I have two toenails which grow a bit sideways (#3 and #4 above) and can cut adjacent toes sometimes. I don't cut them super short to avoid ingrown problems arising.
Step 1: Materials:
1. Friendly Plastic
2. Microwave oven or stove top
I came up with a simple solution: Friendly Plastic.
Friendly Plastic is a thermoplastic, similar to hot-glue, but it is smooth when cooled, as well as much stronger.
I take a small amount, heat it directly in a microwave (around 20 seconds) and encase the tip/edge of the toenail with a small amount, this dulls the sharp edge of the nail and toe cutting/scratching stops.
Friendly Plastic can be softened in hot water, but wet, it does not stick to the nail as well.
If the 'cap' should fall off, it can be easily glued back on with a bit of white glue, slotting the nail into the cap.
Hope this helps someone!