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Journal of Prosthetic Dentistry

Comparison of external, internal flat-to-flat, and conical implant abutment connections for implant-supported prostheses: A systematic review and network meta-analysis of randomized clinical trials

Open AccessPublished:November 11, 2021DOI:https://doi.org/10.1016/j.prosdent.2021.09.029

      Abstract

      Statement of problem

      The implant abutment connection interface has been considered one of the major factors affecting the outcome of implant therapy. However, drawbacks of traditional meta-analyses are the inability to compare more than 2 treatments at a time, which complicates the decision-making process for dental clinicians, and the lack of a network meta-analysis.

      Purpose

      The purpose of this network meta-analysis was to assess whether the implant abutment connection influences the outcome of implant-supported prostheses.

      Material and methods

      An electronic search was undertaken to identify all randomized clinical trials comparing the effect of at least 2 different implant abutment connection designs published from 2009 up to May 2020. Outcome variables were implant survival rate, peri-implant marginal bone loss, and biologic and prosthetic complication rates at 12 months after prosthetic loading. Relevant information was extracted, and quality and risk of bias assessed. Pairwise meta-analyses and network meta-analyses based on a multivariate random-effects meta-regression were performed to assess the comparisons (α=.05 for all analyses).

      Results

      For peri-implant marginal bone loss and prosthetic complications, conical interfaces were determined to be the most effective, with significant differences when compared with external hexagonal connections (P=.011 and P=.038, respectively). No significant differences were found among the implant abutment connections in terms of survival and biologic complications (P>.05 in all direct, indirect, and mixed comparisons).

      Conclusions

      After 1 year of loading, conical connections showed lower marginal bone loss and fewer prosthetic complications than external hexagonal connections. However, the implant abutment connection design had no influence on the implant survival and biologic complication rates.
      Clinical Implications
      Based on this systematic review and network meta-analysis of randomized clinical trials, dental clinicians are advised to use implant systems with a conical implant abutment connection in patients with risk factors for marginal bone loss and/or prosthetic complications.
      Over recent decades, the use of dental implants for oral rehabilitation has shown good long-term results in a wide variety of situations.
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      The effect of internal versus external abutment connection modes on crestal bone changes around dental implants: a radiographic analysis.
      Dental implant connections can be classified into external and internal, with internal connections being further divided into passive joint or flat-to-flat systems (such as triangles, hexagons, octagons) and conical or Morse taper interfaces. External connections are characterized by having the interface above the platform of the implant.
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      The influence of bone quality on the biomechanical behavior of a tooth-implant fixed partial denture: a three-dimensional finite element analysis.
      Moreover, in vitro studies have reported that internal connections, particularly conical ones, reduce the implant abutment gap and subsequent bacterial penetration.
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      Effect of platform switching on peri-implant bone levels: a randomized clinical trial.
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      Microbiological assessment of the implant abutment interface in different connections: cross-sectional study after 5 years of functional loading.
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      • Michalakis K.
      • Vigolo P.
      • Vult von Steyern P.
      • Zwahlen M.
      • Sailer I.
      Internal vs. external connections for abutments/reconstructions: a systematic review.
      ,
      • Lemos C.A.A.
      • Verri F.R.
      • Bonfante E.A.
      • Santiago Júnior J.F.
      • Pellizzer E.P.
      Comparison of external and internal implant abutment connections for implant supported prostheses. A systematic review and meta-analysis.
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      Evaluation of marginal bone loss of dental implants with internal or external connections and its association with other variables: a systematic review.
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      The influence of implant abutment connection to peri-implant bone loss: a systematic review and meta-analysis.
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      • Bergoli C.D.
      Influence of different implant abutment connection designs on the mechanical and biological behavior of single-tooth implants in the maxillary esthetic zone: a systematic review.
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      • Zembic A.
      A systematic review of the influence of the implant abutment connection on the clinical outcomes of ceramic and metal implant abutments supporting fixed implant reconstructions.
      However, a potential drawback of traditional meta-analyses is the inability to compare more than 2 treatments at a time, which complicates the clinician’s decision-making process. Moreover, the absence of direct comparisons among more than 2 interventions means that traditional meta-analysis cannot estimate the resulting comparative benefits and drawbacks.
      • Tonin F.S.
      • Rotta I.
      • Mendes A.M.
      • Pontarolo R.
      Network meta-analysis: a technique to gather evidence from direct and indirect comparisons.
      Network meta-analysis (NMA), also known as multiple treatment meta-analysis or mixed treatment meta-analysis, overcomes this limitation.
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      • Chaimani A.
      • Li T.
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      Therefore, the aim of the present study was to analyze the relevant data from randomized clinical trials (RCTs) and assess which implant abutment connection design (external, internal flat-to-flat, or conical) is the most effective for restoring missing teeth with dental implants. Two null hypotheses were formulated: that the implant survival rate and complications (mechanical or biologic) would be similar for all the different prosthetic interface connections and that no differences in terms of peri-implant MBL would be identified among the implant abutment connections.

      Material and methods

      This study adhered to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses for Network Meta-Analyses (PRISMA-NMA) statement
      • Hutton B.
      • Salanti G.
      • Caldwell D.M.
      • Chaimani A.
      • Schmid C.H.
      • Cameron C.
      • et al.
      The PRISMA extension statement for reporting of systematic reviews incorporating network meta-analyses of health care interventions: checklist and explanations.
      (Supplemental Table 1, available online) and was registered in the international database of prospectively registered systematic reviews in health and social care (PROSPERO) under number CRD42018099154.
      The patients, intervention, comparison, outcomes, and time (PICOT) question to be addressed was as follows: In people with missing teeth replaced by dental implants in completely or partially edentulous mandibular or maxillary alveolar arches (P), what is the effect of external, internal flat-to-flat, or conical implant abutment connection design (I) on implant survival rate, peri-implant MBL, biologic complication rate, and prosthetic complication rate (O) when compared with a positive control implant abutment connection design (C) within the first 12 months of functional loading (T)?
      The inclusion criteria were RCTs including split mouth and/or multiarm designs comparing 2 or 3 different implant abutment connection designs with a minimum follow-up of 12 months after prosthetic loading. The review excluded trials published before 2009 and/or with fewer than 10 participants/implants in the control and/or intervention group.
      The primary outcome was implant survival. The secondary outcome measurements were radiographic peri-implant MBL—from prosthesis delivery to 12 months after functional loading—and biologic and prosthetic complications. Peri-implant MBL was expressed in millimeters, whereas implant survival and biologic and prosthetic complications were expressed in absolute values and percentages.
      An electronic search of the MEDLINE (OVID), the Cochrane Library (Wiley), Scopus (Elsevier), and the Web of Science (Thomson Reuters) databases up to May 1, 2020, was conducted to identify all relevant human studies published as of 2009, without language restrictions (Supplemental Table 2, available online). Additionally, non–peer-reviewed literature was searched (OpenGrey, 2011), as well as the US National Institutes of Health (National Institutes of Health, 2000), to identify additional potential candidates to be included. The research was completed by checking the reference lists of the selected articles and reviews.
      Two reviewers (O.C.-F., L.R.-P.) independently selected the studies in accordance with the inclusion criteria. A third reviewer (R.F.) resolved any disagreements. The Cohen kappa coefficient (κ) was calculated to measure the level of agreement of the reviewers. The authors were contacted when necessary for clarification of missing information. When multiple reports from the same study were identified, the first publication addressing the outcomes of interest 12 months after the prosthetic loading was included. The data were extracted independently by 2 reviewers (O.C.-F., L.R.-P.) under the supervision of a third reviewer (R.F.). Tables were created to summarize the following data (if available): author(s), year of publication, country of origin, study design, and details related to participants, intervention(s), and outcomes.
      As suggested in the Cochrane Handbook for Systematic Reviews of Interventions (version 5.1.0), 2 reviewers (O.C.-F., L.R.-P.) independently evaluated the risk of bias and methodological quality of each RCT by using the Cochrane Collaboration Risk of Bias Tool.
      • Higgins J.P.T.
      • Green S.
      Cochrane handbook for systematic reviews of interventions.
      Except for the blinding domain, which was assessed separately for clinical and radiological outcomes, the others were judged at the study level.
      Pairwise meta-analyses (PMA) using a random-effects model were performed for the studies that directly compared different implant abutment connection designs. For dichotomous outcomes, odds ratios (ORs) with 95% confidence intervals (CIs) were used to estimate the effect of an intervention. For continuous outcomes, mean differences (MDs) and standard deviations were used to summarize the data for each group. A χ2 P value <.10 and an I2 value greater than 50% were interpreted as indicating significant heterogeneity.
      • Higgins J.P.T.
      • Thompson S.G.
      Quantifying heterogeneity in a meta-analysis.
      Consequently, subgroups of different characteristics based on variations in the experimental treatment protocol (such as RCT design, risk-of-bias quality, insertion timing, load timing, platform switching, and implant design) were isolated and subjected to linear meta-regression to identify them as possible sources of covariance. Had any cluster contained ≥10 meta-analyzed trials, publication bias analysis would have been performed.
      • Higgins J.P.T.
      • Green S.
      Cochrane handbook for systematic reviews of interventions.
      Subsequently, an NMA was conducted to compare the implant abutment connections for each outcome variable simultaneously. To review the network geometry, a network graph was generated and analyzed: each implant abutment connection cluster was drawn as a node, and direct comparisons between them were represented by links between the nodes. The NMA was based on a multivariate random-effects metaregression.
      • Higgins J.P.T.
      • Jackson D.
      • Barrett J.K.
      • Lu G.
      • Ades A.E.
      • White I.R.
      Consistency and inconsistency in network meta-analysis: concepts and models for multi-arm studies.
      Inconsistency was assessed substantively by comparing the results obtained through PMA and NMA and statistically by fitting both consistency and inconsistency through design-by-treatment interaction models.
      • Higgins J.P.T.
      • Jackson D.
      • Barrett J.K.
      • Lu G.
      • Ades A.E.
      • White I.R.
      Consistency and inconsistency in network meta-analysis: concepts and models for multi-arm studies.
      Outcome variables were ranked by using the surface under the cumulative ranking (SUCRA) curve.
      • Salanti G.
      • Ades A.E.
      • Ioannidis J.P.A.
      Graphical methods and numerical summaries for presenting results from multiple-treatment meta-analysis: an overview and tutorial.
      The SUCRA is a numeric presentation of the overall ranking and presents a single number associated with each treatment, with values ranging from 0% to 100%.
      • Salanti G.
      • Ades A.E.
      • Ioannidis J.P.A.
      Graphical methods and numerical summaries for presenting results from multiple-treatment meta-analysis: an overview and tutorial.
      A high SUCRA value (close to 100) indicates that a particular implant abutment connection is very likely to be the best, or one of the best. Conversely, SUCRA values close to 0 suggest that the interface is probably the worst.
      The statistical analysis was carried out with software programs (Stata14; StataCorp, Review Manager 5.3; The Cochrane Collaboration) (α=.05 for all analyses).

