Introduction

The main objective of root canal sealer is to provide a fluid tight seal between the root canal system and periodontium. Thus it’s the sealer which provides the fluid tight seal and gutta percha (GP) fills the core space. There are enough scientific evidences to prove that the root canal system is connected with the periodontium apically, laterally and furcally. Properly sealing of all these portals of entry to periodontium will lead to successful endodontic treatment. The better the seal, the better is the prognosis.

Ideal properties of root canal sealers [1, 2]

The ideal properties of root canal sealers can be classified as biological, physico-chemical and antimicrobial.

Biological- Sealer should be biocompatible, that is it should be well tolerated by the periradicular tissues, should not hamper tissue repair but should aid or stimulate regeneration. It should neither be mutagenic or carcinogenic.

Physico-chemical- It should provide excellent apical and lateral seal after setting. It should be dimensionally stable, easy to manipulate, have sufficient working time, non staining, radiolabel and can be removed easily if required.

Antimicrobial-Sealer should be bacteriocidal.

Types of root canal sealers-
Commonly used sealers are as follows

Zinc oxide – eugenol (ZOE) based cements-

These sealers are available in powder liquid form.  The basic ingredient of powder is zinc oxide .To increase radiopacity, silver and/or barium sulphate can be added to it. Silver used may cause staining. Liquid contains eugenol. [1]
E.g. Tubli-seal (Kerr manufacturing company), Tubli seal EWT (extended working time) Express.

Tubli-seal (Kerr manufacturing company)
Composition: It comes in base paste containing zinc oxide, oleo resin, bismuth trioxide, thymol iodide, oils and waxes. While the catalyst paste contains eugenol, polymerized resins and annidalin. [4]

Properties:

1. Cement hardens in about 2hrs at 37degree C.
2. Bismuth trioxide gives radiopacity without staining.
3. Setting reaction of ZOE mixture is chelation reaction. Eugenol being GP solvent, during setting it may soften the GP increasing it’s bonding to the sealer. These sealers show low bond strength to dentin (0.068Mpa) than to gutta percha (0.99Mpa).
4. ZOE cements provoke severe inflammatory reaction. Eugenol is the major cause of toxicity but zinc also shows cytotoxic effects.

Calcium hydroxide (Ca (OH)2) containing cements -

Ca (OH)2 is added to ZOE cement to reduce the irritating effect of eugenol and also to get its additional disinfecting, antibacterial and osteogenic effect. The bacterial growth is inhibited due to alkaline effect of Ca (OH)2. These sealers may stimulate sterile biological closure of the apical seal. They have very long setting time (3 days), low solubility shrinkage, and are radiopaque, biocompatible. [1]
E.g. Seal apex (Kerr manufacturing company), Apexit Plus (Ivoclar Vivadent).

Epoxy resin based sealers-

They are generally supplied in two paste form as one containing epoxide resin and other is amine paste. These sealers have advantages like more radiopacity, less solubility, slight or no shrinkage on setting, excellent adhesion property and tissue compatibility. Following are 2 examples that are studied in detail.

AH Plus (Dentsply)

AH Plus is the better version of AH26, in which the disadvantages of AH26 like tendency of discoloration and formaldehyde release are eliminated, retaining all it’s good properties. It is supplied in two pastes form. Now the auto mixing double barrel syringe is also available with adjustable intracoronal tips called AH Plus jet. AH Plus has relatively long working time about 4 hrs. [3]

Composition: Supplied in epoxide paste containing bisphenol-A and F as epoxy resin, calcium tungstate, zirconium oxide, silica and iron oxide pigments and amine paste containing dibenzylediamine, aminoadmantace, tricyclodecane-diamine, calcium tungstate zirconium oxide, silica and silicone oil.

Properties:

1. It is highly radiopaque, even in thin layers (13.6mm/mmAl), has low solubility irrespective of medium (appro.0.31%), very low shrinkage (appro.1.76%) and low linear expansion (appro.0.129 ± 0.08).Thus it‘s dimensional stability is good.
2. Finely ground calcium tungstate with an average particle size of 8µm and finely ground zirconium oxide with particle size of1.5µm gives AH Plus the film thickness about 26µm, which is in the range specified by ISO standards for root canal materials (should be below 50µm).
3. AH Plus has good adhesion to dentin and to gutta percha (about 4Mpa), which increases if EDTA is applied before sealing the canal and further increases to about 7Mpa after Er:YAG laser treatment of root canal.
4. Being slightly thixotropic, AH Plus has improved handling properties. AH Plus has flow of 36mm as per the ISO standards (>25mm).
5. It is a very biocompatible material without showing any toxicity.

Table 1 – Comparison of physical properties of Tubli Seal and AH Plus

Ez Fill (Essential Dental Systems)

Ez Fill [4] is available in powder/gel form along with bi-directional spiral. A double barrel syringe with mixing tips, Ez Fill Express is available for easy application.

