Influence of obturation technique on penetration depth and adaptation of a bioceramic root canal sealer.

AIM: Evaluation of the impact of three different obturation techniques on the penetration depth and adaptation of a bioceramic root canal sealer(BioRoot RCS) to root dentin using scanning electron microscope and confocal laser scanning microscope.
MATERIALS AND METHODS: Recently extracted ninety mandibular premolar teeth of similar dimensions (±0.2 mm) with single canals and straight roots were segregated into three experimental groups (n = 30 each) based on the method of obturation used, i.e., lateral compaction technique, warm vertical compaction technique, and injectable thermoplasticized technique. After obturation, half of the root samples (n = 15) in each group were sectioned horizontally by hard tissue microtome at 3, 6, and 9 mm, respectively, from root apex for measuring sealer penetration depth with a confocal laser scanning microscope. Longitudinal sections of the samples (n = 15) were used for measuring the adaptation of sealers to radicular dentin using a scanning electron microscope. STATISTICAL ANALYSIS: Intergroup comparison of sealer penetration depth and adaptation to root dentin was analyzed using one-way ANOVA, and pairwise comparisons were made using Tukey's post hoc test.
RESULTS: Warm vertical condensation technique showed deeper root dentin penetration of the sealer. Better adaptation of the sealer to apical root dentin with minimal voids (P ≤ 0.05) was achieved with warm vertical condensation in comparison to the injectable gutta-percha method and lateral condensation obturating techniques.
CONCLUSION: At all three root levels (coronal, middle, and apical), warm vertical condensation technique exhibited more sealer penetration with minimum gaps, whereas lateral condensation technique exhibited more gaps and less sealer penetration. Copyright:

INTRODUCTION

The successful outcome of endodontic treatment relies on complete removal of the infected pulp, effective disinfection of the root canal with adequate biomechanical preparation, and obtaining hermetic apical seal of the canal space with obturating materials.[1] A few obturating systems have been recommended to accomplish a fluid-tight three-dimensional seal of root canals. The type and form of gutta-percha (GP) utilized, along with sealer material, vary among these strategies.

The lateral compaction system (LC) is very effective as it confines the root canal filling inside the root apex. Several reports have suggested that LC cannot fill the spaces efficiently and causes voids or spaces due to the nonhomogeneous conveyance of sealers.[2]

In warm vertical compaction (WVC) technique, the filling material is plasticized by heat and is carried into the root canal using heated pluggers. Once the root apical portion is compacted with obturating material, the backfilling of the coronal portion is done. The benefit of this method is the plasticized obturating material can adapt well to the root canal abnormalities and isthmuses and results in dense compaction with a good seal at all root canal entry portals. This method ensures the homogeneity of GP in the root canal and can be more efficacious in the obturation of the lateral canal than the LC method.[3]

Injectable thermoplasticized obturation utilizes an injectable syringe system that delivers viable obturations. This technique is less time-consuming, allows good conformation to root canal anatomy, has a lesser chance of porosity, and creates denser obturation than LC procedure.[4]

Along with the compaction technique, sealers have a crucial part in attaining a hermetic seal of root canals. The fundamental purpose of a sealer material is to seal the voids between lateral cones and GP core along the canal walls.[5] Lack of adhesive bonding between core GP, conventional sealers, and root dentin has encouraged the introduction of newer sealers. Resin-based sealers have been widely used; however, currently, volumetric shrinkage, discharge of toxic products like formaldehyde, expanded working time, and tooth staining are disadvantages associated with these sealers.

