Final answer:
The most commonly used permanent cement for a stainless steel crown on a primary tooth is glass ionomer cement, known for its strength and nonirritating qualities.
Step-by-step explanation:
The permanent cement most commonly selected for cementing a stainless steel crown on a primary tooth is glass ionomer cement. This type of cement is favored due to its good overall strength, nonirritating quality to the pulp, and its ability to release fluoride, which helps prevent further decay. Glass ionomer cement bonds chemically to both the tooth structure and the stainless steel crown, which contributes to its retention and durability.