‘How often do you brush, Ralph?” a dentist asks Chief Wiggum’s son in Last Exit to Springfield, frequently cited as one of The Simpsons’ best ever episodes. “Three times a day, sir!” chirps the hapless Ralph, only to have the cold glare of the dental lamp shone in his face along with his orthodontist’s ire: “Why must you turn my office into a house of lies?”

If this scene seems familiar, it’s probably because you have been interrogated once too often about how often you floss. Invented almost 200 years ago, flossing has never caught on in quite the same way as a twice-daily brush – and a few years ago, a decent-sized study put the dental profession on the defensive by claiming that it might not actually be all that worthwhile. But the NHS didn’t change its recommendations on interdental care, and oral health specialists are as persistent as ever. So what should you be doing?

First, what about that study? Well, in 2016 the Associated Press published a piece based on freedom of information requests to the US departments of health and human services and agriculture for evidence in favour of flossing and concluded that the evidence for flossing was “weak, very unreliable” and carried “a moderate to large potential for bias”. Stories at the time pointed to another review of studies from 2015, claiming that it showed “very inconsistent/weak evidence” for flossing.

Before you toss the floss, though, there are a couple of problems with all this. First, that frequently quoted 2015 study looked specifically at periodontitis, a severe form of gum disease that is among the leading causes of tooth loss in adults, not the effectiveness of flossing more broadly (gingivitis, also considered in the study, is less serious, but can escalate). More generally, it is very difficult to conduct good long-term studies on flossing because many people will lie about their health-based behaviour – whether that is how much they drink, how often they exercise or how they take care of their teeth.

Over the long term, it is also difficult to ensure test subjects are flossing for long enough, or using the correct technique, even if they think they are doing everything right. And in a study published this year, researchers found that people who learned and consistently used proper flossing technique showed a significant reduction in gum bleeding compared with people who just carried on with whatever strategy they were using. As bleeding gums can be an early indicator of gum disease, that is a pretty significant finding.

“If you never floss your teeth, you’re missing out on a crucial part of oral hygiene,” says Dr Thomas Servos, of the University of Texas Health school of dentistry in Houston. “Flossing helps to remove plaque and food particles from between your teeth and areas that your toothbrush might not reach effectively.”

This means that flossing can help to manage or prevent halitosis, as well as managing the buildup of plaque that can otherwise only be removed by a professional when it turns into tartar. There is also (limited) evidence that flossing might improve your oral microbiome, so your mouth is healthier overall. “There are a number of options for what we call interdental care, including tape, picks, and brushes, and your choice of floss can impact on effectiveness, comfort and ease of use, so finding the right type for your teeth is important,” says Servos.

“Using proper technique ensures that you effectively remove debris without causing harm to your gums,” he adds. “Use a gentle back-and-forth motion and avoid snapping the floss into place, which can harm your gums. Make sure to clean both sides of each tooth – and don’t force it. If you haven’t flossed regularly, your gums might bleed initially due to inflammation or gingivitis. However, consistent flossing should improve gum health and reduce bleeding.”

Ideally, you should floss at least once a day – consistency matters more than frequency, so consider pairing it up with another regular daily activity, such as your morning shower or evening audiobook. And yes, dentists really can tell whether you do it or not. Don’t turn your dental surgery into a house of lies.