Implant-supported tooth replacement offers a tremendous benefit to patients. In order to assure the long-term success of implant therapy, it is important to understand the complex biologic environment that is present around implants. Implants are biomedical devices that exist under functional demands within an environment shaped by the biologic interactions between the microbial biofilm and the immune response. Maintenance of peri-implant tissue health is therefore critical to the long-term survival, success and benefit of implant therapy for the patient.

After completing this ITI Academy Module, you should be able to: recognize the anatomic characteristics of the healthy peri-implant soft tissue, describe how microbial biofilms form on implants and lead to inflammation of the peri-implant soft tissue and supporting bone, identify the effects of inflammation on the peri-implant soft tissues and supporting bone, and list the clinical parameters that are required to monitor the health of the peri-implant soft tissue and supporting bone.

The peri-implant soft tissue includes the epithelium and the supporting connective tissue as shown here histologically. Together, these tissues form a structural and functional unit interfacing with the implant surface. They provide a seal between the underlying bone supporting the implant and the oral environment. This is referred to as the biologic width. The biologic width is always present but its dimensions, beyond certain minimums, may vary. There is always some amount of connective tissue separating the bone from the epithelium. It is important to know that the dimensions of the biologic width may be affected by both the anatomic position in which the implant is placed and by the implant design. Therefore, we cannot consider a healthy site as having specific dimensions for these tissues.

The peri-implant soft tissue or mucosa forms a sulcus similar to that found around teeth. The interface of the soft tissue with the implant is formed by an epithelial and a connective tissue component. The oral epithelium within the sulcular-implant-soft-tissue interface includes the sulcular epithelium. It lines the sulcus and interfaces directly with the oral environment. This is evident in the image of a site where the implant crown has been removed. The other part of the oral epithelium is the junctional epithelium that attaches directly to the implant surface apical to the sulcular epithelium through specific hemi-desmosomal attachments. These derive from the epithelial cells and extend to the connective tissue.

The connective tissue portion of the biologic width creates a biologically defined distance between the epithelium and bone along the implant surface. The connective tissue overlying the bone adapts to the implant surfaces with dense bands of collagen fibers that tend to run parallel to the implant surfaces. In health, this tissue functions very much like that around teeth, but with inflammation a probe may easily penetrate into the connective tissue, more than around teeth.

In health, the clinical appearance of the peri-implant soft tissue is influenced by the type of epithelium present. The epithelium may be keratinized or non-keratinized. Keratinized or masticatory mucosa has a less vascular or red appearance. It is supported by dense, collagen-rich connective tissue with a firm attachment to the periosteum, which makes it less mobile with manipulation. Non-keratinized or alveolar mucosa may appear more vascular or red. It contains more elastic fibers and fewer collagen fibers, giving it less stability in its attachment to the periosteum. This results in more mobility with manipulation. In health, the underlying connective tissue affects the clinical appearance of the peri-implant tissue. The underlying connective tissue determines the presence or absence of keratinization of the epithelium through biological interactions. This means that surgical procedures may be performed to develop areas of keratinized tissue.

Studies have examined the benefit of having keratinized peri-implant soft tissue with mixed results. This means, the true value of keratinized mucosa remains to be determined. While keratinized tissue may not be an absolute advantage, it may offer case-specific advantages that warrant surgical interventions to develop keratinized tissue at planned implant sites. Most studies showing a benefit have considered a minimum of 2 mm of apical-coronal width sufficient. Current thinking suggests that benefits of keratinized tissue include making it easier for the patient to perform oral hygiene procedures around the implant, which in turn may result in less susceptibility to inflammation, recession of the soft tissue margin and crestal bone loss. While it is not clear from the literature that keratinized epithelium is required for tissue health and stability, there may be concerns with implants lacking keratinized tissue.

It is important to remember that the implant system's design may affect the dimensions or position of the peri-implant tissues. The body maintains a biologic dimension of epithelium and connective tissue separating the oral environment from the osseous tissue, which is the biologic width. In this picture an external abutment attachment placed on the implant at the osseous crest may lead to remodeling of the crestal bone and a modification of the connective tissue as the epithelium migrates apical to the implant-abutment interface. One of the advantages gained with platform-switching is that this apical migration of the biologic width is less likely to occur.

