It may have been entirely innocent, maybe it was just to relax/distract you while time was passing. But its never happened to me at the dentist and I'm sure is not part of usual practice in Australia. As a she who uses hair product, I'd be upset that my hairdo had been messed up. Totally different at the hairdresser since its when they are washing your hair.
The most I'd do is let the dentist know it happened, and you thought it a bit weird. And state whether you want it to happen again or not.