Can fluoride mouthwash & toothpaste stop or reverse tooth decay?

If mild, yes: If the decay is just getting started (often called a white spot lesion) then yes, it may be reversible. A good product for this is mi paste plus, which contains bio-available calcium, phosphate and fluoride. If the decay is already an acutal hole then no, you need a filling to treat this, it is too late to "reverse" it.

Remineralizing: Research shows that Fluoride helps prevent cavities in children and adults by making teeth more resistant to the acid attacks that cause cavities. Fluoride helps rebuild (remineralize) weakened tooth enamel and reverse early signs of decay. When you brush your teeth with Fluoride toothpaste, or use other Fluoride dental products, you are providing a “topical” benefit.

Perhaps: There are certain toothpastes that have additives that can recalcify small tooth decay. The more effective ones need a prescription. Talk to your dentist.

Not Usually: That is like asking if a good carpenter can stop or reverse a fire. No. You will need a dentist to stop the decay process and repair the tooth. Only good proper brushing/cleaning can prevent a new tooth decay. Toothpaste helps but is not the magical miracle worker by itself.

No: The only way to prevent tooth decay is by having a good oral care, meaning proper brushing and flossing and seeing your dentist twice a year for an exam and a professional cleaning.

REVERSE TOOTH DECAY: As dr. Zinati said tooth decay is best prevented with good oral hygiene and regular dental visits with xray. There are oral products available today that "remineralize" incipiant (small decay areas) in the enamel. Renamel is one by sensodyne. Re-hardens the enamel for small cavities only. Larger cavities must be addressed by your dentist.

Yes, some: Only for small, incipient caries/decay... Always brush and floss well, and see your dentist/hygienist routinely for check ups and cleanings.