Abstract
Erosive wear undermines the structural properties of enamel resulting in irreversible enamel loss. A thin protein layer formed from natural saliva on tooth surfaces, acquired enamel pellicle (AEP), protects against erosive wear. The exact components in saliva responsible for such protection are not yet known. We prepared three solutions containing different components: proteins and ions [natural saliva (NS)], minerals with no proteins [artificial saliva (AS)] and neither proteins nor ions [deionised water (DW)]. To assess the protection of the three solutions against citric acid enamel erosion, enamel specimens were immersed in the corresponding solution for 24 h. All specimens were then exposed to five erosion cycles, each consisted of a further 30 min immersion in the same solution followed by 10-min erosion. Mean step height using a non-contacting profilometer, mean surface microhardness (SMH) using Knoop microhardness tester (final SMH), and roughness and 2D profiles using atomic force microscopy were measured after five cycles. The final SMH values were compared to the starting values (after 24 hr). NS group had significantly less tissue loss but greater SMH change (P < 0.0001) than AS and DW groups. Specimens in NS were softer and rougher (P < 0.001) but less eroded than specimens in AS and DW.
Highlights
Erosive wear has become a prevalent oral health problem, affecting an increasing proportion of the population worldwide[1]
Immersing the enamel specimens in natural saliva (NS) and artificial saliva (AS) prior to the erosion cycle resulted in significant surface microhardness change (SMHC) just by incubation in these solutions without any acidic challenge
The results of this study indicate that immersion of enamel specimens in NS for 24 h prior to acid exposure offered the best protection against step height formation [3.80 (0.59) μm], but with a greater Knoop microhardness change [249.4 (19.56) KNH] compared to AS [6.34 (0.55) μm and 181.87 (20.48) KHN, respectively] and deionised water (DW) [8.80 (1.28) μm and 167.12 (15.68) KHN, respectively]
Summary
Erosive wear has become a prevalent oral health problem, affecting an increasing proportion of the population worldwide[1]. Natural saliva (NS) and artificial saliva (AS) (which contains the minerals but not the proteins of saliva) have been used in in vitro erosive wear models to assess the demineralisation/remineralisation process of erosive wear. Saliva is supersaturated with minerals such as calcium, phosphate and fluoride, which help maintain the physical and chemical integrity of the tooth structure[8, 9], and contains more than 1,000 different proteins[10]. Some studies have related the protective effects of the AEP to its mineral content[19,20,21], whereas others have attributed these effects to its protein components[12, 22,23,24]. Natural saliva is commonly replaced by artificial saliva in in vitro studies due to issues relating to collection, storage and degradation of human saliva[25,26,27]. The most commonly used and currently available formulations of artificial saliva[21] fall into three types: electrolytes with carboxymethylcellulose (CMC)[28, 30], electrolytes with mucin[25] or electrolytes only[31]
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