Journal of Conservative Dentistry

ORIGINAL ARTICLE
Year
: 2016  |  Volume : 19  |  Issue : 4  |  Page : 317--322

Expansion of Gutta-percha in contact with various concentrations of zinc oxide-eugenol sealer: A three-dimensional volumetric study using spiral computed tomography


Mahima Tilakchand, Abhishek Jain, Balaram Naik 
 Department of Conservative Dentistry and Endodontics, S.D.M. College of Dental Sciences and Hospital, Sattur, Dharwad, Karnataka, India

Correspondence Address:
Dr. Mahima Tilakchand
Department of Conservative Dentistry and Endodontics, S.D.M. College of Dental Sciences and Hospital, Sattur, Dharwad - 580 009, Karnataka
India

Abstract

Aim: The purpose of this study was to evaluate the three-dimensional expansion of Gutta-percha (GP), at various powder/liquid ratios, of a zinc oxide-eugenol (ZOE)-based sealer using spiral computed tomography (SCT). Materials and Methods: Thirty-five freshly extracted human mandibular premolars were selected for this study. Cleaning and shaping were performed in all the teeth initially with hand K-files up to #25 and finally with RaCe rotary instruments (25/06). Teeth were randomly divided into five groups of 7 teeth each. Specimens were scanned using SCT. They were then viewed both cross-sectionally and longitudinally, with a constant thickness of 1 mm/slice. The volume of root canal in each tooth was estimated. Obturation was performed by GP points (25/04) and ZOE-based root canal sealer in all groups with different powder-liquid ratio. Groups 1, 2, 3, and 4, had powder/liquid ratio of 1:1, 1:2, 1:3, and 1:4, respectively, while in the control group, no sealer was used. The obturation was performed by sealer coated single cone GP. A second SCT scan was performed to determine the volume of GP and sealer in all four groups 1 day after obturation. The third and fourth SCT scans were taken 7 and 30 days after obturation, respectively. The mean volume of GP per group was calculated. Data were statistically analyzed using one-way ANOVA. Inter-group comparisons were done using Scheffe post hoc multiple comparisons test. Results: All groups with sealer showed expansion of GP at both 7th day and 30th day, which was statistically significant from the GP volume at 1st day. Groups 2 and 3 with powder/liquid ratio of 1:2 and 1:3 gave the highest mean volume values during 30 days period and showed significant expansion in comparison with Groups 1 and 4 with powder/liquid ratio of 1:1 and 1:4, respectively. Conclusion: Increasing the ratio of eugenol in sealer resulted in the volumetric expansion of GP. However, further studies should be performed to confirm the expansion of GP, leading to the achievement of fluid impervious seal.



How to cite this article:
Tilakchand M, Jain A, Naik B. Expansion of Gutta-percha in contact with various concentrations of zinc oxide-eugenol sealer: A three-dimensional volumetric study using spiral computed tomography.J Conserv Dent 2016;19:317-322


How to cite this URL:
Tilakchand M, Jain A, Naik B. Expansion of Gutta-percha in contact with various concentrations of zinc oxide-eugenol sealer: A three-dimensional volumetric study using spiral computed tomography. J Conserv Dent [serial online] 2016 [cited 2019 Dec 6 ];19:317-322
Available from: http://www.jcd.org.in/text.asp?2016/19/4/317/186450


Full Text

 Introduction



One of the keys to successful root canal therapy is to adequately obturate the prepared root canal space. Root canal obturation aims to provide a complete filling of the root canal in all dimensions to create a fluid-tight seal to prevent ingress of bacteria and their toxins and their flow into periapical tissues.[1] The objective of root canal filling procedure, therefore, should be the total three-dimensional (3D) filling of the root canals and all the accessory canals. In everyday practice, too little emphasis was given to the paramount problem of eliminating the root canal system as an entity, by its total obturation, in spite of significant data which were produced, demonstrating astonishing failure in the absence of 3D filling.[2]

