Author: Daniel H. Ward, DDS

Dental Clinics of North America · February 2001

Philosophers and mathematicians have long been fascinated by the relation­ship between mathematics and nature. The ancient Greek philosopher Pytha­gorus defined a divine or golden proportion, which “explains beauty in nature as it relates to the science of numbers.”4 This proportion was used in ancient Greek architecture to design the Parthenon. Leonardo da Vinci used the golden proportion in his classic drawings of human anatomy. The practical correlations between proportions and beauty have carried forward to the present.


Plastic surgeons have long used the idea of proportions to define desirable facial relationships. The rule of thirds divides the face vertically into three approx­imately equal segments: the superior border of the face is the trichion (ideal hairline), the junction between the upper and middle thirds is the nasion, the junction of the middle and lower third is subnasale, and the inferior border is the menton.8 If the lower third of the face (subnasale to menton) subsequently is subdivided into thirds, the ideal position of the incisal plane is at the junction of the upper and middle thirds.


that the width of the ideal central incisor should be 1/16 the interzygomatic width.3 Another common rule of smile design is that the widths of the anterior six teeth as viewed from the frontal should be in golden proportion to the intercommissural width.6 The rule of thirds and the 1/16 rule were combined in the Trubyte Tooth Indicator (Dentsply International, York, PA), which can be used as a guide in selecting denture teeth.

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One Comment

  1. malika

    thank you ,for sharing information.

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