Endodontic Sealers And Obturating Materials Notes

Endodontic Sealers And Obturating Materials

Following the cleaning, debriding and enlarging of the root canals, the canals spaces are sealed or obturated to prevent reinfection and colonization by bacteria.

Why obturate canals?

Microorganisms and their byproducts are the major cause of pulpal and periapical disease. However, it is difficult to consistently and totally disinfect root canal systems. Therefore, the goal of three-dimensional obturation is to provide an impermeable fluid tight seal within the entire root canal system, to prevent oral and apical microleakage.

Read And Learn More: Basic Dental Materials Notes

Successful obturation requires the use of materials and techniques capable of densely filling the entire root canal system and providing a fluid tight seal from the apical segment of the canal to the cavosurface margin in order to prevent reinfection. This also implies that an adequate coronal filling or restoration be placed to prevent oral bacterial microleakage. It has been shown that endodontic treatment success is dependent both on the quality of the obturation and the final restoration. The quality of the endodontic obturation is evaluated using radiographic images upon completion.

The objectives of modern nonsurgical endodontic treatment are

• To provide a clean and bacteria free.
• To provide an apical seal. This prevents the ingress of fluids that will provide nutrients for canal bacteria and also prevents irritants leaving the canal and entering the periapical tissues.
• To provide a ‘coronal’ seal. This prevents recontamination due to the ingress of oral microorganisms from the coronal end.

Root Canal Obturating Materials

Historically a wide variety of materials and techniques have been used in an attempt to produce an impervious seal of the tooth root apex ranging from orange wood through to precious metals and dental cements. During the Civil War, a material called “Hill’s stopping” (which contained gutta-percha, quick lime, quartz and feldspar) was used.

The most widely used root-canal sealing technique is a combination of root obturating points and canal sealer cements.

A root canal filling material should prevent infection/reinfection of treated root canals. Together with an acceptable level of biocompatibility (inert material) this will provide the basis for promoting healing of the periodontal tissues and for maintaining a healthy periapical environment.

Classification of Root canal obturating materials

Root canal obturating materials may be classified as

• Solid core, e.g. Silver
• Plastic/Semi solid core, e.g. Gutta-percha, Resilon
• Paste type, e.g. iRoot SP

Silver points

• Silver points or cones were introduced by Jasper in 1941. Silver cones were the most widely used solid-core metallic filling material between 1940 to 1960 because of their bactericidal effect. Points of gold, iridioplatinum, and tantalum were also available. These have been largely replaced by gutta-percha and are rarely used currently. They are largely of historical interest.

Root Canal Obturating Materials Advantages

• They had a bactericidal effect.
• Can be used in narrow and curved canals.
• Silver has more rigidity than gutta-percha, and hence can be pushed into tightly fitting canals and around curves where it is difficult to force gutta-percha.

Root Canal Obturating Materials Disadvantages

• Silver points/cones have a circular cross section unlike the canals which may be oval hence a poor lateral seal.
• Could show high levels of corrosion especially due to the dissolution of the sealers.
• Corrosion products are cytotoxic.
• Retrievability may be difficult in cases where retreatment is desired.
• Preparation of canal for post and core reconstruction difficult.

The disadvantages of silver points far outweigh their advantages and their use has been largely discontinued. However, they present an important evolutionary stage in the development of root canal filling materials.

Gutta – Percha

• Gutta-percha is a polymeric resin-like material obtained from the coagulation of latex produced by Palaquium gutta tree (commonly known as the Isonandra gutta tree). Gutta-percha is a name derived from the Malay words ‘getah’ meaning gum and pertja’ (name of the tree in Malay). Long before Gutta-percha was introduced into the western world, it was used in crude form by the natives of Malaysian archipelago for making knife handles, walking sticks and other purposes.

Manufacture of gutta-percha (Obach’s technique)

• The obtained pulp is mixed with water and heated to 75 °C to release the Gutta-percha threads and then cooled to 45 °C. The flocculated Gutta-percha called “yellow Gutta” contains 60% poly isoprene and 40% contaminants (resin, protein, dirt and water). Yellow Gutta is mixed with cold industrial gasoline at below 0 °C temperature. This treatment not only flocculates the Gutta percha but also dissolves resins and denatures any residual proteins. After removal of cold gasoline, deresinated Gutta threads are dissolved in warm water at 75 °C and dirt particulate is allowed to precipitate. Residual greenish yellow solution is bleached with activated clay, filtered to remove any particulate and then steam distilled to remove the gasoline. “Final ultra pure” gutta-percha has a gasoline scent, before it is modified with fillers into its final commercial product formulation.

