The effect of iodine-containing materials on the bonding strength of AH 26®

A study by Drs. Elya Bartanovsky, David Keinan, Joshua Moshonov, and Michael Solomonov encourages caution in the use of iodine-containing material, especially before obturation with sealer based on epoxy resin

Abstract

The purpose of this study was to examine the influence of iodine-containing irrigation solutions or dressings, or the addition of iodoform powder to AH 26® (Dentsply) on the bonding strength of AH 26.

The iodine-containing materials in endodontics showed good antibacterial and antifungal properties, as well as good penetration to the dentinal tubules. The remaining iodine can affect the quality of sealing by reducing the contact surface between the sealer and the dentin and also by interfering with sealer setting. A total of 100 freshly extracted human teeth were selected. The root canals were enlarged using GTÒ files to size 50 and taper 12% at the apex. The teeth were divided into four groups:

1. Control group – Canals were laterally compacted  with gutta percha using AH 26 as the sealer.
2. Iodoform powder group – Applying the same protocol, iodoform powder was added to AH 26 during preparation.
3. IKI group – Prior to obturation, the canals were irrigated with 5% IKI for 10 min.
4. Metapex™ (Meta Dental Corp.) group Canals were medicated with Metapex for 2 weeks, irrigated and laterally compacted using gutta percha and AH 26 as sealer.

All samples were kept in moist gauze for 1 week at 37ºC. Then, 3-mm thick root sections were made, and the shear strength between the gutta percha with the sealer and the dentin was measured. Our findings show that iodine-containing compounds reduce the bonding strength of AH 26. The addition of iodoform powder reduced the bonding strength to the greatest extent.

Introduction

One of the main goals of endodontic treatment is to heal or prevent apical periodontitis.1 In case of infection, the success of the treatment depends on the extent of bacterial elimination from the root canal system. This is mainly achieved through meticulous chemo-mechanical preparation of the canals, supplemented with antibacterial irrigation and intracanal antimicrobial medication between visits when required.2,3

Currently, calcium hydroxide is the most widely used dressing, and sodium hypo-chlorite is the most popular irrigant. However, total elimination of the microorganisms from the root canal system cannot be predictably achieved by applying the above-mentioned measures.4 Earlier studies showed the resistance of Enterococcus faecalis5 and Candida albicans6 to the irrigation solutions and dressings usually used in the course of endodontic treatment. The two microorganisms are  the most frequently found during retreatment or posttreatment of periodontitis.7 Furthermore, the efficacy of calcium hydroxide and sodium hypochlorite is influenced by dentinal tubule infection, and some microoganisms are able to penetrate tubules up to the CDJ.8

Therefore, clinicians have been searching for new and more efficient irrigants, dressings, and methods of elimination or at least maximum reduction of microorganisms from the root canal system, which consists of main, lateral, and accessory canals, isthmuses, and dentinal tubules.

One of the debatable points in endodontic treatment is the use of iodine-containing disinfectants such as IKI, povidone-iodine for irrigation and Metapex, Vitapex® (Neo Dental International Inc.), or ENDOFlas (calcium hydroxide mixed with iodoform) as intracanal medication.9 These iodine-containing materials have shown good antibacterial and antifungal properties.10 Moreover, they exhibit low cytotoxicity,11,12 and are fast acting.13 They also have a good penetration ability.14 However, due to this property they penetrate deep into the dentinal tubules, rendering complete cleaning of the root canal system of iodine impossible. The remaining iodine can affect the quality of sealing by reducing the contact surface between sealer and dentin, as seen, for example, with calcium hydroxide15 or by interfering with sealer setting, particularly if the canals are medicated between appointments.16

Many clinicians tend to mix known materials in an attempt to create new and better sealers. The addition of iodoform to AH 26 is one of the most popular do-it-yourself prescriptions and aims “to create a good sealer with prominent antibacterial properties.” However, the problem is that such modifications can affect the basic physical properties of the sealer material and decrease the quality of sealing.

Aim

The purpose of this study was to examine the effect of iodine-containing irrigation solutions, dressings, or the addition of iodoform powder to AH 26 on its bonding strength.

Materials and methods

A total of 100 freshly extracted human teeth comprising single-rooted premolars with one canal, upper incisors, and palatal roots of upper molars were used in this study. After extraction, all teeth were stored in moistened gauze. In the course of the chemo-mechanical preparation, the coronal and the middle-third of the canals were enlarged with GT NiTI 0.12 to size 50, and the apical third was manually prepared with SS instruments to MAF size 30-45. During cleaning and shaping, irrigation was performed using 10-15 ml of 2.5% NaOCl. Following instrumentation, the canals were irrigated for 1 minute with EDTA followed by 1 minute of NaOCl, and finally 1 minute of EDTA.17 Before obturation, all the canals were dried with paper points, until there was no visible sign of moisture.

