Without a doubt, Jim Parsons' career completely changed when he took on the role of Sheldon on 'The Big Bang Theory'.

In truth, his audition seemed a little too perfect, and Chuck Lorre would even debate about casting him, doubting if he would be able to give the same performance over and over again. Looking at his run on the show, it is safe to say he was able to do so and then some.

It was his decision to end the show and it left the cast in shock, the likes of Kaley Cuoco couldn't believe it was all coming to an end. However, who knows, a reboot can take place down the road.

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Hardcore fans of the show notice just about everything and that includes the little things, like Sheldon's smile. We'll take a look at theories as to why he might've been hiding his teeth during the show.

Jim Parsons' Co-Star on 'Big Bang Theory' Mayim Bialik Is A Freak When It Comes To Dental Care

During an interview alongside Dear Doctor, 'Big Bang Theory' star Mayim Bialik revealed that she's quite the health freak when it comes to her teeth, and that also includes the teeth of her children.

The star revealed that she makes her children avoid certain foods in order to keep their dental hygiene strong.

“Being vegan means that a lot of candy is limited and I'm kind of glad for that,” she said. “Most candy has dairy in it. They've never had M&Ms or anything like that because those are dairy.”

“We really try to encourage their palate to appreciate fruit in its natural state and sweet things in their natural state so they're not constantly craving that,” she said. “It's a battle for all parents.”

She also stated that candy is off-limits during Hollywood and instead, they are bribed with a Lego set, not a bad trade-off.

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In addition to being strong oral care like brushing, the family is also very big on flossing as well.

In truth, this fits in perfectly with Jim Parsons' 'Big Bang Theory' character of Sheldon.

Jim Parsons' Sheldon Character Was All About Proper Hygiene On The Show

Although he didn't smile all that much during the first seasons, perhaps because of teeth issues, the character itself was huge on proper hygiene, as we saw throughout the show's run.

When speaking alongside Jimmy Fallon, the actor revealed that Sheldon would be perfect and well-equipped for the current pandemic.

"He was built for this. This is the moment he was waiting for. I was saying earlier, we had an entire episode – which I didn't think about until recently – where he did like a Shel-bot where he had like a video screen on a remote-control wheelie thing. And that was when people still needed to get together in groups, and so he would just send that out and sit in his room."

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Things might've been a little different for the actor behind Sheldon, Jim Parsons. Fans on Reddit asked the question as to why the actor rarely smiles during his first couple of seasons. Others would also further indicate that his teeth looked black.

Fans Noticed Jim Parsons Rarely Smiling With His Teeth For The First Few Seasons And It Might Be Because Of Dental Issues

Was Sheldon not showing his teeth part of his identity? Well, maybe not given that it was never addressed on the show.

However, fans on Reddit are wondering why this was the case early on?

"In different shots through the first few seasons (1-4 about) it sometimes looks like Sheldon (Jim Parsons) is purposefully hiding his teeth. Is he hiding orthodontia or something, or was it just an acting choice, or character quirk of the actor/character?"

Surprisingly, despite its huge fanbase, nobody had a direct answer for the question via Reddit, nor was it ever addressed anywhere else.

Philosophy Question did ask as to why his teeth were black, and the reasoning for it is, "Teeth are vulnerable to discoloration, which can happen due to staining from foods and drinks such as coffee or red wine. If this is left untreated, not only could you be in extreme pain, but the tooth could begin to die and will almost certainly go black."

It'll forever be a mystery as to why this was the case.

The two scenarios are, it was part of his character or, Parsons didn't want to show his teeth while on the show, perhaps until they got fixed up to his liking.

Or, we might be looking into this a little bit too much, and it is neither of the two.

NEXT - 10 Facts About Jim Parsons' Private Life