“Mouth frown arcs” — dental and skeletal characteristics

Drs. Mark E. DeMaria, Donald Rinchuse, Daniel Rinchuse, and Thomas Zullo investigate particular dentofacial characteristics of patients with frown arcs

Abstract

Introduction
The purpose of this study was to investigate whether subjects with “mouth frown arcs” (lips at repose are turned down at the commissures) have any particular dentofacial characteristics as compared with subjects who do not possess “mouth frown arcs” (non-frown arc group, also called the control group).

Method
From a population of approximately 3,200, 94 subjects were selected based upon having mouth frown arcs versus not having mouth frown arcs (control group). Seventy-four subjects possessed frown arcs, and 20 subjects had non-frown arcs. Subjects in the mouth frown arc group were then classified as being mild, moderate, or severe. Various dental and skeletal measurements were performed to determine how many subjects in the frown and non-frown arc groups possessed various dento-skeletal characteristics. Subjects’ Angle’s classifications were evaluated through pretreatment intraoral photos, while the vertical and maxilla-mandible skeletal relationships were determined from cephalometrics (Sassoui and Steiner Analyses). Using SPSS software, Pearson Chi Square Analyses were performed to test whether there was a statistical relationship between the dentofacial characteristics previously described and a mouth frown arc.

Results
There was no statistically significant (P = <0.05) relationship between mouth frown arc and various dentofacial characteristics. However, subjects with mouth frown arcs (of any magnitude) tended (P = 0.087) to have proportionally more skeletal Class IIIs and less skeletal Class IIs then subjects with non-frown arcs.

Conclusions
There was a tendency (not statistically significant at P = >0.05) for subjects with mouth frown arcs to have proportionately more skeletal Class IIIs and less Class IIs than subjects with non-frown arcs.

Introduction

A frown is a unique facial expression that involves the action of many muscles.1-9  The famous naturalist and biologist Charles Darwin previously had described the act of frowning as “the furrowing of the brow which leads to a rise in the upper lip and down turning of the corners of the mouth.”10 It is hypothesized that humans share an “adaptive quality to frowning which allows for social communication or a negative emotional state.”10 This adaption crosses cultural lines and is one of many nonverbal actions that can express how a person is feeling at that particular moment.

The opening sentence in an article posted on Psychology Today reads, “If you frown all the time, it is likely you feel a certain amount of pain, or at least discomfort.”11 A study in 2012, published in the Journal of Psychiatric Research,12 concluded that botox may be a viable treatment for depression by inhibiting the muscles necessary to frown from contracting, again illustrating the universal connection of frowning with sadness. Another study investigating the effect of brow lowering, as seen in a frown, on the perception of laugher in a static photograph versus a dynamic video resulted in participants rating the laughter of those in static photographs as being more malicious, less intense, and less benevolent than in dynamic videos.11    Studies have illustrated that minimal exposure to a frown can influence what one thinks of the frowning individual, even if the exposure is brief. “When shown a 30-second video clip (without audio) of a frowning college professor, students tended to rate the professor poorly on evaluations.”10-12

All of these studies had focused on the frown in the more broad sense of a facial expression, involving more than just the downturning of the mouth. In North America, however, the frown is typically thought of as a purposeful expression dealing solely with the mouth; however, it is recognized that the true definition includes not only features of the mouth, but also the eyebrows and forehead.10 In addition to those who can purposefully create a mouth frown with voluntary contraction of 11 facial muscles (Figure 1), it can be seen as part of the natural aging process with soft tissue sag and the development of marionette lines (Figure 2).10-13,16 “The frown lines make my whole mouth look like a big frown. People say I look unhappy when I just feel normal. I look like a miserably unhappy person, which really puts people off. It’s far from attractive and completely belies what I’m feeling on the inside!”11 That is the plea of a 57-year-old dealing with a mouth frown developed from the natural aging process. Parenthetically, Sarver13 has observed that typically the philtrum position is ideally located 2 mm to 3 mm shorter than the commissure height, but it is highly variable with age. Usually, however, over the patient’s lifetime, the vertical position of the philtrum lengthens at a faster rate than the commissures do, which contributes to flattening of the upper lip.13

