Mineral Trioxide Aggregate (MTA)
Mineral trioxide aggregate is bioactive silicate that is made of a mixture of tricalcium silicate, dicalcium silicate, tricalcium aluminate, tetracalcium aluminoferrate, calcium sulphate and bismuth oxide. There are numerous MT A products available in Australia including, but not
limited to, ProRoot MT A, Endocem MT A and Endoseal MT A. Given the similarities between the products this paper will use MT A as an umbrella tem1s for all these MT A based cements. The bioactivity of MT A has been proven in multiple studies, and is comprehensively covered in a review by Parirokh and Torabinejad in 2010.

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There is no unifonnly accepted definition ofbiosilicates amongst the dental literature. Due to this I will attempt to construct a suitable definition for this paper. Firslty, the bio component relates to the word bioactive, which is most simply defined as “having an effect on or
eliciting a response.from living tissue, organism, or cell ” 1 . Secondly, silicates are a common class of naturally occurring minerals that share the same basic structural unit of a silicon tetrahedron, the chemistry of which is outside the scope of this paper. Based on these previous statements we can define biosilicates for this essay as any silicate-based dental material that elicits a response fi’om the living cellular tissue within, or around, teeth and their supporting structures. These biosilicates, in conjunction with non-silicate-based materials, front the new wave of reparative dental materials that are currently being used.
The primary application of these bioactive materials in paediatric dentistry includes treatment of dental trauma, along with pulp therapy in primary and immature permanent teeth. This paper will discuss the clinical applications of these products in further detail whilst comparing them to other popular non-silicate-based products.

TheraCal™ (Bisco Inc, Schamburg, IL, USA) is another calcium-silicate based product, however the unique property of this material is that it is resin modified, making it a light cured calcium silicate cement. The composition profile for TC is mixture of calcium oxide, calcium silicate particles, strontium glass, fumed silica, resin containing BisGMA and other filler materials. The manufacturer has indicated TC be suitable for indirect and direct pulp cappmg.

Compared to MTA, Biodentine™ (Septodont Ltd., Saint Maur des Fausse’s, France) is a relatively new product, having only been released in the past ten years. Like MT A, BD is a calcium-silicate based cement, with a composition profile of tricalcium silicate, di calcium silicate, calcium carbonate, oxide filler, iron oxide shading and zirconium oxide. The biocompatibility of BD has been demonstrated in multiple studies, with the significant findings being its ability to stimulate odontoblast activity, odontoblastic cell differentiation and apposition of reparative and reactionary dentine 4’5. The manufacturer claims that it is
suitable for clinical use in areas such as pulp capping, pulpotomy, enamel and/or dentine pennanent and temporary restorations, root sealing (following perforation), internal/external resorption and apexification. Some have said that BD is an improved version of MT A, with the fonner having easier handling and manipulability, along with superior physical qualities and a faster setting time 6

Pulpotomy
Pulpotomies are a common procedure when treating grossly carious primary teeth. Typically, they are indicated after accidental pulpal exposure following removal of extensive caries, or when a tooth has irreversible inflammation with no indication for extraction. Following
coronal pulp amputation and attaining haemostasis a therapeutic medicament must be placed in the pulpotomy site with the goal of placement being tissue regeneration and healing at the site of amputation. When placed clinically, MT A acts as both an agent for treating pulpal inflammation but has the added benefit of having physical attributes allowing it to act as a base for a restoration to be placed upon. Studies suggest the bioactivity of MT A is attributed
to stimulation of cytokine release from fibroblasts within the pulpal tissue, which goes on to stimulate hard tissue fonnation 7
. Further studies have found evidence of stimulated natural
dentine repair at the sites ofpulpal exposure after being treated long tenn with MTA 8.

