im going to assume you are starting year 13 in a couple of weeks if so this will be the timeline:
Sept 2022 - July 2023* = This is your Year 13, during which you revise and get the best grades you can. You may also want to volunteer, work experience, read books and basically anything to fill a personal statement. AND REVISE UCAT
May - June 2023** = UCAT registration opens - so sign up and book a date. Book a date early enough so if you don't do well you can re-route
August 2023 = You get your A-Level result and have smashed it.
August 2023 - Sept 2023 = Write your personal statement and start your UCAS application. Your school is able to still be your reference just ask them. You may want to start interview prep
15th October 2023 = This is the deadline for Oxbridge/Med/Dentistry applications.
15th October 2023 - June 2024 = Interview and offers.
July - September 2024 = Finally have a relaxed summer
September or October 2024 = You start dentistry
* I don't know if you still want to apply with the rest of your cohort, if so just do what your school wants you to do - then follow this timeline
** The dates for UCAT changes every year so just keep an eye out for this.