Recently developed calcium silicate-based bioceramic sealers are more favored as they possess the ability of calcium release and bioactivity.[6] BioRoot RCS (Septodont, Saint-Maur-des-Fosses Cedex, France) sealer contains a powder component consisting of tricalcium silicate, povidone, and zirconium oxide and liquid component consisting of calcium chloride and water. BioRoot RCS has shown to exhibit less toxicity on periodontal tissue and has initiated growth factors secretion with osteogenic and angiogenic properties.[7] It also induces hard tissue barrier formation by discharging a significant amount of calcium to produce a calcium phosphate phase in the presence of a physiologic solution.[7]

Sealer penetrability into root dentin and marginal sealing ability are significant criteria for the success of endodontic treatment. Ideally, a sealer should have low surface tension for better penetration into irregularities and good wettability for a hermetic seal. Root canal sealer, which has excellent penetration and adaptation, will have a beneficial impact on obturation by enhancing the area of surface contact of obturating material and root canal dentin that improves the sealability.[8]

Sealer cement penetration into tubules of root dentin is determined by various factors, including the elimination of the smear layer, dentin permeability, and filling technique. Hence, it is critical to analyze the penetration and adaptation of sealers to root dentin during various obturation methods.[9] Although there are few studies reported in the literature evaluating adaptation and penetration depth of BioRoot RCS sealers, using LC technique, research is scarce in assessing the impact of various other obturation techniques on the penetration and adaptation of bioceramic sealers. Therefore, the present research aims to compare the impact of routinely used LC system, with warm vertical and injectable thermoplasticized GP obturation methods on BioRoot RCS sealers penetration, and adaptation to root dentin. Although both warm vertical and injectable GP obturations are plasticized GP techniques, injectable obturation is the most commonly used technique by clinician due to its ease of use and less time-consuming, and also, the mode of compaction is different for both techniques, so the objective of the present study was to compare the two thermoplasticized techniques and to evaluate which technique is better in terms of good sealer penetration. The null hypothesis tested was the depth of penetration and adaptation of BioRoot RCS to root dentin would not differ with the technique of obturation.

MATERIALS AND METHODS

The State Health University approved the present study. Ethical clearance was sought from the review board (D178601025) of the institute. Ninety caries-free sound, single-rooted mandibular premolar teeth, with similar measurements (±0.2 mm) in buccolingual and mesiodistal aspects, were utilized in this study. The sample size was estimated using G power 3.1 software, and 15 samples were designated as the minimum ideal size for each group to test both the parameters with an alpha error probability of 0.05.

Preoperative radiographs and surgical loupes at ×2.5 magnification (Stac Dental Instruments Inc., Canada) were used to confirm that the samples had a single patent canal, devoid of root caries or restorations, open apices, fractures, or craze lines. Then, samples were placed in 0.9% physiological saline and were used within 4 months after extraction.

For all the samples, coronal access was prepared using the #245 bur (Mani Inc., Tochigi, Japan). For accurate working length determination, both radiographic and electronic apex locators were used. Roots of all teeth samples were wrapped with an aluminum foil of thickness 0.2 mm and were then embedded in metal matrices containing autopolymerizing acrylic resin. Later, polyvinyl siloxane impression material was manipulated and placed into the space for simulating periodontal ligament. The length of all the collected samples was measured and standardized to 21 ± 1 mm.

Biomechanical preparation was done with MTwo Ni-Ti files (VDW GmbH, Bayerwaldstr, Germany) using a 35/0.04 master apical file. The samples were alternatively flushed with 3% NaOCl (2 ml) irrigation and 17% EDTA (RC Help Prime Dental Products Pvt. Ltd., India) for smear layer clearing. Sterile physiologic saline (5 ml) was used as the last irrigant.

Grouping method

Specimens were separated into three groups (n = 30), each based on the method of obturation, i.e., Group 1: Cold LC method, Group 2: WVC method (System B™ Sybron Endodontics, Orange, CA, USA), and Group 3: Injectable thermoplasticized obturation with I-Fill GP obturation system (Denjoy Dental Co., Ltd, Changsha, China). BioRoot RCS sealer (Septodont, Saint-Maur-des-Fosses Cedex, France) was used in all the obturating systems.

Lateral condensation technique

A standardized sealer coated master GP of size 35/.04 (Dentsply Maillefer, Switzerland) was selected. By utilizing #30 finger spreader, GP cone was displaced to one side, and accessory cones were positioned into the spreader space following its removal. This procedure was continued till the spreader no longer penetrates beyond 3 mm of canal orifice.

