Comparison of the effect of self-assembling peptide P11-4 on post-bleaching shade stability and microhardness with different bioactive remineralization agents

This in vitro study aimed to evaluate and compare the efficacy of six remineralization protocols—including a self-assembling peptide (SAP) P11-4 (Curodont™ Protect), a surface pre-reacted glass-ionomer agent (PRG Pro-Care Gel), nano-hydroxyapatite (Apa Care Repair), casein phosphopeptide-amorphous calcium phosphate (Tooth Mousse), fluoride (ReminPro), and a control—on enamel microhardness recovery and color stability following in-office bleaching with 35% hydrogen peroxide. Thirty caries-free premolars were sectioned to obtain enamel specimens. Baseline (T0) color (CIEDE2000) and microhardness (Vickers, 300 g/15s) were measured. All samples underwent a standardized bleaching protocol (three 8-minute cycles, total 24 min). Post-bleaching measurements (T1) were taken. Specimens were randomly assigned to six groups (n = 5): Control (artificial saliva), ReminPro, Tooth Mousse, Apa Care Repair, PRG Pro-Care Gel, and Curodont™ Protect. Remineralization agents were applied four times over 28 days. Final measurements (T2) were taken after 28 days in artificial saliva. Data were analyzed using Two-Way Repeated Measures ANOVA with Bonferroni post-hoc tests (α = 0.05). Bleaching significantly reduced enamel microhardness in all groups (p < 0.001). After 28 days, all agents promoted microhardness recovery compared to control (p < 0.001). Curodont™ Protect achieved microhardness values statistically equivalent to baseline, performing significantly better than all other agents. Microhardness hierarchy: Curodont™ Protect > PRG Pro-Care Gel > Apa Care Repair ≈ Tooth Mousse > ReminPro > Control. For ΔE, a significant time effect was observed (p < 0.001), but no significant intergroup differences were found (p = 0.726). A significant interaction was found for ΔL (p = 0.020), with Curodont™ Protect showing final lightness statistically indistinguishable from baseline. The choice of remineralizing agent influences enamel recovery after bleaching, particularly regarding mechanical properties. While all agents provided comparable ΔE stabilization, SAP P11-4 was uniquely effective, enabling near-complete microhardness recovery and distinct return of lightness to baseline. S-PRG and nano-hydroxyapatite also demonstrated strong efficacy. Within the limitations of this in vitro study, biomimetic agents such as SAP P11-4 may offer advantages for structural recovery and shade perception following in-office bleaching. Further clinical studies are warranted to confirm these findings.