The peri-implant tissues are the tissues that surround the osseointegrated implants and are divided into the soft and hard tissue compartments. The soft tissue compartment, known as the peri-implant mucosa, is the tissue being referred to when the term ‘peri-implant tissues’ is used. This tissue is formed during the healing process that follows once implant placement and healing abutment connection has been completed for two-piece implants and following implant placement when a one-piece implant is placed. This soft tissue implant interface plays an important role as it forms a biological seal around the implant providing protection against the oral surrounding. The seal also isolates the implant and bone from the oral environment through an attachment which limits the ingrowth of bacterial plaque thereby preventing disease at this interface.
Whilst the concept of osseointegration is widely accepted, as the demand for implant treatment increases, an understanding of this soft tissue seal, its role and the factors that can affect it are essential to ensure the long-term stability of the tissues and the implant restoration and its successful outcome. A number of factors will influence the stability of this seal and include the degree of keratinised tissue present, the abutment materials and surface topography of the implant. Some of these factors will be identified at the outset during the early planning stages and knowing these will help plan a regime directed at reducing their impact. Thus, pretreatment planning is not only important for the provision of the prosthesis but is also critical to help ensure that factors that could place the future stability of the peri-implant tissues at risk are identified and managed as early as possible and the patient made aware of their implications.
An understanding of the similarities and differences between the tooth–soft tissue interface and the peri-implant soft tissue will also help provide a clearer recognition of deviations from health and the possible reasons (Table 6.1). The main differences between these two interfaces lie in the following areas:
Table 6.1 Similarities and Differences between the Tissues around Teeth and the Peri-Implant Tissue.
|Features||Tissues around Teeth||Peri-Implant Tissues|
|Gingival sulcus depth||Shallow on average around 2–3 mm||Variable and is dependent on the depth at which the implant is placed and the abutment length and restoration margin|
|Junctional epithelium||Hemidesmosome attachment to enamel||Hemidesmosome attachment to titanium|
|Gingival fibres||Complex array of fibres inserting into the cementum about the crestal bone and onto the periosteum||No fibre insertion into the implant; fibres are oriented parallel, or circumferential to the long axis of the implant|
|Connective tissue attachment||Well-organised collagen fibre bundles running perpendicular to the root cementum||Structure that is rich in collagen but no fibroblasts and vascularity|
|Blood supply||Numerous vascular anastomoses between the vessels from the periodontal ligament space, and gingival connective tissue||Fewer blood vessels and majority of the supply coming from the underlying periosteum|
|Biologic width||Junctional epithelium – 0.97 mm; CTA – 1.07 mm||JE = 1.88 mm and CT = 1.05 mm|
- Junctional Epithelial Component
Both teeth and implants have a long junctional epithelium which is also known as the barrier epithelium. Around implants, this is thinner and longer and has a hemidesmosomal attachment with the transmucosal abutment and a thin basal layer. This feature along with the collagen fibre orientation increases the risk of bacterial penetration around the implant (Figure 6.1a, b).
- Connective Tissue Component
There is a higher fibre content around implants with a lower cellular content and the collagen fibres are arranged parallel to the implant surface with fewer fibroblasts in contrast to teeth where the fibres are perpendicular. As a result, when assessing the peri-implant tissues with a probe, a deeper depth will be noted when compared to teeth and the mean bleeding on probing is also much higher. The delicate nature of the tissue also makes this area more sensitive to pressure and increase in probing pressure/force may lead to trauma to the tissues (Figure 6.2).
The vascularity around implants comes from the periosteum of the bone with few to no blood vessels in the zone adjacent to the implant surface. This reduced vascularity affects the healing by reducing the number of circulating neutrophils and B cells in the area.
- Periodontal Ligament
Implants lack a periodontal ligament and thus when disease or injury due to occlusal trauma takes place, the effects are transmitted to the bone directly.
- Healing Response of the Tissues
The cellular response around teeth and implants is different as the sites around implants are infiltrated with B cells and plasma cells. Due to this, and the lack of a tight supracrestal connective tissue compartment, disease progression is much more rapid around peri-implant tissues. The number of circulating neutrophils and B cells is also reduced due to the reduced vascular blood supply.
- Biologic Width
This width varies around implants and is dependant on the depth of the implant placement. It ranges upto 3 mm (1–1.8 mm junctional epithelium and 1–2 mm connective tissue attachment). When the width is reduced, marginal bone resorption will take place. Factors that may influence its dimensions are the type of implant (one vs two piece), implant material (titanium, gold alloy, zirconium) implant surface characteristics (surface topography, macrodesign), loading protocol and the flap design used for implant placement. Whilst it is thought that these factors will affect the biologic width, the degree to which this happens remains unclear (Figure 6.3a, b).