Warm vertical condensation technique

After checking fit of master GP cone of size 35/0.04, appropriate pluggers (System B™ plugger) that penetrated 5–7 mm short of the working length were selected. The heat source of the obturation unit (Elements system; System B™, SybronEndo, Kerr Endodontics, Orange, CA, USA) was adjusted to 200°C, and the heated prefitted plugger was used to compact the GP in the apical 4 mm. Backfilling of the root canal was done up to 1 mm underneath the CEJ.

Injectable thermoplasticized gutta-percha technique

The I-Fill GP obturation system was activated to temperature of 200°C. The needle with 0.04 taper was positioned 3–5 mm short of the apex. GP was introduced passively without applying apical pressure until the entire root canal was filled and compacted gently utilizing the I-Fill pen.

Evaluation of penetration depth of sealer

For examining the sealer penetration depth in root samples, 45 teeth (n = 15 each group) were obturated using a sealer mixed with rhodamine dye and were analyzed for fluorescence. Hard tissue microtome (Leica SP1600, Leica Biosystems, Germany) was used with copious water coolant to section the teeth. Horizontal sections were obtained at 3, 6, and 9 mm, respectively, from root apex to observe sealer penetration at apical, middle, and coronal potions. Sections were viewed with a confocal laser scanning microscope (CSLM 890, Carl Zeiss, Germany) to evaluate sealer penetration into dentinal tubules. The fluorescence depicted the extent of sealer penetration at ×10 magnification. The software has settings that allowed the rhodamine dye to be identified and displayed on the screen. The infiltrated areas (dentinal tubules) showed red fluorescence, and the un-infiltrated areas appeared darkened.

The penetration depth (PDmax) was calibrated at buccal, lingual, mesial, and distal standardized points. The root dentin wall was considered as the reference position in each section. The penetration depth was measured in predetermined regions, i.e., coronal, middle, and apical third, for each root sample at a standardized point, i.e., from the canal wall to the maximum extension of the penetrated red fluorescence area. To obtain a single mean value of penetration depth of each section, an average of all the four measured readings, i.e., buccal, lingual, mesial, and distal, is taken to gain one mean value for each section in millimicrons.

Evaluation of sealer adaptation to root dentin

For analyzing the adaptation and percentage of gap formation at root dentin and sealer interface, 45 teeth (n = 15 for each group) were used. Vertical sections of the roots were obtained to assess the adaptation through scanning electron microscopy. All the sections were thoroughly rinsed underwater for 1 min and were allowed to dry. Right before the microscopic analysis, the specimens were desiccated involving ascending ethanol steps, and then, they were assembled on an aluminum stub and gold sputter coated for electrical conductivity, and observed with SEM (Carl Zeiss, Model: Neon 40), at ×2000 magnification.

The representative area of the maximum amount of gap present between the sealer and dentinal tubules on both the mesial and distal aspects of the sample was analyzed, and these dentin-sealer interfacial gaps were measured utilizing software Image J.

Statistical analysis was performed using SPSS software version 21 (IBM,Armonk,NY,USA). The penetration depth of sealer in the three groups was compared using Tukey's multiple post hoc test. Sealer adaptation between the three groups was compared using one-way ANOVA. Pairwise comparisons of three groups pertaining to penetration depth and adaptation were performed using Tukey's multiple post hoc test. Statistical significance was fixed at a 95% confidence level.

RESULTS

WVC technique showed a statistically significant higher sealer penetration depth at coronal, middle, and apical levels than the injectable GP and lateral condensation techniques (P > 0.05) [Table 1 and Figure 1]. Within the same group, all the three obturation techniques exhibited significantly more penetration into the root dentin coronally, followed by middle third and least penetration in the apical levels [Table 1].

