Actress Lindsay Lohan shocked onlookers with stained and decaying teeth, when she posed on the red carpet at the premiere of THQ's Saints Row: The Third, in Los Angeles on Thursday night.

Lohan's teeth became the talk of the evening for many guests at the party and people could not help but speculate as to what must have gone wrong for the 25-year-old's teeth to have become so brown, chipped and rotten.

Now, what exactly caused the star's teeth to look so unacceptable?

Well, a top dentist from New York City's Arch Dental Associates', Pankaj Singh, could have the answer. He suggests that in addition to neglect, drug use could also be a contributing factor.

This type of damage appears to be from a combination of smoking, drug use and a lack of personal care. Smoking causes yellowing of the teeth, which we definitely see here in this picture. However, at such a young age, smoking wouldn't cause the decay and browning you see around the gums. Damage like that is something we see in patients who are using or have used drugs, Dr. Singh was reported as saying, to Gather News.

The actress, who started her career as a child fashion model, is still a beautiful actress, insisted her spokesperson, who refused to offer an explanation for her poor dental health, reported the Daily Mail.

She's been on the cover of Vanity Fair and the top beauty and fashion magazines. She's a beautiful and glamorous actress, Lindsay's representative, Steve Honig, told People magazine.

With everything going on - from deteriorating public education to rampant homelessness to international unrest - there is no way I'm going to comment on Lindsay's teeth, added an irritated Honig.