It seems the "lack of patients" rumor will never die. Ask any 3rd or 4th year and you'll almost certainly find they have an adequate if not oppressive number of patients to care for. Regardless, you will quickly learn when you enter clinic that it's not the number of patients that is important, but rather the treatments each one requires. We have a lot of very complex cases. Frankly, many of them probably should be treated by grad pros, but they are overloaded as it is. Common sense should convince you: Los Angeles is one of the biggest cities in the US, only has 2 dental schools, and UCLA's fees are less than half that of a private practice. It would be impossible to have a shortage of patients.
Yes you will be stressed if you come to UCLA. More stressed than any other dental school? Maybe. No way of knowing.
As for negatives: There are a few people I don't like talking to in the administration. Classes seem excessive and irrelevant at times. Tuition went up a lot since I was a 1st year. Now it's around $25K a year.