Jede Zahnbürste sollte alle drei Monate gewechselt werden.

• jede + singular noun = “each” item individually
• alle + plural noun = “all” items as a group
Here, you’re advising to replace each toothbrush every three months, not replace all toothbrushes at once.

In German, passive voice shifts focus from the person doing the action to the action itself.
• Active: Man wechselt jede Zahnbürste alle drei Monate.
• Passive: Jede Zahnbürste sollte alle drei Monate gewechselt werden.
You don’t specify “who” changes it—only that “it should be changed.”

• muss = have to (strong obligation)
• soll = should (present recommendation)
• sollte = should (past tense form, more polite/less direct)
sollte softens the recommendation, making it sound like general advice rather than a strict rule.

A modal verb (sollte) plus a passive construction uses two infinitives. Word order in main clauses:
… sollte … gewechselt werden.
Both infinitives go to the clause‑final position in the sequence they appear in the verb phrase.

It’s the accusative of time (time span). In German you often use accusative for expressions of duration or frequency:
• alle drei Monate = “every three months”
You could also place it at the beginning: Alle drei Monate sollte jede Zahnbürste gewechselt werden.

Most German nouns have a grammatical gender you must memorize. Zahnbürste is feminine, so you use:
• Nominative singular: die Zahnbürste
• With jede, which declines like an indefinite article, you get jede Zahnbürste.

Yes. In active form you need a subject like man or wir:
• Man sollte jede Zahnbürste alle drei Monate wechseln.
Here man is an indefinite pronoun (“one/you/people in general”), and wechseln is the active verb.