Degree of conversion of two-step etch-and-rinse adhesives: in situ micro-Raman analysis

Objectives: DC of three commercial two-step etch-and-rinse adhesives across the dentine– adhesive interface was investigated using micro-Raman spectroscopy. The hypothesis tested was that no difference in DC would exist among the adhesives tested. Methods: Adper Scotchbond 1XT (3M ESPE), Prime&Bond NT (Dentsply DeTrey), and Ambar (FGM) were applied on human dentine disks (n = 9). Composite increments of 2 mm were then applied on the adhesive surface. Raman spectra were collected along the dentine– adhesive interface. The relative intensities of the peaks associated with the mineral (PO4 3- at 960 cm-1) and the adhesive (C  C at 1640 cm-1; phenyl C identify the adhesive within the hybrid layer and calculate its DC. Results: Adper Scotchbond 1XT and Ambar showed similar DC (79 +/- 7% and 77 +/- 7%, respectively), while a lower DC was found for Prime&Bond NT (70 +/- 7%; p < 0.05). Conclusions: The hypothesis tested was rejected because differences were found among the adhesives tested. The difference in DC among the three adhesive systems can be attributed to different monomer compositions and solvents. Further studies are needed to correlate DC with other mechanical properties of these adhesives. Clinical significance: Insufficient polymerization of an adhesive can result in a weak hybrid layer, and the presence of unreacted monomers may result in degradation of the polymeric network, decreasing the strength and longevity of the bond. In the present study, Adper Scotchbond 1XT and Ambar performed significantly better than Prime&Bond NT.