Fillings can 'do more harm than good', researchers warn

Medical practice

"Having a filling can increase the risk of tooth decay in neighbouring teeth," reports The Times. Researchers found evidence that, in some cases, fillings were more of a stop-gap than a cure for tooth decay…

"Having a filling can increase the risk of tooth decay in neighbouring teeth," reports The Times. Researchers found evidence that, in some cases, fillings were more of a stop-gap than a cure for tooth decay – and could even actually contribute to the problem.

This headline was prompted by a new study carried out by researchers in Norway, which assessed whether having fillings increases the risk of decay in the surrounding teeth. The study included more than 700 people who needed fillings, monitoring the health of the neighbouring teeth for almost five years.

It found that almost 40% of healthy neighbouring teeth remained decay-free, but around 60% of people experienced decay of the enamel (the hard surface of a tooth) or dentine (the tissue found inside a tooth).

For those who already had decay of the enamel on neighbouring teeth at the start of the study, more than 40% saw decay progress into the dentine. Both patient and dentist-related factors influenced the progression of decay in teeth near to a newly-placed filling, with poor dental hygiene being a key factor.

The results suggest that unless you address the underlying causes that led to the need to have a filling in the first place, their use could be counterproductive.

To reduce your risk of tooth decay, it is important to brush your teeth twice a day, floss at least once a day, use a fluoride mouthwash after brushing and flossing, and limit how much sugary food and drinks you have.  

Where did the story come from?

The study was carried out by researchers from the Nordic Institute of Dental Materials and the University of Oslo, and was funded by the Norwegian Directorate of Health. It was published in the peer-reviewed Journal of Dentistry.

The findings have been presented accurately by the UK media. However, most of the reporting does not explain that there is no certainty that any of the risk factors observed are the cause of tooth decay.

The Daily Telegraph pointed out that while these findings might cause concern, fillings are currently the best solution we have for tooth decay. Left untreated, tooth decay leads to further problems, such as cavities (holes in the teeth), gum disease or dental abscesses (collections of pus at the end of the teeth or in the gums). The paper also highlights the importance of taking care of your teeth and reducing sugar consumption to minimise risk.  

What kind of research was this?

This longitudinal study aimed to identify risk factors for the development of decay on teeth next to new fillings. This was part of a larger study assessing the longevity of fillings.

While this is a good way of observing what happens over a period of time, this design is unable to prove cause and effect.  

What did the research involve?

A sample of participants from the main study was chosen to investigate the condition of teeth in contact with fillings.

Participants were aged 17 or over, had neighbouring teeth in contact with fillings, and the teeth:

  • were permanent
  • were initially sound or had decay confined to enamel
  • had an observation time of at least four years
  • had an endpoint score available (a rating of how successful the filling was in treating tooth decay)

For those with multiple fillings, only one neighbouring tooth was selected at random in each participant.

Information was collected on patient-related variables, including:

  • age
  • sex
  • oral hygiene
  • decay

Tooth-related variables included:

  • tooth type
  • position in jaw
  • mouth side
  • filling details

The dentist's age and use of a protective shield were recorded. Dentists were required to record the participants' oral hygiene as good, medium or poor.

Statistical analyses were performed for teeth in good condition, and those with decay, to assess the development and progression of the decay.  

What were the basic results?

The 750 participants in the study were followed for an average period of 4.9 years. The mean age of the participants was 15.1 years.

The study found that 38.8% of neighbouring tooth surfaces without decay remained healthy for the duration of the study. However, just over a third (34%) of participants developed decay in the enamel, and more than a quarter (27.2%) experienced decay into the dentine. For participants with decayed enamel at the beginning of the study, 57.3% remained in and 42.7% progressed into dentine.

The factors researchers identified that increased the risk of a participant developing decay in sound teeth were poor or medium oral hygiene – this increased the risk by 53% – and a higher number of decayed, missing and filled teeth at the beginning of the study. Back teeth and the teeth on the right side of the mouth (for right-handed participants) were also associated with a higher risk.

The dentists providing treatment had a significant impact on the development of decay. For example, the teeth of neighbouring fillings placed by one dentist had an increased risk of developing decay during follow-up, while the risk of decay was reduced when placed by other dentists.   

How did the researchers interpret the results?

The researchers concluded that both patient and dentist-related variables are risk factors for the development of decay surfaces in contact with newly-placed fillings.

They said clinicians should be aware of a notable risk of developing cavities as a result of decay on the adjacent tooth surface, especially in higher-risk patients with existing decay.

They also advised that clinicians should consider greater use of preventative strategies or non-operative treatment, which should be evaluated and repeated at every check-up. 


This longitudinal study aimed to assess risk factors for decay in teeth next to newly-placed fillings. The study found that around 60% of people experienced decay of the enamel or dentine in previously healthy neighbouring teeth.

In teeth with existing decay of the enamel at the start of the study, more than 40% progressed into the dentine. The researchers found that both patient and dentist-related factors were associated with the risk of the progression of decay.

This study has a good sample size, but because of its design, it is unable to prove causation. Though the study found patient factors and the treating dentist had an influence on the outcome in their statistical modelling, this cannot prove this is the direct cause. Nevertheless, poor dental hygiene is a known risk factor for dental decay and may have been why the filling was needed in the first place.

If teeth are decayed, restorative treatment with fillings may be the only option. However, you can take steps to reduce your risk of developing tooth decay by:

  • brushing your teeth twice a day with fluoride toothpaste 
  • using a fluoride mouthwash
  • flossing your teeth at least once a day – your dentist can give advice or refer you to a dental hygienist
  • leading a healthy lifestyle – eat well, don't smoke, and limit how much alcohol you drink
  • encouraging good dental habits in children from a young age
  • having regular check-ups with your dentist – they can advise you on how frequently you need to have a check-up; depending on the state of your teeth and gums, frequency can vary from every three months to every two years

For more advice, read our guide to good dental health.

Article Metadata Date Published: Di, 22 Aug 2017
Author: Zana Technologies GmbH
NHS Choices