Assessment and Evaluation of Soft Tissue Measurements between Various Mandibular Divergences in the South Indian Population: A Cephalometric Study.

Aim: The aim of this study is to evaluate the association between the mandibular divergent patterns and soft tissue chin (STC) thickness measured at different chin levels in nongrowing patients. Methodology: Pretreatment lateral cephalograms of 400 adult patients were segregated into four groups based on mandibular divergence pattern defined by the mandibular plane to cranial base angle (average 32° ± 5°), Group I with low angle (below 27°), Group II with medium low angle (28°-32°), Group III with medium high angle (33°-36°), and Group IV with high angle (above 37°). STC thickness was measured between Pog-Pog' (pogonion), Gn-Gn' (gnathion), and Me-Me' (menton), thickness and height of the upper and lower lips were also measured. Statistical analysis was done using one-way analysis of variance followed by post hoc Tukey analysis.
Results: A significant difference in the STC thickness at Pog, Gn, and Me was observed among all four groups with hyperdivergent patterns, showing decreased STC thickness than the hypodivergent mandibular pattern. Thickness of the upper and lower lips was greater in hypodivergent mandible, whereas height of the lips was greater in hyperdivergent mandible. Copyright:

INTRODUCTION

Facial soft tissue contains muscles, face, and skin which develop over the underlying skeletal structures.[1] Function and esthetics depends on the balance between the skeletal and soft tissue framework. The most important area that influences esthetics is the morphology and dimension of the mandibular symphysis. It is the most variable and unstable area that influences the diagnosis and treatment planning in growing as well as adult patients. With the paradigm shift toward achieving soft tissue profile, a thorough knowledge of the underlying jaw disproportion, growth pattern, and soft tissue constraints is essential in planning the treatment.[23]

The introduction of cephalometry has aided in the diagnosis of the growth pattern of the individual which can be horizontal, vertical, or average and the correlation between the soft tissue thickness and the growth pattern can also be studied. The most commonly used analytical method to know the growth pattern is the one described by tweed use of the Frankfort-mandibular plane angle to diagnosis and plan the treatment.[45]

Various studies have been conducted to study the influence of growth pattern on soft tissue, but minimal studies have been done to correlate the divergent pattern of mandible and soft tissue thickness.[67] Hence, the aim of this study is to correlate the association of the soft tissue chin (STC) and lip thickness in different divergent mandibular patterns.

METHODOLOGY

Four hundred pretreatment lateral cephalograms of adult patients between 16 and 30 years, with various mandibular divergent patterns, were taken. Patients over the age of 16 years with apparent facial symmetry (clinically determined), all permanent teeth up to the second molars, no previous history of orthodontic treatment, and no previous history of trauma or surgery in the craniofacial region were included in the study, whereas patients with a history of orthodontic intervention and unacceptable radiograph quality were excluded from the study. Samples were classified into four groups: Group I (low angle), Group II (medium low angle), Group III (medium high angle), and Group IV (high angle), with each group comprising 100 pretreatment lateral cephalograms. In each of the four groups, morphology of the mandibular symphysis and STC thickness were associated. A cephalometer with an orbital pointer was used to standardize the Frankfort horizontal plane. STC thickness at Pog-Pog', Gn-Gn', and Me-Me' [Figure 1] and upper and lower lips thickness (LLT) and height were correlated with different divergent groups [Figure 2]. Statistical analysis was done with the results obtained using analysis of variance (ANOVA) and post hoc Tukey analysis.

Figure 1

Soft tissue chin thickness at three different levels

Figure 2

Soft tissue lip measurement -ULT, ULH, LLT, and LLH

RESULTS

GROUP I has the highest value of 11.6, 9.48, and 7.1, soft tissue thickness in Pog-Pog', Gn-Gn', and Me-Me', while GROUP IV has the lowest value of 9.3, 6.5, and 5.3 among the four groups [Table 1 and Graph 1].

Table 1

Mean values for four variables measured in each group of STC

Group	n	Minimum	Maximum	Mean	Std. deviation
Group I
Pog	100	7.30	14.00	11.6670	1.98950
Gn	100	6.67	11.29	9.4850	1.50814
Me	100	7.00	7.50	7.1840	0.21627
Group II
Pog	100	7.20	13.90	11.3717	1.92619
Gn	100	6.34	9.29	8.4010	0.88450
Me	100	6.00	6.32	6.1580	0.11728
Group III
Pog	100	6.50	12.50	10.5200	1.82840
Gn	100	6.30	8.90	7.3330	0.65238
Me	100	6.00	6.98	6.0790	2.04981
Group IV
Pog	100	6.54	10.81	9.3870	1.38244
Gn	100	5.02	7.79	6.5370	0.74504
Me	100	4.27	6.52	5.3010	0.85677

Graph 1

The mean values of four variables in each group of soft tissue chin

Group IV has the greatest mean value of 26.9 and Group I has the lowest mean value of 23.17 for four variables examined in each group of upper lip height (ULH) [Table 2 and Graph 2]. One-way comparison of the four groupings using the ANOVA test for ULH, with test value of 545.518 and P < 0.001, reveals that the difference is statistically significant [Table 3 and Graph 3].

