Recent advances and modifications of intermediary materials.

 

Pulp vitality protection after carious lesions or traumatic injuries is an Inspiring challenge. Pulp-capping materials are essential demand to protect the pulp from chemical, thermal and' other toxic stimuli. Basing on these considerations we will illustrate some of the recent materials introduced in the operative field to protect the pulp-dentin complex (MTA, Theracal, Biodentin). We will show their composition, different properties and their indications.

Introduction

Intermediary materials are materials placed between dentin (sometimes pulp) and restorative material to provide pulpal protection, they are adjuncts to the restorative material and together they form the restorative system.

Abase is any substance placed under a restoration that blocks out undercut in the preparation, acting as a chemical or thermal barrier to the pulp and' control the thickness of overlaying restoration. 

 

A cavity liner is a fluid paste applied in a thin layer as protective between dentin and restorative material, liners should be used in layers thicker than 0.5 mm. 

The sound dentin is the best barrier between the pulp and restoration, so further removal of diseased dentin is required the cavity depth increase and the dentin bridge decrease, so we use intermediary materials to provide pulpal protection to achieve this the intermediary materials should provide a sedative action to the pulp, provide no further irritation, compatible with pulp dentin organ, stimulate reparative dentin formation, improve the marginal sealing and adaptation to the cavity walls, should possess thermal and electrical insulating capacity at minimal film thickness, sufficient strength to resist fracture under mechanical strength, minimum effective film thickness, not interfere with the setting and adaptation time of restorative material, should resist the degradation in the oral fluids, be easy to apply and have adequate workability

Discussion

• MTA:

MTA was at first presented in the gray form (GMTA), anyway because of staining capability of the GMTA white type of MTA (WMTA) was presented. Since initiation, MTA quickly picked up acknowledgment among dentists and has been broadly explored as a potential material to seal the pathways of correspondence between the tooth root and the outer surfaces. It is supplied in powder and liquid. Because of prevalent biocompatibility, bioactivity furthermore, sealing capacity, MTA is utilized for both.

MTA Mixing

 

 

■ The Composition: is extensively like Portland cements. MTA is a complex

synthetic compound made out of different mineral phases which included basic oxides of different components. Several investigations assessed the essential elemental composition of MTA and revealed that calcium, silica, bismuth' and oxygen involve the primary components present in MTA. As per the MTA patent, calcium and silica are the fundamental receptive components though bismuth was included for radiopacity. The Material utilized within the patent comprised of calcium oxide (50-75 wt %), silica oxide (15-25 wt %) and' aluminum oxide, together these oxides established 70-95 wt % of MTA. The compositional imaging of the two types of MTA introduced oxygen appropriation all through crystalline also, amorphous phases which demonstrated that all components in MTA were available in their oxide form. Moreover, chemical contrasts between the two types of MTA that WMTA contained generally fewer contents of iron oxide aluminum oxide and'. ,  (2, 3)magnesium oxide.

ü Particle size: and morphology of a biomaterial is significant because it fundamentally influences the physical properties. Numerous examinations have researched Particle size and shape of MTA and revealed that MTA molecule size range is less 1 µm to around 30 µm in any case, incidentally' particles up to 50 µm were likewise revealed. The two types of MTA contained irregular particles. WMTA Includes small irregular particles with some lengthened needle_ like particles though, GMTA contained huge small particles alongside little just as prolonged particles

ü The Solubility: of MTA is affected by the powder/water proportion utilized for its mixing. A higher measure of water leads to greater porosity and more solubility in the set structure of MTA by causing more calcium discharge.

ü Compressive strength: Reactive phases of MTA have distinctive hydration rates, C2S hydrates at a slower rate than C3S, accordingly mechanical properties of MTA may take a few days to come to their maximum. MTA shows moderately less compressive strength contrasted with amalgam, G.I cements also, composites which can be impacted by powder/water proportion utilized, sort of the liquid of the mix, pH of the mixing fluid and' the surrounding environment also, the conditions of storage.

