Water distribution in dentin matrices: Bound vs. unbound water

Abstract

Objectives This work measured the amount of bound versus unbound water in completely-demineralized dentin. Methods Dentin beams prepared from extracted human teeth were completely demineralized, rinsed and dried to constant mass. They were rehydrated in 41% relative humidity (RH), while gravimetrically measuring their mass increase until the first plateau was reached at 0.064 (vacuum) or 0.116 g H2O/g dry mass (Drierite). The specimens were then exposed to 60% RH until attaining the second plateau at 0.220 (vacuum) or 0.191 g H2O/g dry mass (Drierite), and subsequently exposed to 99% RH until attaining the third plateau at 0.493 (vacuum) or 0.401 g H2O/g dry mass (Drierite). Results Exposure of the first layer of bound water to 0% RH for 5 min produced a −0.3% loss of bound water; in the second layer of bound water it caused a −3.3% loss of bound water; in the third layer it caused a −6% loss of bound water. Immersion in 100% ethanol or acetone for 5 min produced a 2.8 and 1.9% loss of bound water from the first layer, respectively; it caused a −4 and −7% loss of bound water in the second layer, respectively; and a −17 and −23% loss of bound water in the third layer.. Bound water represented 21–25% of total dentin water. Chemical dehydration of water-saturated dentin with ethanol/acetone for 1 min only removed between 25 to 35% of unbound water, respectively. Significance Attempts to remove bound water by evaporation were not very successful. Chemical dehydration with 100% acetone was more successful than 100% ethanol especially the third layer of bound water. Since unbound water represents between 75–79% of total matrix water, the more such water can be removed, the more resin can be infiltrated.

Uninfiltrated Collagen in Hybrid Layers produced after Reduced Acid-etching Time on Primary and Permanent Dentin

“…Water present in etched dentin keeps collagen fibrils expanded and can be classified as free (unbound) and collagen-bound water. 24 While free water represents approximately 75 to 79% of total water content in demineralized dentin, 21 to 25% is bound water. 24 The application of polar solvents, such as ethanol and acetone may chemically dehydrate dentin, creating a more favorable environment for adhesive infiltration.…”

“…24 While free water represents approximately 75 to 79% of total water content in demineralized dentin, 21 to 25% is bound water. 24 The application of polar solvents, such as ethanol and acetone may chemically dehydrate dentin, creating a more favorable environment for adhesive infiltration. However, Agee et al 24 demonstrated that when applied for 60 seconds on dentin, ethanol and acetone remove respectively, 25 and 34% of unbound water, leaving behind most of the total water content permeating collagen fibrils.…”

“…24 The application of polar solvents, such as ethanol and acetone may chemically dehydrate dentin, creating a more favorable environment for adhesive infiltration. However, Agee et al 24 demonstrated that when applied for 60 seconds on dentin, ethanol and acetone remove respectively, 25 and 34% of unbound water, leaving behind most of the total water content permeating collagen fibrils. Remaining water impairs monomer infiltration and is used by proteases to degrade unprotected collagen in the hybrid layer.…”

Influência da solução irrigadora na formação de defeitos dentinários após preparo com Sistema Reciproc®

“…Cerca de 20% a 25% da dentina é constituída de água. A dentina perde cerca de 10% de água após a extração do dente, se este for mantido em ambiente completamente seco em tempo superior a cinco minutos 22 . Os efeitos deletérios sobre a matriz de colágeno e proteoglicano podem atuar como um desencadeador para a contração da dentina, induzindo um aumento da tensão e da propagação de fissuras; além disso, em última análise, podem contribuir para a significativa redução na resistência à fratura 23 .…”

“…O conhecimento atual indica que a fratura começa a partir de microfissuras na dentina radicular e estudos laboratoriais têm ligado a sua formação com alguns procedimentos endodônticos de rotina, tais como preparo do canal radicular, obturação e retratamento 22 . Os resultados desta pesquisa contrastam com estudos anteriores, considerando que os defeitos dentinários observados nas imagens após a instrumentação e a secção, na verdade, já poderiam existir no pré-operatório, não sendo, portanto, visíveis ao microspópio.…”