The Children's Hospital at Westmead says prolonged feeding with bottles of breast milk andinfant formula are linked to the problem, especially at night, when children suck on bottles in their cots for extended periods.

The hospital's head of dental services, Associate Professor Richard Widmer, said naturally occurring lactose was present in both breast milk and formula. When combined with plaque in a baby's mouth, it could erode the enamel of primary teeth.

"Ideally, children should go straight from breast to cup, avoiding bottles altogether," Professor Widmer said.

Although it has become widely accepted that babies should not go to sleep suckling on juice, cordial or other sweet drinks, the warning about milk is likely to come as a shock to many mothers.

Professor Widmer said the hospital had been removing teeth, under general anaesthetic, from babies as young as 12 months due to bottle-feeding infants at bedtime.

Paediatric dentists had noticed a pattern of decay on the back of the upper front teeth, indicating the cause was drink from a bottle that had been held between the child's tongue and teeth for prolonged periods.

"We see more kids with decay, and we're struggling to get them all done," Professor Widmer said.

"Some of the littlies are in pain. It is difficult some days."

The waiting time for dental surgeries under general anaesthetic is between nine and 12 months.

Professor Widmer said that in a group of 100 five-year-olds, as many as one-third would have some form of tooth decay and as many as nine per cent severe decay.

He said primary teeth were important because they helped children chew food properly, develop proper speech and guide permanent teeth into the right place.

Even when teeth had not formed, it was important to establish good habits and not let a child become accustomed to sucking on a bottle at night, Professor Widmer said.

Bottle-linked decay was more prevalent in the Aboriginal and Torres Strait Islander community, among people from lower socio-economic or non-English-speaking backgrounds, and in rural areas that suffered from a lack of services, he said.

"The biggest fears for me as a clinician are the bottle-feeding and the honey on the dummy." There was also a problem among single or younger mothers who might be struggling to cope when their child became emotional, Professor Widmer said.

"They think, 'I put a mouthful of sugary, sweet stuff in their mouth and the baby doesn't cry,' " he said.

Of the 600 children he treated in emergency each year, as many as 15 per cent had presented with severe tooth decay.

Professor Widmer advocates taking children to the dentist from the age of one and no later than two, and brushing as their first teeth appear."The golden message is two minutes brushing twice a day with fluoride," he said. "I understand parents are busy, but that's the gold standard - brushing before school and before bed."

Angus Cameron, the head of paediatric dentistry at Sydney University and Westmead Hospital, said tooth decay was so bad in some infants that they had to have every one of their primary teeth removed.

Dietitian Susie Burrell said there was also a strong link between the consumption of sweet drinks and weight issues later in life.

"Ideally, water should be the drink of choice for everyone," Ms Burrell said.

"If reduced-fat milk is chosen, it should be consumed with meals and out of a cup."

Lauren Rossi, 35, of Greenacre, said she had been giving her daughter Mia, 11 months, a bottle in bed since she was recently weaned off her breast. "I found giving her a bottle to go to sleep was really helpful," Ms Rossi said.

"I would bottle-feed her at night, which progressed to giving her the bottle in bed, but she never sucked once she fell asleep.

"But her teeth are fine. I can't really comment generally but, in my situation, there hasn't been a problem."