Abstract
The aim of this study was to evaluate the physicochemical properties of experimental adhesives containing tailored fluoridated calcium phosphate fillers. Five experimental resins were formulated, one contained no calcium phosphate filler (Control) and the other four resins contained 40wt% of calcium phosphate fillers doped with increasing concentration of fluoride: adhesives CaP (no fluoride), CaP-2F (2wt% F), CaP-4F (4wt% F) and CaP-8F (8wt% F). Resin specimens were prepared for three-point bending test to evaluate the elastic modulus (E) and flexural strength (FS) at 24h and after 2 months of water storage. Disk-shaped specimens were prepared to analyze the water sorption (Ws) according to ISO 4049. The degree of conversion (DC) of the tested resins was also assessed through FTIR. Statistical analysis was performed with ANOVA and Tukey’s test (p 0.05) compared to the filler-free resin. However, these same experimental resins showed the highest E after water storage. All resins had a significant reduction of the FS after water storage (p<0.001), but at lower percentage rate for those experimental resins containing fluoride-free CaP or fluoride-doped CaP-2F.. These latter experimental resins achieved similar Ws to control filler-free resin. Conversely, those resins containing 4wt% or and 8wt% fluoride-doped CaP promoted had a significant Ws increase (p<0.05). In conclusion, the incorporation of calcium phosphate particles without fluoride and or with 2wt% fluoride may represent be a promising strategy to generate adhesive resins with specific physicochemical properties. Fluoride incorporation in CaP fillers for dental resin adhesive should be performed at low concentrations in order to avoid excessive water sorption and decrease of polymerization.
Highlights
Resin composite restorations are the foremost procedure in modern restorative dentistry as such materials present optimal esthetics and appropriate mechanical properties to replace those dental hard tissues that were lost for different causes
The highest DC was attained with the adhesive resin containing no filler (78.1%), and it was significantly different (p < 0.001) compared to calcium phosphates (CaP)-4F and calcium phosphates with 8 wt% fluoride (CaP-8F); these latter two materials attained the lowest degree of conversion
The adhesive resin containing the fluoride-free calcium phosphates (CaP) and that doped with 2 wt% fluoride (CaP-2F) achieved similar DC values to the control filler-free resin (p = 0.439 and p = 0.596, respectively)
Summary
Resin composite restorations are the foremost procedure in modern restorative dentistry as such materials present optimal esthetics and appropriate mechanical properties to replace those dental hard tissues that were lost for different causes (e.g., caries and tooth wear). Bonding to dentin is still an important challenge due to the presence of dentinal tubules as well as the pulpal fluid, which make the use of hydrophilic monomers necessary to accomplish proper resin hybridization (Van Landuyt et al, 2008; Sauro et al, 2009, Van Meerbeek et al, 2020) Such hydrophilic components, if present in high concentration, can decrease the mechanical properties of adhesive resins (Ito et al, 2005), and increase water sorption (Feitosa et al, 2014), permeability (Sauro et al, 2009; Feitosa et al, 2019), and hydrolytic degradation (Ferracane, 2006; Sauro et al, 2019)
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