A child who brushes their teeth after every meal and doesn't consume a lot of sugar might still get rotten teeth. But why?
For decades this has baffled parents who thought they were doing all they could to protect their children's teeth.
Today, research has uncovered some answers after the University of Auckland and Starship Children's Hospital examined information collected by the country's largest longitudinal study of child development, Growing Up in New Zealand.
It turns out refined starches - such as white bread, rice, noodles and some breakfast cereals - can be just as damaging for children's teeth.
The study - funded by the Starship Foundation - cross-referenced dental records of more than 4000 children with information about their dental hygiene and food consumption, which was collected when they were 2 years old.
Lead author on the study, University of Auckland public health physician, Dr Simon Thornley, said the biggest surprise was the strong link between refined starches and dental decay.
"This should inform our oral health promotion work in this country because many people would not be aware that frequently consuming foods such as white bread, rice and noodles could put children at greater risk of dental caries [cavities]," he says.
Foods with greater risk included white bread, white rice, noodles, refined breakfast cereals, fruit juice, sugar-sweetened soft drinks, ice cream, confectionery and cake.
Thornley said colleagues who had researched dental care in Cambodia - where rice and noodles were a staple of their diet - found similar results.
Comparatively, the study found a lower number of dental caries in children who had a frequent intake of wholemeal or whole wheat bread, vegetables from the brassica family such as broccoli, and cheese.
The study authors note that behaviours associated with fewer dental caries included:
• Brushing teeth more regularly
• Parental help with tooth brushing
• Brushing teeth after a snack or a drink.
Thornley said it was positive to learn that three-quarters of all children studied had no cavities at their first community dental appointment.
But ethnicity and socio-economic status were strongly associated with tooth decay.
Pacific children were four times more likely than Pākehā children to have four or more dental caries at their first community dental appointment. Asian and Māori children were twice as likely to have four or more dental caries at their first appointment.
"The link between socioeconomic status and diet reinforces what we've learned from other research that poverty and deprivation mean people are less likely to be able to afford good quality food that is nutritious and beneficial for overall health, including oral health."
Paediatric dentist at Starship Children's Hospital, Dr Katie Bach, said thousands of New Zealand children faced hospital treatment every year because of tooth decay.
"Dental caries is the leading cause of avoidable hospital treatment for children in this country and action is needed to ensure that children do not have to endure potentially invasive oral surgery."
Saraid Thompson thought she was doing everything right to prevent her children's teeth from rotting.
She steered them clear of fruit juice, soft drinks and sugary foods.
The Auckland mum-of-four said she was vigilant about making sure all her kids brushed their teeth after every meal.
And it seemed to be working. Her first three children had no issues with their teeth.
Then, when her youngest Harry was 6 years old, he had to get two rotting teeth surgically removed.
"It was really horrible. He was really scared and as a parent I remember feeling really embarrassed, like I had failed my son."
Yet, to the best of her knowledge, Harry had a reasonably healthy diet and good dental hygiene.
"I thought I had done everything right."
When Thompson found out about the link between refined starches and dental decay from the Growing Up in New Zealand study it immediately made sense to her.
Though Harry didn't consume a lot of sugar, he was a "massive sushi fan" and ate a lot of white rice and rice crackers.
"As he was my youngest, we were on the go a lot and so sushi was always an easy option, which he loved."
She said he would have sushi at least three times a week and would often have more rice for dinner.
"Sugar and juices have always been evil. There has been a lot of information about that but I have never heard the impact refined starches can have on teeth, until now.
"I've known white bread nutritionally isn't brilliant but I never thought of it as a contributor to tooth decay."
Thompson said if she had known she would have made more effort to opt for brown rice instead of white rice and been wary of how much refined starches her children were consuming.
"I think it's really important that parents have as much information as possible so that choices are available and we know how to best protect our children."