I don't know what to think either, but the last thing I would think is that Hannah did not have regular dental care from early childhood onward.
It's possible that she has been identified based on dental records, and that information is being withheld/delayed for some reason. It's possible that her teeth were not intact. I could see Jesse thinking that since Morgan was identified through dental records, he should destroy her teeth. I think he felt very lucky in terms of getting away with rape and murder, and I suspect that he attributed some of that luck to hiding the body until little could be learned from the remains.
One reason I'm confident that Hannah had regular dental care is because she was born in England (moving to the US when she was five) where dental care is free for children. That is, it would have been common practice for her parents to ensure that Hannah had the same care as other children, regardless of where she lived. What I'm saying is that her parents would have thought it was normal for Hannah to have lifelong dental care. That's just an opinion ...
"The NHS provides, among other things, primary care, in-patient care, long-term healthcare, psychiatric care and treatments, ophthalmology, and dentistry.
All treatment is free with the exception of certain charges for prescriptions, dentistry and ophthalmology (which themselves are free to children, certain students in full-time education, the elderly, the unemployed and those on low incomes). "
http://en.wikipedia.org/wiki/Universal_health_coverage_by_country