Statement of the problem: Presently, there are no generally accepted standards for designing smiles using tooth proportion relationships.
Purpose: The purpose of this study was to determine whether North American dentists prefer smile designs created using the recurring esthetic dental (RED) proportion, other mathematically defined tooth proportion relationships, or naturally occurring tooth-to-tooth width proportions previously reported to occur in the North American population.
Materials and methods: Three hundred and one North American dentists were surveyed to determine their preferences of imaged smiles exhibiting different anterior tooth width proportions and the primary proportion influencing their decision. One-sample t-tests were used to compare preferences of constructed smiles. Pearson's Chi-square test was used to assess the independence of the relationship between the subjects' demographic attributes and the factors reported as being instrumental in their decision processes.
Results: Fifty-seven percent of dentists surveyed preferred the smiles with the 70% RED proportion over the smiles with the naturally occurring maxillary anterior tooth width proportions in normal-length teeth. Dentists preferred the smiles of the naturally occurring maxillary tooth proportions (70%) and the 70% RED proportion (75%) over the golden proportion. In smiles with tall teeth, the golden proportion was preferred by 58% of the surveyed dentists over the naturally occurring tooth-to-tooth width proportions as previously defined by Preston. Sixty-two percent of dentists cited the overall balance as the primary factor affecting their selection. Twenty-three percent made their selection based on the size of the maxillary central incisors, whereas 15% used other teeth or factors.
Conclusion: Smiles created using the principles of the RED proportion were preferred by a majority of dentists surveyed. The majority of dentists reported that overall balance was the primary factor affecting their selection.
Clinical significance: The RED proportion may be useful in creating smiles preferred by North American dentists. Seventy-five percent of North American dentists preferred using the RED proportion when designing smiles with normal-length teeth over using the golden proportion, which has been a pseudostandard in esthetic dentistry. Applying the golden proportion universally in smile design should be reconsidered as it was found to be the least pleasing and accepted in this study for normal-length teeth.