Silithium

Silithium is a material found in comets.

In 2371, a comet in the Gamma Quadrant containing silithium was drawn towards the Bajoran wormhole. Benjamin Sisko and Kira Nerys stopped the silithium comet from collapsing the wormhole by shielding the comet with the shields of a shuttlepod. Some silithium leaked out, allowing communications through the wormhole. 

Silithium infusions were later used in certain circumstances to send messages through the wormhole. 

In 2376, the USS Defiant (NX-74205) (II) used silithium to send a message to Deep Space 9 through the wormhole from a new wormhole relay station.