Endodontic Materials

This article presents a review of materials currently used in the practice of endodontics. Current endodontic materials include those that have been thoroughly tested by scientific investigation, clinical usage, and time, as well as others that are the result of new knowledge in the field of dental materials. Article sections are devoted to obturation materials, sealers, irrigation materials, smear layer removal, root-end filling materials, and intracanal medicaments. Knowing the particular qualities of materials can aid the clinician in choosing those that are appropriate for a given situation. Properties, components, and rationale for the materials’ use are presented to aid the clinician in choosing materials for a particular need.

Current endodontic materials include those that have been thoroughly tested by scientific investigation, clinical usage, and time, as well as others that are the result of new knowledge in the field of dental materials. Knowing the particular qualities of materials can aid the clinician in choosing those that are appropriate for a given situation. Conversely, knowing the outcomes of clinical usage of materials can aid research into developing new and better endodontic materials. This continuum of research, development, use, and outcomes gives promise of new materials to meet existing needs.

Obturation materials

Gutta percha

Gutta percha is the most common root filling material in use today. This is interesting, because it is one of the oldest dental materials currently being used. The history of gutta percha goes back much earlier than its introduction into dentistry in the late nineteenth century. It is thought that in a 1656 book, John Trandescant, an Englishman, was referring to gutta percha when he wrote about “mazer wood,” a pliable material that could be warmed in water and formed to different shapes .

In 1843, Dr. Jose D’Almeida of Singapore presented specimens called gutta percha to the Royal Asiatic Society of England. This rediscovery of gutta percha, with its property of being pliable when warmed and of stable dimensions in cool water, led it to be used as the first successful insulation material for underwater telegraph lines in 1848 . The 1850s found gutta percha being used for an amazing array of items, including thread, surgical instruments, garments, gloves, pipes, pillows, maps, tents, and carpets. Golf balls made of gutta percha were widely used and referred to as “gutties” until the 1920s.

The fascination with gutta percha in manufacturing was short-lived, in part because of the property that made it popular initially. Its plasticity at slightly elevated temperatures allowed it to be formed into a myriad of products, but they lacked dimensional stability with changes in temperature. Also, vulcanization of rubber, a natural isomer of gutta percha, gave a product of considerably more dimensional stability, and a usable alternative to gutta percha. Only its use in golf balls and in dentistry survived into the twentieth century.

The introduction of gutta percha into dentistry is credited to Dr. Asa Hill, a Connecticut dentist. As a result of a search for a plastic restorative material, he produced a mixture of gutta percha and carbonate of lime and quartz as “Hill’s Stopping” in 1847 . It became a widely used restorative material. In 1867, Dr. G.A. Bowman reported using gutta percha to fill root canals. By 1887, S.S. White was manufacturing gutta percha points.

Gutta percha is produced from the juice of trees of the sapodilla family, which are indigenous to Malaysia, Indonesia, and Brazil. Natural rubber and gutta percha are polymers of the same monomer, isoprene (C 5 H 8 ), with rubber being the cis isomer and gutta percha the trans isomer ( Fig. 1 ). In 1942, C.W. Bunn reported that the crystalline phase of gutta percha could exist in two forms: (1) alpha phase, and (2) beta phase . The alpha phase is the naturally occurring form of gutta percha from the tree. If this is heated above 65°C, it melts into an amorphous form. If the amorphous material is cooled very slowly (0.5°C per hour) it recrystallizes into the alpha phase. If the amorphous material is cooled faster, it recrystallizes as the beta phase.

Fig. 1
Isomers of isoprene.

The beta phase of gutta percha is used in commercially prepared dental gutta percha for endodontic use. By weight, dental gutta percha contains only about 20% gutta percha. Zinc oxide comprises about 75% of dental gutta percha. The remaining components are various combinations of metal sulfates (for radiopacity) along with waxes and resins . The precise percentages of the components of a company’s dental gutta percha are usually proprietary secrets, but as a group, dental gutta percha is about one fourth organic (gutta percha, waxes, resins) and three fourths inorganic (zinc oxide, metal sulfates).

