Mili q purification system

The incisor teeth were extracted without visible fractures. After extraction, teeth were disinfected in aqueous 0.5% Chloramine-T solution (Poch S.A., Gliwice, Poland) for 24 h and stored in a 0.9% NaCl solution at 4°C for no longer than 7 days [38 –40 (link)]. Before the examination, each tooth was immersed for 5 min in deionized water and then dried in a desiccator for 24 h under vacuum conditions to remove water from the tooth’s exterior surface. All the reagents used were of analytical grade and were dissolved in deionized water (16 MΩ) purified via a Mili-Q purification system (Milipore, Bedford, MA, USA).
The teeth were weighed and measured before an examination. The shape of the upper incisors and the length of incisors’ clinical crowns (incisal edge) along with the pigmented enamel length were evaluated using the digital microscope (VHS-2000, Keyence Corp., Osaka, Japan). The curvature of the incisor was approximated by the homocentric circles with outer (R_out) and inner (R_in) radiuses as presented in Fig 1. The thickness of the teeth was calculated as a difference between both radiuses.

All the used reagents (reagent or analytical grade) were used as received and obtained from Sigma-Aldrich, except N,N,N′-trimethyl-1,3-propanediamine (Alfa Chemistry). Deuterated solvents were purchased from Sigma-Aldrich. Organic solvents (analytical grade) were obtained from Avantor Performance Materials. Triethylamine was dried with solid calcium hydride (1 g per 50 mL of solvent) followed by distillation over this drying agent. Water used in all experiments was double-distilled (synthetic procedures) or purified by a Millipore (Bedford, MA) miliQ purification system (conductometric measurements).