Dentists in certain areas are paid so handsomely that they make more money than the average doctor. Back in 1996, dentists earned less than physicians. The primary reason why dentists make so much money in the United States is because they are scarce. In fact, there are currently only around 200,000 practicing dentists in the US.
What the 50th percentile (or median salary) implies is that 50% of dentists make less than the median and 50% of dentists make more.