Effect of the Functional Appliances on Skeletal, Dentoalveolar, and Facial Soft Tissue Characteristics

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript evaluating Twin-Block functional appliance effects on adolescent Class II malocclusion patients through combined 2D cephalometric and 3D facial scanning analyses. While the research topic demonstrates clinical value and methodological innovation, several aspects of methodology, statistical analysis, and presentation need to be addressed.

1. Representative Case Illustration To enhance reader comprehension, please include a typical case as an illustrative figure. This should comprise pre- and post-treatment 2D cephalometric tracings with landmark identifications, 3D facial models, and registered color difference maps. Such illustration would significantly improve methodological clarity and result credibility for your readers.

2. Introduction and Literature Review Your introduction requires streamlining with more focused content. The Class II malocclusion background (lines 34-40) appears overly broad and needs condensation. Please include a brief review of functional appliance treatment status, mentioning other mainstream appliances (Herbst, Invisalign, etc.) alongside Twin-Block to better establish your study's unique contribution and necessity.

3. Growth Analysis and Study Design Since you studied adolescent subjects during growth periods using a self-controlled design, please incorporate comprehensive discussion regarding mandibular growth differentiation. Treatment effects versus natural development should be clearly distinguished, preferably with established longitudinal growth data referenced for comparison to strengthen your conclusions.

4. 3D Methodology and Validation Your 3D facial scanning methodology requires enhanced rigor and transparency. The "tragus-pogonion" linear distance used as an "effective mandibular length" indicator lacks adequate literature support. Please validate this measurement with relevant studies demonstrating its clinical significance. Additionally, provide detailed anatomical definitions of "stable regions" (forehead, nasal root, suborbital areas) used for 3D registration, along with methods for eliminating head posture and facial expression confounding factors.

5. Statistical Analysis and Presentation Please adopt the three-line table format for standardized statistical presentation and ensure complete annotations for all figures, particularly adding color bars with clear numerical units (mm) for heat maps (Fig.3, Fig.4). Additionally, table captions should provide clear unit annotations (mm) and concise explanations of analytical methodologies to enhance reader comprehension of the three-dimensional facial surface changes observed following Twin-Block treatment.

Author Response

Thank you for your suggestions.

Comment: 1. Representative Case Illustration To enhance reader comprehension, please include a typical case as an illustrative figure. This should comprise pre- and post-treatment 2D cephalometric tracings with landmark identifications, 3D facial models, and registered color difference maps. Such illustration would significantly improve methodological clarity and result credibility for your readers.

Response: We added new Figures to illustrate better typical case, with noted differences.

Comment: 2. Introduction and Literature Review Your introduction requires streamlining with more focused content. The Class II malocclusion background (lines 34-40) appears overly broad and needs condensation. Please include a brief review of functional appliance treatment status, mentioning other mainstream appliances (Herbst, Invisalign, etc.) alongside Twin-Block to better establish your study's unique contribution and necessity.

Response: The Class II malocclusion background is shortened and other appliances are mentioned. In text:  Functional appliances are frequently used during growth phase to encourage forward movement of the lower jaw. They have shown short-term success in correcting Class II malocclusions by decreasing overjet mostly due to tipping of the lower front teeth [4]. Several appliances play a crucial role in modifying mandibular growth. Traditional ap-pliances such as the Twin Block, Herbst appliance and the various activators are commonly used [5]. The Herbst appliance uses a telescopic rod to advance the mandible while also preventing the maxilla from moving forward while Twin Block appliance uses upper and lower plates to reposition mandible forward. The activator type appliances apply masticatory muscles’ forces to move the mandible forward. Additionally, advancements in orthodontics have led to the development of functional clear aligners which can include mandibular advancement elements like custom attachments and elastics [6]. These studies mainly measured effects on hard and soft tissues using lateral cephs, and not soft tissue scans. Our study focuses on therapy with functional appliance Twin Block and the impact of this therapy on soft tissue, with traditional cephalometric characteristics used to demonstrate effects of the Twin block therapy.

Comment: 3. Growth Analysis and Study Design Since you studied adolescent subjects during growth periods using a self-controlled design, please incorporate comprehensive discussion regarding mandibular growth differentiation. Treatment effects versus natural development should be clearly distinguished, preferably with established longitudinal growth data referenced for comparison to strengthen your conclusions.