ü Push out strength: MTA has lower push out strength. Because C2S has Hydraulic nature and the hydration rate is slow makes pushes out the strength of MTA liable to be influenced by pH, humidity, time after mixing 'and storage conditions.

ü Radiopacity: Bismuth oxide_ make MTA radiopaque, which is adequate to make MTA conspicuous on radiographs .In any case, the radiopacity of MTA is less than amalgam and gutta_ percha.

ü Porosity: in a set structure of MTA is influenced by powder/water proportion,expansion of bismuth oxide, entrapment of air during mixing material and' pH

ü Sealing capacity and marginal adaptation: of endodontic filling materials' is of central significance since leakage of irritants from contaminated root canals to encompassing periradicular tissues represents a larger part of endodontic disappointments. The sealing capacity of MTA was broadly assessed by (leakage of dyes, liquid filtration, protein what's' more, bacterial leakage) and had indicated a predominant sealing capacity for MTA contrasted with amalgam, IRM and super EBA. The setting reaction of MTA is followed by expansion which may lessen gaps at MTA interface.

ü The setting reaction of MTA: is a complex procedure contingent upon the specific extents of mineral phases, their temperature 'and purity of the mix. On hydration calcium silicates present in MTA experiences hydrolysis furthermore, produce calcium silicate hydrate and calcium hydroxide.

(CaO+H2OCa(OH)2) On hydration' any abundance calcium oxide promptly reacts and forms calcium hydroxide. (2(3CaO.SiO2) + 6H2O 3CaO2.SiO2.3H2O+ 3Ca (OH)2) While C2S and C3S react with water to create calcium silicate hydrate (C-S-H) and calcium hydroxide. The C3S is the most significant mineral in MTA and takes part in the arrangement of C-SH to give early strength. Then again, C2S reacts slowly and result in the final strength of the set material. 

ü Biological properties: MTA is a non-neurotoxic and non-mutagenic material which doesn't apply unfavorable impacts on microcirculation, along these lines; it is considered as the least cytotoxic dental material. MTA has great interaction with mineral tissue forming cells and result in collagen release. MTA goes about as an organically dynamic substrate for bone_ forming cells and upregulates the production of interleukin and shows insignificant or no inflammatory reaction when setting in contact with soft tissues. On account of MTA, the formation of hard dentin bridge is quicker thick and with good structural integrity in correlation with calcium hydroxide .the enlistment of mineral tissue formation by MTA is credited to its fantastic sealing capacity, biocompatibility, alkalinity and other material qualities

Disadvantages:

The principle disadvantages of MTA incorporate a discoloration potential incorporation of toxic components in the material composition, difficult handling, long setting time (this makes MTA cannot be applied in 1 visit), high material cost, nonattendance of a known dissolvable for this material. To overcome these disadvantages, efforts have been made; But, adding or removing any different components may influence MTA's optimal characteristics.

ü Clinical applications: MTA is a material of decision for various endodontic applications such as pulpotomy, apexification (MTA has a fruitful impact for the treatment of teeth with necrotic pulps and open apexes. GMTA requires less time to form apical barrier contrasted with calcium hydroxide), perforation repair, root_ end filling, pulp capping.

There are other recent types based on MTA. From these types, we will take about: - MTA Fillapex Sealer. It is a new endodontic sealer that combines between the Advantages of MTA and superior canal obturation. It is supplied in two pastes. MTA Which is found in MTA fill apex is more stable providing a continuos release of calcium Ions for the remeneralization process and maintain PH, so has antibacterial effect. It does not cause discoloration to the tooth structure. Indications: It is indicated in root canal filling with of permanent teeth. The boiling point of it is (150 deg.ce.), so it can be used in thermal condensation technique with gutta-percha. Advantages: Excellent flow, it can penetrate and fill lateral canals. Easy handling and insertion. Allow adequate working time. Biocompatibility, allowing formation of new tissue without causing any inflammation. TheraCal LC: It is light-cured introduced in a single paste calcium silicate-based material advanced by the maker for use as a direct and indirect pulp capping material and as a defensive base and liner for use with cements , restorative , or other base materials .