Chemical structure of gutta-percha

• Gutta-percha is 1,4-trans-polyisoprene isomer (natural gutta-percha) CH2 groups are on opposite sides of the double bond for each successive monomer.
• Since its molecular structure is close to that of natural rubber, which is a cis-isomer of polyisoprene, it has a number of similarities but a difference in form makes it to behave more like crystalline polymers. Thus it not exhibit the classic elastic properties of rubber

Forms of gutta-percha

Gutta-percha exists in three forms

α – (or alpha form)—runny, tacky and sticky

β – (or beta form)—solid, compactible and ductile

γ – (or gamma form)—amorphous and unstable form

The β form is used with mechanical condensation techniques.

The α form is used with the thermomechanical and injectable techniques.

Supplied as

• Solid core Gutta-percha points
  • Standardized points
  • Nonstandardized points
• Thermomechanical compactible Gutta-percha points
• Thermoplasticized Gutta-percha
  • Solid core system
  • Injectable form
• Medicated Gutta-percha
  • Iodoform containing
  • Calcium hydroxide containing
  • Chlorhexidine containing
  • Tetracycline containing

Gutta-percha used for the above techniques are supplied in point or pellet form.

• Tapered points of varying sizes. The sizes range from 15 to 80. The various sizes are usually color coded for easy identification.
• Pellet form is used for the injectable technique

Composition of commercial gutta-percha

Thermoplasticized Gutta-percha

• Gutta-percha may also be delivered to the canal in fluid form through a syringe. The gutta-percha is melted in the chamber of the device and injected into the canal starting apically and proceeding coronally. This is known as “backfilling” .
• There are many such devices available in the market. The Obtura 3, Calamus, Elements, HotShot, and Ultrafil 3D are examples of such devices. The Obtura III system heats the gutta-percha to 160 °C, whereas the Ultrafil 3D system employs a low-temperature gutta-percha that is heated to 90 °C.
• The Obtura 3 system (Obtura Spartan) consists of a hand-held “gun” that contains a chamber surrounded by a heating element into which pellets of gutta-percha are loaded. Silver needles (varying gauges of 20, 23, and 25) are attached to deliver the thermoplasticized material to the canal. The control unit allows the operator to adjust the temperature and thus the viscosity of the gutta-percha.
• Thermoplastic techniques are often indicated in cases with irregularities in the canal or internal resorption

 

Drawbacks

• The difficulties with this system include lack of length control. Both overextension and under extension can occur. To overcome this drawback, a hybrid technique may be used, in which the clinician begins filling the canal by the lateral compaction technique. When the master cone and several accessory cones have been placed so that the mass is firmly lodged in the apical portion of the canal, a hot plugger is introduced, searing the points off approximately 4 to 5 mm from the apex. Light vertical compaction is applied to restore the integrity of the apical plug of gutta-percha. The remainder of the canal is then filled with thermoplasticized gutta-percha injected as previously described.

Properties

• At raised temperatures, gutta-percha behaves like other plastic materials (thermoplastic), softening above 65 °C, melting at 100 °C, and in the a-form beyond 160 °C without decomposing while remaining soft and fluid.

Removal of gutta-percha

Occasionally gutta-percha requires to be removed for retreatment or placement of a post for reconstruction of the tooth.

This can be achieved with the aid of

• Rotary instruments like NiTi (Protaper retreatment series)
• Gutta-percha solvents like Chloroform or xylol
• Thermosoftening.

Advantages and Disadvantages of Gutta-percha

Gutta-percha Advantages

• It is compactible and adapts excellently to the irregularities and contour of the canal by the lateral and vertical condensation method.
• It can be softened and made plastic by heat or by organic solvents (eucalyptol, chloroform, xylol, turpentine).
• It is inert.
• It is dimensional stable; when unaltered by organic solvents, it will not shrink.
• It is tissue tolerant (nonallergenic).
• It will not discolor the tooth structure.
• It is radiopaque.
• It can be easily removed from the canal when retreatment is indicated.

Gutta-percha Disadvantages

• It lacks rigidity. The smallest, standardized gutta-percha cones are relatively more difficult to use unless canals are enlarged above size no. 25.
• It lacks adhesive quality. Gutta-percha does not adhere to the canal walls; consequently, a sealer is required. The necessary use of a cementing agent introduces the risk of tissue irritating sealers.
• Gutta-percha does not bond to any sealers.
• It can be easily displaced by pressure.
• Gutta-percha is almost wholly dependent on a coronal seal to prevent the apical migration of bacteria if it is challenged by coronal leakage.

Resilon-Epiphany Root canal obturating System

This system is an alternative to gutta-percha. It consists of resin obturating points sealed with dual cure, hydrophilic resin sealer.

