Aesthetic Zone ratios is one of many ways to evaluate the appearance of a patients smile, and also to plan for changes that will improve overall aesthetics.
In the last article on using aesthetic zone ratios we looked at comparing the width to the height. This ratio allows us to gather data and diagnose issues like vertical maxillary excess and hypermobile lip that cause this ratio to be larger than normal.
Anterior Segment Ratio
The next of the four ratios compares the width of the total esthetic zone, all of the teeth visible between the commissures at a full smile, and the width of just the anterior segment, between the distal of the canines. The first thing to do is measure the two distances. This can be done in pixels by inserting a line over a full smile photo, or measured with a mm ruler on a printed photograph. Make sure your line is placed at the inside of the soft tissue near the commissures. The relationship to real width is irrelevant as we are going to use a ratio. We then divide the width of the anterior segment by the width of the esthetic zone and multiply by 100.
Arch Width Ratio= (Anterior Segment Width/ Esthetic Zone width) x 100
Smiles that are rated as attractive have an anterior segment width ratio between 59-75%, and the average ratio is 66%. The percentages do not have a gender or age bias which makes relying on these numbers easy. If the ration is too small or too large I start to wonder about arch space issues. Often with patients with a large midline diastema you will see this ratio be larger than 75%. In these cases or cases with inadequate space I want to make sure we use wax-ups and mock-ups to ascertain that we can meet the patients aesthetic demands without the addition of ortho to the treatment plan.