Comparisons of facial soft tissue characteristics in adult patients with various mandibular divergence patterns (2025)

Background

The alignment of craniofacial structures in three dimensions—transverse, vertical, and sagittal—determines facial esthetics. While skeletal and dental factors influence these outcomes, soft tissue characteristics, especially facial soft tissue (FST) thickness, are increasingly recognized as important. However, few studies have examined the impact of vertical facial divergence on soft tissue variation, particularly in the middle and lower thirds of the face.

Objective

This study aimed to evaluate the association between vertical facial divergence and facial soft tissue characteristics of lower and upper thirds in adult patients.

Methods

A total of 120 non-growing individuals (60 men, 60 women) with an average age of 27.87 years (range: 18–56) seeking orthodontic treatment were included. Participants were stratified into four groups based on mandibular plane inclination to anterior cranial base (MP/SN): Group 1: MP-SN ≤ 27°, group 2: 27°< MP-SN ≤ 32º, group 3: 32°< MP-SN < 37°, and group 4: MP-SN ≥ 37°. Lateral cephalometric radiographs were used to measure FST thickness in the horizontal plane at specific anatomical landmarks, including the base of the forehead, nose, lips, and chin. Additionally, lip length, chin projection, and angular inclinations were assessed. Group comparisons were performed using one-way ANOVA followed by the post-hoc Benferroni test. The strength of the linear relationship between variables was investigated using the Pearson correlation test. Statistical significance was set at p = 0.05.

Results

Significant differences in facial soft tissue characteristics were observed across groups. Hyperdivergent individuals (Group 4) exhibited significantly (p < 0.001) increased total facial height (TFH), lower facial height (LFH), and longer upper and lower lips compared to hypodivergent individuals (Group 1). Group 4 also had thinner soft tissue (p < 0.001) at the chin (Gn-Gn’ and Me-Me’). Shallower mental sulcus and more obtuse chin angle existed in Group 4. Gender differences were noted in chin extension and throat angle. Positive correlations were found between MP/SN and various soft tissue measurements, including lip length and chin projection. No statistically significant differences were observed among the four groups in the upper face neither in linear nor in angular measurements.

Conclusions

Vertical facial divergence significantly influences soft tissue characteristics, particularly in the lower third of the face. Hyperdivergent individuals exhibit increased lip length and reduced chin thickness. Nose length and projection did not differ between the different divergent groups. These findings have clinical implications for orthodontic treatment planning, highlighting the need for individualized approaches based on vertical facial patterns.

Facial esthetics are determined by the harmonious alignment of craniofacial structures across three dimensions: transverse, vertical, and sagittal [1]. Both the facial soft tissue (FST) and the underlying skeletal framework contribute to this balance. However, the development of these anatomical elements may not always occur in concordance [2], potentially impacting the outcome of orthodontic treatments. These outcomes are influenced not only by skeletal and dental factors but also by soft tissue considerations. With the increasing recognition of the significance of soft tissue balance in orthodontic treatment planning, the thickness of facial soft tissue has gained prominence in this field [3].

]Despite extensive research on the relationship between soft tissue and the sagittal position of underlying skeletal structures [4,5,6,7,8,9,10,11], few studies have explored soft tissue variations in different vertical facial patterns. Kurkcuoglu et al. [12] found that vertical growth patterns could influence facial soft tissue thickness, with reduced values often observed in individuals with longer faces. Similarly, vertical growers were noted to have thicker and longer soft tissue features compared to those with shorter facial patterns, possibly as a compensatory mechanism to mask vertical dysplasia [13]. Adult patients with hyperdivergent vertical patterns were shown to have reduced soft tissue thickness in the chin compared to those with normal or hypodivergent patterns. Additionally, individuals with hyperdivergent patterns exhibited significantly smaller soft tissue thickness at the Gnathion and Menton [14]. Halazonetis et al. [15] reported that patients with open bite malocclusion, often associated with increased vertical dimension, had a more obtuse nasolabial angle compared to those with normal overbite. Further research has also shown that vertical facial divergence can affect lip thickness and position, impacting overall facial harmony and balance.[16,17,18,19,20].

