Comparison of Soft Tissue Changes Produced by Two Different Appliances on Mixed Dentition Children

Objective This study was focused on comparing and analyzing the soft tissue changes induced by Reverse Twin-Block (RTB) and Reverse Pull Face Mask (RPFM) in early and late mixed dentition Malay children having Class III malocclusion. Methods This cross-sectional study includes a total sample of 95 Malay children of both early (8-9 years) and late (10-11 years) mixed dentition stages. The comparison was between 49 samples treated by RTB and 46 samples treated by RPFM. Both pre- and posttreatment changes were assessed with Holdaway's analysis using the CASSOS software. In each cephalogram, 71 anatomic landmarks were traced. Descriptive and multiple regression analyses were performed for statistical evaluation. Results Statistically significant changes were noticed in soft tissue facial angle, subnasale to H-line, skeletal profile convexity, upper lip strain, H-line angle, lower lip to H-line, and inferior sulcus to H-line measurements. Gender disparity was noticed in upper lip strain. Other significant changes were influenced by the type of appliance. However, the mean differences were minute to notice clinically. Age difference did not have any effect on the treatment changes. Conclusions RPFM revealed treatment outcome with more protruded upper lip than RTB.


Introduction
Treatment of Class III malocclusion in mixed dentition children is considered as a challenging case. As the outcome after growth cessation is unpredictable, orthodontists prefer to treat this particular malocclusion during mixed dentition stage to utilize the effect of the growth spurt as well as reducing the chances of future surgical intervention [1,2]. The primary goal of orthodontic treatment includes facial esthetics, functional efficiency, and balanced occlusion [1]. Soft tissue change is one of the key factors in improving facial esthetics during orthodontic treatment [3]. Class III malocclusion, either due to retruded maxilla or protruded mandible or by both, exhibits a concave facial profile. Mixed dentition stage is the crucial time to start treatment using orthodontic appliance as sutures are not calcified yet. Some significant changes in dentofacial development take place during this stage [4]. Although soft tissue changes are influenced by the underlying hard tissue changes, the variation in the soft tissue thickness during this stage also contributes greatly [5].
Several studies have successfully used Reverse Twin-Block (RTB) and Reverse Pull Face Mask (RPFM) appliances to treat Class III malocclusion in growing children by modifying the craniofacial growth [2,[6][7][8][9][10][11][12][13][14]. Whenever there was an evaluation of the clinical effects of these appliances, soft tissue changes were never considered as a prime factor. Holdaway's analysis introduced eleven soft tissue measurements which are renowned for evaluating facial profile harmony [15]. It is well established that considering soft tissue changes during treatment planning brings best possible soft tissue profile [16]. There are only few studies reporting the treatment effect of RTB but none of them emphasized on the soft tissue changes [10][11][12]. Several studies were found to evaluate the effects of RPFM but still focusing on the dentoskeletal effects [2,[6][7][8][9][10]13]. Seehra et al. compared both of these appliance's efficacy but the evaluation of soft tissue changes was yet unrevealed.
The ideal time to start the treatment of Class III malocclusion is after the eruption of upper permanent incisors, that is, the beginning of mixed dentition stage [17]. But the debate of whether the treatment should be started immediately or can be delayed until late stage is still unresolved [18]. It is imperative to analyze which appliance brings better efficacy and what should be the ideal age of starting treatment. Hence, the current study is aimed at comparing and analyzing the soft tissue changes produced by RTB and RPFM in early and late mixed dentition Malay children having Class III malocclusion.  [19]. Tabachnik and Fidell formula was used for sample size calculation; N > 50 + 8 m, where m = number of independent variables [20]. Malay children of age 8-9 and 10-11 years having Class III deciduous canine relationship/Class III molar relationship with overjet (-1 to -5 mm) containing clear pre-and posttreatment cephalograms were included in this study. Dental parameter was used for inclusion criteria as the use of cephalogram for sample selection is not ethical. Any patient with craniofacial anomaly, history of facial trauma, and previous orthodontic therapy was excluded. Based on the selection criteria, the samples were extracted from a previously conducted randomized clinical trial [21]. Finally, 49 samples were under RTB and 46 samples were under RPFM. Each group of samples was divided into two age groups, early (8-9 years) and late (10-11 years) mixed dentition groups. The materials used in this study were as follows: (1) pre-and posttreatment lateral cephalograms (Figures 1 and 2) collected retrospectively from the Hospital Universiti Sains Malaysia (HUSM) archive with permission and (2) the Computer-Assisted Simulation System for Orthognathic Surgery (CASSOS 2001, Hong Kong) software for cephalometric tracing and measurements. The flow diagram of the study is presented in Figure 3. Each sample's date of birth and the date of pretreatment cephalogram were used to calculate the age at the beginning of the treatment. This study was located at School of Dental Sciences, Universiti Sains Malaysia.

