Tom's of Maine, a privately-owned natural toothpaste maker that once attacked larger corporations for adding artificial sweeteners to oral hygiene products, is being bought by Colgate-Palmolive for $100 million, company officials announced Tuesday.

Under the deal, Colgate will acquire an 86% stake in the Kennebunk, Maine-based company, which was founded in 1970 and today has annual sales of more than $50 million.

"We chose Colgate as our partner because they have the global expertise to help take Tom's of Maine to the next level," co-founders Tom and Kate Chappell said in a joint statement Tuesday. "Just as importantly, we see Colgate as an excellent fit with our own cultural values."

According to Colgate, the market for natural oral and personal care products is worth more than $3 billion and growing by 15% a year.

In a statement, Reuben Mark, the chairman and CEO of Colgate, called the purchase an "exciting partnership with growth opportunities for both companies."

The deal, which is still subject to regulatory approval, is expected to close in the second quarter of this year.