Hi..an x ray is required to give diagnosis. It might either require extraction or root canal treatment. Regards

Visit your dentist after he takes an x Ray would decide as to weather it would require a root canal or extraction depending on severity of the problem

Hello Your cavity issue needs to be sorted out first. Visit a dental practitioner for an appropriate treatment of the problem. Ignoring the issue may result in an irreversible damage to the tooth requiring extraction. To prevent cavities brush regularly twice daily preferably after meals and use a good mouthwash. Also Decrease your sweet food and drinks consumption frequency and get scaling (cleaning) procedure every 6 months. For more elaborate information consult a dentist at the earliest.