Why a black spot on your tooth might not be bad news
Author: Dr Alexandra Jones, Co-Founder and Board Chair
Most of us see a black or brown mark on a tooth and instantly think, “Decay!”. And you may well be right.
The thought of decay can be scary because once it gets going it inevitably progresses - right? Well, the science is a whole lot more subtle than that.
Did you know that sometimes, that dark patch is actually a sign your mouth is healing itself?
Tooth decay isn’t a one-way street. It’s often a slow, dynamic process that’s constantly swinging between damage and repair. Think of it as a balance between two forces:
Demineralisation: when acids produced by bacteria in dental plaque pull minerals (like calcium and phosphate) out of your enamel.
Remineralisation: when those same minerals are replaced, often with the help of your saliva and fluoride.
When the balance tips too far toward acid attack, you get active decay. But when conditions improve by eating less sugar, better brushing, and maintaining healthy saliva, the process can stop and even reverse.
The weakened enamel can actually re-harden. This is known as arrested decay.
So why does arrested decay look black?
When the decay process stops, the previously soft and chalky enamel becomes firm again as minerals flow back in. The area often darkens, from light brown to almost black and the surface hardens.
That colour change isn’t the tooth “getting worse”, it’s actually evidence of remineralisation and stability. The bacteria have been brought under control, and the tooth is no longer losing mineral, it’s holding steady.
Your saliva does far more than keep your mouth moist. It’s your mouth’s natural buffering and repair system.
It neutralises acids after you eat. It delivers calcium, phosphate, and fluoride ions that rebuild the crystals that make up teeth.
It also washes away food particles and harmful bacteria.
Healthy saliva flow can literally stop early decay in its tracks, especially when supported by fluoride toothpaste and good oral hygiene.
So if you want to support this natural repair process, some tips include:
Brushing twice daily with fluoride toothpaste: fluoride boosts tooth surface repair
Stay hydrated: dehydration slows saliva flow and reduces its protective power
Snack less often: frequent snacking keeps acid levels high - give your teeth recovery time between meals.
Eat crunchy veg and whole foods: they stimulate saliva and support overall oral health.
Avoid smoking: it dries your mouth and disrupts the oral microbiome.
If a dark spot on a tooth surface is rough, feeling softer, changing shape, or causing sensitivity or pain, it’s best to see a dental professional. Dentists can tell whether the spot is inactive (arrested) or still active decay.
Of course there are lots of things that colour change on a tooth surface or within a tooth can represent, decay is just one of the possibilities.
But here’s the most gorgeous and remarkable bit of science: arrested tooth decay is tougher and more resistant to future attacks. It’s literally been tested and made stronger!