I am a little confused with your question - do you mean the baby is getting one tooth ? That is normal and not a reason for any tension. Baby will get twenty teeth over the next few months.

my daughter got her first tooth a day before her birthday...I was scared too, coz my elder one git at 5 months...I checked with my Pediac , and he said it's pretty normal...just give ur child lots of teethers to chew on... and it's believed d babies who get teeth late, don't have too much discomfort