Measuring Shrinkage in the Root Canal Using Holographic Interferometry

Objectives: Objective of this study was to introduce holographic interpherometry as a new method for detecting and measuring polymerization stress and shrinkage created as a result of cementing esthetic intracanal posts with adhesive dual curing cement. Methods: Holographic interpherometry is a double exposition method based on recording two holograms on the same photo plate. Position and distribution of interference fringes point to position and amplitude of the deformation created between the two expositions. Each of the 13 premolars was prepared for post placement and fixed in the holder of the interpherometric set. After fixation, each sample was etched, adhesive was applied (DSC Excite), polymerized and FRC Postec composite post was placed with Variolink II dual cure cement(all Ivoclar, Vivadent Schaan Liechtenstein). First hologram was recorded. In the next phase the sample was cured using ESC mode of the Astralis 10 polymerization device (Ivoclar, Vivadent Schaan Liechtenstein) and second hologram was recorded. Photo plate was developed and resulting hologram or interpherogram registered with CCD camera and transferred into 8 bit two dimensional information in the form of light and dark stripes or interpherence fringes. Results: Visible interpherence fringes at the root surface prove the existence of the polymerization stress and shrinkage in the root canal during cementation of the esthetic intracanal posts with dual curing adhesive cements. Conclusion: Holographic interpherometry enables determining the exact size, density and location of the deformation in the root canal and based on that information performance of further quantitative and qualitative analysis.