Comparison of Shear Bond Strength, Adhesive Remnant and Precision Fit between Conventional Lingual Retainers and Customised CAD/CAM Fabricated Lingual Retainers: An In-vitro Study

Abstract

Introduction: Fixed lingual bonded retainers offer the comfort of aesthetics and reduced tissue irritation after orthodontic treatment but are wrought with frequent bond failures. Numerous techniques have been used to adapt the retainer to the lingual surface of the lower anterior teeth, but research on customised lower lingual retainers is scarce. Aim: To evaluate and compare the Shear Bond Strength (SBS), Adhesive Remnant Index scores (ARI), and precision fit of a novel Computer-aided Designing-Computer-aided Machining/ Manufacturing (CAD-CAM) fabricated retainer and conventional retainers. Materials and Methods: This invitro study was conducted at the Department of Orthodontics, and Dentofacial Orthopaedics, SRM Dental College, Ramapuram, Chennai-89 from June 2022 to February 2023. It included a total of 360 human mandibular anterior teeth were collected and embedded in acrylic blocks in groups of six to simulate the mandibular anterior arch form. A total of 60 retainers made of braided Stainless Steel (SS) wires, co-axial wires, customised through CAD/CAM technology were evaluated. The retainers were bonded to the lingual aspect of the teeth using composite resin. A universal testing machine was used for testing SBS. Precision fit was observed using Exocad software. Statistical analysis included one-way Analysis of Variance (ANOVA) for SBS, Kruskal-Wallis for ARI score, and Mann-Whitney U test for precision fit. Results: The CAD-CAM retainers had a more precise fit when compared to conventional retainers (p=0.009). SBS was highest for CAD-CAM fabricated retainer and lowest in the co-axial retainer, and this finding was statistically significant (p<0.001). The CAD-CAM retainer had the highest mean rank in ARI scores (33.90) when compared to braided SS and co-axial wire. Conclusion: The CAD-CAM fabricated retainers would be more effective clinically, as higher bond strength due to precise fit would reduce the failure rate, thus preventing relapse and minimising chairside time.