Manual toothbrushes are simply manipulated by the hand. In choosing an effective manual tooth brush, it is chiefly important to consider difficult-to-reach areas, such as those between teeth or on the side of teeth, along the gum line. Despite competing companies' advertisement, no toothbrush head design has been proven as the most effective. Moreover, most studies find that there is no marked change in brushing effectiveness when variable such as bristle design, brush shape or texture are tested. On the other hand, an individual's specific dental status or brushing technique may call for one design or another. The success of manual tooth brushing depends largely upon technique, so the "best" brush is one that is used correctly. One must brush in the right direction with the right motion, refrain from too much force, and brush for an appropriate amount of time (at least two minutes). Normally, it is best to choose a manual toothbrush with "soft" bristles, as categorized by the manufacturer. While it is true that toothbrushes with harsh bristles could perhaps wipe away dental plaque more readily than those with gentler bristles, stiff bristles can have an abrasive effect on soft oral tissue.