Lower incisor retention with fixed or vacum formed retainers

Objectives: (1) assess change in lower incisor irregularity at 12 months post-debond with fixed (BR) or vacuum-formed (VFR) retainers and (2) assess lower incisor irregularity with regard to patient reported wear of VFR. Methods: Following ethical approval, 85 consecutive patients (38 males; 47 females) wearing upper and lower fixed appliances were recruited. Prior to debond, each patient was randomly assigned to receive either a BR (0.018in multistrand, 3M Unitek, CA, USA; canine to canine bonded to each tooth separately) or VFR (Essix CŪ). Informed consent was obtained from each subject or their parent/guardian. Fitting of each retainer type followed a standardised protocol. For the VFR, patients were instructed to wear it full time for one year, except at mealtimes. Study models taken at retainer placement (T1) and at 12 months review (T2) were scored using Little's irregularity index with digital callipers (Ultra-Call Mark III, Fowler Co., Inc, MA, USA). At review, a questionnaire regarding wear of VFR was completed. Results: 48 BRs and 37 VFRs were fitted. Data were available for 48 BRs and 37 VFRs at debond, and 47 BRs and 37 VFRs at review. Mean Little's irregularity at debond was 0.37mm (SD 0.41mm) for BR cases and 0.42mm(SD 0.38mm) for the VFR cases. Mean Little's irregularity index score at review was 0.43mm (SD 0.41mm) for BR cases and 1.03mm (SD 1.28mm) for VFR cases (p< 0.031; Mann-Whitney test). Patient reported wear of the VFR varied: all the time (n=13), most of time (n=21), hardly ever (n=3). Little's irregularity index was correlated to reported wear for the VFR (p<0.002; Kruksal Wallis). Conclusion: More lower incisor irregularity was recorded at review in cases retained with a VFR than with a BR. The change in lower incisor irregularity with VFR was related to reported wear.