Double seal

Introduction

Ultimate goal of root canal therapy is to conquer the complex root canal system by perfect

obturation.

Even after a three dimensional obturation of the system, coronal restoration may fail to provide a

perfect seal and may permit the movement of microorganisms or their toxins along the canal wall

to the periapical tissue, leading to the failure of the treatment.

It has been reported that the bacteria are capable of penetrating coronally into the root filled

canals leading to reinfection, which has been confirmed by many investigators.

Role of coronal seal

High success rates of endodontically treated teeth and the fact that root fillings per se are not leak

proof, the quality of the coronal restoration seems to be important in preventing bacteria from

corono-apical penetration.

Because no sealer cement or obturation technique consistently prevents percolation through the

canal, it is critical to maintain adequate coronal seal to prevent microleakage into the canal

space.

Over the years, various materials referred to as Intraorifice barriers have been sought by

investigators to prevent coronal micro leakage and help produce a secondary seal for obturated

teeth.

Various causes for coronal leakage are:

Delay in placing the coronal restorative material,

Dissolution of the restoration,

Inadequate thickness of the restoration,

Fracture of the tooth

Fracture of the restoration

The coronal restoration may also be affected by various chemicals like the intracanal

medicaments or bleaching agents used.

Materials used for coronal seal

These include Amalgam, Intermediate Restorative Material, Glass Ionomer, Composites, Cavit,

Resin bonded cements, Dental Adhesives, Super-EBA, TERM, Coltosol, White and Grey MTA.

All of the above materials have been examined individually except for Glass Ionomer,

Intermediate Restorative Material and Cavit which were examined in combination.

Double seal

It is technique of coronal seal using combination of materials to overcome the disadvantages of

each whilst utilizing the advantages of both.

Different Conventional restorative materials used in Double-seal technique as coronal

sealants:

1) Cavit over gutta-percha followed by IRM as the final seal

It involves placing cavit as deeper layer material inside the pulp chamber and access cavity. IRM

is then used as the outer material which is exposed to loading and the oral cavity.

This double layer functions in several ways:

The outer layer of IRM is an antibacterial agent

IRM is less soluble, wear is less and is stronger

The inner layer of cavit prevent any moisture from reaching the root canal system

The white color of IRM material is readily visible when the clinician needs to remove it at a

subsequent visit

IRM is also a cheaper material that is easily and quickly mixed and placed in the tooth

It sets quickly and therefore no waiting period after placement

2) Glass Ionomer Type II over gutta-percha followed by Light cure Composite Resin as the

final seal

This laminate or sandwich technique has been suggested primarily for decreasing

microleakage.

The combined ionomer-composite restoration provides a reliable chemical bond to dentin,

micromechanical bonding of the composite to ionomer surface, and an acceptable esthetic result.

3) Mineral Trioxide Aggregate over gutta-percha followed by Intermediate restorative material

as the final seal

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4) Mineral Trioxide Aggregate over gutta-percha followed by Glass Ionomer Type II as the

final seal

A study was conducted by Hardy et al using MTA for furcation repair showed a better seal when

a secondary seal was placed over MTA rather than when used alone.

5) Dycal over gutta-percha followed by Glass Ionomer Type II as the final seal

This combination is routinely used in direct and indirect pulp capping restoration procedures and

a double seal of glass ionomer successfully used for producing an optimal coronal seal.

Problems associated with individual material:

Composite:

Polymerization shrinkage and inadequate adhesion to cavity walls are problems with the

composites. Leakage in composites may also be attributed to the C-factor or configuration factor

of the root canals, which refers to the ratio of bonded to unbonded surfaces, which may increase

the polymerization shrinkage. Hence this might have contributed to the microleakage.

GIC:

The imperfect sealing of the GIC linings might be explained by their hydrophilic properties,

microgaps, and/or porosities. Initial bond strength to dentin of GIC is not strong enough to

withstand immediate loading stresses.

Chemically cured GIC has shown significant leakage in various microleakage studies by Arnold

et al, Alhadainy, Banomyong et al and Hardy et al

Also when GIC was used in thickness of 2mm as a coronal barrier, leakage was significantly

more when compared to a 4mm thickness in a study done by Barthel et al, owing to the

importance of different thickness of the material.

IRM:

Several studies have been carried out to evaluate the sealing ability of IRM and have shown

controversial results.

Arnold et al, Pisano et al, Barthel et al and Tselnik et al which have shown the poor sealing

ability of IRM, but is different with the studies by Jacquot et al, Imura et al and Zaia et al which

has shown IRM to possess better sealing abilities.

The poor sealing ability of IRM may be linked to the fact that powder and liquid have to be

mixed together to produce the paste to be inserted. This mixing is the cause of reduced

homogeneity. IRM seems to be more difficult to pack into an access cavity than other materials.

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