A dematerialisation circuit was an essential part of a Type 40 TARDIS which enabled it to dematerialise from normal space into the Time Vortex and rematerialise back from it. (DW: Terror of the Autons) During his exile on Earth, the Time Lords removed the dematerialisation codes from The Doctor's mind and made the dematerialisation circuit of his TARDIS inactive. He coveted the working dematerialisation circuit of the Master's TARDIS, which ultimately proved incompatible with his own ship. (DW: Terror of the Autons, The Mind of Evil, EDA: The Eight Doctors)
Once the Time Lords had rescinded his exile after his defeat of the renegade Time Lord Omega, they restored the Doctor's knowledge of the dematerialisation codes. (DW: The Three Doctors)
Dalek time travel devices contained mini-dematerialisation circuits. (DW: Day of the Daleks)