This study was aimed at analyzing the surface properties of a universal resin composite and evaluating the effect of preheating on its physicochemical properties. Two commercial resin composites were used under two conditions: Filtek Universal Restorative (UR); UR preheated (URH); Filtek Supreme (FS) and FS preheated (FSH). The film thickness (FT) test (n = 10) was done using two glass slabs under compression. Flexural strength (FLS) and modulus (FLM) were evaluated using a three-point flexion test (n = 10). Polymerization shrinkage stress (PSS) was evaluated in a universal testing machine (n = 5). Gap width (GW) between composite and mold was measured in internally polished metallic molds (n = 10). The degree of conversion (DC) was evaluated by Fourier Transform Infrared spectroscopy (n = 3). The morphology of the filler particles was checked by scanning electron microscope (SEM) and EDX analysis. Surface gloss (SG) and surface roughness (SR) were evaluated before and after mechanical brushing (n = 10). The outcomes were submitted to 2-way ANOVA and Tukey's test (α = 0.05). Lower mean values of FT were observed for the preheated groups when compared to the non-preheated groups. URH and FSH showed higher mean values of FLS and FLM when compared with UR and FS. No differences were observed between groups in the PSS test. The GW was higher for the UR and FS groups when compared with URH and FSH. The DC was higher for preheated resin composites when compared to the non-preheated groups. The SR of the UR composite was higher than the FS after mechanical brushing, while the SG was higher for the FS groups. In conclusion, the universal resin composite tested generally presented similar physicochemical properties compared with the nanofilled resin composite and either similar or slightly inferior surface properties. The preheating improved or maintained all properties evaluated.

Dental resin composites are widely used in clinical settings but often face longevity issues due to the development and accumulation of microcracks, which eventually lead to larger cracks and restoration failure. The incorporation of microcapsules into these resins has been explored to introduce self-healing capability, potentially extending the lifespan of the restorations. This study aims to enhance the performance of self-healing dental resins by optimizing the microcapsules–resin matrix physicochemical interactions. Poly(urea–formaldehyde) (PUF) microcapsules were reinforced with melamine and subsequently subjected to surface functionalization with 3-aminopropyltriethoxysilane (APTES) and (3-mercaptopropyl)trimethoxysilane (MPTMS). Additionally, microcapsules were functionalized with a bilayer approach, incorporating tetraethyl orthosilicate (TEOS) with either APTES or MPTMS. X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA) confirmed an increased Si:C ratio from 0.006 to 0.165. The functionalization process did not adversely affect the structure of the microcapsules or their healing agent volume. Compared to PUF controls, the functionalized microcapsules demonstrated enhanced healing efficiency, with TEOS/MPTMS-functionalized microcapsules showing the highest performance, showing a toughness recovery of up to 35%. This work introduces a novel approach to functionalization of microcapsules by employing advanced silanizing agents such as APTES and MPTMS, and pioneering bilayer functionalization protocols through their combination with TEOS.

Approximately 50% of resin-based dental restorations fail within ten years, mainly due to secondary caries and material fractures. Incorporating self-healing microcapsules containing resin-based agents that polymerize upon release offers a promising strategy to repair microcracks and extend restoration longevity. Poly(urea–formaldehyde) (PUF) microcapsules are commonly used, but formaldehyde cytotoxicity remains a concern. This study developed alternative microcapsules by integrating melamine into the polymeric shell (PUMF) and functionalizing surfaces with methacrylate (TMSPM) or thiol (MPTMS) silanes, with or without a TEOS pre-coating, to reduce formaldehyde release and enhance biocompatibility. Microcapsules were synthesized via double-emulsion, encapsulating triethylene glycol dimethacrylate (TEGDMA), and characterized for morphology, mechanical stability, functionalization efficiency, formaldehyde release, and cytotoxicity. Melamine increased mechanical and morphological stability, surface roughness, and core retention, especially under functionalization, but also raised formaldehyde release in unmodified capsules. Functionalization with TMSPM and MPTMS significantly reduced formaldehyde release from both PUF and PUMF capsules. Metabolic assays showed dental pulp stem cells were more sensitive to TEGDMA, while fibroblasts were affected by TEGDMA combined with prolonged formaldehyde exposure. Overall, melamine-reinforced functionalized microcapsules exhibit improved stability, controlled formaldehyde release, and enhanced biocompatibility, supporting their potential as next-generation self-healing dental materials.