Further still, some people do not specifically have to activate the 11 muscles responsible for producing the frown or be elderly, but nonetheless, have a similar expression on their faces even while in natural repose.10-19 The “mouth frown arc” is the curve of the lips forming a down-open curve (Figure 3).5-9  In pop culture, the expression of the mouth frown arc can be seen with digital text as a colon followed by a convex parenthesis, or L.10 It may be due to the natural dental and facial skeletal characteristics that underlie the soft tissue of those with reposed mouth frowns; i.e., “mouth frown arcs.”

This investigation aims to explore whether there are particular dental and facial skeletal characteristics of those with a non-aged (young subjects), “natural/reposed” mouth frown arc (not those purposely frowning or who appear to be frowning due to soft tissue old age changes) (Figure 2), as compared to those in a control group who do not possess this arc. The null hypothesis was that there are no statistically significant differences in the dental and facial skeletal characteristics of subjects with mouth frown arcs and those who do not possess mouth frown arcs.

Method

From a population of approximately 3,200 subjects at Seton Hill University Center for Orthodontics in Greensburg, Pennsylvania, 94 subjects were selected based on having mouth frown arcs versus not having mouth frown arcs (non-frown arc/control group). A subject was determined to have a frown arc if it appeared that the commissures of the lip were below the midpoint of the junction of the philtrum in repose (Figure 4). Seventy-four subjects possessed frown arcs, and 20 subjects had non-frown arcs. The frown arc group was divided into categories of mild (22), moderate (28), and severe (24). To help control certain extrinsic factors, only subjects 25 years and younger were included in this study. Subjects with a loss of the vertical dimension due to attrition, extracted teeth, congenitally missing teeth, pathology, or trauma, were excluded, as well as subjects who had undergone surgical intervention or previous orthodontic treatment.

Subjects were initially screened for frown and non-frown arcs by visual inspection. Final determination was made by mathematical measures. That is, a frown arc ratio was calculated for subjects by measurement of the width of the lips by a horizontal straight line from right commissure to left commissure; depth was determined by a vertical straight line from the philtrum of the lips to a tangent to the width line (Figure 4). The frown arc group was divided into categories of mild, moderate, and severe by inspection of the ratios and looking for natural division separation “breaks” in the data.

Various dental and skeletal measurements were performed to determine how many subjects in the frown (and for each of the three frown arc categories) and non-frown arc groups possessed the various dento-skeletal characteristics. The dental and skeletal classes (categories) were:

Dental

  • Angle’s Classification
    •       Class I
    •       Class II
    •       Class III

Skeletal

  • Anterior-posterior
    •       Class I
    •       Class II
    •       Class III
  • Vertical
    •       Normal
    •       Deep
    •       Open
  • Maxilla-Mandible relationship
    • Maxilla
      • – Normal
      • – Deficient
      • – Excess
    • Mandible
      • – Normal
      • – Deficient
      • – Excess

The skeletal categories were determined by the Sassouni Analysis, which is based upon individual patient proportions and not on average group norms or comparisons to an ideal through the use of facial planes and arcs (Figure 5).14-15 It analyzes true skeletal proportions rather than dentoalveolar (i.e., Points A and B) by using ANS and pogonion, which are skeletal landmarks, whereas other analyses focus on ANB which is a dentoalveolar measure (e.g., SNA-SNB ). The reader can get a better understanding of the Sassouni Analysis  by reading the article by Araujo in the 2015 AJODO as well as the book by Athanasiou.14-15 Using this cephalometric analysis, it was possible to determine subjects anterior-posterior, maxilla-mandible relationship, and examples are presented throughout Figures 5-8. The vertical skeletal component of the study was gleaned from the Steiner analysis, specifically SN-MP (Figure 9). SN-MP is the angle formed by a line connecting sella to nasion and its intersection with a line drawn along the mandibular plane.14

Dental categories were determined by visual inspection of pretreatment intraoral photos. All subjects who were selected had a definitive Angle’s classification. No subject, for instance, had missing or unerupted permanent teeth, which may make Angle’s classification ambiguous.