The system consists of three parts 

• Resilon – A thermoplastic synthetic polymer-based (polyester) root canal filling material, as the major component.
• Epiphany sealer – A resin-based composite that forms a bond to the dentin wall and the core material. It sets with a chemical reactions and halogen curing light.
• Primer – Which prepares the canal wall for contact with Resilon and the sealer.

Primer The primer is a self-etching system that is cured by the sealer. The primer penetrates all the dentinal tubules. The bonding procedure is preceded by irrigating with a 17% solution of EDTA. This last process is necessary for removing oxide radicals from the NaOCl and peroxides irrigants. Failure to do so can interfere with the curing of the dentin bonding agent.

Sealer The sealer bonds to the primer thereby eliminating potential for microleakage. The sealer used in this system is a dual cure bis-GMA, ethoxylated bis-GMA, UDMA, hydrophilic difunctional methacrylate. Fillers like calcium hydroxide, barium sulphate and barium glass are present 7% by weight. It contains the catalyst that initiates curing of self-etching primer in the dentinal tubules.

Obturator

The Resilon obturator is a thermoplastic polyester and contains the following components: (1) Bioactive glass, (2) barium sulfate and (3) bismuth oxychloride. The bioglass is a unique component that forms calcium/phosphate when in contact with body fluid. It does not dissolve in fluid but instead it releases ions to stimulate the formulation of osseous tissue. As already mentioned, its radiopacity is better than gutta-percha, condenses laterally and vertically like gutta-percha and softens at around 70 to 85 °C. The Resilon obturator bonds to the surface of the sealer which in turn bonds to the primer that has hybridized with the tubular surfaces.

Thinning Resin In addition to the above, many systems include a thinning resin, which may be added to thin the sealer to the desired viscosity.

Paste-type obturating materials

Various paste-type products have been tried as the sole obturating materials because they have sufficient volume stability to maintain a seal. These include zinc oxide-eugenol based pastes, epoxy resins (AH-26), AH-Plus, Ketac-Endo, polyvinyl resins (Diaket), calcium hydroxide, etc. Many of these are dual use, i.e. they may be used as sole obturating material or as sealer (when combined with gutta-percha).

Paste-type obturating materials Disadvantages

• Removal of a hard set cement can be a challenge if retreatment is required.
• Risk of microleakage when used as the sole obturating material.

Because of these inherent problems, use of a hard setting non-thermoplastic, non-soluble cement type filling material as the sole obturating material is not routinely recommended.

Root Canal Sealers

The sealer plays an important role in the obturation of root canal. Gutta-percha cannot entirely obliterate the spaces within the root canal because of its physical limitations. The sealer fills all the spaces, the gutta-percha is unable to fill. Factors like the shape of the canal, defects within the canal, internal resorption, iatrogenic damage, accessory canals, etc., make intimate sealing of the root canal system a challenging task. A total hermetic seal of the root canal system is necessary to prevent the ingress of bacteria and reinfection of the canal. The sealer also acts as a binding agent, to the dentin and to the core material, which usually is gutta-percha.

Ideal requirements of a root canal sealer

• It should be tacky when mixed.
• It should adhere well to the gutta-percha and the canal wall when set.
• It should make a hermetic seal.
• It should be radiopaque so that it can be visualized in the radiograph.
• The particles should be very fine so that they can mix easily with the liquid.
• It should not shrink upon setting.
• It should not stain tooth structure.
• It should be bacteriostatic.
• It should set slowly to provide suitable working time.
• It should be insoluble in tissue fluids.
• It should be tissue tolerant, that is, nonirritating or toxic to periradicular tissue.
• It should be soluble in a solvent if it is necessary to remove the root canal filling.
• It should not provoke an immune response in periradicular tissue.
• It should be neither mutagenic nor carcinogenic.

Root Canal Sealers Classification

Endodontic sealers can be broadly classified based on the principal components that react and set to form the binding matrix

Zinc Oxide-Eugenol-Based sealers

Commercial names Tubli-Seal (SybronEndo), Pulp canal sealer (SybronEndo), Roth’s cement, Proco-sol

Rickert’s formula based (silver containing)

• The earliest sealers were made by dissolving gutta-percha in solvents like chloroform and was termed ‘chloropercha’. These sealers had problems resulting from shrinkage. Rickert’s formula was developed in 1931 as an alternative to the chloropercha technique.

Composition

• The silver was added for its radiopacity and germicidal qualities. It has excellent lubricating and adhesive qualities, and sets in about half an hour. However the silver content caused discoloration of tooth structure. Pulp canal sealer is based on Rickert’s formula.