]We noticed anatomical variances among other tissues, particularly the lips, in line with a prior study on the relationship between mandibular divergence and soft tissue thickness assessed at various chin levels [14]. Although there has not been much attention paid to this subject in the literature, knowing how the vertical dimension affects the overlying soft tissue is essential for both diagnostic and therapeutic purposes. Thus, clinicians can precisely detect all layers causing malocclusions and unattractive facial features. They can also plan more effectively and deliver the optimal outcomes for their patients.

Orthodontists have primarily focused on examining facial soft tissue characteristics in the lower facial third, such as the lips and chin. However, they have yet to explore potential differences in the middle face, including the base of the forehead and nose bridge, across various vertical facial patterns (e.g., long versus short faces).

The aim of this study was to evaluate the association between vertical facial divergence and facial soft tissue characteristics in the middle and lower thirds of the face among adult subjects.

120 non-growing individuals seeking orthodontic treatment (60 men and 60 women) were included in this investigation, with an average age of 27.87 years (range: 18–56 years) (Table1). Participants in the research had to be older than 18 years of age, have well-defined and recognizable facial features on the lateral cephalogram obtained at repose with no lip tension. Sagittal relationship between the jaws was not factored in as an inclusion criteria. We excluded participants who had undergone orthodontic and/or orthognathic surgery in the past, had a cranio-facial abnormality, or had any form of distortion or ambiguous soft or hard tissue structures on lateral cephalometric radiographs. We received the approval of the Institutional Review Board (IRB) to proceed with this research. The IRB ID is: OTO.AM.02. Consent to participate was deemed unnecessary.

The lateral cephalometric radiographs were taken using the same digital cephalostat (GE, Instrumentar ium, Tuusula, Finland) in a standardized method and in a natural head position. All cephalometric measurements were done using CliniView Dental Imaging software provided by the cephalostat manufacturer. Angular and linear measurements of FST thicknesses, length and position were measured at glabella, nose, upper and lower lips, chin, and throat (Table2; Fig.1).

To determine the intra-observer reliability, a single investigator repeated all angular and linear cephalometric measurements on 20 randomly selected cephalographs.

The sample was stratified into four subgroups (n = 30 each) based on pre-treatment cephalometric mandibular plane (MP) inclination to anterior cranial base (SN)- MP/SN: Group 1- Hypodivergent: MP-SN ≤ 27°; Group 2- Normodivergent with (-1SD): 27°< MP/SN ≤ 32°; Group 3- Normodivergent with (+ 1SD) 32°< MP-SN < 37º; Group 4- Hyperdivergent: MP-SN ≥ 37° (Table1). Subjects were included in the study until a minimum of 30 participants was reached in each group. This sample size ensured the applicability of the central limit theorem, which assumes that the data in each group follows a normal distribution.

Statistical analysis

SPSS software (Chicago, IL), version 28.0 was used for statistical computation. The intraclass correlation coefficient helped determine examiner variability of repeated measurements. Levene’s statistical test was used to test the equality of variances between the groups. Age difference between genders in the total sample was evaluated with the Student’s t-test. Two-way analysis of variance (ANOVA) and post-hoc test (Bonferroni) was used for multiple comparisons (cephalometric angular and linear measurements) among the four groups. The Pearson correlation coefficient gauged the relationship between STF measurements and mandibular divergence angle. Statistical significance was set at P 0.05.

Following data collection, a post-hoc power analysis was conducted on the primary statistically significant dependent variables, which represent key indicators (lower facial height, upper lip length, lower lip length, and chin thickness). The power ranged from 0.960 to 0.991, with a medium effect size (0.456 < effect size < 0.523).

High intraclass correlation coefficients were obtained for the intra examiner repeated measurements (0.993 < r < 0.997). Age was not statistically significantly different for men or women across the four groups or between men and women within each of the four groups (Table1).

