The Impact of Dentin Primers on Collagen Secondary Structure: An Infrared Spectroscopic Analysis Using Amide III...

To investigate how dentin primers with different compositions and etching strategies affect collagen secondary structures in human dentin.

Flat mid-coronal dentin from extracted molars (n = 10/group) was treated with six primers representing etch-and-rinse (HEMA, MP3M, MIP) or self-etch (DECO, SEBO, SECU) strategies. Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectra were acquired at baseline, after etching or self-etching and after priming. Demineralization (DM) was estimated from phosphate/Amide I ratios, while collagen secondary structure and crosslink maturity were derived from Amide III and Amide I bands. Data were analyzed with paired and between-group non-parametric tests and Benjamini-Hochberg correction for multiple comparisons.

Etch-and-rinse protocols produced higher DM than self-etch treatments. HEMA solution, MP3M, and SEBO caused significant α-helix loss with concomitant β-sheet increase, whereas MIP, DECO and SECU did not induce significant changes in collagen conformation or crosslink maturity. Higher final DM was associated with poorer α-helix recovery at specimen level.

Among the systems tested, dentin primers differed in their impact on collagen secondary structure; HEMA-rich formulations were structurally disruptive in this model, whereas polyacrylic-acid- and 4-META-based self-etch systems largely preserved the native secondary structures. DM extent was associated with collagen unfolding and may help inform primer design for more durable dentin bonding strategies.

The choice of etching strategy and dentin primer should not be based solely on handling or immediate bond strength. Different systems induce distinct biochemical changes in dentin collagen secondary structure, which may critically influence hybrid layer stability and the long-term performance of adhesive restorations.