Evaluation of the Differences in the Stability of Alveolar Bone around Dental Implant and Implant Failure between Platform Matching and Platform Switching: A Systematic Review and Meta-Analysis

Abstract

Background: This research was designed to carry out a meta-analysis in order to evaluate the dissimilarities in the stability of alveolar bone round dental implants and implant failure between platform switching (PS) and platform mating (PM). Methods: The investigation utilized a comprehensive search strategy that incorporated controlled vocabulary (MeSH) and free-text terms. This search was performed by two reviewers to identify published systematic reviews. Three major electronic databases, including Medline via PubMed, the Cochrane database, and Embase, were searched up to November 2023. Results: Initially, 466 articles were identified, but only twelve studies met the criteria for inclusion in the meta-analysis. The results showed that the pooled mean difference for reducing marginal bone loss (MBL) was −0.60 (95% confidence interval (CI), −0.91 to −0.28; p < 0.01). A sensitivity analysis was conducted by excluding a single study, which yielded a result of −0.46 (95% CI, −0.66 to −0.25; p < 0.01). The test for overall effect was significant (p < 0.01), and it revealed that there were significant differences between subgroups. However, the meta-analysis on implant failure did not show a significant difference between PS and PM implants. Conclusions: In conclusion, the study found that PS implants are more effective in reducing MBL compared to PM implants. Nevertheless, no significant difference was observed in the long-term effectiveness of reducing MBL and implant failure rate.

1. Introduction

The use of platform matching in implant dentistry entails selecting an abutment with a diameter identical to that of the implant platform. On the other hand, the platform-switching approach involves using an abutment with a smaller diameter than the implant platform [1]. Research has indicated that this technique can help preserve the crestal bone surrounding the implants [2]. A defining characteristic of platform switching is the presence of an implant collar and platform that control the micro-gap [3]. However, there is ongoing debate about the effectiveness of this approach. Studies have shown that Morse taper connections, when combined with platform switching, can lead to reduced inflammation and potential bone loss in the peri-implant soft tissues [4]. Furthermore, the 11-degree Morse taper has demonstrated superior resistance to microbial leakage compared to butt–joint connections [5]. Nevertheless, a prior randomized controlled study conducted over one year revealed that conical implant–abutment connections yield comparable peri-implant tissue responses with both platform switching and non-platform switching abutments [6].

Previous investigations have demonstrated that the clinical and radiographic outcomes were similar between implants restored using platform-switching and platform-matching [7]. Furthermore, a study did not reveal any significant discrepancies in peri-implant marginal bone changes after one year of prosthetic loading between platform-switched implants with a conical connection that were inserted 1 or 2 mm subcrestally [8]. The results of the previously mentioned study disclosed no statistically significant distinctions between platform-switched implants and platform-matched implants in terms of pocket depths during a 6-year follow-up period, with the exception of the loading phase at 24 months and at 72 months [9].

However, several positive outcomes have been reported in relation to platform switching [8,9,10]. The subcrestal placement of implants with platform-switching and an internal conical connection exhibited reduced MBL and demonstrated greater probing depth and peri-implant soft tissue height compared to implants placed at the crestal level after 1 year of functional loading [9]. Similarly, a clinical investigation evaluated the effects of platform switching and the subcrestal placement of implants, suggesting that this approach may be effective in preventing bone loss and preserving esthetics around dental implants [10]. Additionally, a 2 mm subcrestal placement resulted in deeper implant positioning after 1 year of prosthetic loading, with no exposure of the treated implant surface and a potential preventive effect against subsequent peri-implant pathology [8]. Consequently, this study aims to conduct a meta-analysis to assess the differences in the stability of alveolar bone around dental implants and implant failure between platform switching and platform mating. The null hypothesis proposes that there will be no significant difference in the stability of dental implants.

