“…In the current study, the ranges of the retentive force of PEEK and GBP materials were 3.70–1.68 and 2.90–1.43 N, respectively ( Table 2 ). These values were close to the clasp retentive force of polymeric materials tested in some studies, especially for pressed and milled PEEK materials, and slightly lower than other literature values [ 6 , 8 , 11 , 12 , 15 , 19 , 20 , 29 , 30 , 31 , 34 ]. As there is no standardized method for clasp retention measurement, variations could be seen between different studies, and therefore the comparison should be limited to articles with the same design, such as analog material, aging method, rate of displacement, number of pull-off cycles, clasp attachment site, amount of undercut tested, and shape of the specimens [ 7 , 11 , 12 , 29 , 32 , 41 ].…”