or serous exudates. Apical Barrier Techniques While apexification with pastes has been highly successful, alternative treatments using artificial barriers that allow immediate obturation of the canal have replaced these procedures. The use of MTA as the apical barrier has become the standard as most of the inherent disadvantages of calcium hydroxide therapy, including increased cost, patient compliance with the multiple appointments and possible root fracture can be eliminated. The use of MTA as an apical barrier was reported in 1996. 9 Subsequent research 10 showed that MTA induced apical hard tissue formation more often than osteogenic protein-1 or calcium hydroxide while producing less inflammation. MTA is a hydrophilic material requiring the presence of moisture to set. Hydration of the powder produces a colloidal gel with a ph of 12.5 that solidifies into a hard structure requiring a setting time of approximately 4 hours. 11 Dye and bacterial leakage studies 12-17 have shown the seal of MTA to be superior or equal to amalgam, Super-EBA, and IRM, common materials used as root-end fillings. In a dye study 18 in which the same materials were contaminated with blood, MTA leaked significantly less than the others. Also, the presence or absence of blood had no significant effect on the amount of dye leakage. MTA is less cytotoxic than amalgam, IRM, or Super-EBA. 12,19,20 Studies 11,21 have demonstrated MTA to be biocompatible, free of inflammation, and demonstrated direct bony opposition on implanted specimens. MTA has been shown to be osteoconductive and promote osteogenesis when implanted intraosseously. 22 MTA offers a biologically active substrate for bone cells and stimulates interleukin production. 23 Torabinejad and coworkers 24 have demonstrated a complete layer of cementum when using MTA as a root-end filling in monkeys. Further research 25 has proven MTA to be cementoconductive

in tissue cultures with cementoblast attachment to the material and production of mineralized matrix. When compared with Ketac-Endo (glass ionomer), MTA exhibited better biologic properties, was free of inflammation, and demonstrated total closure of the apical foramen with cementum. 26 MTA Barrier Technique In the apexification technique the canal is cleaned and disinfected as in any endodontic procedure. The use of a rubber dam is mandatory. The length of the canal is established and the canal is cleaned as thoroughly as possible with frequent sodium hypochlorite irrigation to remove debris from the canal. Cleansing is complicated because the canal diverges apically. Sonic and ultrasonic devices are extremely helpful in debriding the canal. After thorough debridement the canal is dried and medicated with a slurry of calcium hydroxide paste and sealed with a temporary filling. The physical environment has been shown 27 to have an effect on MTA. Acidic environment of ph 5 adversely affects the physical properties and hydration of MTA as well as weakening the microhardness. Thus an acidic environment as would be present with infection or suppuration must be cleared up before application of MTA. When the tooth is free of signs and symptoms of infection, it is reisolated with the rubber dam and the canal reentered. It is usually not necessary to anesthetize the tooth at this appointment. The canal is thoroughly flushed and cleansed of all the calcium hydroxide medicament. It is then dried and a plug of MTA is compacted into the apical 4 to 5 mm. Study 28 of various thicknesses of MTA used as a root-end filling has shown 4 mm was significantly more effective than lesser amounts in preventing dye leakage. The properly mixed MTA is placed into the access opening with an amalgam carrier and condensed into the apical area with the blunt end of very large paper points. For the initial condensation, the paper points are measured 1 to 2 mm short of the working length to prevent apical extrusion of the MTA. Carefully measured large blunt ended pluggers may also be useful in packing the material. Assessment of the adequacy of the apical plug is verified radiographically. Once a plug of 4 mm is achieved, all excess MTA is removed from the canal. The walls of the canal are scrubbed with dampened large paper points and cotton tipped plastic applicators (normally used to apply bonding agents) to remove all MTA smear from the inner root surface. This is necessary because the