      Results

      The initial electronic database search returned 1363 references. Nine articles were excluded after full-text evaluation.
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      • Lee E.J.
      • Kim J.Y.
      • Seol Y.J.
      • Han J.S.
      • Kim T.I.
      • et al.
      The effect of internal versus external abutment connection modes on crestal bone changes around dental implants: a radiographic analysis.
      ,
      • Arnhart C.
      • Kielbassa A.M.
      • Martinez-de Fuentes R.
      • Goldstein M.
      • Jackowski J.
      • Lorenzoni M.
      • et al.
      Comparison of variable-thread tapered implant designs to a standard tapered implant design after immediate loading. A 3-year multicentre randomised controlled trial.
      • Cooper L.
      • Reside G.
      • Stanford C.
      • Barwacz C.
      • Feine J.
      • Nader S.
      • et al.
      Three-year prospective randomized comparative assessment of anterior maxillary single implants with different abutment interfaces.
      • Esposito M.
      • Maghaireh H.
      • Pistilli R.
      • Grusovin M.G.
      • Lee S.T.
      • Trullenque-Eriksson A.
      • et al.
      Dental implants with internal versus external connections: 5-year post-loading results from a pragmatic multicenter randomised controlled trial.
      • Pozzi A.
      • Tallarico M.
      • Moy P.K.
      Three-year post-loading results of a randomised, controlled, split-mouth trial comparing implants with different prosthetic interfaces and design in partially posterior edentulous mandibles.
      • Bilhan H.
      • Kutay O.
      • Arat S.
      • Çekici A.
      • Cehreli M.C.
      Astra Tech, Brånemark, and ITI implants in the rehabilitation of partial edentulism: two-year results.
      • Kaminaka A.
      • Nakano T.
      • Ono S.
      • Kato T.
      • Yatani H.
      Cone-beam computed tomography evaluation of horizontal and vertical dimensional changes in buccal peri-implant alveolar bone and soft tissue: a 1-year prospective clinical study.
      • Lin M.I.
      • Shen Y.W.
      • Huang H.L.
      • Hsu J.T.
      • Fuh L.J.
      A retrospective study of implant abutment connections on crestal bone level.
      • Palaska I.
      • Tsaousoglou P.
      • Vouros I.
      • Konstantinidis A.
      • Menexes G.
      Influence of placement depth and abutment connection pattern on bone remodeling around 1-stage implants: a prospective randomized controlled clinical trial.
      Altogether, 18 RCTs fulfilled the eligibility criteria and were selected for qualitative and quantitative synthesis (Table 1).
      • Cannata M.
      • Grandi T.
      • Samarani R.
      • Svezia L.
      • Grandi G.
      A comparison of two implants with conical vs internal hex connections: 1-year post-loading results from a multicentre, randomised controlled trial.
      • Canullo L.
      • Rosa J.C.
      • Pinto V.S.
      • Francischone C.E.
      • Götz W.
      Inward-inclined implant platform for the amplified platform-switching concept: 18-month follow-up report of a prospective randomized matched-pair controlled trial.
      • Cooper L.
      • Reside G.
      • Stanford C.
      • Barwacz C.
      • Feine J.
      • Nader S.
      • et al.
      A Multicenter randomized comparative trial of implants with different abutment interfaces to replace anterior maxillary single teeth.
      • Cooper L.
      • Tarnow D.
      • Froum S.
      • Moriarty J.
      • De Kok I.
      Comparison of marginal bone changes with internal conus and external hexagon design implant systems: a prospective, randomized study.
      • Crespi R.
      • Capparè P.
      • Gherlone E.
      Radiographic evaluation of marginal bone levels around platform-switched and non-platform-switched implants used in an immediate loading protocol.
      • Esposito M.
      • Maghaireh H.
      • Pistilli R.
      • Grusovin M.G.
      • Lee S.T.
      • Gualini F.
      • et al.
      Dental implants with internal versus external connections: 1-year post-loading results from a pragmatic multicenter randomised controlled trial.
      • Felice P.
      • Barausse C.
      • Blasone R.
      • Favaretto G.
      • Stacchi C.
      • Calvo M.
      • et al.
      A comparison of two dental implant systems in partially edentulous patients: 1-year post-loading results from a pragmatic multicentre randomised controlled trial.
      • Glibert M.
      • Vervaeke S.
      • Jacquet W.
      • Vermeersch K.
      • Östman P.O.
      • De Bruyn H.
      A randomized controlled clinical trial to assess crestal bone remodeling of four different implant designs.
      • Gultekin B.A.
      • Gultekin P.
      • Leblebicioglu B.
      • Basegmez C.
      • Yalcin S.
      Clinical evaluation of marginal bone loss and stability in two types of submerged dental implants.
      • Hsu Y.T.
      • Chan H.L.
      • Rudek I.
      • Bashutski J.
      • Oh W.S.
      • Wang H.L.
      • et al.
      Comparison of clinical and radiographic outcomes of platform-switched implants with a rough collar and platform-matched implants with a smooth collar: a 1-year randomized clinical trial.
      • Kielbassa A.M.
      • de Fuentes R.M.
      • Goldstein M.
      • Arnhart C.
      • Barlattani A.
      • Jackowski J.
      • et al.
      Randomized controlled trial comparing a variable-thread novel tapered and a standard tapered implant: interim one-year results.
      • Kim J.C.
      • Lee J.
      • Kim S.
      • Koo K.T.
      • Kim H.Y.
      • Yeo I.S.L.
      Influence of implant abutment connection structure on peri-implant bone level in a second molar: a 1-year randomized controlled trial.
      • Menini M.
      • Pesce P.
      • Bagnasco F.
      • Carossa M.
      • Mussano F.
      • Pera F.
      Evaluation of internal and external hexagon connections in immediately loaded full-arch rehabilitations: a within-person randomised split-mouth controlled trial.
      • Peñarrocha-Diago M.A.
      • Flichy-Fernández A.J.
      • Alonso-González R.
      • Peñarrocha-Oltra D.
      • Balaguer-Martínez J.
      • Peñarrocha-Diago M.
      Influence of implant neck design and implant abutment connection type on peri-implant health. Radiological study.
      • Pessoa R.S.
      • Sousa R.M.
      • Pereira L.M.
      • Neves F.D.
      • Bezerra F.J.B.
      • Jaecques S.V.N.
      • et al.
      Bone remodeling around implants with external hexagon and morse-taper connections: a randomized, controlled, split-mouth, clinical trial.
      • Pieri F.
      • Aldini N.N.
      • Marchetti C.
      • Corinaldesi G.
      Influence of implant abutment interface design on bone and soft tissue levels around immediately placed and restored single-tooth implants: a randomized controlled clinical trial.
      • Pozzi A.
      • Agliardi E.
      • Tallarico M.
      • Barlattani A.
      Clinical and radiological outcomes of two implants with different prosthetic interfaces and neck configurations: randomized, controlled, split-mouth clinical trial.
      • Sanz-Martín I.
      • Sanz-Sánchez I.
      • Noguerol F.
      • Cok S.
      • Ortiz-Vigón A.
      • Sanz M.
      Randomized controlled clinical trial comparing two dental implants with different neck configurations.
      The reviewer agreement rate was 95.2%, with a κ coefficient of 0.88 (almost perfect agreement). A flowchart of the screening process is shown in Figure 1.
      Table 1Studies selected for qualitative and quantitative synthesis
      Authors, Year

      Country
      DesignSurgical SiteInterventionsManufacturers
      Cannata et al, 2017

      Italy
      • Cannata M.
      • Grandi T.
      • Samarani R.
      • Svezia L.
      • Grandi G.
      A comparison of two implants with conical vs internal hex connections: 1-year post-loading results from a multicentre, randomised controlled trial.
      Multicenter RCT (parallel)Participants partially edentulous in maxilla or mandible, requiring 1 implant-supported prosthesis; residual bone height ≥10 mm and thickness ≥5 mm measured on CT scanCCJDIcon. J Dental Care.
      IFFJDEvolution. J Dental Care.
      Canullo et al, 2012

      Italy
      • Canullo L.
      • Rosa J.C.
      • Pinto V.S.
      • Francischone C.E.
      • Götz W.
      Inward-inclined implant platform for the amplified platform-switching concept: 18-month follow-up report of a prospective randomized matched-pair controlled trial.
      Multicenter RCT (split-mouth)Partially edentulous participants, requiring fixed implant-supported prosthesis in posterior maxilla with 2 adjacent implants; bone thickness wide enough to insert 4-mm-diameter implantsIFFAmplified. P-I Brånemark.
      EHExternal hexagon. P-I Brånemark.
      Cooper et al, 2015

      USA
      • Cooper L.
      • Reside G.
      • Stanford C.
      • Barwacz C.
      • Feine J.
      • Nader S.
      • et al.
      A Multicenter randomized comparative trial of implants with different abutment interfaces to replace anterior maxillary single teeth.
      Multicenter RCT (parallel)Partially edentulous participants, requiring 1 or more single implants in anterior maxilla; bone width ≥5.5 mmCCOsseoSpeed. Dentsply Implants.
      IFFNobelSpeedy Replace. Nobel Biocare.
      IFF + PSNanoTite Certain Prevail. Biomet 3i.
      Cooper et al, 2016

      USA
      • Cooper L.
      • Tarnow D.
      • Froum S.
      • Moriarty J.
      • De Kok I.
      Comparison of marginal bone changes with internal conus and external hexagon design implant systems: a prospective, randomized study.
      Multicenter RCT (parallel)Participants with partial edentulism, Kennedy Class I or II in maxilla or mandible, requiring 2 or 3 dental implants to support individual crowns; bone thickness wide enough to insert 4.5-mm-diameter fixturesCCOsseoSpeed. Dentsply Implants.
      EHOsseotite Standard. Biomet 3i.
      Crespi et al, 2009

      Italy
      • Crespi R.
      • Capparè P.
      • Gherlone E.
      Radiographic evaluation of marginal bone levels around platform-switched and non-platform-switched implants used in an immediate loading protocol.
      RCT (parallel)Participants requiring extraction of 1 or 2 single-rooted teeth, replaced by dental implants; ≥4 mm of bone beyond root apex and preserving 4 bony wallsCCAnkylos Plus. Dentsply Implants.
      EHSeven. Sweden & Martina.
      Esposito et al, 2015

      Italy
      • Esposito M.
      • Maghaireh H.
      • Pistilli R.
      • Grusovin M.G.
      • Lee S.T.
      • Gualini F.
      • et al.
      Dental implants with internal versus external connections: 1-year post-loading results from a pragmatic multicenter randomised controlled trial.
      Multicenter RCT (parallel)Any patient requiring 1 implant-supported prosthesis, with any type of bone quality and jaw locationCCEZ plus. MegaGen Implant.
      EHEZ plus. MegaGen Implant.
      Felice et al, 2014

      Italy
      • Felice P.
      • Barausse C.
      • Blasone R.
      • Favaretto G.
      • Stacchi C.
      • Calvo M.
      • et al.
      A comparison of two dental implant systems in partially edentulous patients: 1-year post-loading results from a pragmatic multicentre randomised controlled trial.
      Multicenter RCT (split-mouth)Any patient, requiring at least 2 implant-supported crowns or partial fixed prostheses supported by ≤3 dental implants; sufficient bone volume to insert ≥9-mm-long and ≥3.8-mm-diameter implantsCCWay Milano. Geass. y
      IFFKentron. Geass.
      Glibert et al, 2018

      Belgium
      • Glibert M.
      • Vervaeke S.
      • Jacquet W.
      • Vermeersch K.
      • Östman P.O.
      • De Bruyn H.
      A randomized controlled clinical trial to assess crestal bone remodeling of four different implant designs.
      RCT (split-mouth)Maxillary edentulous participants; sufficient residual bone volume to insert 4 implants with 4-mm diameter and 9- to 11-mm lengthCCDeep Conical Cylindrical. Southern Implants.
      EHExternal Hex. Southern Implants.
      Gultekin et al, 2013

      Turkey
      • Gultekin B.A.
      • Gultekin P.
      • Leblebicioglu B.
      • Basegmez C.
      • Yalcin S.
      Clinical evaluation of marginal bone loss and stability in two types of submerged dental implants.
      RCT (split-mouth)Participants partially edentulous in axilla or mandible with ≥2 teeth absent; sufficient residual bone volume to place ≥8-mm-long and ≥3.5-mm-diameter implantsCCNobel Active. Nobel Biocare.
      IFFNobel Replace Tapered Groovy. Nobel Biocare. d
      Hsu et al, 2016

