The Role of Adhesive Monomers (۱۰-MDP, ۴-META, HEMA) in Hybrid Layer Formation: Optimizing Chemical Adhesion to Hydroxyapatite and Managing Polymerization Shrinkage Stress

This review analyzes the chemical mechanisms governing the micro-tensile bond strength of indirect nanocomposite restorations to deep dentin, focusing on the role of specific adhesive monomers and the hydrophobic-hydrophilic balance within Immediate Dentin Sealing (IDS) protocols. Drawing on experimental data from four adhesive systems (Optibond FL, SE Bond, G Premio Bond, G۲ Bond), this review examines how monomer chemistry—particularly the functional monomers ۱۰-MDP, ۴-META, and HEMA—affects chemical adhesion to hydroxyapatite (HA) and dentin wettability. The analysis also considers how polymerization shrinkage stress is mitigated through hybrid layer formation and the application of flowable composite liners. Adhesives containing ۱۰-MDP (SE Bond, G۲ Bond) demonstrated stable chemical bonding to HA via nano-layering, while HEMA-rich systems (Optibond FL) enhanced dentin wettability and monomer penetration but increased hydrophilicity. The three-step etch-and-rinse system (Optibond FL) and two-step self-etch systems (SE Bond, G۲ Bond) achieved significantly higher bond strengths (۲۴.۰۳–۲۸.۲۷ MPa) compared to the control group (۱۷.۵۸ MPa) by forming a more hydrophobic, durable hybrid layer. In contrast, the G Premio bond's lower performance was attributed to its specific monomer formulation and solvent composition, which compromised the hybrid layer's integrity under IDS conditions. Optimizing chemical adhesion to deep dentin requires a balanced approach: sufficient hydrophilicity for monomer penetration into demineralized collagen, yet adequate hydrophobicity for hybrid layer stability. The presence of ۱۰-MDP and controlled HEMA content are critical determinants of long-term bond strength. IDS, combined with flowable composite application, effectively manages polymerization shrinkage stress by preserving hybrid layer integrity and reducing dentin permeability. These chemical insights provide evidence-based guidance for selecting adhesive systems in deep dentin restorations.

کلیدواژه ها:

Hybrid layer formation ، Polymerization Shrinkage Stress ، Dentin Wettability ، Chemical Adhesion to HA ، Hydrophobic-Hydrophilic balance