Comparison between two finite-element modelling methods for measuring change in craniofacial form.

Finite-element modelling of form change is a useful morphometric technique for measuring differences between anatomical patterns. Two different finite-element algorithms currently are used. One method requires normalized coordinates as input data, while the second method uses globalized coordinates as input data. This study determines whether the two finite-element methods provide equivalent measures of three-dimensional form change when applied to the nasal septa of embryonic mice. Computer models of the nasal septa from mice of 15 and 17 days gestation were generated. Homologous landmarks were identified so that each nasal septum was represented by a tetrahedral finite-element. These elements were subjected to both finite-element modelling methods. Results show that the two algorithms use different interpolation functions and yield dissimilar intermediate results, but generate identical strain matrices as well as equivalent principal extensions, directions of form change, variables of form change, and graphical displays. Therefore, results are directly comparable from studies using either finite-element modelling method.