Bunnies teeth are naturally designed to grind across the tops of one another to wear down. If they only grind across part of the top of the tooth, then the part that isn't being grinded carries on growing, forming a small spike, or spur.
Foods like hay, grass and leafy herbs and vegetables encourage a rabbits natural side to side jaw action which helps teeth to grind down.
Pellets and a lot of commercial treats cause a rabbit to "chew" and move their jaws in a more up and down motion which doesn't grind the teeth.
Some hays - timothy in particular have an added coarseness which helps to "file/rub" the teeth down.
Spurs should be monitored (usually checked at vaccinations), as if small spikes develop, they can cause ulcers and soreness to the tongue and cheeks. This is when you hear of rabbits having to have regular dental treatment to burr/file down these spikes.
I have a "dental bun". His teeth aren't properly aligned so don't naturally wear down as they should. Some dental problems are hereditary, some are caused by trauma, some are due to the breed. Lops are prone to dental problems as they have a "squished face" and therefore the jaw doesn't always line up as it should.
Hope this helps! :wave: