Align Technology, the people behind Invisalign, have just announced that they have started treating their 4 millionth patient and to celebrate this milestone, they are donating $1 to Operation Smile for every smile tweeted using the hashtag #4millionsmiles.

They have a goal to deliver 400 healing operations and have pledged up to $1 million. Operation Smile is an international medical charity which provides free surgeries for children and young adults in developing countries who are born with cleft lip, cleft palate and other facial deformities.

If you search Twitter for #4millionsmiles, you will see many posts of people smiling, all of which will contribute to raising money for this much needed work.  Their website has an interactive map that displays where posts are coming from and details about the work undertaken by this charity.

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Image: © Invisalign UK