The most common way this happens is if the ring collided with something hard, and at an angle. Whatever the cause may have been, the first order of business would be to replace the prong head.
Why Replacing a Prong Head is Better than Re-Tipping
If your diamond-studded ring is old, or even old enough, then that single faulty prong you discovered might not be the only one with an issue. There could be another worn down prong as well, and it is much simpler and safer to just replace the heads altogether. That means you would not be leaving any weak prongs to break shortly afterward.
Think of it like changing the tires on your car after a long while and plenty of rough driving – normally, you would not just patch up the most problematic one, but get all of them replaced if you could afford it at the time. Replacing the prong head is similar in that it gives lasting results and better safety.