Dental implant was great for several years, 2nd molar from the back lower left, now vry painful esp. when chewing, 360 degree ray looks fine, help!

May be infection: X-Ray not always shows the problem, Clinical exam followed by CT could help to find out any infection, abscess or boneless.

Painful implant?: We can't help you over the internet. The cause needs to be determined by a competent dentist who can clinically examine you, see x-rays and do some tests. Pain on pressure is usually but not always associated with some movement due to the breakdown of integration to bone and ultimate failure of implant. If your General Dentist can't determine the cause, consider seeing a Prosthodontist.

Integration: Once bone "bonds" to a dental implant it is considered integrated. There should be no pain at all. If the integration is lost, then the implant will have to be removed. Radiographs don't always show this.. your dentist needs to try to gently "unscrew" the implant.. if it moves or hurts you, it needs to be removed immediately... it won't get better, but may actually cause bone to break down.

Peri-Implantitis: or peri-implant mucositis is a localized lesion around an osseointegrated implant. Peri-implantitis is not only frequent, but a serious complication.Pain is an unusual feature, which, if present, is usually associated with an acute infection. peri-implant mucositis can be successfully treated if detected early and when combined with effective nonsurgical efforts. See your surgeon for more info.