Biomechanical mapping of porcine dentin and branches with Brillouin confocal VIPA-based microscopy.

Objective: This study aimed to investigate the mechanical properties of porcine dentin using Brillouin confocal microscopy, focusing on its tubules and canaliculi. By mapping the Brillouin shift, we aimed to gain deeper insight into dentin biomechanics and assess how porcine dentin compares to human dentin as a model for dental research.

Design: Porcine molars were prepared by dehydration, precision cutting and polishing. A Brillouin microscope with a dual-VIPA configuration was used for spectral acquisition at 0.3 µm steps. Brillouin frequency shift, full width at half maximum (FWHM) and intensity were analyzed.

Results: Brillouin microscopy identified three distinct zones in porcine dentin: tubules, intertubular regions and branching areas, similar to human dentin. The Brillouin shifts ranged from 17 to 21.5 GHz, with an average around 19 GHz, lower than the 20-25 GHz typically found in human dentin. Mapping revealed branching tubules resembling tree trunks, with intricate branch-like structures in the intertubular regions. Peritubular areas exhibited higher frequency shifts, reaching around 21 GHz, distinguishing them from the more uniform intertubular zones. The dense branch networks surrounded by harder material provided insights into dentin's microstructure. However, challenges in refractive index and density measurements hindered direct conversion of frequency shifts to precise elastic longitudinal modulus values.

Conclusion: This study demonstrated that Brillouin VIPA-based microscopy can effectively map the mechanical properties of porcine dentin. The results show its potential for non-contact, high-resolution mechanical histology in biological tissues, offering promise for studying healthy and diseased mineralized tissues. Further optimization is needed to adapt the technique for human samples, considering differences in optical and mechanical properties.