It is known that missing teeth, especially in the posterior area, is associated with temporomandibular symptoms. ¹ Drift and tipping can cause secondary changes in occlusal contact and overall occlusal function. ² For years, edentulous patients have been treated with a removable prosthesis or cantilever bridge. ³ Studies on dental implants have increased dramatically from 1960 to 1980, while dental implants were used only in people with complete edentulousness. With time pass and increasing research, fixed partial dentures (FPDs) supported by free-standing implants were introduced for the treatment of semiedentulous patients. ⁴ In edentulous patients in the posterior molar region, dealing with limited bone mass should be considered; this is due to the presence of important anatomical structures (maxillary sinus or the inferior alveolar nerve), which is why the treatment plan must be designed accurately. ⁵ Linking the implant to the distal-end natural tooth not only reduces the number of implants required to gain sufficient support but also helps preventing the nerve canals or the maxillary sinus from danger, thereby simplifying the surgical procedure. In addition, this approach can help retain the prosthesis with the corresponding proprioceptive periodontal ligament and eliminate the requirement of cantilever bridges. ⁶ The three-unit bridge that combines a natural tooth and an implant provide extended treatment possibilities for partially edentulous patients. Many studies have examined three-unit porcelain-fused-to-metal tooth-implant-supported prosthesis designs. ⁷ , ⁸ Although some researchers revealed that when the FPD was connected to the three natural abutment teeth and an implant, the bone stress level is minimum, ⁹ some revealed the stress distribution in these restorations is significantly unequal, causing the maximum failure rate for the prosthesis. ¹⁰ However, the combination of natural teeth and implants in clinical practice is controversial. Therefore, the purpose of the current study was to evaluate the outcomes and complications of three-unit porcelain-fused-to-metal tooth-implant-supported prostheses and compare them with implant-supported prostheses.

Search strategy

The present study is a systematic review and meta-analysis. Preferred Reporting Items for Systematic Reviews (PRISMA) was followed meticulously. ¹¹ PICO strategy to answer the research question was formed as following: (it has to be mentioned that in the present study the word “complication” refers to when FPDs have been subjected to at least one technical modification (like reintegration, repair of veneer fracture or fracture of frame) and failure implies the situation that prosthesis or implant cannot be modified, and there is a necessity to exclude the whole part.)

P: Individuals with FPDs

I: Tooth-implant-supported FPDs

C: Implant-supported prostheses

O: Failure rate, complication rate

PRISMA protocol consists of five stages: systematic literature search, study selection, data evaluation, data extraction, and data classification. To achieve the overall aim of the study, in the first step, the studies published in the databases of PubMed, Scopus, Web of Science, and EBSCO until December 1, 2021, were reviewed. A software program (Endnote X7, Thomson, Reuters, New York, USA) was used to manage electronic titles.

Search structures were performed using mesh terms:

(((((“Mouth, Edentulous” [Mesh] OR “Jaw, Edentulous, Partially” [Mesh] OR “Jaw, Edentulous” [Mesh]) OR “Failure of Tooth Eruption, Primary” [Supplementary Concept]) AND “Dental Prosthesis, Implant-Supported” [Mesh]) OR (“Prosthesis Design” [Mesh] OR “Dental Prosthesis Design” [Mesh])) AND “Treatment Outcome” [Mesh]) AND “complications” [Subheading].

Selection criteria

Inclusion criteria

Randomized controlled trial studies, controlled clinical trials, prospective and retrospective cohort studies, and treatment using a combination of tooth-implant-supported prosthesis were included in the study.

Exclusion criteria

In vitro studies, case–control studies, case reports and reviews, single crown, and multiunit prostheses were excluded from the study.

Data extraction and analysis method

Data extracted from the studies included years, study design, number of patients, number of prostheses and implants, number of teeth, and prosthesis design. To extract the data, two-blinded and independent reviewers extracted the data from the abstract and full text of the studies. Before screening, kappa statistics were performed to confirm the level of agreement between the reviewers. Kappa values were higher than 0.80.

