Dentin beyond Its Ontology: A Platform to Produce Dental Adhesives

Given its unique composition and physicochemical stability, dentin obtained from teeth extracted for clinical reasons represents a promising source for the development of functional biomaterials. Photopolymerizable compounds based on demineralized dentin modified with acrylamide groups were developed, with the aim of formulating ester-free adhesive primers. Dentin powder obtained from the crown and root was demineralized and reacted with methacrylic anhydride (MA). Following reaction, dialysis, and lyophilization, the resulting granular and sticky materials were evaluated for their degree of functionalization (methacrylation) using the 2,4,6-trinitrobenzenesulfonic acid (TNBS) assay and infrared (attenuated total reflectance Fourier transform infrared [ATR-FTIR]) spectrometry. The compounds were subsequently suspended in phosphate-buffered saline and collagen-methacrylamide, supplemented with lithium acylphosphinate, injected into custom molds, and photopolymerized using a dental-curing unit, producing 3-dimensional constructs. Morphology, water sorption, solubility, degree of swelling, flexural modulus, biodegradability, and biocompatibility were assessed. TNBS analysis indicated a lower degree of functionalization in methacrylated crown dentin (CD-MA, 41%) than in methacrylated root dentin (RD-MA, 55%), consistent with ATR-FTIR results. CD-MA exhibited greater solubility and swelling, as well as a lower flexural modulus (1.8 ± 0.2 MPa), compared with RD-MA (2.2 ± 0.3 MPa). However, CD-MA and RD-MA demonstrated comparable water sorption, biodegradability, and >95% metabolic activity and cell viability in OD-21 and MDPC-23 cell lines. As a proof of concept, CD-MA, which exhibited the higher yield, was selected for evaluation as an adhesive primer and compared with a commercial methacrylate-based etch-and-rinse adhesive. Specimens bonded with the experimental CD-MA primer showed significantly lower bond strength at the initial evaluation (24 h) than the control group. Nonetheless, after 6 mo of storage in simulated body fluid, the experimental group maintained stable bond strength, whereas the control group exhibited an approximately 30% reduction. Taken together, these findings demonstrate that dentin is a viable raw material for the development of methacrylamide-based dental primers, which exhibit greater bond strength stability than a conventional methacrylate-based adhesive system.