Superiority of areal surface roughness measurement over line-based evaluation in glass-ionomer cements: A three-dimensional in vitro study

Surface roughness plays a key role in dentistry, affecting bacterial adhesion, wear resistance, and material performance. Glass-ionomer cements (GICs), widely used as restorative materials, are particularly sensitive to surface characteristics. However, different measurement methods, specifically line roughness ( Ra ) and area roughness ( Sa ), often yield incomparable results. This study aimed to determine whether significant differences exist between Ra and Sa measurements of GIC surfaces. Fifty block-shaped samples were inserted into a standardized square metal mold. After extrusion, the samples were analyzed using a three-dimensional optical surface measurement system. Sa values were obtained by measuring a 4 mm x 4 mm area to capture the overall surface texture. Ra values were measured along 4 mm lines at five points each, in five orientations: horizontal, vertical, diagonal from bottom left to top right, diagonal from bottom right to top left, and a zig-zag pattern, assessing the influence of measurement direction. Surface roughness values measured using Sa were higher than those obtained using Ra in all directions except for the zig-zag. This discrepancy suggests that line measurements may not fully capture surface texture variations detected by area measurements. Correlational studies using Ra measurements may have underestimated the relationship to other parameters like bacterial adhesion. Standardizing the use of Sa in surface roughness assessments and reporting the measured area size could enhance comparability between studies. Future research should adopt area-based measurements to improve the understanding of how surface roughness impacts dental materials and treatments. Surface parameters are particularly relevant for non-industrially modified surfaces, such as filling polishes. • Surface roughness differs depending on the applied analysis method (Sa vs. Ra). • Sa provides a more comprehensive assessment due to fewer missed surface areas. • Ra values in most directions are lower than Sa, except for zig-zag measurements. • Contactless surface roughness measurement may offer more objective results.