The review followed the PRISMA statement (Moher et al. 2009), the protocol was also registered on the International Prospective Register of Systematic Reviews (PROSPERO) database. Searches were conducted by two independent reviewers in MEDLINE using PubMed and Web of Science databases. Dates were limited to January 2005 to September 2015 and the English language. Manual searches were also carried out in the relevant major journals. Eligibility criteria were as follows: studies published in English describing at least 10 participants evaluating different types of retention system or presented information on implant survival, peri-implant soft tissue reaction, or prosthetic complications in the aftercare period. Exclusions included case reports and case-series and narrative reviews. Two independent reviewers selected studies for inclusion, abstracted data and assessed risk of bias/quality using the Jadad scale (Jadad et al. 1996). Outcome was defined as implant survival, and peri-implant soft tissue reaction related to the extraoral implants and complications caused by the retention systems.
- 12 studies fulfilled the inclusion criteria (2 prospective and 10 retrospective).
- The quality of the evidence was low, 7 scored 0/5 and 5 scored 1/5 on the Jadad scale.
- 492 participants were included, mean age 48 years. All selected studies for meta-analysis were retrospective.
|Primary Outcomes (Implant survival)|
|Overall implant survival rate was||90.1%|
|Secondary outcome (Peri-implant soft tissue reaction)|
|Prosthesis types (n), retention system (bar clips/magnets)|
|Orbital||268, Mostly magnets|
|Large facial||14, 8,6|
- Retention system failure 29 of 159 implants with magnets (18.2), 25 of 79 implants with bars (31.6)
the authors concluded
The limited data collected indicate that the type of retention system appears not to affect the prosthetic treatment outcome or the survival of extraoral implants, and no definitive conclusions as to the best retention system can be drawn. Further well-designed research such as randomized clinical trials (RCTs) comparing both options should be performed considering participant preferences.
The results of this review should be considered with caution as the main limiting factor (which the author does address in the discussion section) was the quality of the primary research. By its very nature, the area for study does not lend itself to large numbers of participants or the undertaking of RCTs. It was interesting to note that the author used the Jadad scale to assess quality even though there were no RCTs and the use of this scale is explicitly discourages in the Cochrane Handbook of Systematic Reviews of Interventions (Higgins & Green 2009) since it has a strong emphasis on reporting rather than conduct.
The small sample sizes compound the problem of the type of defect, site, duration of study and prosthesis. The author cites survival rates in the results but they contain neither time frame nor confidence intervals, also a definition for the grading scale for peri-implant soft tissue reaction is missing.
An interesting area for discussion is whether the included studies are cohort studies or case-series (Agha et al. 2016; Dekkers et al 2012) as the studies the authors included resemble an amalgamation of multiple case-reports rather than a clearly structured study cohort or RCT. In this review the difficulty in producing any ‘high quality’ survival data figures would add more weight to defining the studies as case-series, since a central feature of a cohort study is that it enables anabsolute risk estimate for the outcome to be calculated.
Brandao, T.B. et al., 2016. A systematic comparison of bar-clips versus magnets. Journal of Prosthetic Dentistry, 117(2), p.321–326.e2.
Agha, R.A. et al., 2016. Systematic review of the methodological and reporting quality of case series in surgery. British Journal of Surgery, 103, pp.1253–1258.
Dekkers OM,et al. Distinguishing case series from cohort studies. Ann Intern Med. 2012;156:37-40.
Higgins, J. & Green, S., 2009. 8.3.3 Quality scales and Cochrane reviews. Cochrane Handbook for Systematic Reviews of Interventions, p.192. Available at: http://handbook.cochrane.org/chapter_8/8_3_3_quality_scales_and_cochrane_reviews.htm [Accessed March 18, 2017].
Jadad, A.R. et al., 1996. Assessing the quality of reports of randomized clinical trials: Is blinding necessary? Controlled Clinical Trials, 17(1), pp.1–12.
Moher, D. et al., 2009. Preferred Reporting Items for Systematic Reviews and Meta-Analyses : The PRISMA Statement. , 6(7).