This disclosure relates to toothbrushes and to methods of operating toothbrushes. In some embodiments, a method of operating a toothbrush includes measuring an actual cleaning time of a first teeth cleaning process, comparing the actual cleaning time of the first teeth cleaning process to a standard cleaning time, and determining a target cleaning time of a second, subsequent teeth cleaning process. In certain embodiments, the target cleaning time of the second teeth cleaning process is the standard cleaning time plus additional time when the actual cleaning time of the first cleaning process is less than the standard cleaning time.