Enhancement in knowledge about oral hygiene measures and regular visits to dental practitioners have decreased tooth loss, and there is a notable shift toward more partially edentulous patients than completely edentulous patients.¹ Implant-supported restoration provides a predictable restorative option for partial edentulism.² The long-term success of restorative treatment depends not only on the osseointegration of the implant but also on the prosthetic factors that may affect peri-implant health and esthetics.³ Consequently, to facilitate the decision-making process regarding the choice of prosthesis type, clinicians seek evidence-based clinical data that provide insights into the survival rates and complication rates associated with each restoration type.⁴

Many restorative materials are being introduced for implant-supported prostheses. Among these materials, metal ceramic has long been considered the gold standard due to its exceptional strength and mechanical stability.⁵ However, prolonged use shows mucosal discoloration and occasional allergic reactions, making it a less favorable choice for restoration than all-ceramic restorations.⁶ All-ceramic restorations provide superior esthetics in comparison to metal-ceramic restorations. It also requires much less tooth reduction and can be fabricated more rapidly with digital workflow.⁷

In the past, all-ceramic restoration was primarily indicated for the anterior region and single-unit crowns, owing to its limited strength and mechanical instability. Recent advancements, including the development of various all-ceramic materials such as lithium disilicate, leucite-reinforced glass ceramic, alumina, and zirconia, alongside notable improvements in computer-aided design and computer-aided manufacturing (CAD-CAM) technology, have rendered it suitable for use in the posterior areas and for multiunit fixed dental prostheses (FDPs).⁸

In the pursuit of the ideal esthetic restorative material, numerous all-ceramic restorations were introduced. Still, due to zirconia's excellent mechanical and biocompatible properties, it has been extensively used for single- and multiple-unit FDPs. Initially, zirconia was employed as a core material, however, due to its increased opacity was veneered with feldspathic or leucite-reinforced feldspathic porcelain. Nonetheless, the core–veneer interface presented as one of the weakest aspects of these restorations; hence, ceramic chipping or cracking is possible due to an incompatible coefficient of thermal expansion (CTE) between core and ceramic materials or inadequate adhesion of the veneering material to the core.⁹ To address these concerns, innovative ceramics, like monolithic zirconia crowns, have emerged to minimize the risk of such catastrophic failures.¹⁰

Zirconia ceramic is a polycrystalline material characterized by an arrangement of metal–oxygen ionic bonds without a glassy phase, rendering it structurally robust.¹¹ It is a polymorphic material as it exists in three forms: monoclinic, tetragonal, and cubic. The tetragonal phase is mechanically most stable. Notably, zirconium oxide elicits a minimal tissue reaction and demonstrates less inflammatory infiltrate and bacterial adhesion, thereby establishing its superior biocompatibility in comparison to other restorative materials.⁹

Chipping, a common mechanical complication affecting approximately 10%–15% of ceramic restorations, often arises due to the mismatch of CTE between the zirconia ceramic core and the veneered ceramic layer.¹² Clinically, chipping is classified into three grades based on the type of repair required: Grade I (slight chipping treated by surface polishing), Grade II (moderate chipping treated with composite resin), and Grade III (severe chipping exposing the zirconia core that requires replacement of prosthesis).⁵,¹³ Zirconia restorations are typically fabricated using the CAD-CAM technique, employing either hard machining, which involves milling the fully sintered zirconia block, or soft machining, where presintered blocks are milled, typically trimmed 25% larger.¹⁴

In a previous systematic review, Lemos et al.¹⁵ conducted a comparison between ceramic and metal-ceramic implant-supported prostheses, encompassing both single- and multi-unit prostheses. The study concluded that both types exhibited similar rates of mechanical and biological complications, as well as comparable prosthesis survival rates. In the present systematic review, our aim was to assess the survival rate and mechanical complications associated with zirconia ceramic, in comparison to metal-ceramic implant-supported multiunit FDPs.

The systematic review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. The study was registered with the International Prospective Register of Systematic Reviews database having registration number CRD42021278891. Inclusion criteria comprised studies that directly compared metal-ceramic and zirconia-ceramic implant-supported multiunit FDPs within the same study, with a minimum period of 1-year follow-up. The review included randomized controlled trials (RCTs) and retrospective studies. Excluded studies encompassed in vitro and animal studies, those assessing only one type of material without direct comparison, case series, case reports, studies with fewer than 10 patients, and studies focusing solely on implant-supported single crowns.

A review question was designed on the criteria of population, intervention, comparison, and outcome: “In partially edentulous patients undergoing rehabilitation with implant-supported multiunit FDPs, do zirconia-ceramic FDPs demonstrate the comparable rates of mechanical complications and prosthesis survival compared to metal-ceramic FDPs?” The population (P) consisted of partially edentulous patients rehabilitated with implant-supported multiunit FDPs, and intervention (I) was zirconia-ceramic FDPs, comparison (C) with metal-ceramic FDPs. The outcomes (O) were the mechanical complication and prosthesis survival rates.

Criteria for study selection

Two independent reviewers (GS and NT) searched in online databases, including MEDLINE (PubMed), Scopus, and Cochrane, up until December 2022, using a set of predefined keywords such as “dental implant,” “zirconia,” “zirconia-ceramic,” “metal-ceramic,” “survival,” and “complication.” Any disagreement between the reviewers was resolved by a third reviewer (SP). Furthermore, a meticulous hand search was performed in prominent dental journals such as The Journal of Prosthetic Dentistry, The Journal of Indian Prosthodontic Society, The International Journal of Prosthodontics, The Journal of Prosthodontics, and Clinical Oral Implant Research, to ensure no relevant articles were overlooked. In addition, the search was supplemented by screening the references of the included studies for any additional pertinent literature.

