Implant prosthodontics encompasses a unique blend of biomaterials, biomechanics, and biology, and some amount of failures are inevitable. Though there is a wide range of failures in implant prosthodontics, the most common ones are related to technical complications, most of which can be prevented through proper treatment planning and appropriate choices in material selection and treatment techniques. This article describes the etiology, management, and prevention of the most common complications and failures in contemporary implant fixed and removable prosthodontics.
Key points
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Though there is a wide range of failures in implant prosthodontics, the most common ones are related to technical complications, most of which can be prevented through proper treatment planning and appropriate choices in material selection and treatment techniques. This article will describe the most common complications and failures in contemporary implant prosthodontics.
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Most common complications in fixed implant prosthodontics are porcelain fractures, screw loosening or stripping, residual cement issues, and loss of proximal contact.
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Most common complications in removable implant prosthodontics are wear of attachments, denture fracture, and denture teeth fracture/debonding.
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Thorough treatment planning and use of meticulous technique can prevent some of these complications (such as screw loosening or prosthesis fracture), whereas others (such as proximal contact loss or loss of retention of nylon attachments) may be unavoidable consequences of implant therapy.
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Regular follow-up care is imperative to enhance the long-term success and longevity of implant-supported restorations.
Introduction
Dental implants have become the gold standard for replacing missing teeth, offering superior functionality and esthetics compared to traditional forms of tooth replacement. However, prosthesis-related complications continue to pose significant challenges. These complications can affect the longevity and performance of implant-supported restorations, impacting clinical outcomes and patient satisfaction. , The 3 most catastrophic failures in implant dentistry are implant failure, implant fracture, and prosthesis framework fracture, all of which render the treatment unsuccessful and mandate retreatment. Fortunately, the prevalence of these 3 catastrophic failures is low and has allowed implant dentistry to progress through 5 decades. Though a myriad of additional complications can occur in implant prosthodontics, this article focuses on the most common failures and complications encountered in clinical practice.
Common prosthesis-related issues include screw loosening , and/or stripping, porcelain chipping, proximal contact loss (PCL), , and wear of prosthetic components. Each of these problems can lead to discomfort, compromised function, and/or additional treatment requirements. Understanding the causes and preventive measures for these complications is essential for dental professionals to improve the reliability of implant prosthetics and ensure long-term success. As dental technology and materials advance, ongoing research and clinical vigilance are necessary to prevent and address these complications effectively and enhance the durability and performance of implant-supported prostheses.
Complications with fixed implant-supported restorations
Screw Loosening
Screw-retained restorations have become immensely popular due to digital workflows and simplicity in fabrication. Screw loosening in this type of restorations is a common complication, with reported prevalence rates up to 6%, depending on the type of prosthesis. , However, it is likely that the rate of screw loosening is higher than reported dates in the literature. Although not catastrophic, this can significantly impact the success of implant therapy and patient satisfaction if it occurs repeatedly.
Etiology
Understanding the factors contributing to screw loosening and the methods to mitigate this issue is crucial for improving clinical outcomes. Several factors influence screw loosening, including the type and quality of implant-abutment connection, quality of the impression and restoration, the presence of parafunctional habits, the use of cantilevers, and the type of restoration. The earlier implant systems used external hexagon connections, which, due to their nature of flat-to-flat connection, often experienced higher rates of screw loosening. This led to the development of internal hexagonal and conical connections, which significantly reduced such complications. Additionally, the introduction of torque wrenches to deliver higher torque became a standard protocol.
The mechanism primarily responsible for screw loosening is known as the “settling effect.” Despite the high precision of industrial manufacturing, microscopic roughness remains on the implant and abutment surfaces. When these surfaces come into contact under loading, micromovements cause the rough spots to flatten, resulting in a loss of preload, which is the initial force applied to the screw. Approximately 2% to 10% of the initial preload is lost due to this settling effect, reducing the torque required to loosen the screw. To combat the settling effect, prudent manufacturers provide prefabricated metal bases for abutments, aiming for a smoother and more precise fit. Additionally, polishing tools are sometimes used after fabrication to enhance the fit between the abutment and the implant.
Single crowns are more prone to screw loosening compared to fixed partial dentures (FPDs). Single crowns have to withstand torsional forces alone, whereas FPDs distribute these forces across multiple supports, thereby reducing the load on individual screws. Screw loosening is also prevalent in complete-arch fixed implant-supported prosthesis. Inadequate anterior–posterior spread can result in an uneven force distribution, where excessive loading on certain implants causes micromovements at the implant–abutment interface. These micromovements can gradually lead to the loosening of the retaining screws in these prostheses. Moreover, a lack of passive fit (due to inaccurate impressions or casts) can cause tension and strain in the screws upon tightening, which, combined with functional stresses, leads to a loss of preload over time. This loss of preload diminishes the stability of the prosthesis, increasing the likelihood of screw loosening.
Management
Clinical management of screw loosening varies depending on the type of restoration. In screw-retained restorations, the first choice of treatment is straightforward—removing the filling material from the access hole and retightening the screw or replacing the screw with a new one. Repeated screw loosening in long span or complex prosthesis will require reassessment of the cast and remaking a new impression. However, for cement-retained restorations, the process is more complex. It often involves drilling through the crown to access the screw, which can sometimes necessitate the destruction and replacement of the crown if removal is not possible. A retrieval matrix can be useful in minimizing the damage to the restoration and allows a quicker access to the screw ( Fig. 1 A, B ).