2. Materials and Methods

2.1. Protocol and Eligibility Criteria

The present systematic review follows the guidelines established by the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA), as outlined in the pertinent literature [11]. The central inquiry of this systematic review concerns the discrepancies between platform matching and platform switching of dental implant–abutment configurations. Eligible participants comprised individuals who received dental implant treatment. Interventions involved in this systematic review pertained to platform switching implant–abutment configurations (PS implant), whereas comparisons were made between platform matching implant–abutment configurations (PM implant). The primary outcomes of interest were peri-implant MBL and implant failure rate. Study designs incorporated in the review were limited to randomized controlled trials (RCTs) and were restricted to studies that focused on adult participants. In addition to in vitro and animal studies, biomechanical studies, finite element analysis studies, studies involving removable implant-supported prosthesis, review articles, literature reviews, interviews, case reports, case–control studies, retrospective studies, and studies published in languages other than English, studies employing these designs were excluded from the review.

2.2. Information Sources and Search Strategy

Two researchers (SHH and WJP) carried out an extensive search using both controlled vocabulary (MeSH) and free-text phrases to identify relevant published systematic reviews. This search included three primary electronic databases: Medline via PubMed, the Cochrane database, and Embase, with searches conducted until 21 November 2023. Additionally, a manual examination of the references of all obtained full-text articles was conducted to identify any relevant studies that may have been missed by the electronic searches. The search for the grey literature, including unpublished data, was conducted on the ProQuest (<https://www.proquest.com>, assessed on 21 November 2023) and OpenGrey Europe (<http://www.opengrey.eu>, assessed on 21 November 2023) platforms. The search results were then organized using the EndNote reference management software (Version 21, Private, Philadelphia, PA, USA) to remove duplicates. The method involved contacting the primary authors of selected studies via email over two consecutive weeks to clarify specific details of the study or to request raw data if needed. The search methodology was customized according to the specific needs of each database. Additional information on the search strategy can be found in Supplementary Material Table S1.

2.3. Study Selection and Data Extraction

The eligibility of the selected papers was assessed by two independent reviewers (SHH and WJP), who were blind to each other’s evaluations. In cases where there were discrepancies, a third author (JBP) was consulted to reach a consensus. The full texts of the articles that met the initial criteria were then assessed by the same two reviewers to determine their suitability for inclusion in the final analysis. The inter-rater agreement between the reviewers was quantitatively assessed using the Kappa test. The data were extracted from the included studies according to the PICOS question and were organized into fields, including general information (author name, publication year, and nationality), participants (number of patients, number of implants, immediate/delayed loading, implant system, implant diameter/length, implant sites), intervention/comparison (implant connection type), and outcomes (peri-implant MBL and implant failure rate after 1, 3, 5, and 10 years from loading).

2.4. Risk-of-Bias Assessment

The assessment of bias in randomized studies was conducted using the Cochrane Risk-Of-Bias (ROB 2.0) tool by the reviewers. The assessment checklist encompassed different aspects, such as the randomization process to check for selection bias, deviations from the planned interventions to address performance bias, incompleteness of outcome data to tackle attrition bias, the method of outcomes measurement to address detection bias, the selection of reported results to address reporting bias, and overall bias. The studies were classified based on their risk of bias into low-risk, some concerns, or high-risk categories. The quality evaluation of the studies that fulfilled the inclusion criteria was conducted by two reviewers, SHH, and WJP.

2.5. Data Synthesis and Analysis

Meta-analysis was accomplished utilizing R (Version 3.5.0; R Project for Statistical Computing). The mean difference (MD) together with the 95% confidence interval (CI) acted as the summary statistics. For the meta-analysis, a random-effects model was implemented. The level of significance was set at 0.05. To evaluate the variability among the studies, both the I² static and the chi-square test were executed.

3. Results

3.1. Study Selection and Data Extraction

The preliminary search yielded 466 articles. Following the elimination of 249 duplicates, the titles and abstracts of the remaining 217 articles were examined, and 173 articles were found to be ineligible. Subsequently, the full-text of the 44 articles that passed the initial screening was assessed against the inclusion and exclusion criteria. A total of 32 articles were found to be ineligible, resulting in a final sample of 12 articles that met the criteria for inclusion. The screening process is illustrated in Figure 1, and the reasons for excluding articles are provided in Supplementary Material Table S2. Table 1 summarizes the key features of the studies included in this analysis.

