A rapid, efficient, and facile solution for dental hypersensitivity: The tannin–iron complex

Dental hypersensitivity due to exposure of dentinal tubules under the enamel layer to saliva is a very popular and highly elusive technology priority in dentistry. Blocking water flow within exposed dentinal tubules is a key principle for curing dental hypersensitivity. Some salts used in “at home” solutions remineralize the tubules inside by concentrating saliva ingredients. An “in-office” option of applying dense resin sealants on the tubule entrance has only localized effects on well-defined sore spots. We report a self-assembled film that was formed by facile, rapid (4 min), and efficient (approximately 0.5 g/L concentration) dip-coating of teeth in an aqueous solution containing a tannic acid–iron(III) complex. It quickly and effectively occluded the dentinal tubules of human teeth. It withstood intense tooth brushing and induced hydroxyapatite remineralisation within the dentinal tubules. This strategy holds great promise for future applications as an effective and user-friendly desensitizer for managing dental hypersensitivity.


Materials
Polytetrafluoroethylene (PTFE) membrane filter (0.2 µm pore size, Whatman PLC, UK) were all cleaned in methanol just before use. Polystyrene (PS) film was prepared by cutting a PS Petri dish.
TA/Fe 3+ coating on PS film, PS 24 wells cell culture plate, and PTFE membrane PS film, PS 24 wells cell culture plate, and PTFE membrane were coated with the TA/Fe 3+ complex film as follows. TA (0.4 g/L) and iron(III) chloride (0.1 g/L) were dissolved and the pH of this solution was subsequently raised by adding 10X Tris buffered saline (TBS) to pH 8 solutions. Tooth slices were immersed in the TA/Fe 3+ solution for 1 min, and this dipping process for each slice was repeated 4 times.
The TA/FeCl3 solution was newly prepared each time because we observed that the coating solution rapidly produced a TA/Fe 3+ complex film within the first 1 minute. Figure S1. SEM images of a polytetrafluoroethylene (PTFE) filter membrane microholes (a) without TA/Fe 3+ coating and (b) with TA/Fe 3+ coating.
The TA/Fe 3+ coating sealed the microholes on the PTFE filter membrane. Figure S2. Schematics of tooth slice preparation, tooth slice etching, and tooth slice coating methods.
The tooth slices were acid-etched with phosphoric acid etching gel for 30 seconds, then rinsed with sufficient DI (deionized) water. Gluma was applied to the tooth slice and then leaved for 60 s. The excess of Gluma was rinsed with DI water. Figure S3. SEM images of (a) diluted Gluma-coated and (b) original Gluma-coated tooth slices.

XPS analysis on calcium absorption of TA/Fe 3+ -complex film 3 .
X-ray photoelectron spectroscopy (XPS) analysis was conducted with a PHI 5800 ESCA System at 2 × 10 −6 tor with a monochromatic Al Kα (1486.6 eV) anode (250 W, 10 kV, 27 mA). All binding energies were tuned to the main hydrocarbon peak, C 1s (284.6 eV). All XPS spectra were evaluated using CasaXPS. TA/Fe 3+ -coated PTFE membrane was immersed in 50 mM Ca2Cl aqueous solution for 12 h, then fully washed with DI water and acetone. To investigate calcium absorption of TA/Fe 3+ complex, wide-scan XPS spectra and calcium 2p XPS narrow-scan spectra of the TA/Fe 3+ -coated PTFE membrane were obtained. In the Ca 2p narrow scan XPS spectra of the TA/Fe 3+ coated polytetrafluoroethylene (PTFE) filter membrane, the notable Ca 2p peaks suggests that TA/Fe 3+ complex film absorbed calcium ions on the surface. Dentinal fluid flow measurement consists of three main parts: (1) a glass capillary and photo-sensor to detect the fluid movement, (2) a stepping motor, lead screw, and ball nut to track the fluid movement; and 3) a rotary encoder to record the fluid movement ( Supplementary Fig. 6). The water reservoir and the tooth slice was connected at both ends of the water filled glass capillary with an internal diameter of 0.5 mm. A photo transistor detected the movement of an air bubble trapped within the capillary during dentinal fluid flow measurement. The air bubble position that represent fluid flow was tracked by stepping motor, and the rotary encoder translated the air bubble movement to the electric signal. The electric signal was translated into the amount of fluid flow within the dentinal tubules. It was reported that the minimum measurable volume of water movement using this system is approximately 0.196 nL.
A tooth slice sample was connected to a glass capillary by silicone tubing. A hydrostatic pressure of 200 mmH2O was applied throughout all of the procedures with a water reservoir. The temperature and relative humidity of the environment were ~20 °C and ~30%, respectively. After the tooth slice was connected, this instrument underwent a stabilizing time of 10 minutes. Then, the amount of water infiltration in a new tooth slice was first measured for 10 min, and the standard graph of the tooth slice was constructed; the amount of water infiltration vs time. After coating treatment, the amount of water infiltration in the coated tooth slice was again measured for 10 min, and the amount was compared to the standard value.