When Should I Brush My Teeth?

Why first thing in the morning might be the smartest time to reach for your toothbrush.

Most of us have been brushing our teeth for so long that we barely think about when we do it. Get up, have breakfast, brush your teeth and head out the door. It seems perfectly sensible. After all, you've just eaten, so surely that's the best time to clean your teeth?

Not necessarily.

The timing of your brushing can make quite a difference to what is happening on the surface of your teeth. Once you understand a little about the chemistry of your mouth, you might decide to rearrange your morning routine.

The best time to brush your teeth in the morning is before breakfast, ideally as soon as you get up.

Stay with me.

Your Mouth Has Been Busy While You Were Sleeping

While you were enjoying a good night's sleep, the bacteria in your mouth were getting on with their lives. Your mouth is home to hundreds of different microbial species, many of which are perfectly harmless or even beneficial. Others, particularly when supplied with plenty of sugar, can contribute to tooth decay.

During sleep, saliva production drops considerably. This is perfectly normal, but it means there is less saliva available to wash away bacterial waste products, neutralise acids and help regulate the environment around your teeth.

By morning, the bacterial communities living in dental plaque have had several relatively undisturbed hours to develop. That familiar morning breath is one reminder that your oral microbes haven't been sleeping quite as soundly as you have.

Brushing when you get up disrupts much of this accumulated biofilm (plaque) before you introduce breakfast into the equation. It also gives your teeth a fresh start before the first meal of the day.

To understand why that matters, we need to look at what happens every time you eat.

Every Meal Starts a Little Chemistry Experiment

Your teeth might look like solid, unchanging structures, but their surfaces are involved in a continuous exchange of minerals with the fluid surrounding them.

When you eat fermentable carbohydrates, bacteria living in dental plaque have a feast of their own. Fermentable carbohydrates are simply sugars and starches that oral bacteria can break down and use for energy. That includes the obvious sugary foods such as biscuits, cakes, sweets and sweetened drinks, but also everyday starchy foods such as bread, rice, pasta, potatoes, crackers and breakfast cereals.

Some starches are broken down into sugars by enzymes in your saliva, making them available to bacteria. These bacteria then produce and release organic acids which cause the pH in dental plaque to quickly fall. How much acid is produced depends partly on how easily the carbohydrate is broken down, how sticky the food is and how long it remains in your mouth.

For anyone whose school chemistry is a little rusty, pH is simply a measure of how acidic or alkaline something is. A pH of 7 is neutral, while lower numbers indicate increasing acidity.

Under normal resting conditions, the environment around your teeth is usually somewhere near neutral, but within minutes of eating something sugary (readily fermentable), the pH in plaque will fall.

This is where things get interesting.

Meet the Stephan Curve

In the 1940s, a researcher named Robert Stephan demonstrated what happens to plaque acidity after sugar is introduced into the mouth.

He found that plaque pH drops rapidly, often reaching its lowest point within minutes. It then gradually recovers as saliva clears away sugars, dilutes acids and neutralises the acidic environment.

This pattern became known as the Stephan curve, and it remains one of the most useful concepts for understanding tooth decay.

The important point is that the drop in pH happens quickly, but recovery takes considerably longer. Depending on the food, the amount of plaque and how much saliva you produce, it may take 60 minutes or more for the environment to return to normal.

During that recovery period, your teeth are experiencing some interesting changes.

Your Teeth Are Constantly Losing and Gaining Minerals

Tooth enamel is largely made from a calcium phosphate mineral called hydroxyapatite. Although it is the hardest substance in the human body, it is not chemically indestructible.

When the environment around enamel becomes sufficiently acidic, calcium and phosphate begin to dissolve out of its surface. This is called demineralisation.

For enamel, a pH of around 5.5 is often used as the traditional point at which mineral loss becomes more likely. In reality, the precise threshold varies with the chemistry of the surrounding fluid.

Exposed tooth roots are more vulnerable. Their dentine and cementum (the root surface) can begin losing minerals at a higher pH, often somewhere around 6.2 to 6.7. This is not a big change.

Fortunately, your mouth has evolved an elegant repair system.

As saliva gradually restores the pH, calcium and phosphate can move back into partially demineralised enamel. This process is called remineralisation.

