BIOACTIVITY (APATITE FORMING ABILITY) OF COMMERCIAL AND EXPERIMENTAL POLYSILOXANE-GUTTAPERCHA ENDODONTIC SEALERS. CALCIUM RELEASING, ALKALINIZING ACTIVITY, ESEM-EDX MORPHOLOGICAL ANALYSIS

INTRODUCTION There is a growing interest in sealers with bioactive (apatite forming) and biointeractive (release of biologically relevant ions) properties, especially when dealing with wide apices of immature and retreated teeth, root internal resorptions, blood contamination and refractory periapical lesions with large bone defects. OBJECTIVES The aim of this study was to assess the chemical properties (alkalinizing activity, calcium release) and the bioac- tivity (apatite forming ability) of experimental Polysiloxane-guttapercha Calcium Silicate-containing cements in simulated wet root canals. The ability to nucleate calcium phosphate on their surface upon immersion in a simulated body fluid (SBF) has been evaluated using Environmental Scanning Electronic Microscopy (ESEM) and Energy-dispersive X-ray analy- sis (EDX). MATERIALS AND METHODS A polysiloxane-guttapercha based sealer (GuttaFlow 2, Coltène/Whaledent Inc.) was mixed with three different calcium silicates materials, namely Calcium Silicates and Di Calcium Phosphate (CaSi/DCPD), Calcium Silicates (CaSi) and Hydroxyapatite (CaSi/HA) and Bioroot RCS (Septodont, Saint-Maur-de-Fosses, France). 4 experimental formulations were obtained: GuttaFlow 2 + 20% CaSi/DC GuttaFlow 2 + 20% CaSi/HAGuttaFlow 2 + 20% BioRoot RCS GuttaFlow 2 + 30% BioRoot RCS Materials were compacted into polyvinylchloride molds (8 mm diameter, 1.6 mm height; n=8 per group), imme- diately immersed in 10 mL of deionized water (pH 7.18) into polypropylene sealed containers and stored at 37°C. The soaking water was replaced at each endpoint (3 h and 1,3,7,14,28 days) and analyzed for pH and calcium content. Analyses were carried out under magnetic stirring at room temperature (24°C) by using a multiparameter laboratory meter (inoLab 750, WTW, Weilheim, Germany) connected to a selective electrode (Sen Tix Sur; WTW) for pH measurements or a calcium probe (Calcium ion electrode, Eutech Instruments Pte Ldt, Singapore. ESEM (Zeiss EVO 50; Carl Zeiss, Oberkochen, Germany) connected to a secondary electron detector for energy dispersive X-ray analysis (EDX; Oxford INCA 350 EDS, Abingdon, UK) was used to investigate apatite forming abil- ity on samples immediately immersed in Hank Balanced Saline Solution (HBSS), after 3 and 28 days. RESULTS All the materials demonstrated the ability to alkalinize the pH from 3 hours to 24 hours. These values were con- stant until 28 days. Calcium release demonstrated a progressive increase from 3 hours to 28 days. After 28 days immersion in HBSS, a layer of CaP was detected on all the experimental samples. DISCUSSION Conventional Guttaflow 2 does not release calcium ions, nor proved to alkalinize the local environment. Sealers with bioactive (apatite forming) and biointeractive properties may represent a new frontier for endodontic ther- apy. Release of biologically relevant ions (i.e Ca++ and OH-) may be useful for mineralizing cells activation and proving a slight antibacterial activity. Moreover, an alkaline environment favours apatite precipitation. All these conditions may allow a faster healing of the periapical bone. CONCLUSION Nano spherulites particles were detected in all formulations. Their composition was mainly calcium-phosphate and apatite. EDX confirmed the presence of calcium and phosphate