Physicochemical and biological properties of a novel injectable polyurethane system for root canal filling

Figures & data

Figure 1 FTIR spectra of IPDI, PTMEG, and different PU-based composites.

Notes: Wave number is denoted by ν. The names of the tested sealers begin with PU. PU0 is 0 wt% silver phosphate (Ag₃PO₄). Similarly, PU1 is 1 wt% Ag₃PO₄, PU3 is 3 wt% Ag₃PO₄, and PU5 is 5 wt% Ag₃PO₄. For each of these sealers, the corresponding NCO-terminated PU prepolymer begins with the prefix “Pre-”.

Abbreviations: au, arbitrary units; FTIR, Fourier transform infrared; IPDI, isophorone di-isocyanate; PTMEG, polytetramethylene ether glycol; PU, polyurethane; NCO, isocyanate.

Figure 2 The FTIR spectra of PU-based sealers in zones 500–4,000 cm⁻¹.

Notes: Each PU-based sealer is made from a mixture of Component A and Component B. Component A is an NCO-terminated PU prepolymer. Component B is a mixture of dibutyltin dilaurate, triethanolamine, and PEG. PU0 is 0 wt% silver phosphate (Ag₃PO₄). Similarly, PU1 is 1 wt% Ag₃PO₄, PU3 is 3 wt% Ag₃PO₄, and PU5 is 5 wt% Ag₃PO_4.

Abbreviations: PU, polyurethane; au, arbitrary units; FTIR, Fourier transform infrared; NCO, isocyanate; PEG, polyethylene glycol.

Figure 3 NCO decay in PU-based sealers.

Notes: The variation of NCO decay in FTIR spectra of PU0 (A), PU1 (B), PU3 (C) and PU5 (D) against cure time: 0, 30, 60, 120, 180, 240, 300, 360, and 420 minutes. The names of the tested sealers begin with PU. PU0 is 0 wt% silver phosphate (Ag₃PO₄). Similarly, PU1 is 1 wt% Ag₃PO₄, PU3 is 3 wt% Ag₃PO₄, and PU5 is 5 wt% Ag₃PO₄.

Abbreviations: NCO, isocyanate; PU, polyurethane; FTIR, Fourier transform infrared.

Figure 4 Kinetics of NCO conversion.

Notes: Changes of NCO at different times during the curing process (A). The relationship between p and the curing time of PU-based sealers (B–D). The conversion of NCO during polymerization is represented by p. The integrated absorption area at the initial time is represented by A₀. The integrated absorption area at time t during the process is represented by A_t. The final integrated absorption area is represented by A_∞. The names of the tested sealers begin with PU. PU0 is 0 wt% silver phosphate (Ag₃PO₄). Similarly, PU1 is 1 wt% Ag₃PO₄, PU3 is 3 wt% Ag₃PO₄, and PU5 is 5 wt% Ag₃PO₄.

Abbreviations: NCO, isocyanate; PU, polyurethane.

Table 1 Rate constants and fitting results for the curing process of PU

Order	Parameter	PU0	PU1	PU3	PU5
First-order	k0	0.003246	−0.002688	−0.008720	−0.006857
	C	−0.078792	0.062712	−0.019953	0.012787
	R^2	0.977269	0.961936	0.980816	0.988903
Second-order	k0	0.007086	0.004781	0.089402	0.038921
	C	0.882516	0.785163	−5.457348	−1.470421
	R^2	0.945718	0.895708	0.642805	0.739532
Third-order	k0	0.035134	0.018554	0.452174	0.277507
	C	−0.653286	−0.195858	−23.310087	−17.462346
	R^2	0.814334	0.784843	0.573360	0.594581

Notes: The constant k₀ is related to the rate constants, which depend on temperature. R² is the correlation coefficient. The strength of the linear correlation between points increases proportionally as R² gets closer to 1. AH Plus is the commercial sealer that was used as a positive control. The names of the tested sealers begin with PU. PU0 is 0 wt% silver phosphate (Ag₃PO₄). Similarly, PU1 is 1 wt% Ag₃PO₄, PU3 is 3 wt% Ag₃PO₄, and PU5 is 5 wt% Ag₃PO₄.

Abbreviations: C, constant; PU, polyurethane.