In other words, your teeth spend much of their lives moving through a natural cycle of mineral loss and mineral repair. This is not a design flaw. It is evolutionary biology.

Problems develop when the balance is repeatedly pushed towards mineral loss, particularly when the teeth are exposed to frequent acid challenges without enough time for recovery.

Why Snacking Can Be Harder on Teeth Than Meals

Imagine eating a piece of cake with lunch, then leaving your mouth alone for several hours.

The bacteria in plaque metabolise the sugars, acidity increases and some mineral loss may occur. Saliva then gradually restores the environment, allowing the natural repair process to resume.

Now imagine eating that same piece of cake in small portions throughout the afternoon. A bite at one o'clock, another at two, a sweetened cuppa at three and a few more bites at four. Then home for dinner.

Each exposure triggers another fall in plaque pH. Instead of one acid challenge followed by a long recovery period, your teeth spend more time in conditions that favour mineral loss.

Please keep in mind it isn't just cake and sweets. Regularly nibbling on crackers, bread, chips or other starchy foods will also keep acid producing bacteria supplied with fuel. Some of these foods are particularly good at sticking around in the grooves and spaces between your teeth. A slow release situation.

This is why the frequency of carbohydrate consumption is easily or more important than the total amount.

It also explains why constantly sipping sweetened drinks can be particularly troublesome. Even small amounts of sugar will repeatedly feed acid producing bacteria.

Our teeth generally cope much better with distinct meals than a continuous supply of snacks.

So Why Not Brush Straight After Eating?

This brings us back to the toothbrush.

When you eat or drink something acidic, such as citrus fruit, fruit juice or a soft drink, the acids temporarily soften the outermost enamel surface. Brushing during this period will increase mechanical wear before saliva has had time to restore the mineral balance.

Acids produced by plaque bacteria after carbohydrate consumption also alter the mineral equilibrium at the tooth surface, although this is not quite the same process as directly bathing your teeth in an acidic drink.

Allowing saliva some time to do its work is a sensible precaution, particularly after acidic foods and drinks.

A commonly recommended waiting period is at leasst 60 minutes after an acidic exposure. For those who prefer a more conservative approach, waiting up to two hours gives the mouth plenty of opportunity to recover.

There is another advantage to brushing before breakfast. You remove much of the plaque before the bacteria receive their first substantial supply of fermentable carbohydrates for the day.

Fewer plaque bacteria means less potential for acid production, although brushing does not eliminate the oral microbiome, nor should it.

The Case for Brushing First Thing in the Morning

Putting all this together, brushing when you first wake up makes a great deal of sense.

Your mouth has experienced several hours of reduced salivary flow, plaque has accumulated overnight and breakfast is about to provide a fresh supply of nutrients to the bacteria living on your teeth.

By brushing before you eat, you disrupt that plaque, reduce the number of acid producing bacteria on the tooth surfaces and avoid the question of whether your breakfast has left your enamel temporarily more vulnerable to abrasion.

There is also a practical advantage. Brushing first thing means the job is done before the morning rush begins. You don't have to worry about how long to wait after breakfast, whether your orange juice was particularly acidic or whether you have enough time before leaving for work.

What About Brushing Before Bed?

During the night, saliva flow decreases and its protective effects are reduced. Going to sleep with a substantial layer of plaque and food debris on your teeth gives acid producing bacteria an extended opportunity to operate in an environment with less salivary protection.

Brushing before bed and avoiding further snacks or sweetened drinks afterwards helps minimise that risk. Just make sure you haven’t had that evening nibble too recently.

The kiss goodnight will be a little nicer too.

The Primal Dentist's Take

Our mouths evolved with the capacity to maintain and repair the mineral surfaces of our teeth. Saliva, oral microbes and tooth enamel are part of a finely balanced biological system that has been operating for a very long time.

What has changed is the frequency with which many of us eat, the availability of refined carbohydrates and acidic drinks, and the amount of time our teeth spend recovering from repeated acid challenges.

Understanding the Stephan curve gives us a useful insight into how to work with that biology rather than against it.

Brush first thing in the morning, before breakfast. Perhaps again before bed. Give your teeth some breathing space between meals, and let saliva do the job it evolved to do.

Better dental health isn't about brushing longer or buying a more expensive toothbrush.

It's more about knowing when to use it.