Grossman’s and Roth’s formula based (Silver free ZOE sealers)

• This includes most current ZOE sealers. In 1958, Grossman introduced a nonstaining ZOE cement as a substitute for Rickert’s formula. This formulation is considered standard by which other cements are measured because it reasonably meets most of Grossman’s requirements for sealers. Many current sealers are still based on Grossman’s formula.

Composition

Therapeutic sealers

• The first formaldehyde containing sealer was introduced by Sargenti in 1954 (also called Sargenti’s Paste). These sealers constantly release antimicrobial formalin. Formalin is highly cytotoxic.
• Therapeutic sealers contain antibiotics, bactericidal and anti-inflammatory agents. Bactericidal agents include formaldehyde and iodoform. Antiinflammatory agents include hydrocortisone, prednisolone, etc.

Commercial names

• Formaldehyde containing – N2/RC2B, SPAD, Riebler’s paste (drug combination consisting of zinc oxide, barium sulfate, formalin and resorcinol), etc.
• Corticosteroid containing – Endomethasone, Endofill, etc.

Composition

Advantages

• Good antibacterial effect.
• Good anti-inflammatory effect.

Disadvantages

• Irreversible damage to the nerve tissue.
• Causes coagulation necrosis of the tissues.

Epoxy Resin – Based Sealers

• Commercial names Diaket, AH-26, AH Plus (Dentsply), Adseal.

Diaket

• Diaket was introduced by Schmidt in 1951. During setting, a resin-reinforced chelate is formed between zinc oxide and diketone. It has a high resistance to absorption.

Advantages

• Good adhesion.
• Sets quickly in the root canal.
• Low solubility and good volume stability.
• Superior tensile strength.

Disadvantages

• It is highly toxic.
• It is nonresorbable and forms fibrous encapsulation if extruded into the periapical tissues.

AH-26

• AH-26 was introduced by Schroeder 1957. It is an epoxy resin based sealer. It is a powder-liquid system.

Composition

Manipulation and setting

• AH 26 powder and resin are mixed to produce a root canal filling material. As it sets traces of formaldehyde are temporarily released, which initially makes it antibacterial. It is not sensitive to moisture and will even set under water.
• However, it will not set in the presence of hydrogen peroxide. It sets slowly, in 24 to 36 hours. It has strong adhesive properties.

Disadvantages

• Slight contraction while setting.
• Delayed setting.
• Staining.

AH- Plus

• AH Plus is an epoxy-amine resin based two paste root canal sealer. Epoxy paste contains radiopaque fillers.

Composition

• Epoxide paste contains bisphenol-A and F as epoxy resin, calcium tungstate, zirconium oxide, silica and iron oxide pigments and
• Amine paste contains dibenzylediamine, aminoadmantace, tricyclodecane-diamine, calcium tungstate zirconium oxide, silica and silicone oil.

Advantages over AH-26

• Less toxic.
• New amines added to maintain the natural color of the tooth.
• Half the film thickness.
• Better flow.
• Four-hour working time.
• Eight-hour setting time allows for corrections of fillings.
• Increased radiopacity.

Epiphany Root canal Sealer

• Epiphany as described earlier is a dual cure, hydrophilic resin obturating material/sealer system.

Calcium Hydroxide Based Sealers

Dentists have been using calcium-based chemicals in clinical practice for over a century. Calcium hydroxide was introduced to endodontics by Herman in 1920 for its pulp-repairing ability. In endodontics, it is mainly used for pulp-capping procedures, as an intracanal medicament, in some apexification techniques, and as a component of several root canal sealers.

The two most important reasons for using calcium hydroxide as a root-filling material are stimulation of the periapical tissues in order to maintain health or promote healing and secondly for its antimicrobial effects. The exact mechanisms are unknown, but the following mechanisms of actions have been proposed.

• Calcium hydroxide is antibacterial depending on the availability of free hydroxyl ions. It has a very high pH (hydroxyl group) that encourages repair and active calcification. There is an initial degenerative response in the immediate vicinity followed rapidly by a mineralization and ossification response.
• The alkaline pH of calcium hydroxide neutralizes lactic acid from osteoclasts and prevents dissolution of mineralized components of teeth. This pH also activates alkaline phosphatase that plays an important role in hard tissue formation.
• Calcium hydroxide denatures proteins found in the root canal.
• Calcium hydroxide activates the calcium-dependent adenosine triphosphatase reaction associated with hard tissue formation.
• Calcium hydroxide diffuses through dentinal tubules and may communicate with the periodontal ligament space to arrest external root resorption and accelerate healing.