Gutta percha cones are usually supplied by the manufacturer after having been sterilized by irradiation. For chairside sterilization, cones can be placed in 5.25% sodium hypochlorate (NaOCl) for 1 minute . Gutta percha can be dissolved by organic solvents such as chloroform, halothane, and xylene.

Gutta percha alone cannot hermetically seal a canal, because it has no adhesive qualities. It requires a sealer to provide a seal of the canal-gutta percha interface. Gutta percha is often applied to a canal with some type of condensation pressure. This may be with a lateral condensing force applied with a spreader, or a vertical condensing force applied with a plugger. Both methods are designed to give better adaptation of gutta percha to the anatomic intricacies of the canal system; however, it has been shown that gutta percha cannot be truly compressed, but is compacted when pressure is applied .

Prolonged storage of gutta percha cones results in the cones becoming brittle, especially if exposed to air, light, and elevated temperature. This is thought to be caused by oxidation of the cones, and possibly from conversion of the beta crystalline phase to the naturally occurring alpha crystalline phase . Refrigeration of gutta percha can extend the shelf life.

The biocompatibility of gutta percha has been thoroughly tested through cytotoxicity, mutagenicity, implantation, and usage tests . The tests proved gutta percha to be biocompatible as a root filling material. In comparison to endodontic sealers, gutta percha shows less toxicity.

Resilon

Recently, a new material has been introduced that brings dentin bonding technology to root canal obturation. The principle of chemically bonding the root-filling material to the canal wall appears to have great potential for improving both the apical and coronal seal of the canal.

Resilon (Resilon Research, LLC, Madison, Connecticut) is a thermoplastic synthetic polymer based on polymers of polyester containing bioactive glass and radiopaque fillers . The filler content is approximately 65% by weight. Resilon handles like gutta percha, and is available in the same variety of master cones and accessory cones. Also, Resilon pellets are available to use in backfilling with thermoplasticized techniques. Thus, Resilon can be used in the same obturation techniques as gutta percha. The sealer used with Resilon is Epiphany Root Canal Sealant (Pentron Clinical Technologies, Wallingford, Connecticut). It is a dual-curable dentin resin composite sealer. The matrix is a mixture of ethoxylated glycidylmethacrylate and Bisphenol A epoxy (Bis-GMA), urethane dimethacrylate (UDMA), and hydrophilic difunctional methacrylates. The total filler content is about 70% by weight, and is composed of calcium hydroxide, barium sulfate, barium glass, and silica. A canal filled with this system is said to create a “mono-block” , in which the Resilon bonds to the Epiphany sealer, which in turn bonds to the dentin wall.

As with other dentin bonding systems, etching and priming of the dentin surface is required to achieve a chemical bond. Instructions for using the Resilon system include rinsing with 17% ethylenediaminetetraacetic acid (EDTA) to remove the smear layer, followed by Epiphany Primer, a self-etch primer containing sulfonic acid terminated functional monomer, hydroxethyl methacrylate (HEMA), water, and polymerization initiator. Then, the Epiphany Root Canal Sealant is applied to the canal followed by the Resilon core. After the canal is obturated, light curing for 40 seconds will cure the coronal 2 mm of the canal, and self-curing of the remainder of the canal will occur in 15 to 30 minutes . Retreatment of Resilon-filled canals is possible, because the material can be softened and dissolved by chloroform.

Some in vitro tests have shown the Resilon system superior to gutta percha/sealer in leakage testing, whereas others have shown no significant difference. In a dog model, Shipper and colleagues found less apical periodontitis associated with teeth filled with the Resilon system than those filled with gutta percha/sealer. An in vitro test showed increased resistance to fracture for teeth filled with the Resilon system compared with those filled with standard gutta percha techniques.

Some concern has been raised regarding the potential for alkaline or enzymatic hydrolysis of the polymer in Resilon, and the success of dentinal bonding in the confines of the root canal system . These and other in vitro and clinical usage and success studies are sure to be evaluated for this obturation system.

Sealers

To provide a fluid-tight seal of the canal space, a sealer is required along with the core obturating material. Because of this, the sealer has as much or more importance than the core material in providing a successful clinical outcome. Grossman described a number of properties that would be found in an ideal sealer. Although no sealer possesses all these properties, some have more than others. Grossman’s criteria are outlined in Table 1 .