3.2. Risk of Bias Assessment

The summary of the risk of bias and overall risk of bias score for each field in the included articles are illustrated in Figure 2. Across all articles, the potential impact of blinding of patients and personnel was considered. In total, one trial was categorized as having a low risk of bias; the remaining trials exhibited some concerns regarding bias. This trial was deemed to have a low risk of bias due to its employment of a suitable randomization process, dependable measurement of outcomes, and unbiased selection of the reported results. The primary reasons for the concerns regarding bias in the other trials were unclear selection of the reported results.

3.3. Meta-Analysis

3.3.1. Marginal Bone Loss

Taking into account the diverse range of subjects, research backgrounds, and research periods, a random-effects model was employed. Furthermore, the high level of I² values (87%; p < 0.01) indicated substantial heterogeneity among the studies. To account for this heterogeneity, a subgroup analysis was performed, dividing the literature into four subgroups based on the loading time frame: 1 year, 3 years, 5 years, and 10 years. Given the considerable heterogeneity among the studies, the between-study variance was not assumed to be equal in the meta-ANOVA analysis (Version 3.5.0; R Project for Statistical Computing).

A total of twelve articles (Cooper et al., 2021 [12]; Lago et al., 2019 [13]; Lago et al., 2018 [14]; Telleman et al., 2017 [15]; Sanz-Martin et al., 2017 [16]; Canullo et al., 2017 [17]; Rocha et al., 2016 [18]; Pozzi et al., 2014 [19]; Pozzi et al., 2012 [22]; Guerra et al., 2014 [20]; Telleman et al., 2013 [21]; Fernández-Formoso et al., 2012 [23]) examined the differences in MBL between PS implants and PM implants. The forest plots (Figure 3) depict the consolidated data. The results of the meta-analysis demonstrated that the pooled MD for reducing MBL in PS implants compared with PM implants was −0.60 (95% CI, −0.91 to −0.28; p < 0.01). The overall test for effect was significant (p < 0.01), and it revealed that there were significant differences among the subgroups (p = 0.01).

One Year after Loading

Nine included articles (Lago et al., 2019 [13]; Lago et al., 2018 [14]; Telleman et al., 2017 [15]; Sanz-Martin et al., 2017 [16]; Rocha et al., 2016 [18]; Guerra et al., 2014 [20]; Telleman et al., 2013 [21]; Pozzi et al., 2012 [22]; Fernandez-Formoso et al., 2012 [23]) evaluated the differences in MBL between press-fit (PS) and parallel-walled (PM) implants one year after loading. A high level of heterogeneity (p = 89%; p < 0.01) was observed among the studies. The meta-analysis results showed that the pooled mean difference in MBL reduction between PS and PM implants was −0.70 (95% CI, −1.16 to −0.25; p < 0.01). The forest plot favored PS implants with less MBL compared with PM implants (Figure 3).

Three Years after Loading

Three included articles (Lago et al., 2019 [13]; Rocha et al., 2016 [18]; Pozzi et al., 2014 [19]) examined the MBL differences between PS and PM implants three years after loading. The I² values (30%; p = 0.24) indicated low heterogeneity among the studies. The meta-analysis results showed that the pooled mean difference in MBL reduction between PS and PM implants was −0.22 (95% CI, −0.49 to 0.55; p = 0.11). The forest plot still favored PS implants with less MBL compared with PM implants (Figure 3).

Five Years after Loading

Three included articles (Cooper et al., 2021 [12]; Lago et al., 2018 [14]; Telleman et al., 2017 [15]) assessed the differences of MBL between PS implants and PM implants 5 years after loading. A high level of the I² values (91%; p < 0.01) indicated significant heterogeneity among the studies. The results of the meta-analysis showed that the pooled MD of reducing MBL in PS implants compared with PM implants were −0.43 (95% CI, −1.10 to 0.23; p = 0.20). The forest plot favors PS implants with less MBL compared with PM implants (Figure 3).

