If amoxocilin didn't work for a tooth infection, can metronidazole work?

NOT always.: Metronidazole works better for anaerobic infections than amoxicillin. My first choice for dental infections is Amoxicillin unless the infection is "periodontal" in nature. Then i add flagyl/Metronidazole to my Amoxicillin rx.

ABX: Different abx can work better with different strains of bacteria. But if you have a "tooth infection" then you need that treated no matter what abx you are on. Root canal, periodontal treatment my be needed to remove the source, the abx is only a patch until you have it treated. See your dentist.

Underlying cause ...: If your "tooth infection" is more of an abscess, or is much more extensive an aggressive that what was expected, neither Amoxicillin nor Metronidazole will be effective- there is only so much antibiotics can control an infection- what is likely needed is a debridement or incision & drainage or extraction of the infected tissue in the infected site.