Table 1
Properties of and criteria for an ideal sealer
Properties Criteria
Should be tacky when mixed to provide good adhesion between it and the canal wall when set. The sealer should adhere to the obturating material, usually gutta percha, when placed in the canal, and should adhere to the canal wall with its irregularities to completely fill the canal space.
Should make a hermetic seal. The core material itself does not provide an adhesive seal to the canal wall. To create and maintain a fluid-tight seal of the canal is a prime requirement of a sealer.
Should be radiopaque. The sealer should contribute to the radiopacity of the root filling for visualization on radiographs and evaluation of obturation of lateral canals and apical ramifications.
Should not shrink upon setting. Any shrinkage of the sealer would tend to create gaps at the dentin interface or within the core material, compromising the seal.
Should not stain tooth structure. Components of sealer should not leach into dentin leading to coronal or cervical discoloration of the crown.
Should be bacteriostatic, or at least not encourage bacterial growth. This property is desirable, but increasing the antibacterial qualities of a sealer also increases its toxicity to host tissues.
Should set slowly. A sealer must have ample working time to allow for placement during obturation and adjustment in the case of immediate post-space preparation.
Should be insoluble in tissue fluids. Stability of sealer when set is a prime factor in maintaining a hermetic seal over time. This is compromised if fluid contact causes dissolution of the sealer.
Should be tissue-tolerant. Biocompatibility of the sealer promotes periradicular repair. Most sealers tend to be more tissue-toxic in the unset state and considerably less toxic when fully set.
Should be soluble in a common solvent. To allow for retreatment or post-space preparation, the sealer and the core material should be removable. This can be facilitated by using a solvent.
Data from Grossman L. Endodontic practice. 11th edition. Philadelphia: Lea and Febiger; 1988. p. 255.

Although no sealer meets all properties of Grossman’s ideal sealer, there are many sealers available that are clinically acceptable and widely used. They can be classified into the general groups of zinc oxide-eugenol–based, polymers, calcium hydroxide-based, glass-ionomer, and resin-based.

Zinc oxide-eugenol–based sealers

These sealers have a long history of successful use, and have been the standard against which many newer sealers have been measured. Based on zinc oxide powder mixed with eugenol, numerous proprietary variations have been applied to these basic components to enhance various qualities of the sealer, such as dentin adhesion, reducing inflammation, or antibacterial action.

Grossman’s formula (non-staining), introduced in 1958, is an industry standard for zinc oxide-eugenol sealers . The components of the powder, listed below, are mixed with eugenol to form the sealer:

  • Zinc oxide 42%

  • Staybellite resin 27%

  • Bismuth subcarbonate 15%

  • Barium sulfate 15%

  • Sodium borate 1%

The resin component is added to increase the adhesive quality of the sealer. Also, the resin can react with zinc to produce a matrix-stabilized zincresinate that decreases the solubility of the sealer . Barium sulfate increases radiopacity. The proportion of bismuth subcarbonate to sodium borate regulates the working and setting times of the sealer. A number of zinc oxide-eugenol sealers are variations from this original formula.

The setting reaction of the sealer is by formation of zinc eugenolate crystals embedded with zinc oxide. Free eugenol is present as the material sets and decreases as the setting process continues. It is the free eugenol that contributes most to the cytotoxicity of freshly mixed, unset sealer.

All zinc oxide-eugenol sealers have ample working time, but will set faster in the presence of body temperature and humidity than on a mixing slab. Smaller particle size of the zinc oxide component will increase the setting time. Longer and more vigorous spatulation while mixing will decrease setting time .

Calcium hydroxide-based sealers

Several sealers have been marketed that contain calcium hydroxide as part of a zinc oxide-eugenol or epoxy material. These sealers were developed with the idea of taking advantage of the biocompatibility and possible bioactivity of calcium hydroxide when placed adjacent to vital tissue in pulp caps or apexification; however, to be effective in this respect, calcium hydroxide must dissociate into calcium and hydroxyl ions. For this to occur, it would require the sealer to break down or dissolve to some degree. If dissolution of the calcium hydroxide component occurred, the likelihood of the sealing ability being compromised would increase.

