We need more information and photos please.  How old is the oak?  Are only a few branches affected?  Any changes in the surrounding area?  Has this happened before?

We need more information and photos please.  How old is the oak?  Are only a few branches affected?  Any changes in the surrounding area?  Has this happened before?

Without more information such as type of oak and a picture of the leaves and entire tree we cannot assess the problem.  There are multiple reasons for dark edges on oaks. Some are minor such as drought related; others are fatal such as oak wilt. Compare what you are seeing with the following website.  If this is a high value tree you may want an onsite assessment by a certified tree professional.  See the second website.
1. https://apps.extension.umn.edu/garden/diagnose/plant/deciduous/oak/leavesbrownedges.html

2. https://extension.umn.edu/planting-and-growing-guides/how-hire-tree-care-professional