The replacement of missing teeth by means of endosseous implants has been proven to be a successful treatment modality for both completely and partially edentulous patients. This concept is based on the biological phenomenon of osseointegration. For a good long-term outcome of an implant-supported reconstruction, both hard and soft tissue need to be stable and to provide an adequate support for the prosthetic reconstruction. There are various risk factors that may affect the success and survival rates. A clinician planning an implant therapy needs to know the risk factors that contribute to the different types of complications that can occur after implant treatment.

After completing this ITI Academy Module, you should be able to define implant survival and implant success and to distinguish between them, identify the different types of complications that may be involved in implant therapy, identify the risk factors for these complications, and describe the survival and success outcomes for implant-supported single- and multi-unit fixed dental prostheses.

Survival is defined as the implant being present in the patient's mouth at the time of examination. The definition of survival does not give any indication of whether complications are present or not.

Implants are deemed to be successful if they are present without complications and fulfill defined criteria over the observation period. Many definitions of success have been published but most include evaluation of pain, paresthesia, inflammation, infection, mobility and bone loss. While early definitions focused mainly on the success of the implant body itself, later definitions have included the prosthesis as well as patient-centered outcomes such as function and esthetics.

Therefore, surviving implants are not necessarily successful implants. In some cases implants may present with a history of peri-implantitis, progressive bone loss around the implant or other complications but are still considered as surviving implants. This is illustrated by the case shown here of a two-unit implant-supported FPD replacing the maxillary canine and first premolar. Despite the loss of hard and soft tissue and the associated esthetic complications, the implant is considered to be a surviving implant.

Definition of Implant Survival and Success, Key Learning Points: Implant survival is defined as the implant remaining present in the patient's mouth. Implant survival does not indicate whether complications are present or not. Implants are defined as successful if no complications are present, and they fulfill defined criteria over the observation period. Both the implant body and the prosthesis need to be evaluated when determining survival and success.

Next we will discuss implant-related complications. These include biological, mechanical, and technical complications. Implants may also have esthetic complications, which are often caused by positioning errors and/or lack of sufficient hard and soft tissue volume. Esthetic complications can also arise as a consequence of biological, mechanical, and technical complications. This module will focus on biological, mechanical, and technical complications. Esthetic complications will be dealt with in other modules.

First we will focus on biological complications. Inflammatory lesions that develop in the tissues around implants are commonly termed peri-implant diseases. They are classified as peri-implant mucositis or peri-implantitis. Both display similar clinical presentations such as an inflammation characterized by redness and swelling, suppuration, and bleeding on probing or BOP. The clinical image clearly shows such a marked inflammation with bleeding after probing.

Peri-implant mucositis is reversible and is not associated with bone loss. In contrast, peri-implantitis is associated with the loss of supporting bone around the implant. The radiographs shown here demonstrate a saucer-like bone defect due to peri-implantitis that has resulted in at least 50% bone loss around the affected implants.

Mechanical complications are mainly related to problems or failure of a prefabricated component caused by mechanical forces. They include prosthetic screw or abutment loosening and prosthetic screw or abutment fracture.

Another type of mechanical complication is fracture of the implant itself, as seen in this radiograph. The coronal part of the implant has detached and is no longer integrated to the bone.

Technical complications are mainly problems related to the laboratory-fabricated superstructure or its materials. They include fracture of the veneering material, framework fracture, and loss of cement retention of the prosthesis. In this clinical case, both the veneering material and the framework have fractured.

Types of Implant-Related Complications, Key Learning Points: Peri-implant diseases are defined as inflammatory lesions that develop in the tissues around implants. Peri-implant mucositis and peri-implantitis present similar clinical characteristics such as redness and swelling, suppuration, and bleeding on probing. Unlike peri-implant mucositis, peri-implantitis is associated with loss of supporting bone around the implant. Mechanical complications are related to problems or failure of a prefabricated component. These are caused by mechanical forces such as prosthetic screw or abutment loosening, prosthetic screw or abutment fracture, or implant fracture. Technical complications are mainly related to the materials and design of the implant components, such as fracture of the veneering material, framework fracture, or loss of cement retention of reconstructions.

Next, we examine the risk factors for implant-related complications and begin with biological complications. The following factors are associated with a high risk for biological complications or peri-implant diseases: poor oral hygiene or inaccessibility for oral hygiene, smoking, and a history of periodontal disease. These factors will be described in the following slides.

Poor oral hygiene and inaccessibility of the prosthesis for oral hygiene measures are risk factors for biological complications. It's been shown that peri-implantitis is associated with poor or no access for appropriate oral hygiene measures. In contrast, good accessibility for plaque control is rarely associated with peri-implantitis. Another study has demonstrated that patients who do not completely adhere to the maintenance program for proper oral hygiene have a higher rate of implant failure.

Several studies have reported an increased risk of peri-implant mucositis, marginal bone loss, and peri-implantitis in smokers compared to non-smokers. A systematic review including one prospective and five retrospective studies has demonstrated an association between smoking and peri-implantitis as well as a significant increase in marginal bone loss in smokers compared to non-smokers.

In treated periodontitis-susceptible patients, residual pockets of 5 millimeters or more represent a significant risk for the development of peri-implantitis and implant loss due to host-related factors. Patients who are in supportive periodontal therapy but who have developed re-infections are at greater risk for peri-implantitis and implant loss than periodontally stable patients.

Mechanical and technical failures and complications play a major role in implant dentistry. They may lead to increased rates of repairs and remakes, wastage of resources such as time and finances, and may even affect the patient’s quality of life. A systematic review which included 33 publications concluded that the following factors were associated with an increased risk for mechanical and technical complications: absence of a metal framework in removable dental prostheses, presence of cantilever extensions with more than 15 millimeters in full-arch fixed dental prostheses or FDPs.

Bruxism, the length of the reconstruction - which means that three- and four-unit FDPs are at higher risk than one- and two-unit reconstructions, and a previous history of complications.

In contrast, the following factors were NOT associated with an increased risk for mechanical and technical complications: the presence of cantilever extensions in short-span FDPs, the presence of cantilever extensions of less than 15 millimeters in full-arch FDPs, the type of retention of prostheses, which means screw-retained or cemented.

Risk Factors for Implant-Related Complications, Key Learning Points: Risk factors associated with biological complications are: poor oral hygiene or inaccessibility for oral hygiene, smoking, and a history of periodontal disease.

Risk factors for mechanical and technical complications are: the absence of a metal framework in removable dental prostheses, the presence of cantilever extensions of more than 15 millimeters in full-arch fixed dental prostheses (FDPs), bruxism, the length of the reconstruction, which means that three- and four-unit FPDs are at higher risk than one- and two-unit FPDs, and a history of complications.

Clinicians undertaking implant therapy for their patients need to have a good understanding of the outcomes of treatment. This part of the module will now present data on the survival and success of both the implants and the prostheses they support. Modern implant systems have high survival rates of at least 95% over a 10-year period as shown in this graph, which depicts the results of five studies that report on at least 10 years of patient follow-up. Implant therapy may therefore be regarded as a very predictable treatment when considering the survival of implants over extended periods of time.

These studies vary in the number of patients included, the number of implants placed, and the type of implant prosthesis used, which included single-tooth replacements and short-span, long-span, and full-arch FPDs. The surfaces of titanium implants in these studies have been roughened using different treatments, including acid etching, sandblasting, and anodic oxidation. It is also important to recognize that study conditions may differ from the daily general practice setting. Clinicians should select implant systems that are thoroughly researched and have properly documented survival data.

In a recent systematic review by Pjetursson and co-workers, the survival and complication rates of implant-supported prostheses in 31 clinical studies published in the year 2000 or earlier were compared to 108 studies published after 2000. The authors concluded that as a general observation, there were higher survival and lower complication rates reported in the newer studies, reflecting improvements in clinical techniques, implant design, and prosthodontic components. In the following section, results of the systematic review of the studies published after 2000 will be presented.

The 5-year survival rates of implant-supported prostheses were reported as follows: For single-unit FDPs, the survival rate was 97.2% compared to 96.4% for multi-unit FPDs, and 95.8% for full-arch or complete FDPs. Another way of looking at the data is to say that the studies showed that an average of 1 in 179 single-unit FDPs failed each year. For multi-unit FDPs, 1 in 139 reconstructions failed annually. The corresponding annual failure rate for complete FDPs was 1 in 119.

Data was also presented for the 5-year survival rates of implant-supported prostheses based on the mode of prosthesis retention. From data derived from 32 studies, the 5-year survival rate of cement-retained prostheses was 97.9%, indicating that 1 in 238 cement-retained prostheses failed. Based on 26 studies, the survival rate for screw-retained prostheses was 96.8%, which equates to a failure rate of about 1 in 156 prosthetic reconstructions.

Next we will look at complications for implant prostheses, beginning with biological complications. These include peri-implant hard and soft tissues. The 5-year biological complication rate was 6.4% for single-unit FDPs. Based on this data, an average of 1 in every 78 single-unit implant crowns developed a biological complication each year. For multi-unit FDPs, the 5-year biological complication rate was 9.4%, or about 1 in 53 FPDs each year.

The following are the complication rates for abutment or screw loosening. For single-unit FDPs, the 5-year complication rate was 5.6%. On an annual basis, this represents a relatively low complication rate of about 1 in 89 single implant crowns. 4% of multi-unit FDPs had abutment or screw loosening problems. This was a rather infrequent complication, affecting about 1 in 125 prostheses each year. In contrast, abutment or screw loosening seemed to be twice as common in complete fixed dental prostheses, with a 5-year complication rate of 9%, or about 1 in 56 prostheses annually. When considering only cemented prostheses, the 5-year rate of abutment or screw loosening was 3.1%. This is a relatively infrequent complication affecting about 1 in 161 cemented prostheses each year. In contrast, screw-retained prostheses had a much higher complication rate of 10.8% over 5 years, or 1 in 46 prostheses each year. Overall, the 5-year complication rate for abutment or screw loosening was 8.7% or an average of 1 in about 57 prostheses annually.

