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Optimizing orthodontic adhesives with bioinspired tannic acid: An integrated approach to improve Bond strength and
Xiaoqian Ding1, Xin Li2, Cynthia Kar Yung Yiu3
1Paediatric Dentistry and Orthodontics, Faculty of Dentistry, The University of Hong Kong, Prince Philip Dental Hospital, 34 Hospital Road, Sai Ying Pun, Hong Kong, China; Outpatient Department at Longfor Guangnian, The Affiliated Stomatological Hospital of Chongqing Medical University, No.426 Songshibei Road, Yubei District, Chongqing 401147, China.
Objective:
To evaluate the effect of incorporating tannic acid (TA) into a moisture-insensitive orthodontic primer on wet-bonding performance, resistance to cariogenic bacteria, cytocompatibility, and degree of conversion.
Methods:
Two hundred extracted human premolars were assigned to four groups: a control using a commercial moisture-insensitive primer (MIP; 3 M, USA) and three TA-modified primers with TA incorporated into MIP at 0.04, 0.08, or 0.12 mg/μL. Cytocompatibility was assessed via CCK-8 assay, and degree of conversion (DC) was measured. Under simulated moisture contamination, bracket shear bond strength (SBS) and the adhesive remnant index (ARI) were measured before and after 2000 thermocycles. Bonding interfaces and enamel surfaces were examined using scanning electron microscopy (SEM). Resistance against Streptococcus mutans (S. mutans) was determined through colony-forming unit (CFU) counts, crystal violet (CV) staining, and SEM biofilm visualization.
Results:
Cytocompatibility and DC were comparable across all groups. Under simulated moist conditions, all TA-modified primers achieved significantly higher bracket SBS than the control both immediately and after thermal cycling, with the 0.08 mg/μL TA formulation showing the greatest improvement. Experimental groups yielded higher ARI scores than the control, with no enamel defects observed. The 0.08 mg/μL formulation significantly suppressed S. mutans, reducing CFUs and biofilm accumulation.
Significance:
Incorporating 0.08 mg/μL TA into the MIP creates a dual-function orthodontic primer that improves bond durability in moist conditions while simultaneously providing resistance to Streptococcus mutans, without compromising cytocompatibility or polymerization efficiency. This formulation offers a promising clinical solution for reducing bracket failure and preventing white spot lesions in orthodontic patients.
