Three-dimensional assessment of soft tissue changes associated with bone-anchored maxillary protraction protocols

Introduction

The aim of this study was to assess the 3-dimensional soft tissue changes in growing Class III patients with maxillary deficiency associated with 2 bone-anchored maxillary protraction protocols in relation to an untreated control group of Class III patients.

Methods

Growing skeletal Class III patients between the ages of 10 and 14 years participated in this study. In group 1 (n = 10), skeletally anchored facemasks were used with miniplates placed at the zygomatic buttress. In group 2 (n = 10), the patients were treated with Class III elastics extending from infrazygomatic miniplates in the maxilla to symphyseal miniplates in the mandible. Group 3 (n = 10) was an untreated control group. Three-dimensional stereophotogrammetry images were acquired before and after treatment, and then superimposed and analyzed. In addition, lateral cephalometric radiographs were analyzed.

Results

The maxilla moved forward significantly in groups 1 and 2 compared with the untreated control group (group 1, 4.87 mm; group 2, 5.81 mm). The 3-dimensional soft tissue analysis showed significant treatment effects; the major changes were observed in the upper lips, cheeks, and middle of the face, which had a significant positive sagittal displacement in both treatment groups. The lower lip and chin area showed significant negative sagittal changes that indicated that the soft tissue growth in this area was restrained with backward displacement especially in group 1 more than in group 2.

Conclusions

The 2 bone-anchored maxillary protraction protocols effectively improved the Class III concave soft tissue profile.

Highlights

  • We studied 3D soft tissue changes in 2 bone-anchored maxillary protraction protocols.

  • There were positive sagittal displacements in the upper lips, cheeks, and middle of the face.

  • The lower lip and chin areas showed significant negative sagittal changes.

  • The 2 protocols effectively improved the Class III concave soft tissue profile.

Dentofacial deformities affect a person’s quality of life, self-image, social behavior, and public perception, causing him or her to be perceived as less attractive, less successful, and less socially acceptable. Orthodontic treatment is considered a powerful tool to alter soft tissue facial form and to improve facial esthetics; furthermore, increasing numbers of patients seek orthodontic treatment primarily to improve their dentofacial appearance and subsequently their psychosocial health.

Class III patients with a concave facial profile, a retrusive nasomaxillary area, and a protrusive lower face and lips are often more concerned about their profiles than their dental occlusion. However, achieving a harmonious soft tissue profile is sometimes difficult because a Class III malocclusion is one of the most challenging problems confronting the orthodontist.

Many two-dimensional cephalometric and photographic analyses have been used to quantify the facial soft tissues. However, 2-dimensional measurements have limited validity and reliability when used for the evaluation of the 3-dimensional (3D) face. Hence, there is increased interest in viable 3D imaging tools for soft tissue assessment such as cone-beam computed tomography and laser scanners. However, cone-beam computed tomography is invasive because of the large amount of radiation used. Moreover, laser surface scanning procedures are so slow that distortions can occur on the scanned image due to motion, and there are safety issues in exposing the eyes to the laser beam. Three-dimensional stereophotogrammetry can acquire 3D images by combining photographs captured from various angles with synchronous digital cameras. The advantages of this method are the lack of motion artifacts because of the short imaging time, high color resolution, no harm for the patients, quick configuration, imaging via advanced software, ease of archiving, and 3D storage of patient images.

The aim of this study was to evaluate 3D facial soft tissue changes associated with 2 bone-anchored maxillary protraction protocols: skeletally anchored facemask with miniplates, and Class III elastics from infrazygomatic miniplates in the maxilla to the symphyseal miniplate in the mandible, in relation to an untreated control group using an innovative approach consisting of 3D stereophotogrammetry and sophisticated software.

Material and methods

Thirty growing skeletal Class III patients participated in this study according to the following inclusion criteria: they were 10 to 14 years of age at the start of treatment with a prepubertal stage of skeletal maturity according to the cervical vertebral maturation method. All had a skeletal Class III malocclusion because of a maxillary deficiency, an Angle Class III molar relationship, or an anterior crossbite without an anteroposterior functional shift. The patients and their parents were informed about the study, and the parents signed consent forms. In addition, an assent form was required for the children who participated in the study. The study was approved by the research ethical committees of the institutional review boards at Tanta University in Egypt and the University of Illinois at Chicago.

