Department of Conservative Dentistry

Department of Conservative Dentistry

Retrograde Filling Materials

Retrograde Root Canal Filling Materials

Introduction

A retrograde root canal filling is done when the canal is poorly sealed from the surrounding tissues.The purpose of a root-end filling is to establish, as well as possible, a hermetic seal of all apical avenues in the tooth from the oral environment to the periradicular tissues.The following literature is a discussion of the various materials that have been used for retrograde filling. The main consideration regarding the materials being used as retrograde fillings is the fact that these materials come in very close contact with the periapical tissues.

A plethora of materials have been evaluated, with leakage, histocompatibility, and toxicitystudies, in an attempt to identify the "perfect" rootend filling material. To date none exists, and recommendations can only be made on what appears to be the best tolerated, clinically successful material. Therefore, the endodontic surgeon must be cognizant that the success of the procedure does not lie in the essence of the 'apical filling material used, and that this material will not compensate for lack of proper nonsurgical management of the root canalsystem. Inaddition, it must also be understood that lack of understanding of the materials to be used, coupled with their improper use, could contribute to ultimate failure on either a short- or longterm basis.

Ideal requirements of a root end filling material

According to Gartner and Dorn, a suitable root-end filling material should be

(l) Able to prevent leakage of bacteria and their by-products into the periradicular tissues

(2) Nontoxic

(3) Biocompatible with the host tissues

(4) Non carcinogenic

(5) Insoluble in tissue fluids

(6) Dimensionally stable

(7) Unaffected by moisture during setting

(8) Easy to use

(9) Radiopaque

(10) One might add it should not stain tissue (tattoo).

Materials used – properties and manipulation

The following list of materials have been identified as root-end filling materials in either scientific evaluation or clinical usage. The parameters of each material are discussed as to their acceptability and technique. A brief outlook on the manipulation of these materials is also given.

1) Gutta-percha.

2) Silver cones.

3) Amalgam.

4) Zinc oxide-eugenol.

5) Cavit.

6) Polycarboxylates.

7) Composites.

8) Zinc phosphate.

9) Gold foil.

10) Glass ionomers.

11) Miscellaneous materials.

Before going into the details of the various materials used for retro-grade filing, a small review of the root canal sealers that are used along with these materials inorder to provide an impervious seal at the apex is needed.

Root canal sealers

Root canal sealers, used in conjunction with a solidcore obturating material, are intended to cooperatively effect a fluid-tight or hermetic seal throughout the root canal system. To achieve this goal, and promote periradicular healing, the sealer must possess certain characteristics:

1. It is non-irritating,
2. It has a hermetic sealing ability with dimensional stability,
3. It is bacteriocidal or static,
4. It is insoluble in tissue fluids, and adheres to the dentinal surface.

These factors will have a direct bearing on the seal of the canal system subsequent to root-end resection and on the periradicular healing at the resected root face, with or without a root-end filling. Commercial sealers are generally grouped as

• Zinc oxide-eugenol based,
• Noneugenol based, and
• Therapeutic based.

Of importance in the first group is that residual eugenol that remains after sealer set can affect the sealer's properties or the periradicular tissue response.

Noneugenol based sealers use solvents, such as chloroform or eucalyptol, which have demonstrated toxicity in the initial stages of sealer set.

Therapeutic sealers contain materials such as iodoform, paraformaldehyde, or trioxymethylene, which are claimed to have therapeutic properties. However, this issue is highly controversial and clinical reports of adverse periradicular tissue response would tend to question the efficacy of these sealers. This is especially true when these sealers are used as the sole root canal filling material. Subsequent to resection in roots filled with these sealers, there is significant contact of these sealers with the periradicular tissues, which may resuJt in extensive tissue destruction, with or without a root-end filling.

Recently, calcium hydroxide based sealers have been developed. Thus far, evaluations of these materials have shown mixed results regarding both physical properties and tissue compatibility.

Initially, all sealers can cause tissue inflammationand cellular damage. The severity of the damage and its continuation appears to be related to the nature of the material, its physical properties, its setting time, and quantity or surface area of the material in contact with the tissues.

Gutta-Percha

Since gutta-percha is considered to be relatively nonresorbable and impervious to tissue fluid dissolution, its biocompatibility and physical adaptability to the root canal wall must be considered. The more effective an obturating material is in sealing the root canal system, and maintaining that seal, the more compatible it is likely to be.

Composition of the gutta-percha

Chemical analysis of currently available dental gutta-percha has revealed the following composition:

• Gutta-percha from 18.9 to 21.8%,
• Zinc oxide from 56.1 to 75.3%,
• Heavy metal sulfates from 1.5 to 17.3%,
• Waxes and resins from 1 to 4.1%.

Properties

Semi-solid filling materials such as gutta-perchashould have high rigidity, flexibility, and yield strength. Because of the need to have a material which can be readily condensed and adapted to the irregularities of the canal system, gutta-percha should also have a high percentage elongation and low resilience.