A hermetic seal cannot be obtained without the use of a sealer because Gutta-percha (GP) does not bond to dentin walls. In addition, the adhesion of a root canal sealer to both GP and to root dentin would be desirable in stabilizing the apical seal.[3] An ideal endodontic sealer should, in part, adhere firmly both to dentin and to GP. Differences in the adhesive properties of endodontic sealers may be expected, because their interaction with either dentin or GP may vary with their chemical composition.[3],[4] Zinc oxide-eugenol (ZOE) sealer firmly bonds to dentin and GP.[3] Setting reaction of ZOE mixture is a chelation reaction occurring with zinc ion of the zinc oxide. This reaction may also occur with the zinc oxide phase of GP, which ranges from 50% to 70% according to the manufacturer.[4] In addition, eugenol is a solvent of GP that may soften it during setting reaction and increase bonding of sealer to GP.[3]

Root canal fillings may be prone to bacterial penetration along their entire length. Dimensional changes of root canal sealers over time may introduce gaps and channels along the sealer/GP or sealer/dentin interface, channels which may be large enough to permit micro-organisms to pass along the spaces.[5],[6] Polymerization shrinkage of ZOE-based sealers can lead to stress development on root canal walls, resulting in marginal gaps, microleakage, and clinical failures. Forces of polymerization shrinkage can exceed its bond strength to root dentin, permitting debonding on one side of the root canal filling to relieve stress.[6]

With or without sealer, GP has a reduction in leakage over time, which indicated an increase in volume. This expansion of GP compensates for sealer dissolution, resulting in decreased leakage of the canal system.[7] Volumetric expansion of GP occurred in contact with eugenol thereby creating a better seal overtime.[8] The expansion is attributed to free eugenol released from ZOE-based sealer and contact time of eugenol with GP.[9]

It was thought that free eugenol component of freshly mixed ZOE sealer can seep out and cause various cytotoxic effects on gingival fibroblasts, periodontal ligament cells, and osteoblast-like cells.[10] However, it was found that leakage of eugenol into periapical tissues is very low, and it dramatically decreases over time.[11]

Spiral computed tomography (SCT) is a useful tool in 3D intracanal volume measurement without sectioning specimens,[12] as cross-sectional observation of structures that are difficult to visualize with conventional X-ray are possible with this method. SCT, a noninvasive technique gives a 3D interpretation at various levels. Use of SCT also avoids loss of material, yields reproducible results; the specimen can be used for further research and specific location of the voids can be determined accurately.[1] By the use of SCT, morphology of bone, teeth or root canals can be visualized and the effect of instrumentation on root canal morphology can also be assessed. SCT can show changes over time with respect to surface area and volume of the tissues.[13]

The purpose of this study was to evaluate the 3D expansion of GP at various powder/liquid ratios of ZOE-based sealer using SCT.

 Materials and Methods



Teeth selection

This study utilized 35 freshly extracted human mandibular premolars teeth, which were stored in saline solution. Collection, storage, sterilization, and handling of extracted teeth were according to the guidelines and regulations given by occupational safety and health administration.

The criteria for tooth selection were single root, single canal, no caries, and no developmental and morphological defects. Soft tissue remnants and calculus were removed. All specimens were checked for number and curvature of root and root canals clinically and radiographically. Teeth with single straight canals were chosen, whereas teeth with incompletely formed apices, calcified canals, fractures, or resorption were excluded.

Tooth preparation

The sample teeth were decoronated at cementoenamel junction (CEJ) to obtain standardization in all the groups. A #10 file was introduced in the canal until tip was visible at the root apex; working length was derived by subtracting 0.5 mm from the measured length. Teeth were mounted in wax blocks made of modeling wax. Cleaning and shaping were performed in all the teeth initially with hand K-files up to #25 and finally with RaCe rotary instruments (25/06) (FKG Dentaire Swiss Dental Products, La Chaux-de-fonds, Switzerland). About 2 ml solution of 5.25% sodium hypochlorite (Vensons, India) and 2 ml solution of saline was used as irrigant between each file size. Ethylenediaminetetraacetic acid (RC-Prep, Premier Dental, India) was used as the irrigant once complete biomechanical preparation was done followed by rinsing with saline.

Teeth were randomly divided into five groups of 7 teeth each. Specimens were scanned using SCT (Siemens AG, Munich, Germany). They were then viewed under high resolution both cross-sectionally and longitudinally, with a constant thickness of 1 mm/slice.