      USA
      • Hsu Y.T.
      • Chan H.L.
      • Rudek I.
      • Bashutski J.
      • Oh W.S.
      • Wang H.L.
      • et al.
      Comparison of clinical and radiographic outcomes of platform-switched implants with a rough collar and platform-matched implants with a smooth collar: a 1-year randomized clinical trial.
      RCT (parallel)Participants with single-tooth gap in esthetic zone; sufficient bone volume for single implant as measured on CT scanCCSuperLine. Dentium.
      IFFZimmer Tapered Screw-Vent. Zimmer Dental.
      Kielbassa et al, 2009 Germany
      • Kielbassa A.M.
      • de Fuentes R.M.
      • Goldstein M.
      • Arnhart C.
      • Barlattani A.
      • Jackowski J.
      • et al.
      Randomized controlled trial comparing a variable-thread novel tapered and a standard tapered implant: interim one-year results.
      Multicenter RCT (parallel)Participants missing ≥1 teeth in maxilla or mandible; sufficient residual bone volume to place ≥10-mm-long and ≥3.5-mm-diameter implantsCCNobelActive. Nobel Biocare.
      IFFNobelReplace Tapered Groovy. Nobel Biocare.
      EHNobelActive. Nobel Biocare.
      Kim et al, 2019

      Republic of Korea
      • Kim J.C.
      • Lee J.
      • Kim S.
      • Koo K.T.
      • Kim H.Y.
      • Yeo I.S.L.
      Influence of implant abutment connection structure on peri-implant bone level in a second molar: a 1-year randomized controlled trial.
      RCT (parallel)Participants who need to restore single mandibular second molar; residual bone height ≥9 mm and thickness ≥9 mm measured on CT scanCCLuna. Shinhung.
      EHSola. Shinhung.
      Menini et al, 2019

      Italy
      • Menini M.
      • Pesce P.
      • Bagnasco F.
      • Carossa M.
      • Mussano F.
      • Pera F.
      Evaluation of internal and external hexagon connections in immediately loaded full-arch rehabilitations: a within-person randomised split-mouth controlled trial.
      Multicenter RCT (split-mouth)Participants with unfavorable prognoses for maxillary or mandibular dentition demanding immediate fixed-implant prosthesisIFFShelta. Sweden & Martina.
      EHSyra. Sweden & Martina.
      Peñarrocha-Diago et al, 2013

      Spain
      • Peñarrocha-Diago M.A.
      • Flichy-Fernández A.J.
      • Alonso-González R.
      • Peñarrocha-Oltra D.
      • Balaguer-Martínez J.
      • Peñarrocha-Diago M.
      Influence of implant neck design and implant abutment connection type on peri-implant health. Radiological study.
      RCT (parallel)Maxillary or mandibular edentulous participants; sufficient residual bone volume to insert 2-8 implants; residual bone height ≥6 mm and thickness ≥7 mm measured on CT scanCCInHex. Mozo-Grau.
      EHOsseous. Mozo-Grau.
      Pessoa et al, 2017

      Brazil
      • Pessoa R.S.
      • Sousa R.M.
      • Pereira L.M.
      • Neves F.D.
      • Bezerra F.J.B.
      • Jaecques S.V.N.
      • et al.
      Bone remodeling around implants with external hexagon and morse-taper connections: a randomized, controlled, split-mouth, clinical trial.
      RCT (split-mouth)Mandibular edentulous participants; sufficient residual bone volume, measured on CT scan, to insert 4 implants 13 mm in length and 3.8 mm in diameter.CCUnitite. SIN.
      EHUnitite. SIN.
      Pieri et al, 2011

      Italy
      • Pieri F.
      • Aldini N.N.
      • Marchetti C.
      • Corinaldesi G.
      Influence of implant abutment interface design on bone and soft tissue levels around immediately placed and restored single-tooth implants: a randomized controlled clinical trial.
      RCT (parallel)Participants requiring extraction of 1 maxillary premolar, replaced by dental implant, with ≥4 mm of bone beyond root apex and preserving 4 bony wallsCCSmiler. Samo Biomedica.
      IFFSmiler. Samo Biomedica.
      Pozzi et al, 2014

      Italy
      • Pozzi A.
      • Agliardi E.
      • Tallarico M.
      • Barlattani A.
      Clinical and radiological outcomes of two implants with different prosthetic interfaces and neck configurations: randomized, controlled, split-mouth clinical trial.
      RCT (split-mouth)Participants partially edentulous in mandible, Kennedy Class I. II or III, requiring ≥2 single implant-supported crowns; sufficient bone volumes to accommodate dental implants without augmentation procedureCCNobelActive. Nobel Biocare.
      EHNobelSpeedy Groovy. Nobel Biocare.
      Sanz-Martín et al, 2017

