Factors influencing soft tissue profile changes following orthodontic treatment in patients with Class II Division 1 malocclusion

Abstract

Background: Several studies have shown soft tissue profile changes after orthodontic treatment in Class II Division 1 patients. However, a few studies have described factors influencing the soft tissue changes. The purpose of this study was to investigate the factors influencing the soft tissue profile changes following orthodontic treatment in Class II Division 1 patients.

Methods: The subjects comprised 104 Thai patients age 8-16 years who presented Class II Division 1 malocclusions and were treated with different orthodontic modalities comprising cervical headgear, Class II traction and extraction of the four first premolars. The profile changes were evaluated from the lateral cephalograms before and after treatment by means of the X-Y coordinate system. Significant soft tissue profile changes were evaluated by paired t test at a 0.05 significance level. The correlations among significant soft tissue changes and independent variables comprising treatment modality, age, sex, pretreatment skeletal, dental and soft tissue morphology were evaluated by stepwise multiple regression analysis at a 0.05 significance level.

Results: The multiple regression analysis indicated that different treatment modalities, age, sex, pretreatment skeletal, dental and soft tissue morphology were related to the profile changes. The predictive power of these variables on the soft tissue profile changes ranged from 9.9 to 40.3%.

Conclusions: Prediction of the soft tissue profile changes following treatment of Class II Division 1 malocclusion from initial patient morphology, age, sex and types of treatment was complicated and required several variables to explain their variations. Upper lip change in horizontal direction could be found only at the stomion superius and was less predictable than those of the lower lip. Variations in upper lip retraction at the stomion superius were explained by types of treatment (R(2) = 0.099), whereas protrusion of the lower lip at the labrale inferius was correlated with initial inclination of the lower incisor (L1 to NB), jaw relation (ANB angle), lower lip thickness and sex (R(2) = 0.403). Prediction of chin protrusion at the soft tissue pogonion was also low predictable (R(2) = 0.190) depending upon sex, age and initial mandibular plane angle (SN-GoGn). Additionally, age and sex also had mainly effect on change of the soft tissue profile in the vertical direction.

Keywords: Class II Division 1 malocclusion; Factors; Orthodontic treatment; Soft tissue profile changes.

Fig. 1

Cephalometric landmarks. 1 S (sella turcica), 2 N (nasion), 3 A (subspinale), 4 B (supramentale), 5 Pg (pogonion), 6 Gn (gnathion), 7 Me (menton), 8 Go (gonion), 9 ANS (anterior nasal spine), 10 PNS (posterior nasal spine), 11 maxillary central incisor edge, 12 the most anterior labial point of maxillary central incisor, 13 maxillary central incisor apex, 14 mandibular central incisor edge, 15 the most anterior labial point of mandibular central incisor, 16 mandibular central incisor apex, 17 Po (porion), 18 Or (orbitale), 19 Pr (pronasale), 20 Cm (columella), 21 Sn (subnasale), 22 Sls (superior labial sulcus), 23 Ls (labrale superius), 24 Ss (stomion superius), 25 Si (stomion inferius), 26 Li (labrale inferius), 27 Ils (inferior labial sulcus), 28 Pg’ (soft tissue pogonion), and 29 Me’ (soft tissue menton)

Fig. 2

Reference points and reference planes utilized for evaluation of the soft tissue profile changes. Line 1 X-axis: FH plane of T1. Line 2 Y-axis: perpendicular plane to FH at the nasion point of T1

Fig. 3

Angular and linear measurements utilized for evaluation of skeletal, dental, and soft tissue morphology before treatment. 1 SNA angle, 2 SNB angle, 3 ANB angle, 4 SN-GoGn angle, 5 U1-NA (angle), 6 U1-NA (linear), 7 L1-NB (angle), 8 L1-NB (linear), 9 nasolabial angle: NLA (Cm-Sn-Ls angle), 10 labiomental angle: LMA (Li-Ils-Pg’ angle), 11 upper lip length (Sn-Ss), 12 lower lip length (Ils-Si), 13 upper lip thickness (the labial surface of U1 to Ls), and 14 lower lip thickness (the labial surface of L1 to Li)