Composition: It has non-eugenol base and epoxy/amine system, consists of bismuth oxide as a primary radiopacifying agent. It also contains zirconium dioxide, fumed silica and iron oxide. [7]

Properties:

1. It is very radiopaque, no shrinkage, in fact there is mild expansion, which                                            assures an intimate fit.
2. Due to hydrophobic nature, it is highly resistant to water degradation to ensure a long lasting seal.
3. It bonds chemically and physically to dentin and gutta percha, showing excellent adhesion properties
4. It is a very biocompatible material

It meets ADA specification No 57 and ISO 6876:2001(endodontic filling material) specification including physical properties such as flow, film thickness, dimensional stability and disintegration. [7]

Sealers which are not commonly used are as follows

Para formaldehyde cements

It mainly has zinc oxide, with para-formaldehyde, eugenol, phenyl mercuric borate, lead tetraoxide and corticosteroids. Para formaldehyde [1] is highly irritating and destructive to tissue; lead is toxic to human organs. Corticosteroids reduce postoperative pain. It has not been proved as a permanent disinfectant.  E.g. N2.

Glass ionomer based cements

Glass ionomer cements [2] have fluoride ion leaching property. They have chemical bond with dentin of canal wall and so have excellent adhesion property. They may bond to GP as polycarboxylic acid present may react with zinc component of the GP. E.g. Ketac Endo (3MESPE) – it shows stronger bond to dentin (0.74Mpa) than to the gutta percha (0.14Mpa). But these cements are not commonly used as they are very difficult to remove if required.

Application of sealer-

After canal cleaning and shaping, dentin has smear layer containing dentin, pulpal and bacterial debris. Conditioning solutions and/or weak organic acids are used to remove this layer off dentin surface to enhance the dentin and sealer bond strength. Solutions used are 17% aqueous EDTA, 5.25% sodium hypochlorite, 35% phosphoric acid, 10% polycyclic acid, 6% citric acid. Recently Er: YAG laser is used. [2]. 17% aqueous EDTA is found to be more effective and so is commonly used.

Methods of application of sealer

Commonly, sealers are used along with gutta percha points for obturation. Sealers can be carried and applied to the canal with help of gutta percha points, reamers, paper points, lentulo spiral and bi-directional spiral.
Flexible pluggers- The selected GP master cone is coated with sealer and carried to the canal. The canal wall is coated with sealer by pumping or simultaneously rotating movement in a counterclockwise direction of GP point.
Lentulo spiral- It has consistently spaced spirals which provide outstanding flexibility in distributing sealer evenly through the canal system. Apply sealer on to the tip of lentulo; advance it slowly to the apex running at slow speed. Avoid formation of bubbles in the material and overfilling of the canal. Withdraw lentulo very slowly still running at slow speed. After this gutta percha point is placed in pumping action. Lentulo spiral has tendency to push the sealer apically.
Bi-directional spiral- It has coronal grooved spirals directing apically carry the sealer in apical direction while the apical reverse spirals flows the cement in coronal direction simultaneously. The two independent flows of cement collide where the grooved spirals change the direction. At this point of collision the cement is forced to travel laterally filling the lateral canals or any other invaginations present. It allows coronal path of exit for the sealer preventing it going through the apex which is not possible with lentulo spiral. With it single gutta percha cone technique is used for obturation ensuring proper seal.

After sealing and obturating the canal properly all the excess cement and gutta percha is removed from the coronal portion of the tooth. Coronal seal is achieved by the filling with a core built up material.

Conclusion

ZOE based sealers have reasonably good properties but they release free eugenol which is very irritating to periapical tissues. Some modified cements which do not release free eugenol are now available. Ca (OH) 2 addition to the sealer does not reveal any great advantage. Para-formaldehyde cements are cytotoxic. Corticosteroid addition may suppress the immune response and may mask the inflammatory response of the periapical tissues. Glass ionomer based cements have chemical bonding with the canal dentin but have a weak bond with GP, leading to leakage. Also these sealers are very difficult to remove if necessary. Thus the epoxy resin based sealers being biocompatible and having good physical properties are the widely used root canal sealers.

Reference

1. Louis I. Grossman, Seymour Oliet, Carlos E. Del Rio, Endodontic Practice, Chapter 14, Obturation of the root canal, 255-259.
2. Zaki A. Malallah, The role of root canal sealer in successful endodontics, Bahrain Dental Society Newsletter, March 2006, Volume 1, 10-16.
3. URL www.dentsply.com Accessed on 15 April 2009.
4. URL www.edsdental.com Accessed on16 April 2009.
5. Richard Van Noort, Introduction to dental materials, Chapter 2, Endodontic materials, edition 2,174.
6. S. Al-Nazhan physical properties of root canal filling materials, Saudi Dental journal1989, Volume1-1, 27-29.
7. URL www.fda.gov/cdrh/pdf6 (k063856.007) Accessed on 17 April 2009.