Ask the Experts Answer

What are the limitations of using a self-etch adhesive?

• One disadvantage of self-etch adhesives is that although the primer is acidic (pH just over 2.0); this is not acidic enough to adequately etch sclerotic dentin, tertiary dentin and uncut enamel. A pH below this range would provide higher bond strengths to enamel but would result in poor occlusal dentin bonds.
• Water sorption of self-etch adhesive interfaces is still considered the most important factor relating to bond degradation. The 1-step self-etch adhesives are specifically formulated to etch (i.e. high concentration of hydrophilic acidic monomers), prime and bond; all in one single step. Contributing to water sorption of these 1- step self-etch adhesives is the higher concentration of acidic monomers (lower pH) in an attempt by researchers and manufacturers to achieve improved etching of enamel. The simplicity of these adhesives comes at the expense of their high affinity for water, even after cure (i.e. polymerization). Such hydrophilicity turns them into a semi-permeable membrane, which allows for water transfusion across the cured adhesive system. This results in lower bond strength, water bubbles and water tree formation. It is documented that 1-step self-etch adhesives generally cannot provide durable bonds, especially on dentin.
  
  It was postulated by BISCO that highly cross-linked polymers could effectively block water molecule's attack, and exhibit lower water sorption, resulting in improved clinical durability. This concept is supported by a 2 year clinical study (Reis et al) where All-Bond SE, used in both the 1-step or 2-step protocol, resulted in high retention rates.