This radiograph demonstrates alterations in the contours of the osseous tissue to re-establish the biologic width apical to the implant-abutment interface. It is easy to envision the junctional epithelium extending several millimeters apical to the osseous crest of the adjacent teeth, an alteration that would be considered to result in healthy dimensions for this site. The location and distance of the epithelium and connective tissue components along the implant surface may vary. This means that there may be a wide range of dimensions in health for sulcus depth, length of junctional epithelium, location of the osseous crest, and the height or amount of intermediate connective tissue. Therefore, variations in the measured clinical dimensions of the peri-implant soft tissue may reflect differences in implant design and position relative to the osseous tissue rather than disease. It is important to keep this in mind when evaluating peri-implant tissues, especially when measuring probing depth.

Anatomic Characteristics of Peri-Implant Tissue, Key Learning Points: The tissues forming the biologic width are the epithelium and connective tissue. They seal the bone tissue supporting the implant from the oral environment. The tissues forming the biologic width adapt to the implant and prosthesis surface. Keratinization of the epithelium determines the clinical appearance of the soft tissue which means epithelial tissue lacking keratinization has a more vascular appearance and is more mobile. The type of connective tissue supporting the epithelium determines keratinization. This means that surgical procedures may be possible to enhance the keratinized tissue present at implant sites. Though not shown consistently in studies, it appears that keratinized soft tissue may be of benefit to the health of peri-implant tissues. Implant design and position may affect soft tissue dimensions, such as probing depth. This means there is no predetermined maximum probing depth indicating health.

The implant exists within the complex and dynamic microbial environment of the oral cavity. The microbial biofilm which forms on exposed surfaces in the oral cavity is often referred to as dental plaque. The biofilm itself is a complex microbial environment made up of bacterial cells, cell products and extracellular matrix. The biofilm represents a dynamic ecological system evolving over time through interactions between the oral environment, the microbes and the host.

Biofilm forms, matures and evolves on all exposed implant surfaces on which it is not disrupted. Implant design characteristics may contribute to biofilm formation, for example, the connection design between implant components such as the implant-abutment interface or the implant-prosthesis interface. Also, the roughness of the implant surface may affect both the amount and composition of the biofilm, with rougher surfaces having greater amounts of biofilm formation than smooth surfaces. Interestingly, the effects of more recent alterations in implant surface chemistry may also have an influence on biofilm formation. However, this is not sufficiently understood at this time.

Biofilm forms on implants in several stages. Bacteria initially adhere to salivary proteins on implant surfaces exposed to the oral environment. The bacterial number increases over time. As the biofilm matures, the types of bacteria adhering to the surface change over time and increasingly pathogenic bacteria may become more prominent. These bacteria may stimulate an inflammatory response as indicated by the arrows in the photograph. Not surprisingly, many of these pathogenic bacteria are the same as those that cause periodontal disease.

The microbial biofilm may directly affect the peri-implant tissues in two ways. First, microbial pathogens produce a number of molecules that stimulate a host inflammatory response. Bacterially-derived molecules such as endotoxins or lipopolysaccharides stimulate an inflammatory response leading to clinically evident changes. Second, bacterial proteinases directly cause tissue degradation. They are proteins that are released into the tissue and are capable of directly degrading components of the connective tissue. Together, these molecules lead to an inflammatory tissue response with degradation of the collagen fibers in the connective tissue. Over time, this degradative response may extend toward the osseous tissue ultimately resulting in bone loss around the implant. Since the microbial biofilm has the potential to affect the supporting tissues of an implant, monitoring the biofilm formation is important to maintaining positive clinical outcomes for implants. A direct association between oral hygiene and peri-implant bone loss has been identified. As the maturation of the biofilm leads to soft tissue inflammation, evaluation of the inflammatory state of the peri-implant soft tissues may be an important indicator of the patient's oral hygiene.

Peri-Implant Biofilm, Key Learning Points: Biofilm or dental plaque forming on dental implants represents a complex microbial ecological system. The implant design and surface characteristics influence biofilm formation. Maturation of the biofilm leads to an increased number of pathogenic organisms. Microbially-derived molecules stimulate an inflammatory response and tissue degradation. Clinical assessment of biofilm formation is critical in monitoring the health of the peri-implant tissues as poor oral hygiene leads to inflammation and possibly bone loss.

The inflammatory response affects the peri-implant soft tissues in multiple ways that may be detected through the clinical evaluation. Understanding these biologic effects is critical to correctly interpret these findings. The inflammatory response is directed at eliminating the microbial challenge, but this response may also have adverse effects on the tissues. The inflammatory tissue response leads to increased blood flow, increased porosity of the capillaries, cellular infiltration, and to the degradation of structural proteins in the connective tissue and supporting bone. All these changes may become evident through clinical evaluation.

The host response or inflammation initially relies on the infiltration of white blood cells such as polymorphonuclear leukocytes and others into the sulcular area to fight the infection. The cellular infiltration provides an important part of the host defense to the microbial challenge, but if heavy enough it may contribute to the clinical appearance of suppuration. As inflammatory cells migrate into the tissues, they release a number of enzymes that degrade structural components of the soft tissues. The degradation of the collagen component may lead to a reduction of fibrotic tissue, allowing the probe tip to penetrate to the osseous crest which is indicated by increased probing depths. With the release of inflammatory mediators there is also a disruption of the sulcular epithelial integrity. This may be evident as bleeding on probing. This bleeding response along with clinical signs of tissue redness and edema is also influenced by the vasodilation and extracellular infiltration associated with inflammation. In the worst case this inflammatory response may extend apically towards the supporting bone and result in loss of bone support for the implant.

Effects of Peri-Implant Inflammation, Key Learning Points: Recognition of the clinical signs of inflammation and infection are critical to monitoring the peri-implant tissues. Tissue changes associated with an inflammatory response include increased vascularity which is seen as redness as well as edema or swelling. Increased probing depth represents a disruption of the connective tissue that may or may not include bone loss. Bleeding on probing is associated with inflammation and may indicate poor oral hygiene. Radiographic signs of bone loss need to be assessed in conjunction with clinical findings.

The examination of the peri-implant soft tissue may include the collection of the following information: Clinical signs of inflammation and infection such as redness, swelling, suppuration and pain should be evaluated. In addition, the evaluation should include, oral hygiene with plaque or biofilm formation, bleeding on probing or BOP, peri-implant probing depth or PD and finally, radiographic signs of bone loss. The timing and frequency of radiographic assessments need to be determined based on concerns regarding potential changes which are evident upon clinical examination. These evaluations in conjunction with the clinical assessments mentioned before should be performed to fully appreciate the overall health of the tissues and identify possible bone loss.

In order to fully appreciate any changes occurring to the implant, it is important to establish a baseline assessment following insertion of an implant prosthesis. This gives a frame of reference to identify changes that may be the result of the initial treatment rather than the result of a subsequently developing inflammatory disease. Probing depths and the position of the soft tissue margin are two important characteristics to note. Similarly, any radiographic evidence of bone levels following the prosthetic prosthesis allows differentiation of normal bone remodeling during the first few months following surgery from pathogenic bone loss later on.

Oral hygiene or the presence of biofilm or plaque may be assessed using one of several approaches. The assessment typically involves lightly wiping the probe tip along the sulcular area of the implant surface. Plaque may simply be recorded as being present or absent at the implant or at a given surface of an implant. Similarly plaque may be assessed using a relative scale for the implant that records amounts of plaque using a relative abundance scale. Zero means that no plaque is detected. A score of one means plaque is only seen by running a probe across the surface. When plaque is seen by direct visual inspection, it is given a score of two. A score of three is recorded when there is an abundance of soft matter.

