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Table of Contents   
ORIGINAL ARTICLE  
Year : 2013  |  Volume : 16  |  Issue : 3  |  Page : 213-218
Microleakage of adhesive resinous materials in root canals


UCLA School of Dentistry, Los Angeles, California, USA

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Date of Submission06-Sep-2012
Date of Decision08-Oct-2012
Date of Acceptance29-Jan-2013
Date of Web Publication4-May-2013
 

   Abstract 

Aim: The purpose of this study was to compare the in vitro micro-leakage resistance of adhesive resin materials to long-used zinc oxide-eugenol and epoxy resin sealers.
Materials and Methods: Seven materials, five test (Real Seal, Real Seal XT, Panavia F 2.0, Infinity Syringeable, GCEM) and two controls (Tubliseal, AH Plus), were evaluated for micro-leakage resistance in a bovine incisor root model, with 12 roots per material. Teeth were root canal treated, stored in water, artificially aged by thermal-cycling, stained with silver nitrate, sectioned to yield eight measurement points per tooth (four coronal and four apical), giving 672 measurement points. Stain penetration was measured using digital positioners and a toolmakers microscope; then analyzed using descriptive statistics, two-way analysis of variance and multiple comparisons testing ( P < 0.05).
Results: All modern adhesive resinous materials leaked significantly less than long-used zinc oxide-eugenol and epoxy resin sealers ( P < 0.05). Mean leakage values and their associated (standard deviations) in mm were: Infinity Syringeable 2.5 (1.5), Real Seal XT 3.2 (1.4), Real Seal 3.4 (1.6), Panavia F 2.0 3.8 (2.7), GCEM 4.2 (1.8), Tubli-seal 5.4 (2.8), AH Plus 6.3 (2.3). Overall, more leakage occurred apically than coronally ( P < 0.0001). Many materials exhibited dimensional instability: Marked contraction, expansion, or lack of cohesion.
Conclusion: A variety of adhesive resinous materials, endodontic sealers and crown cements, reduced micro-leakage in comparison to long and widely used zinc oxide- eugenol and epoxy sealers.

Keywords: Adhesive; canal; leakage; resin; root; sealer

How to cite this article:
Wong JG, Caputo AA, Li P, White SN. Microleakage of adhesive resinous materials in root canals. J Conserv Dent 2013;16:213-8

How to cite this URL:
Wong JG, Caputo AA, Li P, White SN. Microleakage of adhesive resinous materials in root canals. J Conserv Dent [serial online] 2013 [cited 2019 Jul 15];16:213-8. Available from: http://www.jcd.org.in/text.asp?2013/16/3/213/111316

   Introduction Top


Exclusion of bacteria from the root canal system is a key factor in maintaining periradicular health. [1] Obturation should remove potential habitats for the growth of bacteria as well as preventing their ingress or egress through coronal or apical micro-leakage. Sealers should prevent leakage and be dimensionally stable. [2],[3],[4],[5],[6],[7] Leakage primarily occurs at the sealer-dentin interface, but it can also occur at the interface between the sealer and the obturating material, and even within the sealer and obturating materials. [4],[5],[6],[7]

Zinc oxide-eugenol based endodontic sealers have been used widely for more than a century. Epoxy resin endodontic sealers have also been widely used for several decades. Many studies have demonstrated that widely used sealers undergo considerable micro-leakage and have poor dimensional stability. [2],[3],[4],[5],[6],[7]

Modern adhesive resinous sealers have the potential to reduce leakage. The use of surface active monomers and low-viscosity oligomers facilitates superior physico-chemical wetting of dentin as well as penetration in to dentin tubules to achieve mechanical interlocking and tubule occlusion. Modern adhesive resin crown and bridge cements have dramatically reduced dentinal micro-leakage both in vitro and in vivo. [8],[9],[10] Inclusion of substantial amounts of inorganic filler substantially improved the mechanical stability of resinous materials. [11],[12],[13]

Unfortunately, resins shrink when they undergo polymerization, pulling away from dentinal surfaces. The problem of setting or polymerization shrinkage becomes particularly acute when sealers or cements have a large bonded surface area in proportion to the un-bonded free surface area available for stress relaxation, or what is called a high C-factor. [14],[15],[16] These root canal sealers are challenged by an exceptionally high C-factor, leading to residual stress or de-bonding. Furthermore, resinous materials that are lightly filled or poorly cross-linked can imbibe excessive amounts of water leading to expansion or disintegration.

