Tooth enamel structure in the koala, Phascolarctos cinereus: some functional interpretations

Area of Science:

• Paleontology
• Zoology
• Materials Science

Background:

• Marsupial enamel structure, specifically Pattern 2 in koalas, is examined for its wear resistance.
• Molar teeth sectorial crests exhibit wear patterns indicating a labial to lingual direction.
• Understanding enamel's structural adaptations can inform biomimetic material design.

Purpose of the Study:

• To determine if Pattern 2 marsupial enamel in koalas is adapted to resist wear on molar teeth sectorial crests.
• To analyze the structural organization of enamel leading and trailing edges.
• To investigate the relationship between enamel rod angulation and wear resistance.

Main Methods:

• Light and scanning electron microscopy were used to examine 96 leading and trailing enamel edges from 12 koala molars.
• Samples were prepared as ground sections, polished/etched surfaces, or polished/etched whole mounts.
• Sputter coating with gold was applied for scanning electron microscopy.

Main Results:

• Leading and trailing enamel edges exhibit differences in thickness and enamel rod orientation.
• Leading edge rods are angled at 25 degrees to the tooth's long axis, crossing the worn surface at 60-70 degrees.
• Trailing edge rods are angled at 5 degrees to the long axis, crossing the worn surface at 90 degrees.
• Inter-rod sheets align with wear striations, forming palisades that resist occlusal forces and abrasion.

Conclusions:

• Koala Pattern 2 enamel on sectorial crests is structurally adapted for wear resistance.
• The specific angles of enamel rods and the alignment of inter-rod substance enhance resistance to occlusal forces and abrasion.
• This adaptation highlights the functional significance of enamel microstructure in herbivorous mammals.