Stock and Customized Abutments Supporting Implant Restorations: Current Aspects and Future Perspectives of Biological and Mechanical Complications

Dental implantology has advanced significantly in the last few decades, transforming restorative dentistry and providing patients with better oral health, appearance, and quality of life. Custom abutments, one of the essential elements of implant-supported restorations, have drawn a lot of interest due to their capacity to offer exact and customized solutions to satisfy the various needs of individual patients.

Custom abutments are made with greater customization and flexibility than typical stock abutments thanks to the use of computer-aided design and manufacturing (CAD-CAM) technologies. Custom abutments are painstakingly built based on digital scans or imprints of the patient’s implant site, allowing for optimal fit, function, and esthetics. This is in contrast to stock abutments, which are prefabricated and come in predefined forms and sizes. Based on this, the current editorial’s goal was to critically examine the evidence-based literature about stock and custom abutments in dental implantology. We will pay particular attention to important topics such as their cost-effectiveness, complications, clinical applications, esthetic results, functional performance, and design concepts as well as production methods.

According to the results of a recent retrospective analysis [1], single and multiple cement-retained posterior implant-supported restoration employing customized CAD/CAM titanium abutments showed a high survival rate at up to 10-year follow-up, and there were no statistically significant differences when implant position, implant diameter, implant length, single versus multiple unit dental implant restoration, and dental arch were compared. For the 67 single-unit and 129 multiple-unit posterior implant-supported restorations analyzed, four mechanical complications were recorded: two cases of screw loosening, one case of chipping or fracture of veneering materials, and one case of crown decementation. No screw or abutment fractures were observed. Otherwise, another retrospective study showed that of the 172 single posterior implant restorations supported by stock titanium abutments [2], 14 mechanical complications (8.2%) were recorded. In particular, three abutment fractures, two screw loosenings, two screw fractures, one implant fracture, two chipping/fractures of veneering materials, and four decementations of the superstructure occurred. However, the conclusion was that single posterior implant-supported restorations using prefabricated titanium abutments remain a clinically acceptable treatment in terms of prosthetic procedure and cost-effectiveness [2].

A recent study by Schepke et al. [3] showed that there is no discernible difference in the fracture toughness of the CAD/CAM zirconia abutments compared to their pristine copies. In contrast, the stock zirconia abutments exhibited a significant reduction in fracture toughness, despite the fact that the maximum fracture toughness values were still greater than the 250 N human chewing force. However, only a conical connection in the anterior zone allowed for a good fit and stability with zirconia abutments; using zirconia abutments in the posterior area and an internal hexagon connection is not advised [4].

Furthermore, compared to a whole zirconia abutment, abutments with titanium inserts exhibited greater fracture resistance. The zirconia abutments’ fracture patterns are impacted by titanium implants. The likelihood of a horizontal fracture surface increases with the presence of titanium reinforcement in the event of a fracture. If titanium inserts are not used, the likelihood of an oblique fracture increases. Additionally, the titanium insert shields the implant–abutment link by keeping the zirconia abutment’s buccal fracture surface away from the implant platform [5].

Recent in vitro investigations assessed the one-piece CAD/CAM zirconia abutments’ static load fracture resistance in comparison to stock zirconia abutments, demonstrating that one-piece CAD/CAM zirconia abutments have lower static fracture loads than their stock counterparts [6,7].

Furthermore, two-piece CAD/CAM zirconia abutments are a comparable substitute for titanium abutments in a single-implant restoration in the anterior area, and dynamic loading can increase the fracture resistance of zirconia abutments [8]. Compared to two-piece CAD/CAM zirconia abutments and titanium abutments, one-piece CAD/CAM zirconia abutments offered less advantageous mechanical properties in fracture stresses. Similarly, two-piece CAD/CAM zirconia abutments with an internal hexagonal connection showed a higher fracture resistance than single-piece CAD/CAM zirconia and stock zirconia abutments, according to research by Schepke et al. [9] and Gehrke et al. [10]. Based on these findings, single premolar and molar tooth replacements, which are high-load locations, may benefit clinically from two-piece abutments.

On the other hand, screw-retained implant crowns based on CAD/CAM zirconia abutments with a conical connection demonstrated excellent clinical performance, suggesting their use for the replacement of missing anterior teeth and premolars, according to a prospective cohort study by Fonseca et al. [11], which had a follow-up of 4.5–8.8 years.

Moreover, CAD/CAM zirconia abutments and stock titanium abutments can both withstand functional forces when the implant–abutment interface is evaluated following the dynamic loading of conventional titanium abutments. The microgap values at this interface are comparable to one another [12].

In relation to peri-implant soft tissues, Lops et al. [13] demonstrated that, in restorations supported by stock abutments—both for titanium and zirconia abutments—the mean papillary recession index (REC) was higher than for CAD/CAM abutments. After two years of follow-up, a slight papilla regrowth was also observed.

All prosthetic parameters, including the emergence file, thickness, finish line position, and outside shape, are adjustable thanks to CAD/CAM abutments [14]. For these reasons, a CAD/CAM abutment could prevent excessive papilla compression and enhance papilla support [14]. Furthermore, because titanium and zirconia are biocompatible, the type of abutment material had no discernible impact on the degree of papillary recession in either stock or CAD/CAM abutments [15].

Paek and colleagues demonstrated that there is no discernible difference in screw loosening between the titanium stock abutment and titanium CAD/CAM abutment following 5000 cycles of cyclic loading, with a force ranging from 10 N to 250 N. This indicates that the CAD/CAM abutment’s connection to the fixture is just as stable as the stock abutments [16]. Nevertheless, it is important to keep in mind that the dynamical force used in the aforementioned research [16] ranged from 10 N to 250 N, which is significantly less than the masticatory forces that humans can apply, which range from 300 to 500 N [17]. Thus, more research is being conducted in order to assess how CAD/CAM abutments behave mechanically when subjected to maximum load scenarios. Apicella et al., analyzing the fit using radiography and scanning electron microscopy (SEM) in order to determine the precision of the implant–abutment connection between the CAD/CAM and stock abutments, indicated that the fit achieved with CAD/CAM abutments was comparable to that of the stock abutments [18].

Compared to CAD/CAM titanium abutments, in vitro investigations on stock titanium abutments revealed a noticeably larger volume of material involved in the implant–abutment interaction [19]. Actually, compared to a CAD/CAM abutment attached to the same implant system, the frictional fit obtained with the stock abutment is superior [20].

Additionally, it has been noted that there are no appreciable differences between zirconia CAD/CAM abutments and titanium stock abutments when it comes to micromotion at the implant–abutment interface, which is a major factor in determining the success of an implant over the long term. This is because excessive micromotion can lead to technical issues such as screw loosening and a subsequent fracture [21].

According to the most recent research, there are more mechanical and esthetic benefits to using CAD/CAM abutments than stock abutments [22].

With CAD/CAM abutments, the clinician can customize the abutment parameters for implant rehabilitation while still preserving the superior mechanical qualities and protecting the soft tissue. Nevertheless, there are still several benefits to using stock abutments, including the possibility of corrosion, the amount of effort and money spent, and the fit of the implant–abutment connection as determined in vitro. In order to give clinicians evidence-based insights into the effectiveness and utility of stock and custom abutments in contemporary implant dentistry, randomized controlled trials, prospective cohort studies, systematic reviews, and meta-analyses are ultimately required. This will help clinicians make more informed decisions and improve patient care.