Date of Graduation


Document Type


Degree Type



School of Dentistry



Committee Chair

Chris Martin

Committee Member

Peter Ngan

Committee Member

Susan Morgan


Background and Objectives: More so than ever, the public is becoming exceedingly aware of esthetics, and will evaluate their treatment outcome based upon the improvement to their smile and overall enhancement of their facial appearance. Smile arc is considered to be a key component of facial esthetics. Literature has demonstrated that orthodontic treatment mechanics utilizing traditional brackets and wires can cause flattening of the smile arc and that smiles with flatter arcs are judged to be less attractive. The aim of this study was to determine whether clear aligner therapy can help to preserve or improve the smile arc when compared to traditional bracket orthodontics.

Experimental Design and Methods: A sample of 98 subjects that had completed comprehensive orthodontic treatment (50 treated using clear aligners, 48 treated using traditional orthodontic brackets) and had existing pre and post-treatment posed smiling photographs, were selected. 15 orthodontic experts (8 residents and 7 WVU faculty orthodontists) were asked to view a presentation of all the pre and post-treatment smiling photos and to evaluate whether orthodontic treatment had: a) improved the smile arc, b) maintained or had no clinically significant effect on the smile arc, or c) flattened the smile arc. Data was assessed to determine whether there was a difference in orthodontic treatment outcome, specifically smile arc, using the aforementioned treatment modalities. The data was analyzed using chi squared analysis, a generalized linear mixed model analysis, as well as probability testing.

Results: The results of analyses for 12 out of 15 raters demonstrated that there was a statistically significant association between treatment modality and smile arc evaluation. When all raters were considered collectively, they evaluated 17.3% of clear aligner treated subjects to have flattened smile arcs compared to 49.7% of bracket treated subjects. (p

Conclusions: There is a significant effect of orthodontic treatment modality on smile arc outcome evaluation by orthodontic experts. Orthodontic expert raters evaluated a significantly lower percentage of clear aligner treated subjects to have flattened smile arcs compared to bracket treated subjects and a significantly higher percentage of clear aligner subjects to have improved smile arcs compared to bracket treated subjects. Patients treated with clear aligners have a higher probability of being evaluated to have improved or maintained smile arcs compared to those treated with brackets.