Hiya, I've done biomed transfer to medicine this year (starting med this sept) so hopefully can help a bit. Definitely agree with Salamander's comment about transfer being very competitive - about 80 for med, 20 for dent showed interest in the transfer lecture but there were only up to 7 places available for med and 2 for dentistry and I know in 2020 they only filled 1 of the dent places.
For me I needed over 75% across my modules and over 65% in every individual module. There's also interview and ucat, as is the case with standard entry. I'm aware the dentistry transfer scheme is very similar to the med one I did, but they made my friend who got dent offer do another ucat in the summer before starting, whereas for med I could use my previous year score. You need to be mentally prepared to do three years of biomed if you're not successful in the transfer so make sure you're confident in your decision - but I wish you the best and if you succeed it makes getting in feel even sweeter!