The area of prepared root canal in each slice was measured from CEJ to the apex of the root. The volume of root canal in each tooth was estimated with the aid of Syngo Software (Siemens AG, Munich, Germany).

Before obturation, root canals were dried with a #25 paper point. Obturation was performed by GP points (25/04) and a ZOE-based root canal sealer (RC Fill, Prime Dental Products, India) in all groups with different powder-liquid ratio, which was:

Group 1 - Powder/liquid ratio of ZOE sealer 1:1Group 2 - Powder/liquid ratio of ZOE sealer 1:2Group 3 - Powder/liquid ratio of ZOE sealer 1:3Group 4 - Powder/liquid ratio of ZOE sealer 1:4Control Group - No sealer was used.

For the purpose of standardization, sealer was not applied onto the canal walls. The GP cones were individually coated uniformly with the sealer by dipping for 5 s. The obturation was performed by sealer coated single cone GP (25/04).

A second SCT scan was performed to determine the volume of GP and sealer in all four groups 1 day after obturation. Obturated volume of root canal in each tooth was calculated. The third and fourth SCT scans were taken 7 and 30 days after obturation, respectively. The mean volume and percentage volume of GP per group were calculated.

Statistical analysis

Data were statistically analyzed using one-way analysis of variance. Inter-group comparisons were done by Scheffe post hoc multiple comparisons test.

 Results



On 3D volumetric analysis of volume of root canals after biomechanical preparation and volume of GP after 1, 7 and 30 days were recorded with the help of SCT and the values were recorded in cubic centimeter.

The obturated mean volume of root canals and standard deviation after 1, 7, and 30 days are given in [Table 1]. The mean volumes of root canals in all five groups were statistically comparable (P Ë 0.05) [Figure 1] and [Figure 2].{Table 1}{Figure 1}{Figure 2}

The Groups 2 and 3 have the highest mean volume values during the period of 30 days and were significantly different in comparison with Groups 1, 4 and control group (P Ë 0.05).

Volume of GP increased at both 7th day and at 30th day in all groups where ZOE-based sealer was usedIncreasing the ratio of eugenol in the ZOE sealer, from powder/liquid ratio of 1:1–1:2 or 1:3 leads to more volumetric expansion of GP at both 7th day and 30th day period, whilst 1:1 and 1:4 showed least volumetric expansion of GP.

 Discussion



The final objective of endodontic procedure should be total obturation of the root canal space. Biologic necessity requires elimination of protein degradation products, bacteria and bacterial toxins from infected and necrotic root canals, which is performed by cleaning, shaping and total obturation of the root canal system. Sealing off of the complex root canal system from periodontal ligament and bone ensures the health of the attachment apparatus against breakdown of the endodontic origin.[2]

GP has for many years been widely used as a solid material in root fillings with different types of sealers, is usually considered the best material for root canal obturation.[4]

Various types of sealers can be used along with GP for obturation of root canal space. All the sealers which are used for obturation inherently shows shrinkage behavior during setting, this shrinkage associated with setting might jeopardize the seal of root canal, leading to root canal failure.[5],[6]

Among various sealers used, ZOE-based sealers are commonly used because of its cost effectiveness, ease of availability and bacteriostatic property. Kardon et al. have shown that urethane dimethacrylate-based resin sealers can be used along with GP cones.[14] However, Hammad et al. performed a study to evaluate the setting shrinkage behavior of recently developed resin-based sealer compared to that of ZOE-based sealer and concluded that ZOE sealer exhibited statistically lesser shrinkage when compared to that of resin-based sealers.[6] Ørstavik et al. also performed a similar study and found that resin-based sealers showed more shrinkage after setting compared to that of ZOE-based sealers.[5] Whereas study done by Kazemi et al. showed that ZOE-based sealer showed significant more setting shrinkage compared to resin-based sealer.[15]

ZOE remains the base component in many modern endodontic sealers. Eugenol remains in excess in fresh mixes of ZOE, where it is not entirely crystallized as zinc eugenolate. The surface of set material undergoes hydrolysis, with the release of free eugenol into adjacent fluids.[8] When GP cones are kept in contact with eugenol, they expand dramatically in size and this remarkable increase in GP dimensions measured several hundred percent increase and this expansion continued even after 4.5 years.[8] Chandrasekhar et al. evaluated expansion of GP in contact with various concentration of ZOE-based sealers and concluded that as powder/liquid ratio of ZOE-based sealer decreases, volumetric expansion of GP cones increases.[9]

In this study, along with GP cones, RC-Fill is used as a sealer, which is a ZOE-based sealer with extended working time. This slow setting eugenol sealer causes a significant expansion of the obturated mass.

