A new imaging technique for measuring the surface strains applied to dentine

Objectives: To investigate possible variation in directional material properties of dentine in relationship to tubule orientation using a new optical imaging technique. Method: The optical imaging technique records photometrically a grid pattern formed by using a transmission electron microscope grid as a template on the polished surface of the dentine. The grid pattern is silhouetted onto the sample surface using standard techniques. Compression (c) and diametral compression (dc) tests were undertaken using a servo hydraulic testing machine (MTS model 810) acting on rectangular blocks of dentine with dimensions 1.5 x 1.0 x 1.0 mm (for c) and cylindrical samples with dimensions 2.1 mm in diameter and 1-1.5 mm thick (for de), respectively. The samples were cut using a diamond wheel and miniature lathe and the cut surfaces polished. Images due to a changing load profile were captured and stored as digitised files on a computer for later analysis. The precision is mainly determined by the pixel resolution of the charged-coupled device camera. Results: Preliminary results show the value of elastic modulus of dentine (10.4 +/- 2.9 GPa) to be similar to those previously reported in the literature. Very small localised strains at the surface of a sample can be observed qualitatively and measured quantitatively by reference to the line spacing (similar to 85 mu m). Maximum strength varied with tubule orientation and (compressive/tensile) stress. Conclusion: Very small samples of dentine may be investigated for strain in more than one direction using the imaging technique described. These results may be more appropriate for finding relative directional change rather than obtaining the elastic properties of the dentine. (C) 2000 Elsevier Science Ltd. All rights reserved.