2.2.
Appliances. The RTB group received treatment with RTB originally designed by Clark ( Figure 4) [22]. Adams clasps on the molars and premolars/deciduous molars in the upper block and in the lower block ball clasps on the incisors were added for retention. The inclined bite planes were angulated at 70°towards the occlusal plane with no labial bow. Fulltime wear was encouraged, except during tooth brushing and contact sports. The RPFM group received treatment through Delaire type of facemask with a chin cup, and no expansion screw was attached ( Figure 5(a)). A maxillary acrylic splint was used as an intraoral appliance which was banded to the maxillary first permanent molars and first deciduous molars ( Figure 5(b)). It covered the maxillary posterior teeth, and the thickness was about two to three millimeters on the occlusal and buccal surface. The extra-and intraoral parts were attached with heavy elastics from the maxillary vestibular hooks (1.0 mm stainless steel wire) to the crossbar of the face mask. The direction of elastic traction was downward and forward. About 400 g of force was applied bilaterally, and 14 hours per day of appliance wear was advised.
Both of the treatment groups received appliance therapy for eight-month period, and then, the treatment change was compared using posttreatment lateral cephalograms. The pre-and posttreatment photographic images of RPFM and RTB appliances are presented in Figures 6 and 7, respectively.
2.3. Cephalometric Analysis. All cephalograms were taken by the same operator with the same cephalostat. The samples were in centric occlusion and positioned as Frankfort horizontal plane parallel to the floor. All the headfilms were then digitized by VIDAR's DiagnosticPRO® Advantage film digitizer (2010; Herndon, VA, USA) and saved in JPEG format at a resolution, 96 dpi, 1642 × 2086 pixels, and 24 bit grayscale. The cephalograms were traced using the CASSOS software. Images were imported, and 71 landmarks were identified manually using a mouse-driven cursor following

Statistical Analysis.
One calibrated researcher traced the lateral cephalograms to avoid interexaminer bias. This researcher was trained and calibrated by a standard examiner. Twenty cephalograms were retraced after two weeks to check the method error using Dahlberg's formula, and it was negligible [23]. All statistical analyses were performed using IBM SPSS Statistics for Windows, Version 22.0 (IBM Corp., Armonk, NY, USA) with significant level set at P < :05. The Kolmogorov-Smirnov test proved normal distribution of data in both groups (P > :05). Descriptive statistics for means and standard deviation (SD) of each dependent variable were calculated. Multiple regression analysis was performed for evaluation and comparison of the effect of age, sex, and type of appliance on each dependent variable. Dichotomous variables were coded as gender (0 = male and 1 = female), age (0 = early and 1 = late), and type of appliance (0 = RTB and 1 = RPFM).

3.1.
Sample. This study focused on comparison between 49 samples treated with RTB and 46 samples treated with RPFM. RTB group had 24 early and 25 late, whereas RPFM group had 20 early and 26 late mixed dentition children.

Descriptive Statistics of Cephalometric Measurements of RPFM Group.
Descriptive data of the pretreatment, posttreatment, and treatment changes are presented for early mixed dentition group in Table 1 and for late mixed dentition group in Table 2. 3.3. Descriptive Statistics of Cephalometric Measurements of RTB Group. Descriptive data of the pretreatment, posttreatment, and treatment changes are presented for early mixed dentition group in Table 3 and for late mixed dentition group in Table 4.

