Specimen preparation

Forty freshly extracted teeth according to selection criteria were chosen. The collected samples were thoroughly cleaned free of debris or calculus by ultrasonic scaler (EMS, Switzerland) and kept in 0.1% thymol solution (Sigma-Aldrich chemicals Pvt. Ltd., USA) at room temperature for disinfection and later stored in normal saline (Otsuka Pharmaceutical India Pvt. Ltd., Ahmedabad, India) until use. Each tooth was decoronated horizontally at cementoenamel junction labiolingually using a flat diamond abrasive disc (Sunny Superhard Tools Co Ltd, India) mounted on a slow-speed micromotor straight handpiece (NSK, Japan) under water coolant to obtain 12 mm standardized length of root. The coronal part of each canal for all decoronated teeth was preflared with round diamond abrasive (BR-46; Mani Inc., Japan) mounted on airotor handpiece (W&H, Austria) under water coolant.

The working length was determined just 0.5 mm short of apical foramen using size #15 K-file (Mani Inc., Japan) for each root canal. Biomechanical preparation of root canals was done with K-files by step back technique, initially with size #15 up to master apical size #40, along with copious irrigation using saline in a syringe with 30-gauge side-vented needle throughout the instrumentation to prevent clogging of debris in root canals. For achieving a uniform internal diameter of root canals, the canals were prepared with peeso reamers mounted on a slow-speed contrangled micromotor (NSK Japan), from size #1 to size #4 (Mani Inc., Japan). Two horizontal slices of thickness 2 mm were sectioned from the middle third of the root with a flat diamond abrasive disc mounted on a slow-speed straight micromotor handpiece under water coolant. The thickness was reconfirmed using a digital vernier caliper (Panama Orthodontics Inc., USA) with an accuracy of 0.001 mm to maintain the standardization of slices.

All the sectioned samples were cleaned by flushing them in individual containers, measuring 20 ml each, with 5.25% sodium hypochlorite (Coltene Whaledent Pvt. Ltd., Maharashtra, India) for 1 min, followed by distilled water for 1 min and finally with 17% EDTA (Prime dental Pvt. Ltd., Thane) for 1 min to remove the smear layer. This procedure for removing the smear layer was repeated for two cycles for thorough removal of both organic and inorganic debris and at the end, the samples were cleaned with distilled water for 1 min. After smear layer removal, the samples were dried with 80-size absorbent paper points (Medicept Dental Pvt. Ltd., India) and arranged on a clean, dry glass slab.

Biodentine (Septodont, St. Maur-des-Fosses, France) was manipulated as per manufacturer's instructions. The mixed Biodentine, which had putty-like consistency, was collected and packed into prepared root canals, using an MTA carrier (Waldent Innovations Pvt. Ltd., India), followed by condensation with hand plugger (GDC, India) and was left undisturbed for 12 min to allow initial setting of the material. The samples were later stored at 37°C and 100% humidity (Remi Instruments Ltd., India) for 1 week to enable a complete set of Biodentine.

After the complete set, all the samples were embedded horizontally into self-cure acrylic resin (DPI, India) using plastic molds to obtain the required 80 specimens [Figure 1]. The prepared specimens were polished using 600 grit silicon carbide paper to get a smooth surface and subjected to Vicker's microhardness test (Shimadzu HMV-G31DT ENG 230V Micro Vickers Hardness Tester, Japan) [Figure 2]. For the measurement of microhardness on radicular dentin, an indentation was placed 0.5 mm away from the root canal wall. Each determined location on Biodentine and radicular dentin was loaded with a pyramid diamond indenter point with weight of 100 g and dwell time of 5s. The Vickers hardness number (VHN) values were displayed digitally and noted.

Specimen before subjecting to Vicker's microhardness test

Specimen being subjected to Vicker's microhardness test

The specimens were randomly divided into four groups (n = 20) based on the organic solvents used,

In all groups, the specimens were immersed in a beaker containing the respective organic solvents for a period of 10 min and a magnetic stirrer was placed to ensure complete wetting of all specimens. After removal from respective solutions, specimens were dried with absorbent paper points. The Biodentine and radicular dentin of each specimen was again subjected to Vicker's microhardness test. The mean microhardness values before and after exposure to respective solutions for all groups were calculated and subjected to statistical analysis.