Recent studies on one adhesive resinous sealer, and the prior success of resinous crown and bridge luting cements, suggest that modern resinous materials containing surface active monomers, low-viscosity oligomers, and inorganic filler may substantially reduce dentinal leakage, despite the inherent geometric challenges faced by root canal sealers. [4],[5],[6],[7],[9],[10]

Practical and ethical considerations have limited the measurement of leakage at the sealer-dentin interface in humans and the long-term clinical outcomes of new adhesive sealers. Unlike longitudinal clinical trials, laboratory tests can isolate a single variable and model specific material behaviors and failure modes that might take many years to manifest clinically or that could not be separated from other effects in vivo.

The purpose of this study was to perform a discriminatory and rigorous accelerated in vitro study to compare the micro-leakage resistance at the dentin-sealer interface of widely used zinc oxide-eugenol and epoxy resin sealers, to adhesive resinous sealing materials.


   Materials and Methods Top


The experimental model

An ex vivo root model was used to compare the leakage of established root canal sealers to modern resinous materials containing surface active monomers, low-viscosity oligomers, and inorganic filler. This test was designed to be extremely rigorous and focus upon the sealers themselves, rather than include the confounding effect of obturation materials.

Roots for micro-leakage testing

Bovine jaws were purchased from a slaughterhouse. Because the animals had already been slaughtered for human consumption, institutional review board approval was not required. Bovine teeth were selected because of ease in collection, standardization, known history, and the potential for future repeatability. Bovine root dentin has a microstructure, tubule density and diameter similar to human root dentin. [17],[18] The relatively large root canals purposefully accentuated any effects of volumetric change of the sealers. Teeth were extracted, periodontal tissue debrided, crowns removed to yield standardized roots of 20 mm in length, pulps extirpated, and canals cleaned and shaped with Hedstrom files, up to size 140 (Roydent Johnson City, TN, USA). Teeth were stored in a physiologic saline solution with the addition of thymol, an antiseptic that does not denature dentin. Teeth were kept moist at all times. Immediately before sealing, the canals were irrigated with sodium hypochlorite and ethylenediaminetetraacetic acid (EDTA) rinses to remove the dentinal smear layer. [19] Eighty-four caries-free, single canal bovine incisors were randomly assigned to six sealers, giving 12 teeth per sealer group.

Sealing materials

Seven different materials were included. Their constituents, as described by their manufacturers' material safety data sheets are listed in [Table 1]. Two well-studied and long-used endodontic sealers were used as controls: A zinc oxide-eugenol sealer (Tubli-seal, Sybron, Glendora, CA, USA), and a lightly filled epoxy resin sealer (AH Plus, Dentsply DeTrey, Konstanz, Germany).
Table 1: Materials used for sealing root canals

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Five modern adhesive resinous materials test were included. One of these was a new resin-composite root canal sealer (RealSeal, Sybron, Glendora, CA, USA), also distributed as Epiphany, SimpliFill, Innoendo, and Resinate. A prototype of a new material provisionally named RealSeal XT (Sybron, Glendora, CA, USA), based on components of both RealSeal and AH Plus, was included. Three adhesive crown and bridge luting cements were also included: Panavia F 2.0 (Kurraray, Okayama, Japan); Infinity Syringeable (Den-Mat, Santa Maria, CA, USA); and GCEM (GC, Tokyo, Japan). Infinity Syrinegable is very closely related to Geristore and Geristore Perio/Endo materials. All materials were used according to manufacturers' instructions; however, the crown and bridge luting cements were not recommended by their manufacturers for use as endodontic sealers; they were included in this study for the reasons outlined in the introduction.

Sealing of root canals

Root canals were dried using suction and paper points. Materials were injected in to their respective roots in bulk. In order to provide a rigorous test of the stability of the materials, gutta-percha was not used. Thus, the effects of dimensional change, polymerization shrinkage, swelling, water sorption, dissolution, lack of cohesion, and micro-gap formation were maximized. This study was designed to quickly and efficiently distinguish differences in micro-leakage resistance among sealers at the sealer-dentin interface.

Storage and artificial aging

Sealed teeth were let set for 10 min in air, 50 min in 100% humidity, and submerged in water for 4 weeks. This mimicked the gradual exposure of a dental material to the inherent moisture of dentin, periradicular tissues, and the oral cavity. Prolonged storage in water was used so that the sealers would have time to absorb water, dissolve, undergo hydrolysis, and shrink or swell before measurement of leakage. [11] Next, the sealed teeth were artificially aged by thermal-cycling for 1,000 cycles from 5°C to 55°C. [20] This provided mechanical stresses to the sealer-root interfaces by the differential expansion and contraction of tooth and sealer. [21] After artificial aging the sealed teeth were stored in water for three more weeks.

