Spitting toothpaste

My 4 year old still refuses to spit his toothpaste. I've tried every suggestion from the dentist and the dentist seemed frustrated with me saying me needs to spit it out now at his age. I understand he should be but the moment I pull the toothbrush out he swallows it all I've tried making it a game I've tried literally everything. Any advice on how to make him spit the toothpaste out ? I'm starting to worry since the dentist seemed annoyed by it.