
A dentist has revealed the possible reasons behind why people have yellow teeth despite brushing them twice a day.
Dr Zainab Mackie regularly dishes the dirt on all things dental on her TikTok account, as she enjoys teaching people 'things they never knew about their teeth'.
The oral hygiene expert, based in the US state of Michigan, now boasts more than 912,000 followers on the social media platform.
So, from those figures, it seems that people love learning new things about their gnashers just as much as Dr Mackie loves teaching them.
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A lot of her educational content has gone viral since she first began doling out dental advice online in 2016, including a video about why some people experience teeth discolouration.
The secret to securing a dazzling smile is supposedly brushing, flossing and having regular cleanings - but there's a few folks who still have yellow teeth despite following all these steps.

And according to Dr Mackie, the cause of this unfortunate hue is likely down to lifestyle factors.
In a TikTok video originally shared in 2021, which has been viewed 1.7million times, she explained some possible reasons behind why 'your teeth are yellow even though you always brush them'.
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"You might be brushing too hard, stripping away that white enamel," Dr Mackie said.
The hard outer layer which coats our teeth and protects them from damage can erode away over time, but you can really speed up the process if you're going HAM with your toothbrush twice a day.
The thinning of tooth enamel can lead to teeth yellowing 'as the underlying dentin layer becomes more visible', according to the Dentevim Dental Clinic.
Experts advise using 'gentle circular motions' and 'avoiding excessive pressure' instead of getting too overzealous when you're cleaning your gnashers - as you might be seriously shooting yourself in the foot.
Another explanation for the yellowish colour of your teeth could be your choice of beverage.
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Dr Mackie said: "If you drink too much pop, that's going to stain your teeth."
Fizzy drinks are notoriously regarded as being terrible for your teeth in the world of dentistry, due to their high sugar content, carbonation and vivid colouring.
According to Colgate, all of this stuff is a 'recipe for tooth decay', discolouration and sensitivity.
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But even healthier options can hinder your pearly whites, as Dr Mackie then warned: "Acidic fruit juices are definitely a teeth stainer."
The high acid contents of these drinks can result in your tooth enamel weakening and demineralising over time, and just like over-brushing does, this can cause your teeth to appear yellow.
Colgate explains: "The calcium in saliva can help strengthen enamel, but when the environment in your mouth is too acidic, remineralisation will not occur, which leads to tooth erosion and decay.
"Your teeth might appear slightly yellower as your enamel becomes thinner, exposing the dentin underneath. The edges of your front teeth may lessen in opacity, appearing as if you can almost see through them."
So it might be best to consume your favourite beverage through a straw now on, if you want to achieve a stunning white smile.