Final answer:
Desincrustation is the electrotherapy treatment used for breaking down sebum and liquefying blackheads during deep-pore cleansing.
Step-by-step explanation:
The electrotherapy treatment that can cause sebum to be broken down or blackheads to be liquefied, as in deep-pore cleansing, is desincrustation. Desincrustation is an electrotherapy process that softens and emulsifies sebum and keratin in the follicle. It is typically used during facial treatments to assist with deep-pore cleansing. During this treatment, an alkaline-based solution is applied to the skin, and then a galvanic current is used to create a chemical reaction that emulsifies the sebum, making it easier to remove blackheads and other impurities.