A novel thiolated carboxymethyl chitosan for extrafibrillar dentin demineralization to enhance dentin bond durability

• A novel thiolated carboxymethyl chitosan (TCMC) was synthesized as a dentin demineralization agent. • TCMC achieved selective extrafibrillar demineralization while preserving intrafibrillar hydroxyapatite. • TCMC-treated dentin maintained mechanical properties (hardness, elastic modulus, storage modulus) much closer to sound dentin than phosphoric acid etching, and showed significantly reduced MMP activity. • TCMC generated a dense, collapse-resistant collagen network that established a stable bonding interface. The long-term durability of dentin bonding is compromised by hybrid layer degradation, which conventional demineralization techniques often exacerbate. This study synthesized thiolated carboxymethyl chitosan (TCMC) and evaluated three concentrations (5, 10, and 15 mg/mL) for extrafibrillar dentin demineralization, identifying 10 mg/mL as the optimal concentration for subsequent experiments. Characterization confirmed successful thiolation. TCMC demonstrated superior calcium-chelating ability. Microtensile testing showed that TCMC-treated dentin maintained high bond strength after aging under both dry- and wet-bonding conditions, unlike phosphoric acid (PA) treatment which caused bond failure with dry-bonding. SEM/TEM revealed that TCMC selectively removed extrafibrillar minerals, preserving intrafibrillar hydroxyapatite and generating a collapse-resistant collagen network. Nanoindentation/nano-DMA indicated that the mechanical properties of TCMC-treated dentin remained closer to sound dentin than PA-treated dentin. Zymography showed significantly reduced MMP activity on TCMC-treated surfaces. By enabling selective extrafibrillar demineralization, TCMC facilitates a stable hybrid layer and supports a clinically simplified dry-bonding approach for improved bond durability.