Effect of Doxycycline on the Apical Seal of the Retrograde Filling Materials

Rahmat A. Barkhordar, DMD and Thomas Russel, DMD

Copyright 1998 Journal of the California Dental Association.

In this study, we examined the effect of doxycycline hydrochloride (DH) on apical seal. Results indicated that teeth that were retrofilled with IRM or amalgam following doxycycline irrigation had significantly less dye penetration (p<0.05). Due to its antimicrobial activity, smear layer removal ability, and improvement of apical seal, doxycycline solution may be used as an irrigant.

Tetracyclines have several properties of interest to endodontists and other dentists. They are antimicrobial agents, effective against periodontal pathogens, and concentrate in gingival fluid at levels four times higher than in blood.¹ These antibiotics bind strongly to root surfaces and when released are still biologically active.² Release of tetracyclines from root surfaces provides a sustained level of antimicrobial agent at the site of periodontal ligament diseases.³

This class of antibiotics has also been shown to inhibit mammalian collagenases. Inflammatory diseases such as periodontitis include a pathological excess of tissue collagenases which may be blocked by tetracyclines, leading to enhanced formation of collagen and bone formation.⁴ Doxycycline, a hydroxy derivative of tetracycline, is the most potent anticollagenase antibiotic among commercially available tetracyclines,⁵ and is also relatively more potent against most periodontal pathogens.^6,7

Root surfaces in periodontal pockets undergo subsurface bacterial contamination of cementum and dentin.⁸ As a result, root surfaces accumulate endotoxin⁹ and exhibit collagen loss, which may suppress fibroblast migration and proliferation on contaminated cementum,¹⁰ affecting periodontal regeneration. Root surface conditioning with acidic agents such as tetracyclines removes smear layer and surface contaminants, such as endotoxin,¹¹ At the same time, surface demineralization widens the orifices of dentin tubules¹² and exposes the cementum collagen matrix, stimulating fibroblast attachment and growth.¹³ Monocyte production of resorptive cytokines in response to diseased cementum has been shown to be potently inhibited by tetracyclines.¹⁴

Instrumentation of dentin leads to accumulation of a smear layer¹⁵ covering the dentinal surface and occluding the dentinal tubules, thereby reducing the permeability of dentin.¹⁶ Smear layer contains organic materials including dentinal debris, odontoblastic processes, and blood cells, and consequently, bacteria may penetrate and colonize it.¹⁷ Smear layer also presents a variable interface between a dental material and dentin and prevents filling materials from directly contacting dentin and penetrating dentinal tubules.¹⁸ Because smear layer prevents adaptation of a filling material to the dentinal wall, the seal provided by the material is affected.

Removal of smear layer seems desirable in the situation of apical retrofills, where a filling material is placed in a bacterially contaminated root apex in order to obtain an adequate seal to the root canal, and thereby promote healing. Tetracyclines have been shown to remove smear layer from root surfaces and from within root canals.¹⁹

Doxycycline may be a useful agent in surgical root canal treatment. The present study was designed to assess in vitro the effect of irrigation with doxycycline HCl on the apical seal of retrograde fillings.

Materials and Methods

Sixty human extracted incisors were selected, autoclaved and stored in distilled water. The crowns were removed prior to any evaluation. The root canals were cleaned and shaped to the apex with K files (Kerr, USA) up to #60, rinsed with hypochlorite and obturated with warm gutta-percha and Kerr Root Canal Sealer (Kerr, USA). The apical 2 mm were resected, and a retrofill preparation was made to the depth of a #331 bur (S.S. White, USA). The roots were divided into 6 groups of 10 roots. The apical cavities in Groups 1- 3 were irrigated with saline as a control. The cavities in Groups 4-6 were irrigated with doxycycline HCl, 100 mg/ml. For both irrigants, 10 retrograde cavities were filled with warm gutta-percha using a Touch-N-Heat (Analytic Technology, USA), 10 with Tytin amalgam (Kerr, USA), and 10 with IRM (Caulk, USA).

The treated roots were then stored in a humidor for seven days. The roots were air-dried and painted with two coats of nail polish, except for the apical area. The roots were immersed in 1 percent methylene blue dye for 24 hours. The roots were then sectioned longitudinally, filling materials were removed, and degree of dye penetration measured in a dissecting microscope equipped with a micromeasure grid (magnification x10). The dye penetration was measured from the cavosurface into the root canal system, in millimeters. The mean results were statistically evaluated by a Student-Newman-Keuls test and ANOVA.

Results

Amalgam and IRM retrofills allowed significantly less leakage than gutta-percha for both control and experimental groups. Each retrofill material allowed significantly less dye leakage when preceded by doxycycline irrigation. The results show that the best seal in this study was obtained by IRM and amalgam following doxycycline HCl irrigation (p<0.05) (Fig. 1-2). The results for these two materials were not significantly different.

Figure 1. Example of apical dye penetration of specimen irrigated with a saline and retrofilled with:
A Gutta-percha	B Amalgam	C IRM
Figure 2. Example of apical dye penetration of specimen irrigated with doxycycline-HCl and retrofilled with:
A Gutta-percha	B Amalgam	C IRM

Discussion

Improved apical seal of retro-fillings has been pursued vigorously in an effort to improve the clinical results of apical surgery.²⁰

The results of this study show significantly superior apical seal with IRM and amalgam when preceded by irrigation of the retro-prep with doxycycline HCl. This may be due to the previously demonstrated ability of tetracyclines to remove smear layer from dentinal surfaces in a time dependent manner.²¹ The removal of the loosely attached smear layer from the cavity surfaces with subsequent opening of dentinal tubules and demineralization of dentin, creates a retentive surface for interlocking of restoratives,²² which may be responsible for the improved apical seal seen in this study.²³ The results of this study agree with those of Jodaikin and Austin who found that removal of smear layer with EDTA reduced dye leakage around amalgam restorations.²⁴

Smear layer removal from resected root ends and dentin demineralization by another acidic agent, citric acid, has been shown to be associated with more rapid and complete cementum deposition on the root end. This in turn promotes more rapid dentoalveolar healing.²⁵ Tetracycline and citric acid have been shown to produce comparable morphological changes on root surfaces26 and therefore would be expected to have similar efficacy in promoting healing after apical surgery. Unlike citric acid, however, doxycycline is also a potent antibiotic. The long lasting substantivity of doxycycline HCl on root surfaces supports the concept of using resected root surfaces as a substrate for the deposition and slow release for local doxycycline delivery²⁷.

The present study has demonstrated that irrigation with doxycycline significantly improved the apical seal of two retrofill materials. It shows promise as an adjunct to endodontic therapy, but further studies are needed to evaluate the in vivo efficacy of doxycycline in endodontic systems.

Authors / Rahmat A. Barkhordar, DMD is an associate professor in the Department of Restorative Dentistry at the University of California, San Francisco. Thomas Russel, DMD, is a clinical assistant professor in the Department of Restorative Dentistry at the University of California, San Francisco.

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To request a printed copy of this article, please contact / Rahmat A. Barkhordar, DMD, Associate Professor, Department of Restorative Dentistry, University of California, San Francisco, 707 Parnassus Avenue, San Francisco, CA 94143-0758