Learn French: Tu as fait empirer le problème pour avoir évité le dentiste. - You made the problem worsen for having avoided the dentist.

Pour followed by a simple infinitive usually means in order to (like pour éviter, meaning in order to avoid). When you use pour with the past infinitive (avoir or être + past participle), it expresses the cause of an action that has already been completed. Here, it means for having avoided or because you avoided.

Why is it fait empirer and not just as empiré?

The verb empirer usually means to get worse on its own. To express that you caused something else to get worse, you use the causative construction: faire + infinitive. Therefore, tu as fait empirer translates to you made [it] worsen.

Why does le problème come after both verbs, rather than saying tu as fait le problème empirer?

In the French causative structure (faire + infinitive), the two verbs act as a single block and cannot be separated by the direct object. The noun receiving the action must follow the infinitive, unlike in English where the object sits between the two verbs.

Can I use parce que tu as évité instead of the pour avoir structure?

Yes, parce que tu as évité le dentiste is grammatically correct and means the same thing. The pour + past infinitive structure is a more elegant and concise alternative that you can use whenever the subject of both actions (the person making it worse and the person avoiding the dentist) is exactly the same.