      Spain
      • Sanz-Martín I.
      • Sanz-Sánchez I.
      • Noguerol F.
      • Cok S.
      • Ortiz-Vigón A.
      • Sanz M.
      Randomized controlled clinical trial comparing two dental implants with different neck configurations.
      RCT (parallel)Participants partially edentulous in posterior maxilla or mandible; sufficient residual bone volume to place ≥7-mm-long and ≥3.8-mm-diameter implantsCCPremium TG. Sweden & Martina.
      IFFPremium SP. Sweden & Martina.
      CC, conical connection; EH, external hexagon; IFF, internal flat-to-flat; PS, platform switching; RCT, randomized controlled trial.
      Fourteen of the 18 RCTs included were considered to have a high risk of bias.
      • Cannata M.
      • Grandi T.
      • Samarani R.
      • Svezia L.
      • Grandi G.
      A comparison of two implants with conical vs internal hex connections: 1-year post-loading results from a multicentre, randomised controlled trial.
      ,
      • Cooper L.
      • Reside G.
      • Stanford C.
      • Barwacz C.
      • Feine J.
      • Nader S.
      • et al.
      A Multicenter randomized comparative trial of implants with different abutment interfaces to replace anterior maxillary single teeth.
      ,
      • Cooper L.
      • Tarnow D.
      • Froum S.
      • Moriarty J.
      • De Kok I.
      Comparison of marginal bone changes with internal conus and external hexagon design implant systems: a prospective, randomized study.
      ,
      • Felice P.
      • Barausse C.
      • Blasone R.
      • Favaretto G.
      • Stacchi C.
      • Calvo M.
      • et al.
      A comparison of two dental implant systems in partially edentulous patients: 1-year post-loading results from a pragmatic multicentre randomised controlled trial.
      • Glibert M.
      • Vervaeke S.
      • Jacquet W.
      • Vermeersch K.
      • Östman P.O.
      • De Bruyn H.
      A randomized controlled clinical trial to assess crestal bone remodeling of four different implant designs.
      • Gultekin B.A.
      • Gultekin P.
      • Leblebicioglu B.
      • Basegmez C.
      • Yalcin S.
      Clinical evaluation of marginal bone loss and stability in two types of submerged dental implants.
      • Hsu Y.T.
      • Chan H.L.
      • Rudek I.
      • Bashutski J.
      • Oh W.S.
      • Wang H.L.
      • et al.
      Comparison of clinical and radiographic outcomes of platform-switched implants with a rough collar and platform-matched implants with a smooth collar: a 1-year randomized clinical trial.
      • Kielbassa A.M.
      • de Fuentes R.M.
      • Goldstein M.
      • Arnhart C.
      • Barlattani A.
      • Jackowski J.
      • et al.
      Randomized controlled trial comparing a variable-thread novel tapered and a standard tapered implant: interim one-year results.
      • Kim J.C.
      • Lee J.
      • Kim S.
      • Koo K.T.
      • Kim H.Y.
      • Yeo I.S.L.
      Influence of implant abutment connection structure on peri-implant bone level in a second molar: a 1-year randomized controlled trial.
      • Menini M.
      • Pesce P.
      • Bagnasco F.
      • Carossa M.
      • Mussano F.
      • Pera F.
      Evaluation of internal and external hexagon connections in immediately loaded full-arch rehabilitations: a within-person randomised split-mouth controlled trial.
      • Peñarrocha-Diago M.A.
      • Flichy-Fernández A.J.
      • Alonso-González R.
      • Peñarrocha-Oltra D.
      • Balaguer-Martínez J.
      • Peñarrocha-Diago M.
      Influence of implant neck design and implant abutment connection type on peri-implant health. Radiological study.
      ,
      • Pieri F.
      • Aldini N.N.
      • Marchetti C.
      • Corinaldesi G.
      Influence of implant abutment interface design on bone and soft tissue levels around immediately placed and restored single-tooth implants: a randomized controlled clinical trial.
      • Pozzi A.
      • Agliardi E.
      • Tallarico M.
      • Barlattani A.
      Clinical and radiological outcomes of two implants with different prosthetic interfaces and neck configurations: randomized, controlled, split-mouth clinical trial.
      • Sanz-Martín I.
      • Sanz-Sánchez I.
      • Noguerol F.
      • Cok S.
      • Ortiz-Vigón A.
      • Sanz M.
      Randomized controlled clinical trial comparing two dental implants with different neck configurations.
      Most of the studies showed a high or unclear risk for the blinding of clinical and/or radiological outcomes. Figure 2 and Supplemental Table 3 (available online) summarize the quality of the RCTs included.
      Figure thumbnail gr2
      Figure 2Risk of bias assessment of studies included based on the Cochrane Risk of Bias tool.
      Fifty-two of the 1042 participants in the 18 studies included could not be analyzed because of dropouts within the follow-up period (weighted mean dropout rate: 2.91%). Seven of the trials meta-analyzed had a split-mouth design.
      • Canullo L.
      • Rosa J.C.
      • Pinto V.S.
      • Francischone C.E.
      • Götz W.
      Inward-inclined implant platform for the amplified platform-switching concept: 18-month follow-up report of a prospective randomized matched-pair controlled trial.
      ,
      • Felice P.
      • Barausse C.
      • Blasone R.
      • Favaretto G.
      • Stacchi C.
      • Calvo M.
      • et al.
      A comparison of two dental implant systems in partially edentulous patients: 1-year post-loading results from a pragmatic multicentre randomised controlled trial.
      ,
      • Glibert M.
      • Vervaeke S.
      • Jacquet W.
      • Vermeersch K.
      • Östman P.O.
      • De Bruyn H.
      A randomized controlled clinical trial to assess crestal bone remodeling of four different implant designs.
      ,
      • Gultekin B.A.
      • Gultekin P.
      • Leblebicioglu B.
      • Basegmez C.
      • Yalcin S.
      Clinical evaluation of marginal bone loss and stability in two types of submerged dental implants.
      ,
      • Menini M.
      • Pesce P.
      • Bagnasco F.
      • Carossa M.
      • Mussano F.
      • Pera F.
      Evaluation of internal and external hexagon connections in immediately loaded full-arch rehabilitations: a within-person randomised split-mouth controlled trial.
      ,
      • Pessoa R.S.
      • Sousa R.M.
      • Pereira L.M.
      • Neves F.D.
      • Bezerra F.J.B.
      • Jaecques S.V.N.
      • et al.
      Bone remodeling around implants with external hexagon and morse-taper connections: a randomized, controlled, split-mouth, clinical trial.
      ,
      • Pozzi A.
      • Agliardi E.
      • Tallarico M.
      • Barlattani A.
      Clinical and radiological outcomes of two implants with different prosthetic interfaces and neck configurations: randomized, controlled, split-mouth clinical trial.
      By implant abutment connection type, 344 participants (586 implants) were treated with external interfaces, 393 (526 implants) with internal flat-to-flat designs, and 517 participants (791 implants) with an internal conical connection. The results for each individual RCT included are reported in Table 2.
      Table 2Comparison of studies selected
      VariableStudy, Year
      Cannata et al, 2017
      • Cannata M.
      • Grandi T.
      • Samarani R.
      • Svezia L.
      • Grandi G.
      A comparison of two implants with conical vs internal hex connections: 1-year post-loading results from a multicentre, randomised controlled trial.
      Canullo et al, 2012
      • Canullo L.
      • Rosa J.C.
      • Pinto V.S.
      • Francischone C.E.
      • Götz W.
      Inward-inclined implant platform for the amplified platform-switching concept: 18-month follow-up report of a prospective randomized matched-pair controlled trial.
      Cooper et al, 2015
      • Cooper L.
      • Reside G.
      • Stanford C.
      • Barwacz C.
      • Feine J.
      • Nader S.
      • et al.
      A Multicenter randomized comparative trial of implants with different abutment interfaces to replace anterior maxillary single teeth.
      Cooper et al, 2016
      • Cooper L.
      • Tarnow D.
      • Froum S.
      • Moriarty J.
      • De Kok I.
      Comparison of marginal bone changes with internal conus and external hexagon design implant systems: a prospective, randomized study.
      Intervention
       CON1CCIFFCCCC
       CON2IFFEHIFFEH
      N° of implants (participants) [dropouts]
       CON145 (45) [0]40 (40) [0]48 (48) [0]47 (19) [0]
       CON245 (45) [1]40 (40) [0]93 (93) [4]46 (20) [0]
      Age of participants
       CON1 (SD) [range]52.3 (16.8)58.2 [NR]43 (15)55.2 (11.8)
       CON2 (SD) [range]51.2 (17.3)46 (16.4)51.0 (11.0)
      Platform switching
       CON1YesYesYesYes
       CON2YesNoMixedNo
      Insertion timingPost-extractive & healed sitesHealed sitesHealed sitesHealed sites
      Load timingDelayedDelayedImmediateDelayed
      Prosthesis designISCs & FPDsISCsCemented ISCsCemented ISCs
      Identical macrotopography and microtopographyYesYesNoNo
      Mean MBL
       CON1 (SD)0.56 (0.53)0.44 (0.25)0.22 (0.28)0.48 (0.55)
       CON2 (SD)0.60 (0.62)1.47 (0.46)1.26 (0.83)0.68 (1.2)
      MD (95% CI)-0.04 (-0.28 to 0.20)-1.03 (-1.19 to -0.87)-1.04 (-1.24 to -0.84)-0.20 (-0.59 to 0.19)
      P.745<.001
      Significantly associated (P<.05).
      <.001
      Significantly associated (P<.05).
      .317
      Implant survival
       CON1 (%)44 (97.78)40 (100)48 (100)45 (95.74)
       CON2 (%)45 (100)40 (100)80 (86.02)44 (95.65)
      OR (95% CI)0.33 (0.01-8.22)NC16.27 (0.95-279.83)1.02 (0.14-7.58)
      P-value.496NA.055.982
      Biologic complications
       CON1 (%)2 (4.44)0 (0)NRNR
       CON2 (%)1 (2.22)0 (0)
      OR (95% CI)2.05 (0.18-23.41)NC
      P.565NA
      Technical complications
       CON1 (%)0 (0)NRNR1 (2.13)
       CON2 (%)1 (2.22)11 (23.91)
      OR (95% CI)0.33 (0.01-8.22)0.07 (0.01-0.56)
      P.496.012
      Significantly associated (P<.05).
      VariableStudy, Year
      Crespi et al, 2009
      • Crespi R.
      • Capparè P.
      • Gherlone E.
      Radiographic evaluation of marginal bone levels around platform-switched and non-platform-switched implants used in an immediate loading protocol.
      Esposito et al, 2015
      • Esposito M.
      • Maghaireh H.
      • Pistilli R.
      • Grusovin M.G.
      • Lee S.T.
      • Gualini F.
      • et al.
      Dental implants with internal versus external connections: 1-year post-loading results from a pragmatic multicenter randomised controlled trial.
      Felice et al, 2014
      • Felice P.
      • Barausse C.
      • Blasone R.
      • Favaretto G.
      • Stacchi C.
      • Calvo M.
      • et al.
