Factors associated with the morphology of the mandibular symphysis and soft tissue chin

EVANGELISTA, Karine; SILVA, Maria Alves Garcia Santos; NORMANDO, David; VALLADARES-NETO, José

doi:10.1590/2177-6709.26.4.e2119347.oar

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ORIGINAL ARTICLE • Dental Press J. Orthod. 26 (04) • 2021 • https://doi.org/10.1590/2177-6709.26.4.e2119347.oar copy

Factors associated with the morphology of the mandibular symphysis and soft tissue chin

Authorship SCIMAGO INSTITUTIONS RANKINGS

ABSTRACT

Objectives:

This study aimed to (I) assess the morphology of the symphysis and soft tissue chin associated with sex, age and sagittal/vertical skeletal patterns, and (II) identify the individual and combined contributions of these variables to different portions of the symphysis.

Methods:

This cross-sectional study included 195 lateral cephalometric radiographs from untreated adults. Alveolar, basal, and soft tissue of the symphysis were measured by an X/Y cranial base coordinate system, and divided in accordance to four predictor variables: sex, age, and sagittal/vertical skeletal patterns. Parametric tests were conducted for comparison and correlation purposes, while multiple regression analysis was performed to explore combined interactions.

Results:

Alveolar inclination is related to sagittal and vertical patterns, and both explained 71.4% of the variations. Alveolar thickness is weakly predicted and poorly influenced by age. Symphysis height was 10% higher in males, and associated with a vertical skeletal pattern and sex, and both explained 43.6% of variations. Basal symphyseal shows an individual thickness, is larger in males, and vertically short-positioned with age. Soft tissue chin is not necessarily related to the size of the underling skeletal pattern, and enlarges with age, even in adulthood.

Conclusions:

The symphysis and surrounding tissues are influenced by sex, age, and sagittal and vertical patterns, acting differently on the alveolar, basal and soft tissue portions. Sagittal and vertical skeletal patterns are the strongest association on alveolar symphysis inclination, whereas sex and age acts on the vertical symphysis position and soft tissues thickness.

Keywords:
Chin; Symphysis; Morphology; Adult; Genioplasty

		Horizontal pattern				Vertical pattern				Age
		Class I	Class II	Class III	n	Low MP-angle	Medium MP-angle	High MP-angle	n	< 25	25,0 - 34,9	≥ 35	n
n		60	64	71	195	66	62	67	195	89	49	57	195
Sex (frequency)	Male	30	30	40	100	37	31	32	100	53	20	25	98
Sex (frequency)	Female	30	34	31	95	29	31	35	95	36	29	32	97
Age (years)	Mean (SD)	24.0 (6.2)	3.2 (9.1)	30.7 (11.1)		28.8 (10.4)	29.1 (9.1)	28.7 (9.4)		20.6 (2.5)	28.8 (2.5)	41.3 (6.1)
Age (years)	Min./ Max.	16.4/ 42.7	16.0/ 55.0	16.0/ 63.0		16.0/ 63.0	16.0/ 53.0	16.4/ 55.0		16.0/ 24.0	25.0/ 34.0	35.0/ 63.0
MP- angle	Mean (SD)	30.0 (5.8)	31.5 (7.6)	30.0 (5.6)		23.7 (3.1)	30.2 (1.7)	37.5 (3.1)		29.9 (6.1)	31.1 (5.4)	30.7 (7.3)
MP- angle	Min/ Max	16.0/ 43.5	14.0/ 46.0	17.0/ 42.0		14.0/ 28.0	28.0/ 33.0	34.0/ 46.0		14.0/ 46.0	17.0/ 42.0	16.0/ 44.5
ANB (angle)	Mean (SD)	2.3 (1.2)	6.8 (1.6)	-3.3 (2.3)		-0.9 (4.7)	1.7 (4.6)	2.6 (4.4)		1.5 (4.2)	2.3 (4.7)	1.5 (5.11)
ANB (angle)	Min/ Max	0.0/ 4.0	4.5/ 12.0	-11.0/ -0.5		-11.0/ 9.0	-6.0/ 12.0	-8.0/ 9.0		-11.0/ 10.0	-6.0/ 12.0	-8.0/ 10.0

