Introduction

Quantifying the relative contributions of genetic and environmental influences on morphological variation in dental and facial structures is an important biological problem that continues to attract the interest of anatomists, physical anthropologists, geneticists, and clinicians in medicine and dentistry. Progress in this field has been limited for a number of reasons, including the: (1) complexity of craniofacial growth processes; (2) limited opportunities for experimental investigation in humans; (3) multifactorial mode of inheritance of dental and facial structures; and (4) significant methodological difficulties inherent in accurately describing the form of faces and teeth.

In the study of dentofacial variation, nonmetric, or qualitative, classifications may provide a satisfactory description of variations in shape, but these data cannot always be analyzed appropriately by the more powerful statistical methods. Conversely, metric methods based on combinations of linear and angular variables may provide reasonable representations of size, which are suitable for statistical analysis, but less appropriate for the description of shape variation.

Most genetic studies of dentofacial structures have relied on simple qualitative descriptors or on combinations of linear and angular variables to characterize morphology. These have been analyzed with the classical approaches of quantitative genetics, including twin and family studies, interpopulation comparisons, and the examination of individuals with chromosomal abnormalities.