Hi! I personally would say that any LOR, as long as it is strong and can really speak to who you are as a person/applicant, is valuable! Most schools want LORs from science professors and the limit of letters is usually 4, so having one from a non-science professor could definitely do more good than harm. Same thing for a LOR from a dentist who attended a school you are applying to. If they have kept in contact with the school and have a good relationship with the staff, that's even better! Good luck with everything!