Statistical analysis

Using SPSS software, Chi-Square Analyses (Pearson Chi-Squares) were performed to test whether there was a statistical relationship (P = /<0.05) between Angle’s dental classifications, anterior-posterior and vertical skeletal classifications, and maxilla and mandible anterior-posterior relation as compared with the various categories of frown arcs in mild, moderate, and severe (based on frown arc ratio), as compared with non-frown arcs (controls). For this study, significance (p value or alpha) was 0.694, and the value for observed power is 0.144. Also, multivariate and univariate ANOVA tests were performed to elucidate relationships between frown arc groups (mild, moderate, severe, control) and the measures of frown arc height, width, and ratio. Pairwise comparisons for the measure “frown arc ratio” were also performed.

Results

The results of this study are reported in Tables 1-6. Frown arc ratios were developed and then separated into four categories; one as non-frown arc (control) and three with different severities. The categories, as mentioned in the Methods, were mild, moderate, and severe for mouth frown arcs; a control group of non-frown arc was also established. Data were listed in a frequency distribution. The basis of group formation was close to equal thirds and based upon “natural breaks.” The frown arc ratios ranged from 0.816-13.86, and the control ratios ranged from -0.82 to -13.44. A natural break occurred between the mouth frown arc ratio values 3.8776 and 4.0169, and 29.7% of the cases were = <3.8776 (M=mild). The next natural break to capture approximately a third of the cases was for mouth frown arc ratios between 7.9412 and 8.5873. 32.4% of the cases had frown arc ratios => 8.5873 (severe), while the remaining 37.8% had mouth frown arc ratios between 4.0169 and 7.9412 (moderate). Multivariate (F = 61.428) and univariate Tests (Height F = 172.749; Width F = 4.477; Ratio) F= 332.849) (P = 0.001) reflected that there were differences among the four frown arc groups (severe, moderate, mild, control) and the three frown arch measures (height, width, ratio). The tests for pairwise comparisons showed that for the measure “frown arc ratio,” all possible comparisons were significantly different from one another (Table 1). That is, severe was greater than mild, moderate, and control. Moderate was greater than mild and control. And mild was greater than control. The results for frown arc height were exactly the same. For frown arc width, the only significant difference was between the moderate and control groups. One might conclude that the major contribution of the frown arc ratio is from frown arc height. The Pearson Chi-Square tests showed no statistically significant relationship between frown-arc and non-frown arc for the dental and skeletal classifications studied. Likewise, there was no significant difference among the frown arc group categories (mild, moderate, severe) for any of the dental and skeletal variables (Tables 2-6).

When looking at the value of the Pearson Chi-Square for each of the five chi-square tests, it is evident that none of them achieve a value that is statistically significant. Essentially, there was no significant relationship between mouth frown arc classification and any, or all, of the five measures used in this study.

There was, however, proportionally more skeletal Class IIIs and less skeletal Class IIs in the mouth frown arc group. This was a trend (P=0.087) and not statistically significant at P=> 0.05 (Table 3B). That is, for the frown arc categories mild, moderate, and severe, there were 10, 18, and 14 subjects, respectively, with skeletal class IIIs, compared with 4 subjects in the non-frown arc (control) group. For the skeletal Class IIs, there were 5, 5, and 5 with mild, moderate, and severe frown arcs, compared with 9 with non-frown arcs (Table 3A).

