Oww! Scientists discover the molecule in tooth cells that signals the brain when exposed to cold

There’s little as excruciating as biting into a cold ice-cream and feeling an awful jolt of pain, especially if you’ve been a bit lax in the dental hygiene department.

Researchers from the US and Germany have finally gotten to the root of this pain — identifying the specific cells in teeth, odontoblasts, that sense cold temperatures.

These cells are abundant in special cold-sensitive proteins that are responsible for letting the brain know when you’re eating or drinking something chilled.

According to the team, developing drugs to target these sensors specially could eventually pave the way to new treatments for cold-sensitivity.

Furthermore, the findings also finally explain an age-old home remedy for toothache, clove oil, which happens to contain a chemical that blocks the cold-sensing protein.

Cold sensitivity is often more extreme among people with cavities, where part of a tooth’s protective enamel becomes worn away by films of bacteria and acid.

It is estimated that roughly 2.4 billion people — about a third of the world’s population — have untreated cavities in their permanent, or ‘adult’, teeth. 

There's little as excruciating as biting into a cold ice-cream and feeling an awful jolt of pain, especially if you've been a bit lax in the dental hygiene department. Researchers from the US and Germany have finally gotten to the root of this pain ¿ identifying the specific cells in teeth, odontoblasts, that sense cold temperatures (stock image)

There’s little as excruciating as biting into a cold ice-cream and feeling an awful jolt of pain, especially if you’ve been a bit lax in the dental hygiene department (stock image)

The researchers — led by neurobiologist David Clapham of the Howard Hughes Medical Institute in Maryland — did not originally set out to study teeth.

Instead, their work was focussed on so-called ‘ion channels’, pores in the membranes of cell that act as gates to molecules.

When these channels detect a given signal such as a chemical message or temperature change, they respond by either clamping shut or opening wide.

The latter case lets ions flood into the cell, creating an electrical pulse that travels to other cells and allows the body to communicate information.

Some fifteen years ago, the team determined that one such ion channel — TRPC5 — was highly sensitive to the cold. It was unclear, however, where TRPC5 was used.

The researchers were able to rule out its operation in the skin, at least, publishing in a 2011 paper that mice that lacked the ion channel were still able to feel the cold. 

After that, they ‘hit a dead end’, explained team member and electrophysiologist Katharina Zimmermann, who was originally a member of Professor Clapham’s lab but now works at the Friedrich-Alexander University Erlangen-Nürnberg in Germany.

Inspiration ultimately came, however, when the team was having lunch. Teeth are another area of the body with cold sensitivity — and one that, at that point, worked in a way that was not entirely clear.

Experts from the US and Germany have finally gotten to the root of this pain ¿ captured in this artwork ¿ identifying the specific cells in teeth, odontoblasts, that sense cold temperatures

Experts from the US and Germany have finally gotten to the root of this pain — captured in this artwork — identifying the specific cells in teeth, odontoblasts, that sense cold temperatures

The main theory for how teeth sense cold involved tiny canals inside the teeth that contain fluid that moves when the temperature change.

It was thought that perhaps nerves could sense the direction of this movement, and thus signal whether a tooth was hot or cold.

‘We can’t rule this theory out,’ Professor Clapham said. However, he added that there was no direct evidence in support of it either.

The problem is that fluid movement in teeth is particularly hard to study — as accessing the inner workings of teeth involves cutting through tough layers of enamel and dentin without pulverising the soft pulp that such protects. 

As Professor Zimmerman grimly explained, sometimes teeth being studied in this way ‘just fall to pieces.’ 

Teeth are particularly hard to study, the team explained, as accessing their inner workings involves cutting through tough layers of enamel and dentin without pulverising the soft pulp that such protects. Pictured: a cross section of a a tooth. Odontoblasts can be found located between the pulp cavity and the surrounding layer of dentin

 Teeth are particularly hard to study, the team explained, as accessing their inner workings involves cutting through tough layers of enamel and dentin without pulverising the soft pulp that such protects. Pictured: a cross section of a a tooth. Odontoblasts can be found located between the pulp cavity and the surrounding layer of dentin

Despite these challenges, when Professor Clapham and colleagues examined teeth from human adults, however, they found that they did indeed contain TRPC5 ion channels, as they had formerly guessed.

Moreover, TRPC5 is more abundant in teeth with cavities, which are notoriously more sensitive to cold than their healthy counterparts. 

To investigate further, the team performed experiments on live mice — recording their neural activity as they teeth came into contact with an ice-cold solution. 

In regular mice, the team found that the chill sparked nerve activity. However, mice that lacked TRPC5 or had been treated with a chemical that blocked the ion channel did not react in the same way, suggesting TRPC5 is key to cold sensing in teeth. 

The team traced the location of TRPC5 to a specific type of cell in teeth, 'odontoblasts' (pictured here in green) which can be found between the pulp and the surrounding dentin

The team traced the location of TRPC5 to a specific type of cell in teeth, ‘odontoblasts’ (pictured here in green) which can be found between the pulp and the surrounding dentin

The team also found that one other ion channel in teeth, ‘TRPA1’, also appears to play a role in responding to cold temperatures. 

Finally, the team traced the location of TRPC5 to a specific type of cell in teeth, ‘odontoblasts’, which can be found between the pulp and the surrounding dentin.

When someone bites down into a cold ice cream — especially if they have cavities and exposed dentin — it is these cells packed with TRPC5 that pick up on the cold sensation and send pain signals shooting off to the brain

The full findings of the study were published in the journal Science Advances. 

OWW, TOOTHACHE! 

Causes of toothache

Toothache can be caused by:

  • tooth decay
  • a dental abscess
  • a cracked or damaged tooth
  • a loose or broken filling
  • an infection — this often happens when a tooth (such as a wisdom tooth) has broken the skin, but doesn’t have enough room to fully come through
  • problems with your braces

How to prevent toothache

The best way to prevent toothache is to keep your teeth and gums as healthy as possible.

To do this:

  • have regular dental check-ups
  • cut down on sugary foods and drinks — only have them as an occasional treat at mealtimes
  • brush your teeth twice a day for about 2 minutes with a fluoride toothpaste
  • clean between your teeth using floss or an interdental brush every day to remove food, debris and plaque

When to see a dentist

See a dentist if you have toothache:

  • that lasts more than 2 days
  • that doesn’t go away when you take painkillers
  • with a high temperature, pain when you bite, red gums, or a bad taste in your mouth
  • and your cheek or jaw are swollen

How to ease toothache while waiting for an appointment 

Do:

  • take painkillers, like ibuprofen or paracetamol (children under 16 shouldn’t take aspirin) — a pharmacist can advise you
  • try rinsing your mouth with salt water (children shouldn’t try this)
  • use a pain-relieving gel for your mouth — this can be bought from pharmacies or supermarkets
  • eat soft foods, like yoghurt or scrambled eggs, and try to avoid chewing with the sore tooth

Don’t:

  • eat foods that are sweet, very hot or very cold
  • smoke — it can make some dental problems worse

SOURCE: NHS

source: dailymail.co.uk