Can Resin Monomers and By-Products Damage Collagen?

Hybrid layers degrade due to endogenous collagenolytic enzymes and adhesive hydrolysis. Adhesive hydrolysis releases by-products that, along with uncured monomers, may have an adverse effect on collagen fibrils and contribute to the dissolution of the hybrid layer in resin-dentin bonds. The aim of this study was to investigate the effects of methacrylate monomers and corresponding by-products on collagen type I. Tendon fibers (TFs) from mouse tail were incubated with BisGMA 0.1%, BisEMA 0.1%, UDMA 0.1%, HEMA 0.1%, TEG-DMA 0.1%, methacrylic acid 0.025% (MAA), pyruvic acid 0.025% (PA), trypsin as positive control (PC), and water/ethanol as negative control for 1 h, 6 h, 24 h, 72 h, and 7 d. At each period, the specimens were tested mechanically (tensile strength and elastic modulus) and the storage medium tested for hydroxyproline (HPY) release and expressed as percentage of collagen solubilization (%CS). The TFs were morphologically analyzed by a Nikon-Eclipse 80i microscope. Incubation media and time affected TFs in different ways. The incubation of TFs with PA or MAA caused significant damage to the structure, reducing properties and increasing %CS to levels similar or higher than that of trypsin PC. Incubation in the monomers BisGMA 0.1%, BisEMA 0.1%, UDMA 0.1%, HEMA 0.1%, and TEG-DMA 0.1% did not cause hydroxyproline release, and their effects on the TF mechanical properties varied and were possibly related to dehydration. Methacrylate monomers and their by-products can adversely affect TF structure and properties. The findings indicate that collagen degradation in resin-dentin bonds can also be caused by by-products of the adhesive.