Can MTA be: Miracle trioxide aggregate?

Mineral trioxide aggregate (MTA) has been used for more than 10 years in the dental community and has often been thought of as a material of choice for the endodontist. The dental pulp is closely related to periodontal tissues through apical foramina, accessory canals, and dentinal tubules. Due to this interrelationship, pulpal diseases may influence periodontal health and periodontal infections may affect pulpal integrity. It is estimated that pulpal and periodontal problems are responsible for more than 50% of tooth mortality. Thus, these associations recommend an interdisciplinary approach. MTA appears to exhibit significant results even in periodontal procedures as it is the first restorative material that consistently allows for over-growth of cementum and may facilitate periodontal tissue regeneration. Thus, in the present review, an attempt is made to discuss the clinical applications of MTA as an interdisciplinary approach.

INTRODUCTION

An ideal endodontic material should seal the pathways of communication between root canal and its surrounding tissues. It should also be nontoxic, noncarcinogenic, biocompatible with the host tissues, insoluble in tissue fluids, and dimensionally stable, and presence of moisture should not affect its sealing ability. Existing restorative materials do not possess these ideal characteristics.[1]

Mineral Trioxide Aggregate (MTA) was developed and has been investigated for various applications since early 1990s. MTA was introduced by Torabinejad and colleagues at Lomalinda University and first described in the dental scientific literature in 1993. It was given approval for endodontic use by the US Food and Drug Administration in 1998.[2]

The development of MTA by Torabinejad was truly a landmark event in dentistry and in endodontics, in particular. The many advantages of MTA expanded its use markedly in different fields of dentistry, of which endodontics is the largest field to take advantage of this material.

COMPOSITION OF MTA

MTA is a powder consisting of fine hydrophilic particles that set in the presence of moisture. MTA material is a mixture of a refined Portland cement and bismuth oxide. It contains dicalcium silicate, tricalcium silicate, tricalcium aluminate, and tetracalcium aluminoferrite. It is also reported to contain small amounts of other mineral oxides such as SiO2, CaO2, MgO, K2 SO4, and Na2 SO4, which modify its chemical and physical properties.[34] MTA has a pH of 12.5 after setting, similar to calcium hydroxide or Ca (OH)2.[3] This may impart some antimicrobial properties.[5]

Up to 2002, only one MTA material consisting of gray-colored powder was available. Later white mineral trioxide aggregate (WMTA) was introduced as ProRoot MTA, mainly to address esthetic concerns. Studies reported marginal gingival discoloration by gray MTA (GMTA). The major difference between GMTA and WMTA is in the concentrations of Al2 O3, MgO, and FeO. WMTA was found to have 54.9% less Al2 O3, 56.5% less MgO, and 90.8% less FeO. WMTA was also reported to possess an overall smaller particle size than GMTA. It was also suggested that the reduction in magnesium could also contribute to the lighter color of WMTA.[2] Oviir et al. examined the effects of MTA in vitro on the proliferation of oral keratinocytes and cementoblasts. They compared WMTA with GMTA, and their data revealed that cementoblast proliferation significantly increased when grown on the surface of WMTA, compared with cementoblasts grown on GMTA.[6]

At present, MTA is widely used in endodontic therapy. It has been proposed as the material of choice for root-end filling, pulp capping, pulpotomy for primary teeth, apical barrier formation for teeth with necrotic pulps and open apexes, perforation repair, and apexification [Figure 1].[7]

Figure 1

Clinical applications of MTA

MTA in periodontics

One of the major problems in aging, periodontal disease, tooth implants, transplantation, or replantation remains the repair of the periodontium and the regeneration of periodontal tissues such as cementum, periodontal ligament, and alveolar bone. Current strategies for periodontal repair and regeneration have been directed at enhancing alveolar bone and periodontal ligament regeneration, and have the limitation that they do not completely restore the architecture of the periodontium. Cementogenesis is a critical event for regeneration of periodontal tissues. However, MTA may appear to exhibit significant results even in periodontal procedures, as it is the first restorative material that consistently allows for over growth of cementum[89] and may facilitate periodontal tissue regeneration.[10] It has been recognized as a bioactive material that is hard tissue conductive, hard tissue inductive, and biocompatible.[1] Correlating to this, evidence regarding cementogenesis and osteogenic capacity of MTA has been amassed. Thomson et al. investigated the effects of MTA on cementoblast. Results of their studies suggest that MTA permits cementoblast attachment and growth and also production of mineralized matrix gene and protein expression. MTA can be considered cementoconductive.[11]

The effects of MTA on survival, mineralization, and expression of mineralization-related genes of cementoblasts were investigated by Sema Hakki et al. Results showed that MTA did not have a negative effect on the viability and morphology of cementoblasts and induced biomineralization of cementoblasts at concentrations of 0.02 and 0.002 mg/ml. Moreover, increased bone sialoprotein (BSP) and collagen type-I mRNA (COL-I mRNA) expression were observed at similar concentrations of MTA.[12] Koh et al. investigated the biological response in human osteoblasts and found increased osteocalcin production when cells were grown on MTA, and also, cells in contact with MTA appeared to have high levels of alkaline phosphatase.[13] Studies by Al-Rabeah et al. showed that human alveolar bone cells interact with MTA. They demonstrated the capacity of MTA to support cell attachment, proliferation, and matrix formation.[14] Various other studies like that of Nascimento et al. evaluated bone repair using MTA, combined with or without calcium hydroxide in the bone defects. Results showed that the MTA used was able to induce bone regeneration and had its action optimized when combined with calcium hydroxide.[15] Pinheiro et al. studied the effects of laser phototherapy (LPT) on bone defects grafted with MTA, bone morphogenetic proteins, and guided bone regeneration (GBR). They concluded that the association of the MTA with LPT and/or not with GBR resulted in a better bone repair. The use of the MTA associated to infrared (IR) LPT resulted in a more advanced and quality bone repair.[16]