Periimplant tissues in Health
The health of the peri-implant tissues is essential for long-term stability and should be monitored throughout the planned treatment after implant placement.
Figure 6.4 shows the tissues around a two-piece implant when the healing abutment has been removed. The shape of the tissues has been characterised by the use of a shaped healing abutment for the optimal emergence profile of the prosthesis.
The tight gingival cuff has the same protective function as around teeth and is made up of epithelium and connective tissue which forms during the post-surgical healing period after implant placement. It is thought that with two-piece implant systems, the repeated removal of the healing abutment, leads to the hemidesmosomal attachment being traumatised thus leading to the instability of the gingival margin which can become an issue around implants with thin quality tissue biotype. The benefits of keratinised tissue around dental implants have been discussed previously. The peri-implant soft tissue that forms is described as ‘scar tissue’ which has impaired resistance to bacterial colonisation and the biological seal formed even in healthy tissues is weak and has poor mechanical resistance. When this seal is disturbed, the health of the tissue is compromised leading to disease and ultimately implant failure. The patient’s daily plaque control does play a key role in maintaining the health of the peri-implant tissues.
Healthy peri-implant tissues will have an absence of clinical signs of inflammation (redness and swelling), no bleeding on probing and probing depths < 5 mm although this depth will vary with the depth of the implant fixture placement. The following steps should be followed to detect if the peri-implant tissues are healthy:
- Visual inspection of the tissues which should show no signs of disease.
- Probing pocket depths may vary depending on the depth of implant placement; however, an increase in depth compared to baseline indicates presence of disease.
- Lack of bleeding on probing should be assessed with light forces to minimise the risk of trauma to the tissues.
- Absence of further bone loss > 2 mm measured against the baseline radiographs.
Peri-Implant Tissues: Disease
The prevalence of peri-implant disease is increasing as the demand for implant treatment rises. The early identification of inflammation will help implement prompt and effective intervention which will assist in achieving health. However, the outcome will be dependent on the reasons for the inflammation. The standard checks listed above should be undertaken at every visit to ensure that early signs of disease are not missed.
- Factors to Consider:
The factors that increase the risk of peri-implant disease include (Figure 6.5):
- Patient related:
Ability to maintain an optimal level of plaque control with effective home care regimes; smoking; uncontrolled diabetes, history of periodontitis.
- Prosthesis related:
The design of the prosthesis, its shape and contour will be key to ensuring that the patient can clean around the prosthesis. A poorly designed prosthesis will impede cleaning leading to a higher risk of inflammation and disease.
- Operator related:
Placement of the implants and their proximity to teeth and each other as well as designing the prosthesis.
Peri-implant diseases have been related to biological and mechanical factors. The former relies on the concept of these conditions being infections and are described using the presence of bleeding, changes in the crestal bone levels and deepening of peri-implant pockets. Mechanical factors are related to the unfavourable stresses that can be generated as a result of occlusal trauma leading to marginal bone loss. Bacterial biofilms made of bacteria and saliva colonize the implant surface and have been noted to be responsible for 65% of peri-implant diseases. The daily chemomechanical removal and disruption of this biofilm will reduce the risk of disease. In the partially dentate patient, the migration of bacteria from the teeth to the implants is well known. If not removed efficiently, an inflammatory response is elicited which releases cytokines which enhance the collection of neutrophils. If treatment is implemented at this stage, then the condition will reverse itself; however, if the bacteria continue to persist, then more neutrophils infiltrate the tissues leading to further destruction, with the host response to the inflammation leading to bone loss around the implants. As the situation continues to progress, increased infiltrates of proinflammatory cells responsible for further tissue breakdown is seen with eventual loss of the implant itself. The bacteria that have been implicated in peri-implant disease belong to the group of campylocbacters, aggregatibacter actinomycetum comitans and trepenomena.
- Peri-implant diseases
The two most common peri-implant diseases that have been reported are:
- Periimplant mucositis (Figure 6.6)
- – Defined as the presence of signs of inflammation noted as redness, swelling, line or drop of bleeding within 30 s following probing with no additional bone loss following initial healing. It is reported to resemble gingivitis.
- – Reversible condition.
- – Prevalence reported at 30–62.6% at implant level and 47–80% at patient level.