Sex-based differences in salivary concentrations of resin-derived monomers following orthodontic retainer bonding: a prospective longitudinal study

Objective To investigate whether sex-based differences exist in measured salivary concentrations of monomers following bonding of fixed lingual orthodontic retainers. Methods This prospective longitudinal study included 30 orthodontic patients (18 females and 12 males) who received mandibular bonded lingual retainers using Transbond LR adhesive. Saliva samples were collected at six time points: before debonding (T0), immediately after bracket removal (T1), immediately after retainer bonding (T2), and at 1 h (T3), 1 month (T4), and 6 months post-bonding (T5). BisGMA, TEGDMA and UDMA were quantified using reverse-phase high-performance liquid chromatography (RP-HPLC). Concentrations were expressed as salivary levels (µg/mL) and normalized to the mass of resin placed intra-orally for statistical analysis. Results TEGDMA and BisGMA concentrations peaked at T2 (4.4 ± 5.6 µg/mL and 1.8 ± 3.8 µg/mL, respectively), with significantly higher levels measured in female participants (TEGDMA: 5.6 ± 5.4 µg/mL vs. 2.7 ± 2.6 µg/mL, p = 0.0015; BisGMA: 2.4 ± 4.6 µg/mL vs. 0.8 ± 1.6 µg/mL, p = 0.0037). Concentrations decreased over time, returning to near-baseline levels within one month and remaining low at six months. UDMA concentrations remained low (< 0.5 µg/mL) throughout follow-up. Conclusion Higher salivary concentrations of BisGMA and TEGDMA were observed in female participants at specific time points. These findings reflect differences in measured salivary exposure rather than evidence of systemic exposure or biological effects and should be considered hypothesis-generating. Trial registration This study was registered on ClinicalTrials.gov on June 17, 2020 (NCT04459013).