Staining

The teeth were dried and painted with nail varnish up to the coronal and apical edges to prevent lateral stain penetration through dentinal tubules. Teeth were submerged in a 50% silver nitrate solution for 1 h, then in developer (Rapid Access, Eastman Kodak, Rochester, NY) for another hour. [22] This turned the stain black so that it could be clearly visualized, and stopped further diffusion. This technique represented a rigorous and accelerated test because silver ions are much smaller than bacteria or their toxins and noxious by-products. This technique also facilitated measurement of leakage localized to the sealer-dentin interface; whereas other techniques may not distinguish among leakage at the sealer-dentin interface, leakage through the sealer and obturating material, and through tooth structure.

Sectioning and microscopy

Qualitative visual and microscopic examination of stored specimens was performed. Then teeth were sectioned longitudinally in the buccal-lingual plane at the mesial-distal midpoint. A slow speed saw with fine wafering diamond blade was used with water as a lubricant (Isomet, Buehler, Lake Bluff, IL, USA). This yielded 8 measurement points per tooth, 4 at the coronal and 4 at the apical ends, giving a total sample of 672 measurement points. Linear stain penetration, a continuous parametric variable, along the dentin-sealer interface was measured from the tooth end to the deepest point of dye penetration along the canal wall in a plane parallel to the long axis of the tooth; whereas, scoring systems are non-parametric and more subjective. A monocular toolmakers microscope (Unitron, Bohemia, NY, USA) at ×30 (Bausch and Lomb, Rochester, NY) and digital positioners (Boeckler Instruments, Tucson, AZ, USA) with an accuracy of 0.1 μm were used for examination of the set, aged, and stored sealers and for measurement of leakage. Qualitative examination of the sectioned sealers was performed.

Statistical analyses

Descriptive statistics, leakage means, and standard deviations (SD), were calculated for each sealer. Because a continuous parametric variable, length of stain penetration, was used a powerful parametric statistical approach was applied. Two-way analysis of variance (ANOVA) was used to determine whether, the two main effects of material type and root end influenced leakage (P < 0.05). In the event of differences being found, a-priori the Tukey multiple comparisons test was used to determine, which sealing materials differed from one another (P < 0.05).


   Results Top


Micro-leakage by sealers

Mean sealer leakage values and associated (SD) in mm were plotted in [Figure 1], and are listed as: Infinity Syringeable 2.5 (1.5), RealSeal XT 3.2 (1.4), RealSeal 3.4 (1.6), Panavia F 2.0 3.8 (2.7), GCEM 4.2 (1.8), Tubliseal 5.4 (2.8), AH Plus 6.3 (2.3). All sealers leaked, but a wide, two-fold, range was recorded. Significant differences in sealer type were revealed by ANOVA (P < 0.0001) [Table 2]. Multiple comparisons testing showed that all adhesive materials leaked significantly less than the long-used conventional zinc oxide-eugenol and epoxy resin sealers [Figure 1].
Figure 1: Micro-leakage by sealer type, means and standard deviations, in mm. Similar groups are linked by horizontal lines (P < 0.05); all other groups differed from one another

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Table 2: Two-way analysis of variance for leakage

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Micro-leakage by root end

The apical root end measurement sites recorded significantly more overall leakage than the coronal root end measurement sites (P < 0.0001) [Table 2] and [Figure 2]. This trend was found, to varying degrees, for each of the materials tested.
Figure 2: Micro-leakage by root end, means and standard deviations, in mm. The root ends differed from one another (P < 0.0001)

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Sealer stability

Overall, the materials designed for use as endodontic sealers exhibited more signs of instability than the materials designed for use as crown cements. The Infinity specimens tended to have fewer internal cracks, relatively small micro-gaps, and did not manifest visible dimensional change. The Real Seal specimens had small internal cracks, but had intruded at the coronal and apical root ends indicating substantial contraction. The RealSeal XT prototype material had moderate internal cracks, but did not manifest gross dimensional change. Panavia and G-Cem both had moderate amounts of micro-gaps and cracks throughout the sealer body, but did not manifest substantial overall dimensional change. Tubli-seal was porous, cracked, and had relatively large micro-gaps, but did not manifest substantial overall dimensional change. AH Plus had minor internal cracks, and had extruded beyond the coronal and apical root ends, substantially expanding.


   Discussion Top


Use of adhesive resin sealers may have the potential to reduce the rate of leakage and reinfection [Figure 1]. Consistent with prior leakage studies, all materials leaked [Figure 1]. [2],[5],[6],[7] The importance of protecting root canal treatments with durable leak-resistant coronal restorations must be emphasized. Although, the conditions of this study were purposefully designed to be rigorous, its duration was brief in comparison to the anticipated lifetime of an endodontically treated tooth.

