I had a chest X-ray to rule out pneumonia, a 6mm "nodular type density" seen in the upper left pole, could this be scar tissue?

The radiologist does know what silicone looks like on X-ray, and can tell if the density is in your chest or breast. More testing can clarify what and where it is. If it is in your lung, it is not related to your implants.

Most of the time, when you have a chest x-ray for a condition like pneumonia, more than one x-ray view is obtained.  This would allow the radiologists to determine that the "nodular density" is in your lung and not your chest.  It is unlikely that the density is related to your implants, but discuss this with your plastic surgeon and good luck

I can't tell whether the x-ray showed a density in the lung or the breast. If a silicone gel implant ruptures and any gel gets out beyond the capsule into the breast tissue it can cause a reactive nodule. This shows up as an obvious opaque density on mammograms. If this is a breast density, a mammogram and ultrasound should give you enough information to decide if a biopsy may be necessary. If this nodule is in the lung it is a different story altogether.