Ten Years after Loading

One included article (Canullo et al., 2017 [17]) assessed the differences of MBL between PS implants and PM implants 10 years after loading. The results of the meta-analysis showed that the pooled MD of reducing MBL in PS implants compared with PM implants were −2.02 (95% CI, −3.17 to −0.87; p < 0.01). The forest plot favors PS implants with less MBL compared with PM implants (Figure 3).

3.3.2. Implant Failure

The forest plot of meta-analysis on implant failure showed an insignificant difference between PS and PM implants (Figure 4). A random-effects model was applied, and a low level of the I² values (0%; p = 0.64) indicated insignificant heterogeneity among the studies.

3.3.3. Sensitivity Meta-Analysis

A sensitivity analysis was performed by excluding a single study (Fernandez-Formoso et al., 2012 [23]) from the total of 12 studies on MBL, which was found to affect the aggregate outcomes of the meta-analysis (Figure 5). A high level of the I² values (75%; p < 0.01) indicated significant heterogeneity among the studies (Figure 6). The results of the meta-analysis showed that the pooled MD of reducing MBL in PS implants compared with PM implants were −0.46 (95% CI, −0.66 to −0.25; p < 0.01). The test for overall effect is significant (p < 0.01), and it also revealed that there were significant differences between subgroups (p = 0.02).

3.3.4. Publication Bias Analysis

The funnel plot revealed an asymmetrical pattern (Figure 7). However, the trim-and-fill method did not reveal any studies requiring imputation, and the adjusted overall effect size remained consistent with the initial report. Furthermore, the Egger’s regression test yielded a non-significant result for publication bias, with a p-value of 0.27. Additionally, when each subgroup undergoing meta-analysis was tested for publication bias, both the original estimate effect and the adjusted trim-and-fill analysis demonstrated no relevant differences. The Egger’s regression p-value failed to reach statistical significance in all cases except for subgroup studies conducted three years after loading (as shown in Supplementary Material Table S4).

4. Discussion

This systematic review and meta-analysis was executed to evaluate the stability of alveolar bone loss around dental implants by comparing the radiographic MBL and implant failure rates between platform-switched implants and platform-matched implants. The purpose of this study was to assess the stability of dental implants by comparing the radiographic MBL and implant failure rates between platform-switched implants and platform-matched implants. The study’s findings revealed that platform-switched implants showed a lower incidence of MBL compared to platform-matched implants. Overall, the results of this study demonstrated the usefulness of platform switching as a valuable adjunct to dental implant procedures.

The technique of platform switching can be employed in various implant systems, including those that use an external hexagonal connection. The external hexagonal system is a conventional implant–abutment connection that features a hexagonal fitting on the top of the implant [24]. Implementing platform switching in an external hexagonal system entails using an abutment that is narrower than the top of the implant, which results in a step-down at the implant–abutment interface. Internal implant systems, such as internal hexagonal, internal octagonal, conical (Morse taper) design, or other types of internal fitting mechanisms, are also available [25]. Internal connection systems typically provide a tighter seal at the implant–abutment interface compared to external hex systems, which can enhance mechanical stability and reduce micro-movements [26]. In internal connection systems, platform switching functions similarly by using an abutment that is narrower than the implant platform, moving the junction between the implant and the abutment inward. Studies suggest that different micro-gap configurations exhibit various patterns of bone loss during non-submerged healing, even without prosthetic loading [27]. After 10 years of follow-up, a total bone loss of 0.7 ± 0.4 mm was measured in the equicrestal external hexagonal connection group, while a bone loss of 0.5 ± 0.7 mm was observed in the equicrestal internal Morse taper connection group [28]. It can be inferred that an implant with a wide diameter and external hexagonal connection, restored with a platform-switching abutment, is more effective in reducing bone loss compared to the platform-matching abutment [29].

