An independent multidisciplinary working group tackles the issue and calls for greater scientific enquiry into bone management
The long-term survival of endosseous intra-oral implants has become a public health issue in recent years inasmuch as tens of millions of patients now have one or more of these implants. To ensure implant survival and restorative longevity, the maintenance of marginal bone around these implants is a significant element of treatment and consequently should be the subject of conscientious scientific follow-up. Progressive bone loss may lead to insufficient anchorage, significant infections and even the loss of the implant.
To address the issue of bone maintenance in a scientific and clinically documented manner, Nobel Biocare proposed that an international group of experts be assembled and asked me to moderate the group. The brief was to thoroughly review the current state of knowledge in this area, and to propose how to proceed in the future. Thus the working group on ‘Treatment options for the maintenance of marginal bone around endosseous oral implants’ was born.
Given a free hand to select the most appropriate participants, invitations to join the working group were sent out on the basis of the invitees’ publication and citation records. As the group would ultimately be making both scientific and clinical recommendations, it was important to find authorities in a wide range of disciplines, each directly relevant to the issue of marginal bone maintenance.
Eight independent scientists and clinicians joined the working group and have made valuable contributions ever since: Marco Esposito (United Kingdom), Björn Klinge (Sweden), Joerg Meyle (Germany), Andrea Mombelli (Switzerland), Eric Rompen (Belgium), Tom Van Dyke (United States), Hom-Lay Wang (United States) and Arie-Jan van Winkelhoff (The Netherlands).
All of these renowned authorities joined the group under the proviso that they would be willing to participate on an independent, pro bono basis. For several months last year they reviewed the literature on marginal bone from the perspective of their own fields of study, which include investigational methodology, oral and maxillofacial surgery, periodontology, immunology, biomaterials, oral physiopathology, oral rehabilitation and microbiology.
After exchanging their review papers, the members of the group met for two days at the Karolinska Institute in Stockholm, where the Nobel Assembly chooses the prestigious Nobel Prize laureate in physiology or medicine each year. Björn Klinge served as host.
Nobel Biocare very generously covered the working group’s travel expenses in good faith since its inception, and done so without intervening in any way in the discussions or demanding a quid pro quo of any sort. The company also provided a subsequent public discussion forum for the group at the Europerio 7 meetings in Vienna.
Revised review papers, consensus statements and clinical guidelines were published in their entirety in the interim between these two meetings in a single-topic supplement to the European Journal of Oral Implantology (2012, 1 supplement: 1–106).
Key causes of marginal bone loss addressed
The group identified a series of possible causes of marginal bone loss. These can be divided into two groups: those playing a role soon after implant insertion and those occurring at a (much) later stage.
Among the causes leading to marginal bone resorption soon after implant placement, surgical trauma (either by overheating or undue compression of the surrounding bone) is well documented. As the Swedish orthopaedic surgeon, Per-Ingvar Brånemark, learned in his early studies of osseointegration, in order to prevent such unintended trauma, it is of the utmost importance to treat bone as a living tissue.
Other causes of resorption are less well documented, but are represented in the scientific literature nevertheless, and hardly in doubt. To give three examples: When implants are placed in a jawbone with very limited bone volume, dehiscences often result, which leads to proximal bone resorption; although reluctantly reported, subgingival cement remnants generally result in substantial bone resorption; and placement of an implant too deep can also provoke marginal bone loss.
At a later stage, several weeks or months after prosthesis installation, occlusal overload has been recognised as another potential cause of marginal bone loss. In situations like these, occlusal adjustments or other biomechanical interventions are called for to stabilise the bone.
Nowadays, a proclivity for optimising esthetics, or even cosmetics, sometimes leads to repeated removal of the abutment. These disruptions of the connective tissue seal can result in bone loss. The same applies to insufficient biological width. The colonisation of the implant surfaces by bacterial biofilms has been associated with chronic inflammation of the marginal tissues and subsequent bone loss. A proper oral hygiene regimen is the appropriate response in circumstances such as these. Corrosion at the implant/abutment surface is scarcely documented, yet it remains another suspected cause of bone resorption.