Endodontic materials should be resistant to dislocating forces such as functional pressure or condensation for good long term prognosis. Since past decade there has been a greater utilization of bioceramic materials in endodontics. Mineral trioxide aggregate (MTA), a calcium silicate based hydraulic cement (CSC) is widely used for perforation repair, root-end filling, pulpotomy, apexification and regenerative procedures. MTA has several desirable properties such as biocompatibility, superior sealing ability, and the ability to set in the presence of moisture and wet environment. However, MTA posses some notable shortcomings such as long setting time, poor immediate washout resistance and difficult handling property. In few recent studies, to improve the physicochemical properties of MTA, the addition of calcium chloride (CaCl ₂) to MTA ¹ with the concentration of 2%–15% has been proposed ¹ to reduce the setting time of the material ² , ³ with similar biocompatibility. ⁴

Biodentine (Septodont, Saint Maur des Fosses, France) is a more recent CSC with improved physical properties and reduced setting time as compared to MTA. ¹ Biodentine powder is mainly composed of tricalcium silicate, calcium carbonate (filler material) and zirconium oxide (radiopacifier), whilst the liquid consists of CaCl ₂(used as a setting accelerator) and a hydro soluble polymer (water-reducing/super plasticizing agent). This biomaterial is considered as a biocompatible and bioactive dentine substitute and has been indicated for coronal and radicular restorations. ¹

Nanotechnology can be beneficial in producing and constructing advanced biomaterials with exclusive biological, chemical and physical properties. ⁵ In present study Nano Biodentine (NBD) has been included to evaluate its adhesive properties compared to Biodentine.

Indirect Ultrasonic agitation has been proposed as an effective mode of increasing the packability and density of endodontic materials as well as the compressive strength of hydraulic cements. ⁶

Till date, a little information is available on the bond strength and adhesive properties of CaCl ₂modified MTA and NBD to radicular canal dentin with the indirect ultrasonic activation. This current study evaluates the push out bond strength of CaCl ₂modified MTA and NBD with manual placement and indirect ultrasonic activation techniques.

An in vitro experimental study was conducted on recently extracted human mandibular premolars with single root, extracted due to periodontal and orthodontic considerations between July and September 2018 at department of conservative dentistry and endodontics, SIBAR institute of dental sciences, Takkellapadu, Guntur, and Andhra Pradesh, India. Institutional ethical clearance was obtained. The sample size was calculated using Raosoft online sample size calculator and the power of study set was 80%. The criteria for teeth selection included the presence of single rooted teeth with canal curvature between 5° and 10°, the absence of any micro cracks on dentinal walls under stereomicroscope at 4X magnification, absence of internal and external resorption or calcification and with complete formation of root apex. Each tooth was radiographed both buccolingually and mesiodistally to detect any possible calcifications. After a thorough screening, a total of 120 samples were considered for the inclusion in this in vitro study.

Specimen preparation

The collected single rooted human mandibular premolars were decoronated at the cementoenamel junction with a diamond disc (Wuxi xiangsheng industrial and trading co.) mounted on a micro motor (NSK Ti-max Nao 95LS) under water coolant. A total of 120 samples were selected, which were sectioned perpendicular to the long axis at mid coronal third of root to attain dentin discs of 2mm thickness using Isomet precision cutter (Buehler Inc). While selecting, these discs were gauged with a customized acrylic gauge for a standardized internal diameter. The root sections were immersed in 17% EDTA (Vista Dental Products, U.S.A) followed by water rinse and then in 2.5% sodium hypochlorite (PrevestDenpro Dental Products, India) each for 1 min to remove the smear layer. They were then cleansed with distilled water in an ultrasonic bath. Later, the root canal surfaces of the samples were dried with a dehydrating solution using absorbent points (Hydrol, septodont).

Experimental procedure

The root sections were randomly assigned into 6 groups:

Group I: Nano Biodentine-manual (NBDM) (n = 20)

Manipulation

MTA (DentsplyMaillefer, Ballaigues, Switzerland) and Biodentine (Septodont, Saint Maur des Fosses, France) were manipulated according to the manufacturer's instructions. To achieve uniformity while manipulation all the materials used in present study has been mixed using a capsule attached to a mechanical activator (Ultramat-2). MTA and 5% Calcium chloride were mixed in a 3:1proportionas previously suggested. ¹ Nano Biodentine (NBD), obtained by Ball milling of Biodentine in a zirconia ball-mill machine (Gold Belt Global) for 24 h. The particle size of final product has been evaluated and confirmed to be in the range of 2.3–5 nm by Dynamic light scattering (Department of Biochemistry, Osmania University, Hyderabad). To enable the condensation of the materials, the specimens were placed over a tinfoil, which was stabilized on a customized elastomeric block Figure 1. Figure 1

Customized elastomeric block.

Box plot diagram represents distribution of push out bond strength values with standard deviation Figure 6. Push out bond strength was higher in Group VI (BDU), and least with Group II (MM). Intergroup comparison revealed a Statistically significant differenceamong most of the groups (P < 0.05) except between Group II versus III, between Group III versus V and between Group I versus II, III, IV, V. Mean push out bond strength values had suggested the bond strength values in the following order: Figure 6

Box plot diagram represents distribution of push out bond strength values with standard deviation.