Table 1

Comparison of three groups and pairwise comparison of three groups (lateral condensation, warm vertical, and injectable gutta-percha) and three regions (coronal, middle, and apical) with mean penetration depth by Tukey’s multiple post hoc procedures

Groups	LC			WV			IGP
Mean±SD	697.21±217.03			844.00±208.30			816.57±199.41
Groups × regions	LC in coronal	LC in middle	LC in apical	WV in coronal	WV in middle	WV in apical	IGP in coronal	IGP in middle	IGP in apical
Mean±SD	908.83±16.12	778.98±17.38	403.82±10.06	1095.36±33.00	842.16±24.16	594.47±16.60	1052.44±23.45	824.04±31.93	573.22±17.11
LC in coronal	-
LC in middle	0.0001*	-
LC in apical	0.0001*	0.0001*	-
WV in coronal	0.0001*	0.0001*	0.0001*	-
WV in middle	0.0001*	0.0001*	0.0001*	0.0001*	-
WV in apical	0.0001*	0.0001*	0.0001*	0.0001*	0.0001*	-
IGP in coronal (P)	0.0001*	0.0001*	0.0001*	0.0001*	0.0001*	0.0001*	-
IGP in middle	0.0001*	0.0001*	0.0001*	0.0001*	0.3889	0.0001*	0.0001*	-
IGP in apical	0.0001*	0.0001*	0.0001*	0.0001*	0.0001*	0.1823	0.0001*	0.0001*	-

*P<0.001 indicates statistically significant. IGP: Injectable gutta-percha, WV: Warm vertical, LC: Lateral condensation, SD: Standard deviation

Figure 1

Confocal microscopic images of sealer penetration depth in lateral condensation, warm vertical, injectable gutta-percha technique (a) lateral condensation technique at 9 mm, (b) lateral condensation technique at 6 mm, (c) lateral condensation technique at 3 mm, (d) warm vertical condensation technique at 9 mm, (e) warm vertical condensation technique at 6 mm, (f) warm vertical condensation technique at 3 mm, (g) injectable gutta-percha technique at 9 mm, (h) injectable gutta-percha technique at 6 mm, (i) injectable gutta-percha technique at 3 mm

Pairwise comparisons of WVC with LC showed that in all the three regions, WVC showed statistically significant higher penetration depth than LC. When comparing WVC with injectable GP technique, WVC showed significantly higher penetration depth at the coronal third than LC [Table 1]. However, at middle and apical thirds, no significant difference was observed between them. Pairwise comparison of injectable GP technique with LC showed significantly higher penetration depth in all the three regions than LC [Table 1].

With regard to sealer adaptation, warm vertical condensation technique has shown statistically better adaptation with the least number of gaps between the radicular dentin and obturation material [Table 2 and Figure 2]. The intermediate adaptation was shown by the injectable GP technique, and the lateral condensation technique showed poor adaptation with more voids. A statistically significant difference existed between all three groups [Table 2].

Table 2

Intergroup comparison of adaptation and percentage gap formation at root dentin and sealer interface following obturation with three different techniques using one-way ANOVA and pairwise comparisons

SEM adaptation	LC	WV	IGP	F	P
Mean±SD	9.45±1.17	4.11±0.90	6.00±0.47	138.418	0.001
LC (P)	-	0.001*	0.001*	-	-
WV (P)	0.001*	-	0.001*
IGP (P)	0.001*	0.001*	-

*P<0.001 indicates statistically significant. SD: Standard deviation, SEM: Scanning electron microscopy, IGP: Injectable gutta-percha, WV: Warm vertical, LC: Lateral condensation

Figure 2

Scanning electron microscopic images of apical adaptation (a) lateral condensation technique, (b) warm vertical condensation technique, (c) injectable gutta-percha technique

DISCUSSION

Attaining a hermetic seal of biomechanically prepared root apex is of utmost importance to prevent reinfection. Three-dimensional obturation also initiates and encourages repair and regeneration. Hence, filling the root canal with a nonreactive, biologically compatible material is the ultimate goal of endodontic therapy.[10] Several techniques have been used to attain three-dimensional obturation, and in all these methods, GP was used as the core material and cement with the flowable property as the sealer.