Linear measurements

TFH was more increased (131.72 ± 8.03mm) in Group 4 of hyperdivergent mandibles, significantly higher than Groups 1 and 3 (p < 0.001). Group comparisons 1–2 and 1–3 showed no significant differences. Mean values of LFH increased across groups, with Group 4 reaching 75.66 ± 7.17mm and significant differences were observed between Groups 1 and 4 (p < 0.001), as well as 2–4 (p < 0.001) and 3–4 (p < 0.001). The ratio LFH/TFH increased steadily, peaking in Group 4 (57.37 ± 2.93%). Differences were significant across most comparisons (p < 0.001), except for 1–2 and 1–3. (Table3).

Group 4 had the longest upper lip UL (23.31 ± 2.81mm), with significant differences between Groups 1 and 4 (p < 0.001) and 2–4 (p = 0.03). In addition, lower lip was more elongated (21.53 ± 3.43mm) in group 4, significantly differing from Groups 1 and 4 (p < 0.001). A significant increase in UL vermillion height St-Lbs was noted in Group 4 compared to Groups 1 (p = 0.001), 2 and 3 (p = 0.04). Although the LL vermillion height statiscally different when all 4 groups were compared, it was more increased in group 2 and was only significantly different between groups 1 and 2 (p = 0.038).

Mean values of soft tissue chin thickness at gnation (Gn-Gn’) declined progressively, with Group 4 having the lowest (6.89 ± 2.81mm) (Table3). Significant differences were found between Groups 1 and 4 (p < 0.001) and 2–4 (p = 0.04). Similarly, chin thickness at menton (Me-Me’) were the smallest (6.25 ± 1.61mm) in group 4, significantly different from Group 1 (p = 0.002) (Table3).

Angular measurements

No significant differences were observed in the sagittal plane among the four groups. Specifically, the ANB angle did not show statistical significance when compared across the groups (p = 0.767). Additionally, when ANB was categorized into skeletal classifications (Class I, Class II, and Class III), the chi-square test revealed no significant association (p = 0.535).

Group 4 showed the highest nasal tip inclination (TgCol/H) with an angular value (23.37 ± 8.77°), significantly different between Groups 1 and 4 (p = 0.01). A consistent increase was observed in the mental sulcus (LbiB’/TgPog), being the shallowest in group 4 (p = 0.003) with significant differences noted between Groups 1 and 4 (p = 0.002). in addition, group 4 demonstrated a considerable increase in the chin angle (TgPog/TgMe) value (140.6 ± 164.68°), with significant differences between Groups 1 and 4 (p = 0.03).

Opposite to the lower facial measurements, no statistically significant differences were observed among the four groups in the upper face neither in linear nor in angular measurements (Table4).

When stratified based on gender, comparisons between male and females were mostly not significant except for the position of the chin in the sagittal plane where males showed to have the chin more extended (Th_Pog_l; 61.40 ± 29.85mm) compared to females (54.38 ± 14.06mm). Moreover, the throat angle seemed to be more obtuse in females (TgMe_T; 132.92 ± 18.6°) compared to males (120.90 ± 23.15°).

Statistically significant positive correlations were found between MP/SN and measurements: Total facial height, UL length, LL length, soft tissue thickness at B point, tip of nose (inclination and projection), lower lip angulation and chin prominence/projection. Negative statistically significant correlations were observed between MP/SN and chin thickness at the level of Gnathion and Menton.

The investigation into soft tissue characteristics in relation to mandibular divergence is essential for understanding the multifaceted aspects influencing facial esthetics and orthodontic outcomes. This investigation aligns with existing literature emphasizing the importance of considering both skeletal and soft tissue components in orthodontic diagnosis and treatment planning. The observed variations in soft tissue thickness across different vertical divergence patterns underscore the intricate relationship between skeletal and soft tissue structures. The findings corroborate earlier studies highlighting the impact of vertical dimension on facial esthetics [14, 15]. Notably, subjects with hyperdivergent patterns exhibited increased total and lower facial height, which were statistically significant differences among the groups. Subjects with hyperdivergent patterns (Group 4) exhibited increased TFH and LFH compared to those with hypodivergent patterns (Group 1).

