(a) Preoperative condition. (b) Post-operative condition—maxillary and mandibular full-arch fixed implant-supported prostheses
The first misconception is that this treatment is a single procedure. Although marketed to be an efficient approach to address multiple dental problems in a single session, this is an oversimplification. Like most prosthodontic treatments, it is a process rather than a single procedure. There are five clearly defined phases of treatment and each has its own intricacies and challenges. These include the diagnostic phase, surgical procedure, transitional prosthodontic phase, definitive prosthodontic phase and maintenance phase. And, in order to achieve overall success, practitioners must be able to identify, prevent and address complications that may arise in each phase.
The second misconception is that this treatment is mainly a unique surgical technique. Although made popular by the novel use of tilted implants and ability to avoid grafting procedures , the fact remains that this is a prosthodontic treatment with a strong surgical component. This is important to recognize because the surgical intervention, which can be highly successful, can also result in considerable prosthetic complications. This will be emphasized in the discussion of the planning and surgical phases of care.
Additionally, another misconception is that biologic and prosthetic complications are mutually exclusive. Biologic complications are defined as those that relate to dental implant osseointegration, bone-level changes and soft-tissue responses. Prosthetic complications , on the other hand, are typically defined as treatments, adjustments, repairs or replacement of the implant prostheses . However, this dichotomy was conveniently created to simplify the reporting of complications. In fact, an interplay exists between prosthetic and biologic complications. Improper prosthesis contours, for instance, can result in soft-tissue inflammation.
Lastly, a final clarification regarding prosthetic complications is that the material selected for the fabrication of the prosthesis will play an important role. Owing to the longevity of its use, the metal-acrylic prosthesis is by far the most studied type of full-arch fixed implant-supported prosthesis . While other materials such as metal-ceramic and zirconia have been utilized, their outcomes have been less frequently reported and have shorter follow-up periods . Metal-acrylic prostheses are the most common and remain the benchmark to which other prostheses are measured. As such, these will be the focus.
14.2 Prosthetic Complications in General
The simplest approach to present prosthetic complications is to review the findings of the overall treatment process. Within the past few years, three systematic reviews [9, 11, 12] have been published that synthesize the evidence of prospective studies that examine complications with metal-acrylic full-arch fixed implant-supported prostheses.
In general, these prostheses have favourable outcomes with survival rates that range from 93 to 100% after 5 years and 82 to100% after 10 years . Yet, many different kinds of prosthodontic complications can occur. These can be categorized as being either structural, cosmetic or functional . Structural complications pertain to issues with mechanical and technical aspects of the implant components and prostheses, while aesthetic and functional complications are related to patient-specific factors.
Aesthetic and functional complications , on the other hand, have been less reported because of the subjective nature of their assessment. Historically, patients have reported very high satisfaction with their prostheses, particularly if they had experience with removable dentures . In the studies included in the systematic reviews, a very low incidence of patients (2% complication rate)  found their prostheses unsatisfactory in terms of form, function and aesthetics. Recent surveys also indicate that these prostheses typically satisfy patient’s expectations .
Phonetics , however, is one of the more common functional complications reported . This was particularly apparent in the past when prosthetically driven implant placement was not as mainstream. Hence, implants would be placed outside the intended confines of the prosthesis, resulting in irregular lingual contours of the prosthesis, which are less conducive to smooth articulations with the tongue. Furthermore, this scenario has also been reported more commonly in patients with long-standing complete edentulism that have grown accustomed to complete palatal coverage.
It should be noted that while many prosthetic complications are inevitable and result from material limitations, others result from iatrogenic errors in planning and execution. The complex nature of the procedure is such that significant clinical experience is required to avoid complications . It is very possible that studies report low complication rate with aesthetics and function simply because these are conducted in experienced centres with experts performing the treatment.
14.3 Prosthetic Complications in Each Phase of Treatment
As previously discussed, the steps in the treatment process include the diagnostic phase, surgical procedure, transitional prosthodontic phase, definitive prosthodontic phase and maintenance phase. Each of these phases has key factors to consider in order to reduce the incidence of structural, aesthetic and functional prosthetic complications.
14.3.1 The Diagnostic Phase
The importance of this phase cannot be overemphasized. It entails carefully examining the patient and gathering a series of detailed records, including photos and mounted casts, in order to facilitate the key decisions that will impact the final prosthodontic result.
Complications arising from this phase are iatrogenic in nature. They will lead to a suboptimal prosthesis from either a mechanical or an aesthetic perspective. They typically arise from the failure to recognize one or all of the following four main patient features: occlusal vertical dimension, transition zone relative to the smile line, lip support and centric relation position.
22.214.171.124 Occlusal Vertical Dimension and Restorative Space
As mentioned previously, the most commonly used material for fixed implant-supported prostheses is acrylic/resin. One drawback is that this is a generally weak material and derives its strength from bulk. As a result, ≈12–15 mm of restorative space is required per arch. Otherwise, the prostheses will have higher chances of fracturing.
As a result, in most scenarios, there is a need to create the necessary restorative space. This can be achieved in two ways: surgical reduction of the alveolar ridge or increase in vertical dimension of occlusion (OVD). In many cases, a combination of the two must be performed, but it is not always possible.
Therefore, a determination of the patient’s occlusal vertical dimension (OVD) is crucial. If there is a loss of OVD, then there is the potential to gain restorative space by increasing the OVD. If there is no loss of OVD, then the only method to create restorative space is to reduce the alveolar ridge. This too may not always be feasible because, on occasion, the necessary alveolar ridge reduction results in inadequate remaining bone for the placement of dental implants [18, 19].
126.96.36.199 The Transition Zone
The transition zone is the prosthesis-gingival junction. In a non-posed smile, if the transition zone is revealed, then additional alveolar ridge reduction must be performed at the time of surgery. This is true even if there is adequate restorative space for the fixed prosthesis. Otherwise, the contrast from synthetic pink acrylic and natural pink gingiva will be evident and this will result in a highly suboptimal aesthetics.