Does saliva really kill sperm?

Okay, so I have been reading up on this and it's pretty much 50/50. Some people say the acidity and the ability to break proteins down in the saliva, is what kill the sperm. Some say it's fine and it doesn't phase it. How do I really find out the truth? I read there is a story of a woman getting pregnant by oral sex and replacing the sperm to herself. Then sued him for child support?????