Vibrational investigation on the in vitro bioactivity of commercial and experimental calcium-silicate cements for root-end endodontic therapy.

Portland cements are hydraulic calcium-silicate materials able to set in moist environment. White Portland cements are composed of tricalcium silicate (alite), dicalcium silicate (belite), tricalcium aluminate and calcium sulphate. Grey Portland cements also contain a ferrite phase (aluminoferrite) and other transition metals (Cr and Mn) and metalloids (As). In the last decade, calcium-silicate hydraulic cements have received great attention in endodontics because able to set in presence of blood and other biological fluids. In the 1990s a first calcium-silicate cement MTA (Mineral Trioxide Aggregate) was developed as root-end filling material. Recent investigations demonstrated that MTA and calcium-silicate cements are bioactive materials, i.e. they are able to spontaneously form a calcium-phosphate layer when immersed in physiological-like fluids. This bone-like apatite layer can support new tissue formation and the integration in bone tissue and represents an essential requirement for an artificial material to be considered osteoconductive and osteoinductive. This study was aimed at comparatively investigating the bioactivity of commercial calcium-silicate cements (ProRoot white MTA, Angelus grey MTA, Angelus white MTA, TechBiosealer root end) and an experimental calcium-silicate cement (wTC) upon ageing for different times (from 1 to 28 days), at 37°C, in Dulbecco’s Phosphate buffered saline (DPBS). With the exception of wTC, all the cements contained bismuth oxide for radiopacity. ATR/FT-IR and micro-Raman spectroscopy were used to investigate the presence of deposits on the cement surface and the composition changes as a function of storage time (hydration of anhydrite/gypsum and formation of ettringite; hydration of belite/alite and formation of hydrated silicates). Spectroscopic analyses showed that after one day of ageing all the cements formed an apatite deposit on their surface, as revealed by the appearance of the bands at about 1030, 600 and 560 cm-1 (IR) and 960 cm-1 (Raman). The thickness of the deposit was evaluated by the I960(phosphate)/I990(cement) (Raman) and I1030(phosphate)/I950(cement) (IR) ratios obtained on the surfaces of the samples. After one day in DPBS, only in Angelus grey MTA the bands of the cement near 830-850 cm-1 became undetectable due to the high thickness of the superficial apatite deposit suggesting that Angelus grey MTA possesses the highest bioactivity. At increasing storage times in DPBS (14-28 days), the thickness of the deposit increased as well as its crystallinity and the bands of a B-type carbonated apatite appeared at 1460-1415, 1025, 960, 600-560 cm-1 (IR) and 1074,1050, 965, 606-595- 436 cm-1 (Raman). All cements produced and released Ca(OH)2. Its formation was monitored by the trend of the 3640 cm-1 IR band and its release was detected by pH measurements. In conclusion, all calcium-silicate cements resulted bioactive. The higher bioactivity found for Angelus grey MTA must be further investigated considering the presence in its composition of transition metals.