These pages comprise the Electronic Appendix to Evans (2003, unpublished Ph.D. thesis, Monash University, Melbourne).

Abstract
    The relationship between tooth form and function is a long-standing issue in the realm of functional morphology. However, in contrast to many other aspects of functional morphology, where many concepts and methods from engineering have been embraced, functional dental morphology has in many ways lagged behind in the application of these principles. The complexity and poor understanding of engineering applications such as tool function and fracture mechanics, which can be seen as analogous to the function of teeth and the fracture of food, have meant that techniques that allow the prediction of dental function from morphology have been lacking. This thesis seeks to address this deficit by the comprehensive application of several aspects of engineering to the issue of how teeth work, specifically, how the shape of an insectivore’s teeth can be related to function.
    The first major step in understanding dental function was to use engineering principles of machine tools to directly relate shape characteristics of teeth to how they will function. The result is a set of shape parameters, any alteration in which can be used to predict the relative change in the amount of force or energy that would be required for a tooth to function. These functional parameters are: tip sharpness and edge sharpness for cusps; rake, relief and approach angles, food capture and fragment clearance for crests.
    Using these shape parameters as the dimensions of a multidimensional morphospace that includes all possible tooth shapes, only a very limited number will allow proper occlusion of the cusps and crests and have advantageous characteristics for all of the functional parameters listed above. From a search of this morphospace, the very few tooth shapes that do meet these criteria are remarkably similar to several tooth forms or structures that occur in extinct and extant mammals. These shapes can be considered ‘ideal’ in that they are very close to the morphology predicted to be the best functional shape. It appears, then, that these tooth forms are ideal functional shapes and are relatively unconstrained by the development and evolutionary history of mammals.
    These ideal forms were then used to construct virtual three-dimensional model teeth that very closely emulate the shape and function of real tooth forms such as zalambdodont, insectivore premolars, dilambdodont and tribosphenic.
    New fluorescent confocal imaging techniques for three-dimensional reconstruction of small teeth were developed and used to measure the important functional characteristics of microbat teeth. The use of Virtual Reality Modelling Language (VRML) allows the three-dimensional reconstruction of tooth occlusion of mammalian teeth for the first time, representing a significant improvement on the use of occlusal diagrams to understand tooth occlusion. Measurements of the functional parameters from the digital tooth reconstructions demonstrate significant quantitative differences in morphological characters that predict a change in tooth function with wear, which has not been achieved with alternative approaches.
    The concept of ‘hardness’ has long been used to describe the biomechanical properties of many groups of animals. However, due to the lack of a consistent definition, and the multitude of uses to which the term has been put, the use of the term ‘intractability’ has been advocated in this thesis to represent the extent to which the structural strength, stiffness and toughness are increased in a foodstuff. The thickness of the cuticle of an insect was found to be a good measure of the intractability of cuticle. The tremendous advantage of the use of cuticle thickness as a measure of the biomechanical properties of invertebrates means that the properties of a living insectivore can be directly quantified according to the thickness of the cuticle in its faeces. The quantitative measurement of intractability obtained through this technique can be used in correlations with adaptations of the masticatory apparatus, including tooth and skull morphology. This is a major advance on previous measures of the biomechanical properties of insectivore diets, and may represent the best technique of any dietary group in assessing the properties of its diet.
    Comparisons between microbats that specialise on intractable or tractable insects illustrate some functional differences between tooth shape that arguably relate more to the risk of tooth fracture and increased wear rather than differences in the biomechanical properties of the diet. This conclusion challenges current views of insectivore tooth form and function.
    Data gathered on the sharpness of microbat teeth was used to reassess the theoretical and empirical aspects of the scaling of tooth sharpness with body size. For large animals, it appears that the effect of tooth wear has the greatest influence on tooth sharpness, but the influence of development may be more important in smaller mammals.
    Finally, aspects of general tooth morphology are addressed. Mammals of all sizes that consume tough foods will require crests for the forced crack propagation (cutting) of dietary items. It is suggested that cusps represent an adaptation to the concentration of forces, and therefore would be more prevalent in tooth forms of smaller animals with a smaller absolute bite force. This would predict that cusps are not required in larger animals, with larger bite forces, and their tooth forms should be dominated by crests. This is generally borne out in many groups of mammals.

Thesis Manuscript

Table of contents, Abstract and Introduction (pdf)

Full thesis (pdf)

Electronic Appendix

Chapter 2 – The Tooth of Perfection: Functional and Spatial Constraints on Mammalian Tooth Shape

Chapter 3 – Spatial and Functional Modelling of Carnivore and Insectivore Molariform Teeth

Chapter 4 – Confocal Imaging, Visualisation and 3-D Surface Measurement of Small Mammalian Teeth
 

3-D Models

A VRML browser is required to view the .wrl files on these pages. CosmoPlayer v. 2.1 is recommended for PC, and Cortona VRML Client is recommended for Mac. Both of these are plug-ins for Netscape and Internet Explorer. CosmoPlayer is included on this CD-ROM. Full instructions and advice for installing CosmoPlayer for Netscape is given in the instruct.txt file and in the enclosed instruction sheet.

VRML browser plug-ins for Netscape and Internet Explorer can also be downloaded from the web:
 

PC	CosmoPlayer
Mac	Cortona

Instructions for how to use CosmoPlayer.

Full specifications of VRML 97 are given at the Web3D Consortium, http://www.web3d.org/ and http://www.web3d.org/fs_specifications.htm.

Alistair Evans, May 2003