During a visit to the dentist today I noticed all the equipment that are now common place since my childhood visits. As Laurie54’s MonoMonday challenge is 20th century inventions I thought a rechargeable electric toothbrush might be suitable.   
The first usable electric toothbrush was introduced in 1954 but it was considered dangerous because it was charged on the bathroom wall in the proximity to water.  In 1961 a cordless rechargeable electric toothbrush became available.  The batteries in the brush could be charged by placing the brush on a base unit attached to an electricity supply and then they were able to be used many times before the batteries needed recharging.  Now technology, and especially battery technology, has made modern electric toothbrushes smaller, more powerful and more effective at cleaning teeth than the normal manual toothbrush