Abstract: Objective: To modify the preparation method of nanometer calcium hydroxide (nano-Ca(OH)₂) and assess the preliminarily biological safety for root canal therapy. Methods: Nano-Ca(OH)₂ was prepared by use of synthetic nano-precipitation titration of Ca(OH)₂ materials with the raw materials for CaCl₂ and NaOH as well as polyethylene glycol (PEG). According to modified method, the whole procedure was as following: PEG parceled first CaCl₂ and reacted with NaOH, and ultrasonic wave was used to vibrate reaction so that to accelerate production of nano-Ca(OH)₂ and prevent agglomeration of particles, as well as drying method of heterogeneous azeotropic distillation was made to divergence the nano-Ca(OH)₂ gel. The infrared spectroscopy and transmission electron microscopy were used to detecte the physical and chemical characteristics of nano-Ca(OH)₂. Nano-Ca(OH)₂ paste that was mixed with medical iodoform and glycerol was used as root canal therapy. The scanning electron microscopy was used to observe the shape of specimens. The experiments were divided into negative group, positive group, and Nano-Ca(OH)₂ paste group. Results: The modified treatment had higher automaticity, could isolate bacterial and dust particle, and decrease manufacture time, work intensity, and cost. The nano-powder distributed much more evenly without agglomeration. The nano-article of Ca(OH)₂ was about 100-200nm, in the round and hammer shape. As nano-Ca(OH)₂ paste, it had dense structure, compact arrangement, and smooth surface, which was better than ordinary Ca(OH)₂ paste. Furthermore, nano-Ca(OH)₂ paste could not interact with hemoglobin and maintain the morphological integrity and smooth surface of red blood cells. Hemoglobin value was sign-ificantly decreased in nano-Ca(OH)₂ paste group compared with positive group (P<0.01). Conclusion: The modified manufacture method was scientific and reasonable. Nano-level and uniform Ca(OH)₂ was produced, which could prevent the hemolytic of humanred blood cells and be used as paste for root canal therapy.

Key words: Nanometer calcium hydroxide, Modification of manufacturing method, Physical characterization, Biological safety