      A comparison of two dental implant systems in partially edentulous patients: 1-year post-loading results from a pragmatic multicentre randomised controlled trial.
      Glibert et al, 2018
      • Glibert M.
      • Vervaeke S.
      • Jacquet W.
      • Vermeersch K.
      • Östman P.O.
      • De Bruyn H.
      A randomized controlled clinical trial to assess crestal bone remodeling of four different implant designs.
      Intervention
       CON1CCCCCCCC
       CON2EHEHIFFEH
      N° of implants (participants) [dropouts]
       CON130 (22) [0]154 (98) [7]71 (64) [6]42 (21) [1]
       CON234 (23) [0]173 (102) [2]73 (64) [6]42 (21) [1]
      Age of participants
       CON1 (SD) [range]48.7 [25-67]52.5 (14.1)52.0 [19-80]65.0 [44-86]
       CON2 (SD) [range]50.1 (14.5)
      Platform switching
       CON1YesYesYesYes
       CON2NoNoNoYes
      Insertion timingPost-extractivePost-extractive & healed sitesPost-extractive & healed sitesHealed sites
      Load timingImmediateImmediate & delayedDelayedImmediate
      Prosthesis designISCs & FPDsISCs. FPDs. FCDs & ODsISCs & FPDsODs
      Identical macrotopography and microtopographyNoYesNoYes
      Mean MBL
       CON1 (SD)0.2 (0.43)0.94 (0.84)0.73 (0.59)0.25 (0.37)
       CON2 (SD)0.17 (0.39)1 (1.03)0.84 (0.59)0.31 (0.41)
      MD (95% CI)0.03 (-0.17 to 0.23)-0.06 (-0.37 to 0.25)-0.11 (-0.30 to 0.08)-0.06 (-0.23 to 0.11)
      P-value.772.702.268.491
      Implant survival
       CON1 (%)30 (100)152 (98.70)71 (100)42 (100)
       CON2 (%)34 (100)170 (98.27)70 (95.89)39 (92.86)
      OR (95% CI)NC1.34 (0.22-8.13)7.10 (0.36-139.95)7.53 (0.38-150.46)
      PNA.75.198.186
      Biologic complications
       CON1 (%)0 (0)2 (1.30)1 (1.41)NR
       CON2 (%)0 (0)1 (0.58)1 (1.37)
      OR (95% CI)NC2.26 (0.20-25.21)1.03 (0.06-16.77)
      PNA.507.984
      Technical complications
       CON1 (%)0 (0)5 (3.25)0 (0)NR
       CON2 (%)3 (8.82)10 (5.78)0 (0)
      OR (95% CI)0.15 (0.01-2.98)0.55 (0.18-1.64)NC
      P.212.281NA
      VariableStudy, Year
      Gultekin et al, 2013
      • Gultekin B.A.
      • Gultekin P.
      • Leblebicioglu B.
      • Basegmez C.
      • Yalcin S.
      Clinical evaluation of marginal bone loss and stability in two types of submerged dental implants.
      Hsu et al, 2016
      • Hsu Y.T.
      • Chan H.L.
      • Rudek I.
      • Bashutski J.
      • Oh W.S.
      • Wang H.L.
      • et al.
      Comparison of clinical and radiographic outcomes of platform-switched implants with a rough collar and platform-matched implants with a smooth collar: a 1-year randomized clinical trial.
      Kielbassa et al, 2009
      • Kielbassa A.M.
      • de Fuentes R.M.
      • Goldstein M.
      • Arnhart C.
      • Barlattani A.
      • Jackowski J.
      • et al.
      Randomized controlled trial comparing a variable-thread novel tapered and a standard tapered implant: interim one-year results.
      Kielbassa et al, 2009
      • Kielbassa A.M.
      • de Fuentes R.M.
      • Goldstein M.
      • Arnhart C.
      • Barlattani A.
      • Jackowski J.
      • et al.
      Randomized controlled trial comparing a variable-thread novel tapered and a standard tapered implant: interim one-year results.
      Intervention
       CON1CCCCCCCC
       CON2IFFIFFIFFEH
      N° of implants (participants) [dropouts]
       CON143 (21) [2]13 (13) [0]58 (32) [1]59 (32) [1]
       CON250 (21) [2]13 (13) [0]63 (30) [1]41 (26) [4]
      Age of participants
      CON1 (SD) [range]41.3 [19-59]58.5 (14.1)49.5 (13.1)49.5 (13.1)
      CON2 (SD) [range]56.9 (10.9)46.9 (14.6)49.9 (13.6)
      Platform switching
       CON1YesYesYesYes
       CON2NoNoNoNo
      Insertion timingHealed sitesHealed sitesHealed sitesHealed sites
      Load timingDelayedDelayedImmediateImmediate
      Prosthesis designNRISCsISCs. FDPs & FCDsISCs. FDPs & FCDs
      Identical macrotopography and microtopographyNoNoNoNo
      Mean MBL
       CON1 (SD)0.35 (0.13)0.21 (0.56)0.95 (1.37)0.95 (1.37)
       CON2 (SD)0.83 (0.16)0.74 (0.47)0.63 (1.18)0.64 (0.97)
      MD (95% CI)-0.48 (-0.54 to -0.42)-0.53 (-0.93 to -0.13)0.32 (-0.22 to 0.86)0.31 (-0.21 to 0.83)
      P<.001
      Significantly associated (P<.05).
      .015
      Significantly associated (P<.05).
      .246.247
      Implant survival
       CON1 (%)43 (100)13 (100)56 (96.55)57 (96.61)
       CON2 (%)50 (100)13 (100)60 (95.24)40 (97.56)
      OR (95% CI)NCNC1.40 (0.23-8.26)0.71 (0.06-8.13)
      P-valueNANA.489.785
      Biologic complications
       CON1 (%)NR0 (0)1 (1.72)1 (1.69)
       CON2 (%)0 (0)1 (1.59)1 (2.44)
      OR (95% CI)NC1.09 (0.07-17.80)0.69 (0.04-11.35)
      PNA.953.795
      Technical complications
       CON1 (%)NRNR5 (8.62)4 (6.78)
       CON2 (%)4 (6.35)3 (7.32)
      OR (95% CI)1.39 (0.35-5.45)0.92 (0.19-4.35)
      P.636.918
      VariableStudy, Year
      Kielbassa et al, 2009
      • Kielbassa A.M.
      • de Fuentes R.M.
      • Goldstein M.
      • Arnhart C.
      • Barlattani A.
      • Jackowski J.
      • et al.
      Randomized controlled trial comparing a variable-thread novel tapered and a standard tapered implant: interim one-year results.
      Kim et al, 2019
      • Kim J.C.
      • Lee J.
      • Kim S.
      • Koo K.T.
      • Kim H.Y.
      • Yeo I.S.L.
      Influence of implant abutment connection structure on peri-implant bone level in a second molar: a 1-year randomized controlled trial.
      Menini et al, 2019
      • Menini M.
      • Pesce P.
      • Bagnasco F.
      • Carossa M.
      • Mussano F.
      • Pera F.
      Evaluation of internal and external hexagon connections in immediately loaded full-arch rehabilitations: a within-person randomised split-mouth controlled trial.
      Peñarrocha-Diago et al, 2013
      • Peñarrocha-Diago M.A.
      • Flichy-Fernández A.J.
      • Alonso-González R.
      • Peñarrocha-Oltra D.
      • Balaguer-Martínez J.
      • Peñarrocha-Diago M.
      Influence of implant neck design and implant abutment connection type on peri-implant health. Radiological study.
      Intervention
       CON1IFFCCIFFCC
       CON2EHEHEHEH
      N° of implants (participants) [dropouts]
       CON162 (30) [1]11 (11) [1]40 (20) [0]72 (7) [2]
       CON241 (27) [4]11 (11) [1]43 (20) [0]69 (8) [1]
      Age of participants
       CON1 (SD) [range]46.9 (14.6)NR [20-66]64.0 [47-79]56.9 [44-77]
       CON2 (SD) [range]49.9 (13.6)
      Platform switching
       CON1NoYesNoYes
       CON2NoNoNoNo
      Insertion timingHealed sitesHealed sitesPost-extractiveHealed sites
      Load timingImmediateDelayedImmediateDelayed
      Prosthesis designISCs. FDPs & FCDsISCsFCDsFCDs & OD
      Identical macrotopography and microtopographyNoYesYesNo
      Mean MBL
       CON1 (SD)0.63 (1.18)0.04 (0.63)1.64 (0.77)0.12 (0.17)
       CON2 (SD)0.64 (0.97)0.59 (0.95)1.53 (0.83)0.38 (0.51)
      MD (95% CI)-0.01 (-0.49 to 0.47)-0.55 (-1.22 to 0.12)0.11 (-0.23 to 0.45)-0.26 (-0.36 to -0.16)
      P-value.968.126.533<.001
      Significantly associated (P<.05).
      Implant survival
       CON1 (%)60 (96.77)11 (100)39 (97.50)71 (98.61)
       CON2 (%)39 (95.12)11 (100)42 (97.67)68 (98.55)
      OR (95% CI)1.54 (0.21-11.38)NC0.93 (0.06-15.36)1.04 (0.06-17.03)
      P-value.673NA.959.976
      Biologic complications
       CON1 (%)0 (0)0 (0)0 (0)1 (1.39)
       CON2 (%)1 (2.44)0 (0)0 (0)1 (1.45)
      OR (95% CI)0.22 (0.01-5.43)NCNC0.96 (0.06-15.62)
      P.352NANA.976
      Technical complications
       CON1 (%)4 (6.45)0 (0)1 (2.50)NR
       CON2 (%)3 (7.32)2 (18.18)2 (5.00)
      OR (95% CI)0.87 (0.19-4.12)0.17 (0.01-3.88)0.53 (0.05-6.03)
      P.864.263.606
      VariableStudy, Year
      Pessoa et al, 2017
      • Pessoa R.S.
      • Sousa R.M.
      • Pereira L.M.
      • Neves F.D.
      • Bezerra F.J.B.
      • Jaecques S.V.N.
      • et al.
      Bone remodeling around implants with external hexagon and morse-taper connections: a randomized, controlled, split-mouth, clinical trial.
      Pieri et al, 2011
      • Pieri F.
      • Aldini N.N.
      • Marchetti C.
      • Corinaldesi G.
      Influence of implant abutment interface design on bone and soft tissue levels around immediately placed and restored single-tooth implants: a randomized controlled clinical trial.
      Pozzi et al, 2014
      • Pozzi A.
      • Agliardi E.
      • Tallarico M.
      • Barlattani A.
      Clinical and radiological outcomes of two implants with different prosthetic interfaces and neck configurations: randomized, controlled, split-mouth clinical trial.
      Sanz-Martín et al, 2017
      • Sanz-Martín I.
      • Sanz-Sánchez I.
      • Noguerol F.
      • Cok S.
      • Ortiz-Vigón A.
      • Sanz M.
      Randomized controlled clinical trial comparing two dental implants with different neck configurations.
      Intervention
       CON1CCCCCCCC
       CON2EHIFFEHIFF
      N° of implants (participants) [dropouts]
       CON112 (12) [0]19 (19) [1]34 (34) [0]33 (19) [6]
       CON212 (12) [0]19 (19) [1]34 (34) [0]28 (18) [4]
      Age of participants
       CON1 (SD) [range]63.1 [18-75]45.8 [26-67]52.2 [39-59]57.7 (11.9)
       CON2 (SD) [range]46.6 [32-65]59.7 (10.5)
      Platform switching
       CON1YesYesYesNo
       CON2NoNoNoYes
      Insertion timingHealed sitesPost-extractiveHealed sitesHealed sites
      Load timingImmediateImmediateDelayedDelayed
      Prosthesis designFCDsScrewed ISCsCemented ISCsISCs & FPDs
      Identical macrotopography and microtopographyYesYesNoNo
      Mean MBL
       CON1 (SD)0.17 (0.54)0.19 (0.17)0.51 (0.34)0.26 (0.22)
       CON2 (SD)1.17 (0.44)0.49 (0.25)1.1 (0.52)0.11 (0.2)
      MD (95% CI)-1.00 (-1.39 to -0.61)-0.30 (-0.44 to -0.16)-0.59 (-0.84 to -0.34)0.15 (0.01-0.29)
      P<.001
      Significantly associated (P<.05).
      <.001
      Significantly associated (P<.05).
      <.001
      Significantly associated (P<.05).
      .037
      Significantly associated (P<.05).
      Implant survival
       CON1 (%)12 (100)18 (94.74)34 (100)33 (100)
       CON2 (%)12 (100)19 (100)34 (100)26 (92.9)
      OR (95% CI)NC0.32 (0.01-8.26)NC6.32 (0.29-137.37)
      PNA.489NA.241
      Biologic complications
       CON1 (%)0 (0)1 (5.26)0 (0)2 (6.06)
       CON2 (%)0 (0)0 (0)0 (0)3 (10.71)
      OR (95% CI)NC3.16 (0.12-82.64)NC0.54 (0.08-3.47)
      P-valueNA.489NA.514
      Technical complications
       CON1 (%)NR0 (0)NR0 (0)
       CON2 (%)2 (10.53)4 (14.29)
      OR (95% CI)0.18 (0.01-4.00)0.08 (0.00-1.58)
      P.278.097
      CC, conical connection; CI, confidence interval; CON1, connection 1; CON2, connection 2; EH, external hexagon; FCDs, fixed complete dentures; FPDs, fixed partial dentures; IFF, internal flat-to-flat; ISCs, implant-supported crown; MD, mean difference; NA, not applicable; NC, not calculable; NR, not reported; ODs, overdentures; OR, odds ratio; SD, standard deviation.
