Manya
Don't worry, I had the same problem with my second-born, I was freaking out that only his upper front teeth came thro' at 10 months old. Anyway, spoke to our dentist ( Dr Raymond Lee, very good and gentle with kids and his practice has really good patient leaflets on pregnancy and teeth and dummy sucking etc)- anyway he reassured me that it's perfectly normal for teeth NOT to come out in sequence. What they tell you in all the books is an average only, not every kid has their teeth coming thro at 6-7 months old and not everyone has their upper teeth coming thro- the most important bit is that if the tooth on one side comes thro' then the tooth on the other side should also appear in the mouth within 1 yr, if not you should take your child to see the dentist, incase there's anything stopping the teeth coming thro' the gums.
oh yes, he also mentioned that boys teeth ON AVERAGE come through later than girls, guess it's kinda equivalent to girls maturing quicker than boys!