Association Between Salivary Enzyme Composition and the Surface Degradation of Contemporary Resin Composite Restorative Materials

Abstract

Background: Resin composite materials are widely used for direct dental restorations because of their favorable esthetics, adhesive properties, and conservative preparation requirements. Despite continuous improvements in resin chemistry and filler technology, these materials remain susceptible to degradation in the oral environment. Saliva contains several enzymes capable of interacting with resin matrices and potentially accelerating hydrolytic and proteolytic deterioration. The extent to which salivary enzyme composition is associated with clinically detectable surface degradation of contemporary resin composite restorations remains an important area of investigation.

Objective: To determine the association between salivary enzyme composition and surface degradation of contemporary resin composite restorative materials, with particular emphasis on salivary esterase activity, surface roughness, microhardness, and microscopic surface changes.

Methodology: This analytical cross-sectional study was conducted at Rashid Latif Dental College from January 2025 to June 2025 and included 78 participants with resin composite restorations. After obtaining written informed consent, the selected resin composite restorations were carefully retrieved from the oral cavity, labeled, and transferred to the laboratory for analysis. Unstimulated whole saliva was collected under standardized conditions, and salivary flow rate, pH, esterase activity, amylase, protease, matrix metalloproteinase-8 (MMP-8), and matrix metalloproteinase-9 (MMP-9) were measured. All 78 retrieved restoration specimens were evaluated for surface roughness and Vickers microhardness, and all underwent scanning electron microscopy (SEM) for assessment of microscopic surface degradation, including surface pits, filler exposure, resin matrix erosion, and microcracks. Correlations between salivary and surface parameters, group comparisons, and multivariable regression analysis were performed. A p-value <0.05 was considered statistically significant.

Results: The mean age of participants was 34.7 ± 9.2 years, and 42 (53.8%) were females. All 78 retrieved resin composite restoration specimens were successfully evaluated for surface roughness, Vickers microhardness, and SEM-based microscopic degradation. Mean salivary esterase activity was 18.6 ± 6.1 U/mL, while mean surface roughness was 0.39 ± 0.14 µm and mean Vickers microhardness was 67.8 ± 8.9 VHN. SEM assessment demonstrated mild, moderate, and marked surface degradation in 33 (42.3%), 27 (34.6%), and 18 (23.1%) specimens, respectively. Salivary esterase activity showed a significant positive correlation with surface roughness (r = 0.56, p < 0.001) and an inverse correlation with microhardness (r = −0.48, p < 0.001). Specimens from participants with high esterase activity demonstrated greater surface roughness than those with low esterase activity (0.46 ± 0.13 vs. 0.32 ± 0.11 µm, p < 0.001) and lower microhardness (63.9 ± 8.4 vs. 71.7 ± 7.5 VHN, p < 0.001). Lower salivary pH and longer restoration duration were also independently associated with greater surface deterioration.

Conclusion: Higher salivary esterase activity was significantly associated with greater surface roughness, reduced microhardness, and more pronounced microscopic degradation of contemporary resin composite restorations. Salivary pH, restoration duration, and composite material type also influenced surface integrity. These findings suggest that patient-specific salivary biochemical characteristics may contribute to variation in the long-term clinical performance of resin-based restorative materials.