Variable	Identification	Type	Definition
Alveolar symphysis
Inclination	IMPA	Angular (degrees)	Angulation between the long axis of mandibular incisor (L1-AL1) and the mandibular plane (MP).
Thickness	B-B’’	Linear (mm)	Linear distance between points B and B’’.
Height	I1-Me	Linear (mm)	Linear distance between points I1 and Me, representing the alveolar and basal heights, and including the mandibular incisor.
Basal symphysis
Inclination	AL1Me.MP	Angular (degrees)	Angulation between the height of basal symphysis (AL1-Me) and the mandibular plane (MP).
Thickness	Pog-Pog’’	Linear (mm)	Linear distance between points Pog and Pog’’.
Horizontal position	V-Gn	Linear (mm)	Minor linear distance between line V and point Gn, representing the sagittal position of the symphysis on the face.
Vertical position	H-Gn	Linear (mm)	Minor linear distance between line H and point Gn, representing the vertical position of the symphysis on the face.
Soft tissue chin
Projection in relation to Glabella	G’perp-Pog’	Linear (mm)	Minor linear distance between line G’perp and point Pog’, representing the sagittal projection of the chin.
Thickness (Pog)	Pog-Pog’	Linear (mm)	Minor linear distance between points Pog and Pog’, representing the anterior thickness of the chin soft tissue.
Thickness (Gn)	Gn-Gn’	Linear (mm)	Minor linear distance between points Gn and Gn’, representing the more anteroinferior thickness of the chin soft tissue.
Thickness (Me)	Me-Me’	Linear (mm)	Minor linear distance between points Me and Me’, representing the inferior thickness of the chin soft tissue.

	Sagittal pattern (n=195)			Vertical pattern (n=195)			Age (years) (n=193)			Sex (n=195)
	Class I (n=60)	Class II (n=64)	Class III (n=71)	Low MP (n=66)	Medium MP (n=62)	High MP (n=67)	>25 (n=89)	25-34,9 (n=49)	≥35 (n=50)	Male (n=100)	Female (n=95)	P- value
Alveolar symphysis
IMPA (degrees)	95.0 (6.4)^A	103.9 (8.9)^B	83.8 (7.6)^C	97.0 (12.0)^A	94.3 (11.8)^B	90.0 (9.4)^C	95.8 (11.07)^A	93.4 (12.7) ^A	92.4 (11.6) ^A	94.04 (11.5)	93.7 (11.3)	0.849
B-B” (mm)	6.9 (1.0)^A	7.1 (1.7)^A	5.9 (1.2)^B	7.2 (1.5)^A	6.6 (1.4)^B	5.9 (0.9)^C	6.7 (1.4)^A	6.7 (1.4)^A	6.2 (1.4)^A	6.8 (1.5)	6.4 (1.2)	0.219
I1-Me (mm)	41.8 (3.2)^A	42.8 (4.2)^A	42.1 (3.8)^A	40.7 (3.1)^A	42.1 (3.6)^B	44.0 (3.7)^C	41.6 (4.0)^A	42.1 (3.4)^A	42.1 (3.9)^A	44.1 (3.5)	40.3 (3.0)	< 0.001
Basal symphysis
A1Me.MP (degrees)	71.3 (4.8)^A	74.8 (8.8)^B	69.7 (8.2)^A	72.9 (7.1)^A	72.6 (9.2)^A	70.1 (6.9)^A	72.3 (8.1)^A	71.4 (7.8)^A	72.2 (8.6)^A	71.2 (8.0)	72.5 (7.6)	0.178
Pog-Pog’’ (mm)	14.1 (2.0)^A	14.8 (2.2)^A	14.3 (1.8)^A	14.7 (2.2)^A	14.6 (2.1)^A	14.0 (1.2)^A	14.4 (1.9)^A	14.6 (1.8)^A	14.3 (2.2)^A	14.9 (1.9)	13.9 (2.0)	< 0.001
V-Gn (mm)	62.7 (8.1)^A	56.4 (9.4)^B	72.3 (9.2)^C	71.5 (9.0)^A	64.1 (9.2)^B	56.9 (10.1)^C	63.7 (9.3)^A	63.9 (11.8)^A	65.0 (12.2)^A	67.2 (10.5)	61.0 (11.0)	< 0.001
H-Gn (mm)	108.1 (8.2)^A	105.5 (14.1)^A	108.5 (9.5)^A	102.4 (7.8)^A	108.4 (14.0)^B	111.4 (8.4)^C	108.4 (15.5)^A	107.0 (8.2)^AB	105.1 (9.7)^B	111.4 (12.2)	103.1 (7.3)	< 0.001
Soft tissue chin
G’perp-Pog’ (mm)	-3.2 (7.1)^A	-8.6 (7.8)^B	7.1 (7.5)^C	4.4 (9.3)^A	-0.9 (9.1)^B	-7.0 (8.1)^C	-1.5 (9.1)^A	-1.1 (10.8)^A	0.2 (10.7)^A	-0.8 (9.8)	-1.6 (10.3)	0.480
Pog-Pog’ (mm)	11.8 (2.1)^A	12.8 (2.5)^B	12.4 (2.5)^AB	12.5 (2.8)^A	12.3 (2.4)^A	12.3 (2.00)^A	12.0 (2.3)^A	11.8 (2.4)^AB	13.3 (2.3)^B	12.9 (2.6)	11.8 (2.0)	0.002
Gn-Gn’ (mm)	9.6 (2.4)^A	10.5 (2.8)^A	10.6 (2.9)^A	11.0 (3.0)^A	10.4 (2.6)^A	9.4 (2.4)^B	8.9 (2.3)^A	9.6 (2.0)^A	11.6 (2.8)^B	10.8 (2.8)	9.7 (2.5)	0.006
Me-Me’ (mm)	8.3 (2.0)^A	8.4 (2.5)^A	9.0 (2.3)^A	8.5 (2.6)^A	8.7 (2.1)^A	8.4 (2.1)^A	8.3 (2.0)^A	8.1 (2.1)^A	9.1 (2.4)^B	9.3 (2.5)	7.8 (1.7)	<0.001