The following are the complication rates for abutment or screw fractures. Overall, this type of technical complication is an infrequent occurrence. For single-unit FDPs, the 5-year rate of abutment or screw fracture was 0.3%, or about 1 in 1,667 single implant crowns. For multi-unit FDPs, the complication rate was 0.8 % after 5 years, or 1 in 625 prostheses annually. Complete FDPs had a 5-year rate of abutment or screw fractures of 5.8%. This complication was therefore much more common in this type of prosthesis compared to single crowns and multi-unit prostheses, involving 1 in 86 complete dental prostheses. With cemented prostheses as a group, no abutment or screw fractures were reported in the studies over a 5-year period. Screw-retained prostheses, however, had a complication rate of 4.1% over 5 years, or 1 in 122 prostheses each year. Overall, the 5-year rate of abutment or screw fracture was 2.8%, or 1 in 179 prostheses.

Fracture of the implant itself is a major complication, as it can result in loss of the prosthesis and is often complicated to manage. Fortunately, the 5-year rate of fracture of implants is very low. For single implant crowns, the systematic review calculated a 5-year implant fracture rate of 0.08%, or an average of 1 in 6,250 implants annually. The rate of fracture was over five times higher in multi-unit FDPs, reported as 0.5% over 5 years, or about 1 in 1,000 implants annually.

Loss of retention for a cemented prosthesis that resulted in loosening or detachment of the prosthesis could only be analyzed for single-unit implant crowns. The 5-year rate of loss of retention was 3.1%. Annually, an average of 1 in about 161 crowns had this type of complication.

Another type of technical complication is fracture of the veneering material. This is a common complication. Single implant crowns were reported to have a 5-year complication rate of 3.2%, or 1 in 156 crowns annually. In contrast, fracture of the veneering material was more common in multi-unit FDPs, with a rate of 7.7% over 5 years. Annually, this complication affected 1 in 65 prostheses. By far the most common prostheses to have this complication are complete fixed dental prostheses. The systematic review calculated that 25.3% of prostheses were affected over 5 years. This is equivalent to 1 in 20 prostheses affected each year. Overall, the 5-year rate of fracture of veneering materials was 16.7%, or about 1 in 30 prostheses.

In summary, a range of biological, technical, and mechanical complications can occur with dental implants and the prostheses they support. For single- and multi-unit fixed dental prostheses, the 5-year rate of complications was 27.3%. This means that on an annual basis, about 1 in 18 of these prostheses had a complication of one type or another. For complete fixed dental prostheses, the 5-year rate of complications was twice that of single and partial fixed dental prostheses at 53.2%, which is equivalent to 1 in 9 prostheses annually. When comparing cemented to screw-retained prostheses, the 5-year complication rate was 16.3% for cemented prostheses, or 1 in 31 prostheses annually. The corresponding rate for screw-retained prostheses was 31%, or 1 in 16 prostheses every year. Overall, 27.1% of implant-supported prostheses developed a complication over a 5-year period, which represents about 1 in 18 prostheses every year.

Although high survival rates of implants and the prosthodontic reconstructions they support may be anticipated, biological, technical, and mechanical problems are a frequent occurrence. Management of these complications often involves additional chairside time, and they can often be time-consuming and costly to treat. Both the treating clinician and patient need to be aware that ongoing maintenance, repairs, and re-treatment are often necessary with implant-supported prostheses. At all times, clinicians should take steps to minimize the risk of complications wherever possible.

Survival and Success Rates of Single- and Multi-Unit Implant FDPs, Key Learning Points: Overall, an improvement in the survival and success outcomes for both implant body and implant prostheses has been shown when comparing newer studies to older studies that were published in the year 2000 or earlier. The 10-year survival rate of well-documented implant systems is greater than 95%. The 5-year survival rates of single-unit, multi-unit, and complete implant-supported prostheses is greater than 95% in studies published after the year 2000.

The 5-year complication rates of single-unit, multi-unit, and complete fixed dental prostheses combined from studies published after the year 2000 were as follows: Biological complication rates ranged from 6.4 to 9.4%. Abutment or screw loosening was 8.7%. Abutment or screw fracture was 2.8%. Implant fracture was 0.5% or less. Loss of retention of cemented single crowns was 3.1%. Fracture of veneering materials was 16.7%. Fracture of the framework was 0.2%.

The 5-year complication rates according to prosthesis type and mode of retention from studies published after the year 2000 are as follows: Single- and multi-unit FDPs was 27.1%, Complete FDPs was 53.2%, Cemented prostheses were 16.3%, Screw-retained prostheses were 31%, The overall complication rate for implant-supported FDP was 27.1%.

Implant and Prosthesis Survival and Success, Module Summary: The replacement of missing teeth by means of endosseous implants has been proven to be a successful treatment modality for both completely and partially edentulous patients. Implant survival and success are based on different criteria and both should be considered when reporting implant-related outcomes and predictability. In general, recent clinical studies published after the year 2000 have reported higher implant and prosthesis survival rates and lower biological, mechanical, and technical complication rates, suggesting a positive learning curve in implant dentistry. Understanding of the implant-related complications and their associated risk factors will enable clinicians to improve treatment planning, manage these complications, and avoid future complications.