not all electric brushes are made equal. my dad's best friend is an oral surgeon so i know a fair bit about teef

They are definitely, without a question, much more effective at cleaning your teeth. My guess is coincidence vs. you had a poor technique when it came to using them

that doesnt seem like the cause, my teeth were really way cleaner and efficiently brushed than with a manual. with a manual you can definitely go too hard on the enamel if you are aggressive. electrics now have sensors that detect pressure. are rinsing the brush heads before and after using them? or you using it way after 3-4 months? or you using it on your gums or too much.