[TYPO3-mvc] How to remove 1:n from persistence

[Heiko Kromm | Paints]

Hi, 

I have a model which has an 1:n attribute. 
If I remove one item of the attribute with: 
$myModel->removeMyAttribute($attributeToRemove); 
The item is removed from myModel, but stays in persistence. 
I have to update a lot of the relation attributes, and therefore I there are a lot of unused elements in my database. 

How do I get rid of the elements in my database? 

Thanks 
Heiko