The concept of platform switching focuses on strategically moving the inflammatory cell layer away from the crucial bone interface to prevent crestal bone loss, a prevalent issue near implants. This mechanism was investigated in a study that assessed the distribution and density of inflammatory cells around implants with supracrestal, crestal, or subcrestal implant–abutment interfaces [28]. The results demonstrated a consistent pattern of peri-implant inflammation across all groups, characterized by a peak accumulation of neutrophilic polymorphonuclear leukocytes (neutrophils) at or directly coronal to the interface [30]. Platform switching is distinguished by specific features in the implant–abutment connection designed to effectively manage bacterial proliferation [3]. A comparative analysis revealed that platform-matched implants placed at the crestal level exhibited a significantly higher mean bacterial load in the peri-implant sulcus fluid compared to those with platform switching [7]. These observations emphasize the potential of platform switching to improve peri-implant health by reducing the inflammatory burden and bacterial presence at critical tissue interfaces.

The use of platform-switched implants has been demonstrated to facilitate lower stress levels within the peri-implant bone, resulting in a more uniform distribution of stress [31]. Advanced finite element modeling was employed to evaluate mechanical parameters such as von Mises stresses, deformations, and strain energies, revealing reduced values in the peri-implant bone for platform-switched configurations, which may contribute to mitigating MBL [30]. This protective effect likely underlies the reduced extent of marginal bone resorption observed. However, a concomitant increase in stress concentration was noted in the prosthetic components of the implant system when using platform-switched implants [32]. Further in vitro experimental studies have corroborated these findings, showing increased mechanical parameters in the abutment, implant, and screw within the platform-switched configuration compared to the platform-matched setup. Despite these differences, mechanical complications in the implant prosthetic components were found to be non-significant between the two configurations [30]. The relatively higher stress observed in the abutment does not typically result in premature implant failure, attributed to the robust strength of titanium alloys [32]. Moreover, the lack of significant differences in failure rates between the two platforms substantiates the assertion that platform switching does not detrimentally impact the overall prognosis of the implants [31]. This aligns with the results reported in the present study and may provide valuable insights for clinical consideration.

Despite the thorough methodology of our meta-analysis, which incorporated an extensive search strategy and strict adherence to PRISMA guidelines, several limitations warrant acknowledgment. Additionally, the potential for publication bias, as indicated by the asymmetry in the funnel plot, cannot be entirely disregarded, although statistical adjustment methods did not uncover a significant impact. Further research employing standardized protocols and extended follow-up periods is necessary to more clearly elucidate the long-term benefits of platform switching. The clinical implications of these findings must also be carefully weighed. Although the preservation of marginal bone is crucial for the durability and aesthetic success of implant-supported prostheses, the unchanged rates of implant failure suggest that platform switching should not be considered a panacea for implant failures.

5. Conclusions

Emerging evidence suggests that platform-switched implants may offer advantages in terms of marginal bone preservation. However, this advantage does not seem to extend to implant survival rates, which appear to be comparable for both platform-switched and platform-matched implants. Clinicians should carefully consider these findings in light of individual patient factors when planning implant therapy. To further confirm these outcomes and inform the development of best practice guidelines in implant dentistry, additional high-quality randomized controlled trials with extended follow-up periods are necessary.

Author Contributions

Conceptualization, S.-H.H., N.J.K., W.-J.P. and J.-B.P.; formal analysis, S.-H.H., N.J.K., W.-J.P. and J.-B.P.; writing—original draft preparation, S.-H.H., N.J.K., W.-J.P. and J.-B.P.; and writing—review and editing, S.-H.H., N.J.K., W.-J.P. and J.-B.P. All authors have read and agreed to the published version of the manuscript.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflicts of interest.

Footnotes

Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Figures and Table

Figure 1. Flow chart illustrating the process regarding the articles that have been encompassed within the systematic reviews.

Figure 2. Risk of bias. (A) Summary of the risk of bias in the included studies [12,13,14,15,16,17,18,19,20,21,22,23]. (B) Overall risk-of-bias score for each field.

Figure 3. Forest plot illustrating the comparison between platform switching and platform matching for marginal bone loss on follow-up monitoring.

