Dentistry and Medicine are two completely different careers. They are both very hard to get into, and both require serious commitment.
If you have it in your mind to apply to both (which you cannot do on UCAS) then this is usually a red flag since the professions are completely different and suggests that there are reasons other than genuine passion and interest for applying - for example, family pressures, perceptions about status or money, etc. Have you done any work experience in Dentistry? Universities require a minimum of 2 weeks of shadowing a dentist.
People that apply to Dentistry or Medicine have been preparing for a long time, it has been their dream and they have done plenty of work experience, volunteering, reading around the subject, spoken to people in the field, gotten advice from school, etc.
Dental schools ask for AAA-A*AA and even applicants with those grades get rejected because the universities look at their UCAS personal statement, evidence of volunteering and passion, work experience in various sectors of dentistry, resits, MMI interview performance, manual dexterity skills and UCAT (UKCAT) grade.
Your GCSE grades are very low, and it is a common mistake for students to assume they can go from low GCSE grades to high A-Level grades; I have seen it happen a lot where students are unrealistic about their abilities and end up getting even lower A-Level grades.
Good luck