A survey of orthodontists’ perceptions of smile esthetics

Drs. Alys M. Murdoch, Daniel Rinchuse, Thomas Zullo, and Daniel DiBagno explore a survey and literature to define the ideal orthodontic outcome

Abstract

Introduction

The aim of this study was to investigate what orthodontists’ perceive as the important aspects of smile esthetics. It investigated whether orthodontists agree with the current literature involving the smile and smile esthetics. This study attempted to determine what orthodontists find important when treatment planning a case, finishing a case, and generally improving a patient’s smile esthetics.

Methods

An email invitation from the American Association of Orthodontists (AAO) Partners in Education was sent to a random sample of AAO members in the United States and Canada (n = 2,300), requesting participation in a 10-question online survey (SurveyMonkey®) regarding different aspects of smile esthetics. The email blasts provided by the AAO were sent to these participants twice, spaced out approximately 6 weeks, to maximize the return rate. A total of 112 orthodontists participated in the survey.

Results

It was found that there was consistency among orthodontists with considerations for how the face will change over time and that achieving a consonant smile is an important consideration in orthodontic smile esthetics. In addition, according to the survey, most orthodontists (over 70%) agree or strongly agree with the following: Centering the maxillary midline with the facial midline is more important than centering the maxillary and mandibular midlines with each other; midline deviations of less than 2 mm are visually acceptable; canine-protected occlusion is a goal of treatment; and buccal corridors are important in smile esthetic treatment planning. However, when determining if smile esthetics are more important than achieving an Angle’s Class I occlusion, 43.75% agree or strongly agree, and 43.75% remain neutral. Finally, when determining if four premolar extractions cause negative effects on smile esthetics, 76.57% of respondents disagree or strongly disagree. There were no statistically significant differences between male and female respondents. There was a statistically significant difference on two questions. First, orthodontists in practice for 20 years or less thought that smile esthetics were slightly more important than did those in practice for more than 20 years. Second, orthodontists in practice for more than 20 years thought that canine-protected occlusion was slightly more important than those in practice for 20 years or less.

Conclusions

Most (98.20%) orthodontists surveyed account for facial changes and aging when treatment planning children. According to this survey, over 70% of orthodontists believe achieving a consonant smile, midline deviations of less than 2 mm, canine-protected occlusion, buccal corridors, and centering the maxillary midline with the facial midline are all important aspects of smile esthetics. In addition, most (76.57%) orthodontists feel that four premolar extractions will not cause harm to smile esthetics. There were inconsistencies when determining if smile esthetics are more important than achieving an Angle’s Class I occlusion. However, generally speaking, the surveyed orthodontists seem to be adhering to the evidence-based topics of smile esthetics.

Introduction

Orthodontists can have different definitions and understandings of the various aspects of smile esthetics, which they believe are important for orthodontic diagnosis and treatment planning. Kaya, et al., wrote that ideas of facial esthetics are thought of as being subjectively based rather than evidence based.¹ Therefore, this makes it difficult to determine the essential features of the smile that should be considered when treatment planning. Isiksal, et al., state that even though the occlusal relationship is the primary basis of orthodontic treatment, more emphasis is being placed on the paramount dentofacial features necessary for facial esthetics.²

Stedman’s Medical Dictionary defines esthetics as a branch of philosophy that is focused on art and beauty.³ The new paradigm for orthodontic treatment is based on the soft tissue relationships and not necessarily on Angle’s ideal occlusal relationships.⁴ In addition, it has been found that when patients are pursuing orthodontic treatment, they are looking for an improvement of their appearance, hoping to increase their quality of life.⁵ Therefore, are orthodontists including smile esthetics as part of diagnosis and treatment planning? Janson, et al., published a systematic review, including articles of average and high quality. They described a set of certain features related to smile attractiveness, which should be considered when preparing an orthodontic treatment plan.⁶ The list ranges from maxillary gingival display, buccal corridors, smile arc, and maxillary to mandibular midlines, overbite, occlusal plane, maxillary midline in relation to the face, and maxillary gingival height discrepancies.

