Most dentists still recommend at least 2 minutes at a time. Some naysayers have complained that over brushing can lead to erosion of the gum line. The problem turns out to be more a problem of the pressure applied than the length of time spent brushing. Dr. Guarna recommends using the non-dominant hand.
Dr. Sesemann from WebMD recommends that you divide the mouth into four quarters, and do each for thirty seconds. He also points out that some electric toothbrushes come with an automatic timer to set you straight. Getting the proper bristles is also important. If they are too stiff they can damage the gums.
Sesemann also says “three times is best.” So it may just be your grandmother was right on the money. Since there is evidence to show that plaque on the teeth can indicate plaque in the arteries, proper oral hygiene is essential. The secret is to make sure it is a routine part of your day.