Figure 2. A horizontal pattern of degradation within the hybrid layer, as illustrated by the radiographs and TEMs of primary molars that were retrieved from the second clinical subject (Control group, a, c, and e; Experimental chlorhexidine group, b, d, and f). C, resin composite; A, adhesive; H, hybrid layer; D, dentin. (a) Bitewing radiograph showing the Class I restoration in tooth 85 (control, circled). (b) Bitewing radiograph showing the Class I restoration in tooth 75 (experimental, circled). (c) Undemineralized, unstained, silver-impregnated section from the control tooth, showing that the top 1.5–2 µm (asterisk) of the hybrid layer (between open arrows) was almost completely impregnated with silver deposits. (d) The same type of section from the experimental tooth, showing sparsely distributed silver deposits (pointer) that occurred predominantly at the base of the hybrid layer (between open arrows). (e) Demineralized section from the control tooth that was stained with phosphotungstic acid and uranyl acetate. Partial degradation of the collagen fibrils along the top 1–1.5 µm (asterisk) into non-banded, microfibrillar strands (i.e., gelatin; high magnification not shown) of the hybrid layer (between open arrowheads) corresponded to the region of heavy silver deposits depicted in Fig. 2c. (f) The same type of section from the experimental tooth, showing the absence of degradation from the hybrid layer (between open arrowheads) when chlorhexidine was used as an MMP inhibitor.