Electric tooth bushes appear to be slightly better than manual, but you can make up for it with good manual technique and taking long enough. Flossing is a pain in the neck and I can only imagine the most diligent of people doing this every day or so. Even my dentist admitted he struggles to do it. Mind you he did then try to sell me a fancy water jet machine as an alternative. So keeping your teeth good is important, you need them for a long while, but I think you could get away with a manual tooth bush, twice daily thorough brushing and occasional flossing