I high fire all my porcelain jewellery at 1285 degrees in an electric kiln in my home studio in Castlemaine.
Porcelain and ceramics are very tough, vitrifying during the firing process, but they can still be broken and damaged by dropping, a sharp knock, and contact by force or pressure against other solid surfaces, ie metal, tiles, glass, steel door handles and stone benches etc.
This means the rings and bangles need to be worn with care, and not while you are actively working or doing activities that may mean the ring will come into contact with other solid objects.
Think of your coffee/tea mugs - they are robust, and great for every day use, but if dropped or knocked against the tap while washing they can chip/ crack/ break.
The best way to fix your jewellery/ ceramic piece if it has been broken, is to use Areldite, a two part epoxy glue. You can buy it at hardware stores. Mix the two parts together well, taking care to use even amounts of both parts, and sparingly apply to the broken edges. Hold the piece together until it is firmly stuck (around 5 mins. If the ceramics has more than one part to glue back, consider gluing and letting it set one piece at a time. Let the glue set for 24 hours, and you will then be able to get more wear out of your piece.