The literature on potential failures of dental implants tends to be somewhat conflicting, if not confusing. The overall success rate of dental implants is about 95% although some authorities claim that it is higher (i.e., about 98%) whereas others suggest that it might only be 93%. Regardless of the precise success‐to‐failure ratio, dental implants are still one of the most successful procedures a general dentist can perform and, as indicated in Chapter 16, one of the most profitable.
Recognizing a Failing Implant
When there has been inadequate and incomplete osseointegration, the predominant indicator is mobility of the implant. Initially, this mobility may only be detectable by a dentist or hygienist but as failure progresses, the initial limited mobility will progress to movement of the prosthetic crown on mastication and even on talking. Other indications of the lack/loss of osseointegration and potential implant failure may include pain, swelling, or infection although in the long term, once there is significant loss of bone around the implant fixture, progressive evulsion and failure occur.
Despite the incredible success of dental implantology, failures still occur and at a rate of 8.16% in the maxilla and 4.93% in the mandible, regardless of the majority of risk factors [1, 2]. Many factors may be involved in such failures, but these data suggest that, for the average dentist performing 100 implant procedures per year, between 2 and 10 failures will occur on an annual basis. These failures follow what is known as a stochastic variation, namely that they are randomly determined and/or distributed. In other words, implant failures occur in a random pattern which may be analyzed statistically but they cannot be predicted precisely, and they will occur “sporadically.” If an implant is placed in a compromised site it is much easier to find a “cause and effect” which may lead to implant failure. Some of these “cause and effects” include poor bone quality, low or no initial stability of the implant, and presence of infection or granulation tissue.
Risk Factors for a Failed Dental Implant
There are many reports in the literature regarding the statistically significant factors that affect implant survival, but the data are not clear‐cut. Certain factors may impact the success or failure of implants in both the short‐term, i.e., failure within 12 months of surgery, implant placement and restoration – what are known as early implant failures, and those occurring long‐term, i.e., after 12+ months. The term early implant failure also applies to implants that failed prior to restoration and loading.
Broadly speaking, implant failure risks fall into two broad categories: intrinsic and extrinsic.
Intrinsic failures include the following:
- Failure of the implant system or any of its components
- Poor, inadequate, or incomplete osseointegration following placement
- Presence of infection or periodontal disease
- Poor bone quality at the implant site
- Nonideal osteotomy or insertion procedures
- Presence of diabetes mellitus or osteoporotic bone
- Galvanic corrosion between the implant and restorations
- Incorrect or improper selection of the implant
Thus, whereas patient age and gender, body mass index (BMI) may not significantly affect implant survival, success factors such as periodontal disease, smoking and systemic disease can impact implant survival [1–5].
Extrinsic failures are those arising from external influences, including:
- Excessive loading on the implant or the attached prosthesis
- Poor positioning of the implant
- Steroids use
Some implant failures may be operator‐related, others are ascribable to inherent (intrinsic) issues related to the patient, the quality of bone at the implant site and finally, but relatively rarely, some are due to failure of a component of the implant system.
Overall, it appears that the most reported conditions contributing to implant failure are:
- Non‐osseous integration and fibrous encapsulation
- Certain prescription medications
- Hardware failure
- Periodontal disease 
For clarity in this context, peri‐implant mucositis is gingival inflammation found only around the soft tissues of the dental implant but with no loss of marginal bone beyond normal resorption. Although peri‐implant mucositis may be successfully treated and is reversible if caught early, if untreated, it is a precursor to peri‐implantitis with its eventual bone destruction and loss of the implant.
In contrast, oral mucositis (OM) is an inflammatory, erosive and/or ulcerative process within the mouth, usually caused by radiation or chemotherapy. OM is often accompanied by severe pain and difficulty in eating, and can severely impact a person’s quality of life, nutritional intake, and continuing treatment for cancer.
It is interesting that, in contrast to the quite extensive data available on patient‐related and implant component factors in early implant failures, there is relatively little reported information available on the surgeon’s role in early implant failures. However, in relative terms, dentists that place more implants in sites with poor bone quality have a greater overall percentage of early implant failures. Placing implants in compromised sites can sometimes be due to lack of experience but may not always be avoidable. This is almost predictable since bone quality at the implant site is one determining factor in the success or failure of the implant.
One major study  has addressed this operator issue by analyzing implant failures that occurred after a total of 11 074 implant operations were performed at a specialist clinic over a period of 28 years. The study evaluated the results for 8808 individual patients treated by 23 different dentists, 21 of whom were specialists in oral surgery or periodontology. Of these large number of operations, early implant failures were found for only 616 operations (5.6%). Interestingly, most of these failures occurred with edentulous upper jaws. It was also found that there were statistically significant differences between male and female surgeons, implants placed in maxillae vs mandibles and the nature of the implant surface. The study indicated that although early failure rates decreased when implant bodies with a moderately roughened surface were placed, the relationship between failure rates and surgeons stayed the same although it is likely that case selection and operator experience contributed to the observed data.
There is little data available on relative success/failure rates for different types of implants or those from different manufacturers. It appears overall, however, that implant height (i.e., body length), implant type (cylindrical or tapered) and one‐stage or two‐stage placement has no statistically significant effect on success or failure although many studies directed at these effects were not well controlled. Nevertheless, the literature indicates that modern implants with tapered bodies and roughened surfaces exhibit higher success rates than the early smooth surface implant bodies.
It should be mentioned here that mini‐mplants, i.e., those with narrower diameters and platforms are recommended for very limited sites, i.e., those with minimal access or close spacing between remaining teeth. The corollary to this is that the mass of implant osseointegrated with bone is less than that with a conventional implant. Due to these factors, mini‐implants should be used with caution.
Failure of implant hardware is unusual, if not comparatively rare. An interesting example is the following. An implant was restored using a custom milled Ti base/zirconia restoration, (Fig. 15.1).
The patient complained that the restoration appeared to be loose and the dentist simply torqued it back in place. When the restoration crown loosened again, clinical examination indicated that the “hex” of the titanium implant body had fractured off and the anti‐rotation protection was lost, (Fig. 15.2a,b).