remainder of the canal will be obliterated with bonded composite resin to strengthen the root. Otherwise, there will not be a bonded resin-dentin interface. Moisture to promote setting is provided by placing a very wet cotton pellet in the canal to provide moisture for the setting reaction. The pellet should not contact the MTA since fibers of the cotton will become impregnated into the material. Excess water in the access preparation is dried with cotton pellets and the opening sealed with cavit. At a subsequent appointment, the tooth is reisolated and the cavit and cotton removed. Hard set of the MTA is verified with an endodontic file or probe. If for some reason the MTA has not hardened, the canal can be recleansed and the procedure repeated. Restoration After Apexification Because of the thin dentinal walls there has traditionally been a high percentage of root fractures during and after apexification. Clinically, the placement of acid-etch bonded composite resin has virtually eliminated these fractures. Restoration of the immature tooth after placement of the apical plug of MTA must be designed to strengthen the tooth as much as possible. The use of newer dentinal bonding techniques has been shown to strengthen endodontically treated teeth to levels close to that of intact teeth. 29,30 Another recent study 31 demonstrated significantly greater resistance to root fracture after placement of a 4 mm thick apical plug of MTA followed by an intracanal composite resin when compared with MTA followed by guttapercha and sealer. Other research 32 using resin modified glass ionomer with a translucent curing post showed significantly increased resistance to root fracture as compared with guttapercha alone in teeth with open apices. Prior to placement of the composite resin, the dentin is acid etched, and a dentin bonding agent is applied to the internal surfaces of the canal and light cured. The etching and bonding is directly over the MTA plug and no guttapercha is placed in the canal. Unless a post is needed, the following technique is recommended for placement of the composite resin. Following acid etching and placement of the dentin bonding agent, 2 mm increments of condensable light cure composite resin Esthet-X (Dentsply Caulk, Milford, DE) or Alert (Pentron Clinical Technologies LLC, Wellingford, CT) are placed in the canal and cured until the canal and access opening are obliterated. Utilization of this technique strengthens the weak roots and has virtually eliminated fractures.

If a core is needed for crown placement, a Luminex post (Luminex System, Dentatus USA, New York, NY) without serrations is used to create post space. In this technique, a light-curing composite resin is placed in the canal, care being taken to avoid trapping of bubbles. The Luminex post is placed to the depth of the preparation and the composite cured by transmitting light through the post. Because the composite does not bond to the smooth post, it can be gently removed and a corresponding metal Dentatus post cemented into the space with a resin cement. A composite buildup for crown retention may then be completed. REFERENCES 1. Abedi HR et al: The use of mineral trioxide aggregate cement (MTA) as a direct pulp-capping agent, J Endod 22:199, 1996 (abstract). 2. Junn DJ, McMillan P, Bakland LK, Torabinejad M: Quantitative assessment of dentin bridge formation following pulp-capping with mineral trioxide aggregate (MTA), J Endod 24:278, 1998 (abstract). 3. Myers K, Kaminski E, Lautenschlater E: The effects of mineral trioxide aggregate on the dog pulp, J Endod 22:198, 1996. 4. Pitt-Ford TR et al: Mineral trioxide aggregate as a pulp-capping material, J Am Dent Assoc 127:1491, 1996. 5. Tziafas D et al: The dentinogenic effect of mineral trioxide aggregate (MTA) in short-term capping experiments, Int Endod J 35:245-54, 2002. 6. Aeinehchi M et al: Mineral trioxide aggregate (MTA) and calcium hydroxide as pulpcapping agents in human teeth: a preliminary report, Int Endod J 36:225, 2003. 7. Tittle KW et al: Apical closure induction using bone growth factors and mineral trioxide aggregate, J Endod 22:198, 1996 (abstract #41). 8. Sarkar NK, Caicedo R, Ritwik P, Moiseyeva R, Kawashima I: Physicochemical basis of the biologic properties of mineral trioxide aggregate, J Endod 31:97, 2005. 9. Thomson TS, Berry JE, Somerman MJ, Kirkwood KL: Cementoblasts maintain expression of osteocalcin in the presence of mineral trioxide aggregate, J Endod 29:407, 2003. 10. Shabahang S et al: A comparative study of root-end induction using osteogenic protein-i, calcium hydroxide, and mineral trioxide aggregate in dogs, J Endod 25:1, 1999.