      Significantly associated (P<.05).
      The survival and biologic analyses included 18 (1903 implants in 1042 participants)
      • Cannata M.
      • Grandi T.
      • Samarani R.
      • Svezia L.
      • Grandi G.
      A comparison of two implants with conical vs internal hex connections: 1-year post-loading results from a multicentre, randomised controlled trial.
      • Canullo L.
      • Rosa J.C.
      • Pinto V.S.
      • Francischone C.E.
      • Götz W.
      Inward-inclined implant platform for the amplified platform-switching concept: 18-month follow-up report of a prospective randomized matched-pair controlled trial.
      • Cooper L.
      • Reside G.
      • Stanford C.
      • Barwacz C.
      • Feine J.
      • Nader S.
      • et al.
      A Multicenter randomized comparative trial of implants with different abutment interfaces to replace anterior maxillary single teeth.
      • Cooper L.
      • Tarnow D.
      • Froum S.
      • Moriarty J.
      • De Kok I.
      Comparison of marginal bone changes with internal conus and external hexagon design implant systems: a prospective, randomized study.
      • Crespi R.
      • Capparè P.
      • Gherlone E.
      Radiographic evaluation of marginal bone levels around platform-switched and non-platform-switched implants used in an immediate loading protocol.
      • Esposito M.
      • Maghaireh H.
      • Pistilli R.
      • Grusovin M.G.
      • Lee S.T.
      • Gualini F.
      • et al.
      Dental implants with internal versus external connections: 1-year post-loading results from a pragmatic multicenter randomised controlled trial.
      • Felice P.
      • Barausse C.
      • Blasone R.
      • Favaretto G.
      • Stacchi C.
      • Calvo M.
      • et al.
      A comparison of two dental implant systems in partially edentulous patients: 1-year post-loading results from a pragmatic multicentre randomised controlled trial.
      • Glibert M.
      • Vervaeke S.
      • Jacquet W.
      • Vermeersch K.
      • Östman P.O.
      • De Bruyn H.
      A randomized controlled clinical trial to assess crestal bone remodeling of four different implant designs.
      • Gultekin B.A.
      • Gultekin P.
      • Leblebicioglu B.
      • Basegmez C.
      • Yalcin S.
      Clinical evaluation of marginal bone loss and stability in two types of submerged dental implants.
      • Hsu Y.T.
      • Chan H.L.
      • Rudek I.
      • Bashutski J.
      • Oh W.S.
      • Wang H.L.
      • et al.
      Comparison of clinical and radiographic outcomes of platform-switched implants with a rough collar and platform-matched implants with a smooth collar: a 1-year randomized clinical trial.
      • Kielbassa A.M.
      • de Fuentes R.M.
      • Goldstein M.
      • Arnhart C.
      • Barlattani A.
      • Jackowski J.
      • et al.
      Randomized controlled trial comparing a variable-thread novel tapered and a standard tapered implant: interim one-year results.
      • Kim J.C.
      • Lee J.
      • Kim S.
      • Koo K.T.
      • Kim H.Y.
      • Yeo I.S.L.
      Influence of implant abutment connection structure on peri-implant bone level in a second molar: a 1-year randomized controlled trial.
      • Menini M.
      • Pesce P.
      • Bagnasco F.
      • Carossa M.
      • Mussano F.
      • Pera F.
      Evaluation of internal and external hexagon connections in immediately loaded full-arch rehabilitations: a within-person randomised split-mouth controlled trial.
      • Peñarrocha-Diago M.A.
      • Flichy-Fernández A.J.
      • Alonso-González R.
      • Peñarrocha-Oltra D.
      • Balaguer-Martínez J.
      • Peñarrocha-Diago M.
      Influence of implant neck design and implant abutment connection type on peri-implant health. Radiological study.
      • Pessoa R.S.
      • Sousa R.M.
      • Pereira L.M.
      • Neves F.D.
      • Bezerra F.J.B.
      • Jaecques S.V.N.
      • et al.
      Bone remodeling around implants with external hexagon and morse-taper connections: a randomized, controlled, split-mouth, clinical trial.
      • Pieri F.
      • Aldini N.N.
      • Marchetti C.
      • Corinaldesi G.
      Influence of implant abutment interface design on bone and soft tissue levels around immediately placed and restored single-tooth implants: a randomized controlled clinical trial.
      • Pozzi A.
      • Agliardi E.
      • Tallarico M.
      • Barlattani A.
      Clinical and radiological outcomes of two implants with different prosthetic interfaces and neck configurations: randomized, controlled, split-mouth clinical trial.
      • Sanz-Martín I.
      • Sanz-Sánchez I.
      • Noguerol F.
      • Cok S.
      • Ortiz-Vigón A.
      • Sanz M.
      Randomized controlled clinical trial comparing two dental implants with different neck configurations.
      and 14 RCTs (1492 implants in 820 participants),
      • Cannata M.
      • Grandi T.
      • Samarani R.
      • Svezia L.
      • Grandi G.
      A comparison of two implants with conical vs internal hex connections: 1-year post-loading results from a multicentre, randomised controlled trial.
      ,
      • Canullo L.
      • Rosa J.C.
      • Pinto V.S.
      • Francischone C.E.
      • Götz W.
      Inward-inclined implant platform for the amplified platform-switching concept: 18-month follow-up report of a prospective randomized matched-pair controlled trial.
      ,
      • Crespi R.
      • Capparè P.
      • Gherlone E.
      Radiographic evaluation of marginal bone levels around platform-switched and non-platform-switched implants used in an immediate loading protocol.
      • Esposito M.
      • Maghaireh H.
      • Pistilli R.
      • Grusovin M.G.
      • Lee S.T.
      • Gualini F.
      • et al.
      Dental implants with internal versus external connections: 1-year post-loading results from a pragmatic multicenter randomised controlled trial.
      • Felice P.
      • Barausse C.
      • Blasone R.
      • Favaretto G.
      • Stacchi C.
      • Calvo M.
      • et al.
      A comparison of two dental implant systems in partially edentulous patients: 1-year post-loading results from a pragmatic multicentre randomised controlled trial.
      ,
      • Hsu Y.T.
      • Chan H.L.
      • Rudek I.
      • Bashutski J.
      • Oh W.S.
      • Wang H.L.
      • et al.
      Comparison of clinical and radiographic outcomes of platform-switched implants with a rough collar and platform-matched implants with a smooth collar: a 1-year randomized clinical trial.
      • Kielbassa A.M.
      • de Fuentes R.M.
      • Goldstein M.
      • Arnhart C.
      • Barlattani A.
      • Jackowski J.
      • et al.
      Randomized controlled trial comparing a variable-thread novel tapered and a standard tapered implant: interim one-year results.
      • Kim J.C.
      • Lee J.
      • Kim S.
      • Koo K.T.
      • Kim H.Y.
      • Yeo I.S.L.
      Influence of implant abutment connection structure on peri-implant bone level in a second molar: a 1-year randomized controlled trial.
      • Menini M.
      • Pesce P.
      • Bagnasco F.
      • Carossa M.
      • Mussano F.
      • Pera F.
      Evaluation of internal and external hexagon connections in immediately loaded full-arch rehabilitations: a within-person randomised split-mouth controlled trial.
      • Peñarrocha-Diago M.A.
      • Flichy-Fernández A.J.
      • Alonso-González R.
      • Peñarrocha-Oltra D.
      • Balaguer-Martínez J.
      • Peñarrocha-Diago M.
      Influence of implant neck design and implant abutment connection type on peri-implant health. Radiological study.
      • Pessoa R.S.
      • Sousa R.M.
      • Pereira L.M.
      • Neves F.D.
      • Bezerra F.J.B.
      • Jaecques S.V.N.
      • et al.
      Bone remodeling around implants with external hexagon and morse-taper connections: a randomized, controlled, split-mouth, clinical trial.
      • Pieri F.
      • Aldini N.N.
      • Marchetti C.
      • Corinaldesi G.
      Influence of implant abutment interface design on bone and soft tissue levels around immediately placed and restored single-tooth implants: a randomized controlled clinical trial.
      • Pozzi A.
      • Agliardi E.
      • Tallarico M.
      • Barlattani A.
      Clinical and radiological outcomes of two implants with different prosthetic interfaces and neck configurations: randomized, controlled, split-mouth clinical trial.
      • Sanz-Martín I.
      • Sanz-Sánchez I.
      • Noguerol F.
      • Cok S.
      • Ortiz-Vigón A.
      • Sanz M.
      Randomized controlled clinical trial comparing two dental implants with different neck configurations.
      respectively (Table 2 and Fig. 3A, 3B ). No statistically significant differences among any of the implant abutment connections assessed were found in either the PMAs of direct comparisons or the NMA model (P>.05 in all direct, indirect, and mixed comparisons) (Table 3 and Supplemental Figs. 1, 2, available online).
      Figure thumbnail gr3
      Figure 3Network meta-analysis graph (net diagram). Each node represents one implant abutment connection category (cluster). A, Implant survival. B, Biologic complications. C, Peri-implant marginal bone loss. D, Prosthetic complications. CC, conical connection; EH, external hexagonal; IFF, internal flat-to-flat.
      Table 3Results for comparisons of implant abutment connections
      VariablePMA MBL (mm)NMA MBL
      Number of StudiesNumber of ImplantsMD (95% CI)PI2MD (95% CI)P
      CC vs
       IFF8638-0.27 (-0.53 to 0.02).04
      Significantly associated (P<.05).
      95%-0.20 (-0.48.0.07).154
       EH9710-0.25 (-0.45 to -0.05).01
      Significantly associated (P<.05).
      81%-0.35 (-0.62.-0.08).011
      Significantly associated (P<.05).
      IFF vs
       EH3237-0.33 (-1.18 to 0.53).4695%-0.14 (-0.48.0.19).420
      VariablePMA SurvivalNMA Survival
      Number of studiesNumber of ImplantsSurvival Rate
      (number of surviving implants)/total randomized.
      OR (95% CI)PI2OR (95% CI)P
      CC vs
      IFF8714326/330 vs 363/3842.21 (0.66-7.45).2015%1.86 (0.78-4.39).240
      EH9923454/461 vs 452/4621.32 (0.48-3.66).590%1.40 (0.64- 3.06).449
      IFF vs
      EH3266121/124 vs 139/1421.30 (0.25-6.62).750%0.76 (0.29-1.99).695
      PMA Biologic ComplicationsNMA Biologic Complications
      VariableNumber of StudiesNumber of ImplantsBiologic Rate
      (number of prosthetic complications)/total randomized.
      OR (95% CI)PI2OR (95% CI)P
      CC vs
       IFF64807/239 vs 6/2411.05 (0.26-4.22).890%1.26 (0.48-3.35).654
       EH77464/372 vs 3/3741.23 (0.27-5.66).790%1.00 (0.36-2.77)1.00
      IFF vs
       EH32660/142 vs 1/1240.22 (0.01-5.73).35NA0.79 (0.22-2.80).730
