Sophie Waller, of St Dennis, Cornwall, died in December 2005 of renal failure caused by starvation and dehydration.
She suffered an apparent extreme dental phobia and refused to eat, sleep or drink after her milk teeth came loose.
She underwent an operation in hospital to remove the teeth but this failed to cure the problem, the hearing was told.
Sophie’s parents, Richard and Janet Waller, told the inquest at Truro City Hall she had been scared of dentists and had refused to eat or talk when a milk tooth became loose.
Richard and Janet Waller
She was sent to the Royal Cornwall Hospital in November 2005 to have the teeth taken out under general anaesthetic.
Following the operation however, she would not open her mouth to eat or talk and was given a feeding tube on the ward.
She left hospital on 17 November and was taken home on the understanding a bed would still be waiting for her in hospital.
After she seemed to respond positively at home and after a physical and psychological assessment on 21 November she was officially discharged.
But her notes were then sent to the wrong GP and she was not seen by another medical professional before she died, the hearing was told.
She was found dead in her bed at home on 2 December.
She lost 11kg (23lbs) in the month before she died.
Cornwall Coroner Dr Emma Carlyon, who recorded a narrative verdict, said the severity of her condition had not been realised and this had “prevented her from receiving the medical support that could have prevented her death”.
After the verdict, the hospital apologised to the family.
The Royal Cornwall Hospitals Trust said: “Everyone involved in Sophie’s care was deeply saddened by her death and we offer our apologies and most sincere condolences to her family.
“Care around any child is a multi-agency and multi-disciplinary process, working closely with the whole family.
“With hindsight it can be seen that there were shortcomings in communication between health organisations and with Sophie’s parents, for which we apologise.”
The trust said a clinical review was carried out after her death and that recommendations it had made had been implemented.
A family friend, Elaine Panks, read a statement on behalf of the family.
It said: “It has been a very emotional and distressing time. No words can express how we have felt and still feel.
“The only justification for Sophie’s death is that procedures have and will be changed and will hopefully save another child’s life.”
Dr Carlyon said she was “pleased” all the agencies involved had made changes after their own independent reviews.