Setting of calcium hydroxide-based sealers in root canals

The setting time of calcium hydroxide-based sealers the root canal is dependent upon the availability of moisture. The setting reaction can progress very quickly even in canals which have been inadequately dried. The amount of moisture required for the setting reaction reaches the root canal by means of the dentinal tubules. The material begins to set at the apex, as dentin is thinnest in this region and the apical foramen admits additional moisture.

CRCS (Calciobiotic Root Canal Sealer)

CRCS is essentially a ZOE/eucalyptol sealer to which calcium hydroxide has been added for its called osteogenic effect.

CRCS takes 3 days to set fully in either dry or humid environments. It also shows very little water sorption. This means it is quite stable, which improves its sealant qualities, but brings into question its ability to stimulate cementum and/or bone formation. If the calcium hydroxide is not released from the cement, it cannot exert an osteogenic effect, and thus its intended role is negated

Sealapex

Sealapex is a zinc oxide based calcium hydroxide sealer containing polymeric resin. It is available as a two paste system.

Advantages

• Biocompatible
• Extruded material resorbs in 4 months
• Good therapeutic effect.

Disadvantages

• Long setting time.
• Absorbs water while setting and expands.
• Poor cohesive strength.

Apexit Plus

• Apexit Plus is a radiopaque, non-shrinking root canal sealer paste that is based on calcium hydroxide. It is available as a two paste system. It is used for the permanent obturation of root canals and it is suitable for use in conjunction with all obturation techniques involving gutta-percha.

Working and setting characteristics

• Long working time (over 3 hours at room temperature)
• Setting Time – 3–5 hours in normal canals. Up to 10 hours in extremely dry canals.

Advantages

• Excellent tissue tolerance.
• Durable sealing of the root canal due to the slight setting expansion.
• Its easy flowing composition allows the material to adapt well even to morphologically complicated canals.
• Convenient application (static mix syringe and intracanal tip).
• Better seal than that provided by Sealapex.

Glass Ionomer – Based Sealers

Commercial name Ketac-Endo

Advantages

• Biocompatible.
• Chemical bonding with the root dentine, hence strengthens the root.
• Less solubility
• Dimensionally stable.
• Less technique sensitive.

Disadvantages

• Extruded sealer is highly resistant to resorption (delayed resorption).
• Retrievability is difficult.

Silicon-Based Sealers

The silicon-based sealers are based on the polydimethyl siloxane system.

Commercial names RoekoSeal (Coltene) and Guttaflow (Langenau).

Composition

RoekoSeal – Polydimethylsiloxane, silicone oil, zirconium oxide.

Gutta flow – Polydimethylsiloxane, silicone oil, zirconium oxide, gutta-percha.

Properties

• Excellent flow properties and good spreadability.
• Contains nanosilver which prevent further spread of bacteria.
• Good adaptability and tight seal of the root canal.
• Flowable cold filling system.
• Solubility is virtually zero.
• Excellent radiopacity.
• The included nanosilver can also have a preserving effect in the canal. The chemical type and concentration of the silver does not cause corrosion or color changes in the GuttaFlow.
• A Gutta-percha containing silicone sealer expands slightly and thus leakage was reported to be less than the AH-26 over a period of 12 months.
• Very good biocompatibility with lower cytotoxicity than the AH Plus.
• More easily removed from the canals than a resin-based sealer.

Disadvantages

• Poor wettability of Gutta Flow
• Gutta Flow does not adhere chemically to the canal wall.
• Due to its viscosity, it is more likely to be extruded into the periapical tissue when placed under pressure.

Mineral trioxide aggregate (MTA)

• The first reported use of Portland cement in dental literature dates to 1878, when Dr. Witte in Germany published a case report on using Portland cement to fill root canals. At the time the material itself was relatively new as Portland cement was invented in 1824. Mineral trioxide aggregate (MTA) was first described in modern dental scientific literature in 1995. It was developed at Loma Linda University, California, USA, by Torabinejad and Dean White who subsequently obtained two US patents for this Portland cement-based endodontic material, which became known as mineral trioxide aggregate (MTA). Since then, over 20 patents have been issued in the USA and the EU for materials that include Portland cement for dentistry.
• The term mineral trioxide aggregate (MTA) was coined from the three oxides present in Portland cement namely, calcia, silica and alumina (CaO, SiO2 and Al2O3). Furthermore, the powder particles of cement are in aggregate form.

Indications

Mineral trioxide aggregate materials are indicated for various restorative, endodontic, and regenerative dental procedures.

• Vital pulp therapy (pulp capping and pulpotomy)
• Apexification
• Perforation repair (lateral and furcation)
• Root-end filling
• Internal bleaching
• Resorption repair
• As sealer and as obturating material (partial or complete).