11. Torabinejad M et al: Cytotoxicity of four root end filling materials, J Endod 21:489, 1995. 12. Torabinejad M et al: Dye leakage of four root-end filling materials: effects of blood contamination, J Endod 20:159, 1994. 13. Torabinejad M et al: Tissue reaction to implanted root-end filling materials in the tibio and mandible of guinea pigs, J Endod 24:468, 1998. 14. Bates CF, Carnes DL, del Rio CE: Longitudinal sealing ability of mineral trioxide aggregate as a root end filling material, J Endod 22:575, 1996. 15. Torabinejad M et al: Physical and chemical properties of a new root-end filling material, J Endod 21:349-53, 1995. 16. Fischer EJ, Arens DE, Miller CH: Bacterial leakage of mineral trioxide aggregate as compared with zinc-free amalgam, intermediate restorative material, and Super-EBA as a root-end filling material, J Endod 24:176, 1998. 17. Aqrabawi J: Sealing ability of amalgam, super EBA cement, and MTA when used as retrograde filling materials, Br Dent J 188:266, 2000. 18. Torabinejad M, Watson TF, Pitt-Ford TR: The sealing ability of a mineral trioxide aggregate as a retrograde root filling material, J Endod 19:591, 1993. 19. Osorio RM, Hefti A, Vertucci FJ, Shawley AL: Cytotoxicity of endodontic materials, J Endod 24:91, 1998. 20. Keiser K, Johnson CC, Tipton DA: Cytotoxicity of mineral trioxide aggregate using human periodontal ligament fibroblasts, J Endod 26:288, 2000. 21. Mitchell PJ, Pitt-Ford TR, Torabinejad M, McDonald F: Osteoblast biocompatibility of mineral trioxide aggregate, Biomaterials 20:167, 1999. 22. Moretton TR, Brown CE Jr, Legan JJ, Kafrawy AH: Tissue reactions after subcutaneous and intraosseous implantation of mineral trioxide aggregate and ethoxybenzoic acid cement, J Biomed Mater Res 52:528, 2000. 23. Koh ET et al: Mineral trioxide aggregate stimulates cytokine production in human osteoblasts, J Bone Min Res 10S:S406, 1995. 24. Torabinejad M et al: Histologic assessment of mineral trioxide aggregate as a root- end filling in monkeys, J Endod 23:225, 1997. 25. Tittle KW et al: Apical closure induction using bone growth factors and mineral trioxide aggregate, J Endod 22:198, 1996 (abstract #41). 26. Holland R et al: Reaction of dogs' teeth to root canal filling with mineral trioxide aggregate or a glass ionomer sealer, J Endod 25:728, 1999. 27. Lee YL et al: Effects of physiological environments on the hydration behavior of mineral trioxide aggregate, Biomaterials 25:787, 2004.

28. Valois CR, Costa ED, Jr: Influence of the thickness of mineral trioxide aggregate on scaling ability of root-end fillings in vitro, Oral Surg Oral Med Oral Pathol Oral Radial Endod 97:108, 2004. 29. Hernandez R, Bader S, Boston D, Trope M: Resistance to fracture of endodontically treated premolars restored with new generation dentin bonding systems, Int Endod J 27:281, 1994. 30. Katebzadeh N, Dalton BC, Trope M: Strengthening immature teeth during and after apexification, J Endod 24:256, 1998. 31. Lawley GR et al: Evaluation of ultrasonically placed MTA and fracture resistance intracanal composite resin in a model of apexification, J Endod 30:167, 2004. 32. Goldberg F et al: Reinforcing effect of a resin glass ionomer in the restoration of immature roots in vitro, Dent Traumatol 18:70, 2002. 33. Faraco IM Jr, Holland R: Response of the pulp of dogs to capping with mineral trioxide aggregate or a calcium hydroxide cement, Dent Traumatol 17:163, 2001.