      PMA Prosthetic ComplicationsNMA Prosthetic Complications
      VariableNumber of StudiesNumber of ImplantsProsthetic Rate2OR (95% CI)PI2OR (95% CI)P
      CC vs
       IFF54545/226 vs 11/2280.47 (0.11-1.92).2926%0.63 (0.49-1.52).109
       EH560610/301 vs 29/3050.36 (0.14-0.92).03
      Significantly associated (P<.05).
      21%0.35 (0.13-0.95).038
      Significantly associated (P<.05).
      IFF vs
       EH21865/102 vs 5/840.75 (0.20-2.80).670%0.72 (0.25-2.10).556
      CC, conical connection; CI, confidence interval; EH, external hexagon; IFF, internal flat-to-flat; MD, mean difference; NA, not applicable; NMA, network meta-analysis; OR, odds ratio; PMA, pairwise meta-analysis.
      a Significantly associated (P<.05).
      b (number of surviving implants)/total randomized.
      c (number of prosthetic complications)/total randomized.
      The peri-implant MBL analysis included 18 studies involving 1585 implants in 1042 participants (Table 2 and Fig. 3C).
      • Cannata M.
      • Grandi T.
      • Samarani R.
      • Svezia L.
      • Grandi G.
      A comparison of two implants with conical vs internal hex connections: 1-year post-loading results from a multicentre, randomised controlled trial.
      • Canullo L.
      • Rosa J.C.
      • Pinto V.S.
      • Francischone C.E.
      • Götz W.
      Inward-inclined implant platform for the amplified platform-switching concept: 18-month follow-up report of a prospective randomized matched-pair controlled trial.
      • Cooper L.
      • Reside G.
      • Stanford C.
      • Barwacz C.
      • Feine J.
      • Nader S.
      • et al.
      A Multicenter randomized comparative trial of implants with different abutment interfaces to replace anterior maxillary single teeth.
      • Cooper L.
      • Tarnow D.
      • Froum S.
      • Moriarty J.
      • De Kok I.
      Comparison of marginal bone changes with internal conus and external hexagon design implant systems: a prospective, randomized study.
      • Crespi R.
      • Capparè P.
      • Gherlone E.
      Radiographic evaluation of marginal bone levels around platform-switched and non-platform-switched implants used in an immediate loading protocol.
      • Esposito M.
      • Maghaireh H.
      • Pistilli R.
      • Grusovin M.G.
      • Lee S.T.
      • Gualini F.
      • et al.
      Dental implants with internal versus external connections: 1-year post-loading results from a pragmatic multicenter randomised controlled trial.
      • Felice P.
      • Barausse C.
      • Blasone R.
      • Favaretto G.
      • Stacchi C.
      • Calvo M.
      • et al.
      A comparison of two dental implant systems in partially edentulous patients: 1-year post-loading results from a pragmatic multicentre randomised controlled trial.
      • Glibert M.
      • Vervaeke S.
      • Jacquet W.
      • Vermeersch K.
      • Östman P.O.
      • De Bruyn H.
      A randomized controlled clinical trial to assess crestal bone remodeling of four different implant designs.
      • Gultekin B.A.
      • Gultekin P.
      • Leblebicioglu B.
      • Basegmez C.
      • Yalcin S.
      Clinical evaluation of marginal bone loss and stability in two types of submerged dental implants.
      • Hsu Y.T.
      • Chan H.L.
      • Rudek I.
      • Bashutski J.
      • Oh W.S.
      • Wang H.L.
      • et al.
      Comparison of clinical and radiographic outcomes of platform-switched implants with a rough collar and platform-matched implants with a smooth collar: a 1-year randomized clinical trial.
      • Kielbassa A.M.
      • de Fuentes R.M.
      • Goldstein M.
      • Arnhart C.
      • Barlattani A.
      • Jackowski J.
      • et al.
      Randomized controlled trial comparing a variable-thread novel tapered and a standard tapered implant: interim one-year results.
      • Kim J.C.
      • Lee J.
      • Kim S.
      • Koo K.T.
      • Kim H.Y.
      • Yeo I.S.L.
      Influence of implant abutment connection structure on peri-implant bone level in a second molar: a 1-year randomized controlled trial.
      • Menini M.
      • Pesce P.
      • Bagnasco F.
      • Carossa M.
      • Mussano F.
      • Pera F.
      Evaluation of internal and external hexagon connections in immediately loaded full-arch rehabilitations: a within-person randomised split-mouth controlled trial.
      • Peñarrocha-Diago M.A.
      • Flichy-Fernández A.J.
      • Alonso-González R.
      • Peñarrocha-Oltra D.
      • Balaguer-Martínez J.
      • Peñarrocha-Diago M.
      Influence of implant neck design and implant abutment connection type on peri-implant health. Radiological study.
      • Pessoa R.S.
      • Sousa R.M.
      • Pereira L.M.
      • Neves F.D.
      • Bezerra F.J.B.
      • Jaecques S.V.N.
      • et al.
      Bone remodeling around implants with external hexagon and morse-taper connections: a randomized, controlled, split-mouth, clinical trial.
      • Pieri F.
      • Aldini N.N.
      • Marchetti C.
      • Corinaldesi G.
      Influence of implant abutment interface design on bone and soft tissue levels around immediately placed and restored single-tooth implants: a randomized controlled clinical trial.
      • Pozzi A.
      • Agliardi E.
      • Tallarico M.
      • Barlattani A.
      Clinical and radiological outcomes of two implants with different prosthetic interfaces and neck configurations: randomized, controlled, split-mouth clinical trial.
      • Sanz-Martín I.
      • Sanz-Sánchez I.
      • Noguerol F.
      • Cok S.
      • Ortiz-Vigón A.
      • Sanz M.
      Randomized controlled clinical trial comparing two dental implants with different neck configurations.
      Meta-analysis of the direct comparisons showed significantly less peri-implant MBL in conical connections when compared with external (MD: -0.25 mm; 95% CI: -0.43 to -0.05; P=.01; I2: 81%) and internal flat-to-flat (MD: -0.27 mm; 95% CI: -0.53 to -0.02; P=.04; I2: 95%) interfaces. No statistically significant differences were found between internal flat-to-flat and external designs (MD: -0.33 mm; 95% CI: -1.18 to 0.53; P=.46; I2: 95%) (Table 3 and Supplemental Fig. 3, available online). Heterogeneity was explained by differences in the methodological quality (conical versus external designs), prosthetic loading approach (internal flat-to-flat versus external), and insertion timing of the studies (conical versus internal flat-to-flat). The results were homogeneous and consistent with the overall analysis when only studies with low risk of bias, postextractive implant placement, and immediate prosthetic loading were selected (Supplemental Fig. 4, available online). The NMA model revealed statistically significant differences for the comparison between conical and external implant abutment interfaces (MD: -0.35 mm; 95% CI: -0.62 to -0.08; P=.011) (Table 3).
      Ten of the RCTs included evaluated the prosthetic complications rate in 834 participants (1246 implants) (Table 2 and Fig. 3D).
      • Cannata M.
      • Grandi T.
      • Samarani R.
      • Svezia L.
      • Grandi G.
      A comparison of two implants with conical vs internal hex connections: 1-year post-loading results from a multicentre, randomised controlled trial.
      ,
      • Cooper L.
      • Tarnow D.
      • Froum S.
      • Moriarty J.
      • De Kok I.
      Comparison of marginal bone changes with internal conus and external hexagon design implant systems: a prospective, randomized study.
      • Crespi R.
      • Capparè P.
      • Gherlone E.
      Radiographic evaluation of marginal bone levels around platform-switched and non-platform-switched implants used in an immediate loading protocol.
      • Esposito M.
      • Maghaireh H.
      • Pistilli R.
      • Grusovin M.G.
      • Lee S.T.
      • Gualini F.
      • et al.
      Dental implants with internal versus external connections: 1-year post-loading results from a pragmatic multicenter randomised controlled trial.
      • Felice P.
      • Barausse C.
      • Blasone R.
      • Favaretto G.
      • Stacchi C.
      • Calvo M.
      • et al.
      A comparison of two dental implant systems in partially edentulous patients: 1-year post-loading results from a pragmatic multicentre randomised controlled trial.
      ,
      • Kielbassa A.M.
      • de Fuentes R.M.
      • Goldstein M.
      • Arnhart C.
      • Barlattani A.
      • Jackowski J.
      • et al.
      Randomized controlled trial comparing a variable-thread novel tapered and a standard tapered implant: interim one-year results.
      • Kim J.C.
      • Lee J.
      • Kim S.
      • Koo K.T.
      • Kim H.Y.
      • Yeo I.S.L.
      Influence of implant abutment connection structure on peri-implant bone level in a second molar: a 1-year randomized controlled trial.
      • Menini M.
      • Pesce P.
      • Bagnasco F.
      • Carossa M.
      • Mussano F.
      • Pera F.
      Evaluation of internal and external hexagon connections in immediately loaded full-arch rehabilitations: a within-person randomised split-mouth controlled trial.
      ,
      • Pieri F.
      • Aldini N.N.
      • Marchetti C.
      • Corinaldesi G.
      Influence of implant abutment interface design on bone and soft tissue levels around immediately placed and restored single-tooth implants: a randomized controlled clinical trial.
      • Sanz-Martín I.
      • Sanz-Sánchez I.
      • Noguerol F.
      • Cok S.
      • Ortiz-Vigón A.
      • Sanz M.
      Randomized controlled clinical trial comparing two dental implants with different neck configurations.
      Statistically significant differences were found between conical and external implant abutment connections in the PMAs of direct comparisons (OR: 0.36; 95% CI 0.14 to 0.92; P=.03; I2: 21%) (Table 3 and Supplemental Fig. 5, available online) and in the NMA model (OR: 0.35; 95% CI 0.13 to 0.95; P=.038) (Table 3). Regarding treatment ranking, conical implant abutment designs provided the best results for implant survival (82.9%), peri-implant MBL (96.3%), and prosthetic complications (93.9%) (Fig. 4).
      Figure thumbnail gr4
      Figure 4Illustration of surface under cumulative ranking (SUCRA) analysis for implant survival, biologic complications, peri-implant marginal bone loss, and prosthetic complications. MBL, marginal bone loss.
      For all the outcomes measured (implant survival, peri-implant MBL, and prosthetic and biologic complication rates), no significant inconsistency was identified within the evidence networks as a whole (P>.05) (Supplemental Table 4, available online). In addition, the direct estimate of the summary effect did not differ from the indirect estimate in most comparisons.