The factors that can influence sealer adaptation to root canal walls are surface energy, cleanliness, surface tension, and the sealer's wettability. Sealer penetration into tubules of dentin may serve as a mechanical blockade against the recolonization of bacteria into dentin tubules. Bioceramic root canal sealers also exhibit bactericidal activity against certain species inside dentinal tubules. Thus, adequate sealer penetration and adaptation prevents reinfection and promotes the healing of endodontic lesions.[11]

BioRoot RCS used in this study is a tricalcium silicate sealer that provides a favorable condition for tissue healing by hydroxyapatite mineralization of the dentin, which encourages root canal sealing, with their excellent bioactive properties.[121314] BioRoot RCS has been reported to elevate concentrations of calcium from calcium phosphate crystals when interacted with physiologic solution.[15] Due to these biological advantages of BioRoot RCS over other sealers, its penetration and adaptation capacity was evaluated with different obturation techniques.

The present study results revealed the highest depth of penetration of sealer into radicular dentin for WVC, followed by injectable GP technique and least penetration in LC technique. GP in WVC method (System B) is plasticized with heat carrier. After heat application, sustained apical pressure is preserved after continuous-wave compaction. Due to this sustained pressure, GP is moved apically and laterally by compaction pressure leading to three-dimensional obturation of the canal space, which might be the reason behind the highest sealer penetration in the warm vertical condensation group as compared to LC. This outcome is in accordance with the study conducted by Basavanna et al. 2014.[16]

In the injectable thermoplasticized GP obturation, plasticized GP was injected passively without applying any apical pressure till entire root canal was filled and compacted later gently using I-Fill pen, whereas in WVC, continuous pressure was applied for compaction of plasticized GP with appropriate plugger allowing better flow and penetration of sealer. This could explain the better outcome of WVC compared to injectable system.

Among all the obturation techniques tested, the sealer penetration at 9 mm level (coronal level) was significantly deeper than 6 mm and 3 mm (middle and apical portion) of the root canal from the apex. The regional disparity can be attributed to an increased incidence of complexities in the root apical third anatomy and dentin sclerosis in root apex, which can deter deeper penetration of sealers into the dentinal tubule. Another reason for the discrepancy might be the inadequate smear removal in the middle and apical portion of root canals. Moreover, the lower number and reduced dentinal tubule diameter in the apical region may result in lesser penetration of sealer.[17]

In comparison to the mesiodistal direction, the penetration depth of the sealant was discovered to be higher in the buccolingual direction. This may be linked to a “butterfly effect” phenomenon, which is seen in root cross-sections due to enhanced sclerosis in the tubules of the mesial and distal aspects of the lumen of the root canal, which appears like a butterfly.[18]

The sealing of the apical region is a crucial task that can be obtained through proper obturation. Considering the adaptation and proportion of gap formation at root dentin and sealant interface, warm vertical condensation showed the least amount of gaps. In contrast, injectable GP showed intermediate adaptation, and the lateral condensation method revealed poor adaptation with more voids. Poorer outcomes for lateral condensation technique compared to the other groups were reported in previous studies due to voids formation, spreader tracts, and absence of surface distribution of sealer adaptation to canal walls.[216] The LC technique resulted in a nonhomogeneous flow of sealer along the root canal wall, which might be the reason for the appearance of high interfacial gaps.[19]

In contrast, warm vertical and injectable thermoplasticized systems utilize heat to plasticize GP allowing for the lateral and vertical flow of material, ensuring good surface adaptation leading to a denser root canal filling which in turn attributes to better adaptation and flow of sealer.[20] The results of the present study also correlate with findings of another recent study wherein WVC has provided the highest percentage of root-filled area compared to injectable GP and LC and techniques.[21] As there was a significant difference in sealer penetration depth and adaptation observed for all the three groups, the null hypothesis was rejected based on the results of the present study.

In the present study, only teeth with straight canals were enrolled. Curved canals can be difficult and may complicate the proper cleaning of the root. Hence, further research regarding the depth of penetration and three-dimensional sealing of the obturation system could be investigated in curved root canals and multirooted teeth for better clinical assessment.

CONCLUSION

The inference reached based on the outcome of the present in vitro study showed the highest depth of penetration and adaptation of BioRoot RCS to root dentin in the warm vertical condensation technique followed by injectable GP technique and lateral condensation technique. Further in vivo studies are warranted to assess the clinical outcome.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.