	ANB (Sagittal discrepancy)			MP-angle (Vertical discrepancy)			Sex^a			Age (years)
	Β value (CI 95%)	r	P- value	Β value (CI 95%)	r	P- value	Β value (CI 95%)	r	P- value	Β value (CI 95%)	r	P- value
Alveolar symphysis
IMPA	1.85 (1.62/2.08)	0.567	< 0.001**	-0.47 (-0.72/ -0.23)	0.07	<0.001**	0.31 (-2.92/3.55)	0	0.849	-0.13 (-0.14/0.12)	0	0.853
B-B’’	0.08 (0.04/0.12)	0.079	< 0.001**	-0.09 (-0.12/-0.06)	0.166	<0.001**	0.36 (-0.03/0.77)	0.017	0.073	-0.007 (-0.02/0.01)	0.003	0.439
I1-Me	0.07 (-0.04/0.19)	0.009	0.199	0.22 (0.15/0.30)	0.149	<0.001**	3.71 (2.78/4.64)	0.243	<0.001**	-0.006 (-0.05/0.03)	0	0.809
Basal symphysis
A1Me.MP	0.51 (0.28/0.74)	0.092	< 0.001**	-0.24 (-0.41/-0.07)	0.04	0.005**	-1.2 (-3.5/0.93)	0.007	0.255	0.02 (-0.06/0.11)	0.002	0.585
Pog-Pog’’	0.02 (-0.03/0.08)	0.003	0.447	-0.05 (-0.10/-0.01)	0.033	0.01**	1.02 (0.46/1.59)	0.063	<0.001**	0.001 (-0.02/0.02)	0	0.943
V-Gn	-1.54 (-1.80/-1.28)	0.41	< 0.001**	-1.03 (-1.23/-0.83)	0.351	<0.001**	6.19 (3.15/9.22)	0.077	<0.001**	0.00 (-0.13/0.13)	0	0.997
H-Gn	-0.17 (-0.50/0.16)	0.005	0.313	0.59 (0.36/0.82)	0.12	0.001**	8.26 (5.40/11.13)	0.143	<0.001**	-0.11 (-0.24/0.01)	0.016	0.07
Soft tissue chin
G’perp-Pog’	-1.51 (-1.73/-1.29)	0.489	< 0.001**	-0.84 (-1.03/-0.65)	0.285	<0.001**	0.77 (-2.06/3.62)	0.001	0.591	0.02 (-0.09/0.14)	0.001	0.670
Pog-Pog’	0.03 (-0.04/0.10)	0.004	0.368	-0.02 (-0.07/0.03)	0.003	0.467	1.09 (0.42/1.76)	0.051	0.001**	0.03 (0.008/0.06)	0.032	0.013*
Gn-Gn’	-0.02 (-0.11/0.05)	0.002	0.541	-0.11 (-0.17/-0.53)	0.068	<0.001**	1.11 (0.35/1.88)	0.041	0.004**	0.06 (0.02/0.09)	0.068	<0.001**
Me-Me’	-0.04 (-0.11/0.02)	0.007	0.246	0.01 (-0.04/0.06)	0.001	0.700	1.51 (0.90/2.12)	0.111	<0.001**	0.02 (-0.003/0.05)	0.016	0.08

