Toothbrush for cleaning safety razor

Yeah if they had any loose plating or something it probably wouldn't be a good idea. But how many times does your silverware and other metal objects go through the dishwasher without damage? Add the fact that your not going to be cleaning your razor nearly as often as silverware. I think putting it on the top rack of the dishwasher would be perfectly safe. I do understand your concerns though. I guess for me, it would depend on the razor.

I use a toothbrush but it is not an adult's. I fear the bristles may be too coarse particularly for the old Rolls and GEM razors.
A child's toothbrush is much softer and being smaller fits more easily onto the tiny nooks and crannies.
Ordinary Irish Spring hand soap does a good cleaning job.
"Nice and easy does it every time."

A toothbrush (but not toothpaste, too abrasive in the long run), Scrubbing Bubbles are all good options. Another effective way of cleaning safety razors is an ultrasonic cleaner. https://www.youtube.com/watch?v=CqPMFy1RKNw

the only thing I'd caution for when using an ultrasonic cleaner (I have one and have used it in the past to clean some REALLY gunked up razors) is that it could cause damage to the razor's plating, especially if it's really old. I would just put it on short clean cycles and check it thoroughly after each cycle.

Soft toothbrush and Dawn soap. Even though a dishwasher MIGHT be safe, I am not risking it. JMO.