Coherences between micro-mechanical properties and degree of cure

Objectives: to evaluate the coherence between micro-mechanical properties and degree of cure on a nano-composite at clinical relevant depth.

Methods: An methacrylate based nano-hybrid composite (Filtek Supreme XT, 3M ESPE, A3-Dentin, LOT: 5AP) was polymerised in a mould 2mm high for 5, 10, 20 and 40 seconds with an LED curing unit (Freelight2, 3M ESPE, 1241 mW/cm²). The mechanical properties were determined at micro scale (HV=harness, E=modulus of elasticity, Cr=creep and We/Wtot=elastic/plastic deformation) after storing the samples for 24 hours in distilled water at 37 °C. Degree of cure (DC) as function of curing time was determined in real time during the first 10 minutes after photo-initiation, as well as 24h after storage in distilled water at 37°C (FTIR-Spectrometer with an attenuated total reflectance accessory, Nexus, Thermo Nicolet, Madison, USA). All properties were measured at 2mm depth, at the bottom of the samples.

Results: Data were analyzed by ANOVA. Tukey HSD multiple comparisons were used to identify statistical homogeneous subsets as indicated by superscript letters (a = 0.05). A general linear model of variance and eta-squared statistic was performed to determine the influence of curing time on the measured parameter.

Conclusion: As showed by partial eta squared statistic, the curing time is going to have a greater effect on the modulus of elasticity (0.997), closely followed by HV (0.988), Cr (-0.974), n (0.976) and DC (24h= 0.804; 10min=0.902). The Pearson correlation between the parameters was also very high, varying between 0.85 and 0.91.