Table 2

Comparison of the four group using one way ANOVA test STC

	Sum of squares	df	Mean square	F	Sig.
Pog
Between Groups	313.733	3	104.578	32.371	0.000
Within Groups	1279.326	396	3.231
Total	1593.059	399
Gn
Between Groups	493.640	3	164.547	163.018	0.000
Within Groups	399.714	396	1.009
Total	893.354	399
Me
Between Groups	179.134	3	59.711	47.805	0.000
Within Groups	494.632	396	1.249
Total	673.766	399

Graph 2

The mean values of upper lip height and lower lip height

Table 3

Mean values for four variables measured in each group of upper LIP height

ULH	n	Minimum	Maximum	Mean	Std. deviation
Group I	100	22.30	23.94	23.1720	0.46111
Group II	100	24.10	26.90	24.8456	0.67676
Group III	100	24.30	27.70	25.7590	0.97324
Group IV	100	26.30	27.60	26.9000	0.43099

Graph 3

The mean values of upper lip thickness and lower lip thickness

GROUP IV has the highest value of 46.29 and GROUP I has the lowest value of 43.06 for lower lip height (LLH). The mean values for four variables tested in each group of LLH between the four groups show that Group IV has the highest value of 46.29 and Group I has the lowest value of 43.06. The difference between the four groups using the one-way ANOVA test for LLH is statistically significant, with test value of 1416.443 and P < 0.001.

Group I has the greatest value of 17.52 and Group IV has the lowest value of 14.90 for four variables tested in each group of upper lip thickness (ULT). Using a one-way comparison, the four groups were compared. With test value of 2165.95 and P < 0.001, the ANOVA test for ULT demonstrates that the difference is statistically significant.

GROUP I has the greatest value of 19.3 and GROUP IV has the lowest value of 16.41 in terms of mean values for four variables examined in each group of LLT. Using a one-way comparison, the four groups were compared. With test value of 151.369 and P of 0.001, the difference in LLT is statistically significant. Multiple analyses of STC in Pog-Pog', ULH, LLH, and ULT, as well as comparisons between groups, reveal a statistically significant difference with P < 0.001.

DISCUSSION

Many hard tissue parameters were evaluated in classic cephalograms, but soft tissue parameters were limited and the shift in the treatment planning to establish soft tissue balance has necessitated the importance of measuring the soft tissue parameters in detail.[89]

The goal of this study was to assess and evaluate the relationship between different mandibular divergence patterns and the soft tissue of the chin and lip. The mean values of all the soft tissue characteristics exhibited a positive connection when descriptive statistics were calculated for all variables. The results demonstrate that there is no statistically significant difference in Pog-Pog' between Group I and Group II, although there is a significant difference in STC at Gn-Gn' and Me-Me'.

At Me and Gn, only Group IV was statistically substantially different from Group I among the four groups. In all variables, there is a highly significant difference between Group I and Group IV (0.000). With increasing facial divergence, the STC thickness appears to adapt to severe hyper divergence, likely through increased stretching of soft tissue in the chin and lip. There was a statistical difference between the groups in terms of upper and lower lips thickness and length.

The groups, however, were judged to be distinct in terms of upper and LLH. Lips were much longer in Group IV, followed by significantly shorter lips in Group III, Group II, and Group I. When the four groups were compared on lip thickness, Group I had the thickest lips, followed by Group II, which had the thinnest lips. As a result of the extreme hyperdivergent mandible in Group IV, the upper and lower lips were thinner.

The findings of this study are similar to those of Burstone, who concluded in the 1950s that average measures were associated with profile excellence and that the components of the face exhibit individual diversity in growth duration, size, and pattern.[10] Blanchette et al. conducted another study that found a substantial link between facial pattern and soft tissue growth, and their findings are similar to those of the current study.[11]

Authors like Foley and Duncan demonstrated an increase in 7 mm of STC from 14 to 20 years of age, while Subtelny did a study to indicate an increase in chin prominence, which was more related to skeletal alterations than soft tissue changes.[1213] Macari and Hanna analyzed and found that the STC thickness differed significantly between hyper- and hypodivergent people with distinct mandibular divergence patterns, and soft tissue growth has a substantial impact on an individual's growth pattern.[14] This study's indicated that all parts of the soft tissue profile do not directly follow the underlying skeletal profile. Some areas were found to diverge from the underlying skeletal structures, while other areas showed a strong tendency to follow skeletal changes directly.[15]

CONCLUSION

According to the results obtained from the study, hyperdivergent mandible has a thinner chin at Gn and Me with decreased upper and LLT and increased lip height, whereas hypodivergent mandibles have thicker upper and lower lips and decreased lip height and more soft tissue lip thickness.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.