COMPARATIVE EVALUATION OF TENSILE BOND STRENGTH OF ENDODONTIC SEALERS TO DENTIN AND GUTTA PERCHA-AN IN-VITRO STUDY

Introduction: The root canal therapy is done with the intention to seal it off from any fluid leaks, thus enhancing the longevity of the therapy. The seal between the obturating material and the dentinal walls of the root surface is done by the endodontic sealer. The sealer is designed in such a way that it has to mould itself with the curves and follow the shapes of the


Introduction:
The root canal therapy is done with the intention to seal it off from any fluid leaks, thus enhancing the longevity of the therapy. The seal between the obturating material and the dentinal walls of the root surface is done by the endodontic sealer. 1 The sealer is designed in such a way that it has to mould itself with the curves and follow the shapes of the root dentinal wall. It should also allow the proper placement of the obtuartion material in the canal. 2 Most commonly the sealers used in the endodontic therapy are resin-based sealers, calcium hydroxide, and zinc oxide eugenol. There has been however a continuous quest for newer root canal sealers. 3 There are newly introduced calcium silicate based sealers called Bioceramic sealer, Bio Root RCS. They are available as powder liquid composition. The powder constitutes Calcium silicates, Calcium phosphate monobasic, calcium silicate Zirconium oxide, Calcium hydroxide. 4 The most commonly used new variant of resin sealer is 'MTA Fillapex'. This MTA sealer is available in 2 paste system. It is a two paste system consisting of MTA, bismuth oxide, salicylate resins, pigments, silica nanoparticles. This sealer has been known to possess a good ability to seal the root canal, along with possessing the antibacterial ability. There are also various notable properties of the sealer that make them a choice among the resin sealers like lesser solubility and good biocompatibility. 5 AH Plus sealer and Sealapex sealer are the 2 varieties of root sealers. The first sealer has Calcium tungstate, Diepoxide, Zirconium oxide N,N-dibenzyl-5-Oxanonane-diamine-1,9 TCD-diamine1-adamantane amine. The sealapex has Barium sulphate, Calcium hydroxide, Titanium dioxide, Zinc oxide, Zinc striate. 6 The bond strength between the radicular dentin and the sealer can be evaluated with the use of the tensile test. 7 Tensile forces acting between two surfaces normally determine the bond strength between two materials. 8 Hence in this we conducted an in-vitro study to compare the tensile bond strength of endodontic sealers to dentin and Gutta Percha.

Material and Methods
Thirty six single-rooted extracted maxillary and mandibular human canine and premolar teeth with matured apices and without the fractures or root defects were included in the present study. The teeth were sectioned at the CEJ at low speed using a diamond cutting bur. Normal saline was used to store the sectioned roots. Protaper hand instruments were used to negotiate the canal and the canal was enlarged and shaped to the size of F3. The instrumentation was done 1mm short of the root apex with the help of the radiograph. 3% sodium hypochlorite was used as irrigation and with the final irrigation done with 'ethylene diamine tetra acetic acid 17%' and saline. The teeth were then preserved in normal saline till further categorised into 4 GROUPS. In Group Ⅰ (MTA Fill apex), the self-mixing tip with the syringe is used to mix the sealer. Later GP cone of size 30 with taper 0.04 placed to working length that is coated with sealer. Excess length of the GP point is burned to the orifice level. 2 hours is the setting time for the sealer according to the manufacturer's instructions. Later the tensile strength is checked for.
In Group Ⅱ (BioRootRCS), the canal is filled upto two-thirds using the syringe tip that's provided. Later the obtuartion with the matching GP cone was done and the remaining cone out of the root at the cej trimmed with the bur. 4 hours is the setting time for the sealer according to the manufacturer's instructions.
In Group Ⅲ (Sealapex), the two paste system is manipulated according to the instructions of manufacturer and a homogenous mix is attained. Sealapex was applied to the full length of the root canal. Later the gutta-percha point was done to working length measured. Setting time was fourty five minutes.
In Group Ⅳ (AH Plus), the two paste system is manipulated according to the instructions of manufacturer and a homogenous mix is attained. A creamy homogenous mixture was obtained. After thorough drying of canals AH Plus sealer was applied, tips of dry disinfected gutta-percha points dipped into the AH Plus sealer and placed up to the working length. Setting time is 8h.
Temporary Filling Material was used to fill the coronal portion of the teeth and stored at 95% relative humidity and 37°C for 24 h. Using a hard tissue microtome the teeth were sectioned horizontally into thick slices of 2 mm. 'The filling material was loaded with a 1-mm diameter cylindrical stainless steel plunger, and should provide almost complete coverage over the main cone without touching the canal wall. Loading was performed on a universal testing machine at a speed of 0.5 mm/ min until deboning occurred. The load was applied in an apical-coronal direction to avoid any interference because of the root canal taper. The bond strength value in megapascals (MPa) was computed by dividing the maximum load needed to dislodge the filling material in Newton's by the interfacial area (mm2).' 9 Finally, 36 specimens were tested for each group of sealers. Each sample was fixed to the universal testing machine (Zwick, 1494, Germany). At this point the tensile bond strength of the sealant to gutta-percha was measured at a crosshead speed of 1mm/min and using a 20kg load cell. The maximum load (gm.) at tensile failure divided by the cross-section of bonded area (28.26 mm2) was expressed as tensile bond strength in MPa. 8