The patients were divided into 3 equal groups using a random number table. All patients were treated by the same operator (M.H.E).

  • Group 1 (n = 10) included 6 boys and 4 girls with a mean age of 11.9 ± 1.3 years. They were treated with facemasks anchored with miniplates in the zygomatic buttress area of the maxilla (skeletally anchored facemask).

  • Group 2 (n = 10) included 7 boys and 3 girls with a mean age of 12.24 ± 1 years. They were treated using Class III elastics extending from infrazygomatic miniplates in the maxilla to symphyseal miniplates in the mandible.

  • Group 3 (n = 10) included 7 boys and 3 girls with a mean age of 11.7 ± 1.6 years. For the control group, records were taken before and after the observation period to distinguish treatment changes from growth changes. Then these patients started treatment.

For the facemask miniplate protocol, 2 anchor surgical miniplates (55-0851; Stryker Leibinger, Freiburg, Germany) were placed 1 at each zygomatic buttress area. Surgical miniplates were adapted and bent according to the anatomy of the zygomatic buttress in a curvilinear pattern according to the anatomic shape of the zygomatic buttress area and fixed with 3 self-tapping bone screws per side (2-mm diameter, 6-mm length; 50-20706; Stryker Leibinger). The distal end of the miniplate was exposed through the keratinized attached gingiva near the canine to prevent gingival irritation, and the end holes of the miniplates were cut to create hooks for elastics. Three weeks after the surgery, an orthopedic force of 400 to 500 g per side was applied by heavy extraoral elastics directed 30° downward and forward from the occlusal plane from the miniplates to the facemasks. The patients were asked to replace the elastics once each day. A removable maxillary biteplate covering the posterior occlusal surfaces was placed to eliminate occlusal interference in the incisor region until correction of the anterior crossbite was obtained ( Fig 1 ).

Fig 1
Facemask anchored with miniplates fixed in the zygomatic buttress.

For the Class III elastics and miniplate protocol, 4 straight miniplates (55-0851; Stryker Leibinger) were placed. In the maxilla, straight surgical miniplates, 25 mm or 6 holes in length, were adapted to the anatomy of the infrazygomatic buttress and fixed with 3 self-tapping bone screws per side (2-mm diameter, 6-mm length; 50-20706; Stryker Leibinger). In the mandible, straight miniplates of 21 mm or 5 holes in length were adapted to the bone anatomy inferiorly between the mandibular lateral incisors and canines and fixed with 2 or 3 self-tapping bone screws per side so that the upper screw was at the level of root apices. All mucoperiosteal flaps were secured and sutured, exposing the ends of the miniplates over the keratinized attached gingiva to prevent gingival irritation. The distal end holes of the miniplates were cut to create hooks for elastics.

Three weeks after the surgery, the miniplates were loaded with Class III elastics on each side to provide a force of approximately 250 g to each side. The patients were instructed to wear the elastics 24 hours per day. The elastics were replaced at least once each day. A removable biteplate covering the occlusal surface of maxillary teeth was placed to eliminate occlusal interference in the incisor region until correction of the anterior crossbite was obtained ( Fig 2 ).

Fig 2
Class III elastics extending from infrazygomatic miniplates in the maxilla to symphyseal miniplates in the mandible.

The decision to discontinue orthopedic treatment in groups 1 and 2 was made by the operator when the patients had 3 to 4 mm of positive anterior overjet.

For each patient, a lateral cephalogram and facial moulage were obtained before treatment (T1) and at the end of protraction therapy or the observation period (T2), All facial moulages were scanned with the Facial Insight 3D Scanner (Motion View Software, Chattanooga, Tenn). Hence, 3D photographs of all patients and controls were acquired. All subjects were in centric occlusion, with relaxed facial musculature and lips. The 3D photographs were imported in stereolithography binary file format (*.stl) into an advanced processing software package (Geomagic Control 14; Geomagic, Research Triangle Park, NC) for further analysis.

All 3D photographs were acquired in a similar way and had the same orientation. The facial soft tissue changes after maxillary protraction were evaluated by superimposition of the T1 and T2 3D photographs for every patient by a surface-based registration, Maal et al concluded that surface-based registration is an accurate method to compare 3D photographs of the same subject at different times rather than reference frame-based registration.

