Current D1 here
short answer: it depends, your learning curve or how fast you adapt will depend on where you went to undergrad and what dental school you are attending.
assuming you are coming from a challenging curriculum in undergrad or have been to a dental hygiene/ masters program, you should be able to adapt fairly quickly. The pace of dental school curriculum is absolutely exhausting, time is your biggest enemy, and that's no exaggeration. To be frank, it will probably take you a good three exams(about a month) to understand your best way to manage time and study and from what I hear, it gets dramatically harder so you have to continue to adapt. The material itself is not necessarily harder than undergrad but it comes in unbelievably huge bulks.
now, If you come from a less challenging undergrad (usually if your school was not competitive among its own students, internally and/or did not rank within the higher ranks nationally, this would apply to you) then it really depends on the dental school you attend. Some as you can see have test banks, some DO NOT. If your school doesn't have test banks, it will take you about two months to adapt. It's absolutely key to realize that you can always make more time. It seems impossible but you have to sacrifice certain things to gain this time. If you are feeling comfortable and find yourself having free time, there's something wrong because settling in and having free time are not options in dental school. My best advice, ALWAYS stay ahead of the lectures. There will be very few opportunities to do this, but you'll know when they show up, take advantage, instead of getting comfortable get ahead.