Nanopore Structure Buildup during Endodontic Cement Hydration Studied by Time-Domain Nuclear Magnetic Resonance of Lower and Higher Mobility ¹H

Abstract

Time-domain nuclear magnetic resonance (TD-NMR) of (1)H nuclei has been used to monitor and model changes of endodontic cement pastes during hydration, from the initial reaction period up to hours and days. The (1)H in the samples are divided into two major spin groups by fitting each free induction decay, acquired after the second pulse of an inversion recovery (I-R) pulse sequence with variable interpulse delay, by the sum of a quasi-Gaussian (signal from low mobility nuclei) and an exponential (from higher mobility nuclei). The extrapolations to zero time of the signals from the two spin groups give two sets of I-R data that have been analyzed to give quasi-continuous T(1) distributions. After about a day, two clearly solid components appear. From a day to a few days, three liquid populations are identified, one of them mainly in the low-mobility spin group, which later merge, giving a single T(1) or T(2) peak. The rapid onset of the solid components, at the cost of the liquid, and the rapid changes of the relaxation time distributions of all components are clear indicators of the amount and kinetics of reaction products formation (C-S-H gel and Portlandite) and of the C-S-H micronanoporous structure buildup and evolution. At 30 days of hydration, the very short T(1) and T(2) liquid component (T(1) congruent with 200 micros and T(2) congruent with 50 micros) can be assigned to C-S-H intralayer water (thickness of the order of fractions of a nanometer) and the remaining liquid signal to interlayer water (thickness of the order of 1 nm). Comparisons are made among a widely used commercial endodontic cement paste and two more recent commercial pastes, with additive compounds to make the hydration process faster and to increase the workability. Parameters can be extracted from the data to characterize the different kinetics and nanostructure of the pore space formed up to 30 days. The parameters are in agreement with the expected effects of the additives, so the parameters can be used to optimize the formulation of new pastes, in order to improve their therapeutic performance.

Stone porosity, wettability changes and other features detected by MRI and NMR relaxometry: a more than 15‐year study

“…With relaxometry, the kinetics of formation and changes of the multi‐scale porosity of the so‐called C‐S‐H gel in the cement, as well as the effects of different additives, can be monitored …”

Investigation of the First Sorption Cycle of White Portland Cement by 1H NMR

“…1.2) of cementitious materials and their evolution during hydration and drying/wetting processes (see Sect. 1.3) [2,[11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. Currently, publications related to NMR techniques to study the sorption isotherm process are quite limited and overall, they suffer from the different types of sample preparation.…”

“…NMR Relaxometry methods allow one to study water in different chemical-physical environments inside porous media and in specific cement-based materials, by distinguishing different 1 H populations [11,16,17,[23][24][25][26][27][28][29]. Using different experimental NMR methods, it is possible to assess the water transport through the pore system, to determine physical properties, such as specific surface area, porosity, and pore size distribution.…”

“…Halperin et al [14] in 1994 applied the NMR fast exchange theory on cement and linked relaxation times with pore sizes and specific surface areas. A lot of different studies were carried out on cementitious materials in the following years [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27], including the study of pore-resolved isotherm by Muller et al in 2013 [16], the systematic study of the cement pore structure in 2016 by Gajewicz et al [17], investigations about the evolution of cement paste microstructure during bleeding by Ji et al [19], and during hydration [23][24][25][26][27], or application of more complex NMR Relaxometry techniques, such as Fast Field Cycling NMR by Korb [18] or 2D-NMR experiments by McDonald et al [21,22].…”

Calcium silicate materials in endodontics

“…60 The hydration of the cement, kinetics of the reaction and nanostructure formation have been studied using timedomain nuclear magnetic resonance and this revealed a faster set for the material than ProRoot white MTA. 61 The material is bioactive with the formation of apatite on its surface, biocompatible and with good apical seal. [62][63][64] MTA Plus (manufactured by Prevest-Denpro, Jammu City, India for Avalon Biomed, Bradenton, FL, USA) is a powder-liquid system with the option of mixing the powder (tricalcium and dicalcium silicate, bismuth oxide, calcium sulphate and silica) with either water or an anti-washout gel (AWG), the latter accelerating the set of the material, as per manufacturer's claim, to one hour.…”