The manufacturers recommend using a powder/liquid ratio of 1:1, whereas we chose to use decreasing ratios of powder to liquid in groups ranging from 1:1 in first group, 1:2 in second group, 1:3 in third group, 1:4 in fourth group and in control we did not use any sealer. Reason of using varying powder/liquid ratio of sealer was to see its effect on the expansion of GP, used as a core material, if any.

It is generally believed that as in the case of cements, altering the powder-liquid ratio of ZOE-based sealer may also affect the physical and mechanical properties of the sealer. However, study done by Camps et al. where they investigated the effects of modifications of the powder-liquid ratio on the physical properties recommended by ISO standards as well as on other clinically relevant properties of ZOE-based root canal sealers concluded that variation in powder-liquid ratio did not influence the physical properties, dimensional changes and apical leakage of sealers.[16] Although, modifications in the powder-liquid ratio changes the flow and radiopacity of the sealer, which can be considered relatively less important characteristics of sealer.

It is thought that free eugenol component of freshly mixed ZOE sealer can seep out and cause various cytotoxic effects on human gingival fibroblasts, periodontal ligament cells and osteoblast-like cells.[10],[17] Gerosa et al. showed that pure eugenol is cytotoxic and represents one of the ingredients responsible for cytotoxicity in ZOE-based endodontic sealer but it is toxic only when just mixed and its cytotoxicity decreases over time, and ZOE-based sealer shows any cytotoxic effect only when it is extruded beyond the apical foramen and comes in direct contact with cells of periodontal ligament and alveolar bone; it does not have any cytotoxic effect if confined within the root canal.[10] Hashieh et al. reported that leakage of eugenol into periapical tissue is very low and it dramatically decreases over time.[11] Therefore, it can be assumed that ZOE-based endodontic sealer does not seem to release eugenol in amount sufficient to be highly cytotoxic. Still strict adherence to the working length has to be followed and over instrumentation and over obturation has to be avoided with ZOE-based sealer too, similar to that in other sealers. Studies done by Wu et al. and Kontakiotis et al. have shown that sealers applied as thin layers provide a better apical seal than the apical seal obtained by thick layer of sealer application.[7],[18]

The introduction of NiTi alloy allow the manufacture of endodontic instruments that are capable of preparing curved root canals with safety, less deviation and in less working time, in comparison with instruments made of stainless steel. RaCe endodontic files have alternating cutting edge along the file length due to alternating twisted and untwisted segments to reduce screw-in effect.

In this study, cleaning and shaping were performed using RaCe rotary instruments (25/06). To evaluate the percentage of visible expansion of GP points, a single cone obturation using a less tapered cone of GP (25/04) was used to provide space for expansion of GP, if any.

Nair and Nair have shown that SCT is a noninvasive technique that gives a 3D interpretation at various levels.[19] SCT imaging of root canals showed it to be a highly accurate and nondestructive method for the evaluation of root canal fillings and their constituents. Although resolution is not as high as that of conventional radiographs, the availability of 3D information, a relatively higher resolution and a significantly lower dose than CT makes SCT imaging the modality of choice in challenging situations demanding localization and characterization of root canals. 3D volume measurements are possible with SCT without sectioning specimens thus avoids loss of material, yields reproducible results, and the specimens can be used for further research.[1],[12] In our study, volume analysis was done with SCT. Volume analysis gives a more accurate measure than surface area measurement. With SCT, 3D volume measurements are possible without sectioning the specimens and thus avoiding the loss of material during sectioning.[20]

The percentage of expansion at a specific location can be determined accurately and a volumetric analysis of root canal fillings can be done with the help of SCT.[12]

Hence, SCT was chosen as a tool for investigating the volumetric expansion of GP in this study.

