Comparative Evaluation of Fracture Resistance of Bioceramics as Obturating Material with and without Guttapercha

Introduction

Endodontically treated teeth tend to become weak and prone to fracture when compared to vital teeth.¹ The durability and strength of a root canal treated tooth hinge on the extent of the remaining tooth structure. Numerous factors that affect the fracture resistance during root canal treatment includes the extent of removal of caries/ tooth structure, dehydration of dentin, instrumentation of root canal system, effects of root canal irrigation and also uncontrolled pressure during obturation. In addition, the occlusal load forces directed on the tooth also act as a contributing factor for root fracture.² Therefore, the materials and techniques adopted during root canal treatment should reinforce the remaining tooth structure.

Obturation is an essential step for the success of root canal-treated teeth which includes obturation using core filling material along with sealer for the three-dimensional filling of the root canal, accessory canals and lateral canals.³ Several obturating materials are available today, but guttapercha remains the gold standard. Along with the materials, the obturation technique also plays a critical role in the success of root canal therapy. The technique of cold lateral compaction is frequently instructed and employed in obturation procedures. However, its drawbacks include voids and incomplete adaption of gutta-percha.⁴ In recent times, several obturating techniques have been developed for optimal three-dimensional obturation.⁵

Root canal sealers play a crucial role in establishing a fluid-tight seal, effectively preventing apical leakage and potential reinfection by sealing the accessory and lateral canals between the root dentin and gutta-percha.⁶ The choice of an ideal sealer is not only to seal the root dentin-wall, but also to be well tolerated by the peri-radicular tissues when extruded and should be easy to manipulate, and possess adequate adhesion properties. Zinc oxide eugenol is a traditional sealer used for obturation. It is biocompatible and is commonly used as root canal sealer. AH plus is an epoxy resin-based sealer which reinforces the remaining tooth structure because of its good mechanical, physical and chemical properties such as high radioopacity, minimal polymerization shrinkage, low solubility and biocompatibility.^7,8

Bioceramics are designed to use for medical and dental applications in present day practice. Alumina, zirconia, bioactive glass, glass ceramics, hydroxyapatite, and calcium phosphates are components of bioceramic sealers. They are categorized as either bioactive or bioinert materials, depending on their interaction with the surrounding living tissues.⁹ Bioceramic root canal sealers have become popular because of their improved chemical and physical properties. The bioceramic sealers aim to regenerate the diseased and necrotic tissues rather than replacing them with some conventional replacement materials.¹⁰ Bioceramics have been widely used in different endodontic procedures like apical fillings, apexification procedures, and as root canal sealer, etc. due to its biocompatibility with osteogenic, and cementogenic potential. Various bioceramic sealers are used during root canal treatment viz., BioRoot RCS, EndoCPM sealer, MTA Fillapex, etc.¹¹

Till date, there are no studies reported regarding evaluation of bioceramic sealers alone as an obturating material. Due to the inherent characteristics of bioceramics, this in vitro study sought to assess the fracture resistance of endodontically treated teeth filled with bioceramic sealer (BioRoot RCS), AH plus, and ZOE. The evaluation included both with and without gutta-percha, employing various obturating techniques.

Materials & Methods

Ethical clearance was obtained from the institution for this study (Reference No.IEC/2021-22/S-18) and the study was conducted accordingly. Sample size was estimated using power package of R programming language R code version 3.5 (R Core Team, Microsoft open source software, USA) by Balanced One-way analysis of variance power calculation with effect size 0.335, power of study 80%, level of significance 0.05 (5%). Based on this, a total sample size of 90 was included in the present study.

Sample preparation

Ninety human single rooted mandibular premolar teeth that were extracted for orthodontic reasons were collected and placed in saline until use. Stains, calculus and soft tissues on the teeth were removed using ultrasonic scaler (Woodpecker, Meerut, India). All the teeth were radiographed using Radiovisiography (RVG) (Kodak RVG 5200, Japan) for the presence of single canal, and specimens were inspected under stereomicroscope (Lynx, Mumbai, India) at 12x magnification to detect any preexisting cracks or craze lines. The teeth were decoronated with diamond disc (TR13; Mani, Utsunomiya, Japan) and contraangle hand piece with copious coolant and the root length was standardized to 13 mm using digital Vernier calipers (Altraco Inc., Sausalito, California, USA).

Endodontic access opening was done in all the specimens using round bur No. 2 (Dentsply, Malliefer, Ballaigues, Switzerland). Working length was determined using 10 K-file (Mani, Tochigi, Japan) by placing it till apical foramen, and then subtracting 0.5 mm from this length. The specimens in group 1 were instrumented with K files (Mani, Tochigi, Japan) till size 35/02, and in step back technique till size 80 in 1 mm increments. In groups 2 and 3, specimens were instrumented using NeoEndo rotary file system (Orikam, Gurgaon, Haryana) till size 25/06. Root canals were irrigated using 5 mL sodium hypochlorite (3% NaOCl) (Vishal Private limited, Ahmadabad, India) and normal saline (Prayag Ltd, Mumbai, India) in between each file using a 27-gauge needle. The samples were then irrigated with 5 mL of 17% EDTA irrigating solution (Prevest Den Pro, Jammu, India) to remove the smear layer, and were finally flushed with normal saline, followed by drying with paper points (Dentsply, Malliefer, Ballaigues, Switzerland). Then the specimens were randomly divided into three groups (n=60) for obturation.

