When the dwarves finished they presented Odin with Gleipnir, a chain made of six mythical intgriendients: the sound of a cat's feet, the roots of a mountain, a bear's sinews, a woman's beard, a fish's breath, and a bird's spit.
With these six ingredients the resulting chain was as smooth as ribbon, but as strong as iron would be too mortals. When it was announced that the chain was going to be put on Fenrir on the island of Lyngvi, Fenrir himself was doubting if he would be able to escape.
It was time to put the chains on Fenrir. The god of law and justice, Tyr came forward and placed his hand in Fenrir's mouth, he was the only god of the Æsir brave enough to risk himself to protect his people. Finally Fenrir allowed himself to have the chains put on. It was a sucsess due to Tyr's bravery. Every time Fenrir tried to escape he failed.
In rage of not being able to escape and the gods' strategy to contain him, Fenrir bit off Tyr's hand. the gods were pleased that Fenrir was still chained, of coarse with the exemption of Tyr, the Æsir looped the chain through a large rock named Gjöll, and put onto it a large rock called Thviti, trapping Fenrir permanently to one spot.
Fenrir extricating howls ended up with a sword being shoved in his mouth between his two jaws, the sword keeps his mouth wide, silencing him until the time of Ragnarök. Then and only then will Fenrir see freedom.