There are no objective data to show that calcium hydroxide-based sealers possess the biologic effects associated with calcium hydroxide paste. The short-term sealing ability of the sealers has proved adequate , but questions about long-term stability remain .

Polymer-based sealers

Epoxy resins and a polyketone compound are examples of polymers used as endodontic sealers. The epoxy resin materials show good handling characteristics and adhesion to dentin , but significant toxicity in the unset state . Interestingly, after 24 hours, the epoxy sealer has one of the lowest toxicities of endodontic sealers .

The polyketone sealer is a resin-reinforced chelate formed between zinc oxide and diketone . The material has a tacky consistency, that while providing good adhesion to dentin, contributes to its somewhat difficult handling characteristics. The solubility is low , but cellular toxicity has been shown to be elevated .

Glass-ionomer sealers

Glass-ionomer sealer has the advantage of chemically bonding to dentin. This offers the potential of improving the seal and possibly strengthening the root against fracture. Some studies have shown that canals obturated using gutta percha with glass ionomer sealer were more resistant to fracture than when other sealers were used , whereas other studies showed no difference .

Glass-ionomer materials tend to show good biocompatibility . The glass-ionomer sealer is viscous and has a shorter working time than many other sealers. Because of its hardness and relative insolubility in gutta percha solvents, retreatment can be more difficult .

Sealers

To provide a fluid-tight seal of the canal space, a sealer is required along with the core obturating material. Because of this, the sealer has as much or more importance than the core material in providing a successful clinical outcome. Grossman described a number of properties that would be found in an ideal sealer. Although no sealer possesses all these properties, some have more than others. Grossman’s criteria are outlined in Table 1 .

Table 1
Properties of and criteria for an ideal sealer
Properties Criteria
Should be tacky when mixed to provide good adhesion between it and the canal wall when set. The sealer should adhere to the obturating material, usually gutta percha, when placed in the canal, and should adhere to the canal wall with its irregularities to completely fill the canal space.
Should make a hermetic seal. The core material itself does not provide an adhesive seal to the canal wall. To create and maintain a fluid-tight seal of the canal is a prime requirement of a sealer.
Should be radiopaque. The sealer should contribute to the radiopacity of the root filling for visualization on radiographs and evaluation of obturation of lateral canals and apical ramifications.
Should not shrink upon setting. Any shrinkage of the sealer would tend to create gaps at the dentin interface or within the core material, compromising the seal.
Should not stain tooth structure. Components of sealer should not leach into dentin leading to coronal or cervical discoloration of the crown.
Should be bacteriostatic, or at least not encourage bacterial growth. This property is desirable, but increasing the antibacterial qualities of a sealer also increases its toxicity to host tissues.
Should set slowly. A sealer must have ample working time to allow for placement during obturation and adjustment in the case of immediate post-space preparation.
Should be insoluble in tissue fluids. Stability of sealer when set is a prime factor in maintaining a hermetic seal over time. This is compromised if fluid contact causes dissolution of the sealer.
Should be tissue-tolerant. Biocompatibility of the sealer promotes periradicular repair. Most sealers tend to be more tissue-toxic in the unset state and considerably less toxic when fully set.
Should be soluble in a common solvent. To allow for retreatment or post-space preparation, the sealer and the core material should be removable. This can be facilitated by using a solvent.
Data from Grossman L. Endodontic practice. 11th edition. Philadelphia: Lea and Febiger; 1988. p. 255.

Although no sealer meets all properties of Grossman’s ideal sealer, there are many sealers available that are clinically acceptable and widely used. They can be classified into the general groups of zinc oxide-eugenol–based, polymers, calcium hydroxide-based, glass-ionomer, and resin-based.

Zinc oxide-eugenol–based sealers

These sealers have a long history of successful use, and have been the standard against which many newer sealers have been measured. Based on zinc oxide powder mixed with eugenol, numerous proprietary variations have been applied to these basic components to enhance various qualities of the sealer, such as dentin adhesion, reducing inflammation, or antibacterial action.

