Measure of the hygroscopic expansion of human dentin

TL;DR

This study quantifies how human dentin expands with humidity changes, showing that hygroscopic expansion could impact the longevity of dental restorations despite minimal effects on elastic properties.

Contribution

It provides the first precise measurement of dentin's hygroscopic expansion coefficient and compares it to thermal expansion, highlighting its potential clinical significance.

Findings

Dentin expands by about 0.006% per %RH increase.

Elastic properties like Young's modulus are unaffected by humidity.

Hygroscopic expansion exceeds thermal expansion during dental procedures.

Abstract

Background: Direct dental restoration implies a drying of the dentin substrate. This drying may induce significant strain in the dentin, affecting the bonding efficiency of the restoration. Objective: We measure the dilatation of dentine under changes of relative humidity as well as the impact of humidity on dentin elastic properties. This investigates the role of relative humidity variation during dental surgery on restoration lifetime. Methods: We have coupled an environmental chamber to control both temperature and humidity on the sample, with an optical microscope to measure precisely the strain on the sample surface, after a quantification of the measurement noise. This set-up is used on carefully prepared samples placed on a compression device to measure the elastic parameters. Results: Dentin dilates when the relative humidity increases, with a coefficient of hygroscopic expansion of typically 6.10-3 %.(%RH)-1. This dilatation occurs in about ten minutes. Young modulus and Poisson's ratio are not modified by the variation of relative humidity. Conclusions: Hygroscopic expansion is an order of magnitude larger than thermal expansion during dental surgery: around 0.3% with respect to 0.03%. These levels are low with respect to dental rupture, but may induce a significant decrease of the life-expectancy of a restoration.