Can this tooth be saved. Number 7 had previous root canal and now abscess may have cracked root?

Only a well-trained Endodontist can answer your particular situation. In general though, a tooth that has failed Root Canal once already, and is now reinfected, should probablybe extracted and replaced ith an implant. Much more predictable.

There are a number of tests that can be done to determine the issue with the tooth including X-Ray films, peril-probing depths, 3D imaging etc. An endodontist would be a good start as they will be able to give you a diagnosis and prognosis for the tooth. One of the benefits of 3D imaging in the area you are having the abscess is that it can be used to help with diagnosis of the current situation and if the tooth does need to be extracted, the image would help as a guide for possibly placing an immediate implant. Generally the long term prognosis for a failed root canal treated tooth is not great but it depends on the situation. Some can be retreated successfully and others need to be removed. See if you can get a referral to a good endodontist in your area.

Maxillary laterals are very thin, so often simply crowning them weakens them enough that they break. Root canal them and they are MORE fragile. I assume the tooth was crowned after the root canal (as all teeth should be crowned after a root canal to prevent fracture), so the next step likely is removal and implant or bridge. If you opt for an apicoectomy, you lose precious bone that may be needed for an implant in the future.