Your undergrad performance affects your admission for both. I don't really know much about admission requirements to Dental School, but I know for Medical School you need EC's, letters of recommendations, a good MCAT (good DAT for Dental School), shadow and clinical hours, good GPA, research experience, etc. High School doesn't matter at all for Med School or Dental School, so don't worry about that 🙂. Like I said I'm sure the requirements for Dental School are similar, but I'm not going to say what they are because I'm really not sure, and have never looked in the requirements for Dental School.