I'm worried about my teen's porn habit

By the age of 15 more than 50 per cent of teenagers have looked at porn. For teenage boys, this can quickly become a habit. Research points to a link between porn use and sexual violence, with young men the most likely offenders.  

So how can we help our teens understand that curiosity around sex is normal but the violence and degradation depicted in porn is not? And how can we help set them up to have healthy, respectful relationships?