The roots were randomly divided into four groups of 25 teeth each:

1. Control group – The canals were filled with gutta percha, using AH 26 and complementary gutta-percha points by lateral compaction with a NiTi finger spreader. Upon completion of obturation, a No. 4 Mashtou Plugger was used to add a vertical condensation component in the coronal third of the canals. The specimens were then sealed with temporary Coltozol (Weach company in all materials and instruments) filling.
2. Iodoform powder group – Using the same protocol, iodoform powder was added to the AH 26 in a 1:6.ratio during mixture of its components.
3. IKI 5% irrigation solution group – After chemomechanical preparation and smear layer removal, the canals were irrigated with 5% IKI for 10 minutes and then dried with paper points. The canals were filled with gutta percha and AH 26 using the lateral condensation technique as described above for the control canals.
4. Metapex group- After drying with paper points, the canals were medicated with Metapex, and the teeth were sealed coronally with Coltozol filling. After 2 weeks, the teeth were reopened, irrigated with NaOCl, and instrumented with an MAF one size larger than before. The canals were then irrigated for 1 minute with EDTA, followed by NaOCl and EDTA to remove the  smear layer18 and dried using paper points. The canals were filled with gutta-percha and AH 26 using the lateral condensation technique as described above for the control canals.

All samples were kept in moist gauze for 1 week at 37ºC, in order to get complete setting of the sealers. One week later, all the teeth were decoronated with a diamond bur just below the CEJ. The other cut was 3 mm below the CEJ in order to get 3 mm root slices.
The 3 mm thick slices were glued to a Plexiglas frame and placed in a perpendicular plane to the upper jaw of the Instron 3366 device. A modified pin was fixed to the upper jaw of the Instron 3366 device in order to test the bond strength between the obturated mass of gutta percha and sealer to the dentin walls. The upper pin penetrated freely without touching canal walls. Shear strength between the gutta percha with the sealer and dentin was measured. A T-test was used for statistical evaluation of the differences.

Results

The minimum and maximum shear strength values (in MPa) for all four groups are shown in Table 1. The differences between group 1 and group 2 and 4 were statistically significant (p < 0.05). There were also significant (p < 0.05) differences between group 2 and groups 3 and 4. The mean values are marked (Figure 1).

Discussion

The result of our study confirms that iodine-containing materials affect the sealer’s physical qualities. This magnitude of this effect is varied by different materials.

Tagger, et al.,18 developed effective model to measure the adhesion of endodontic sealers to the dentin surface. They used flat dentin slices placed in an Instron device with a chisel fixed to the upper moving jaw. In order to mimic more accurately the conditions in the root, we modified this model. We used 3-mm root slices in which the sealers contact the dentin of the canal walls, and we also used a 1-mm diameter pin, which was fixed to the moving jaw.

Clinicians have also been trying to add during the course of endodontic treatment more and more efficient irrigants and/ or dressing materials in order to eliminate microorganisms from the root canal system. Several studies have shown good results by using iodine-containing materials.19-22 However, the influence of those materials in the adhesive strength of the endodontic sealers was not studied. The concept of tight seal of the root canal space by endodontic sealers in order to prevent leakage is well established.23-25 Our study further encourages the prudent clinician to take care while using iodine-containing material. The greatest extent of reducing bond strength was found due to addition of iodoform to AH 26 powder, while irrigation with 5% IKI for 10 minutes had the weakest effect on AH 26 bonding strength. The accepted explanation for the reduced shear strength to some degree is due to reduced contact surface between AH 26 and the dentin wall15 due to remnants of the material. The different results may be explained by the dependence on the quantity of the iodine compound, its fluid, or particle form, and the duration of contact between the iodine compound and the dentin wall.

In addition, practitioners must be aware of a possible allergic reaction to iodine  compounds26,27 and the possibility of color changes in the tooth.28

Our findings serve as a basis for the following recommendations:

1. Iodoform powder should not be added to AH 26, because it strongly affects the bonding strength of the sealer.
2. Iodine-based antibacterial dressings should not be the first choice of treatment for endodontic infection.
3. The clinical implication of reduced bonding strength may result in increased microleakage leading to late failure.

Our results warrant further investigation of the influence of antibacterial iodine-containing irrigants and dressings on such known sealers as AH Plus® and members of the ZnOE group.

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