For the initial register of T1 and T2 scans, 9 markers were used as references to superimpose the images: (1) left endocanthion, (2) left exocanthion, (3) right endocanthion, (4) right exocanthion, (5) soft tissue nasion, (6) left palpebrale superius, (7) left palpebrale inferius, (8) right palpebrale superius, and (9) right palpebrale inferius. The 3D photographs at T1 were set as fixed, and the T2 3D photographs were set as floating objects. For more refining of the superimpositions, the final register was made on the wide surface starting from right and left exocanthion and extending upward over all the forehead on the area that would not be influenced by the treatment. The T1 and T2 3D images were superimposed with the same coordinate system ( Fig 3 ). For the 3D analysis of each subject, the T1 face scan was set as a reference, and the T2 scan was set as the test, and then the 3D compare analysis was performed. The 3D compare analysis generated a 3D color-coded map that displayed the areas and magnitudes of changes in facial soft tissues between the T1 (reference) and T2 (test) scans ( Figs 4 and 5 ).

Fig 3
A, Points marked for initial approximate registration based on point landmarks for pretreatment and posttreatment face scans: 1 , right endocanthion; 2 , left endocanthion; 3 , right exocanthion; 4 , left exocanthion; 5 , soft tissue nasion; 6 , right palpebrale superius; 7 , left palpebrale superius; 8 , right palpebrale inferius; 9 , left palpebrale inferius. B, The final superimposition is made on the wide surface area starting from right and left exocanthions and extending upward over the forehead on the area that would not be influenced by the treatment.

Fig 4
Three-dimensional color-coded map displays the areas and magnitudes of changes in the facial soft tissues before and after bone-anchored maxillary protraction between the T1 and T2 scans; soft tissue landmarks selected to measure the magnitudes of deviation are right and left buccale point (Bc), right and left point of cheek (Ch), subnasale (Sn), labiale superius (Ls), labiale inferius (Li), soft tissue B-point (B’), soft tissue pogonion (Pg’), and soft tissue menton (Me’).

Fig 5
Three-dimensional color-coded map displays the areas and magnitudes of changes in the facial soft tissues of an untreated Class III patient at T1 and T2.

Soft tissue landmarks, including right and left buccale points, right and left points of the cheek, subnasale, labiale superius, labiale inferius, soft tissue B-point, soft tissue pogonion, and soft tissue menton, were defined using the Create Annotation function in the Geomagic Control 14 software. The Annotation function measured the magnitude of deviation between the T1 and T2 scans at the selected points corresponding to x-, y-, and z-axes (Dx, deviation in the transverse direction; Dy, deviation in the vertical direction; Dz, deviation in the anteroposterior direction) ( Fig 4 ). The magnitudes of deviations were analyzed statistically.

Cephalometric radiographs were obtained at T1 and T2 for all subjects to evaluate the amounts of maxillary advancement and the changes. Hence, the soft tissue changes were compared with actual skeletal movements. All cephalometric radiographs were scanned and analyzed by 1 investigator (M.H.E) using software (version 11.7; Dolphin Imaging and Management Solutions, Chatsworth, Calif). The analysis consisted of the following.

  • 1.

    The reference system described by Tollaro et al constructed through 2 lines ( Fig 6 ):

    • Stable basicranial line, which extends from the most superior point of the anterior wall of sella turcica at the junction with tuberculum sellae (point T) and drawn tangent to lamina cribrosa of the ethmoid bone; these basicranial structures do not undergo remodeling after the age of 4 to 5 years ; and vertical T, a line constructed perpendicular to the stable basicranial line and passing through point T.

    Fig 6
    Measurements based on stable basicranial line (SBL) and vertical T (VertT): 1 , Or-VertT; 2 , Ptm-VertT; 3 , A-VertT; 4 , A’-VertT; 5 , B-VertT; 6 , B’-VertT; 7 , Pg’-VertT.
  • 2.

    Angular measures (SNA, SNB, ANB, SNO, SN-GoGn, SN-palatal plane, gonial angle, U1-palatal plane, L1-MP) ( Fig 7 ).

