Influence of simulated gastric acid exposure on surface characteristics and color stability of flowable and packable...

This study aimed to evaluate the effects of simulated gastric acid exposure on the surface roughness, gloss, and color stability of flowable and packable bulk-fill composite resins.

Five composite materials were evaluated: a universal composite-Estelite Σ Quick (Tokuyama Dental, Japan) [EQ]; two packable bulk-fill composites-Filtek One Bulk Fill Restorative (3M ESPE, USA) [FR] and Tetric N-Ceram Bulk-Fill (Ivoclar Vivadent, Liechtenstein) [TN]; and two flowable bulk-fill composites-Estelite Bulk-Fill Flow (Tokuyama Dental, Japan) [EF] and Hi-Fill Bulk-Flow (FSM Dental, Türkiye) [HF]. Standardized disc-shaped specimens (n = 12 per group) were fabricated using Mylar strips; no finishing or polishing procedures were performed on the specimen surfaces. Baseline measurements of surface roughness (Ra), gloss (GU), and color parameters (for ΔE₀₀ calculation) were obtained prior to exposure using a contact profilometer, glossmeter, and spectrophotometer, respectively. The specimens were then subjected to simulated gastric acid (pH 1.2) for durations corresponding to 1 year (3 h) and 5 years (15 h) of cumulative exposure. Following each exposure period, all measurements were repeated. Color change (ΔE₀₀) were calculated according to CIE2000 formula.

Simulated gastric acid exposure resulted in a significant increase in surface roughness and color change, along with a reduction in gloss values in most materials (p < 0.05). Surface roughness increased significantly in all groups except EQ (p > 0.05), with the highest values observed in the TN group in a 5-year simulation (0.43 ± 0.25 μm; p = 0.037). Gloss values significantly decreased in all materials (p ≤ 0.007), although FR exhibited a more limited reduction, reaching significance only after prolonged exposure (p = 0.017), and maintained the highest gloss after 5 years of simulation (74.9 ± 8.9 GU). ΔE₀₀ increased significantly in all groups over time (p < 0.001), with the greatest change observed in EQ (3.18 ± 0.7).

Simulated gastric acid exposure compromised the surface and optical properties of all tested composites, with flowable bulk-fill materials demonstrating greater susceptibility than packable counterparts. FR exhibited superior performance, preserving gloss and maintaining color changes within clinically acceptable limits (ΔE₀₀≤1.8). These findings highlight the pivotal influence of filler content, resin matrix composition, and photoinitiator system on composite resistance to acid-induced surface degradation and optical instability.