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The high survival rates reported for endosseous implants have established them as a predictable restorative option for replacement of multiple teeth as well as a single missing tooth.1,2 Classic and more recently introduced implant surfaces have shown survival rates in the high 90th percentile.3,4 However, because the studies reporting these rates were performed by experienced clinicians using implant systems with which they were familiar, together with meticulous screening of study participants, these rates are generally higher than those achieved by most clinicians in their offices.5 Moreover, when the concept of implant survival is compared to implant success, these rates decrease even further. This is especially true if implant success is defined as an implant free of complications. In fact, two literature reviews reported that when using the latter as a definition for implant success, 61% of patients after 5 years with implant-supported fixed partial dentures (FPDs)6 and 50% of patients after 10 years with combined tooth/implant FPDs reported no complications.7
Classifying Complications
A thorough discussion of the classifications of implant complications is beyond the scope of this article; however, an overview is presented here. Complications can be classified broadly into three categories: minor, major reversible, and major nonreversible. A minor complication would include crown loosening, fracture of an abutment screw, or chipped veneer or crown. Major reversible complications would include implant fracture, post-restorative implant failure, or damage to an abutment tooth. A major nonreversible complication would include an aspirated implant, an implant or implant preparation permanently damaging the inferior alveolar nerve, or a fractured maxilla or mandible.
A more precise classification divides complications by the following categories: surgical (intraoperative); biologic; related to augmentation procedures; related to placement and loading protocols; prosthetic or mechanical; and esthetic and phonetic.8 In using these more specific classifications, the treatment protocols for each can be more easily described.
Pre-Surgical Prevention
In general, the best treatment for a complication is its prevention. Risk assessment is essential for prevention of complications and preparation for those that do occur. This begins with a thorough interview of the patient to determine medical history, current medical conditions, and past and current medications.
Thorough Medical History
An aging population makes taking a thorough history even more important; many patients presenting for implant surgery have at least one systemic condition and are taking at least one medication that may affect the implant surgery and lead to complications. Examples include patients taking anticoagulants (eg, aspirin, warfarin, clopidogrel), patients taking immunosuppressant drugs or long-term cortisones, or patients having taken or who are taking bisphosphonates long term. Before implant surgery, these patients require medical consultations and testing for certain values such as international normalized ratio, bleeding time, and serum C-terminal peptide levels.9 Many patients with their physicians’ prior approval can stop anticoagulants for a specified time before surgery, thus decreasing the risk for hemorrhage intraoperatively or postoperatively. The same is true for patients taking bisphosphonates who can be advised with their physicians’ approval to go on a “drug holiday.”
For patients with diabetes mellitus or hypertension, implant surgery should be postponed until blood values and blood pressure readings are acceptable. For diabetes, if the patient’s glycosylated hemoglobin (HbAlC) levels are too high, a referral to the treating physician to improve glycemic control should be given to reduce the risk for implant complications. HbAlC levels of less than 7% are desired, with greater than 8% being an indication for physician referral. Conversely, a patient with diabetes exhibiting signs of hypoglycemia, which would include disorientation, weakness, or irregular behavior, should be given glucose and immediately referred to the physician.
Blood pressure values should also be in normal range (120/80 mm Hg or lower) before surgery. If patients with hypertension do not have their conditions well controlled, the clinician should refer them to their physicians and postpone implant surgery until control is obtained.
Site Assessment
In addition to taking a thorough medical history, an examination of the implant site is essential before surgery. The site should be determined by the prosthetic treatment plan, with an ideal wax-up locating the ideal position of the implant-supported restoration. Site evaluation includes a clinical examination and taking radiographs and computed tomography (CT) or cone-beam computed tomography (CBCT) scans. The three-dimensional (3D) radiographs not only can help determine bone morphology and bone density but are invaluable in precisely locating anatomic structures such as the inferior alveolar and mental nerves, incisive canal, and infraorbital and greater palatine nerves. They also can help the clinician more accurately find the anterior and posterior maxillary sinuses and arteries and septa. Computer software systems can then allow simulated implant placement, anticipating and preventing surgical complications, perforation, and damage to nerves or the sinus membranes. Axial sections of CT and CBCT scans can help clinicians detect narrow or irregular alveolar ridges, thus aiding in determining the implant diameter, length, and shape (eg, cylindrical, tapered).