    Fig 7
    Angular measurements (SNA, SNB, ANB, SNO, SN-GoGn, SN-palatal plane, gonial angle, U1-palatal plane, L1-MP).
  • 3.

    Linear measures (A-Na Perp, Co-A, Co-Gn, U6-VRmx, overjet, overbite) ( Fig 8 ).

    Fig 8
    Linear measurements (A-Na Perp, Co-A, Co-Gn, U6-VRmx, overjet, overbite).

To assess the reliability of the measurements on the face scans and cephalometric radiographs, 10 patients were randomly selected, and all measurements were repeated 3 weeks after the initial measurements by the same operator.

As a measure of reliability, intraclass correlation coefficients were computed to investigate the reliability of the method used by the investigators. An intraclass correlation coefficient of approximately 0.99 and a 95% confidence interval ranging from 0.678 to 0.999 for all variables in this study indicate very good reliability of the method we used.

Statistical analysis

For the 3D soft tissue analysis of the face scan data, the assumption of normal distribution was verified using the Shapiro-Wilk test. One-way analysis of variance (ANOVA) was used to test the mean differences among the 3 levels of the variables in the study, a P value of ≤0.05 was set to be statistically significant, and the Bonferroni multiple comparison was done when needed.

For the cephalometric analysis data, the assumption of normal distribution was verified using the Shapiro-Wilk test. One-way ANOVA and 1-sample Student t tests were performed. A P value of ≤0.05 was set to be statistically significant. The Shapiro-Wilk test showed that most variables in the study had a normal distribution. Descriptive statistics were computed for all variables. Based on the distribution of the raw data, mean differences from the T1 measurements, and the differences between measurements (T2-T1) among the 3 study groups were investigated using 1-way ANOVA, followed by the Bonferroni multiple comparison. For each group separately, the 1-sample t test was performed for the mean differences between times (T2-T1). Parametric tests were used, and nonparametric tests were performed when needed; similar results were found. All calculations and tests were carried out using SPSS Statistics for Windows (version 22.0; IBM, Armonk, NY).

Results

There were no statistically significant differences between the 3 groups at T1 for ages and the analyzed cephalometric parameters ( Table I ). There were significant active treatment effects in the changes between T1 and T2 in groups 1 and 2. The changes from T1 to T2 in the 3 groups are shown in Table II .

Table I
Descriptive statistics for starting forms at T1 and comparison of groups using 1-way ANOVA
Parameter Group 1 Group 2 Group 3 P
MP + FM MP + Cl III elastics Control
Mean SD Mean SD Mean SD
Age (y) 11.92 1.29 12.24 1.08 11.67 1.64 NS
Anteroposterior relationship Or-VertT (mm) 44.05 3.74 44.1 2.63 44.18 3.6 NS
Ptm-VertT (mm) 12.45 2.22 12.48 1.76 12.57 2.51 NS
A-VertT (mm) 54.84 4.77 54.3 3.72 54.02 5.37273 NS
B-VertT (mm) 52.92 5.42 52.5 4.91 52.77 5.76 NS
Pg-VertT (mm) 52.03 6.02 51.71 4.97 51.61 6.3 NS
SNA (°) 76.99 2.06 76.57 2.06 77.18 2.36 NS
SNB (°) 80.58 2.26 80.09 1.58 81.23 3.85 NS
ANB (°) −3.59 2.43 −3.52 1.36 −2.53 3.62 NS
SNO (°) 53.26 3.46 52.29 4.28 55.78 3.64 NS
(A-Na Perp) (mm) −4.25 1.99 −4.35 1.77 −4.05 3.01 NS
(Co-A) (mm) 72.34 4.95 72.16 3.74 72.81 4.43 NS
(Co-Gn)(mm) 102.86 4.97 103.06 6.24 103.82 7.04 NS
Wits appraisal (mm) −8.37 2.86 −8.47 1.94 −8.34 3.16 NS
Vertical relationship LAFH (ANS-Me) (mm) 57.02 3.21 59.43 4.08 60.16 4.24 NS
SN-GoGn (°) 34.71 5.52 36.23 3.66 37.17 5.02 NS
SN-palatal plane (°) 9 3.57 10.91 3.05 11.12 4.1 NS
Gonial angle (°) 131.52 5.86 129.95 3.87 132.42 5.78 NS
U1-palatal plane (°) 116.8 6.6 117.06 6.39 115.59 7.32 NS
IMPA (L1-MP) (°) 86.84 7.68 87.92 6.39 86.65 7.32 NS
Dental relationship U6-VRmx (mm) 16.88 3.39 16.981 1.86 15.35 1.82 NS
Overbite (mm) 3.67 2.61 3.07 1.69 2.45 1.93 NS
Overjet (mm) −4.17 1.23 −4.14 1.34 −3.52 1.33 NS
Soft tissue relationship A’-VertT (mm) 69.61 5.92 69.61 4.23 69.54 6.04 NS
B’-VertT (mm) 68.82 5.84 67.5 5 68.12 7.07 NS
Pg’-VertT (mm) 67.07 8.67 66.01 4.94 68.24 8.55 NS

