Introduction
This retrospective pilot study assessed the pre- and posttreatment lip profile changes among adult patients with Class II Division 1 malocclusion of varied growth patterns and compared these changes with patients with a skeletal Class I relationship, to identify the dental, skeletal, and soft tissue cephalometric variables that altered the posttreatment lip profile.
Methods
A total of 33 digital cephalograms were divided into 4 study groups based on the mandibular plane (Mp-SN) angle: group 1 (control, skeletal Class I; mean angle = 21.5°) (n = 8), group 2 (Class II Division 1 malocclusion; low angle = <26°) (n = 8), group 3 (Class II Division 1 malocclusion; intermediate angle = 26°-38°) (n = 9), and group 4 (Class II Division 1 malocclusion; high angle = >38°) (n = 8).
Results
We observed a significant decrease in SNA, ANB, maxillary incisor to NA (degrees and millimeters), and soft tissue parameters, especially lip strain and lower lip to E line and upper lip to E line. Posttreatment intergroup comparison showed a significant increase of Mp-SN, and this increase was greater in group 3, followed by group 4 as compared with group 1. In addition, statistically significant differences in SNA, ANB, mandibular incisor to NB (degrees) and IMPA, and H angle in groups 2-4 were observed.
Conclusions
Patients with Class II Division 1 malocclusion showed a significant decrease in SNA, ANB, maxillary incisor to NA, and all soft tissue parameters in posttreatment compared with group 1. Thus, the soft tissue changes resulted in a similar profile to patients in group 1, who are considered to have an aesthetically pleasing posttreatment profile.
Highlights
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Lip strain, lower lip thickness, lip length, and nasolabial angle were reduced in groups 2, 3 and 4.
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Group 3 (intermediate angle) had a more protrusive profile than group 4 (high angle).
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Group 3 (intermediate angle) had more mandibular incisor proclination than group 4 (high angle).
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Group 3 (intermediate angle) showed a greater reduction in ANB angle than group 4 (high angle).
Class II Division 1 malocclusion is characterized by a convex facial profile, lip strain, lip trap, and proclination of maxillary anterior teeth, which are common reasons for seeking orthodontic treatment. The cephalometric changes produced by (maxillary 2 premolar) extraction treatment protocol are reduced nasolabial angle, upper lip retraction, uprighting of maxillary incisors, and a straighter profile. Thus, orthodontic treatment not only alters the dentoskeletal framework but may indirectly produce soft tissue changes in the facial profile.
Soft tissue profile alterations in thickness, length, and tonicity were studied using cephalometry. Several researchers have focused primarily on evaluating the soft tissue thickness of either Class I skeletal subjects or among other skeletal classifications. Oliver compared patients with thinner lips to thicker lips and established a correlation between dental and soft tissue changes. Utsuno et al , found a greater difference in the soft tissue thickness between skeletal Class II and Class III, with Class I being intermediate.
The effect of changes in the mandibular growth pattern on the facial profile was emphasized by only a few researchers. Blanchette et al showed thicker and longer soft tissue drape in patients with vertical growth compared with those with a short facial pattern. This result was due to a compensatory mechanism to mask the vertical dysplasia and produce a normal facial profile. Macari and Hanna reported that soft tissue thickness was smaller at Gn and Me (in contrast to Pog) in adults with hyperdivergent patterns compared with normal and hypodivergent patterns. Thus, any changes in the mandibular plane (Mp-SN) could affect the posttreatment facial profiles adversely and need to be considered during treatment planning.
In addition, there was insufficient orthodontic research to suggest that maxillary 2 premolar extraction in patients with Class II Division 1 malocclusion resulted in a posttreatment profile comparable to a Class I profile. Therefore, a pilot study was designed to evaluate the lip profile changes in treated patients with Class II Division 1 malocclusion of varied mandibular growth patterns compared with patients with a skeletal Class I relationship. Thus, we have justified the need for a pilot study to identify the dental, skeletal, and soft tissue cephalometric variables that would alter the posttreatment lip profile in patients with Class II Division 1 malocclusion who underwent maxillary 2 premolar extraction.
The present study aimed to (1) assess the pre- and posttreatment lip profiles changes among patients with Class II Division 1 malocclusion of varied mandibular growth patterns, (2) compare the lip profile changes with patients with a skeletal Class I relationship, and (3) identify the dental, skeletal, and soft tissue cephalometric variables that altered the posttreatment lip profile.
