Hi.
To be clear with you, Dentistry is highly competitive, its no joke. Your GCSEs and A levels grades, any work experience and the UCAT. The UCAT is quite intense and you will absolutely the highest score possible. This isn't to scare you, but to be real. You could even line optometry up as an insurance.
Optometry is not nearly as difficult to get into, i can only speak anecdotally, but financially it can be rewarding. When its compared to dentistry, its clear if finances are your main objective or a priority, then try for dentistry.
Both courses are long time commitment. Dentistry will be 5 years uni and an additional 1-2 in foundation training. Optom will be 3 years uni and 1 year in placement.
Be very sure on your choice before you attend uni. I hope this helps and good luck.