A decade back, most of us would use a brush on baby teeth only after a year or 18 months when quite a few teeth were visible but, now the earlier the better.

Try not to put a baby to sleep with a bottle in the mouth.
Wipe the baby’s mouth and gums with a clean, wet and soft cloth or gauze; you don’t need toothpaste at this point. This will prevent bacteria from clinging to the baby’s gums. These bacteria can leave a plaque that can damage infant teeth as they erupt.
Usually babies get their first tooth between 6 – 8 months, though some babies have been known to get their first teeth as early as 4 months.
Gently wipe with a soft cloth when you find teeth erupting to clean them. You can use a soft brush with a small head and a large handle.
As baby teeth develop - a small amount of fluoride –will be beneficial as this mineral prevents tooth decay and strengthens tooth enamel at the same time. Use only a small smear of toothpaste as too much can lead to fluorosis.
According to experts your baby should see a dentist in the first year as you can get useful advice on teething, fluoride, thumb sucking and teeth care.
Babies can be given a clean and cool teething ring which is not too small – to swallow. A baby derives a lot of comfort when you rub the swollen gums with a clean finger.
Avoid giving the infant fruit juices, sodas or any kind of sugary drinks as these can lead to tooth decay. A bacterium feeds on sugar and produces acid which attacks teeth.
Mothers are aware that a gentle brushing of baby teeth is initiated when the first tooth sprouts– at about 6 months, though scientists urge parents to take care of the gums earlier as there is a lot of bacteria present- even in a baby’s mouth.
'Like many other diseases, dental cavities are a result of many bacteria in a community, not just one pathogen,' Prof Swanson said, in a study conducted by the University of Illinois.
He added: 'We now recognize that the 'window of infectivity,' which was thought to occur between 19 and 33 months of age years ago, really occurs at a much younger age.'
'Having a drink of juice from a cup in one sitting is better than sucking it over several hours from a bottle or carton because the mouth releases acid that causes decay for about 20 minutes after each sugar-eating episode.'
Source-Medindia