Sophia Robb broke her retainer trying to stop her self from screaming when Michael B Jordan stripped off his shirt for the first time in Black Panther.

The 18-year-old from the San Francisco Bay area in California had no history of habitual teeth grinding, and never had problems with her braces.

But anticipation and excitement can have similar effects on the body to this stress, including, for Sophia, jaw-clenching so fierce it broke her retainer.

When she went to get it fixed, her orthodontist posted Sophia's story on Tumblr, where she found and tweeted it, earning her Jordan's attention and an offer to pay to replace the broken retainers.

We break down how Sophia's excitement could have made her clench her teeth so hard she broke a steel bar in her mouth.

'it was pure unadulterated Michael B Jordan': The sight of the shirtless Black Panther actor excited 18-year-old Sophia Robb so much that she clenched her teeth and broke her retainer

'I was definitely the girl that took extra-good care of her braces,' Sophia says.

'I think that makes this even funnier, everything had been fine up until Black Panther.'

Until a year ago, Sophia wore braces, just like four million other Americans.

But for most people, orthodontia doesn't end when the brackets come off.

After wearing braces, many people are fitted with retainers of one form or another to make sure that their teeth stay where they are.

Sophia was fitted with a permanent bonded retainer, which was glued to the back of her lower teeth.

The common, unmovable retainer is held in place with a strong chemical bonding material, similar to blue, that keeps it attached to the enamel on the backs of the teeth.

Other kinds of clear plastic retainers can be used to prevent teeth clenching or grinding, known as bruxism, but Sophia's metal one was vulnerable to being damaged by grinding.

'Bruxism is muscular activity controlled by brain,' explained Dr Eunjung Jo, a dentist at Astor Smile in New York City.

'Signs and symptoms of the breakdown of [bruxing] include broken retainers, dental fillings, sensitive teeth, worn and broken teeth...and jaw pain and clicking,' she says.

'I've clenched my jaw before, but it's never caused a problem,' Sophia says.

But then she went to see Michael B Jordan in Black Panther.

'I was dedicated to sit through the entire thing, I wasn't going to miss a second,' Sophia says.

'There's this specific scene - I don't want to spoil anything - but he takes his shirt off for the first time.

'In an effort not to scream or break my best friend's hand that I had been holding the entire time.

'So I clenched my jaw and pressed my tongue against the retainer so hard that I felt a pop,' Sophia says.

The scream-stifling, retainer-breaking clench 'was all pure unadulterated Michael Be Jordan,' she says.

The dislodged retainer caused her a little discomfort, and her friend asked if they needed to leave the theater for the orthodontic emergency.

'Absolutely not, we have another hour to go,' Sophia replied.

The next day she went to get it fixed and her orthodontist asked how it had broken out. Sophia was embarrassed, but her doctor convinced her he needed to know 'for medical reasons, to know how to fix it.'

Sophia Robb, 18, is not a habitual bruxer, but excitement gave her a stress reaction so she clenched her teeth hard enough to break her her retainer

Sophia's orthodontist posted her story on Tumblr, and it went viral

Most teeth grinding and clenching happens while people sleep and may be due to a poorly-aligned bite.

Though Dr Jo notes that there is no known link between sexual desire and bruxing, clenching may be a reaction to stress or anxiety, and even excitement.

Clenching, or bruxing, is a way of getting out pent up aggression or energy, not unlike clenching your fist so you can express that feeling without actually acting out.

About 40 million people in the US brux, and it is especially common among young people and children.

This can be a response to try to regulate stress hormones, according to Pro Teeth Guard - and maybe other hormones in Sophia's case.

She finally caved and told her orthodontist how she'd broken the retainer. The whole office had a good laugh and Sophia left with a new retainer.

But two days later she saw a Tumblr post an orthodontist had written about a 17-year-patient of his who had broken a retainer the same way Sophia had.

'This tiny 17-year-old girl thirsting so godd**n hard she busted steel,' he wrote.

Sophia thought: 'I have to be this girl's best friend, where is she?'

But quickly she realized the post was actually about her, and tweeted it herself.

Next thing she knew, she had a tweet and a direct message from the very cause of her predicament and the object of her desire: Michael B Jordan.

'Since I feel partly responsible for breaking your retainers let me know if I can replace them,' he tweeted at her.

'Then it just blew up. I had like no Twitter followers, then I had 7,400 followers, overnight,' Sophia says.

Happily, her retainer had already been replaced - costing $50, and covered entirely by her insurance.

Her teeth should stay perfectly straight, which is a good thing, because next time he is in the Bay area, Jordan said he would be happy to pose for a picture with Sophia and her orthodontist.