Effect of gastric acids on surface topography and bending properties of esthetic coated nickel-titanium orthodontic archwires



The purpose of this study was to evaluate the effect of simulated gastric acid solution on surface topography and bending properties of esthetic coated nickel-titanium (NiTi) archwires.

Materials and methods

Three brands of as-received white-coated superelastic NiTi upper archwires were used in this study: Dany, Perfect, and Nitanium. Uncoated metallic areas for each white-coated NiTi archwire were used for comparison with the coated areas. The specimens for each archwire were divided into two groups according to coating as follows: Group A, uncoated, and group B, coated. Then, each group was further subdivided into two subgroups according to the immersion medium as follows: Subgroup 1, immersed in artificial saliva, and subgroup 2, immersed in simulated gastric acid. Surface roughness, surface morphology, and three-point bending test were performed. The data were analyzed statistically using ANOVA and Tukey test.


The archwires immersed in simulated gastric acid solution showed significantly higher surface roughness and lower forces on loading and unloading than the archwires immersed in artificial saliva (P < 0.001). Perfect archwire showed significantly the highest surface roughness compared with Dany and Nitanium archwires (P < 0.001). The uncoated archwires showed higher loading and unloading forces compared with coated archwires for all groups (P < 0.001). Nitanium archwire showed the lowest loading and unloading forces at different deflections (P < 0.001).


The simulated gastric acid solution decreased considerably the amount of force applied at a given deflection. The loading-deflection and surface roughness properties of coated archwires were affected by the type of coating material.

Clinical relevance

The impact of gastric acids on surface and mechanical properties of orthodontic archwires depend on type of coating materials.

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Correspondence to Shaymaa Elsaka.

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Elsaka, S., Hassan, A. & Elnaghy, A. Effect of gastric acids on surface topography and bending properties of esthetic coated nickel-titanium orthodontic archwires. Clin Oral Invest 25, 1319–1326 (2021). https://doi.org/10.1007/s00784-020-03438-7

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  • Artificial saliva
  • Coated archwire
  • Gastric acid
  • Surface roughness
  • Surface topography
  • Three-point bending