10&1/2 months old, recently weaned .. can low fever and teething cause lack of urination and constipation. ? hasn't had a wet diaper in over 8 hours

Dehydration : Teething should not be directly the reason for lack of urinations , it's possible he did not eat or drank any thing , that leads to dehydrating child , .

Not really: My concern is that the baby is not getting enough fluids. If you are sure he has not wet his diaper in 8 hours ( it may be hard to tell with the new super absorbent diapers) , i would suggest calling his doctor.

MD visit required: Your child sound dehydrated, and this can lead to a more serious situation. You should bring the child to the pediatrician to rule out any additional issues. Lack of fluids is a significant issue for all children. If you are unable to reach your pediatrician, your safest bet is the pediatric er.