Prevention
Preventive measures are essential for reducing the incidence of screw loosening. These include an accurate impression technique (digital or conventional), using high-quality manufacturer’s abutment and screw (genuine implant components), ensuring accurate fit and alignment during the construction of the restoration, avoiding cantilevers, carefully controlling occlusion to prevent interferences, and selecting high-quality implant components by trusted implant manufacturers. , Additionally, using properly calibrated torque wrenches to apply the manufacturer’s recommended torque and fabricating occlusal devices for patients with bruxism can further mitigate the risk. Lastly, the occlusal scheme used with implant restorations can play a role in reducing the likelihood of screw loosening after delivery. Adjustments such as narrowing the occlusal table, reducing cusp inclination, and ensuring centric contacts have been proposed to help reduce occlusal stress on implants, thus minimizing the risk of screw loosening.
Proximal Contact Loss
PCL between implant restorations and adjacent natural teeth is a common complication in prosthetic dentistry, affecting the functionality and longevity of implant-supported prostheses. , , This issue can lead to various clinical problems, including food impaction, caries, periodontal and/or peri-implant disease, and patient discomfort. , , , , ,
Incidence and etiology
PCL is highly prevalent, with incidence rates varying widely across studies. Recent systematic reviews have indicated that PCL rates can range from 17% to 66%, , , , , with higher rates often observed in the posterior regions, particularly in the mandible. The loss of proximal contact predominantly occurs at the mesial contact points but is not limited to them, affecting distal contacts as well. This condition can lead to significant clinical consequences, such as increased probing depths, bleeding on probing, periodontal defects, and peri-implant complications.
The development of PCL is multifactorial. One primary cause is the natural mesial drift of teeth, a phenomenon where natural teeth gradually move toward the midline of the dental arch over time. This movement is facilitated by the presence of the periodontal ligament, which is absent in implants. As a result, implants remain stationary while adjacent natural teeth continue to drift mesially, leading to the creation of gaps or loss of contact ( Fig. 2 A, B ). Other contributing factors include bone loss on adjacent teeth, increased implant probing depth, changes in occlusion, and tight proximal contacts at the time of restoration placement. , ,
The physics of vibration, elastic and inelastic collisions, and stress waves have also been proposed as potential causative factors for PCL. Vibration generated from occlusal forces on implant crowns can be transmitted to adjacent teeth, causing them to move. This vibration can result from both static forces, such as clenching, and dynamic impact forces during mastication. Stress waves generated from these forces may also contribute to the displacement of adjacent teeth.
Management and prevention
Managing PCL involves preventive and corrective approaches. Preventive strategies include ensuring tight proximal contacts at the time of restoration placement and using retainers or splints to minimize tooth movement after restoration. , , , Additionally, occlusal adjustments to avoid contacts on inclined planes and minimize horizontal forces can help reduce the risk of PCL. Corrective measures may involve re-establishing proximal contacts through the addition of prosthetic material or remaking the restoration. Periodic follow-ups and patient education on maintaining oral hygiene are also crucial.
Porcelain Chipping
Due to the burgeoning growth of monolithic zirconia, porcelain chipping has been significantly reduced in contemporary implant prosthodontics. Nevertheless, where esthetic requirements demand use of veneered porcelain, the risk of porcelain fracture remains.
Etiology
The etiology of porcelain chipping includes factors such as bruxism, occlusal overload, improper occlusal design, mismatched thermal expansion coefficients between porcelain and the underlying framework material (zirconia or metal), and suboptimal bonding techniques ( Figs. 3 and 4 A, B ). Implants, unlike natural teeth, lack of periodontal ligament that can absorb and distribute occlusal forces, making them more susceptible to mechanical stress that can cause porcelain chipping.
Management
Management of porcelain chipping initially involves assessing the extent of the damage. Minor chipping of zirconia-based restorations that do not include occlusal or proximal contact areas and are not an esthetic concern may be repolished using porcelain polishing systems. More extensive fractures may require removal of the prosthesis and a laboratory repair, which may include stripping and reapplying the porcelain (when feasible), or a refabrication of the entire restoration using monolithic zirconia.
Prevention
Preventive strategies include designing restorations with a reduced occlusal table to minimize lateral forces, using materials with compatible thermal expansion properties, and ensuring a proper occlusal scheme that avoids excessive force on the porcelain. Additionally, educating patients on avoiding parafunctional habits such as bruxism can significantly reduce the risk of chipping. Regular follow-up appointments are crucial for early detection and management of any signs of porcelain damage.
Screw Stripping
Screw stripping in implant-supported restorations occurs when the threads of the retaining screw are damaged, typically due to excessive torque or misalignment during insertion.
Etiology
Screw stripping is often attributed to the improper application of torque beyond the manufacturer’s recommended levels, using incompatible tools, or repeated tightening and loosening of the screw, which weakens the threads over time. The consequences of screw stripping include compromised retention of the prosthetic components, increased risk of screw loosening, and difficulty in future maintenance or adjustments.
Management
Management of screw stripping involves careful removal of the damaged screw, which may require cutting a slot into the head of the stripped screw with a thin carbide or diamond bur, and usage of a slotted (flathead) driver for screw removal ( Fig. 5 A, B ); alternatively, specialized screw removal tools can be used, exerting caution to avoid further damage to the implant. It is preferable to use the simplest technique possible to remove a stripped screw. Once removed, the internal threads of the implant should be thoroughly inspected for damage. If the implant threads are intact, a new screw can be used, ensuring proper torque application with a calibrated torque wrench. In cases where the implant threads are compromised, more extensive intervention, such as retapping the threads or even replacing the implant, might be necessary.
