Kissing may be the best way to stave off tooth decay - and the more passionate the better!

Talk about killing two birds with one stone: kissing, it turns out, may be the best way to stave off tooth decay.

And, say boffins, the more passionate the clinch, the better the outcome.

Exchange of saliva during a kiss is thought to lower acidity levels, say researchers writing in the Journal of Medical Research.

And 40 seconds seems to hit the sweet spot as far as maximum protection is concerned.

Dentists from the University of Santiago, Ecuador, say their study could offer new strategies for preventing the need for fillings.

It’s all about pH levels - which measure acidity - before and after a smooch.

They say: `’Our study is the first to evaluate whether intimate human interaction can work by transmitting buffering agents through saliva, thus supporting oral pH recovery.’

‘During a French kiss, a substantial volume of saliva is exchanged between partners, and it is plausible that this could introduce buffering agents and bacteria from one individual to another, potentially supporting faster pH normalization.’

Acidity levels can rise by around 25 per cent after sugary drinks, according to the researchers, and it takes around 40 minutes for saliva to return the pH to normal levels.

Dentists plan to use 60 couples aged 18 to 30 to test their work.

They will drink a variety of drinks, including cola, fruit juice. and non-alcoholic beer, and then kiss for a timed 40 seconds.

Their saliva will be tested every five minutes to measure how quickly it returns to normal aided by the kiss.

The dentists say: `No studies to date have explored whether kissing contributes to the recovery of salivary pH following acidic challenges.

‘This represents a novel and unexplored area of research within oral health and preventive dentistry.

‘It would introduce a novel behavioural approach to oral health maintenance.’