Hello,
Most cysts associated with teeth are not dangerous, but they should not be ignored. Many of these cysts develop due to long-standing infection at the root of a tooth and may not cause pain initially, which is why they often go unnoticed.
Based on the X-ray, this appears to be a periapical cyst or chronic infection related to the tooth. Even in the absence of pain, the infection can slowly increase in size and may affect the surrounding bone if left untreated.
Treatment usually involves root canal treatment of the affected tooth, after which the lesion often reduces in size on its own. In some cases, additional minor surgical intervention may be required depending on the size and healing response.
Next Steps
It is advisable not to delay treatment just because there is no pain at present, as postponing can lead to complications later. An in-person evaluation with a dentist will help plan the most appropriate treatment.