Figure. ¹³C NMR spectra of HEMA in the absence or in the presence of dentinal collagen. (A) NMR spectrum of HEMA in the absence of dentinal collagen at pH = 6.3. (B) NMR spectrum of HEMA in the presence of dentinal collagen at pH = 4.1. (C) NMR spectrum of HEMA in the presence of dentinal collagen at pH = 1.7.