Survival rate of two orthodontic bonded retainer wires

Abstract

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:1.In paragraph 1 of the statistical analysis section, the authors mention that lingual retainer survival rates over 12 months were evaluated by means of the Kaplan-Meier test and that differences in retainer survival curves by retainer wire type were evaluated by means of the log-rank test. In Fig 3, the authors draw a Kaplan-Meier curve depicting the cumulative survival rates of group 1 (0.0175-inch 6-stranded stainless steel retainer wire) and group 2 0.0195-inch dead-soft coaxial retainer wire), but the graph touches zero percent in both groups over a 12-month follow-up period. This means that survival or success of the bonded retainer is 0% at the end of 12 months in both groups, although it is 86.8% in group 1 and 81.1% in group 2 according to Table II (log-rank test: χ2 = 0.661; P = 0.416). Figure 3 and Table II completely contradict each other. We think that the graph should be drawn as shown in Figure (Corrected).1Egli F. Bovali E. Kiliaridis S. Cornelis M.A. Indirect vs direct bonding of mandibular fixed retainers in orthodontic patients: comparison of retainer failures and posttreatment stability. A 2-year follow-up of a single-center randomized controlled trial.Am J Orthod Dentofacial Orthop. 2017; 151: 15-27Abstract Full Text Full Text PDF PubMed Scopus (27) Google Scholar, 2Dawson B. Trapp R.G. Research question about means in three or more groups.in: Dawson B. Trapp R.G. Basic and clinical biostatistics. 4th ed. McGraw Hill, New York2004: 163-189Google Scholar2.The authors applied repeated-measures analysis of variance (ANOVA) for irregularity measurements and intercanine distance. Intragroup comparison at different time points is mentioned, but what is the intergroup difference at different time points of the above parameters? In Tables IV and V, 2 different F-values are mentioned, and it seems that the authors have applied 1-way repeated-measures ANOVA separately for each treatment group and not repeated-measures ANOVA for both groups together. Our question is why intergroup repeated-measures ANOVA2Dawson B. Trapp R.G. Research question about means in three or more groups.in: Dawson B. Trapp R.G. Basic and clinical biostatistics. 4th ed. McGraw Hill, New York2004: 163-189Google Scholar was not applied.3.Intergroup comparison (Table VI) of mean irregularity measurement (mm) difference between post-treatment and 12-month retention period (T5-T1) via Mann-Whitney test gives us vital information that mandibular arch irregularity is significantly higher in group 2 than in group I. Similarly, it would also be pertinent to know the results of a Mann-Whitney test for the difference in mean intercanine distance between the 2 groups. This result may help us in localizing the irregularity site so that adequate stress can be given to the areas requiring maximum retention. The authors should comment on why this relevant information was not shared. We emphasize that by no means are we disregarding the efforts of the authors in conducting this trial, but our intention is that correct and relevant information should reach the readers of this journal. Clinical effectiveness of 2 orthodontic retainer wires on mandibular arch retentionAmerican Journal of Orthodontics and Dentofacial OrthopedicsVol. 153Issue 2PreviewThe aim of this study was to evaluate and compare the clinical success of 2 lingual retainer wires. Full-Text PDF Author's responseAmerican Journal of Orthodontics and Dentofacial OrthopedicsVol. 155Issue 1PreviewThank you so much for your interest and the valuable contributions you have made to our work. Full-Text PDF