Material and methods
A total of 33 cephalograms of patients treated between January 2015 and October 2017 were procured for the pilot study. Ethical committee approval was obtained from the institutional ethical committee (approval no. 771/2015) before the start of the study.
Thirty-three (pre- and posttreatment) digital cephalograms were divided into 4 subgroups: (1) 8 cephalograms were used for the control group (group 1) and (2) 25 cephalograms were used for the experimental group (groups 2-4).
The inclusion criteria for group 1 included digital cephalograms with Class I skeletal base (ANB = 1.63° ± 0.52°); dental Class I molar and canine relation, overjet and overbite of 2 mm; no intraarch malocclusion such as crowding, spacing, or rotation of teeth; a full complement of permanent dentition except the third molars; and no change of facial morphology. The 8 cephalograms from group 1 comprised 2 of average or intermediate angle and 6 of low angle, with a mean Mp-SN of 21.5°.
All pre- and posttreatment cephalograms were chosen from adult orthodontic patients (aged 18-24 years) of the same ethnic origin (South Indian population). Their growth completion was confirmed based on the cervical vertebral maturation method. All included patients were treated by maxillary 2 premolar extraction with preadjusted appliance (0.22-in Roth prescription). The leveling wires were used in the following sequence: 0.016-in nickel-titanium (NiTi), 0.018-in NiTi, 0.017 × 0.025-in NiTi, 0.017 × 0.025-in stainless steel (SS), and 0.019 × 0.025-in SS. Individual canine retractions were carried out on 0.017 × 0.025-in SS wires using short elastomeric chains followed by anterior retraction using boot loops made of 0.019 × 0.025-in SS wires. After debonding, bonded lingual retainers and Hawley retainers were provided for full-time wear for the next 6 months. The average treatment time ranged between 21 and 28 months.
The exclusion criteria for both group 1 and group 2 included previous orthodontic treatment or orthognathic surgery, craniofacial anomalies, and nondigitized cephalograms.
The 25 digital cephalograms of the experimental groups (groups 2-4) were selected based on Class II skeletal base (ANB angle = 5.34° ± 1.30°), Angle Class II canine and molar relationship, and mild crowding (arch length discrepancy <2 mm).
The cephalograms were classified on the basis of the Mp-SN angle. A low angle (<26°) (n = 8) was classified as group 2, an intermediate angle (26°-38°) was classified as group 3 (n = 9), and a high angle (>38°) was classified as group 4 (n = 8).
The skeletal (SNA, SNB, ANB, Mp-SN angles, and facial height % [S-Go/N-Me]) and dental parameters (U1 to NA, L1 to NB, incisal Mp-SN angle, interincisal angle) are shown in Figure 1 . In addition, the various soft tissue landmarks, definitions, and measurements are shown in Table I and Figure 2 .
| Landmarks | Definition |
|---|---|
| A | The innermost point on the contour of the maxilla between anterior nasal spine and the incisor |
| B | The innermost point on the contour of the mandible between the incisor and the bony chin |
| S | Sella: the center of sella turcica |
| N | Nasion: the most anterior point of the frontonasal suture |
| Mp | Mandibular plane |
| Pog | Pogonion: the most prominent point on the soft tissue contour of the chin |
| Go | Gonion: point on the angle of mandible at intersection of ramal and mandibular plane |
| Me | Menton: most inferior midline point on the mandibular symphysis |
| Subnasale | The point where the lower border of the nose meets the outer contour of the upper lip |
| U1 | Long axis of the most prominent maxillary central incisor |
| L1 | Long axis of the most prominent mandibular central incisor |
| H line | Line joining the most prominent point of upper lip to soft tissue pogonion |
| E line | Line joining the tip of nose and soft tissue pogonion |
| Linear soft tissue measurements | |
| Thickness of lower lip | Measured from the Li to the most protruding point of the mandibular incisor |
| Thickness of basic lower lip | Measured from the innermost point of the labiomental fold to point B |
| Upper lip strain | The difference between the thickness of upper lip and basic thickness of upper lip |
| Subnasale to H line | The horizontal perpendicular distance from Sn to H line |
| Lower lip to H line | The distance of lower lip in relation to H line |
| E line to upper lip | The horizontal distance between outer contour of upper lip to E line |
| E line to lower lip | The horizontal distance between outer contour of lower lip to E line |
| Length of upper lip | The vertical perpendicular line drawn from Stms to Sn to FH plane |
| Lower lip length | Vertical perpendicular line drawn from the soft tissue point B to Stmi to FH plane |
| Contour of the soft tissues | The entire vertical distance from Sn to Me’ denoted by red dotted line |
| Hard tissue contour | The total vertical distance from ANS to Me’ denoted by blue line |
| Nasolabial angle | The angle measured between base of nose and upper lip tangent |
| H angle | Angle formed by line joining H line and soft tissue nasion to pogonion line |
All digital radiographs were acquired using the same cephalostat (Digital Planmeca ProMax and Cephalometric system; Planmeca, Helsinki, Finland) under standard exposure parameters of 65 mA and 7 kVp. All the cephalograms were processed (DRYPIX Lite; Fujifilm, Tokyo, Japan) and printed onto an x-ray film with a dimension of 8 × 10 cm (Kodak Films, F speed; Kodak, Rochester, NY).
