Water content of ampoule packaged with ProRoot MTA

We are writing to draw attention to an inconsistency in the amount of water in the packages of both white and grey MTA which are commercially available as ProRoot MTA Original (Dentsply International Inc., Johnson City, TN, USA) and ProRoot MTA (Dentsply International Inc.). In each package, there are five sachets (pouches) containing 1 g of ProRoot MTA powder and six ampoules of water. The manufacturer claims that the amount of water inside each ampoule is equal to 0.35 g. This information is written on the sides of each package. However, unfortunately, we have determined that the amounts of water in the ampoules are inconsistent. Our first reaction to this finding was to recheck the accuracy of our measurements. The accuracy of the laboratory digital scale was confirmed by using predetermined standard weights. Afterwards, in an attempt to evaluate the amount of water in each ampoule; 58 ampoules from various packages of ProRoot MTA original (grey) and ProRoot MTA (white) were chosen randomly. The samples were kept at a controlled laboratory temperature (20 C) for 24 h before measurement. The weight of each ampoule with the water inside was measured using a Precisa 80A-200M device (Zürich, Switzerland), an analytical laboratory balance that measures weight to a high degree of accuracy. The analytical balance was stabilized at zero then the weight of each ampoule with the water inside was measured and recorded to an accuracy of three decimal places at 20 C. Then the tip of each ampoule was removed using a surgical scalpel and water was released carefully into a glass container, which had also been kept at 20 C for 24 h. Then, the weight of water was measured (MW) to an accuracy of three decimal places at 20 C. Subsequently the weight of each empty plastic container and the removed tip section were also determined. To calculate the definitive amount of water inside the ampoules, the weight of each empty plastic container and the cut tip were subtracted from the weight of ampoules before opening. The value obtained was considered as the definitive amount of water inside each ampoule (DW). The mean difference of the definitive water (DW) and measured water (MW) was 0.011 g (range: ‘0.30 g, 0.000 g’ with a SD: 0.007). This is the amount of water that could not be released from the plastic ampoule. However, in the clinical situation this amount of water would probably remain in the ampoules. Both the definitive and measured values were compared with the amount of water that the manufacturer claims is inside the ampoules. The results are demonstrated in Figs 1 and 2. The average measured (MW) and definitive weight (DW) of water in the ampoules were 0.211 g (range: ‘0.140 g, 0.270 g’; SD: 0.40) and 0.223 g (range: ‘0.149 g, 0.290 g’; SD: 0.40) respectively. These values are 0.139 g (range: ‘0.210 g, 0.800 g’) and 0.198 g (range: ‘0.201 g, 0.060 g’) less than the amount of water claimed to be inside the ampoules. This lack of consistency in the amount of water inside ProRoot MTA packages is of concern and may explain the uncontrolled and undesirable characteristics of the material in certain clinical and laboratory situations. MTA consists of hydraulic powders that set and harden in the presence of water through the hydration process. According to the US patent number 5 415 547, the principle component of MTA is Portland cement (Torabinejad & Dean 1995). Complete hydration of Portland cement cannot occur if the water/cement ratio is below a certain value (Taylor 1997). The ratio of 0.33 is recommended for MTA (Fridland & Rosado 2003) and this is reflected in the nominal 0.35 g of water that is provided alongside each 1 g of MTA powder by the manufacturer. In the manufacturer’s instructions for use, which can be found inside the package, it is also clearly stated that: ‘Note: 1: Adding too much, or too little liquid will reduce the ultimate strength of the material.’ The setting of Portland cement and thus MTA takes place in two stages. After mixing with water the hydration reaction of calcium silicates begins and results in the formation of a gel consisting of calcium silicate hydrates, which liberates calcium hydroxide. The calcium hydroxide then gradually reacts with the minerals to form other hydrated compounds. The doi:10.1111/j.1365-2591.2009.01541.x