Group 1: Lateral compaction (LC) technique

Group 2: Single cone obturation technique (SC)

Group 3: Complete obturation with sealer without gutta -percha (CS)

Each group was further divided into three subgroups using the following root canal sealers:

A: ZOE sealer (Kerr, Orange, CA, USA)

B: AH plus sealer (Dentsply DE Trey, Konstanz, Germany)

C: BioRoot RCS (Septodont, Saint-Maur-des-Fonds, Switzerland)

In all the subgroups, the sealers were mixed according to manufacturers’ instructions. In subgroup A of all the groups, ZOE cement was manipulated by mixing the powder and liquid on a glass slab until creamy consistency was obtained. In subgroup B, AH plus base and catalyst paste were mixed on a mixing pad and in subgroup C, BioRoot RCS powder and distilled water were mixed. The sealers in each group were placed into the root canal using lentulospirals (Dentsply, Maillefer, Ballaigues, Switzerland). In group 1, lateral compaction was done by placing master cone gutta-percha (35/02) and accessory cones (Dentsply, Maillefer, Ballaigues, Switzerland) were placed using finger spreader until they penetrated no more than 2 mm of the cervical third and compacted. In group 2, single cone gutta-percha 25/06 was placed. Whereas in group 3, sealer was compacted with hand plugger until the canal was completely filled. The excess material was removed and condensed with hand plugger.

Radiographs were taken to ensure proper obturation of all the specimens and were sealed coronally with Cavit (3M ESPE, Seefeld, Germany). All the samples were stored at 370C at 100% humidity for one week for sealers to set. The samples in each subgroup were subjected to fracture resistance.

Evaluation of fracture resistance

Each sample was wrapped in aluminum foil and embedded in acrylic resin placed in a plastic mould. After 24 hours, the samples were removed from the set acrylic mould, the foil was peeled off, and the space was then replaced using polyvinylsiloxane elastomeric impression material to stimulate the periodontal ligament for fracture resistance. Fracture resistance was evaluated using a Universal testing machine (Instron India Pvt. Ltd. Chennai, India). The acrylic moulds were positioned on the lower plate of the Instron machine, upper plate consisting of a 2 mm diameter steel tip of radius 3 mm was placed in the centre of each specimen and vertical load at a speed of 1 mm per minute was placed until fracture occurred. The maximum force applied to fracture the root sample was recorded in Newton (N) and the data obtained was tabulated (Figure 1).

Statistical analysis

The statistical analysis was done using the software, Statistical Package for the Social Sciences (SPSS)) version 23 (IBM statistics, Chicago, USA) using One way ANOVA test, followed by post hoc Tukey’s test and unpaired student ‘t’ test for multiple comparisons among the groups (P ≤0.05).

Results

Among the study groups, group 1 (LC) showed highest fracture resistance, followed by group 2 (SC), and the least fracture resistance was observed in group 3 (CS). Highest mean values were found in group 1C (LC + BioRoot RCS) (17N), followed by 2C (SC with BioRoot RCS) (14.8N) and 3C (complete sealer) (14.1N) (Table 1).

Multiple comparisons using post hoc Tukey test between the groups showed that, among all the groups, subgroup C (BioRoot RCS) exhibited higher fracture resistance compared to subgroup B (AH plus) and subgroup A (ZOE). However, no significance difference was found between subgroup 1A (LC with ZOE) and 2A (SC with ZOE) and between 2C and 3C (Table 2).

Overall, subgroup 1C (BioRoot RCS with LC) showed highest fracture resistance, followed by subgroup 2C (BioRoot RCS with SC), and 3C (BioRoot RCS CS). Least fracture resistance was found in 3A (ZOE with CS) (Figure 2).

Discussion

In addition to the lost tooth structure, various steps in root canal preparation leads to weakening of the tooth structure, such as during access preparation, removal of the unsupported dentin, instrumentation techniques, effects of irrigants used for smear layer removal, etc. The forces exerted during obturation have the potential to compromise the integrity of the remaining tooth structure, thereby elevating the risk of fracture.¹² The primary goal of endodontic treatment is to strengthen the remaining tooth structure. Hence, it is advisable to choose techniques and endodontic materials that contribute to the increased strength of root canal-treated teeth.¹³

The obturating materials and techniques play a vital role in prevention of vertical root fractures. Several materials have been used for obturation. Recently bioceramic sealers have been widely used for endodontic applications such as root end filling, apical filling. The composition of bioceramics allow the sealers to resist bacterial leakage, make them biocompatible i.e., instead of replacing, they help in regenerating the surrounding damaged tissues, create hydroxyapatite. Advantages include being non-cytotoxic, minimal or no shrinkage, stable in the surrounding biotic environment and produce less inflammation in the periapical tissues if extruded apically and can adapt well to the root dentin.¹⁴

Owing to the inherent superior properties of bioceramics, this study was undertaken to evaluate the effect of bioceramic sealer as obturating material compared to lateral condensation and single cone technique and to determine its effect on fracture resistance.

