Light-Embrittled Dental Resin Cements Containing Photodegradable Polyrotaxane Cross-Linkers for Attenuating Debonding Strength

Abstract

Notwithstanding the progress of dental material adhesion on tooth surfaces in the past several decades, debonding strongly adhered restorative materials from tooth surfaces remains a challenging issue. Herein, we propose the use of photodegradable polyrotaxanes (PRXs), which are supramolecular-interlocked polymers comprising α-cyclodextrin threaded along a poly(ethylene glycol) (PEG) axle, as a component of adhesive resin cements to attenuate debonding strength via light irradiation. We synthesized photodegradable PRXs (iNB-PRXs) using internally o-nitrobenzyl ester-introduced PEG as an axle polymer. Notably, approximately 60% of iNB-PRX degraded into its constituent molecules after 5 min of irradiation with ultraviolet (UV) light. Thereafter, iNB-PRX was combined with the clinically utilized adhesive resin cement, and a poly(methyl methacrylate) (PMMA) block was adhered on the surface of bovine dentin using an adhesive resin cement cross-linked with iNB-PRX. Although the PMMA block was successfully adhered onto the dentin with a clinically acceptable adhesive force, the tensile strength of the PMMA-dentin specimens decreased significantly upon UV irradiation for 2 min owing to the UV-induced degradation of the iNB-PRX cross-linker. According to these results, the adhesive resin cement containing photodegradable iNB-PRX cross-linkers is a promising candidate for facilitating the debonding of dental materials from tooth surfaces via UV light irradiation.