There is controversy in the literature concerning which features are most important for the ideal smile. Orthodontists continue to debate which aspects of smile esthetics should be focused on to help improve a patient’s smile. Parekh, et al., state that individuals who have excessive buccal corridors and flat smile arcs are shown to be less attractive.⁷ Whereas, in another study, McNamara, et al., showed that buccal corridors, smile arc, and posterior corridors have no correlation with smile esthetics.⁸ In addition, there have been studies that have defined a particular tooth as the key to smile esthetics. According to Parrini, et al., the maxillary incisors followed by the maxillary canine are most critical when determining smile esthetics.⁹ Another controversy that greatly affects the practicing orthodontist is extraction versus non-extraction, and the impact this has on the overall smile appearance. Some studies showed in patients with ideal occlusions or Class I malocclusions, the treatment modality, whether it be extraction or non-extraction, did not cause a difference in smile esthetics.^1,10

With a constant influx of differing information throughout the literature, it is easy to see why there is not an accepted standard of key features that define smile esthetics, and maybe there cannot be for every patient. Sarver has divided facial esthetics into three categories. First, he defines macroesthetics “to include the profile and vertical dimension, in other words the face.”⁵ Next, are mini-esthetics which are “smile attributes such as buccal corridors, smile arc, incisor display, etc.”⁵ Finally, Sarver describes microesthetics as “the tooth and their many attributes such as contacts and connectors, embrasures, gingival shape and contour.”⁵ These may be considered when analyzing facial and smile esthetics.

Overall, the systematic review performed by Janson, et al., for the purpose of our findings, is considered the gold standard of smile esthetics. It is considered the gold standard here due to hierarchy of evidence (systematic review) and due to low risk of bias according to Janson, et al.⁶ They included 20 articles, 13 of which were high quality and 7 which were average quality. In addition, no low-quality studies were included in the systematic review.⁶ Furthermore, using a grading system defined by Pandis, et al., the introduction of Evidence-Based Clinical Orthodontics, the systematic review is given a grade of 2++.11 A grade of a 2++ means that it is a high-quality systematic review of case controls and cohort studies.¹¹ Current research still continues to show that there is no consensus to the key esthetic features, which should be included in the diagnosis and treatment planning of orthodontic patients.

Materials and methods

A 10-question survey, shown in Table 1, was sent to a randomized sample of orthodontists across the U.S. and Canada via two email blasts through the AAO. The survey was composed of eight questions relating to potential important aspects of smile esthetics and two questions that established the survey demographics.

A finalized copy of the 10-question survey was generated using Survey Monkey. The survey was then forwarded to the AAO for approval. The AAO then sent out an email, including a link to the survey, to a random sample of 2,300 of its members. A letter was distributed with the survey asking for participation as well as an agreement to participate.

The survey link was first distributed on June 8, 2017. Then to increase participation, a second email was sent 6 weeks later on July 20, 2017, to the surveyed population. After data collection, the survey instrument was utilized to compile responses into useful figures and charts. In addition, a t-test was used to provide analyses of responses according to the number of years in practice and gender. (All analyses employed IBM SPSS Statistics v. 24 [IBM Corp. Released 2016. IBM SPSS Statistics for Windows, Version 24.0. Armonk, NY: IBM Corp.]).

Results

Of the 2,300 emails sent to a random sample of orthodontists who are members of the AAO, 112 participated in the survey, amounting to a response rate of approximately 4.48%. The survey was completed anonymously. The important findings from the survey are shown in Table 1.

There was consistency among respondents for including facial changes as a part of their esthetic treatment plan. Most respondents (98.20%) said they agree or strongly agree that when treating children, they consider how the face will change and age over time.

The majority of the respondents (90.18%) agree or strongly agree that they believe achieving a consonant smile should be a consideration in orthodontic smile esthetics. However, there is slightly less consistency in determining whether buccal corridors are important to smile esthetics and treatment planning. Of the respondents, 81.98% agree or strongly agree. Furthermore, 83.93% agree or strongly agree that centering the maxillary midline with the facial midline is more important than centering the maxillary and mandibular midlines with each other.