Table 2 Physical properties of AH Plus and of PU-based sealers

	ISO standards	AH Plus	PU0	PU1	PU3	PU5
Setting time (minutes)	≤4,320	486±21*	422±17^^	408±17^#	313±20^$	250±16^&
Film thickness (μm)	≤50	44.70±1.20*	29.80±3.27^^	32.44±1.78^^	37.21±2.71^$	52.19±1.62^&
Solubility (%)	≤3	0.41±0.18*	0.13±0.07^^	0.23±0.09^^	0.34±0.11*	0.41±0.12*
Dimensional change (%)	Expansion ≤0.1%	1.37±0.68*	1.83±0.41^^	1.88±0.32^#	1.84±0.52^^	1.83±0.26^^

Notes: The names of the tested sealers begin with PU. PU0 is 0 wt% silver phosphate (Ag₃PO₄). Similarly, PU1 is 1 wt% Ag₃PO₄, PU3 is 3 wt% Ag₃PO₄, and PU5 is 5 wt% Ag₃PO₄. AH Plus is the commercial sealer that was used as a positive control. Values followed by different superscript symbols in each row differ significantly and represent the qualitative difference for the values.

Abbreviation: PU, polyurethane.

Figure 5 SEM images of bacterial adhesion on PU-based sealers.

Notes: Images of PU0 (A), PU1 (B), PU3 (C), PU5 (D), and AH Plus (E) sealers after 24 hours of incubation with Streptococcus mutans. The names of the tested sealers begin with PU. PU0 is 0 wt% silver phosphate (Ag₃PO₄). Similarly, PU1 is 1 wt% Ag₃PO₄, PU3 is 3 wt% Ag₃PO₄, and PU5 is 5 wt% Ag₃PO₄. AH Plus is the commercial sealer that was used as a positive control.

Abbreviations: SEM, scanning electron microscopy; PU, polyurethane.

Figure 6 DCT results of fresh samples and 7-day samples.

Notes: Turbidimetric readings for fresh samples (A and B) and 7-day samples (C and D) for 24 hours. The names of the tested sealers begin with PU. PU0 is 0 wt% silver phosphate (Ag₃PO₄). Similarly, PU1 is 1 wt% Ag₃PO₄, PU3 is 3 wt% Ag₃PO₄, and PU5 is 5 wt% Ag₃PO₄. AH Plus is the commercial sealer that was used as a positive control. Part (A) and (C) represent the bacteria that grew in the presence of the tested material, however, part (B) and (D) represent the bacteria that were incubated without the tested material. Namely, the bacteria in the part B came in contact with the material from part (A) for 1 hour, then incubated without tested material. Similarly, the bacteria in the part (D) came in contact with the material from part (B) for 1 hour, then incubated without tested material.

Abbreviations: DCT, direct contact test; PU, polyurethane.

Figure 7 MTT assays of L929 murine fibroblasts.

Notes: MTT assays of L929 murine fibroblasts cultured with the leaching liquor of each of the PU-based sealers, the leaching liquor of AH Plus, and the leaching liquor of the control group for 1 day, 4 days, and 7 days. The names of the tested sealers begin with PU. PU0 is 0 wt% silver phosphate (Ag₃PO₄). Similarly, PU1 is 1 wt% Ag₃PO₄, PU3 is 3 wt% Ag₃PO₄, and PU5 is 5 wt% Ag₃PO₄. AH Plus is the commercial sealer that was used as a positive control. Statistical significance is denoted as follows: *** is significant at P<0.001; ** is signficant at P<0.01; and * is significant at P<0.05.

Abbreviations: MTT, 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-2H-tetrazolium bromide; PU, polyurethane.

Table 3 Various properties of the samples after 7 days of incubation

	Average absorbance (mean ± SD)	Cell relative growth rate (%)	Cytotoxicity level
PU0	1.326±0.017	96.51	1
PU1	1.317±0.007	95.85	1
PU3	1.275±0.010	92.79	1
PU5	0.523±0.013	38.06	3
AH Plus	0.237±0.012	17.24	4
Control	1.374±0.045	100.0	0

Notes: The names of the tested sealers begin with PU. PU0 is 0 wt% silver phosphate (Ag₃PO₄). Similarly, PU1 is 1 wt% Ag₃PO₄, PU3 is 3 wt% Ag₃PO₄, and PU5 is 5 wt% Ag₃PO₄. AH Plus is the commercial sealer that was used as a positive control.

Abbreviations: PU, polyurethane; SD, standard deviation.