Results
Two-way ANOVA and Tukey tests multiple post hoc tests were done for the statistical analysis. there was a statistically significant values noted between the groups, by using Statistical Package for the Social Sciences (SPSS), SPSS 21.0 (IBM Corporation, USA) with the p < 0.05 as significant. The highest bond strength among the groups was found in Group Ⅱ (BioRootRCS). The lowest bond strength was found in Group Ⅰ (MTA Fill apex). Statistically significant difference was also noted among the 4 groups. More of cohesive or mixed failures was observed by the stereomicroscopic evaluation of the specimens.

Discussion
Root canal therapy is done to remove the microorganisms from the teeth. This is attained by proper BMP i.e., cleaning and shaping of the root canal. This helps in single block configuration. 10 The most common obturating material is Gutte percha, however it does not bond to Dentinal walls. The obtuartion with an adept sealer helps in attaining a fluid seal in the root canal. The root canal sealer helps in filling the imperfections, increase adaptation of the root filling material to the canal walls. 8 For the past few years, the adhesion of endodontic sealers to the obtuartion material and the dentin has been of interest. 8,9,10 The clinical success of the root canal therapy depends on the Bond strength of the sealer between the GP, and the radicular dentin. A good Bond strength of the sealer helps in decreasing the detachment from dentin of the GP during restorative procedures. Later during the masticatory function also the good sealer will prevent the dislodgment of the GP cone from the root. The bond between the endodontic sealer and canal walls may be by the micromechanical adhesion or the frictional retention. 11 The bond strength of BioRootRCS, AH Plus and Sealapex may be improved with the use of final rinse of EDTA as after NaOCl. The smear layer may be removed by these irrigants thus exposing the collagen of the radicular dentin. Thus establishing the resin tags into the radicular dentin.
Roughened gutta-percha has shown to increase the bond strength of sealers to gutta-percha in the studies of Lee et al 12  In the present study, the highest bond strength was shown by BioRootRCS compared to all other sealers with a statistically significant difference (P < 0.05). It could be attributed to the self-adhesive nature, that is formed by the chemical bond with dentine. BioRoot RCS has a bioactivity with calcium release, strong alkalizing activity and apatite-forming ability, and adequate radiopacity. 15 Low adhesion of MTA plus may be due to the low adhesion property of its 'taglike structures to root canal dentin'. MTA Plus in direct contact with fluids exhibited partial decalcification of calcium silicate hydrate in contact with the solution, microcracking and leaching of calcium hydroxide. Interaction with a physiological solution resulted in inhibition of hydration. 16

Conclusions
Within the limitations of the present study, BioRoot RCS (Bioceramic Sealer) showed the highest tensile bond strength while MTA Fillapex showed lowest bond strength among all the four groups.