Conversion degree of composites polymerized throughout glass-fibre post: micro-Raman analysis

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Objective: The purpose of this study was to evaluate the degree of conversion (DC) of composite materials cured throughout glass-fibre post, comparing different curing methods at increasing depths. Methods: Three different dual–cure composite cements were employed to lute forty-five glass-fibre posts in a custom canal. Tested materials, chosen in transparent shade, were Calibra (Dentsply), Multilink Automix and Variolink II (Ivoclar – Vivadent). The same halogen lamp (Swiss Master Light, EMS) was employed with different programs (400 mW/cm2 for 120 seconds; 800 mW/cm2 for 60 seconds; 1200 mW/cm2 for 40 s), providing a constant amount of energy (48J). Three groups (n=15) of samples, split by material, were analyzed with MicroRaman Spectrometer Dilor HR Labram at 0° and 180° at the increasing depths of 1mm – 3mm – 5mm – 7 mm starting from the most coronal portion of the post covered in cement. The data collected were statistically analyzed by ANOVA and Student – Newman – Keuls tests (p<0,005) DC was firstly considered for each material at different depths, then as a function of the curing modality. Results: Conversion results do not change sensibly with the increase of the depth: all the tested materials showed average percentages of conversion close to 68%. (Tab. 1) Conclusion: A dual – cure material has to be used in post luting, since the self – curing component ensures an adequate monomer conversion at high depths. Anyway, a unique guideline on time / power of curing and cement cannot be suggested. The features of each luting material are exalted from different curing conditions that should be calibrated.