Effect of phytic acid etchant on the stability of demineralized dentin and dentin bonding

Abstract

OBJECTIVES: Phytic acid (inositol hexakisphosphate, IP6) effectively removes the smear layer, producing high resin-dentin bond strength. This study aimed at demonstrating the effect of IP6 in stabilizing dentin collagen and preventing their collapse induced by strong air-dry. METHODS: Dentin beams were fully demineralized with 1% IP6 (pH1.2) or 10% phosphoric acid (PA). The PA-demineralized beams were untreated or treated with 5% glutaraldehyde (GA) fixation or 1% IP6 (pH7) for 1h, while IP6-demineralized beams underwent no further GA fixation. The beams were subjected to ultimate tensile strength (UTS) testing. For microscopic observation, dentin disks were etched with 1% IP6 or 35% PA. The PA-etched dentin disks were untreated or treated with GA fixation or IP6 for 1min, while IP6-etched disks were not fixed with GA. The etched surfaces and longitudinal sections were observed using a field emission scanning electron microscope (FE-SEM). For bonding test, flat dentin surfaces etched with IP6 or PA were blot-dried (mild) or air-dried for 10s (strong) and bonded with Single Bond Plus (3M ESPE) followed by composite build-ups for microtensile bond strength (μTBS) testing. RESULTS: The IP6-demineralized dentin beams showed significantly higher UTS than PA-demineralized dentin beams. GA and IP6 significantly improved UTS of PA-demineralized dentin beams. FE-SEM observation revealed that dentin collagen network was preserved by GA and IP6. For IP6-etched dentin, there was no significant difference in μTBS between mild and strong air-dried groups; whereas, the μTBS of PA-etched strong air-dried group significantly decreased. CONCLUSION: IP6 showed the same effect as GA to improve UTS of demineralized dentin and to prevent collapse and shrinkage of collagen fibrils. The surface-drying technique, mild or strong, did not influence μTBS when IP6 was used. IP6 may not only properly demineralize dentin but also preserve demineralized dentin matrix simultaneously, which should alleviate risk of collagen-collapse induced by strong air-drying.