The cephalograms were manually traced by a single operator (D.M.) on a transparent tracing paper (8 × 0.003 × 10-in) using a 0.3 mm 2H lead mechanical pencil (Staedtler Mars Micro 775; Mars GmbH & Co KG, Nuernberg, Germany) with the aid of an x-ray viewing box. A protractor and millimeter scale were used to obtain all the angular and linear measurements and entered into an Excel spreadsheet (Microsoft, Redmond, Wash) for statistical evaluation. Ten cephalograms were randomly selected and traced by the same operator within 10 days, and intraclass correlation coefficients were determined (intraclass correlation coefficients = 0.9) (range, 0.8-0.9) for the linear and angular measurements. The method error was 0.5 mm for linear measurements and 1.1° for angular measurements using the Dahlberg formula.
Statistical analysis
SPSS for Windows (version 18.0; SPSS, Chicago, Ill) was used for comparison of the pre- and posttreatment changes and changes between the group. Means and standard deviations were used for intragroup comparison. ANOVA with post-hoc Dunnett test was used for intergroup comparison. Statistical significance was set at 5%.
Results
Table II shows the pre- and posttreatment mean and standard deviation values of the dental, skeletal, and soft tissue parameters in patients with Class II Division 1 malocclusion of varied growth patterns. There was a statistically significant decrease in SNA ( P = 0.033) and ANB ( P < 0.001) angles ( Fig 3 ) and in the maxillary incisor to NA (for both degrees [ P < 0.001] and millimeters [ P < 0.001]) in posttreatment ( Fig 4 ).
| Parameters | Pretreatment | Posttreatment |
|---|---|---|
| Skeletal | ||
| Mp-SN | 31.36 ± 6.62 | 31.38 ± 6.00 |
| SNA | 81.76 ± 3.18 | 80.40 ± 3.61 |
| SNB | 76.46 ± 3.28 | 76.28 ± 3.21 |
| ANB | 5.34 ± 1.30 | 4.00 ± 1.58 |
| Facial height percentage | 67.76 ± 5.43 | 67.98 ± 4.98 |
| Dental | ||
| UI to NA,° | 34.20 ± 8.97 | 26.96 ± 6.45 |
| U1 to NA, mm | 7.76 ± 3.21 | 4.58 ± 1.80 |
| L1 to NB,° | 35.04 ± 6.72 | 35.56 ± 5.28 |
| L1 to NB, mm | 7.48 ± 2.29 | 7.48 ± 2.29 |
| IMPA | 104.68 ± 8.70 | 105.08 ± 6.90 |
| INA | 107.40 ± 9.29 | 111.44 ± 6.92 |
| Soft tissue | ||
| ULS | 4.64 ± 1.19 | 2.04 ± 1.14 |
| LLT | 14.60 ± 1.98 | 13.76 ± 1.39 |
| BLLT | 13.20 ± 3.11 | 12.12 ± 1.62 |
| SN-H | 8.14 ± 2.51 | 6.72 ± 2.51 |
| LL_H | 2.62 ± 2.12 | 2.34 ± 2.09 |
| E_UL | 0.26 ± 2.60 | −1.72 ± 2.75 |
| E_LL | 2.38 ± 3.17 | 0.38 ± 2.74 |
| ULL | 18.46 ± 2.88 | 19.04 ± 3.49 |
| LLL | 14.96 ± 2.59 | 16.78 ± 2.53 |
| STC | 67.64 ± 5.66 | 68.60 ± 5.69 |
| HTC | 62.52 ± 6.51 | 64.44 ± 6.27 |
| NLA | 104.84 ± 13.43 | 107.88 ± 11.92 |
| H angle | 21.48 ± 2.90 | 19.48 ± 3.77 |
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