Most of the respondents (72.97%) agree or strongly agree that maxillary and/or mandibular midline deviations of less than 2 millimeters from each other are visually acceptable. However, 13.51% of respondents were neutral, and 13.51% of respondents disagreed or strongly disagreed with this statement. In addition, 70.00% of respondents agreed or strongly agreed that a canine-protected occlusion is a goal of orthodontic treatment. Meanwhile, 17.27% remained neutral on the subject, and 10.00% disagree.

When asked if smile esthetics were more important than achieving an Angle’s Class I occlusion, there were some differing philosophies, with 43.75% who agreed or strongly agreed and 43.75% who remained neutral. Finally, when determining if four premolar extractions cause negative effects on smile esthetics, most respondents (76.57%) disagreed or strongly disagreed.

Of the 112 respondents, 73.64% were male. In addition, the largest group (53.64%) had been in practice for 20-plus years. When the t-test was performed, it was found that there was no statistically significant difference between male and female orthodontists on any of the subjects shown on Table 2. Of the eight questions, only two had a statistically significant difference (p-value <.05) when comparing number of years in practice. It was determined that respondent orthodontists who had practiced for more than 20 years found canine-protected occlusion slightly more important (p-value .003) and smile esthetics slightly less important (p-value .040) than those who were practicing for less than 20 years, shown on Table 3. Significance levels in Tables 2 and 3 reflect tests of equal variances assumed and equal variances not assumed, respectively.

Discussion

The results of this survey demonstrate that the majority of respondents consider smile esthetics important during treatment planning and when providing orthodontic care. Sarver stated that over the past 2 decades, the shift from hard tissue-based treatment is due to the acknowledgment of smile appearance.¹² Of the surveyed orthodontists, 98.20% believe that when treating children, it is important to consider how the face will change and age over time. Dickens, et al., found that incisor display, gingival display, and lip separation will decrease as we age.¹³ In addition, incisor display is perceived as more youthful.¹³ Therefore, it is important during treatment planning to pay close attention to these esthetic features.

According to this study, most orthodontists, 90.18%, believe that achieving a consonant smile is important for smile esthetics. However, a systematic review performed by Janson, et al., determined that buccal corridors and smile arc alone do not seem to affect smile attractiveness.⁶ Similarly, 81.98% felt that buccal corridors are important to smile esthetics and important for orthodontic diagnosis and treatment planning. However, this can depend on how an orthodontist is viewing the smile arc and/or buccal corridors. Kokich, et al., stated that when determining buccal corridors based from digital manipulations, if enough teeth are removed from the lateral sides of the smile, there is a decrease in overall smile esthetics, and the smile may appear unnatural.¹⁴ Accordingly, Janson, et al., determined that in articles where digital manipulation was used, there was a high correlation between smile arc, buccal corridors, and decreased smile esthetics.⁶ However, in articles where the raters were viewing smiling photographs, no correlation was found between smile arc, buccal corridors, and smile esthetics.⁶

When determining if the position and discrepancy of midlines affects the smile esthetics, 83.93% of respondents found that centering the maxillary midline with the facial midline is more important than centering the maxillary and mandibular midlines with each other. In addition, 72.97% of respondents thought that an intraoral midline discrepancy of less than 2 millimeters is visually acceptable. Johnston, et al., found that as the maxillary midline deviated farther from the facial midline, attractiveness was affected negatively.¹⁵ It has also been stated that a maxillary to facial midline discrepancy of 2 mm can, in fact, be considered normal.^{16, 17} Yet, per Pinho, et al., a midline discrepancy of more than 1 mm is visually unacceptable.¹⁸ Conversely, three additional studies found that deviations of up to 2 mm are acceptable.^19,15,17

When asked if four premolar extractions had negative effects on smile esthetics, 76.57% of the surveyed orthodontists disagreed or strongly disagreed. This follows closely to numerous studies, which have concluded that four premolar extractions do not affect smile esthetics. Meyer, et al., stated that there were no perceived attractiveness differences for extraction and non-extraction groups.20 In addition, Rushing, et al., stated that orthodontists and general dentists were unable to determine which facial profiles belonged to those with or without extractions.²¹ As well, 70% of the respondents believe that canine-protected occlusion is a goal of orthodontic treatment. Rinchuse and Sassouni, found that canine protected occlusion should not be the gold standard or a goal of orthodontic treatment. They found that 97% of the treated and 95% of the untreated subjects in their study, who were judged to have “ideal” static occlusion, had nonworking (balancing) side occlusal contacts.²²