Composition: it contains around 45% wt mineral material (type III Portland cement), 10% wt radiopaque part, 5% wt hydrophilic thickening agent (raged silica) and about 45% resin. The resin contains hydrophobic part like ( BisGMA , triethylene glycol dimethacrylate (TriEDMA or TEGDMA ) and urethane dimethacrylate (UDMA), furthermore it contains a hydrophilic part like (polyethylene glycol dimethacrylate (PEGDMA) and (HEMA)

 

physical and mechanical properties: Out of the blue, TheraCal end up being a material ready to release calcium and hydroxyl particles for a time of at least 28 days , which is significantly more than MTA and huge amounts of Ca particles could activate ATP, which assumes a noteworthy role in the process of mineralization. It is suggested that the resin part of TheraCal (involving hydrophobic and hydrophilic monomers) can advance Ca what's more, OH ions discharge inside the wet operating site (on the pulp of tooth or dentine) and could support the cooperation of the definition with the hydrophilic tooth dentine. The hydrophilic part in TheraCal permits a few water retention that's likely responsible for the start of the hydration reaction of the Portland cement particles with subsequent formation calcium hydroxide ( 8) Hydroxyl ions release during the hydration process result in alkalinization of the surroundings makes an unfavorable condition for bacterial endurance and multiplication .These antibacterial properties are basically required at the dentine/ restoration interface where remaining microbes could additionally increase the danger of re-contamination and secondary caries, specifically when utilizing dental composites which loss any antimicrobial action. The diminish in hydroxyl particle discharge from TheraCal following 7–14 days moving toward the physiological pH may make an ideal domain for the vitality of pulp cell also, metabolic activity with the development of new /reparative tertiary dentine.

 

 Solubility: One of the significant disadvantages of the conventional self-cure CaO and Ca(OH)2-based materials is high solubility and disintegration after some time (inside 1–2 years after application) in tissue liquids, in this way neglecting to give a changeless seal against bacterial intrusion. TheraCal demonstrated low solubility esteems, though the high dissolvability of ProRoot MTA was likely identified with its long setting time, with resulting crumbling of unset material.(8) TheraCal LC is answered to have an appetite-forming capacity. Resultant "apatite covering" assumes a key role is the repair of dentine and mineralization. Its capacity to actuate the arrangement of hydroxyapatite-like crystals could help in the chemical attach to dentine and gives a good biological seal to protect the pulp.

 

 The bond strength: between theraCal LC and composite utilizing the totaletch method showed better bond quality values when contrasted to the selfetch primer. TheraCal LC had higher bond strength than Biodentine when layered with composite materials that are exceptionally translucent influencing last restoration esthetic. Producer suggests setting it in 1 mm layers and for 20 seconds by light curing.

 

Biological properties: theraCal prompted a broad pulp inflammatory response unlike MTA or Biodentin , which causes a higher level of irritation and it is poisonous to pulp fibroblasts .The study credited this to the acrylic monomer Bis-GMA present in the material

 

Clinical applications: Theracal received a great modification to overcome the disadvantages of MTA due to the light curing ability and achieving the concept of '' single visit''. Excellent Handling properties, good Sealing ability and good antimicrobial property, make it a good choice as a pulp capping agent and also it is used as base help to reduce sensitivity of dentin and providing a thermal barrier .

• BioDentin: Biodentine is calcium silicate-based inorganic restorative cement can be used as direct and indirect pulp capping material furthermore, publicized as' bioactive dentine substitute'. It is supplied in pre proportioned capsule .The material is guaranteed to have better physical and biological attributes looked at to other tricalcium silicate cements, as (MTA) and Bioaggregate .

Conclusion:
Based on the previous studies we can say that, these materials have a promising future and great demand because of its satisfactory advantages. It has also low cost in  comparison with root canal treatment; As DPC is not always the most effective choice, But it is never the most costly option. (14) We expect demand on these recent materials to increase and to receive a significant development.