More than 5 million Americans seek orthodontic treatment each year, according to the American Association of Orthodontists. Treatment plans often include traditional braces or aligners; a set of customized plastic pieces that shift improperly aligned teeth slightly over time.

In recent years, these clear, plastic aligners have been steadily growing in popularity as alternatives to bulky, metal braces. Most everyone has heard of Invisalign, and other manufacturers have joined in the market share.

Most notably, aligners have a better aesthetic than traditional metal braces and can be removed for special events or when eating, making them easier to deal with.

Clear aligners and even orthodontic retainers, known collectively as clear overlay appliances (COAs) are made by making a dental impression and using pressure or heat to form the desired shape on a plastic sheet. One drawback is that bacteria frequently build up on COAs and the plastic can easily wear down.

A group of scientists, as reported in the American Chemical Society’s publication Applied Material & Interfaces, has been working to develop simple and affordable coatings to prevent bacteria from growing on them.

Drawing inspiration from super-hydrophilic antibacterial coatings on other medical devices, the group of scientists spent months working on the project:

"The researchers took a polymer sheet made of polyethylene terephthalate that was modified with glycol (PETG) and layered films of carboxymethylcellulose and chitosan on it. This layered film created a super-hydrophilic surface, or a surface that loves water, that prevented bacteria from adhering. When PETG with the film was compared to the bare material, bacterial growth was reduced by 75 percent. The coated plastic also was stronger and more durable, even when tested with artificial saliva and various acidic solutions."

If testing goes as expected, the single most-cited downside of aligners will have been basically eradicated.

But will aligners completely replace metal braces as the first-line treatment for misaligned teeth? Some experts think so.

Before long, the nicknames "metal mouth" and "brace face" may just go the way of VHS tapes and typewriters. Hooray for progress!