engleski

Measuring Composite Polymerization Contraction using Digital Laser Interferometry

Objectives: Digital laser interferometry (DLI) is based on recording interference patterns using an optoelectronic detector (CCD camera) and numerical processing of the recorded information using a computer. This study measured polymerization shrinkage using DLI. Methods: Tetric Ceram composite (Vivadent) was polymerized 40 sec with different curing modes of Elipar Trilight (ESPE), Astralis 7 (Vivadent) and Lux-o-Max unit (Akeda Dental). Ten measurements for each illumination mode were made. The experimental device was designed to allow the photopolymerization of samples (0.65 mm thick) from one side (curing light direction) and the simultaneous measuring of the thickness variation of samples using DLI from the other side (laser light direction). The micrometer with precise reading marks enables the manual compensation of the displacement of the upper surface of the sample. It is used at the end of each measurement to find the final shrinkage. The interference patterns recorded on the computer monitor consistied of concentric fringes, whereas at start the central fringe is located in the middle of the frame. During polymerization the fringe pattern was shifting along left-fighthand direction and the frames were acqired at frequency of 1 frame per second. The analog signal captured by the CCD camera was converted to 8-bit two-dimensional data from which linear contraction was calculated. Results: The highest schrinkage (1.11%± 0.95) was observed with standard mode of Elipar Trilight (intensity of 800 mW/cm2), while the lowest (0.66%± 0.14) with Lux-o-Max unit (50 mW/cm2 first 10 sec, then 150 mW/cm2next 30 sec). Illumination mode that causes largest shrinkage exhibits the largest initial expansion. Futhermore, the modes with low final shrinkage exhibit a very small initial expansion. Conclusion: DLI enables two types of quantitative measurements providing data for the thickness variations of samples continiously during each second of illumination and the total linear shrinkage.

polymerization shrinkage; composite resins; digital laser interferometry

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