Recently, in a systematic review titled “Histological responses of the periodontium to MTA” by Katsamakis et al., it was shown that the results were consistent with regard to MTA's biocompatibility and cementogenic ability. Experimental animal studies show that MTA can promote healing towards regeneration. However, there is a distinct need to examine the clinical performance of MTA in well-controlled prospective human cohort studies.[17]

MTA in combined endo-perio lesions

Various treatment modalities such as the use of guided tissue regeneration alone or in combination with different types of bone grafts, root surface demineralization, enamel matrix derivative, or the application of growth factors have been employed with varying degrees of success in the periodontal regeneration and bone healing process. But considering all the above mentioned beneficial biologic effects of MTA, can MTA enhance this current regeneration scenario? There are various chronic periodontal lesions that may be associated with various tooth-associated defects such as root perforations, furcal perforations, root resorptions, etc., These often pose significant treatment challenges. Therefore, an effective execution of regenerative therapy for periodontal lesion and repair of root surface defects are crucial. Studies by White and Bryant showed that in the treatment of external root resorption and an associated osseous defect, a combined approach utilizing MTA for root surface repair and decalcified freeze-dried bone allograft (DFDBA) and calcium sulphate to address an associated osseous lesion appears to be a viable modality in the treatment of chronic endodontic/periodontal lesions.[18] Baek et al. compared the periapical tissue responses and cementum regeneration in response to three widely used root-end filling materials, amalgam, SuperEBA (super ethoxy benzoic acid), and MTA. MTA showed the most favorable periapical tissue response, with neoformation of cemental coverage over it.[19] Bains et al. obtained favorable clinical results with the use of MTA and platelet-rich fibrin (PRF) in the management of pulpal floor perforation and grade II furcation involvement.[20] Although the overall results in human studies involving MTA materials are very positive, further investigation into the biologic and molecular interactions of MTA with the cells of periodontium is needed.[12]

MECHANISM OF ACTION

MTA is a bioactive material and has the ability to create an ideal environment for healing.[7] It can conduct and induct hard tissue formation.[19] From the time that MTA is placed in direct contact with human tissues, it appears that the material does the following:

Releases calcium ions and facilitates cell attachment and proliferation

Creates antibacterial environment by its alkaline pH

Modulates cytokine production

Encourages differentiation and migration of hard tissue producing cells

Forms hydroxyapatite (or carbonated apatite) on the surface of MTA and provides a biologic seal.[7]

MTA can induce osteoblastic/cementoblastic differentiation of human periodontal ligament cells, which express calcium sensing receptors (CaSR) and bone morphogenetic protein-2 (BMP-2) receptors that are potentially involved in osteogenesis.[21]

The antibacterial and antifungal properties of MTA have been extensively evaluated, and have been attributed to the release of hydroxyl ions, thus creating an antibacterial environment due to high pH. However, the studies present with conflicting reports. An investigation on facultative and strict anaerobic bacteria showed that MTA has an antibacterial effect on some facultative bacteria and has no effect on any species of strict anaerobes.[5] Another investigation reported the antimicrobial activity of MTA-based cements on Micrococcus luteus, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Candida albicans, and Enterococcus faecalis.[22] Conflicting results from antibacterial and antifungal investigations on MTA might be attributed to the various tested species of microorganisms, the source of material prepared, as well as the concentration and the type of MTA used in the studies.[1] Also, the effect of MTA on specific anaerobes is not known. More investigations are required to determine the specific mechanism of action responsible for the bioactivity of MTA.

OTHER ADVANTAGES OF MTA

The setting ability of MTA is uninhibited by blood or water. MTA is biocompatible, nonmutagenic, and non-neurotoxic, and does not produce any adverse effects on microcirculation in the connective tissue.[23]

DRAWBACKS OF MTA

The main drawbacks of MTA include a discoloration potential, presence of toxic elements in the material composition, difficult handling characteristics, long setting time, high material cost, an absence of a known solvent for this material, and the difficulty of its removal after curing.[7]

CONCLUSION

Combined endodontic periodontal lesions represent a real challenge, both for the endodontist and the periodontist. The simultaneous existence of pulpal problems and inflammatory periodontal disease in the same tooth can complicate the treatment of the affected tooth. MTA may be considered beneficial in treatment of such lesions. Reports have strongly suggested that the favorable biologic response exhibited by MTA materials is due to hydroxyapatite formation when these materials are exposed to physiologic solutions. MTA is a promising material with an expanding foundation of research. Owing to applications of MTA in interdisciplinary problems and considering its potential benefits in various disciplines of dentistry like endodontics, pedodontics and periodontics, mineral trioxide aggregate can be appropriately dubbed as miracle trioxide aggregate. However, it should be noted that the supporting data have been overwhelmingly from either in vitro or animal studies. Further longitudinal studies are necessary as at present, insufficient well-designed and controlled clinical studies exist that allow systematic and meta-analysis review of MTA materials in all of its suggested clinical indications.