Implant placement has become a common procedure with predictable outcome and survival rates as high as 95% have been reported. This is true of single- or multiple-tooth replacements. Nonetheless, failures resulting in loss of implant do occur with consequential loss of intended treatment objectives, resulting in disappointment. From a patient’s perspective, this involves additional treatment and associated costs.
The majority of implant failures tend to be early failures—either before a restoration is delivered or soon thereafter. Thereafter, the long-term failures are generally prosthetic phase failures or tend to occur as a result of marginal bone loss and infections.
Peri-implant diseases usually refer to peri-implant mucositis and peri-implantitis. They represent the inflammatory lesions that develop around implants. Peri-implant mucositis is a reversible inflammation limited to the soft tissues, and if the condition is untreated, it may progress to peri-implantitis and extend into the supporting bone with loss of attachment around the implant.
The prevalence of peri-implant mucositis and peri-implantitis is high. Peri-implant mucositis occurs in approximately 80% of subjects (50% of sites) restored with implants and peri-implantitis in between 28 and 56% of subjects (12–40% of sites).
Implants should be reviewed on a regular basis. Patients should be advised to visit their dentist every 6 months to have their teeth and implants checked. Clinical probing using a light force of 0.25 N is essential for diagnosis of peri-implant diseases to identify signs of clinical inflammation in the peri-implant mucosa (i.e., bleeding on probing). Suppuration on probing is frequently associated with bone loss around an implant.
As with periodontal disease, the aetiology of peri-implant mucositis and peri-implantitis is the bacterial biofilm. Modifying risk factors may also be involved—for example, patients with poor oral hygiene, inaccessibility for oral hygiene at implant restorations, smokers, and patients with a history of treated periodontitis who have an increased risk for peri-implantitis. High levels and proportions of Gram-negative anaerobic bacteria at sites with peri-implant mucositis and peri-implantitis have been reported.
Therefore, the treatment should be aimed at disruption or removal of bacterial biofilm and reduction in Gram-negative anaerobic species. Early treatment of peri-implant mucositis is highly desirable in order to limit the progression to peri-implantitis. The former responds well to mechanical nonsurgical therapy with concomitant improvement in oral hygiene maintenance.
On the contrary, peri-implantitis does not seem to respond equally well to mechanical nonsurgical therapy, with or without the use of adjunctive antiseptics or antibiotics. Depending on the extent and severity of bone loss, surgical access to debride the area might be necessary. Regenerative techniques with particulate bone graft materials along with a barrier membrane are performed to reconstruct the peri-implant bone defect. However, re-osseointegration of a contaminated implant surface is unpredictable and lacks scientific evidence.
Implant failures do not only relate to the actual loss of an implant fixture. One should remember that failure or complication associated with the prosthesis is also important. Therefore, at the outset, the patient should be informed about the long-term maintenance requirements, possible complications, and failures that may occur within the restoration.
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In contrast, screw fracture can pose a major challenge to the clinician. Although in the majority of instances, the apical part of the screw is quite loose to allow retrieval with a sharp probe, occasionally a special screw retrieval kit, specifically designed for each implant system, is required.
A cement-retained restoration is usually luted with a temporary (soft) cement. There is no pulp tissue in implants; hence, microleakage is not an issue. Use of soft cement allows easy removal of the restoration should this need arise due to screw loosening or fracture within the underlying abutment or implant. By their nature, such crowns or bridges occasionally debond and require recementation.
Ceramic fracture or delamination from the underlying metal or ceramic core is another common complication. Unlike teeth, implants are ankylosed to bone and therefore the damping or shock-absorbing effect of the periodontal ligament is lacking. Thus, any inadvertent occlusal impact can result in fracture or chipping of brittle ceramic restoration. Furthermore, if the underlying metal or zirconia substructure is not properly designed to provide optimal support for overlying ceramic, fracture or delamination may well ensue.
Removable implant prostheses are not immune to complications or failures either. In fact, research suggests that removable prostheses develop more complications and require a greater long-term maintenance in comparison to fixed prostheses in edentulous patients.