Figure 2. Transmission electron micrographs of acid-etched dentin incubated in artificial saliva for 250 days. (A) Unstained, undemineralized micrograph of phosphoric-acid-etched dentin that was aged in artificial saliva for 250 days. The entire thickness of collagen matrix completely disappeared, exposing the highly irregular demineralization front of the original acid-etched dentin. D, undemineralized dentin; E, epoxy resin. (B) Another unstained, undemineralized micrograph from the 250-day artificial saliva group showing the presence of a thin remnant layer of unstained collagen fibrils (pointer) above the demineralized matrix. D, undemineralized dentin; E, epoxy resin. (C) Stained, demineralized micrograph taken from the same group, showing the disappearance of the bulk of the demineralized collagen matrix. A 1-µm-thick remnant zone of sparsely arranged, banded collagen fibrils (pointer) can be observed over the previously unetched, laboratory-demineralized dentin (D). E, epoxy resin; T, dentinal tubule.