Survival rate of two orthodontic bonded retainer wires

We read the article "Clinical effectiveness of two orthodontic retainer wires on mandibular arch retention" (Gunay F, Oz A. Am J Orthod Dentofacial Orthop 2018; 153:232-8) with great interest. We congratulate the authors for conducting a robust study with an effective study design on this important topic. However, we would seek certain clarifications from the authors on several points:

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