Jonathan Waasdorp, DMD, MS

Following removal of a tooth, some of the bone supporting the tooth in place resorbs and the bone volume decreases.  This is most dramatic in extraction sites where the bone is thin (especially front of mouth in upper jaw).  Bone grafts are placed to minimize the bone resorption and ensure there is adequate bone for implant placement.  In molar sites, although grafts are commonly placed, the sockets are so wide and bone thicker that the normal healing process/resorption doesnt affect positioning of the implant.  Additionally, I typically find the bone fill from a natural clot to be more dense at 3 months than grafted bone that the body is often still remodeling.  So your surgeon may have removed the tooth atraumatically (gently) and made a judgement call that your bone was thick and a clot based healing would be sufficient and provide nice dense bone at 3 months without foreign materials needed. 

The bridge could feel loose for a variety of reasons.  One could be it wasn't fully seated during cementation and the bridge itself is actually loose. It could also be your dentist cemented it temporarily to evaluate esthetics and the temporary cement amount was inadequate and it's too weak of a bond. The bite. The bite being too high can also cause the teeth to move, although this would usually take more time.  If the teeth were loose in temporaries because they were high then this could also be a cause. The darkness at the gum line is most likely from the metal framework of the bridge or tissue inflammation from the cementing process . You should see your dentist to evaluate   

Often times when grafting is done some of the bone particles (especially if the site was "overfilled") work their way through the incision or can be visible through thin tissue.  This is a normal part of the healing process and is most likely what is occurring. However you should follow up with your dentist as soon as possible so this can be confirmed clinically. 

Yes an implant can almost always be used. If the recession is significant bone and tissue regeneration may need to be performed in conjunction with the implant, especially if this is in an esthetically demanding area.  if the recession is only located on the side of the tooth facing your cheek, this is a straightforward procedure.  

Occasionally dental implants fail to fuse with bone during the healing period (early failure) and need to be removed.  Although it happens infrequently, it's very frustrating for all parties involved.  If there is infection present, the site is often cleaned and allowed to heal for 3-6 months before attempting another placement (bone may be placed too).  If it just didn't "take" and there is just a layer of soft tissue around the implant, a larger implant can be placed the same day as long as there is enough bone present.  Although many studies suggest a lower success rate when failed implants are replaced, I typically find them very successful in many instances.   In regards to what you can do to aid the situation, it may have been a factor out of your control (perhaps the adjacent tooth has infection or the prior tooth was infected and not properly cleaned out).   Otherwise, the risk factors for implant failure include things such as smoking, periodontal disease, uncontrolled diabetes, and even antidepressant use.  Excess calcium and Vitamin D probably will not aid the situation, although having a deficiency in these would not help.  Best of luck with your care.