In an article by Batista VES, Bitencourt SB, Bastos NA, Pellizzer EP, Goiato MC, Dos Santos DM. (Influence of the ferrule effect on the failure of fiber-reinforced composite post-and-core restorations: A systematic review and meta-analysis. J Prosthet Dent 2020; 123:239-45), the authors concluded that after 4 studies met the preestablished selection criteria, the results of the systematic review and meta-analysis suggested that the ferrule effect does not significantly reduce the failure rate in fiber-reinforced composite post-and-core restorations. However, 1 of the 4 studies was misrepresented in the data analysis. The study by Bitter et al was the only study not to show a tangible difference in survival of fiber post restorations between the group with a ferrule and the group without a ferrule. This was depicted in Table 2 of the systematic review and meta-analysis claiming that 40 participants were restored with a post on teeth with a ferrule and 21 participants were restored with a post on teeth without a ferrule, leading to a 95% survival rate with a ferrule and 95.1% without a ferrule. However, the authors of the systematic review and meta-analysis misinterpreted the subset of teeth, described in the study by Bitter et al, with “no wall exceeding 2 mm above the gingival level” as being the cohort of 21 participants with teeth without a ferrule. In fact, all crown preparations were performed with a circumferential ferrule of at least 2 mm in the study by Bitter et al (pg. 1478, Material and Methods).
All other selected studies in the systematic review and meta-analysis showed marked differences in survival rate between restorations with and without a ferrule, favoring a ferrule (Table 2). Given this misrepresentation of 25% of the selected studies, the conclusion by the authors that the ferrule effect does not appear to reduce the failure rate of fiber-reinforced composite post-and-core restorations significantly, when compared with its absence, cannot be supported.
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