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.