"They" say the longer it takes for a child's 1st tooth or teeth to come in the stronger they will be. Which lends itself to the thought that they'll be healthier in the long run.
My oldest didn't cut his 1st tooth til he was 9m and my daughter was 9 1/2m old before her 1st tooth came in.
Concerned, as you are now, when my son was about 6m, I asked my mother if she recalled when I started cutting my teeth and she told me around 9m...I've had a few cavities, just recently started going back to the dentist regularly and everything is great, didn't even have pain or have to get my wisdom teeth extracted when they came in...so maybe there is some truth to what "they" say LOL...I wouldn't worry...good luck
Josie