Objective: A liner must perform as a barrier and protect the dental pulpal complex. Calcium-silicate MTA materials recently used for pulp capping demonstrate the ability to form hydroxyapatite when immersed in simulated body fluid (Gandolfi et al. 2009, 2010). TheraCal is a light-curable resin formula which contains CaO mineral oxides, designed to be used as liner and pulp capping material that demonstrates good biocompatibility/absence of cytotoxicity. The aim of this study is to evaluate the ability of this material to form hydroxyapatite when immersed in a phosphate-containing solution. Method: TheraCal (Bisco Inc, USA), Control paste (without mineral oxides) (Bisco Inc, USA), ProRoot MTA (Dentsply, USA) were used. Sample discs (n=10 for each material) were prepared. The materials were placed in a PVC mold (8mm dia x 1.6mm) and light-cured on both surfaces for 20 seconds (per manufacture) using a LED light, after the application of a transparent polyester strip. The discs were de-molded, immersed in 10mL of a phosphate-containing solution (Dulbecco's Phosphate Buffered Saline, DPBS) in a sealed container and stored at 37\ub0C. The surface chemistry, morphology and formation of apatite on samples surface after 1, 7, 14 and 28 days of immersion in DPBS was assessed by ESEM-EDX, micro-Raman and FT-IR techniques. Results: TheraCal demonstrated the capacity to form apatite on its surface after 24 hours immersion in DPBS, as did ProRoot MTA. Amorphous apatite (952 cm-1 Raman band) was detected within the first 24 hours, while a more crystalline apatite (960 cm-1 Raman band) was noticed at 7days. No deposit was detected on the Control. Conclusions: TheraCal is a calcium-releasing material able to induce the formation of apatite and represents a promising material in direct pulp-capping clinical/surgical procedures. The ability to form apatite may play a critical/positive role in new dentin formation