      Discussion

      The NMA tested whether the implant abutment connection had an influence on the outcome of an implant-prosthetic rehabilitation. The results indicated that conical connection groups were associated with significantly less peri-implant MBL and fewer prosthetic complications than external interfaces, without compromising implant survival; thus, the first null hypothesis was partially confirmed and the second rejected.
      Nevertheless, the results of this NMA should be treated with caution because of uncontrolled factors that may also have had a direct impact on the outcomes assessed. Uncontrolled factors included implant-related (diameter, length, macroscopic design, surface treatment, and cervical roughness of the implant),
      • Niu W.
      • Wang P.
      • Zhu S.
      • Liu Z.
      • Ji P.
      Marginal bone loss around dental implants with and without microthreads in the neck: a systematic review and meta-analysis.
      ,
      • Canullo L.
      • Fedele G.R.
      • Iannello G.
      • Jepsen S.
      Platform switching and marginal bone-level alterations: The results of a randomized-controlled trial.
      ,
      • Enkling N.
      • Jöhren P.
      • Klimberg V.
      • Bayer S.
      • Mericske-Stern R.
      • Jepsen S.
      Effect of platform switching on peri-implant bone levels: a randomized clinical trial.
      surgery-related (including clinical situation, flap design, surgical trauma, insertion depth in relation to the alveolar crest, and re-establishment of biologic width),
      • Qian J.
      • Wennerberg A.
      • Albrektsson T.
      Reasons for marginal bone loss around oral implants.
      prosthesis-related (design, materials and configuration, occlusal forces, micromovements of the abutment, and loading protocol),
      • Chen J.
      • Cai M.
      • Yang J.
      • Aldhohrah T.
      • Wang Y.
      Immediate versus early or conventional loading dental implants with fixed prostheses: a systematic review and meta-analysis of randomized controlled clinical trials.
      and patient-related (smoking habit, systemic disease, oral microbiology, individual bone pattern, and peri-implant mucosal tissue thickness).
      • Suárez-López Del Amo F.
      • Lin G.H.
      • Monje A.
      • Galindo-Moreno P.
      • Wang H.L.
      Influence of soft tissue thickness on peri-implant marginal bone loss: a systematic review and meta-analysis.
      ,
      • Galindo-Moreno P.
      • Fauri M.
      • Avila-Ortiz G.
      • Fernández-Barbero J.E.
      • Cabrera-León A.
      • Sánchez-Fernández E.
      Influence of alcohol and tobacco habits on peri-implant marginal bone loss: a prospective study.
      Only 8 of the 18 selected studies
      • Cannata M.
      • Grandi T.
      • Samarani R.
      • Svezia L.
      • Grandi G.
      A comparison of two implants with conical vs internal hex connections: 1-year post-loading results from a multicentre, randomised controlled trial.
      ,
      • Canullo L.
      • Rosa J.C.
      • Pinto V.S.
      • Francischone C.E.
      • Götz W.
      Inward-inclined implant platform for the amplified platform-switching concept: 18-month follow-up report of a prospective randomized matched-pair controlled trial.
      ,
      • Glibert M.
      • Vervaeke S.
      • Jacquet W.
      • Vermeersch K.
      • Östman P.O.
      • De Bruyn H.
      A randomized controlled clinical trial to assess crestal bone remodeling of four different implant designs.
      ,
      • Kim J.C.
      • Lee J.
      • Kim S.
      • Koo K.T.
      • Kim H.Y.
      • Yeo I.S.L.
      Influence of implant abutment connection structure on peri-implant bone level in a second molar: a 1-year randomized controlled trial.
      ,
      • Menini M.
      • Pesce P.
      • Bagnasco F.
      • Carossa M.
      • Mussano F.
      • Pera F.
      Evaluation of internal and external hexagon connections in immediately loaded full-arch rehabilitations: a within-person randomised split-mouth controlled trial.
      ,
      • Pessoa R.S.
      • Sousa R.M.
      • Pereira L.M.
      • Neves F.D.
      • Bezerra F.J.B.
      • Jaecques S.V.N.
      • et al.
      Bone remodeling around implants with external hexagon and morse-taper connections: a randomized, controlled, split-mouth, clinical trial.
      ,
      • Pieri F.
      • Aldini N.N.
      • Marchetti C.
      • Corinaldesi G.
      Influence of implant abutment interface design on bone and soft tissue levels around immediately placed and restored single-tooth implants: a randomized controlled clinical trial.
      ,
      • Sanz-Martín I.
      • Sanz-Sánchez I.
      • Noguerol F.
      • Cok S.
      • Ortiz-Vigón A.
      • Sanz M.
      Randomized controlled clinical trial comparing two dental implants with different neck configurations.
      assessed the impact of the implant abutment connection design when using implants with identical macrodesigns and microdesigns. Such factors could have affected the reliability and quality of the results, thus compromising the transitivity assumption.
      • Rouse B.
      • Chaimani A.
      • Li T.
      Network meta-analysis: an introduction for clinicians.
      Consequently, subanalyses were used to assess the impact of the interface in association with some of these confounders.
      Bias was another challenge in the review, as nearly 3-quarters of the trials presented a potential risk of bias (Fig. 2). In addition, because few of the articles that were reviewed compared the same interventions, publication bias was not assessed.
      • Higgins J.P.T.
      • Green S.
      Cochrane handbook for systematic reviews of interventions.
      In addition, internal validity might be compromised because most of the RCTs were conducted in multiple private practices,
      • Cannata M.
      • Grandi T.
      • Samarani R.
      • Svezia L.
      • Grandi G.
      A comparison of two implants with conical vs internal hex connections: 1-year post-loading results from a multicentre, randomised controlled trial.
      ,
      • Canullo L.
      • Rosa J.C.
      • Pinto V.S.
      • Francischone C.E.
      • Götz W.
      Inward-inclined implant platform for the amplified platform-switching concept: 18-month follow-up report of a prospective randomized matched-pair controlled trial.
      ,
      • Esposito M.
      • Maghaireh H.
      • Pistilli R.
      • Grusovin M.G.
      • Lee S.T.
      • Gualini F.
      • et al.
      Dental implants with internal versus external connections: 1-year post-loading results from a pragmatic multicenter randomised controlled trial.
      ,
      • Felice P.
      • Barausse C.
      • Blasone R.
      • Favaretto G.
      • Stacchi C.
      • Calvo M.
      • et al.
      A comparison of two dental implant systems in partially edentulous patients: 1-year post-loading results from a pragmatic multicentre randomised controlled trial.
      and in 12 studies, implant placements were performed by several surgeons and/or prosthodontists, leading to a potential operator-dependent bias.
      • Cannata M.
      • Grandi T.
      • Samarani R.
      • Svezia L.
      • Grandi G.
      A comparison of two implants with conical vs internal hex connections: 1-year post-loading results from a multicentre, randomised controlled trial.
      • Canullo L.
      • Rosa J.C.
      • Pinto V.S.
      • Francischone C.E.
      • Götz W.
      Inward-inclined implant platform for the amplified platform-switching concept: 18-month follow-up report of a prospective randomized matched-pair controlled trial.
      • Cooper L.
      • Reside G.
      • Stanford C.
      • Barwacz C.
      • Feine J.
      • Nader S.
      • et al.
      A Multicenter randomized comparative trial of implants with different abutment interfaces to replace anterior maxillary single teeth.
      • Cooper L.
      • Tarnow D.
      • Froum S.
      • Moriarty J.
      • De Kok I.
      Comparison of marginal bone changes with internal conus and external hexagon design implant systems: a prospective, randomized study.
      ,
      • Esposito M.
      • Maghaireh H.
      • Pistilli R.
      • Grusovin M.G.
      • Lee S.T.
      • Gualini F.
      • et al.
      Dental implants with internal versus external connections: 1-year post-loading results from a pragmatic multicenter randomised controlled trial.
      ,
      • Felice P.
      • Barausse C.
      • Blasone R.
      • Favaretto G.
      • Stacchi C.
      • Calvo M.
      • et al.
      A comparison of two dental implant systems in partially edentulous patients: 1-year post-loading results from a pragmatic multicentre randomised controlled trial.
      ,
      • Kielbassa A.M.
      • de Fuentes R.M.
      • Goldstein M.
      • Arnhart C.
      • Barlattani A.
      • Jackowski J.
      • et al.
      Randomized controlled trial comparing a variable-thread novel tapered and a standard tapered implant: interim one-year results.
      • Kim J.C.
      • Lee J.
      • Kim S.
      • Koo K.T.
      • Kim H.Y.
      • Yeo I.S.L.
      Influence of implant abutment connection structure on peri-implant bone level in a second molar: a 1-year randomized controlled trial.
      • Menini M.
      • Pesce P.
      • Bagnasco F.
      • Carossa M.
      • Mussano F.
      • Pera F.
      Evaluation of internal and external hexagon connections in immediately loaded full-arch rehabilitations: a within-person randomised split-mouth controlled trial.
      • Peñarrocha-Diago M.A.
      • Flichy-Fernández A.J.
      • Alonso-González R.
      • Peñarrocha-Oltra D.
      • Balaguer-Martínez J.
      • Peñarrocha-Diago M.
      Influence of implant neck design and implant abutment connection type on peri-implant health. Radiological study.
      ,
      • Pozzi A.
      • Agliardi E.
      • Tallarico M.
      • Barlattani A.
      Clinical and radiological outcomes of two implants with different prosthetic interfaces and neck configurations: randomized, controlled, split-mouth clinical trial.
      • Sanz-Martín I.
      • Sanz-Sánchez I.
      • Noguerol F.
      • Cok S.
      • Ortiz-Vigón A.
      • Sanz M.
      Randomized controlled clinical trial comparing two dental implants with different neck configurations.
      Finally, a priori sample size calculation was only determined in 6 of the studies,
      • Cooper L.
      • Tarnow D.
      • Froum S.
      • Moriarty J.
      • De Kok I.
      Comparison of marginal bone changes with internal conus and external hexagon design implant systems: a prospective, randomized study.
      ,
      • Gultekin B.A.
      • Gultekin P.
      • Leblebicioglu B.
      • Basegmez C.
      • Yalcin S.
      Clinical evaluation of marginal bone loss and stability in two types of submerged dental implants.
      ,
      • Kielbassa A.M.
      • de Fuentes R.M.
      • Goldstein M.
      • Arnhart C.
      • Barlattani A.
      • Jackowski J.
      • et al.
      Randomized controlled trial comparing a variable-thread novel tapered and a standard tapered implant: interim one-year results.
      ,
      • Pessoa R.S.
      • Sousa R.M.
      • Pereira L.M.
      • Neves F.D.
      • Bezerra F.J.B.
      • Jaecques S.V.N.
      • et al.
      Bone remodeling around implants with external hexagon and morse-taper connections: a randomized, controlled, split-mouth, clinical trial.
      ,
      • Pozzi A.
      • Agliardi E.
      • Tallarico M.
      • Barlattani A.
      Clinical and radiological outcomes of two implants with different prosthetic interfaces and neck configurations: randomized, controlled, split-mouth clinical trial.
      ,
      • Sanz-Martín I.
      • Sanz-Sánchez I.
      • Noguerol F.
      • Cok S.
      • Ortiz-Vigón A.
      • Sanz M.
      Randomized controlled clinical trial comparing two dental implants with different neck configurations.
      leading to a potentially high type 2 error (failure to reject a false null hypothesis) in the remaining trials.
      Previous studies have reported that internal interfaces, particularly conical ones, are more favorable than external connections,
      • Torcato L.B.
      • Pellizzer E.P.
      • Verri F.R.
      • Falcón-Antenucci R.M.
      • Santiago Júnior J.F.
      • De Faria Almeida D.A.
      Influence of parafunctional loading and prosthetic connection on stress distribution: a 3D finite element analysis.
      ,
      • Jaworski M.E.
      • Melo A.C.
      • Picheth C.M.
      • Sartori I.A.
      Analysis of the bacterial seal at the implant abutment interface in external-hexagon and Morse taper-connection implants: an in vitro study using a new methodology.
      ,
      • Canullo L.
      • Penarrocha-Oltra D.
      • Soldini C.
      • Mazzocco F.
      • Penarrocha M.
      • Covani U.
      Microbiological assessment of the implant abutment interface in different connections: cross-sectional study after 5 years of functional loading.
      ,
      • de Medeiros R.A.
      • Pellizzer E.P.
      • Vechiato Filho A.J.
      • dos Santos D.M.
      • da Silva E.V.F.
      • Goiato M.C.
      Evaluation of marginal bone loss of dental implants with internal or external connections and its association with other variables: a systematic review.
      possibly explaining the results observed in the present meta-analysis, which were consistent with those reported in a recent NMA in terms of peri-implant MBL.
      • Caricasulo R.
      • Malchiodi L.
      • Ghensi P.
      • Fantozzi G.
      • Cucchi A.
      The influence of implant abutment connection to peri-implant bone loss: a systematic review and meta-analysis.
      However, 9 of the articles included in the present review were not included in that article. In addition, 5 articles selected for that article were excluded in the present study: 4 were multiple reports on the same participants,
      • Arnhart C.
      • Kielbassa A.M.
      • Martinez-de Fuentes R.
      • Goldstein M.
      • Jackowski J.
      • Lorenzoni M.
      • et al.
      Comparison of variable-thread tapered implant designs to a standard tapered implant design after immediate loading. A 3-year multicentre randomised controlled trial.
      • Cooper L.
      • Reside G.
      • Stanford C.
      • Barwacz C.
      • Feine J.
      • Nader S.
      • et al.
      Three-year prospective randomized comparative assessment of anterior maxillary single implants with different abutment interfaces.
      • Esposito M.
      • Maghaireh H.
      • Pistilli R.
      • Grusovin M.G.
      • Lee S.T.
      • Trullenque-Eriksson A.
      • et al.
      Dental implants with internal versus external connections: 5-year post-loading results from a pragmatic multicenter randomised controlled trial.
      • Pozzi A.
      • Tallarico M.
      • Moy P.K.
      Three-year post-loading results of a randomised, controlled, split-mouth trial comparing implants with different prosthetic interfaces and design in partially posterior edentulous mandibles.
      and 1 was a prospective observational study.
      • Koo K.T.
      • Lee E.J.
      • Kim J.Y.
      • Seol Y.J.
      • Han J.S.
      • Kim T.I.
      • et al.
      The effect of internal versus external abutment connection modes on crestal bone changes around dental implants: a radiographic analysis.
      Additionally, in the previous meta-analysis, a quantitative analysis was not performed on the complications (technical or biologic) or the survival rate.
      Although survival of an implant is the ultimate goal, maintaining bone levels is a key criterion for implant success. While peri-implant MBL was observed in all the implant abutment connections assessed, in most of the selected studies, it lay within the success criteria range proposed in generally accepted classifications.
      • Misch C.E.
      • Perel M.L.
      • Wang H.L.
      • Sammartino G.
      • Galindo-Moreno P.
      • Trisi P.
      • et al.
      Implant success, survival, and failure: the International Congress of Oral Implantologists (ICOI) Pisa Consensus Conference.
      ,
      • Albrektsson T.
      • Zarb G.
      • Worthington P.
      • Eriksson A.R.
      The long-term efficacy of currently used dental implants: a review and proposed criteria of success.
      Accordingly, further long-term RCTs with larger sample sizes comparing implants with the same macrotopography and microtopography are needed to elucidate the results obtained. Moreover, new success criteria should be developed based on MBL rates over certain time intervals rather than on the peri-implant MBL value after a given time.
      • Galindo-Moreno P.
      • León-Cano A.
      • Ortega-Oller I.
      • Monje A.
      • O Valle F.
      • Catena A.
      Marginal bone loss as success criterion in implant dentistry: beyond 2 mm.
      As the period in function increases, so does the risk of developing a complication.
      • Vetromilla B.M.
      • Brondani L.P.
      • Pereira-Cenci T.
      • Bergoli C.D.
      Influence of different implant abutment connection designs on the mechanical and biological behavior of single-tooth implants in the maxillary esthetic zone: a systematic review.
      For these reasons, although a minimum of 5 years of follow-up is recommended for implant survival and success assessment,
      • Needleman I.
      • Chin S.
      • O’Brien T.
      • Petrie A.
      • Donos N.
      Systematic review of outcome measurements and reference group(s) to evaluate and compare implant success and failure.
      the present authors decided not to introduce time as another potential confounding variable. In fact, only 1 of the selected studies mentions a follow-up period of 5 years
      • Esposito M.
      • Maghaireh H.
      • Pistilli R.
      • Grusovin M.G.
      • Lee S.T.
      • Trullenque-Eriksson A.
      • et al.
      Dental implants with internal versus external connections: 5-year post-loading results from a pragmatic multicenter randomised controlled trial.
      ; the authors reported a steady state in crestal bone levels between 1 and 5 years after loading, with a pattern similar to that of peri-implant MBL between conical and external interfaces.
      • Esposito M.
      • Maghaireh H.
      • Pistilli R.
      • Grusovin M.G.
      • Lee S.T.
      • Trullenque-Eriksson A.
      • et al.
      Dental implants with internal versus external connections: 5-year post-loading results from a pragmatic multicenter randomised controlled trial.
      Interestingly, no mechanical complications were reported in the external group, but conical connections tended to develop more peri-implant diseases, although the difference was not statistically significant.
      Although the implant abutment connection could be considered a risk factor for late implant failure, it has been suggested that its impact on the risk of developing biologic and/or mechanical complications is greater.
      • Lemos C.A.A.
      • Verri F.R.
      • Bonfante E.A.
      • Santiago Júnior J.F.
      • Pellizzer E.P.
      Comparison of external and internal implant abutment connections for implant supported prostheses. A systematic review and meta-analysis.
      The present review confirms this because no differences in terms of survival were found among the connections. However, future long-term RCTs should be conducted to confirm this absence of association.
      Knowledge of the mechanical and functional limitations of implant abutment connection types is essential because they might be directly related to the success of the procedure.
      • Vetromilla B.M.
      • Brondani L.P.
      • Pereira-Cenci T.
      • Bergoli C.D.
      Influence of different implant abutment connection designs on the mechanical and biological behavior of single-tooth implants in the maxillary esthetic zone: a systematic review.
      Despite the short follow-up period, conical interfaces exhibited a significantly lower risk of developing prosthetic complications in comparison with external designs. Nevertheless, several confounding factors such as screw preload torque and abutment materials could have influenced the outcomes.
      • Theoharidou A.
      • Petridis H.P.
      • Tzannas K.
      • Garefis P.
      Abutment screw loosening in single-implant restorations: a systematic review.
      ,
      • Pjetursson B.E.
      • Zarauz C.
      • Strasding M.
      • Sailer I.
      • Zwahlen M.
      • Zembic A.
      A systematic review of the influence of the implant abutment connection on the clinical outcomes of ceramic and metal implant abutments supporting fixed implant reconstructions.

      Conclusions

      Based on the findings of this systematic review and network meta-analysis of RCTs, the following conclusions were drawn:
      • 1.
        Conical implant abutment designs provided the best results for implant survival, peri-implant MBL, and prosthetic complications after 1 year of loading as assessed with NMA.
      • 2.
        For peri-implant MBL and prosthetic complications, conical interfaces showed significant differences when compared with external hexagonal connections.

      CRediT authorship contribution statement

      Octavi Camps-Font: Conceptualization, Methodology, Investigation, Formal analysis, Writing – original draft. Laura Rubianes-Porta: Conceptualization, Methodology, Investigation, Writing – original draft. Eduard Valmaseda-Castellón: Conceptualization, Investigation, Writing – review & editing. Ronald E. Jung: Conceptualization, Writing – review & editing. Cosme Gay-Escoda: Supervision. Rui Figueiredo: Supervision, Project administration.

      Acknowledgments

      The authors thank Mary Georgina Hardinge for English language editing assistance.

      Supplementary data

      Figure thumbnail figs1
      Supplementary Figure 1Forest plots for implant survival (odds ratio), comparing different implant abutment connections at 12 months’ follow-up.
      Figure thumbnail figs2
      Supplementary Figure 2Forest plots for biologic complications (odds ratio), comparing different implant abutment connections at 12 months’ follow-up.
      Figure thumbnail figs3
      Supplementary Figure 3Forest plots for peri-implant marginal bone loss (mean difference), comparing different implant abutment connections at 12 months’ follow-up.
      Figure thumbnail figs4
      Supplementary Figure 4Subgroup analyses for peri-implant marginal bone loss (mean difference). Subsets of studies created based on postextractive implant placement (conical versus internal implant abutment connections), immediate prosthetic load (internal versus external implant abutment connections), and low risk of bias (conical versus external implant abutment connections).
      Figure thumbnail figs5
      Supplementary Figure 5Forest plots for prosthetic complications (odds ratio), comparing different implant abutment connections at 12 months’ follow-up.

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