As the number of patients receiving endosseous intra-oral implants worldwide continues to increase, implant longevity assumes ever greater importance as a public health issue. With progressive bone loss a significant contributory factor in potential infection and ultimate implant failure, the working group's brief was to produce a totally objective, overall assessment of marginal bone management options.
The group's members, each selected for their expertise in a specific area, reviewed the literature on marginal bone from the perspective of their own fields of study, which included investigational methodology, oral and maxillofacial surgery, periodontology, immunology, biomaterials, oral physiopathology, oral rehabilitation and microbiology.
An exchange of review papers was followed by a two day group meeting at the Karolinska Institut in Stockholm, hosted by group member Björn Klinge, and the amended reviews were published as a supplement to the European Journal of Oral Implantology. A public discussion was later held at the Europerio 7 meetings in Vienna this June. The potential causes of marginal bone loss were found to divide temporally, between those which occurred soon after implantation and those resulting from other, discrete provocative factors which occurred later, sometimes much later.
The most well known cause of marginal bone resorption is immediate post-surgery trauma, due to overheating or neighbouring bone compression, and as Per-Ingvar Brånemark discovered in his early studies of osseointegration, it is important to treat bone as living tissue.
Although other causes of relatively rapid resorption are less well documented, their effects are widely recognised. For example, when implants are placed in a jawbone with only limited bone volume, dehiscences often result, which leads to proximal bone resorption; the accidental presence of subgingival cement remnants can also result in significant bone resorption, as well as the too-deep placement of the implant.
Bone loss which occurs several weeks or months after installation may be due to occlusal overload or occlusal adjustments, and so other biomechanical interventions may be required to stabilise the bone.
It should also be noted that attempting to meet a patient's aesthetic aspirations sometimes leads to repeated removal of the abutment, and these multiple disruptions of the connective tissue seal can result in bone loss. Although corrosion at the implant/abutment interface is scarcely documented, it too is a suspected cause of later bone resorption.
Whilst the careful observance by the patient of a strict oral hygiene regime would appear to be a self-evident priority following implant surgery, regrettably this is not always the case. The presence on the implant surfaces of bacterial biofilms predisposes chronic inflammation of the marginal tissues which leads to subsequent bone loss. In such cases introducing an effective daily oral hygiene regimen is the obvious response.
Having identified that there are local, systemic and pathological factors involved in the aetiology of marginal bone loss, the working group concluded that a comprehensive, multidisciplinary treatment plan requiring sanitation of the entire oropharyngeal cavity should be implemented as a preventive measure prior to surgery, with special attention paid to smoking.
The emphasis on maintaining and monitoring oral hygiene should be continued in the long term, especially in patients known to be susceptible to periodontal inflammation.
Most modern surfaces in implants are medium rough, but there is insufficient data to show that they promote peri-implantitis. The single recorded laboratory-based study of experimental peri-implantitis in dogs involved a sample too small to enable valid conclusions.
A significant hindrance in the collating of data in this area is the lack of agreement, or common baselines, on the methodology of recording pathologic marginal bone loss, with the choice of 2 or 3mm showing a dramatic statistical difference. There is also no consensus on differentiating bone loss occurring soon after implantation from that which occurs later.
The group recommends future researchers use radiographs taken at least three months after implant placement as the baseline for the study of marginal bone loss compared with bone levels at the time of installation, or comparisons will remain unfeasible.
Current commercial implant systems show overall instances of peri-implantitis of between five and 20 per cent, while for some individual implants it is below five per cent even after 10 years. It is important to note that smoking, hugely impacts the rate at which peri-implantitis occurs. In a recent study, peri-implantitis among smokers with a history of periodontitis was more than 50 per cent compared with less than three per cent for non-smoking patients, with no peri-implant disease being diagnosed in non-smoking patients who had no periodontal history and demonstrated good hygiene compliance after treatment.
Marginal bone loss can lead to the deepening and subsequent infection of periodontal pockets, further stressing the clinical imperative of taking the appropriate action in respect of its aetiology.
In the opinion of the working group open-flap surgery should be encouraged for the decontamination of the implant surface in the treatment of peri-implantitis. The group found all the documented decontamination protocols (rinsing with saline, mechanical debridement and Er:YAG laser therapy) appeared to be equally effective. Whilst there is some evidence that subgingival, slow-release devices with antimicrobials of the tetracycline group used as an adjunct to mechanical debridement may arrest peri-implantitis, there is no conclusive proof of the benefit of systemic antibiotic therapy.
It should be noted that whichever treatment is chosen, the majority of peri-implantitis lesions will remain unresolved.
Looking to the future, the group has published clinical guidelines, scientifically based on its comprehensive review of the presently available research. Undoubtedly best practice in patient care must always include both preventive measures and the insistence on good maintenance. Without doubt there is a pressing need for further work to identify the incidence and relative importance of the different causes of marginal bone loss and how best to minimise their effects.