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. 2018 Oct 11;2018(10):CD008001. doi: 10.1002/14651858.CD008001.pub2

Kappel 2016.

Methods Trial design: 2‐year follow‐up, randomised parallel group trial
Parallel group randomised trial in which participants were randomly assigned to 1 of 2 attachment systems and special sealed sequentially numbered envelopes containing the randomised allocation were prepared at the beginning of the trial by an external source
Participants Inclusion criteria: edentulous mandibles, adequate dimensions of the vertical and horizontal bone of the inter‐foramina regions (vertically and horizontally at least 1 mm of bone around each implant), and informed consent to participation
Exclusion criteria: drug or alcohol abuse, inadequate vertical or horizontal bone dimensions or quality, less than 35 Ncm insertion torque, pregnant at the time of implant placement, and administration of intravenous bisphosphonates in the last 10 years
Age at baseline (years): mean 69.4
Gender (M/F): 34:12 (73.9% male)
Number of mandibular overdentures randomised: 46 ( mandibular 2‐implant overdentures)
Number of mandibular overdentures evaluated at 1 year: not specified
Number of mandibular overdentures evaluated at 2 years: 43
Interventions Mandibular 2‐implant overdentures ‐ unsplinted prosthodontic design
Test group 1 (n = 23): Locator® attachments (Zest Anchors LLC, Espandido, CA, USA)
Test group 2 (n = 23): egg‐shaped bar (Dolder®, Sub‐TecWirobond® MI bar abutment and Dolder bar joint (BEGO Implant GmbH & Co KG, Bremen, Germany)
Outcomes Prosthodontic maintenance by general categorization
 Patient satisfaction (trial did not use validated criteria for this outcome)
Follow‐up examinations were performed after 3, 6, 12, and 24 months
Unpublished data conforming to Appendix 1; Appendix 2 by authors via email
Notes Location: Germany
Funding source: BEGO Implant Systems GmbH & Co KG, Bremen, Germany: financial and material support
Dr Stefanie Kappel was supported by the Olympia‐Morata programme of the Medical Faculty of the University of Heidelberg, Germany
Patient satisfaction data presented did not use validated criteria ("Patients were asked whether they would recommend the treatment knowing what it entailed")
Kappel 2016 is the primary trial since first report of Kappel 2015 was for less than 1 year of duration
Authors contacted by email (07 February 2017): replies received (15 and 20 February 2017) providing participant numbers in test groups at year 2 plus full prosthodontic maintenance categorization from author (unpublished data) confirming to Appendix 1; Appendix 2
Details of ethical approval: the ethics committee of the Medical Faculty of the University of Heidelberg (S‐208/2010) approved the trial. Registered in the German Registry for Clinical Studies (DRKS 00004245)
Risk of bias
Bias Authors' judgement Support for judgement
Random sequence generation (selection bias) Unclear risk Quote: "Participants were allocated to a treatment group on the basis of the content of the next envelope in the sequence"
Comment: the trial does not include any description of how the sequence was generated
Allocation concealment (selection bias) Unclear risk Quote: "Sealed, sequentially numbered envelopes containing the randomised allocation were prepared by an external source before the trial began"
Comment: it is not clear whether the envelopes were opaque or opened by an independent source not involved in the study
Blinding of participants and personnel (performance bias) 
 All outcomes Low risk The trial did not report blinding, but we judge the risk of bias as low since it is an operative procedure and the outcomes are not likely to be influenced by lack of blinding of participants and personnel
Blinding of outcome assessment (detection bias) 
 Objective outcomes Low risk The trial did not report blinding, however blinding is not possible due to the nature of the intervention, but we judge the risk of bias as low due to the outcomes being objective and are not likely to be influenced by lack of blinding
Blinding of outcome assessment (detection bias) 
 Patient‐reported outcomes High risk The trial did not report blinding, however blinding is not possible due to the nature of the intervention, but we judge the risk of bias as high regarding patient satisfaction due to being subjective and is likely to be influenced by lack of blinding
Incomplete outcome data (attrition bias) 
 All outcomes Low risk Total losses: 3/46 (6.5%)
3 participants were lost to follow‐up because of death or serious illness
Selective reporting (reporting bias) High risk The trial protocol is available, and not all of the trial's pre‐specified outcomes have been reported (ISRCTN: DRKS00004245)
Other bias Low risk None noted