NS , Not significant; MP + FM , facemask anchored with miniplates; MP + Cl III elastics , Class III elastics extending from infrazygomatic miniplates to symphyseal miniplates.

Table II
Descriptive statistics for changes (T2-T1) and comparison by ANOVA and Bonferroni post hoc tests for multiple comparisons
Parameter Group 1 Group 2 Group 3 ANOVA Post hoc test
MP + FM MP + CI III elastics Control
Mean SD Mean SD Mean SD P Groups 1-2 Groups 1-3 Groups 2-3
Treatment period (mo) 8 1.33 8.9 2.33 9.4 1.77 NS NS NS
Anteroposterior relationship Or-VertT (mm) 3.03 1.77 3.88 1.7 0.61 0.54 NS
Ptm-VertT (mm) 2.1 0.9 2.73 0.58 0.49 0.41 NS
A-VertT (mm) 4.87 1.56 5.81 1.23 1.18 0.6 NS
B-VertT (mm) −1.45 0.32 −0.67 0.35 1.67 0.45
Pg-VertT (mm) −1.55 0.35 −0.65 0.09 1.94 0.09
SNA (°) 4.78 1.14 5.65 0.83 0.44 0.49 NS
SNB (°) −1.21 0.85 −0.39 0.59 0.89 0.7 *
ANB (°) 5.99 1.54 6.04 1.16 0.82 0.68 NS
SNO (°) 2.78 0.74 3.29 1.15 0.29 0.39 NS
(A-Na Perp) (mm) 5.55 2.45 6.07 1.29 −0.73 0.6 NS
(Co-A) (mm) 4.8 1.29 5.74 1.2 1.21 2.26 NS
(Co-Gn) (mm) 0.95 0.25 1.74 0.37 2.12 3.34 NS NS NS NS
Wits appraisal (mm) 7.01 2.34 7.32 1.28 −1.03 1.1 NS
Vertical relationship LAFH (ANS-Me) (mm) 2.94 1.68 1 0.18 1.9 1.86 * * NS NS
SN – GoGn (°) 2.03 0.76 −0.98 0.51 −0.53 0.76 NS
SN-palatal plane (°) −0.65 0.24 −0.7 0.86 −0.61 1.17 NS NS NS NS
Gonial angle (Ar-Go-Me) (°) −3.2 0.61 −4.18 0.49 −0.26 0.61 NS
U1-palatal plane (°) 0.25 0.37 0.14 0.44 0.59 0.98 NS NS NS NS
IMPA (L1-MP) (°) −2.56 1.76 1.1 0.18 0.42 0.22 NS
Dental relationship U6-VRmx (mm) 0.14 0.31 0.119 0.06 0.28 0.13 NS NS NS NS
Overbite (mm) −1.48 1.52 −0.65 0.71 0.82 1.05 NS *
Overjet (mm) 7.13 1.25 7.11 1.59 −0.57 0.56 NS
Soft tissue relationship A′-VertT (mm) 5.24 1.98 6.75 2.61 1.22 0.48 NS
B′-VertT (mm) −1.125 1.12 −0.48 0.62 1.69 6.44 * NS NS
Pg’-VertT (mm) −1.08 0.87 −0.72 0.62 1.83 0.2 NS
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Dec 19, 2018 | Posted by in Orthodontics | Comments Off on Three-dimensional assessment of soft tissue changes associated with bone-anchored maxillary protraction protocols
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