However, the main limitation of the SCT is its inability to differentiate GP and sealer because of similar radio-opacity. To overcome this limitation of SCT, that is, difficulty in differentiating GP and sealer, we avoided coating the sealer by using a lentulo spiral onto the canal walls.[12] Instead, we have standardized our samples in all groups by applying the sealer of various ratios in their respective groups by dipping the GP for 5 s.

In this study, the volumetric expansion of GP was measured in the presence of various concentrations of ZOE-based sealers at different time intervals. The aim was to determine which powder/liquid ratio of ZOE sealer causes maximum volumetric expansion of GP and also to evaluate that this expansion was maximum at which time interval.

ZOE-based sealer used in this study was RC-Fill (Prime dental products).

In Group 1, volumetric analysis showed that mean volume of GP at 1st day was least (0.0341 cm 3), and maximum at 30th day (0.0369 cm 3), with intermediate value at 7th day (0.0353 cm 3). The mean differences in the volumes between GP 1st day – GP 7th day, GP 7th day – GP 30th day and GP 1st day – GP 30th day were all statistically significant.

In Group 2, volumetric analysis showed that mean volume of GP at 1st day was least (0.0336 cm 3), and maximum at 30th day (0.0389 cm 3), with intermediate value at 7th day (0.0359 cm 3). The mean differences in the volumes between GP 1st day – GP 7th day, GP 7th day – GP 30th day and GP 1st day – GP 30th day were all statistically significant.

In Group 3, volumetric analysis showed that mean volume of GP at 1st day was least (0.0344 cm 3), and maximum at 30th day (0.0411 cm 3), with intermediate value at 7th day (0.0377 cm 3). The mean differences in the volumes between GP 1st day – GP 7th day, GP 7th day – GP 30th day and GP 1st day – GP 30th day were all statistically significant.

In Group 4, volumetric analysis showed that mean volume of GP at 1st day was least (0.0344 cm 3), and maximum at 30th day (0.0369 cm 3), with intermediate value at 7th day (0.0353 cm 3). The mean differences in the volumes between GP 1st day – GP 7th day, GP 7th day – GP 30th day and GP 1st day – GP 30th day were all statistically significant.

Control Group did not show any change in the volume of GP with time, as no sealer was used in this group.

This trend in increase in the volume of GP with time, in contact with ZOE-based sealer is in accordance to the study done by Michaud et al. and study done by Chandrasekhar et al. which utilizes similar groups and samples.[8],[9]

Intergroup analysis demonstrated that there is statistically significant change in volume of GP in different groups at 7 days and 30 days interval, whereas volumes of GP at 1 day in all the groups do not show any statistically significant change. These findings could be explained by the study by Michaud et al., which states that sufficient amount of time is needed for the expansion in GP to take place. In the case of volumetric analysis at 1 day, sufficient amount of time was not there for the expansion to take place.[8]

There was a statistically significant difference in the volumetric expansion of GP samples in Groups 2 and 3 compared with Groups 1 and 4 during the 30 days period.

An increase in powder/liquid ratio reduced the amount of released eugenol at 1-month interval for ZOE-based sealer.[21] The findings of the present study are in accordance with those of Camp et al., who reported that the higher the powder/liquid ratio, lower the eugenol release, which might be due to the supplementary zinc-oxide particles binding to eugenol as fast as it is released; thus only the outer surface of sealer is prone to eugenol release.[16]

Therefore, a ratio of 1:1 (ZOE) sealer concentration has shown less expansion when compared with 1:2 and 1:3 groups at both 7 and 30 days' time period. The samples in 1:4 groups showed a very minimal expansion after both 7 and 30 days interval, which could be due to insufficient amount of contact time of GP with ZOE sealer, which was very thin in consistency.

 Conclusion



Within the limitations of this study, increasing the ratio of eugenol in sealer resulted in volumetric expansion of GP up till a ratio of 1:3. However, further studies should be performed to confirm expansion and sealing ability of GP of the size corresponding to the prepared canal, leading to the achievement of fluid impervious seal.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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