Pilot study on calculus removal from orthodontic retainers using different mechanical approaches: an in-vitro investigation of the adhesive strength of fixed retainers

Introduction Orthodontic fixed retainers are often a predilection site for calculus build-up. However, standardized protocol for professional mechanical plaque removal (PMPR) does not yet exist that takes into account the slight weakening of the adhesive bond. Material and Methods In this in-vitro study, three cleaning protocols were evaluated: Group A: ultrasonic stainless-steel tip (Piezon PS, EMS Dental); Group B: Polyetheretherketone (PEEK) ultrasonic tip (PI Max, EMS Dental); and Group C: sonic cleaning (SiroTip S1, Sirona Dental Systems). These protocols were assigned artificial lower canine-to-canine segments with individual Twistflex retainers bonded (n = 10/group). Following artificial ageing of the adhesive bond, artificial calculus was applied and removed according to the respective cleaning protocol. After repeating twice, adhesive bond strengths were analysed. Results The Kruskal-Wallis test showed that the choice of instrumentation significantly influences the integrity of the adhesive bond (p = 0.036). Post-hoc pairwise comparisons revealed that Group A had significantly higher shear bond strength compared to Group C (p = 0.028). Conclusions This in-vitro study shows that the type of the PMPR system used has a significant influence on the shear bond strength of fixed retainers. Ultrasound-driven stainless-steel scalers appear to be more gentle than sonic-driven devices. Clinical relevance In clinical practice, the accidental debonding of retainer attachments during PMBR is a frequent complication. The present in-vitro study investigates whether specific cleaning modalities can minimize the risk of compromising the adhesive bonding. Specifically, different cleaning modalities (ultrasonic versus sonic) and various tip materials are evaluated and compared.