Enamel: From brittle to ductile like tribological response

Abstract 

Objectives

To identify the intrinsic nano-scale wear mechanisms of enamel by comparing it with that of highly brittle glass, and highly ductile copper and silver monocrystals.

Methods

A sharp cube corner indenter tip (20–50nm radius) was used to abrade glass, enamel as well as copper and silver monocrystals. Square abraded areas (5μm×5μm, 10μm×10μm) were generated with loads of 50μN for enamel and 100μN for the remaining materials (2D abrasion). The normal load and displacement data were utilized in a complementary manner to support the comparison. In addition normal and lateral forces were simultaneously measured along 10μm single scratched lines (1D abrasion). Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were also used to characterise the worn areas and debris.

Results

The sharp tip cuts into and ploughs the specimens creating a wedge or ridge of material ahead of itself which eventually detaches, for the ductile materials and at high loads in enamel. For glass and enamel at low loads, the indenter tip ploughs into the material and the removed material is redistributed and pressed back into the abraded area.

Conclusions

The wear behaviour of enamel at the nano-level resembles that obtained with glass at low loads (50μN) and that obtained with metal mono-crystals at high load (100μN). The role of the microstructural heterogeneity in the wear behaviour of enamel is considered in the discussion. The relevance to clinical wear of enamel is also considered.

Keywords: Nanoindenter tip, AFM mode, Abrasion, Enamel, Brittle, Ductile, Enamel rod