Discussion

The null hypothesis of no difference (P = <0.05) in the dental and skeletal characteristics between subjects with mouth frown arcs and those without was supported by the finding of this research. However, as noted in the Results, the study found a trend (P = 0.087) for subjects with frown arcs to have proportionately more skeletal Class IIIs and less skeletal Class IIs then subjects with non-frown arcs. Although there is much published on many aspects of lip and smile characteristics, especially related to esthetics, this is the first time (to these authors’ knowledge) that the dentofacial characteristics of mouth frown arc was studied (i.e., described and measured), so there is no literature to compare with.

Although a statistically significant relationship between a frown arc and the underlying dentofacial characteristics was not shown, future research is needed on this topic. If future research shows that there is in fact a relationship between mouth frown arc and various dento-skeletal characteristics, then orthodontists may be able to offer mitigating treatments for mouth frown arc through conventional orthodontic treatment/orthognathic surgery.17-19 It is generally known that the mouth frown arc will typically develop/get worse with age due to natural aging processes (“sagging” of the soft tissues).13,16,17-22  So the question is, does someone who starts with a mouth frown arc have an increased chance for a negative soft tissue response with aging than an individual who does not have a mouth frown arc?1-9, 21-26 In addition to more research that might uncover treatment options for this dentofacial morphology, psychological studies can be undertaken in order to find out what, if any, lasting effects may develop if an individual with a frown arc has to constantly assure others that they are not sad, mad, or angry when they are simply enjoying a moment of silence. Can the impression one displays, through no conscious effort of his/her own, mold them into whom they become as an adult? Are people who are thought of as always being angry or unapproachable, due to no fault of their own, likely to assume that role just because people typically expect that of them — a self-fulfilling prophecy?1-9   Childhood studies of those with a mouth frown arc could look at whether those children are likely to grow up to be bullied, or possibly even the ones who become the bullies.24-26 Those judged and reacted to by society on the way they look and in the way they are reacted upon, those with disfigurements and other dentofacial anomalies, become who they are conditioned to be.22-26 Future studies could also be done with the same methodology, but look at a larger, better categorized sample.

Limitations of this study include it being a descriptive study which does not address the cause-effect or the consequences of having a frown arc. Another possible limitation of this study could be that the dental and the skeletal classes are not equally distributed in nature. For example, Angle found that most individuals possess Class I dental malocclusion, so the finding for the mouth frown arc should account for the fact that certain dental and skeletal characteristics are more probable than others, irrespective of any other variable or action. For instance, Proffit, et al.,17 estimates that approximately 40% of the population is Class I malocclusion, 15% Class II, and only 3% Class III, with the remainder being a combination. In addition, it would have been beneficial if Class III patients with anterior crossbites would have been identified. Furthermore, the results of chi-square analyses must be interpreted with caution when no more than 20% of the cells have expected frequencies less than 5, and this occurred for all analyses, except for that of the mandible. Future studies should have larger samples, especially when so many subcategories are needed.

Conclusions

  • This investigation reported for the first time a description of the “mouth frown arc” and a method for its measurement based on height/width ratios.
  • There was no statistically significant (P = < 0.05) dental and skeletal characteristics of subjects with mouth frown arcs.
  • There was also no relationship among the various degrees of mouth frown arcs (i.e., mild, moderate, severe) and dental and skeletal characteristics.
  • There was, however, a trend (P = 0.087) for subjects with mouth frown arcs to have proportionally more skeletal Class IIIs and less skeletal Class IIs than subjects with non-frown arcs.

Mark DeMaria is a Resident at Seton Hill University Center for Orthodontics in Greensburg, Pennsylvania.

Donald Rinchuse, DMD, MS, MDS, PhD, is in Private Practice in Greensburg Pennsylvania.

Daniel Rinchuse, DDS, MS, MDS, PhD, is Professor and Program Director, Seton Hill University Center for Orthodontics, Greensburg, Pennsylvania.

Thomas Zullo, PhD, is an Adjunct Professor of Biostatistics, Seton Hill University Center for Orthodontics, Greensburg, Pennsylvania.


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