What Is Osseointegration?
You may have heard your implant dentist use the word integration or fusion while discussing your options for using a dental implant to restore a missing tooth or teeth. The most crucial step in restoring or replacing a missing tooth or multiple teeth by implants is the osseointegrating ability of the dental implant to the underlying jaw bone. The science of osseointegration has not only widened the scope of treatment options for edentulous patients, but their consequences directly affect the general systemic health of the patient.
Osseointegration as a concept was first introduced and elaborated by professor Per-Ingvar Branemark (1969), (professor at the Institute of Applied Biotechnology, University of Goteborg). He defined this mechanism of osseointegration of an implant as "A direct structural and functional connection between living bone and the surface of the load-covering implant."
What Are the Current Concepts Surrounding Osseointegration?
In the last few decades, the dental profession, including general dentists and prosthodontists, has demonstrated different techniques and methods to compensate for tooth loss ranging from conventional crowns and bridges to removable or fixed partial dentures. However, an implant scores higher in terms of chewing efficiency and long-term restoration of oral health. The current acceptance of osseointegration is when there is no progressively related movement between the implant and the bone with which it is in direct contact, i.e., it is fixed or anchored and has undergone stable fusion with the jaw bone. Although the term was initially used only with respect to titanium metallic implants, the concept is currently applied to almost all current and previously used biomaterials that do possess the ability to osseointegrate.
Recent evidence suggests that coated implants display more osteoinductive properties compared to uncoated implants that demonstrated only more osteoconductive characteristics. Also, the coagulation-related proteins that attach predominantly to the titanium surface alongside the material's surface properties are shown to impact the regenerative process of the affected tissue.
What Is the Physiological Mechanism of Integration?
The main objective of developing recent biomaterials for any dental application is to improve the quality of osseointegration and considerably shorten the time needed to achieve integration. The designing of implants involves changes in the surface characteristics to obtain a good cellular response in the physiologic environment. Incorporating osteoinductive elements more than osteoconductive elements is heralded by most implantologists as the best measure to achieve primary bone healing. Initially, blood is present only between the implant fixture and bone. However, then a blood clot forms. The blood clot is then transformed by phagocytic cells, such as polymorphonuclear leukocytes, lymphoid cells, macrophages, etc. Occlusal stresses also help in stimulating the surrounding bone. As remodeling occurs, the osseointegrated fixtures can now withstand the tension of masticatory force or stress. The mechanism of osseointegration could be unpredictably affected by a pathological process that would not only cause inflammatory reactions in soft tissue (peri-mucositis) but a subsequent bone loss around an osseointegrated implant (periimplantitis).
As a disease of the current era that correlates to long term implant failure, peri-implantitis is defined as mainly a pathological condition characterized by clinical signs of inflammation such as bleeding on probing (BOP) with or without suppuration, increase in peri-implant probing depths (PPD), and clinical attachment loss (CAL) that would be accomplished alongside radiographic bone loss with plaque accumulation. In the three to six-month period of fusion between the implant and bone, the networks of collagen bundles surround the osteocyte cells and get inserted into glycoprotein layers. Research indicates that approximately a 100 Angstrom glycoprotein layer may be formed due to bone-implant contact. In addition, the Haversian bone also becomes well organized during this phase and forms osteon units.
What Is the Significance of an Implant Seal or Biologic Seal?
Current implant dentists have now recognized that for implants to be successful and survive for the long term in the otherwise hostile environment of the oral cavity, there has to be a productive biologic seal between the implant material and the jaw tissue or bone. Weinmann theorized the concept of a biological seal around implants. More recently, Lavelle also emphasized the necessity for the attached gingiva to adapt to the integrated implant to provide a barrier against bacterial ingress and oral toxins into the space between implant posts and biologic tissues. Dental implants classified based on structure and their bond contact, be it endosteal, transosteal, or subperiosteal, must still possess a superstructure or coronal portion usually supported by a post. This post must pass through the submucosal layer and the covering squamous epithelium into the gingival portion of the oral cavity. This is also known as permucosal passage created between the prosthetic part or the attachment and the bony support of the implant.
This permucosal zone is where initial tissue breaks down when the biological seal is affected. It begins as tissue breakdown and eventually causes tissue necrosis and destroys the soft tissue or seal around the implant. The biologic seal is vital in preventing peri-implantitis or implant infections as it remains a pivotal factor in dental implant longevity. A proper seal serves as a physiologic barrier that would be effective against the potential ingress of toxins, bacterial plaque, or oral debris. Still, it can also be protective against any other harmful substances that contact the implant in the oral cavity. The foreign body agents, known initiators of tissue and cell injury, must be prevented from entering the typical physiologic environment for bone stabilization. Only that can be responsible for the implant to fuse successfully.
Hence, the knowledge or understanding of implant prosthesis has evolved over the last few decades from just an experimental and laboratory-based field into an evidence-based clinical practice for which the most crucial phenomenon of implant success remains "Osseointegration."