Figure 4. Forest plot illustrating the comparison between platform switching and platform matching for implant failure.

Figure 5. Forest plot illustrating the results of sensitivity test.

Figure 6. Forest plot illustrating the comparison between platform switching and platform matching on marginal bone loss after sensitivity analysis.

Figure 7. Funnel plot illustrating the publication bias analysis.

Table 1

Main characteristics of the included studies.

Study Year/Nationality	No. of Patients/Total No. of Implants	Follow-Up Time (Range)	History of Periodontal Disease	Smoking Habit	Implant System	ITI Classification	Bone Grafting	Healing Period/Loading	Implant Diameter/Implant Length	Implant Connection Type	Implant Sites	Implant Failure	Success Rate (%)	Marginal Bone Loss (Mean ± SD, mm)
Cooper 2021/USA [12]	141/141	5 yrs	Not explicitly mentioned	None	OsseoSpeed TX (conical interface), NobelSpeedy (flat-to-flat interface), and NanoTite Certain PREVAIL (PS interface)	delayed	None	Immediate provisionalization	Not explicitly mentioned	Conical (Internal hex), flat-to-flat (external hex), and PS (internal hex) interfaces	Mx	0 conical, 8 flat-to-flat, 6 PS	Conical: 100%; Flat-to-flat: 83.7%; PS: 86.4%	Conical: −0.16 ± 0.45; Flat-to-flat: −0.92 ± 0.70; PS: −0.81 ± 1.06
Lago 2019/Spain [13]	35/100	3 yrs	Not explicitly mentioned	≤10 cigarettes/day	Straumann	delayed	None	≥2 months post-placement	Not explicitly mentioned	Control: Tissue-level (internal hex) vs. Test: Bone-level (internal hex)	Mx/Mn	0	100%	Control: 0.18 ± 0.46, Test: 0.14 ± 0.35
Lago 2018/Spain [14]	100/202	5 yrs	Not explicitly mentioned	None	Straumann	delayed	None	≥2 months post-placement	Diameter	Control: Tissue-level (internal hex) vs. Test: Bone-level (external hex)	Mx/Mn	2 in control, 3 in test	Implied as 98% for control and 96.1% for test	Control: 0.61 ± 0.73, Test: −0.20 ± 0.75
									PM: 4.1, 4.8
									PS: 3.3, 4.1, 4.8
									Length
									8, 10, 12
Telleman 2017/Netherlands [15]	80/113	5 yrs	Not explicitly mentioned	None	Biomet 3i, 8.5 mm length, 58 in control (PM) and 55 in test (PS)	delayed	Performed if dehiscence or fenestrations are <3 mm	Not explicitly mentioned, but assessments at 1 month, 1 year, and 5 years	Diameter	Control: PM (internal hex) vs. Test: PS (internal hex)	Mx/Mn	2 PS implants, 0 PM implant	96.3% survival for PS, 100% for PM	Control group 0.41 ± 0.47 mm, Test group 0.38 ± 0.61 mm
									4.0, 5.0
									Length
									8.5
Sanz-Martin 2017/Spain [16]	47/61	24 mo	Not explicitly mentioned	≤10 cigarettes/day	Sweden & Martina Premium, TG (Transgingival) and SP (PS) implants	delayed	Performed if dehiscence or fenestrations are <3 mm	Prostheses delivered after 12 months	Diameter	Transgingival (internal hex) vs. PS (internal hex)	Mx/Mn	4 PS implants, 2 PM implant	92.8% survival for PS, 93.9% for PM	TG group: Loading to 12 months: −0.27 ± 0.24 mm; SP group: Loading to 12 months: −0.12 ± 0.19 mm
									3.8, 4.25, 5.0
									Length
									7, 8.5, 10, 11.5, 13
Canullo 2017/Italy [17]	19/19	10 yrs	Not explicitly mentioned	≤10 cigarettes/day	Global Implant, Sweden & Martina, 13 mm length, 5.5 mm platform	delayed	Performed if dehiscence or fenestrations are <3 mm	Immediate loading	Diameter	PS (internal hex) vs. PM (internal hex)	Mx	0	100%	Test: 0.18 ± 0.14; Control: 0.80 ± 0.40