	ANB vs MP Angle		ANB vs Sex		ANB vs Age		MP Angle vs Sex		MP Angle vs Age		Sex vs Age		ANB vs MP Angle vs Sex vs age
Measurements	R²	P	R²	P	R²	P	R²	P	R²	P	R²	P	R²	P
Alveolar symphysis
IMPA	0.711	<0.001***	0.566	<0.001***	0.563	<0.001***	0.061	0.001**	0.061	0.001**	0.10	0.966	0.709	<0.001***
B-B’’	0.279	<0.001***	0.091	<0.001***	0.073	<0.001***	0.164	0.007**	0.160	0.017**	0.002	0.456	0.283	<0.001***
I1-Me	0.142	<0.001***	0.250	<0.001***	0.001	0.426	0.436	<0.001***	0.141	<0.001***	0.235	0.152	0.434	<0.001***
Basal symphysis
A1Me.MP	0.144	<0.001***	0.086	<0.001***	0.084	<0.001***	0.041	<0.001***	0.032	0.038*	0.009	0.002**	0.146	<0.001***
Pog-Pog’’	0.030	0.019*	0.058	0.001**	0.007	0.747	0.078	<0.001***	0.024	<0.001***	0.054	<0.001***	0.077	0.001**
V-Gn	0.658	<0.001***	0.464	<0.001***	0.404	<0.001***	0.389	<0.001***	0.345	<0.001***	0.068	<0.001***	0.692	<0.001***
H-Gn	0.127	<0.001***	0.137	<0.001***	0.011	0.127	0.290	<0.001***	0.129	<0.001***	0.149	<0.001***	0.312	<0.001***
Soft tissue chin
G´perp-Pog’	0.673	<0.001***	0.483	<0.001***	0.484	<0.001***	0.278	<0.001***	0.279	<0.001***	0.008	0.788	0.674	<0.001***
Pog-Pog’	0.002	0.455	0.047	0.004**	0.026	0.030*	0.042	0.006**	0.025	0.033*	0.075	<0.001***	0.073	0.001**
Gn-Gn’	0.058	<0.001***	0.032	0.016*	0.060	0.001**	0.089	<0.001***	0.130	<0.001***	0.102	<0.001***	0.153	<0.001***
Me-Me’	0.002	0.435	0.106	<0.001***	0.013	0.110	0.106	<0.001***	0.006	0.206	0.119	<0.001***	0.119	<0.001***

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[1] AUTHORS CONTRIBUTIONS

Karine Evangelista (KE)

Maria Alves Garcia Silva (MAGS)

David Normando (DN)

José Valladares-Neto (JVN)

Conception or design of the study:

KE, JVN.

Data acquisition, analysis or interpretation:

KE, MAGS, DN, JVN.

Writing the article:

KE, MAGS, DN, JVN.

Critical revision of the article:

KE, MAGS, DN, JVN.

Final approval of the article:

KE, MAGS, DN, JVN.

Fundraising:

KE.

Overall responsibility:

MAGS, DN, JVN.