It's natural for people to want to learn, period. We're curious primates and nothing about our evolution says that we should discriminate about what we learn. We have only been conditioned to believe that one subject is interesting and another is not. This is reversible. I used to think studying history and philosophy were pointless. After reading Nietzsche, I still think history and philosophy is pointless.
Unceasingly ask yourself "why?" and "how?" for everything and you'll gradually grow a broad interest. If you ask yourself a "how?" question for any Biology question, you end up answering and asking with another Biochemistry question, then a Chemistry answer, then a Physics question, then a Quantum Physics question, then a Math question, and then a Philosophical question. Ultimately, you'll arrive at an existential question and get all depressed and confused.
You could have any other reasonable occupation (like a social worker) and still be able to "help" other people. You could be a CFO helping a narrow group of people get money and still manage to help humanity in general on your free time. With medicine and dentistry, it is a necessity to draw on basic science and clinical knowledge to do the helping. Doing well in basic science and medicine is about having a certain mindset; it isn't necessarily measured by arbitrary grades. You have to think like a scientist in order to be a good clinician who can make differential diagnosis, treatment plans, and in the case of dentistry, also have the manual dexterity. You have to ask yourself what is the problem, what is the given data, what methods are available, and narrow down the options to the best solution. It's all reasoning and logic sprinkled with a few moments when creative solutions are needed.
Many people have a fantasy where they'll be showered with thanks from grateful patients when they become a physician or dentist and this leads themselves to believe that the act of helping, by itself, is an appropriate motivation to becoming a physician or any other profession. But it isn't the act of helping that attracts them because there many other jobs that serve to help others but receive no thanks. Rather it's their ego of being perceived as a "good" person and the external validation of others via thanksgiving that they are attracted to. As a physician or dentist, this gets old quick and you'll need another form of motivation for you to be happy as a physician or dentist. It must be the actual job that motivates you. Ideal and happy physicians love the practice of medicine which draws on the content of all basic sciences. If you aren't the least bit interested in these core sciences, how could you seriously be infatuated with practice of medicine or dentistry? With dentistry the same is true except that you have to add in the fact that you must love working with your hands, doing tangible things, and seeing quick results.