Grossman’s formula (non-staining), introduced in 1958, is an industry standard for zinc oxide-eugenol sealers . The components of the powder, listed below, are mixed with eugenol to form the sealer:

  • Zinc oxide 42%

  • Staybellite resin 27%

  • Bismuth subcarbonate 15%

  • Barium sulfate 15%

  • Sodium borate 1%

The resin component is added to increase the adhesive quality of the sealer. Also, the resin can react with zinc to produce a matrix-stabilized zincresinate that decreases the solubility of the sealer . Barium sulfate increases radiopacity. The proportion of bismuth subcarbonate to sodium borate regulates the working and setting times of the sealer. A number of zinc oxide-eugenol sealers are variations from this original formula.

The setting reaction of the sealer is by formation of zinc eugenolate crystals embedded with zinc oxide. Free eugenol is present as the material sets and decreases as the setting process continues. It is the free eugenol that contributes most to the cytotoxicity of freshly mixed, unset sealer.

All zinc oxide-eugenol sealers have ample working time, but will set faster in the presence of body temperature and humidity than on a mixing slab. Smaller particle size of the zinc oxide component will increase the setting time. Longer and more vigorous spatulation while mixing will decrease setting time .

Calcium hydroxide-based sealers

Several sealers have been marketed that contain calcium hydroxide as part of a zinc oxide-eugenol or epoxy material. These sealers were developed with the idea of taking advantage of the biocompatibility and possible bioactivity of calcium hydroxide when placed adjacent to vital tissue in pulp caps or apexification; however, to be effective in this respect, calcium hydroxide must dissociate into calcium and hydroxyl ions. For this to occur, it would require the sealer to break down or dissolve to some degree. If dissolution of the calcium hydroxide component occurred, the likelihood of the sealing ability being compromised would increase.

There are no objective data to show that calcium hydroxide-based sealers possess the biologic effects associated with calcium hydroxide paste. The short-term sealing ability of the sealers has proved adequate , but questions about long-term stability remain .

Polymer-based sealers

Epoxy resins and a polyketone compound are examples of polymers used as endodontic sealers. The epoxy resin materials show good handling characteristics and adhesion to dentin , but significant toxicity in the unset state . Interestingly, after 24 hours, the epoxy sealer has one of the lowest toxicities of endodontic sealers .

The polyketone sealer is a resin-reinforced chelate formed between zinc oxide and diketone . The material has a tacky consistency, that while providing good adhesion to dentin, contributes to its somewhat difficult handling characteristics. The solubility is low , but cellular toxicity has been shown to be elevated .

Glass-ionomer sealers

Glass-ionomer sealer has the advantage of chemically bonding to dentin. This offers the potential of improving the seal and possibly strengthening the root against fracture. Some studies have shown that canals obturated using gutta percha with glass ionomer sealer were more resistant to fracture than when other sealers were used , whereas other studies showed no difference .

Glass-ionomer materials tend to show good biocompatibility . The glass-ionomer sealer is viscous and has a shorter working time than many other sealers. Because of its hardness and relative insolubility in gutta percha solvents, retreatment can be more difficult .

Irrigation materials

Thorough irrigation of the canal system during instrumentation is an essential part of the process of rendering the canal system free of tissue, bacteria and bacterial products, and dentinal debris. This creates an environment favorable to successful obturation, and ultimately to clinical success.

Sterile saline

Sterile saline has been recommended by some as an endodontic irrigant. It has the advantage of biocompatibility over other irrigants, and Baker and colleagues concluded through scanning electron microscope (SEM) evaluation that the type of irrigant used was not as important as the volume used in terms of removing canal debris. Using saline as an irrigant relies totally on the physical flushing action of irrigation to remove debris. It has none of the tissue-solvent or antibacterial effects that are beneficial in an endodontic irrigant.

Sodium hypochlorite

The most common endodontic irrigant for many years has been sodium hypochlorite (NaOCl). Its first reported use in modern medicine was in 1915, when Dakin recommended a 0.5% solution of NaOCl for debridement of infected wounds.

