THE INFLUENCE OF CITRIC ACID ON THE MICRO-HARDNESS AND SURFACE ROUGHNESS OF CONTEMPORARY CAD/CAM INDIRECT RESTORATIVE MATERIALS: AN IN VITRO ANALYSIS

Background: Despite their clinical advantages, restorative materials remain susceptible to degradation under intraoral conditions, particularly in acidic environments resulting from dietary habits . Citric acid, commonly present in citrus fruits and beverages, is a prevalent erosive agent with the potential to compromise the long-term integrity of dental restorations7 This in vitro study aimed to assess the effect of citric acid on the micro-hardness and surface roughness of three novel CAD/CAM indirect restorative materials: lithium disilicate (IPS e.max CAD), zirconia-reinforced lithium silicate (ZLS), and resin nano-ceramic (Cerasmart).
Materials and Methods: Sixty standardized rectangular specimens (8 × 5 × 2 mm) were prepared (n = 20/material).
Each group was subdivided into control (immersed in artificial saliva) and experimental (immersed in 2% citric acid,
pH = 3.2) subgroups. A digital Vickers hardness tester was used to detect micro-hardness and atomic force microscopy (AFM) was used to assess surface roughness following a 7-day aging regimen at 37°C.Non-parametric statistical analysis (Mann-Whitney, Kruskal-Wallis) was conducted at a significance level p≤0.01.
Results: Citric acid significantly reduced micro-hardness and increased surface roughness in all materials tested (p
≤ 0.01). Among the groups, zirconia-reinforced lithium silicate exhibited higher resistance, while resin nano-ceramic
demonstrated the most susceptibility to acidic degradation.
Conclusions: Exposure to citric acid led to a significant deterioration in both surface and mechanical integrity, with
material-dependent variations. The findings emphasize the need for cautious material selection in patients with high
dietary acid exposure.