Discussion
Analysis of soft tissue changes provides basic information to achieve esthetic harmony, one of the main goals of orthodontic therapy. Facial appearance is mostly dependent on the soft tissue profile [24]. To acquire knowledge about soft tissue morphology along with dentoskeletal analysis, cephalometric soft tissue analysis is essential [25]. It can never be expected that correction of malocclusion only will eventually improve facial esthetics [26]. Soft tissue profile may vary due to many factors, such as race, age, sex, and type of malocclusion [27,28]. The soft tissue profile is portrayed by chin prominence and thickness; facial profile angle and convexity; nose prominence and nasolabial angle; upper lip length, protrusion, and thickness; lower lip thickness, contour, and relation to the inferior sulcus [3,24,25,[27][28][29]. In our previous studies, craniofacial changes and changes in airway space of these two appliances were compared but detailed comparison of soft tissue changes is focused in this part [30,31]. The mean and standard deviation of pretreatment, posttreatment, and treatment changes values are presented in Tables 1-4. Significant treatment changes were noticed in seven out of eleven measurements, soft tissue facial angle, subnasale to H-line, skeletal profile convexity, upper lip strain, H-line angle, lower lip to H-line, and soft tissue chin thickness (Table 5). Significant treatment changes were associated with type of appliance except upper lip strain, which showed gender disparity.
An innate relationship persists between facial profile convexity and facial esthetics [32]. Facial profile angle and  5 BioMed Research International convexity is established by skeletal profile convexity and Hline angle measurements. An increase in skeletal profile convexity also increases the H-line angle [3]. In this study, children under RPFM group have 0.91 mm more convex skeletal profile and 2.26°larger H-line angle than children under RTB group. This finding suggests an improved soft tissue profile after treatment with RPFM. Soft tissue facial angle and soft tissue chin thickness are associated with chin prominence and thickness [3]. In the current study, soft tissue facial angle in children under RPFM group is 1.35°smaller than in children under RTB group. Soft tissue chin is 0.24 mm thicker in RPFM group than in RTB group. Other studies confirmed that a less concave facial profile is created with decreased soft tissue facial angle or retruded soft tissue pogonion [9,25,33]. Therefore, statistically RPFM-treated children have straighter profile than RTB-treated children, but clinically, the difference is too small to notice. Skeletal profile convexity, H-line angle, soft tissue facial angle, and soft tissue chin thickness measurements revealed that both RPFM and RTB produce a harmonious and straighter profile.
A balance in nasal prominence, lip protrusion, and chin prominence maintains facial harmony [5,34]. No significant difference was noticed in nose prominence after treatment.  Other studies also found gender disparities in lip thickness [38]. However, this small difference is clinically unnoticeable.
In the current study, no significant change was observed in superior sulcus depth, which determines upper lip curl. Other studies also did not notice any significant change [29,34].
The lower lip position and contour were determined by the lower lip to H-line and inferior sulcus to H-line measurements. Lower lip to H-line value was significantly affected by type of appliance. A more retruded lower lip can be seen in RPFM group as the value was 0.55 mm less in children treated by RPFM than in children treated by RTB. But only 0.55 mm does not make any significant difference clinically. Type of appliance has significant impact on inferior sulcus to H-line measurement, but this value has less importance in indicating soft tissue changes [3].
The results from this study demonstrated a significant association of the appliance type with the majority of the variables. The gender disparity was only noticed in upper lip strain. Although these differences are statistically significant, clinically, they are too small to notice. From clinical point of view, these two appliances produced similar treatment effects on soft tissue changes, except upper lip protrusion. The treatment effect was similar in both early and late mixed dentition stages. If the treatment is started at late mixed dentition stage, we get the benefits of better patient cooperation, less time for treatment follow-up, and moreover better treatment outcome.

Conclusion
(i) RPFM showed better treatment outcome with more protruded upper lip than RTB (ii) No significant differences were noticed in the treatment changes between early and late mixed dentition stages (iii) Male children had more strained upper lip than female children, but the difference was clinically negligible

Data Availability
Data that support the findings of this study are available from the corresponding authors, Alam MK and Khamis MF, upon reasonable request.

Conflicts of Interest
No conflict of interest to declare.