Er:YAG Laser Physical Etching and Ultra-High-Molecular-Weight Cross-Linked Sodium Polyacrylate Chemical Etching for a Reliable Dentin Dry Bonding

Dentin bond interface stability is the key issue of dentaladhesionin present clinical dentistry. The concept of selective extrafibrillardemineralization has opened a new way to maintain intrafibrillar mineralsto prevent interface degradation. Here, using ultra-high-molecular-weightsodium polyacrylate [Carbopol (Carbo) > 40 kDa] as a calcium chelator,we challenge this concept and propose a protocol for reliable dentindry bonding. The results of high-resolution transmission electronmicroscopy revealed periodic bands of 67 nm dentin collagen fibrilsafter Carbo etching, and the hydroxyproline concentration increasingwith prolonged chelating time denied the concept of extrafibrillardemineralization. The results that wet and dry bonding with Carbo-baseddemineralization produced a weaker bond strength than the traditionalphosphoric acid wet adhesion suggested that the Carbo-based demineralizationis an unreliable adhesion strategy. A novel protocol of Er:YAG laserphysical etching followed by Carbo chemical etching for dentin adhesionrevealed that a micro-/nano-level rough, rigid, and non-collagen exposeddentin surface was produced, the micro-tensile bond strength was maintainedafter aging under dry and wet bonding modes, and in situ zymographyand nanoleakage within the hybrid layers presented lower signals afteraging. Cell culture in vitro and a rabbit deep dentin adhesion modelin vivo proved that this protocol is safe and biocompatible. Takentogether, the concept of extrafibrillar demineralization is limitedand insufficient to use in the clinic. The strategy of Er:YAG laserphysical etching followed by Carbo chemical etching for dentin adhesionproduces a bonding effect with reliability, durability, and safety.