Does Amitabh Bachchan wear a wig?

Yes, he wears a wig. If you look at his films before he took a break from acting ie. Insaniyat etc. you'll see that he had fairly waspy hair and was thinning. Equally if you take a look at Mrityudaata its fairly obvious that he started off with a poor wig. This followed in a few films until Baghban onwards when the piece looked more authentic. The giveaway is the back of the head where if you look carefully you can see where the wig meets natural hair - in line with the ears. The hairpiece in Waqt and in fact Kyun Ho gaya Naa were the most obvious. Also note carefully that he has no actual parting! You can't see any scalp in his parting at all. That's only because its a hairpiece. There aren't many people who keep a full head to that age save for the likes of Shatrughan Sinha perhaps! Even Dharmendra is sporting a weave to cover his rear bald patch.