Middle Grade Horror

Arnie doesn't like going to his dentist, Doctor Fossil. He likes it even less when one day he shows up to find that Doctor Fossil has been replaced by a "substitute dentist," a strange man wearing a mask who calls himself "Darktor Fondskull." Fondskull works on his teeth, but Arnie starts to have horrible nightmares and finds himself doing awful things in his sleep. Arnie knows it's all tied together with Fondskull, whoever or whatever he is. But how can he stop the demented substitute dentist from controlling him?