2.2. Injectability, initial setting time and mechanical strength of borosilicate glass cements

The injectability of the cement paste was tested in vitro using a procedure described previously [16]. The cement paste, prepared as described above, was transferred into a 5 ml syringe (Kindly Enterprise Development Group Co., Ltd, Shanghai, China) with an opening diameter of 1.7 mm and extruded by applying a force of 150 N at a crosshead speed of 5 mm min⁻¹ using a mechanical testing machine (ZQ-990LA, ZHIQU Test Machine Inc., Dongguan, China). The percent injectability (I) of the cement was determined using the equation:

where M_o is the initial mass of the cement in the syringe, and M is mass remaining in the syringe after the extrusion. Six samples of each cement were tested and the results are expressed as a mean ± SD.

The initial setting time of the cement pastes (prepared as described above) was determined according to methods in Refs. [16,17]. Briefly, a Teflon mold containing six holes (20 mm in diameter × 5 mm) was placed in a water bath at 37 °C. Then the cement paste was injected into the Teflon mold cavity. The initial setting time was determined using Gilmore needles (mass = 114 g; diameter = 2.117 mm). Six samples of each cement group were tested and the results are expressed as a mean ± SD.

The compressive strength of the each cement group after setting (equilibrated for 24 h under constant environmental conditions) was tested in a mechanical testing machine (ZQ-990LA, ZHIQU Test Machine Inc., Dongguan, China). Cylindrical samples (6 mm in diameter × 12 mm) were tested at a crosshead speed of 1.0 mm min⁻¹. Six samples of each cement group were tested and the results are expressed as a mean ± SD.