Real progress in oral health doesn’t come from expensive gadgets, but from better daily habits. That is the conclusion of dentist- periodontist Tim Thomassen in his dissertation Oral Disease Prevention, which he will defend on 12 December at the University of Amsterdam. In his research, he examines how effective different types of toothbrushes are and how much impact the actual time people spend brushing has on oral health.

Worldwide close to 3,5 billion people suffer from oral diseases, such as cavities and gum diseases. Dental plaque often plays a major role in these problems – which is why good brushing is the standard advice. But what does ‘good’ actually mean?

Thomassen investigated various aspects of preventing tooth and gum diseases, including the effectiveness of toothbrushes, brushing duration, and oral hygiene instructions. He reviewed dozens of international clinical studies, combined them in systematic reviews, and conducted several experiments of his own.
‘Expensive technology plays a much smaller role in preventing cavities and gum diseases than many people think,’ Thomassen says. ‘Because the differences between products are often minimal in practice, it is people themselves who ultimately make the biggest difference.’

Which toothbrush should you use: powered or manual?
An oscillating–rotating toothbrush, a high-frequency sonic toothbrush, or just a manual one? The price differences are significant, but does that also apply to how well they clean our teeth?
‘For removing dental plaque, a powered toothbrush performs better than a manual one,’ says Thomassen. ‘But the difference between the two main powered types is negligible in everyday use.’ According to Thomassen, manufacturers would be better off investing in user education and affordable, sustainable designs rather than launching yet another – and often even more expensive – model.

How long should you brush?
The global recommendation is clear: brush twice a day for two minutes to effectively remove dental plaque. Thomassen’s research confirms that two minutes of brushing removes more plaque than one minute. He then examined whether brushing for three minutes works even better. It doesn’t – the added benefit is minimal.

And how long do we actually brush?
People who use a manual toothbrush, still the majority worldwide, brush for less time: on average just under 1.5 minutes. ‘We know brushing works, and fortunately the average brushing time has been increasing in recent years, but many people still don’t brush long enough,’ Thomassen says.

Users of powered toothbrushes do reach the two-minute mark more often, and even exceed it, brushing for almost 2.5 minutes on average. ‘Built-in timers may help people brush longer,’ he notes.

Better information
Finally, Thomassen analysed the brushing advice provided by dental organisations around the world. Only one-third offer clear instructions online. ‘That needs to improve,’ he says. ‘Good oral care starts with accessible, understandable, and practical information that people can apply immediately.’

He therefore advocates for practical guidelines tailored to people’s lifestyles, abilities, and budgets so that good oral care becomes achievable for everyone. ‘There is a clear need for a national oral-care guideline that is evidence-based and adapted to different needs and preferences. Such a guideline would help bridge the gap between research and everyday practice, supporting both patients and oral-health professionals.’

Thomassen hopes that his research can contribute to this goal. Preparations for such a guideline are already underway – the next challenge he is committed to taking on.

Details PhD Thesis
Tim Thomassen, 2025, 'Oral Disease Prevention. Primum est dentes purgare'. Supervisors: Prof. D.E. Slot and Prof. G.A. van der Weijden.

Time and location
Friday, December 12, 14.00-15.30, Aula, Amsterdam