Impact of antibacterial composite resin on salivary pH dynamics in high-caries-risk children: An ex-vivo study

Abstract

Objectives

Composite resin restorations in primary teeth frequently fail due to secondary caries, which result from bacterial colonization and acid production at the tooth–restoration interface. This study aimed to evaluate whether composite resins containing quaternary ammonium silica (QASi), known for their antibacterial properties, can reduce bacterial acidification and lower the risk of secondary caries in high-caries-risk children compared to conventional restoratives.

Methods

Saliva samples (10 µL saliva, ∼10⁶ bacteria) from 34 high-caries-risk children were applied ex vivo directly to three restorative materials: (i) Infinix with 1.5% QASi (Nobio), (ii) Filtek Supreme (3 M), and (iii) amalgam (Silmet). Samples were incubated with growth media supplemented with 2.5% dextrose at 37 °C for 24 hours. Bacterial growth and pH decrease were measured, by turbidity and colour change, every 20 minutes. Controls included saliva alone and a blank polystyrene surface.

Results

Repeated-measures ANOVA showed Infinix had the slowest pH decline, followed by amalgam, while Filtek Supreme’s pH drop matched the control (p<0.001). Infinix also exhibited the lowest bacterial growth rate (p<0.001).

Conclusion

Saliva bacteria from high-caries-risk children exhibit significantly slower pH decrease on Infinix composite resins compared to conventional restoratives.

Clinical significance

Composite resins with quaternary ammonium silica (QASi) fillers effectively inhibit bacterial growth and acid production, helping to prevent secondary caries and enamel demineralization. These bioactive materials offer a promising solution for improving the longevity of restorations, especially in high-caries-risk pediatric patients.