Mechanically, polymers such as gutta-percha are not perfectly elastic, but have both elastic properties and properties of viscous liquids. Therefore, these polymers are referred to as viscoelastic. Clinically, the importance of this viscoelastic property manifests itself during use in the root canal. Guttapercha requires a large, sustained force of condensation over an adequate period of time to deformplastically. The more it deforms, the more it will flow and adapt to the dentin wall, decreasing gaps in the gutta-percha-dentin interface.

The quality of the root canal treatment has a definite effect on the marginal adaptation of gutta-percha subsequent to resection only. However, this result appears to also be dependent on the type of gutta-percha, nature of the sealer used, the condensation technique, type of bur used for resection and operatorskill.

Placement and condensation of gutta-percha

As early as 1916 , the pulling of the gutta-percha through the resected root-end had been advocated to ensure maximum adaptation to the dentin walls. However, this technique has been shown to result in voids in the gutta-percha –dentin interface, as the gutta-percha tends to retract from the walls creating significant gaps at the interface. Most authors have recommended coronal condensation of the gutta-percha into the apicalthird of the canal and through the foramen, prior to removal of the excess material. This approach would tend to ensure a better gutta-percha-sealer adaptation to the dentin walls.

Use of solvents

Various solvent techniques have been advocated toenhance the adaptation of the gutta-percha to the apical portion of the canal prior to resection, to the root apex if no resection is anticipated, or to the resected root surface. Included in these approach has been the use of eucalyptol or chloroform and rosin to soften the gutta-percha cone prior to placement into the apical third of the canal or through the resected root end,or chloroform to soften and adapt the gutta-percha to the foraminal margins at either the natural apex or the resected root end. However, it has been shown that the material loses its dimensional stability as the solvent is evaporated from the mixture.

Type of instrument used for adaptation of gutta-percha

This includes burs, scalpels, spoon excavators, plastic instruments, and burnishers.No studies unequivocally substantiate the best instrument for gutta-percha removal at the apex and the quality of the adaptation appears to be operator dependent.

Temperature of instrument used to remove gutta-percha

This has been a topic of controversy for several years.For years the use of an arm to hot instrument was advocated to smooth or burnish the gutta-percha filling material.

In 1980 this technique was criticized by Tanzilli and coworkersin an SEM study by. They compared the use of a warm plastic instrument in a cutting or searing motion and a cold ball burnisher to adapt the gutta-percha at the resected root end. Discrepancies in the adaptation of the gutta-percha were identified under SEM evaluation. These findings and their subsequent interpretation, especially when compared to cold burnished gutta-percha,created consternation among endodontic surgeons. This was especially true because the cold-burnished gutta-percha appeared to have superior adaptation to both amalgam and gutta percha fills subsequent to root-end resection only. The concept of good marginal adaptation with heated sealed gutta-percha had been challenged and this study was cited as the bench mark for future considerations in the management of apically resected gutta-percha.

SILVER CONES

Silver cones have been used to obturate root canals since the early 1930s. However, their ability to seal the root canal system three-dimensionally has been justifiably challenged, as the circular, tapered natured of the cone provides only a central core material which is surrounded by a sea of root canal sealer. This anatomic problem is accelerated subsequent to angled root-end resection, as large areas of sealer are visible between the cone and dentin wall. These gaps can be especially wide in teeth with wide buccal-lingual canals or which exhibit extensive fins or cul-de-sacs along the facial or lingual anatomy of the canal.

Placement of silver cone

Few reports exist in the dental literature whichaddress the use of a silver cone as the apical filling material at the time of periradicular surgery.

Contemporary studies using silver cones at the time of root-end resection have identified a low level of long-term success and recommend a more bio-compatible material.

In addition to the strong potential for voids and leakage to exist between a resected silver cone and dentin wall, corrosion of the metal-worked cone looms as a major factor for continued periradicular tissue irritation and ultimate failure of resected silver cone cases.

The silver content of the silver cones range from 99.8 to 99.9%, silver salts and sulfur sulfides formed by the contact of the metal-worked or contaminated silver cones have been demonstrated due to extensive corrosion, with pitting and cratering of the cones. However, the tissue cytotoxicity of these corrosive silver salts (silver chloride, silver carbonate, and silver oxide) and sulfur sulfides has been questioned.

The endodontic surgeon should consider the following guidelines concerning silver cones, root-end resection, and root-end fills.

1)Silver cones cannot three-dimensionally obdurate the root canal space, especially in areas coronal to the apex which are likely to be exposed during resection.

2) Resection of a root end containing a silver cone will open voids between the cone and dentin wall.

3)Resection of a silver cone will cause the material to be metal-worked, accentuating its corrosive potential. Over long periods of time, the corrosive products that form may be highly cytotoxic.

4) Silver cones cannot be burnished to "perfect" the apical seal.

5) Ideally, teeth containing silver cones and requiring surgery should be nonsurgically retreated,if possible prior to surgery, removing any silver corrosion products from the root canal system and replacing the silver cone with a well condensed gutta-percha and root canal sealer fill.

