Alistair R. Evans
School of Biological Sciences, Monash University, Victoria 3800,
Australia
This page contains the three-dimensional models of tool forms constructed in Chapter 3 of Evans (2003).
Abstract
The interaction between the two main competing geometric determinants
of teeth (the geometry of function and the geometry of occlusion) were
investigated through the construction of three-dimensional spatial models
of several mammalian tooth forms (carnassial, insectivore premolar, zalambdodont,
dilambdodont and tribosphenic). These models aim to emulate the shape and
function of mammalian teeth. The geometric principles of occlusion relating
to single- and double-crested teeth are reviewed. Function was considered
using engineering principles that relate tooth shape to function. Substantial
similarity between the models and mammalian teeth were achieved. Differences
between the two indicate the influence of tooth strength, geometric relations
between upper and lower teeth (including the presence of the protocone)
and wear on tooth morphology. The concept of ‘autocclusion’ is expanded
to include any morphological features that ensure proper alignment of teeth
on the same tooth and other teeth in the tooth row. It is concluded that
the tooth forms examined are auto-aligning, and do not require additional
morphological guides for correct alignment. The model of therian molars
constructed by Crompton and Sita-Lumsden (1970; Nature 227:
197-199) is reconstructed in three-dimensional space to show that their
hypothesis of crest geometry is erroneous, and that their model is a special
case for a more general class of models.
3-D Models
A VRML browser is required to view the .wrl files on this page. VRML browser plug-ins for Netscape and Internet Explorer: PC (CosmoPlayer); Mac (Cortona).
Instructions for how to use CosmoPlayer.
The following conventions are used in the models on this page:
Lower tool: yellow
Upper tool: blue
Lower tool moves upwards to upper tool following
the occlusal vector (red arrow), and upper tool remains stationary.
Occlusal Geometrical Principles
Single-bladed models
| Simple single-bladed models used as starting points for modelling mammalian teeth, illustrating occlusal geometrical principles. a) symmetrical with vertical movement. Full page |
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| b) symmetrical with latero-vertical movement. Full page |
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| c) asymmetrical with latero-vertical movement. Full page |
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Alistair Evans,
May 2003