Commercial names

The first commercially available product was a gray mineral trioxide aggregate, marketed as ProRoot® MTA (Dentsply). Subsequently for esthetic reasons a tooth-colored or white formulation of MTA was introduced (Dentsply) in 2002.

Currently Many MTA sealer formulations are available. These include Endo CPM Sealer (EGEO SRL, Argentina), MTA Obtura (Angelus, Brazil), MTA Fillapex (Angelus), Endocem MTA (Maruchi, Korea) and ProRoot Endo Sealer (Dentsply Maillefer, Switzerland).

Supplied as

• Powder and liquid form (e.g. ProRoot MTA)
• Two paste – base and catalyst in tubes (MTA Fillapex)
• Two paste – in plunger tubes as static mixing system (MTA Fillapex).

Composition

A wide variation in composition exists between the different products.

ProRoot MTA is calcium silicate-based endodontic sealer. The major components of the powder of are tricalcium silicate and dicalcium silicate, with inclusion of calcium sulfate (gypsum) as setting retardant, bismuth oxide as radiopacifier, and a small amount of tricalcium aluminate. Tricalcium aluminate is necessary for the initial hydration reaction of the cement.

Powder

Liquid

• The liquid component consists of viscous aqueous solution of a water soluble polymer to improve the workability.
• MTA Fillapex is a mineral trioxide aggregate-based, salicylate resin root canal sealer. It is designed to provide a high flow rate and a low film thickness for easy penetration of lateral and accessory canals. It contains 13% MTA and salicylate resin for their antimicrobial and biocompatibility properties. The working time is 23 minutes with a complete set time is approximately 2 hours. MTA Fillapex is a two-paste system and is provided in a 4 g static mixing syringe and 30 g tubes.
• CPM sealer The composition of CPM sealer after mixing is reported to be 50% MTA (SiO2, K2O, Al2O3, SO3, CaO, and Bi2O3), 7% SiO2, 10% CaCO3, 10% Bi2O3,10% BaSO4, 1% propylene glycol alginate, 1% propylene glycol, 1% sodium citrate, and 10% calcium chloride.
• MTA Obtura is a mixture of white MTA with a proprietary viscous liquid.

Difference between white and gray MTA

The difference between the gray and the white materials is the presence of iron in the gray material, which makes up the phase tetracalcium alumino-ferrite.

Comparison of MTA with portland cement

The similarity of MTA with Portland cement was reported in 2000. Further studies comparing the two showed the cements to have similar constituent elements. However, some differences were also noted. The prime difference between the two is the addition of radiopaque fillers to enable radiographic differentiation. Secondly, MTA manufactured for dental use have to pass FDA regulations to enable it to be used in humans, thus components considered harmful have to be eliminated or minimized.

Biological properties

When placed in the canal, it releases calcium activity and causes cell attachment and proliferation, increases the pH, modulates cytokines like interleukin (IL4, IL6, IL8, IL10), and hence causes proliferation, migration, and differentiation of hard tissue producing hydroxyapatite which aids in the formation of physical bond between sealer and MTA.

The polymer did not seem to affect the biocompatibility of the materials and the hydration characteristics were similar to those reported for MTA. Sealers based on MTA have been reported to be biocompatible, stimulate mineralization, and encourage apatite-like crystalline deposits along the apical- and middle-thirds of canal walls. These materials exhibited higher push-out strengths after storage in simulated body fluid and had similar sealing properties to epoxy resin-based sealer when evaluated using the fluid filtration system. Fluoride-doped MTA demonstrated stable sealing up to 6 months, and was significantly better than conventional MTA sealers and comparable to AH Plus. The study supports the suitability of MTA sealers in association with warm GP for root filling.

Manipulation

P/L Ratio The powder liquid ratio of MTA can vary according to its intended use. For use as a sealer a creamy consistency is preferred. For use in perforation repair a putty consistency may be preferred. P/L therefore ranges from 4 to 1 to 2 to 1.

Open a pouch of ProRoot MTA root repair material and dispense the powder onto a mixing pad. Liquid from the ampoule squeeze out onto the mixing pad next to the powder. Gradually incorporate the liquid into the cement with a plastic spatula.

Mixing time Mix the material with the liquid for about one minute to ensure all the powder particles are hydrated.

If needed (one extra ampoule is provided, sterile water can also be used), one or two drops of liquid can be added to make the material into a thick, creamy consistency.

Working time The ProRoot MTA root repair material will set over a period of four hours, but the working time is about five minutes. If more working time is needed, cover the mixed material with a moist gauze pad to prevent evaporation.

Setting time

Traditionally these materials generally have long setting times. Newer products currently being marketed have shorter setting times. Examples include Endocem MTA and Biodentine.

