There is an old saying among surgeons: "If you don't have complications then you're not doing much surgery." Don't let a surgeon tell you they don't have complications. All of us do. Problems with any surgery can develop despite extensive planning, good surgical technique, and even with years of experience. Complications can occur during surgery or in the post-operative phase.
In my experience, problems during surgery are most commonly due to surprises. Despite all our fancy CT scans and testing prior to surgery, there are scenarios where the tumor is more extensive than anticipated. This can require removal of additional bone and/or teeth. After all, if we don't get all the tumor out, we're not helping you since recurrence is definite. Other problems can develop due to complexities of treatment that are not always predictable. Some patients undergoing a fibula reconstruction of the jaw require skin with the fibula to resurface missing tissue in the mouth. There are rare cases where there is not adequate blood supply to this skin which means it's not available to use. We sometimes have to get creative to figure out how to close the hole in the mouth. Sometimes this involves getting skin from another area such as the chest wall supplied the pectoralis muscle. Sometimes it involves just pulling the hole closed with sutures with the plan of additional surgery later to release the tissue.
Although the mouth is scrubbed with antiseptics prior to surgery, the mouth is never completely sterile and there is always the risk of oral bacteria contributing to an infection.
Problems in the post-operative healing phase are probably more common than problems during surgery. For non-vascularized bone grafts, there is an increased risk of infection and loss of graft despite antibiotics. Although the mouth is scrubbed with antiseptics prior to surgery, the mouth is never completely sterile and there is always the risk of oral bacteria contributing to an infection. Even with vascularized grafts (fibula), problems related to loss of blood supply to the bone can cause the fibula to die and require removal. Tumors requiring radiation therapy after surgery have a higher rate of complications. The radiation can lead to poor healing and decreased blood flow to the surgical area resulting in deterioration of the bone graft. Hyperbaric oxygen therapy can sometimes improve wound healing but it is rarely successful alone without additional surgery.
Perhaps the most feared problem is recurrence of the tumor. Although the pathologist looks at the edges of the specimen under a microscope and tells us we have clear margins and all the tumor has been removed, the nature of these tumors is that they can still return. Therefore periodic xrays are useful to watch for recurrence.