Final answer:
Dental floss is the least effective for controlling plaque in class II molar furcations due to its design that does not reach deep into these areas as well as interdental brushes or other specific cleaning tools.
Step-by-step explanation:
When considering the effectiveness of dental hygiene products for controlling plaque in class II molar furcations, dental floss would be the least effective option. This is because floss is designed to clean the tight spaces between teeth but may not adequately reach into the deeper furcations of molar teeth.
Interdental brushes, on the other hand, are specifically designed to clean larger spaces such as furcations and can therefore be more effective. Mouthwash can help reduce plaque and gingivitis overall, but may not reach deep into class II furcations as effectively as mechanical cleaning tools.
Toothpaste containing fluoride offers protection against enamel destruction due to acidic conditions in the mouth and has bacteriostatic properties, but it is the action of brushing that primarily helps to remove plaque in furcated areas.