It has also been stated that the faster setting time is achieved by increasing particle size, adding calcium chloride to the liquid component, and decreasing the liquid content.

Chemistry and setting reaction

MTA sets through a hydration reaction when mixed with water.

MTA + water → calcium hydroxide + calcium silicate hydrate

When MTA is mixed with water a highly alkaline (pH 12) cement matrix comprising of calcium hydroxide and calcium silicate hydrate is formed. A setting expansion of 0.1% is seen which contributes to its sealing ability.

An acidic environment does not interfere with the setting of the MTA.

Properties

• Compressive strength It has been shown that once it is set, it has a compressive strength equal to IRM and Super EBA but less than amalgam. Compressive strength of MTA within 24 hours of mixing was about 40.0 MPa and increases to 67.3 MPa after 21 days. In comparison gray MTA exhibited greater compressive strength than white MTA.
• Setting Expansion Set MTA exhibits a low setting expansion of less than 0.1%.
• Radiopacity MTA is less radio opaque than IRM, amalgam or gutta-percha and has similar radiodensity as Zinc Oxide Eugenol. The mean radiopacity of MTA is 7.17 mm of equivalent thickness of aluminium, which is sufficient to make it easy to visualize radiographically.
• Solubility Although the set MTA shows no signs of solubility, the solubility might increase if more water is used during mixing. The set MTA when exposed to water releases calcium hydroxide is responsible for its cementogenic property.
• Marginal adaptation and sealing ability This property is most vital for any restorative material especially when used for root end filling, repair of perforations, pulp capping or pulpotomy procedures. Bates et al found MTA superior to the other traditional root-end filling materials. MTA expands during setting which may be the reason for its excellent sealing ability. According to Torabinejad et al MTA seals very superiorly and no gaps were found in any of the experimental specimen. However, amalgam, Super EBA and IRM exhibited gaps ranging from 3.8 to 14.9 microns. MTA has also proved itself to be superior in the bacterial leakage test by not allowing the entry of bacteria at the interface. MTA thickness of about 4 mm is sufficient to provide a good seal.
• Antibacterial and antifungal property Torabinejad et al reported that MTA shows no antimicrobial activity against any of the anaerobes but have some effect on five (S. mitis, S. mutans, S. salivarius, Lactobacillus and S. epidermidis) of the nine facultative bacteria. Since most of the flora in the root canal are strict anaerobic bacteria with few facultative anaerobes, MTA may not be beneficial as a direct antibacterial in endodontic practice. However, it can be proclaimed as an antibacterial agent only by virtue of providing a good seal and preventing micro leakage.
• Reaction with other dental materials MTA does not react or interfere with any other restorative material. Glass Ionomer cements or composite resins, used as permanent filling material do not affect the setting of MTA when placed over it. Residual calcium hydroxide may interfere with the adaptation of MTA to dentin thereby reducing its sealing ability either by acting as a mechanical obstacle or by chemically reacting with MTA. This may be important when calcium hydroxide is placed in the cavity in between the appointments prior to the placement of MTA.
• Biocompatibility Kettering and Torabinejad studied MTA in detail and found that it is not mutagenic and is much less cytotoxic compared to Super EBA and IRM. This supports the superiority of MTA over formocresol as a pulpotomy medicament. Genotoxicity tests of cells after treatment of peripheral lymphocytes with MTA showed no DNA damage. On direct contact they produce minimal or no inflammatory reaction in soft tissues and in fact are capable of inducing tissue regeneration.
• Tissue regeneration MTA is capable of activation of cementoblasts and production of cementum. It consistently allows for the overgrowth of cementum and also facilitates regeneration of the periodontal ligament. MTA allows bone healing and eliminates clinical symptoms in many cases. In animal studies, MTA produced cementum growth which was very unique compared to other root-end filling materials. Arens and Torabinejad reported osseous repair of furcation perforations treated with MTA. MTA showed good interaction with bone-forming cells. Investigations by Koh et al revealed that MTA offers a biologically active substrate for bone cells and stimulates interleukin production. MTA is also said to stimulate cytokine production in human osteoblasts.
• Mineralization MTA, just like calcium hydroxide, induces dentin bridge formation and is believed to be due to its sealing property, biocompatibility, alkalinity and other associated properties. Tricalcium oxide in MTA reacts with tissue fluids to form calcium hydroxide, resulting in hard-tissue formation in a manner similar to that of calcium hydroxide cement. In comparison the dentin bridge formed with MTA is faster, thicker with good structural integrity and more complete than with calcium hydroxide. MTA also proves to be better at stimulating reparative dentin formation and maintaining the integrity of the pulp.

