-they will whiten
The word blanquearán is the future form of blanquear in the third person plural.
See the full blanquear conjugation


Si no hay suficiente cantidad presente del agente, entonces que los dientes no se blanquearan. Si se usa demasiado peróxido de carbamida pueden en realidad dañar el esmalte de los dientes.
If there is not enough of the agent present then the teeth will not whiten. If there is too much Carbamide Peroxide used it can actually harm the enamel on the teeth.
Want to Learn Spanish?
Spanish learning for everyone. For free.
SpanishDict Premium
Have you tried it yet? Here's what's included:
Cheat sheets
No ads
Learn offline on iOS
Fun phrasebooks
Learn Spanish faster
Support SpanishDict