Bone loss around an implant: how much is normal, and when is it disease?

After an implant is placed in the bone, the bone around it goes through a period of healing and adaptation. The socket prepared during surgery, the gum making room for itself at the top of the implant and the fitting of the prosthesis can lead to a small amount of remodelling at the bone margin. That is why the definitions paper prepared for the 2017 World Workshop defines a healthy implant as one with 'no additional bone loss after initial healing'. In other words, the criterion is not zero change but a bone level that has stopped moving after healing.

The consensus report of the same workshop adds one more important detail: an implant with reduced bone support can also be healthy. For example, if the bone has stayed lower after an inflammation treated in the past but has been stable for years, this is not disease in itself. What decides it is not where the bone is, but whether it is progressing and whether there is inflammation around it.

On the disease side there are two pictures. Peri-implant mucositis is inflammation that affects only the gum: there is redness, swelling and bleeding on probing, but no additional bone loss after initial healing. Peri-implantitis, in the definition of the consensus report, is a disease associated with bacterial plaque that involves inflammation in the tissue around the implant followed by progressive bone loss. Its findings are bleeding or pus on probing, deepening pockets or recession of the gum margin, and bone loss on the X-ray.

That is why a single X-ray cannot make the distinction. The definitions paper defines peri-implantitis by increasing pocket depth compared with the values recorded after the prosthesis was fitted and by bone loss seen on the X-ray after initial healing. The consensus report also recommends that clinicians take a baseline X-ray and pocket measurement when the prosthesis is completed. If there is no old X-ray, the workshop gives a threshold: together with bleeding on probing, a bone level 3 mm or more lower on the X-ray and a pocket depth of 6 mm or more indicate peri-implantitis.

The pace in the early period gives a clue too. In a study that followed 508 implants in the back of the upper jaw, 96% of the implants that lost more than 2 mm of bone at month 18 had lost 0.44 mm or more at the measurement 6 months after the prosthesis was fitted. The same group's later study of 590 implants proposed loss of more than 0.5 mm 6 months after the prosthesis was fitted as a threshold that should be monitored. These are observational studies from a single research group and not a universal limit; but they show why the X-rays from the first year should be kept.

Peri-implantitis can start earlier than people think. In the study in Sweden that examined 588 randomly selected patients who had received implants 9 years earlier, 45% of the patients had bone loss of more than 0.5 mm together with bleeding or pus, and 14.5% had moderate or severe peri-implantitis with loss of more than 2 mm. In the progression analysis carried out on the same data, by year 3 loss exceeding 0.5 mm had started in 66% of the affected implants, and the loss was progressing not in a straight line but at an increasing pace.

The strongest known causes of bone loss lie with the patient and with care. The peri-implantitis review of the 2017 workshop lists having had gum disease (periodontitis) in the past, inadequate plaque cleaning and not attending regular maintenance after implants as risk factors with strong evidence. For bonding cement left under the gum, the absence of firm gum around the implant and an implant position that makes cleaning difficult, the evidence is limited. While the same review does not find the data on smoking and diabetes conclusive, the European Federation of Periodontology (EFP) lists smoking among the main risk factors.

Bone loss that progresses without any sign of inflammation, on the other hand, is rare. The same review writes that progressive bone loss around an implant is seldom seen when there are no findings of inflammation in the soft tissue. Mechanical causes such as an unbalanced bite or overloading are discussed in clinical practice, but the evidence that these cause bone loss on their own is limited. What it means in practice is this: when progressive loss is seen on the X-ray, inflammation is looked for first.

The first list points more to a bone level that is consistent with the healing period or has remained stable; discuss these with your dentist at your routine check-up. If an item on the second list applies to you, inflammation or progressive loss should be considered and you should not wait for an appointment. The definite distinction is made by examination and X-ray.

The order matters: first an emergency is ruled out, then inflammation is looked for, and last of all the cause and extent of the loss are established.

1. 1

   Emergency signs are asked about

   If there is difficulty breathing, speaking or swallowing, major swelling in the mouth, inability to open the mouth or swelling in the eye, the assessment is carried out in A&E; call 112. If none of these is present, the next steps are carried out in the dental practice.

2. 2

   The gum is examined and the pocket is measured

   With a fine probe, the pocket depth around the implant is measured and it is checked whether there is bleeding or pus. The definitions paper counts increasing pocket depth compared with the measurement after the prosthesis was fitted as one of the criteria for peri-implantitis.

3. 3

   An X-ray is taken and compared with the old one

   A single film shows where the bone is; the comparison shows whether it is progressing. If you have your films from the day of the prosthesis and from later years, take them with you; if they were taken at another clinic, ask for a digital copy.

4. 4

   If there is no old film, the workshop threshold is used

   Together with bleeding, a bone level 3 mm or more lower on the X-ray and a pocket depth of 6 mm or more indicate peri-implantitis even without an old record. Findings below this threshold are assessed with follow-up and a new measurement.

5. 5

   The causes are investigated

   A bridge shape that cannot be cleaned, cement residue left under the gum, a loosened screw, the position of the implant, smoking and past gum disease are asked about and looked at. Treatment carried out without removing the cause does not last.

6. 6

   Treatment is planned in stages

   In the order the EFP describes: first non-surgical professional cleaning and a chlorhexidine mouthwash or gel; reassessment is usually 6 weeks later. If needed, antibiotics, then surgery: a bone graft, correction of bone irregularities or polishing of the exposed surface of the implant.

The options are not rivals to one another; they are usually applied in sequence. Which one suits you is determined by the degree, shape and cause of the loss.

What makes this picture difficult is its silence. The following are decisions made with good intentions that nevertheless use up bone.

Bone that has been lost does not come back by itself. The realistic aim of treatment is to stop the progression and preserve the remaining bone; the measure of success is the level remaining stable on later X-rays.

1. The first assessment

   Examination, pocket measurement and X-ray comparison establish whether the loss belongs to the healing period or to inflammation. If there is inflammation, treatment starts at this stage.

2. Non-surgical treatment and reassessment

   According to the EFP, reassessment is usually carried out 6 weeks later: it is checked whether the bleeding has stopped and whether the pockets have become shallower.

3. Surgery if needed

   It is planned after the inflammation has been brought under control. After healing, the gum level may recede a little and more of the implant may become visible; discuss this from the outset.

4. Long-term follow-up

   With an implant that has experienced bone loss once, the check-up intervals become shorter. The EFP recommends an X-ray once a year; comparing each film with the previous one is the only measure that shows whether treatment has worked.

We do not give a single figure, because the same finding can be settled with one check-up appointment or can extend to the implant being redone. The items that determine the extent:

The stage at which it is caught

A picture affecting only the gum can be settled with non-surgical treatment. A picture that has progressed to the bone calls for surgery, extra sessions and long follow-up.

How many implants are affected

A single area and loss that has spread across the mouth are not the same job. If the cause is shared, the treatment covers the whole mouth too.

Whether the prosthesis will change

If its source is a bridge shape that cannot be cleaned, remaking the prosthesis becomes the large item of the cost.

Whether the implant can be saved

If removal is needed, the process continues with healing, reassessment and a new implant; a far more extensive scenario than acting early.