Admission tutors have a preference for standard qualifications, so self studying a science A level might help strength your application. This is more relevant if you have been out of education for more than three years. But it is best to contact the admission tutors, they will tell you what you need to do strengthen your academics. It is worth familiarising yourself with the UCAS application system, the personal statement is key for mature students.
Organising some work experience with a dental hygienist or dental practice, would be worth doing, the longer the better. It would help to show interest and commitment. Plus you need a reference for UCAS, one from a dental health professional could be helpful.
See if you can go to some open days and talk informally to the admissions tutors.