After obtaining 3D scans of the surgical sites, preparation can be made for dehiscences or fenestrations of the bone and augmentation performed prior to or simultaneously with implant placement.
Intraoperative Complications
Suggested treatment for hemorrhage or hematoma, neurosensory disturbances, and implant malposition encountered during surgery is outlined in Table 1.10
An early determination should be made if the implant osteotomy damaged an adjacent tooth. Usually, this can be ascertained with periapical radiographs of the implant after placement. If tooth damage does occur, the patient should be informed and a determination should be made whether the damaged tooth is salvageable (restorable with or without endodontic therapy) or requires extraction. All options should be explained as risks in the initial patient consent.
Early Implant Failure
Implant loss or failure, mucositis, and peri-implantitis are the three most common biologic complications.
An implant failure is classified as an early failure if it occurs during the first year of prosthetic loading or prior to final restoration.11
Surgical Trauma
The earliest of the etiologies is surgical trauma. This usually occurs in more dense bone (Type I) and is due to overheating during placement or overcompression. To prevent both of these, copious chilled saline should be used along with sharp burs when creating an osteotomy. In dense bone, a tap should be used (even with self-tapping implants) to avoid overcompression. Osteotome use should be limited or avoided in dense bone, especially with press-fit implants. Dense cortical bone also presents less vasculature and may require longer healing periods. This placement protocol should be followed with all implant systems whether surgery is performed flapless or with flap reflection. Decreasing the times of the abutment connection/disconnection has been shown to minimize bone loss around the implant.12 The immediate use of a definitive abutment using the One Abutment - One Time™ (Zimmer Dental, www.zimmerdental.com) concept was shown to preserve the biologic width and minimize physiologic bone loss.13
Occlusal Overload
Another cause of early implant failure is occlusal overload. Occlusion should be checked in provisionals and final restorations using marking film and occlusal indicator wax. Large cantilevers should be avoided, especially in posterior areas. Although the relationship between implant failure and crown-to-implant ratios (particularly on short <10-mm long implants) is a debated topic. A literature review indicated that although the crown-to-implant ratio should not be considered a cause for biologic complications or implant failure, crown-to-implant ratios greater than or equal to 1.5 were associated with mechanical complications such as screw and abutment loosening. Increasing ratios to 2.0 or more was considered a possible cause of posterior abutment fractures.14 Based on these findings, an underengineered case (too few implants) should be avoided.
Another possible etiology of overload is parafunction. Because it appears that bruxism and clenching may be more likely to affect the prosthesis and cause mechanical complications, construction of a night guard prior to surgery is recommended.
Late Implant Failure
Late implant failure can be defined as those that occur after the implant integration and final placement of the prosthesis. The main causes of late implant failure include occlusal overload and peri-implantitis.15
Occlusal Overload
As with early implant failure, implant overload is hard to define and diagnose. It depends on load magnitude, direction, frequency, and duration. Typical indicators of overload include fracture of a porcelain crown, overdenture, or abutment screw, as well as peri-implant bone loss. The treatment of fracture is to remove the crown, screw, or overdenture and replace them. However, the cause of the problem (eg, poor occlusal scheme, underengineered case, bruxism) should be addressed in conjunction with replacement of the fractured screws or prosthesis.
Although a fractured implant may be submerged (buried) and not used to support a prostheses, if there are enough abutments, the most common treatment for a fractured implant and a failing implant that is not mobile is implant removal. This should be performed using an atraumatic method whenever possible.16 The least traumatic method to remove an integrated implant should employ a counter torque ratchet. Special ratchets are available that can be cut to fit into any intact internal connection and can be used to reverse torque the implant. If this fails, the use of piezo tips or thin, sharp diamond burs to remove mesial and/or distal bone will allow reverse torqueing of the implant with little additional removal of bone.