									5.5
									Length
									13
Rocha 2016/Multicenter (Germany, Portugal) [18]	63/135	3 yrs	Not explicitly mentioned	≤10 cigarettes/day	CAMLOG SCREW-LINE implants, Promote plus surface	delayed	None	Conventional loading, 6–14 weeks post-placement	Diameter	PS (internal hex) vs. PM (internal hex)	Mn	2 PS implants, 1 PM implant	97.3% survival for PS, 97.1% for PM	PS: 0.28 ± 0.56 mm, PM: 0.68 ± 0.64 mm over 3 years
									3.8, 4.3, 5.0
									Length
									9, 11, 13
Pozzi 2014/Multicenter (Italy, USA) [19]	34/88	3 yrs	Not explicitly mentioned	≤10 cigarettes/day	NobelActive (NA) and NobelSpeedy Groovy (NSG), Nobel Biocare	delayed	None	Not explicitly mentioned	Diameter	Internal conical connection (NA) vs. External hexagon flat-to-flat (NSG)	Mn	0	100%	NA implants: 0.66 mm; NSG implants: 1.25 mm vertical bone resorption
									PM: 4.1
									PS: 3.9
									Length
									8.5, 10, 11.5, 13
Guerra 2014/Multicenter (Portugal, Germany) [20]	68/146	1 yr	Not explicitly mentioned	≤10 cigarettes/day	CAMLOG SCREW-LINE Implants, Promote plus surface	delayed	None	Minimum of 8 weeks transgingival healing period before definitive restorations	Diameter	PS (internal hex) vs. PM (external hex)	Mx/Mn	2 implants lost in PS group before loading	97.3% for PS, 100% for PM	PS: −0.69 ± 0.68 mm, PM: −0.40 ± 0.46 mm
									3.8, 4.3, 5.0
									Length
									9, 11, 13
Telleman 2013/Netherlands [21]	92/149	1 yr	Not explicitly mentioned	None	NanoTite Certain Prevail (PS) and NanoTite XP Certain (PM), Biomet 3i	delayed	None	Not explicitly mentioned	Diameter	PS (internal hex) vs. PM (external hex)	Mx/Mn	6 in control group, 3 in test group	Control group: 92.1%, Test group: 95.9%	Control (PM) 0.74 ± 0.61 mm, Test (PS) 0.50 ± 0.53 mm
									4.0, 5.0
									Length
									8.5
Pozzi 2012/Multicenter (Italy, USA) [22]	34/88	1 yr	Not explicitly mentioned	≤10 cigarettes/day	NobelActive (NA, internal conical connection with PS) vs. NobelSpeedy Groovy (NSG, external hexagon with flat-to-flat interface), Nobel Biocare	delayed	None	Immediate loading	Diameter	Internal conical (NA) vs. External hexagon (NSG)	Mn	0	100%	PS (NA): −0.37 ± 0.48 mm, PM (NSG): −0.80 ± 0.50 mm
									PM: 4.0
									PS: 4.3
									Length
									10 to 13
Fernandez-Formoso 2012/Spain [23]	51/114	1 yr	Not explicitly mentioned	None	Straumann implants; Standard Plus Type for control (tissue level) and Bone Level Type for test (bone level with PS)	delayed	None	Immediate loading	Diameter	Control: Tissue-level (internal hex),	Mx/Mn	0	100%	Control group: 0.42 mm, Test group (PS): −0.01 mm
									3.3, 4.1, 4.8	Test: Bone-level (internal hex)
									Length
									8 to 14

PS, Platform-switched; PM, Platform-matched; Mx, Maxilla; Mn, Mandible; yr, year; yrs, years; mo, months.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/app14124975/s1, Table S1: Search strategy of the online databases; Table S2: Excluded studies from full-text reading; Table S3: Risk of bias. Table S4: Analyses for publication bias. References [33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63] are cited in the Supplementary Materials.

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