Smiling is always in style (even at funerals), and there’s nothing more confidence-boosting than a mouth full of healthy, pearly-white teeth. Unfortunately, though, “healthy” and “pearl white” rarely go together. Brushing doesn’t remove deep stains, and whitening treatments can erode enamel, increasing the risk of cavities and, ironically, discoloration.
Fortunately, in a recent study ACS Applied Materials & Interfaces reports a new nanoparticle treatment that whitens teeth without damaging them, and also protects them by removing cavity-causing bacteria.
Vicious cycle of tooth decay and discoloration
In 2019, the Institute for Health Metrics and Evaluation published the most comprehensive global study of health: the Global Burden of Disease 2019 study. The researchers analyzed 286 causes of death, 369 diseases and injuries, and 87 risk factors in 204 countries and territories. According to this study, the most common health condition is tooth decay – tooth erosion often caused by sticky, acidic plaques of bacteria.
The first step towards preventing tooth decay is to remove these acidic plaques. Brushing your teeth is a good start, but it can’t remove all bacteria. Eventually, the super-sticky plaque will cover your teeth and will need to be removed by a professional.
Credit: (Lee et al. ACS Applied Materials & Interfaces. 2022)
Unfortunately, not everyone has access to a professional. Therefore, oral engineers are always on the lookout for treatments that will break down stubborn plaque. The problem with such treatments is that they can cause side effects, including discoloration of the teeth, after long-term use. These stains can be removed through clinical whitening methods using high-intensity blue light and hydrogen peroxide. But blue light can damage skin and eyes, and hydrogen peroxide’s strong stain-fighting power also makes it highly corrosive. In other words, compounds that remove plaque-causing bacteria can stain teeth, and stain-removing treatments can damage the surface of teeth, allowing bacteria to attach more easily. This is a vicious cycle of tooth decay and discoloration.
Replace Your Toothpaste With Nanozyme Hydrogel
A few years ago, oral health bioengineers began to explore the possibility of removing plaque with iron oxide nanoparticles. One biomedical material ─ bismuth oxychloride (Bi12O17Cl2) ─ showed promising results. The scientists found that they could precisely control its activation by using green light instead of blue. Once activated, it can whiten teeth and destroy plaque. But unfortunately, bismuth oxychloride doesn’t stick around on teeth long enough to be effective.
Xiaoli Wang and his colleagues at Nanchang University wanted to find a way to make bismuth oxychloride nanoparticles stick to teeth for a longer period of time. Their solution was to add another nanoparticle. Cuprous oxide (Cu2O) has broad-spectrum antibacterial properties, is activated by green light, and forms a hydrogel when mixed with bismuth oxychloride and calcium.
Xiaoli Wang and colleagues hypothesized that applying a nanoparticle hydrogel to a tooth would remove stains and plaque. Credits: Lee et al. ACS Applied Materials & Interfaces, 2022.
Nanoparticle hydrogel whitens teeth and destroys plaque
The team tested the material on human teeth soaked in a mixture of coffee, tea, blueberry juice and soy sauce for 15 days to simulate the natural color of teeth. Next, the teeth were coated in hydrogel and exposed to green light for 1 hour daily. After treatment, the teeth became brighter over time. Additionally, the treatment did not cause any damage to the enamel and killed 94% of the bacteria in the biofilm.
Photographs of human teeth treated with control, base solution of hydrogel without nanoparticles (SA; sodium alginate), and hydrogel (BC-SA) under the treatment of greenlight for 0, 1, 2, and 3 days, respectively. Credits: Lee et al. ACS Applied Materials & Interfaces, 2022.
For many of us, cleaning our teeth in a petri dish and exposing them to green light (GL) for an hour every day isn’t very practical. The team used mice that had been inoculated with cavity-causing bacteria in their mouths to demonstrate that the treatment worked on living organisms’ teeth. The hydrogel was applied to the tooth surface and treated with GL for five minutes twice a day. After 30 days, the post-treatment dental plaque area became significantly smaller, accounting for only 9% of the total dental area.
In humans, if the plaque area is less than 20% of the tooth, it is considered under control. Furthermore, the green-light-activated hydrogel effectively prevented medium and deep cavities from forming on the surface of the animal’s teeth (despite the lack of brushing).
The researchers concluded that their brush-free treatment prevented cavities and made teeth whiter. However, there are still some shortcomings in this study. For example, the viscosity of BC-SA can be improved, and the long-term stability of BC-SA requires further experimental exploration. Nevertheless, it is a promising step towards improving oral health.
This article was reprinted with permission from Big Think, where it was originally published,