Search strategy

(((dental implant[Title/Abstract]) OR (implant[Title/Abstract])) AND ((((zirconia[Title/Abstract]) OR (all ceramic[Title/Abstract])) OR (metal free ceramic[Title/Abstract])) OR (zirconia-ceramic[Title/Abstract]))) AND ((metal-ceramic[Title/Abstract]) OR (porcelain-fused-to-metal[Title/Abstract])).

Risk-of-bias assessment

Risk-of-bias assessment was done using the Cochrane risk-of-bias tool for RCTs Figure 1 and Figure 2, and the Risk of Bias in Nonrandomized Studies-of Interventions (ROBINS-I) tool was used for retrospective studies. The bias analysis is depicted in Table 1.Figure 1

Risk-of-bias assessment of included studies using the Cochrane collaboration tool for risk of bias.

Initially, 818 studies were identified from different electronic databases PubMed – 141, Scopus – 579, and Cochrane – 98. Duplicate studies were removed. Five hundred and eighty-six studies were excluded after screening the titles and abstracts. Both investigators further evaluated 25 full texts. After going through the full text, only six studies (four RCTs¹⁷,¹⁸,¹⁹,²⁰ and two retrospective studies¹²,¹⁶) fulfilled the inclusion criteria and were included in this systematic review Figure 3.Figure 3

The PRISMA flowchart for literature search.

The present systematic review and meta-analysis compared the metal-ceramic and zirconia-ceramic implant-supported multiunit FDPs regarding mechanical complications and survival rate. The study sought to aid clinicians in selecting the most suitable restorative material, considering reduced mechanical complications and a high survival rate. To minimize bias, only studies directly comparing multiunit FDPs were included. The meta-analysis results notably favored metal-ceramic restorations over zirconia ceramic, with the inadequate thickness of both the core and veneer ceramics identified as a key factor contributing to chipping in zirconia-ceramic restorations.¹⁷ Notably, an increase in veneer thickness does not necessarily improve fracture resistance and can compromise the substructure by reducing core thickness. Grade I chipping (minor chipping) was significantly more prevalent in the ceramic group, potentially attributed to the bonding interface between zirconia copings and veneering ceramic. Consequently, zirconia restorations necessitate more meticulous polishing and maintenance compared to their metal-ceramic counterparts.

In a previous systematic review,²¹ where a direct comparison was not made within the same study, the reported survival rate for implant-supported FDPs was 95% after 5 years and 86.7% after 10 years of function. In our study, the survival rate for implant-supported FDPs was notably higher at 96.77%. Notably, the previous study recorded a higher incidence of mechanical complications, amounting to 38.7% for implant-supported FDPs, compared to the 19.17% observed in our study. These findings highlight the enhanced longevity of restorations, which can be attributed to the recent advancements in CAD/CAM technology and ceramic materials.²²,²³ Schönberger et al. demonstrated the improved precision of fit for frameworks milled from semi-sintered regular zirconia and high-translucent zirconia blanks using two different CAD/CAM systems (Cercon/Ceramill).²³

The meta-analysis findings indicated no significant difference in the survival rates between metal-ceramic and zirconia-ceramic restorations. Various factors were identified as contributors to prosthesis failures, encompassing loss of implant due to peri-implantitis, issues related to cement excess, inadequate marginal adaptation, compromised retention, and substantial fractures affecting prosthesis maintenance.¹⁷ Notably, the orientation of the loading force on the prosthesis, particularly lateral and oblique forces, generates tensile stresses that can weaken the substructure and result in chipping.²⁰ The design quality of the prosthesis also plays a crucial role in determining the risk of fracture, considering the absence of a periodontal ligament to absorb shock. When zirconia is used as a core material, the maximum intercuspation factor emerges as a critical determinant of restoration survival. Employing a pressed form for veneer application has shown promise in reducing chipping, as it minimizes porosity and provides a compact structure within the prosthesis.

Considering the limitation of the study, one of the included studies¹⁸ had a follow-up period of only 1 year, although a more extended period is necessary for assessing the prosthesis survival rate. In addition, marginal bone loss was identified as a significant factor influencing implant survival, with the zirconia-ceramic group demonstrating less marginal bone loss when compared to the base metal alloy.¹⁸ The data suggested that while metal-ceramic restorations exhibited fewer mechanical complications than zirconia ceramic, the performance of the material was also influenced by various parameters, including the connector's height and radius of curvature.¹⁹

While metal-ceramic multiunit implant-supported prostheses exhibited fewer mechanical complications than their zirconia-ceramic counterparts, no significant difference was observed in terms of the prosthesis survival rate between the two. Consequently, both treatments prove to be viable options for long-term implant-supported prostheses. It is important to note that the material of the coping alone cannot be held solely responsible for ceramic fractures. Various factors contributing to chipping include the adhesion interface, implant angulation, and the presence of high occlusal points. In addition, the design, quality, and veneer ceramic thickness also play a crucial role in determining the susceptibility to restoration chipping. The presence of marginal gaps can potentially harm the soft tissues surrounding the implant. Notably, zirconia-based FDPs demonstrated significantly improved marginal fit, highlighting their potential superiority in this aspect.

Financial support and sponsorship

Nil.

Conflicts of interest

The authors of this manuscript declare that they have no conflicts of interest, real or perceived, financial or non-financial in this article.