6)A root-end fill is indicated in all cases of root-end resection when a silver cone is present. When cutting a root-end preparation into the resected root containing a silver cone, establish a good finger rest, use high-speed burs, and frequently irrigate the surgical area. Careful cutting is recommended to prevent slipping off the silver cone and gouging or perforating the root surface.

AMALGAM ALLOYS

One of the first reports of placing a root-end amalgam fillingsubsequent to resection is attributed to Farrar.

Controversies and concerns

The main controversies and concerns regarding the use of amalgam:

1)Type of amalgam (high copper versus conventional; zinc versus nonzinc) and its properties.

2)Leakage of amalgam root-end fills and the use ofcavity varnish, including setting expansion and contraction;

3)Tissue compatibility;

4)Preparation and manipulation of the amalgam;

5)Electric potentials - galvanic currents, corrosion and degradation; and

6)Pigmentation or agyria of the surrounding tissues.

It is essential that the endodontic surgeon have aworking knowledge of the properties of amalgam alloys to enhance the potential for successful treatment.

Type of amalgam

Many of the early reports on the use of amalgam forroot-end fills did not specify the nature of amalgam used, while some authors specified the use of copper or silver amalgam. At that time copper (>40% Cu) amalgam was

identified as a tissue irritant and, as the popularity of silver (<6% Cu) amalgam increased, it was rapidly identified as the root-end filling material of choice. Recently, there hasbeen a trend to use high copper-content (>6% Cu) amalgams among mixed reports of varied cellular and tissue responses , and advanced mechanical properties.

Root-end amalgams leak.

Key factors which interact with the discrepancies cited include

• The mean leakage observed and its alteration with time ;
• The standard deviation from the mean leakage observed ;
• The depth of the amalgam ,
• The amount of amalgam corrosion and
• Expansion anticipated (conventional amalgam versus high copper amalgam; zinc versus nonzinc);
• Manipulation of the alloy during preparation and placement ;
• The placement of the alloy in the canal prior to resection versus its use as a root-end fill only ;
• The cleanliness and seal of the root canal system coronal to the root-end fill ; and
• The use of cavity varnish

Endodontic research has identified a significant improvement inthe initial seal of root-end amalgams when a cavityvarnish is used .The useof two coats of varnish to seal not only the walls of the root-end preparation but also the cut dentinal tubules at the root surface has received substantialsupport.

Material preparation and manipulation

The preparation and manipulation of the amalgam alloy at the time of placement is crucial in determining amalgam strength, marginal adaptation,degree of porosity, surface smoothness, and the nature of surface constituents.

However, the ultimate mechanical characteristics will be dependent on the type of alloy chosen and operator management. Some key points to consider relative to alloys placed intraorally are as follows:

1) Amalgams squeezed of their excess mercury have a decrease in their final strength.The Eames 1: 1 ratio technique or that described by Jorgensen and Saito are preferable.

2) Instructions supplied by the manufacturer for trituration should be closely followed. In addition, amalgamators vary considerably in function and performance due to warm-up time, age, changes in line voltage, and changes in capsule weight. Therefore, in an attempt to minimize variations, mixes of amalgam heavier than two spills should be avoided, and single-speed amalgamators or variable-speed amalgamators of a newer design should be used . Also, it has been noted that the setting rate of high copper dispersed phase alloys is more sensitive to varied mixing speeds than spherical alloys.

3)Amalgams are more closely adapted to the confines of the cavity during mechanical rather than hand condensation; however, the use of mechanical condensers may be limited. In addition, the condensation method has a direct bearing on the ultimate leakage demonstrated for both tin-mercury containing and non tin-mercury-containing alloys.

4)Alloys consisting of spherical, or mostly spherical, particles are more fluid under condensation ressures; and the use of a large condenser in a lateral fashion may be desirable because a small head condenser tends to force the amalgam mass away from the areas of condensation. Also, less pressure is required to properly condense these alloys .

5) The high copper-content alloys have been reported to be less susceptible to the variances in operator manipulation .

6)The optimal structure for the amalgam margins can be obtained by overfilling and burnishing of the margins, and removal of the excess by carving. Burnishing of the alloy margins decreases microporosity, improves the marginal adaptation and seal, especially with admixed alloys.

Carving is necessary after burnishing, followed by burnishing to render the surface smoother, thereby discouraging formulation of small corrosion cells on the surface.

The time frame for clinical management of the alloy, including marginal finish, may be reduced or impaired when pressures; and the use of a large condenser in a lateral fashion may be desirable because a small head condenser tends to force the amalgam mass away from the areas of condensation. Also, less pressure is required to properly condense these alloys. The high copper-content alloys have been reported to be less susceptible to the variances in operator manipulation .

Electric potentials - galvanic currents

The placement of a root-end amalgam in a toothwhich has a metallic post or crown restoration couldcreate a galvanic couple, which has the potential togenerate significant amounts of electrical currents.

Tissue staining – argyria

The possibility of argyria subsequent to root-endresection and/or root-end amalgam fillings stemsfrom multiple sources .

1)Amalgam scattered in the surgical site. During placement of the root-end filling.