In the present study, zinc oxide eugenol-based sealer was used as it is a traditional option used along with core filing material as an obturating material. In addition, it gets resorbed if extruded into the periradicular tissues.¹⁵ In the present study, least fracture resistance was noted for ZOE sealer compared to AH Plus and BioRoot RCS. In all the groups, ZOE with lateral condensation was good compared to ZOE with single cone technique and ZOE complete obturation without core filling material. This is because of the higher solubility and least strength of ZOE.¹⁶

AH Plus sealer is a resin-based sealer, and has better physiochemical properties compared to ZOE. Advantages of this epoxy sealer includes, better penetration ability into dentinal tubules with adequate adhesion to root dentinal wall, possess antibacterial properties, is biocompatible, and can be easily removed from the canal if needed.¹⁷ In comparison to ZOE and AH Plus, it has been observed that AH plus required maximum fracture force.¹⁸ The results of the present study are in line with above mentioned studies with AH Plus showing higher fracture resistance compared to ZOE.

Single cone obturation technique has been in use in the current endodontic practice and was introduced to overcome the drawbacks of traditional cold lateral condensation, such as prolonged treatment time, void formation, excess forces generated during obturation. In this study, highest fracture resistance was found in lateral condensation group compared to single cone technique and complete sealer technique, possibly because in cold lateral condensation, the amount of core filling material is more when compared to single cone obturating technique and even the instrumentation was done with hand files which resulted in minimal root dentin removal during shaping. According to Solaiman M et al., single cone obturation technique was found to be inferior compared to cold lateral condensation of resilion or gutta-percha. It was suggested that the geometry of core filling material and the Ni-Ti file used during instrumentation should be well matched for proper adaptation. The size of inconsistency is reported to increase the risk of fracture resistance and in addition, the amount of sealer required in single cone technique to achieve proper adaptation to the dentinal walls is more, which might shrink once it sets. Thus, fracture resistance is less in single cone technique.¹⁹

In this present study, among all the sealers, bioceramic based sealer Bioroot RCS exhibited higher fracture resistance when compared to ZOE or AH Plus, in any of the obturation techniques used. According Almohaimede et al., it is because of the mechanical interlocking bond through the dispersion of the bioceramic sealer molecules into the dentinal tubules. This explains the results of this study in which bioceramic sealers showed highest fracture resistance when compared to AH plus sealer in endodontically treated teeth.²⁰

According to Zhang et al., the bonding of bioceramic sealer to the root dentine includes mechanical intertwine between the sealer particles and the root dentinal walls.²¹ However, Han and Okiji et al., stated that the mineral component of bioceramic sealer penetrates into the dentinal tubules and denatures the collagen fibres, forming mineral infiltrated zone. Hess D et al., reported that the interaction between phosphate ions with calcium hydroxide and calcium silicate hydrogel leads to deposition of hydroxyapatite alongside the mineral infiltrated zone.²² As the bioceramic sealers interact with the fluid in dentinal tubules, biomineralization zone is initiated resulting in mineral tags within the tubules, thereby improving the adhesion within the root canal space. The presence of calcium phosphate ions is the main reason for biocompatibility, preventing adverse reactions when in contact with the surrounding biological tissues.²³ The major advantage is when accidentally extruded through the apical foramen, bioceramics endorse regeneration of the bone instead of periapical complications.^24,25 The study findings indicated that utilizing bioceramic sealers in conjunction with the lateral condensation obturation technique resulted in superior fracture resistance compared to alternative obturation methods and other sealers (ZOE and AH plus). Additionally, there was no significant distinction observed between the single cone obturation technique and complete obturation with sealer when employing BioRoot RCS sealer.

Certain constraints of this investigation include its in vitro nature, which may not faithfully replicate clinical scenarios, and the inherent brittleness of extracted teeth, potentially influencing the study outcomes. Also, smaller sample size, non-inclusion of other bioceramic sealers are to be considered as other limitations. Therefore, further in vivo and in vitro studies are indicated for confident use of bioceramic sealers as a sole obturating material.

Conclusion

The use of the Bioceramic sealer BioRoot RCS, in conjunction with the lateral condensation technique, demonstrated increased fracture resistance in comparison to obturation methods involving single cone or complete sealer. Hence, within the limitations of this study, it can be advocated to use bioceramic sealer along with core material rather than using as a sole obturating material.

Conflict of interest

Nil

Acknowledgements

Nil