Tooth Wear Studied via Single-Particle Interaction with an Enamel Surface
Objectives: The aims were to establish the pattern of microscopic marks made on dental enamel by natural particles.
Methods: A longitudinal section of an orangutan (Pongo pygmaeus) molar was set in resin and polished. Quartz grit particles and silica phytoliths (extracted from Ampelodesmos mauritanicus leaf tissue), <100 μm in size and of known mechanical properties, were mounted on a flat-ended titanium probe. This probe was placed in a nanoindenter (Hysitron Ubi1) to permit ‘scratching' of the molar enamel surface. Fixed vertical forces of between 0.6-1.8 mN were employed for 10-15 μm lateral displacements, while lateral forces were monitored. The enamel surface was then examined by AFM (Agilent 5500) in tapping mode.
Results: Four tests were made with each particle type. Contacts produced marks of differing shapes. Those produced by phytoliths were U-shaped in cross-section, while grit particles formed sharper, more V-shaped, marks associated with enamel chipping. Lateral forces were 30-80% of vertical forces.
Conclusions: The shape of marks reflects the relative hardness of the materials. Quartz is sufficiently hard enough to make rigid plastic contacts with enamel, the contact reflecting the geometry of the quartz particle. In contrast, a phytolith and enamel mutually deformed to produce a smooth impression on the enamel without tissue loss. It can be concluded that phytoliths are not wear agents, but grit particles are. Very low forces may be involved with variable frictional contributions.
Acknowledgements: This study was supported by General Facilities Project GE01/07 from Kuwait University.