Tannkremen smaker mint når hun pusser med tannbørsten.

The -en suffix is the definite article in Norwegian for common-gender (masculine/feminine) nouns.
• tannkrem = “toothpaste” (indefinite)
• tannkremen = “the toothpaste” (definite)

In Norwegian the verb å smake (to taste) can take its object directly. You say “smaker noe” (tastes something) without av.
• Correct: Tannkremen smaker mint (“The toothpaste tastes mint.”)
• You could also say smaker av mint, but it’s less common and more formal.

• når is used for general, habitual or future time clauses (“whenever,” “when someone does something regularly”).
• da is used for a specific past event (“when she did X that one time”).

Since this sentence describes what generally happens whenever she brushes, we use når.

In Norwegian subordinate clauses introduced by a conjunction (here når):

1. Conjunction (når)
2. Subject (hun)
3. Verb (pusser)
4. Remaining elements (med tannbørsten)

This differs from English, which often puts the verb after the subject but doesn’t always rigidly follow V2 or V3 rules.

med means “with” and indicates the instrument used:
• pusse med tannbørsten = “brush with the toothbrush.”

In Norwegian you normally use med + [instrument] to show what tool you’re using.

The definite form tannbørsten (“the toothbrush”) plus context makes it clear it’s her own. Norwegians often drop sin/hennes when it’s obvious:
• hun pusser seg med tannbørsten implicitly means her toothbrush.

If you want to be explicit, you could say sin tannbørste.

• tannkrem is a common-gender noun (sometimes called masculine).
• Indefinite singular: en tannkrem (rare in practice – you often just say tannkrem)
• Definite singular: tannkremen (adds -en)
• Indefinite plural: tannkremer
• Definite plural: tannkremene