In addition to the direct visual inspection of the color and consistency of the tissues, bleeding on probing may provide additional information regarding the level of inflammation along the marginal soft tissues of the implant. This is typically done by visually assessing bleeding following light probing or lightly wiping the probe along the inner aspect of the sulcular area. Bleeding on probing may simply be recorded as being present or absent. The presence of bleeding is associated with tissue inflammation while the absence of bleeding serves as an indicator of healthy tissue. Bleeding on probing may also be assessed using a relative scale as to the degree of inflammation, as shown here. The score provides more detailed information regarding the level of peri-implant inflammation. Zero means there is no bleeding evident when passing the periodontal probe within the peri-implant sulcus. If isolated spots of bleeding are visible, a score of 1 is documented. When a confluent line of blood forms along the sulcus, the score is two and for heavy or profuse bleeding, the score is three.

Interpretation of peri-implant probing depths may be a more complicated process for peri-implant tissue than for periodontal tissue. Factors affecting the value of probing depths around implants may include the implant position. For example, the labial positioning of this implant has contributed to the loss of tissue on the facial aspect of this implant. Other factors are post-surgical healing patterns and tissue thickness. Patients have a natural tissue thickness that may vary between patients and between locations within patients. The design of the implant and prosthesis may influence the soft tissue margin position relative to the depth of probe penetration into the sulcus, or in other words the probing depth. It should be noted that changes in probing depths may occur in the presence of soft tissue inflammation. Under these circumstances the probe tip may largely extend into and through the connective tissue approximating the osseous crest. Such increases in probing depth may indicate soft tissue inflammation, bone loss or both. It is also important to note that soft tissue recession of the marginal tissues may occur, hiding what would otherwise represent as increased probing depths or loss of bone. Therefore, it is critical to assess probing depths or soft tissue margin position using standardized positions on the implant or prosthesis. It is then possible to evaluate changes occurring over time relative to the probe penetrating into connective tissue or extending further, which would suggest bone loss at the site.

In health, the position of the periodontal probe tip should extend to a position approximating the epithelial attachment to the implant surface. The numeric value of the measurement in itself does not indicate pathology. In anticipating the probe tip position around the implant shown in this diagram, it is expected that the probe tip extending to the labial implant shoulder will have a much smaller probing depth than in the proximal areas. It is important to evaluate the probing depths from a fixed landmark and to identify changes over time. No changes in the probing depth along with no change in the soft tissue margin position suggest there is no bone loss. Any changes in probing depths must be assessed with consideration of inflammatory effects. Remember that the probe tip may extend into the connective tissue when the inflammation is approximating the osseous crest. Changes in the soft tissue margin position due to recession, edema or hyperplasia may also affect the interpretation of probing depth findings. In addition, the radiographic interpretation of bone loss may provide critical information in these clinical assessments and should be done when there is concern of possible bone loss based on the clinical findings.

Assessment of Peri-Implant Tissues, Key Learning Points: Monitoring of peri-implant soft tissues requires the integration of clinical findings. The interpretation of clinical findings for implants may differ from those evaluating periodontal tissues. Assessment of the probing depth requires careful interpretation relative to other clinical findings, anatomy and implant characteristics. The radiographic evaluation is important in confirming clinical findings.

Summary of module Monitoring Peri-Implant Tissue Health: It is important to understand the role of the peri-implant soft tissues in protecting the bone tissue from the oral environment. Challenges from the microbial biofilm along the implant and prosthesis surfaces are a major concern to the health of these tissues. Oral hygiene and disruption of microbial biofilm are critical to maintain soft tissue health. Periodic evaluation of the peri-implant tissues is critical to the long-term success of implant therapy. Interpretation of the clinical evaluation must be made in light of the biologic interactions between the host and microbial environment within the context of the implant restoration. Both clinical and radiographic findings play an important role in discriminating health from disease. Early recognition and elimination of inflammation and inflammatory agents remain critical to the prevention of infection and peri-implant bone loss that put the implant at risk. Thus the benefits that implant therapy offers the patient are preserved.