Peri-Implantitis
Peri-implantitis is an inflammatory disease of the soft tissues surrounding an implant, with clinical signs of bleeding on probing (and/or purulence), increased probing depths, and loss of bone that exceeds normal physiologic remodeling.17 Its primary etiology has been attributed to bacteria.18,19 A recent systematic review of the prevalence of peri-implantitis concluded that after 10 years in function, approximately 10% of implants and 20% of patients had peri-implantitis.20 Although a number of reviews have been written on the treatment of peri-implantitis, one of the most recent stated that although “available evidence does not allow any specific recommendations for the therapy of peri-implantitis, successful treatment outcomes at 12 months were reported in the majority of the patients in seven studies.”21 All reviews agree that the earlier the disease is diagnosed and treated, the more predictable the outcomes.
Decision trees have been proposed for the treatment of peri-implantitis.22 However, reviews of the treatment protocols have documented nonsurgical therapy as being inadequate for managing peri-implantitis.23 Although a number of surgical interventions are being used to treat peri-implantitis, differences in definition of the initial disease, treatment protocols, and outcomes make comparisons difficult.
One aspect present in all successful treatment protocols is implant surface decontamination. However, two recent literature reviews, which presented an overview of methods to detoxify the implant surface, have not determined the superiority of one over the others.24,25 Methods of surface decontamination include mechanical debridement followed by saline or chemicals (eg, H2O2, tetracycline), lasers, air powder abrasives, or combinations of the above. A recent case series using a combination approach has reported predictable positive outcomes.26 The protocols were used to treat 170 peri-implantitis-infected implants in 100 patients. The technique included surface decontamination using air powder abrasives with glycine powder followed by use of saline alone. Chemicals including tetracycline, minocycline, or chlorhexidine followed by saline sprays were also used. Treatment of the defects utilized a guided-bone replacement approach with a xenograft and/or allograft with two biologics: enamel matrix derivative and platelet-derived growth factor. The grafts were covered with a resorbable collagen membrane (if keratinized tissue was present) or a subepithelial connective tissue graft (when keratinized tissue was lacking). All flaps were coronally positioned. Similar techniques using various materials for surface decontamination and defect fill have been used but none have reported similarly high numbers of implants or length of follow-up. A peri-implantitis-infected implant that cannot be treated should be removed (using the same atraumatic protocol mentioned previously) and the site augmented with grafted bone, if necessary.
Other Common Complications
Prosthetic or mechanical complications (eg, screw loosening; fracture of screw, abutment, or prosthesis) are also common implant complications. Implant fracture and fracture of restorative materials are usually caused by poor occlusion or implant overload. The treatment of these has been previously discussed. However, detailed discussion of the treatment of implant fractures and complications related to nonoptimal dental implant placement can be obtained in a recently published textbook.27-29
The last of the common complications involves implant esthetics, with the most common cause being implant malposition. Treatment varies from prosthetic ingenuity to surgical removal of the implant. Use of angulated abutments, suprastructures, and/or overdentures may allow retention of a malposed implant. However, the use of pink porcelain or pink composite may leave a patient disappointed with the esthetics.
Conclusion
Many factors must be considered before surgery for implants to help stave off the risk for complications and implant failure. Understanding the nature and types of complications that can occur and detailed preparation are essential for improving the likelihood for success. With prudent precautions such as the patient having well-controlled medical conditions or taking drug holidays from certain medications (under a physician’s supervision), proper imaging, and careful implant planning, the risk for complications can be minimized.
Author Information
Stuart J. Froum, DDS, is recognized as a leading authority on gingival health, periodontal disease diagnosis and treatment, and dental implant placement. He has published more than 130 articles in highly regarded peer-reviewed scientific journals and books. Dr. Froum is the editor of a recently published book, 2nd edition of Dental Implant Complication (published Wiley Blackwell). Dr. Froum is a past president of the American Academy of Periodontology and serves as clinical professor and director of clinical research at the department of periodontology and implant dentistry at New York University Dental Center. He has more than 35 years of surgical experience.
Disclosure
Stuart J. Froum, DDS, has no relevant conflicts of interest to disclose.
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