In the present study, the dentin discs of 2 mm thickness were used for the purpose of push out test measurement. Over estimation of the bond strength may occur if thickness of discs is Increased due to increase the area of friction. ⁷ The chemical and physical properties play a major role in the clinical outcome of root canal filling materials which can be affected by factors such as mixing and placement techniques, delivery system, exposure to various clinical environments, storage conditions and the ratio of the constituent components. ⁸ To fill voids and spaces between the obturant and the tooth structure and to form a fluid tight seal, the root canal filling materials are used with the semisolid or solid core filling material to provide the required adhesion. ⁹ In contemporary endodontics the concept of monoblock has increased the potential of creating good adhesion in root canal walls. ¹⁰ , ¹¹ In the present study all the materials have only one interface that extends circumferentially between the material and the root canal wall which is a primary monoblock.

Hydraulic cements are finely ground materials (powders), yielding complex hydrated products when mixed with water or specific water based component. Any interference in hydration reaction might influence the biological, chemical, and physical properties of the resulting productwith altered clinical performance. ¹²

The conventional Proroot MTA and Bio dentine have been modified in present study by the addition of CaCl ₂and Nanoparticularization respectively.

The addition of CaCl ₂at the concentrations of 2%–15% improves physicochemical properties of MTA and shortens the setting time. However, the shortcomings of this modified material include reduced expansion, coherence which might influence the bond strength with radicular dentin. However, considering the advantages of addition of calcium chloride such as shortened setting time and increased biomineralization, ¹³ altering the mode of placement might aid in compensating the reduced bond strength with root canal dentin. Being a viable tool in endodontics, indirect ultrasonic agitation reduces the size of cement particles and consequently increases the total reactive surface by de-clustering the particles that are clogged to each other ¹⁴ resulting in increased flow, setting, and compaction of the material. ¹⁵ In the current study, Ultrasonic activation of CaCl ₂modified MTA resulted in better bond strength even superior to conventional MTA in accordance with the previous study. Besides ultrasonic placement, presence of nanoparticles also has a positive impact on the penetration of material into the dentinal tubules. There are other factors that might be able to influence the capacity of dentinal tubule penetration of the endodontic filling material: The surface activity of the sealers, the contact angle between sealer and the dentinal walls, the diameter of the opened dentinal tubules and the employed obturation technique. ¹⁶

Materials with Nano particles have better workability, fluidity and positive influence on hydration process resulting in efficient filling of root canal. In present study, NBD demonstrated increased chemical reactivity is due to higher solubility and surface area as observed by shortened setting time compared to conventional Biodentine. This is substantiated by a fact that a given mass of material in nanoparticle form is much more reactive than the same mass of material made up of larger particles. ¹⁷ It was demonstrated that the more the material is soluble, the higher OH ⁻and Ca ²⁺release which is correlated to the higher solubility recorded for BD. This had led to more Ca ²⁺from nanomaterials. ¹⁸ Setting accelerator effect of the nanoparticles acts as seeds and stimulates the nucleation of calcium silicate, accelerating the hydration process (sowing effect), also helps in accelerating the setting time and hydration process. ¹⁹

In the present study, the indirect ultrasonic mode of placement had a better bond strength value than manual with a statistically significant difference. It was observed that Group VI (BDU), has shown highest bond strength values among all other groups. The effective combination of the unaltered hydration which enables the extension of material into the dentinal tubules with indirect ultrasonic activation has resulted in this superior bond strength. However the tubular penetration is lower than that of nanobiodentine with ultrasonic activation which might be due to less particle size of nanobiodentine than Biodentine thus enabling greater penetration. The reduced bond strength of NanoBiodentine compared to Biodentine could be due to the altered density, particle scattering leading to altered hydration characteristics. In the present study, the mean push out bond strength of Group III (BDM) and Group V (MU) had shown similar results with no statistically significant difference, suggestive of ultrasonic activation of MTA could achieve similar results in terms of bond strength even though there is difference in tubular penetration. Except for Groups IV (NBU) and VI (BDU) tubular penetration values are proportionate to push out bond strength values in all the groups of the present study. The greater tubular penetration of Group IV (NBDU) might be due to smaller particle size of nanobiodentine which is further enhanced by indirect ultrasonic activation. However, as previously described it altered the hydration properties resulting in lower bond strength. It was observed that majority of the failures associated with all the groups are of cohesive nature which suggests that the interface between filled material and root dentin was more durable than core material itself. At present the available literature is not sufficient to ensure the long term performance of the bioceramic materials used in the present study. Further research is needed to evaluate the clinical longevity of these modified bioceramic materials.

Within the practical limitations of the current in vitro study, it can be concluded that indirect ultrasonic activation has resulted in superior interfacial bond strength and tubular penetration than the manual compaction. A combination of Biodentine with indirect ultrasonic activation has resulted in superior bond strength compared to all other groups. On the other hand, manual condensation of MTA has demonstrated the lowest bond strength values. Having greater tubular penetration, Nanobiodentine appears to be a promising root canal filling material.

Financial support and sponsorship

Nil.

Conflicts of interest

The authors of this manuscript declare that they have no conflicts of interest, real or perceived, financial or nonfinancial in this article.