Other materials used for therapeutic application during pulpotomies include ferric sulphate, fonnocresol and calcium hydroxide (Ca(OH) 2)
7. So how do these materials compare to the biosilicates? Studies indicate relatively high success rates across the board. A review of these
three products found that primary molar teeth treated after pulpotomy showed relatively equal success rates 9. When comparing pulpotomies treated with MTA to formocresol it was found that MTA had slightly higher success rates (97% to 83%) after both clinical and radiographic
assessment, however the difference was not significant and both product are recommended for use ‘ 0. A more recent comprehensive systematic review that compared treatment outcomes of pulpotomies treated with all four of these products declared that “MTA may be the most efficacious medicament to heal the root pulp aper pulpotomy of a deciduous tooth”II

mechanisms of action and complete list of biological and physical properties are complex, and beyond the scope of this paper, but the relevant end result is that MT A stimulates hard tissue fonnation and forms a tight seal between itself and tooth structure2’3.

Biosilicates clearly have their place in the paediatric dental setting. Older materials, such as MTA, remain as the gold standard for certain procedures, but with the evolution of the calcium silicate-based cements, and a growing body of evidence to support their use, there could be an eventual change. On the other hand, there is promising work in the regenerative fields that is based on non-biosilicate materials. Could this new generation of dental materials make biosilicates obsolete? Only time will tell, and given the nature of dental material research, this could still be some time away. In the meantime, biosilicates will still have an important role to play in the paediatric dental clinics throughout the country.

suggests mineral trioxide aggregate and calcium as the materials of choice for direct pulp capping 17, with some noting MTA being superior to Ca(OH) 2 based on its superior induction ofreparative dentine formation, paired with a greater ability to seal long te1m 26. Studies that
have compared MT A with Ca(OH) 2 found that whilst both materials show signs of clinical success, the failure rate at 2 year follow up was lower in MTA (19. 7% for MT A v 31.5% for Ca(OH) 2)2 7
• When MTA and Ca(OH)2 are compared histologically, MTA showed more success in regard to dentine bridge formation compared to Ca(OH) 2 at various time periods between two months and two years 28
. There are few studies analysing the perfonnance of BD as a direct pulp capping material, however the evidence is weak due to low sample sizes
and/or shmi follow up times. These studies found BD to be successful in stimulating dentine bridge formation 29-32 , and when had comparable results when compared to MT A32.

Regenerative Procedures
This paper has shed light on the application ofbiosilicates, mainly in association with pulpal therapy, and the current alternatives. However, the discussion would not be complete without mentioning a new approach being that of regenerative endodontic techniques (RET). The
basis of RET is to allow continued growth and development of the pulpal system and tooth root/dentin structures, mainly for pulpal injury in very immature permanent teeth. This is achieved by complete disinfection of the root canals, followed by the provision of a scaffold
and a biological signal to promote differentiation oflocal stem cells. Typical RET employ the use of a range of materials and medicaments, such as sodium hypochlorite, EDTA, biantibiotic pastes (metronidazole/ ciprofloxacin) and Ca(OH)/2 ’24. However, a review in 2017 suggested that REP evidence is cuffently too weak to allow it to be a recommended
treatment over MT A and root canal treatment, but states that in the absence of any other treatment option being viable then it can be considered 24.

or MT A, the results showed no significant difference at 6month radiographic review; however after 12 months the MT A showed significantly greater degree of apex closure 23. The American Academy of Pediatric Dentistry advocates the use of calcium hydroxide
initially for decontamination of the root canal, before using MT A for apexification, which is supported by the European Academy of Paediatric Dentistry 17’24’25 More long tenn studies are needed in the comparison of these two products before either is able to be recommended over the other.

Trauma (Direct Pulp Cap)

Traumatic injuries to teeth in the paediatric population presents a set of challenging situations for dental clinicians. The injuries in this population tend to be inflicted upon primary anterior
teeth, or immature pennanent teeth. When primary teeth are involved, the treatment generally involves pulpotomy and a definitive restoration. For immature pennanent teeth the treatment is more complex and is dependent on the degree of root development. If the root has developed enough length, pulp is required to be removed and root canal treatment is indicated then apexification is generally required prior, the details of this again have already been discussed. In situations where complicated dental crown fractures occur in a tooth with undesirable amount of root growth the clinician may wish to attempt apexogenesis to allow continued root development. Apexogenesis can be achieved with IPT, pulpotomy or direct pulp capping. This section will briefly touch on direct pulp capping as IPT and pulpotomy have already been discussed.

