Hey, look you gotta start doubting yourself. Only reason you aren't good enough for dentistry is because you believe you are not. If it's something you want to do, you're willing to put in the work and effort and you believe in yourself than who's to say you're not smart enough? Start changing your thoughts and the way you carry yourself. Every time a negative thought comes into your mind such as "I'm not smart enough", change it to " I am smart enough". Ignore those who make you feel like you can't do something, negative people do you no good. Keep trying with the work experience, out of all the places you contact it takes only one to say yes. Best of luck to you