Twitch star Sketch returned to streaming after a month-long break to reveal he’d been attending a fitness camp and showed off his progress.

Whether flaunting actual grillz or getting creative with makeshift foil versions, the trend has become a fun outlet for self-expression, drawing in millions of users across the app.

Twitch is a livestreaming platform focused on video games. It was founded by Justin Kan in 2011, originally as a spin-off of Justin.tv. The latter started life in 2007 as a single channel, ...