I doubt many pre-dental students would know much about residency requirements. This thread belongs in the "Dental" or "Dental Residents and Practicing Dentists" sections where it'll catch the eyes of people more knowledgeable on the subject
But your question is relatively simple to answer: yes, you need high marks...residency is not handed out as participation trophies to any old dental student, with some specialities being harder to get into than others