Evidence for Common Oral Hygiene Practices

As part of the Open Philanthropy Project’s efforts to understand cross-cutting issues in the social and health sciences, I (Luke Muehlhauser) conducted a rapid review¹ of the evidence supporting some common oral hygiene practices.

My overall tentative conclusion is that there appears to be good evidence that topical fluorides (e.g. various toothpastes) prevent tooth decay, but there is not good evidence that flossing or water fluoridation is beneficial to oral health. There is very little in the way of evidence regarding flossing, even though it seems to me that high-quality randomized studies on this topic would be practical.

1 My process

I spent less than one hour on this rapid review.

Given this limitation, I looked only for systematic reviews released by the Cochrane Collaboration2 (hereafter, “Cochrane”), a good source of reliably high-quality systematic reviews of intervention effectiveness evidence. I also conducted a few Google Scholar keyword searches to see whether I could find compelling articles challenging the Cochrane reviews’ conclusions, but I did not quickly find any such articles.

I looked only for evidence concerning the health benefits of three common oral hygiene practices: topical fluorides (e.g. toothpaste), flossing, and water fluoridation.

2 My findings

2.1 Topical fluorides (e.g. toothpaste)

On the effectiveness of topical fluorides, a 2003 Cochrane review³ concluded:

The review of [randomized or quasi-randomized] trials found that children aged 5 to 16 years who applied fluoride in the form of toothpastes, mouthrinses, gels or varnishes had fewer decayed, missing and filled teeth regardless of whether their drinking water was fluoridated. Supervised use of self applied fluoride increases the benefit. Fluoride varnishes may have a greater effect but more high quality research is needed to be sure of how big a difference these treatments make, and whether they have adverse effects.

Over the next decade, more evidence concerning fluoride varnishes accumulated, and a 2013 Cochrane review⁴ concluded:

The evidence produced has been found to be of moderate quality due to issues with trial designs. However in the 13 trials that looked at children and adolescents with permanent teeth the review found that the young people treated with fluoride varnish experienced on average a 43% reduction in decayed, missing and filled tooth surfaces. In the 10 trials looking at the effect of fluoride varnish on first or baby teeth the evidence suggests a 37% reduction in decayed, missing and filled tooth surfaces. There was little information concerning possible adverse effects or acceptability of treatment.

A 2010 Cochrane review⁵ specific to fluoride toothpaste also concluded:

This review includes 79 [randomized] trials on 73,000 children. As expected the use of toothpaste containing more fluoride is generally associated with less decay. Toothpastes containing at least 1000 parts per million (ppm) fluoride are effective at preventing tooth decay in children, which supports the current international standard level recommended.

2.2 Flossing

A 2011 Cochrane review⁶ concluded:

Twelve trials were included in this review which reported data on two outcomes (dental plaque and gum disease). Trials were of poor quality and conclusions must be viewed as unreliable. The review showed that people who brush and floss regularly have less gum bleeding compared to toothbrushing alone. There was weak, very unreliable evidence of a possible small reduction in plaque. There was no information on other measurements such as tooth decay because the trials were not long enough and detecting early stage decay between teeth is difficult.

2.3 Water fluoridation

A 2015 Cochrane review⁷ concluded:

There is very little contemporary evidence, meeting the review’s inclusion criteria, that has evaluated the effectiveness of water fluoridation for the prevention of caries.

The available data come predominantly from studies conducted prior to 1975, and indicate that water fluoridation is effective at reducing caries levels in both deciduous and permanent dentition in children. Our confidence in the size of the effect estimates is limited by the observational nature of the study designs, the high risk of bias within the studies and, importantly, the applicability of the evidence to current lifestyles. The decision to implement a water fluoridation programme relies upon an understanding of the population’s oral health behaviour (e.g. use of fluoride toothpaste), the availability and uptake of other caries prevention strategies, their diet and consumption of tap water and the movement/migration of the population. There is insufficient evidence to determine whether water fluoridation results in a change in disparities in caries levels across [socioeconomic status]. We did not identify any evidence, meeting the review’s inclusion criteria, to determine the effectiveness of water fluoridation for preventing caries in adults.

2.4 Summary of findings

In short, the relevant Cochrane reviews suggest that:

There is good evidence that topical fluorides (e.g. toothpaste) prevent tooth decay, at least in children in adolescents. I don’t know of a reason to expect adult teeth to respond differently, but I haven’t tried to find such reasons.

There is not good evidence in favor of flossing for preventing tooth decay or gum disease.

There is not good evidence supporting the effectiveness of water fluoridation for preventing dental caries.

There is very little in the way of evidence regarding flossing, even though it seems to me that high-quality randomized studies on this topic would be practical.

3 Sources