Storage

• Powder form MTA pouches must be kept tightly closed and stored in a dry area to avoid degradation by moisture.
• ProRoot MTA root repair material must be placed intraorally immediately after mixing with liquid, to prevent dehydration during setting. Excess water will retard curing process. Excess moisture in cotton pellets should be held to a minimum. The area should not be irrigated after placement of the material.

Placement technique

• Using a rubber dam, debride the root canal system using intracanal instruments, and irrigate with NaOCI. Dry the canal with paper points and isolate the perforation.
• Obturate all the canal space, apical to the perforation.
• The material is prepared according to the manufacturers instruction. Using the carrier, dispense the material into the perforation site. Condense the material into the perforation site using a small plugger, cotton pellets or paper points. Confirm placement material with a radiograph. If an adequate barrier has not been created, rinse the root repair material out of the canal and repeat the procedure.
• Following satisfactory obturation. Take a moist cotton pellet (remove excess moisture) and place in the canal. Seal the access preparation with a temporary restoration for a minimum of four hours. After four hours, or at a subsequent appointment, use a rubber dam and examine the MTA. This cement should be hard. If not, rinse and repeat the application. When the material is hardened, obturate the remaining canal space. The ProRoot MTA root repair material remains as a permanent part of the root canal filling.

Endodontic Solvents

Endodontic treatment may not always be successful and failures may be seen on occasion. If retreatment is indicated, the old endodontic filling materials have to be removed to gain access to the canals. The various removal methods available are solvents, heat and mechanical instrumentation. Silver points are removed by grasping and pulling with a pair of pliers. Gutta-percha and resin-based obturating material removal is usually achieved by a combination of mechanical removal and chemical dissolution. However one must remember that the solvent must act on both the obturating material and sealer for effective cleansing of the canal of old material. Thus an endodontic solvent may be more effective for a particular material and not all. Materials often encountered in the canals include gutta-percha, resin-based sealers, silicone, zinc oxide eugenol and glass ionomer. Most solvents are cytotoxic and potentially carcinogenic and therefore has to be used with proper precautions.

Commonly used solvents for gutta-percha and sealers are

• Xylol or xylene
• Orange oil
• Chloroform
• Halothane
• Rectified turpentine
• Eucalyptol

Commercial names

• For resin-based sealers: Endosolv R (septodont)
• For zinc oxide based sealers: Endosolv E (septodont), DMS 4 (Dentsply).

Xylol or xylene

• Xylene is a colorless, sweet smelling but flammable liquid. Xylene is a petrochemical product and a widely used industrial solvent. Chemically it is an aromatic hydrocarbon mixture consisting of a benzene ring with two methyl groups [dimethylbenzene or C6H4(CH3)2]. Xylene exists in three isomeric forms—ortho, meta and para.
• It is one of the most effective solvents for gutta-percha and resin-based sealers like resilon.

Chloroform

• Chloroform (trichloromethane – CHCl3) is a colorless, sweet-smelling, dense liquid and is considered hazardous.
• It is an effective solvent for gutta-percha and resin based sealers like AH Plus.
• It is not effective for GIC based sealers like Ketac Endo. It has low solubility for CaOH based sealers (Apexit).

Halothane

• Halothane (2-bromo-2-chloro-1,1,1-trifluoroethane) is an inhalational general anesthetic. It is packaged in dark-colored bottles and contains 0.01% thymol as a stabilizing agent.
• It is an effective solvents for gutta-percha and resin-based sealers like AH Plus.
• It is not effective for GIC based sealers like Ketac Endo and ZOE sealers. It has low solubility for CaOH based sealers (Apexit).

Rectified Turpentine

• Spirit of turpentine (syn: oil of turpentine, wood turpentine) is a fluid obtained by the distillation of resin obtained from many trees other than the pines. It is an industrial solvent and paint thinner. Rectified turpentine is obtained by treating turpentine oil with sodium hydroxide, and redistilling. Medically it is used externally as a counterirritant.
• It is an effective solvents for gutta-percha especially if warmed to 70 °C.

Orange Oil Or D-limonene

• Orange oil is an essential oil extracted from the rind of an orange. It is composed of mostly (greater than 90%) d-limonene. D-limonene can be extracted from the oil by distillation. It was originally introduced as a general solvent and cleansing agent for the dental office.
• It is an effective solvent for zinc oxide eugenol sealers and an alternative solvent for thermoplastic gutta-percha.
• It has no effect on resin-based sealers like resilon.

Eucalyptol

• Eucalyptol (C₁₀H₁₈O) is a distillation product of eucalyptus oil. It is natural organic compound that is a colorless liquid with a fresh camphor-like smell and a spicy, cooling taste.
• Compared to the others it is a comparatively less effective solvent for gutta-percha. Its effect increases on heating.