The biosilicates that have been indicated for direct pulp capping of pennanent teeth include
MT A, BD and TC. Although there is literature discussing direct pulp caps in primary teeth, it
is generally not recommended 7,11,20 and will not be discussed in this paper. The literature options for IPT. Rather the literature suggests that the other dental materials such as resinmodified glass ionomer cements, zinc oxide eugenol, calcium hydroxide and dentine bonding agents to be more suitable for IPT7• 18 • Interestingly, cun-ent guidelines from AAPD state that the clinical success of primary teeth undergoing IPT is independent of the clinician’s choice of medicament 17•19• This statement is reinforced locally in Australia, suggesting that the coronal restoration seal and prevention of bacteria re-entry plays a more important role rather
than the choice of pulpal medicament used 20.

Apexification

When an immature permanent tooth requires root canal treatment there is the need for an extensive period of therapeutic canal medication required to promote apexification to allow an acceptable apical seal. The biosilicates that can be used for this hard tissue growth are MT A and Biodentine. MT A is beneficial in this application due to its ability to achieve a tight seal paired with its proven ability to induce bone formation.

The most commonly used material used for apexification in immature pennanent teeth is calcium hydroxide, this stems for work by clinicians including Heithersay, Cvek and many others 21. These papers routinely found that calcium hydroxide could be used in the treatment of immature pennanent teeth to stimulate hard tissue growth to facilitate a more predictable long-tenn endodontic treatment. Comparisons of calcium hydroxide and MT A use on immature pennanent teeth have been performed in the literature. In a review by Kahler et al. it was found that the clinical perfonnance of calcium hydroxide and MT A to be similar in regard to fmiher root maturation, radiographic evidence of healing, tooth survival rates and overall clinical success 22. Interestingly a review by Bonte et al. in 2015 told a different story.

This paper compared the closure of canal apices when treated with either calcium hydroxide

The manufacturers of Biodentine have stated that their product is suitable in the treatment of pulpotomies in vital primary teeth. As BD is relatively new to the market there are limited long term studies on its clinical perfonnance. That being said, the literature exposes some recent short-tenn studies comparing the effectiveness of BD against formocresol. The results found no significant difference between BD and fonnocresol at the 12 month follow up, with both being found to show signs of clinical success 6. With further long-term studies on BD it could prove to be an effective material choice in paediatric dentistry.

Indirect Pulp Cap

Indirect pulp therapy (IPT) is suitable in paediatric dentistry when a tooth shows signs of reversible pulpitis in a tooth with extensive caries, on the proviso that pulp is not exposed during superficial caries removal. The biosilicates that have been reported suitable for this treatment within the literature are MTA and BD. Biodentine has been compared to calcium hydroxide, the current preferred treatment for IPT according to a systematic review by Hayashi 12, and showed comparable and acceptable results when assessed both clinically and radiographically 13, however the study lacks conviction due to a small sample size and the short review time of 12 months. Similarly MT A has been clinically compared with calcium hydroxide, with results again showing radiographic success with no significant difference between the two materials at 6 months in multiple studies14’15. Another study compared two biosilicates, MT A and TC, and found both materials to stimulate tertiary dentine formation in primary teeth undergoing IPT, but again this study lacked strength due to a sho1i tenn review of only 6 months 16. Despite these studies, the current consensus is that biosilicates are not the best options. Neither the American Academy of Pediatric Dentistry (AAPD) 17, or the UK Clinical Guidelines for Paediatric Dentist 7 recommend MT A, TC or BD as treatment

CmTently there is no proven way to rebuild enamel that has been broken or lost due to caries and cavitation in vivo. The current fluoride releasing materials, whilst able to remineralise demineralised tooth structures, are unable to regenerate acellular enamel. There is great opportunity for a true bioactive product that can stimulate natural regeneration of enamel, but at this stage it seems quite a while away. There have been advances in this field; however these involve non-biosilicate materials33 . Weather biosilicates will play a role in the area of
enamel regeneration remains to be seen.

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