title: Light-Cured Self-Etch Adhesives Undergo Hydroxyapatite-Triggered Self-Cure.
abstract: Light cure is a popular mode of curing for dental adhesives. However, it suffers from inadequate light delivery when the restoration site is less accessible, in which case a self-cure mechanism is desirable to salvage any compromised polymerization. We previously reported a novel self-cure system mediated by ethyl 4-(dimethylamino)-benzoate (4E) and hydroxyapatite (HAp). The present work aims to investigate if such self-cure phenomenon takes place in adhesives that underwent prior inadequate light cure and to elucidate if HAp released from the dental etching process is sufficient to trigger it. Model self-etch adhesives were formulated with various components, including bis[2-methacryloyloxy)ethyl]-phosphate (2MP) as acidic monomer and trimethylbenzoyl-diphenylphosphine oxide (TPO) as photoinitiator. In vitro evolution of degree of conversion (DC) of HAp-incorporated adhesives was monitored by infrared spectroscopy during light irradiation and dark storage. Selected adhesives were allowed to etch and extract HAp from enamel, light-cured in situ, and stored in the dark, after which Raman line mapping was used to obtain spatially resolved DC across the enamel-resin interface. Results showed that TPO+4E adhesives reached DC similar to TPO-only counterparts upon completion of light irradiation but underwent another round of initiation that boosted DC to ~100% regardless of HAp level or prior light exposure. When applied to enamel, TPO-only adhesives had ~80% DC in resin, which gradually descended to ~50% in enamel, whereas TPO+4E adhesives consistently scored ~80% DC across the enamel-resin interface. These observations suggest that polymerization of adhesives that underwent insufficient light cure is salvaged by the novel self-cure mechanism, and such salvaging effect can be triggered by HAp released from dental substrate during the etching process.
authors.affiliation: University of Missouri-Kansas City School of Dentistry, Kansas City, MO, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Liu
authors.affiliation: University of Missouri-Kansas City School of Dentistry, Kansas City, MO, USA.
authors.forename: X
authors.initials: X
authors.lastname: Bai
authors.affiliation: University of Missouri-Kansas City School of Dentistry, Kansas City, MO, USA.
authors.forename: Y W
authors.initials: YW
authors.lastname: Liu
authors.affiliation: University of Missouri-Kansas City School of Dentistry, Kansas City, MO, USA Wangyo@umkc.edu.
authors.forename: Y
authors.initials: Y
authors.lastname: Wang
mesh_terms: D003624:Darkness; D003743:Dental Enamel / Q000737:chemistry; D045662:Dental Etching / Q000379:methods*; D017886:Durapatite / Q000737:chemistry*; D055119:Elastic Modulus; D006801:Humans; D008027:Light; D055115:Light-Curing of Dental Adhesives / Q000379:methods*; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry / Q000528:radiation effects; D010755:Organophosphates / Q000737:chemistry / Q000528:radiation effects; D010720:Phosphines / Q000737:chemistry / Q000528:radiation effects; D058567:Photoinitiators, Dental / Q000737:chemistry / Q000528:radiation effects; D018583:Pliability; D058105:Polymerization; D019279:Resin Cements / Q000737:chemistry* / Q000528:radiation effects; D055116:Self-Curing of Dental Resins / Q000379:methods*; D013055:Spectrophotometry, Infrared; D013059:Spectrum Analysis, Raman; D055815:Young Adult; D062366:para-Aminobenzoates / Q000737:chemistry / Q000528:radiation effects
chemical_list: C520678:(2,4,6-trimethylbenzoyl) diphenylphosphine oxide; C000595499:2-methacryloyloxyethyl dihydrogen phosphate; D008689:Methacrylates; D010755:Organophosphates; D010720:Phosphines; D058567:Photoinitiators, Dental; D019279:Resin Cements; D062366:para-Aminobenzoates; C030747:ethyl 4-dimethylaminobenzoate; D017886:Durapatite
keywords: (2,4,6-trimethylbenzoyl) diphenylphosphine oxide; Fourier transform infrared spectroscopy; Raman spectroscopy; chemical-curing of dental adhesives; ethyl 4-dimethylaminobenzoate; light-curing of dental adhesives