There were inconsistencies in agreement when determining if smile esthetics are more important than achieving an Angle’s Class I occlusion. Less than half (43.75%) of respondents said that they remained neutral on the topic. In addition, 43.75% agreed or strongly agreed that smile esthetics are more important than a Class I occlusion. Therefore, these responses may show that this is an area of smile esthetics that requires further research. A study performed by Schlosser, et al., looked at the anterior-posterior position of the maxillary incisors and determined which was the most esthetically pleasing.²³ The least desirable photograph was when the maxillary teeth were retracted 4 mm, which suggested that most orthodontists and laypersons preferred normally protrusive to advanced maxillary teeth but not retracted maxillary anterior teeth.²³ There were a few studies that evaluated the importance of smile esthetics when compared with an Angle’s Class I occlusion. More research is needed to determine if orthodontists prefer to finish cases Angle’s Class I while compromising smile esthetics or if smile esthetics should be the focal point of diagnosis and treatment planning.

There were two questions that demonstrated a statistically significant difference when analyzing years in practice. These questions were canine-protected occlusion is a goal of orthodontic treatment, and smile esthetics are more important than achieving a Class I occlusion. The orthodontists who have been practicing for more than 20 years found slightly more importance in canine-protected occlusion and gave slightly less importance to smile esthetics than those who have been practicing for less than 20 years. This may demonstrate how orthodontics is changing towards the soft tissue paradigm. With regard to the soft tissue paradigm, Proffit, et al., stated, “Both the goals and limitations of modern orthodontics and orthognathic treatment are determined by the soft tissues of the face, not by the teeth and bones.”⁴ In addition, the authors go on to state that we are moving away from the Angle paradigm that was commonly believed in the 20th century when treatment goals were based on occlusion classifications.⁴ There were no statistically significant differences in male or female respondents.

When comparing the outcomes of this study to the results of the systematic review published by Janson, et al., it was found that the surveyed orthodontists (>70%) responses are consistent with the literature demonstrated in the systematic review. Janson, et al., were in agreement that there is no effect on smile esthetics from four premolar extractions, that buccal corridors do not effect smile esthetics, and that a dental midline deviation of 2.2 mm is determined to be clinically acceptable.6 This matches the results of the surveyed orthodontists.

The goal of this survey was to determine orthodontists’ perceptions of smile esthetics and whether orthodontists agree with the current literature involving the smile and smile esthetics. Finally, when discussing the topic of smile esthetics and trying to determine a gold standard, it is important to note that each patient should still be treated on an individual basis.

Conclusions

There have been numerous definitions of what defines the ideal orthodontic outcome. The inconsistency among different schools of thought seems to make the topic of smile esthetics a continuous debate. The purpose of this study was to survey orthodontists throughout the U.S. and Canada to assess their thoughts and beliefs of smile esthetics, their importance in our profession, and their relevance to the current evidence-based literature.

The respondents in this survey demonstrated:

• The majority of orthodontists (98.20%) are taking facial changes and aging into account when treatment planning children.
• Most orthodontists (90.18%) believe that achieving a consonant smile is a consideration of smile esthetics.
• The majority of orthodontists (76.57%) feel that four premolar extractions do not cause negative effects to smile esthetics.
• The most debatable topic is whether smile esthetics are more important than an Angle’s Class I occlusion.
• Most orthodontists (72.97%) feel that a midline deviation of less than 2 mm is visually acceptable and does not harm smile esthetics.
• There was no significant difference in responses from male or female orthodontists.
• Orthodontists in practice for more than 20 years found canine-protected occlusion slightly more important and smile esthetics slightly less important than those in practice for less than 20 years.

Acknowledgments

The authors of this article extend a special thank you to the surveyed members of the AAO who participated in this research topic.