While most differences in angular and linear measurements are observed in the lower third of the face, interestingly, no differences were found in the middle and upper face. This phenotypic variation may be due to the later growth of the mandible, as well as the ability of both the maxilla and mandible to adapt to different growth vectors and various environmental and epigenetic factors, more so than the upper facial features.

The study also investigated the length of the upper and lower lips (UL length and LL length) in relation to mandibular divergence. Hyperdivergent patterns (Group 4) were associated with longer upper and lower lips compared to hypodivergent patterns (Group 1). Understanding these variations is crucial for orthodontists aiming to achieve a balanced and harmonious facial profile during treatment. Furthermore, stratification based on the sagittal relationship of the jaws revealed no statistically significant differences in facial anatomical soft tissue thickness among the groups. These findings indicate that sagittal malocclusion does not appear to have a measurable impact on soft tissue thickness across the evaluated anatomical regions.

Chin thickness measurements at Gnathion and Menton revealed significant differences among the groups. Notably, hyperdivergent individuals (Group 1) exhibited thinner, soft tissue at Gnathion and Menton compared to hypodivergent individuals (Group 4). These differences underscore the influence of mandibular divergence on the overall facial profile and harmony [14]. The shallower mental sulcus and more obtuse chin angle in hyperdivergent patterns further contribute to the understanding of soft tissue changes associated with vertical discrepancies.

Patients with skeletal discrepancies may require a combination of orthodontic and orthognathic surgery to achieve balanced occlusion and facial harmony. Special attention should be given to compensating for reduced chin thickness by advancing the bony symphysis further in patients with a hyperdivergent pattern. Additionally, any increase in upper lip length, particularly in individuals with long face syndrome who are benefiting from orthognathic surgery, should be carefully evaluated. In such cases, a lip lift in combination with maxillary impaction may be considered to ensure optimal results.

The observed gender differences in chin position and throat angle suggest potential variations in soft tissue response to mandibular divergence. While males exhibited a more extended chin, females displayed a more obtuse throat angle. These gender-specific variations emphasize the need for tailored treatment approaches considering individual soft tissue responses.

Clinical implications

The outcomes from this investigation have important clinical implications. Orthodontists and maxillofacial surgeons may use this information to tailor treatment plans based on the patient’s vertical pattern, considering the unique soft tissue changes associated with each category. For instance, individuals with hyperdivergent patterns may require attention to lip length and chin projection to achieve facial balance, while those with hypodivergent patterns may need different strategies to address potential lip retrusion.

The study’s limitations include a cross-sectional design and reliance on lateral cephalometric radiographs, which may not capture the full spectrum of soft tissue dynamics. Future research could benefit from incorporating three-dimensional imaging techniques and longitudinal assessments to enhance the understanding of soft tissue changes over time.

Authors and Affiliations

1. Division of Orthodontics and Dentofacial Orthopedics, Department of Dentofacial Medicine, Faculty of Medicine, American University of Beirut- Lebanon, Beirut, Lebanon

   Anthony T. Macari

2. Clinical associate, Division of Orthodontics and Dentofacial Orthopedics, Department of Dentofacial Medicine, Faculty of Medicine, American University of Beirut- Lebanon, Beirut, Lebanon

   Antoine E. Hanna&Michelle El Chekie

3. Department of Dentofacial Medicine, American University of Beirut Medical Center, 6th Floor, P.O.Box 11-0236, Riad El-Solh, Beirut, 1107 2020, Lebanon

   Antoine E. Hanna

Contributions

A.M. conception; design of the work; interpretation of data; have drafted the work and substantively revised the manuscript; have approved the submitted version.A.H. the acquisition, analysis, interpretation of data; substantively revised the manuscript; have approved the submitted version.M.C. the acquisition, analysis; substantively revised the manuscript; have approved the submitted version.

Corresponding author

Correspondence to Antoine E. Hanna.

Ethics approval and consent to participate

We received the approval of the Institutional Review Board (IRB) to proceed with this research. The IRB ID is: OTO.AM.02. Consent to participate was deemed unnecessary. the study adhered to the Declaration of Helsinki.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.

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