Some babies are born with teeth, some get their first teeth (milk teeth) from about six months old, while others will have still have no teeth by the time they're one. It varies. But most children will have all their milk teeth by the time they're two-and-a-half and will begin to get their first 'second' teeth at the back when they are six years old.
Studies have shown that babies are more likely to suffer a slight rise in temperature when teeth come through the gums. And, for a number of babies, this can make them a little irritable, more inclined to wake up crying at night, more liable to drool and dribble, and needing more soothing and comfort.