NaOCl has a broad-spectrum antimicrobial effect, and is capable of killing bacteria, spores, fungi, and viruses. Concentrations varying from 1% to 5.25% are commonly used, and proponents of each concentration claim effective antimicrobial properties . Used clinically, it is important to replenish NaOCl frequently, because its antimicrobial properties rely on free chlorine from dissociation of NaOCl, and this is what is consumed during tissue breakdown . In small canals or canal ramifications, if NaOCl cannot contact the microbes, the antimicrobial effect is compromised. This is probably why in vivo antimicrobial tests of NaOCl do not always replicate in vitro results. In vitro studies have shown concentrations from 1% to 5% will kill any organism isolated from the root canal, but in vivo, the success of NaOCl depends on canal preparation to remove gross debris and to enlarge the canal so that the NaOCl can penetrate to the apical part of the canal.

NaOCl is usually supplied as a 5.25% solution. The tissue-solvent and antimicrobial effects are increased with elevated temperature, and Cunningham found equal efficiency with 2.6% or 5.25% solutions at 37°C. The effectiveness also increases as the pH is decreased, but at pH less than 9, NaOCl becomes unstable and toxicity of vital tissue is increased . For stability, commercially available NaOCl is buffered to a pH of 11 to 12.5.

Sodium hypochlorite is capable of dissolving tissue as well as the predentin layer of dentin. Some studies have shown better necrotic tissue solvent effects with 5.25% concentrations , whereas others show no difference with concentrations down to 1% . Time of usage and contact time play a part in the solvent effects of NaOCl, so in the clinical setting with NaOCl in the canals for upwards of an hour, it is likely the lower concentrations perform acceptably. Gutta percha cones can be decontaminated by soaking for 1 minute in 1% NaOCl, or for 5 minutes in 0.5% .

Irrigation with NaOCl must be done with care not to inject the solution past the apical foramen into the periradicular tissues. The caustic effects of NaOCl in such an incident are manifested with severe pain, periapical bleeding, and almost immediate swelling . Slow irrigation, light pressure, and use of a non-binding needle will prevent such an occurrence.

Chlorhexidine

Chlorhexidine gluconate, a bisguanide, is an antibacterial material that has attracted attention as an endodontic irrigant. Chlorhexidine in a 0.2% solution has been widely used as an oral rinse for plaque control, whereas a 2% solution is more commonly used as an endodontic irrigant. The antibacterial quality of chlorhexidine raises its potential as an irrigant, but it has no ability to dissolve tissue remnants as NaOCl does. This could contribute to a decreased overall cleaning ability of chlorhexidine when used during endodontic instrumentation. Yamashita and colleagues found the use of 2% chlorhexidine resulted in inferior cleaning of canals when compared with 2.5% NaOCl or 2.5% NaOCl/EDTA. Clegg and coworkers , in an in vitro study, assessed the ability of chlorhexidine and various concentrations of NaOCl to disrupt a polymicrobial biofilm on hemisections of root apices. They found 2% chlorhexidine incapable of disrupting the biofilm, whereas 6%, 3%, 1% NaOCl and 1% NaOCl/MTAD disrupted the biofilm.

Chlorhexidine may not be suitable as a sole irrigant in endodontics, but may be a valuable adjunct to the use of NaOCl. Even though chlorhexidine is less effective against gram-negative than gram-positive bacteria , it is a gram-positive bacterium, Enterococcus faecalis , that is often found in persistent endodontic infections of previously root-filled teeth . Dametto and colleagues compared the antimicrobial activity of 2% chlorhexidine gel, 2% chlorhexidine liquid, and 5.25% NaOCl against E faecalis -infected canals immediately after instrumentation and 7 days after instrumentation. The chlorhexidine gel and liquid were significantly more effective than NaOCl in maintaining low colony forming units of E faecalis at 7 days. Oncag and coworkers also found more residual antibacterial effects for 2% chlorhexidine than for NaOCl. This effect could be caused by the affinity of chlorhexidine to dental hard tissues leading to a persistent antibacterial action . Because of this dentin affinity and the efficacy of chlorhexidine against E faecalis , Zehnder and Stuart and colleagues have suggested using chlorhexidine as a final rinse after canal instrumentation with NaOCl or as an intracanal medicament.

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Jun 15, 2016 | Posted by in Dental Materials | Comments Off on Endodontic Materials
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