The 2019 Nanjing Patent on Piezoelectric Teeth Whitening (US20210052358A1)

Years before the strontium- and calcium-doped powder of CN119430910 — Piezoelectric Ceramic Powder for Whitening and Mineralizing Teeth appeared, a group at Nanjing University of Science and Technology had already filed on the core idea: put a piezoelectric material against the teeth, squeeze it repeatedly, and let the charges it releases break down stains. The US application, published as US20210052358A1 and titled "Teeth whitening product containing piezoelectric material", claims priority from Chinese application CN201910762356.1, filed on 19 August 2019. The listed inventors are Yaojin Wang, Yang Wang, Nana Yang, Xuan Chen, Xinrong Wen, Shuhao Wang, Hanzhou Wu and Bin Yang. For this dossier it serves as prior art: it shows how much of the BSCT (Ba₀.₉Sr₀.₀₅Ca₀.₀₅TiO₃) story was already on file, and what the later patent actually added.

What the patent claims

The applicants position the invention against peroxide bleaching. They argue that high-concentration hydrogen peroxide can harm skin and mucosa, erode enamel and dentin and even injure the pulp. They also say abrasive whiteners damage enamel and make re-staining more likely. Their proposed alternative is described as "efficient, simple, economic, nondestructive and bleach-free".

The scope is deliberately broad. The patent lists BaTiO₃, GaN, ZnSnO₃, (Na,K)NbO₃, ZnO, lead zirconate titanate, lead magnesium niobate and polyvinylidene fluoride as candidate materials, alone or in combination (PMN-PT is given as an example). It says poled material, meaning material whose internal dipoles have been aligned by an electric field, whitens better than unpoled material. The delivery formats are just as wide:

• toothpaste, dentifrice, gel or tooth cleanser carrying the powder;
• chewing gum or a chew, activated by biting;
• toothbrush bristles spun from piezoelectric fibres, activated by bending;
• braces, dentures and similar appliances, activated by friction when the jaws close;
• a dedicated whitening device with its own external stimulation.

The applicants also predict that high-frequency electric toothbrushes will whiten better than manual ones. Their reasoning is that results depend mainly on how many excitation cycles the material receives.

How it is said to work

The mechanism matches what this dossier calls Piezoelectric Catalysis (Piezocatalysis). According to the patent, a polar material carries bound surface charges. When the force on it changes, those charges are released into the surrounding water and react to form "reactive species" that attack stains. When the force stops changing, a new charge balance forms; the next change in force starts the cycle again. The patent therefore requires continuous variation in pressure, not steady pressure. The document speaks only of "reactive species". It does not identify them or measure them, unlike the later BSCT material, which reports superoxide and hydroxyl radicals (see Reactive Oxygen Species (ROS)).

What was actually tested

The patent describes four laboratory examples. All of them use ultrasound in place of brushing or chewing:

1. Dye degradation. Poled and unpoled barium titanate were sonicated in a 5 mg/L rhodamine B solution and absorbance was tracked over time. The patent reports that both degraded the dye and that the poled powder was significantly faster. It credits this to a stronger piezoelectric response.
2. Vinegar-stained teeth. The stained teeth were sonicated for 3 h at 40 W and 1 kHz in a 1 mg/ml suspension of poled barium titanate with a particle size of about 130 nm, and compared with teeth sonicated in clear water. The patent says the powder-treated teeth were "whitened significantly", judged from photographs.
3. Mixed-beverage stains. Teeth stained with black tea, wine, fruity drinks and blueberry juice were sonicated under the same conditions with poled Mn-PMN-PT of about 1 μm. The same outcome is reported.
4. Toxicity and surface damage. Rat thoracic aortic smooth muscle cells were grown with barium titanate at 1 mg/mL or with hydrogen peroxide. The patent reports normal growth with the powder and near-total cell death with peroxide. An electron micrograph is said to show heavy enamel damage after 30% H₂O₂ and an essentially unchanged surface after barium titanate.

What the evidence does and does not show

The examples support a narrow claim: under laboratory sonication, a piezoelectric powder can speed up dye breakdown and lighten stained extracted teeth more than water alone. Several points limit how far that claim can go.

• No brushing, chewing or clinical use was tested. Every product format in the list is extrapolated from ultrasound experiments. The stated 1 kHz is also well below the frequencies usually called ultrasonic, and the document does not explain this.
• The whitening is reported only qualitatively. No colour measurement, shade scale, number of teeth or statistics is given, and there is no comparison with a peroxide whitener on stain removal.
• The safety comparison is uneven. The cells are rat vascular cells, not oral tissue. The peroxide arm is a concentrated bleach at a 15% final concentration, so the result shows that barium titanate is less toxic than strong peroxide. It does not show that the powder is safe in the mouth. The figure list itself is inconsistent, describing Figure 6 as testing 15% H₂O₂ in one place and 30% H₂O₂ in another.
• Lead-containing options are named without discussion. These include PZT and PMN-PT, which is the material used in the third example. The patent does not consider the toxicity of putting them in an oral product.

As with any patent, the applicants' statements are not independent evidence of effect (see Patent as Evidence).

Legal fate

The US application was filed on 14 July 2020 and published on 25 February 2021. According to the Google Patents record, examination produced non-final office actions in August and October 2023, a final rejection on 20 December 2023 and an advisory action on 5 March 2024. The application was abandoned on 29 June 2024 for failure to respond to an office action. The Chinese counterpart, CN110464674B, is listed as active. A rejected US application says nothing about whether the method works. It does mean the broad US claims were never granted.

How it connects to the BSCT trail

Compared with this filing, the later CN119430910 — Piezoelectric Ceramic Powder for Whitening and Mineralizing Teeth is narrower and adds three things. It specifies one doped composition, Ba₀.₉Sr₀.₀₅Ca₀.₀₅TiO₃, made by Sol-Gel Synthesis. It adds a second claimed function, remineralization from released calcium and strontium. And it identifies particular radical species. The basic premise was already on file in 2019: vibration-activated piezoelectric powder in toothpaste as a peroxide-free whitener, with Barium Titanate (BaTiO₃) as the worked example. Google Patents also lists later filings that cite this family. They include Nanjing University of Science and Technology's own pyroelectric whitening product (CN113317996A), a Peking University School of Stomatology ultrasonic-piezoelectric antibacterial toothbrush (CN115381574A), and a Shandong University product based on polytetrafluoroethylene piezoelectric material (CN115252467A). Together these show the idea spreading well before the BSCT paper. For how the BSCT claims compare with their evidence, see BSCT Claims vs. Evidence: The Tooth Powder Dossier Without Clinical Data.