The ROBINS-I was a tool developed to assess the risk of bias in the results of nonrandomized studies that compared the health effects of two or more interventions. ¹²

Risk ratio with 95% confidence interval (CI), fixed effect model, and Mantel–Haenszel formula were calculated. Random effects were used to deal with potential heterogeneity and I ²showed heterogeneity. I ²values above 50% signified moderate-to-high heterogeneity. The meta-analysis was performed using the statistical software Stata/MP v. 16 (The fastest version of Stata, StataCorp, California, US).

A total of 218 articles were found in the initial search. After removing duplicates, entry criteria were applied to the titles of the remaining 203 articles, and an abstract of the remaining articles was reviewed. In this step, 187 articles were excluded from the study. Then, the full text of 16 articles was reviewed, and 11 articles were excluded due to the lack of access to the full text of the article and not being relevant to the title and purpose of the article. Eventually, five studies were selected Figure 1. Figure 1

Flowchart of the literature search and selection criteria

One of the most challenging issues in linking a tooth to an implant is the mobility between the tooth and the implant (10-fold difference). Based on previous studies, when implanting, bending moment with a cantilever effect might be generated under loading force. ⁷ The aim of the current systematic review and meta-analysis study was to evaluate the outcomes and complications of three-unit porcelain-fused-to-metal tooth-implant-supported prostheses in comparison with implant-supported prostheses.

In the present study, no significant difference was observed between the group of three-unit porcelain-fused-to-metal tooth-implant-supported prosthesis and the group of implant-supported prosthesis reconstruction. Meta-analysis showed that both groups were almost similar in overall failure and complication rate of prosthesis and implant. However, a small difference was observed in overall prosthesis failure rate in the three-unit porcelain-fused-to-metal tooth-implant-supported prosthesis group (5.64%) and the implant-supported prosthesis group (5.70%). Moreover, the difference in overall implant failure rate and complication rate in the two groups was not statistically significant

A 4–5 year follow-up study revealed that FPD loss happened similarly in both tooth-implant-supported and implant-supported prosthetics but porcelain fractures occurred more on implants. ¹⁷ In total, clinical outcomes of tooth-implant-supported FPDs were acceptable in such follow-up duration. The findings of the present study are in consistent with mentioned study. Nickenig ¹⁸ reported that implant-supported FPDs technical complications are primarily related to the bridge design. As the use of rigid connectors reveals favorable outcomes in both tooth-implant-supported FPDs and implant-supported FPDs. According to Pratheep et al., when teeth and implants are linked, the FPD pontic should be as short as possible and should not be more than three units. They concluded that the bite force distribution and stress affect the result more than the connector. ⁸ It has been shown that repeated load fatigue is a reason for tooth-implant-supported prosthesis failure. To prevent overload, the number of implants should be increased and the bridge span distance should be reduced, so less load is placed on the tooth and more load is directed to the implant. This approach may optimize the distribution of stress in the system and reduce complications. ¹⁹ One of the limitations of the present study is the lack of randomized clinical trials in the meta-analysis. Further studies in this area, especially randomized clinical trial studies with long follow-up periods and higher sample sizes are required to provide sufficient evidence.

Current meta-analysis shows that there is no significant difference between the two groups (three-unit porcelain-fused-to-metal tooth-implant-supported prosthesis and implant-supported prosthesis reconstruction) in terms of the total failure of implants and prostheses and the complication of implants and prostheses. The findings show that in the implant-supported prosthesis reconstruction group, the rate of total prosthesis failure and the complication of implant and prosthesis complications are higher, whereas the rate of implant failure in the three-unit porcelain-fused-to-metal tooth-implant-supported prosthesis group was higher. Free-standing implants are used in patients who have lost their posterior teeth. To preserve natural teeth and reduce the complications of implant surgery, using a prosthetic treatment plan that can attach natural teeth to the implant can be another effective treatment option.

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 nonfinancial in this article.