The coronal root ends leaked less than the apical ends. This is attributable to increased coronal tubule density, and greater root wall thickness being less susceptible to the effects of thermal cycling. Another micro-leakage investigation reached the same conclusion, but attributed the difference to difficulty in removing apical smear layer. [5] However, the wide-canaled bovine teeth used in this current study were amenable to rinsing with sodium hypochlorite and EDTA.

The long-used conventional zinc oxide-eugenol and epoxy resin sealers leaked significantly more than all of the modern adhesive resinous materials. Zinc-oxide-eugenol materials are otherwise reserved for use as temporary restorative materials, where long-term leakage resistance may not be necessary. Lightly filled epoxy resins were briefly used as fissure sealants, but their poor adhesion and instability, manifested by high-loss rates, prompted their withdrawal from clinical use. [23] Both types of materials have remained in use as endodontic sealers where they are largely protected from the oral environment by coronal restorations. However, coronal restorations may not always provide adequate protection. Therefore, use of more leak-resistant sealers may provide important clinical benefit. The capacity of some resinous materials to reduce radicular dentin leakage was analogous to their success as crown and bridge luting cements [Figure 1]. [8],[9],[10]

The dimensional instability, an extremely undesirable property, of some sealers was consistent with prior studies. [2],[3] Swelling could lead to apical or coronal extrusion and potentially even to root fracture. Contraction could lead to de-bonding and void formation. Another widely used zinc oxide-eugenol sealer (Roth 801 Root Canal Cement, Roth International, Chicago, IL, USA) could not be measured because it failed to set, and continued to flow throughout the long duration of this study. Clearly, there is room for improving the dimensional stability of both conventional endodontic sealers and their potential alternatives.

This study focused upon leakage at the dentin-sealer interface. Leakage through radicular dentin is decreased by adhesive resin crown cements and dentin bonding agents, [10] but has not been extensively studied in the context of endodontic sealers.

Although, one new adhesive resin root canal sealer (RealSeal) has reached the marketplace. Further evolution may optimize the formulation of adhesive resin root canal sealers. A prototype of a derivative of this initial material (RealSeal XT) was included in this study. RealSeal exhibited net contraction suggesting that the effect of polymerization shrinkage dominated those of water sorption. Additional inorganic filler could provide increased stability; however, viscosity could be reduced. The spectrum of included filler sizes and particle shapes would influence handling properties and flow, as would the rate of polymerization. Interestingly, the material which leaked the least in this study was designed for use as a luting cement for crowns, not as an endodontic sealer. However, it has previously been used as an endodontic root end filling material and as a root defect repair material in both endodontic and periodontal therapies. [24],[25]

Despite the inherently unfavorable geometry, C-factor, of root canals, the new adhesive resinous materials sealed relatively well. Although, inclusion of gutta-percha cones or other obturating materials would decrease the amount of bulk sealer used and decrease the net shrinkage, it could actually make the C-factor even more unfavorable because the free surface area available for stress-relaxation would decrease in comparison to the bonded dentinal interfacial area. Therefore, inclusion of gutta-percha or other solid obturating materials might not decrease leakage. Prior work on sealer thickness has indirectly addressed the apparent paradox posed by the C-factor. [26] Clearly further investigation is needed.

Although, increased filler content increases stability and decreases leakage, it could render removal of sealer during retreatment more difficult. The crown and bridge cements would be very difficult to remove, if re-treatment was ever to be needed.

This investigation primarily measured leakage resistance, but this is only one of many factors influencing the choice of a root canal sealer. Clinical choices should be based on a broad range of tests and clinical evidence.


   Conclusions Top


A variety of modern adhesive resinous materials, including, endodontic sealers and several crown cements, reduced endodontic micro-leakage in comparison to long and widely used zinc oxide-eugenol and epoxy sealers in a rigorous in vitro test. Widely used endodontic sealers exhibited dimensional instability that included contraction, or expansion, as well as a lack of cohesion. For all materials, more leakage occurred apically than coronally.


   Acknowledgment Top


Sadly, our dear friend, colleague, mentor, and co-author Angelo Caputo passed away before this work was published. The authors appreciate donations of the sealers used in this study by their respective manufacturers.

 
   References Top

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2.De Moor RJ, De Boever JG. The sealing ability of an epoxy resin root canal sealer used with five gutta-percha obturation techniques. Endod Dent Traumatol 2000;16:291-7.  Back to cited text no. 2
    
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Correspondence Address:
Shane Newport White
UCLA School of Dentistry, CHS 23-010, Los Angeles, CA 90095-1668
USA
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0972-0707.111316

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    Figures

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    Tables

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