Adhesive phase separation at the dentin interface under wet bonding conditions.

Area of Science:

• Materials Science
• Biomaterials Science
• Dental Materials

Background:

• Dentin bonding is crucial for dental restorations.
• Water presence during bonding can lead to adhesive phase separation.
• This separation may compromise the hybrid layer's integrity.

Purpose of the Study:

• To investigate phase separation in 2,2-bis[4(2-hydroxy-3-methacryloyloxy-propyloxy)-phenyl] propane (BisGMA)-based adhesives.
• To analyze the effect of phase separation on the hybrid layer's structural characteristics.
• To understand the molecular composition of phase-separated components.

Main Methods:

• Model BisGMA/HEMA mixtures and a commercial BisGMA-based adhesive (Single Bond) were combined with varying water concentrations.
• Cloud point measurements were used to detect macrophase separation.
• Confocal Raman microspectroscopy (CRM) and scanning electron microscopy (SEM) analyzed molecular structure and interface morphology.

Main Results:

• BisGMA-based adhesives and model mixtures underwent phase separation at approximately 25 vol% water.
• CRM revealed phase-separated particles were BisGMA-rich, and the matrix was HEMA-rich.
• SEM and CRM mapping showed significant porosity at the dentin/adhesive interface, with a decrease in BisGMA contribution within the first micrometer.

Conclusions:

• Adhesive phase separation results in a porous hybrid layer, not an impervious network.
• The hybrid layer consists of hydrophobic BisGMA-rich particles within a hydrophilic HEMA-rich matrix.
• This compromised structure may affect the long-term durability of dental restorations.