Response: Lack of control group was addressed by citing the studies that used control group and compared natural growth and treatment changes. In text: Although the present study did not include a control group, previous research incorporating a control cohort found no statistically significant differences in skeletal discrepancy or overjet which could be contributed to the growth alone in control subjects [15]. Additionally, another study reported an average mandibular length increase of only 0.3 mm due to natural growth, an amount that was not statistically significant, particularly when compared to the treatment group managed with the Twin Block appliance, which exhibited a statistically significant increase in mandibular length [16], similar to our findings. Furthermore, the study of maxillomandibular growth in untreated class II showed that mandibular deficiency will not self-correct during pubertal peak growth [33].

Comment: 4. 3D Methodology and Validation Your 3D facial scanning methodology requires enhanced rigor and transparency. The "tragus-pogonion" linear distance used as an "effective mandibular length" indicator lacks adequate literature support. Please validate this measurement with relevant studies demonstrating its clinical significance. Additionally, provide detailed anatomical definitions of "stable regions" (forehead, nasal root, suborbital areas) used for 3D registration, along with methods for eliminating head posture and facial expression confounding factors.

Response: Provided studies for validating distances between tragus- pogonion – it is often used for measuring changes in soft tissues of the lower jaw and effective mandibular length is used as mesaurement for skeletal changes in mandible. In text: Mandibular skeletal measurements are typically assessed using the linear distance be-tween condylion (Co) and gnathion (Gn), which represents the effective mandibular length [17]. On soft tissue, the tragus is the anatomical landmark most analogous to the condylion. Therefore, the distance between the tragus and pogonion is commonly used to evaluate soft tissue changes in the lower jaw region [18].

Also, added the method registration by using NHP and superimposiotion importance with stable regions of the face. In text: Facial scanning was performed under illumination provided by a ring light with a corre-lated color temperature (CCT) of 3000K. Natural head position (NHP) was used to ensure consistency in image capture as it is proven to be reproducible [18, 19]. Participants were seated on a height-adjustable stool and instructed to align their eyes with the level of the front-facing camera. Seating height was modified as needed to facilitate proper NHP alignment. Prior to scanning, subjects were asked to maintain a relaxed jaw posture with their mouths gently closed. Scans were repeated in cases where any irregularities or de-viations from the required positioning were observed.

This technique improves registration accuracy by reducing the sum of squared distances between matched points in two datasets, often referred to as the reference and target models [24]. To ensure accuracy, it is essential to register these scans using anatomically stable regions. Anatomically stable regions include portions of the forehead, nasal bridge and infraorbital region. Although centrally located, this region lies within the upper third of the face and demonstrates minimal morphological variation due to growth. Its stability makes it particularly suitable for assessing changes in the middle and lower facial thirds, which are more susceptible to developmental and treatment-induced modifications [12, 24, 26].

Comment: 5. Statistical Analysis and Presentation Please adopt the three-line table format for standardized statistical presentation and ensure complete annotations for all figures, particularly adding color bars with clear numerical units (mm) for heat maps (Fig.3, Fig.4). Additionally, table captions should provide clear unit annotations (mm) and concise explanations of analytical methodologies to enhance reader comprehension of the three-dimensional facial surface changes observed following Twin-Block treatment.

Response: The changes were made, with additional explanations and measuring units added.

Reviewer 2 Report

Comments and Suggestions for Authors

Dear authors, it is indeed a wonderful research; kindly take the comments constructively.

Strengths 

The research presents a thorough and contemporary approach by combining 2D cephalometric analysis with 3D facial scanning to enable an in-depth evaluation of treatment results. The use of sophisticated computational methods, including ICP alignment and geodesic measurements, showcases a high level of technical expertise in assessing 3D models. From a statistical standpoint, the authors apply suitable techniques—such as paired t-tests, the Wilcoxon test, intraclass correlation coefficients, and the Kolmogorov–Smirnov test—to effectively examine essential orthodontic parameters, revealing significant alterations in clinically important metrics. Notably, the study focuses on a crucial orthodontic intervention during an essential growth phase, highlighting its importance for treatment planning and clinical decision-making.

 

Lack of a Control Group

• Concern: The lack of a control or untreated group weakens the capacity to ascribe changes solely to the Twin Block appliance as opposed to natural growth.
• Suggestion: This limitation should be examined more thoroughly. If feasible, compare the findings to established normative growth data or controls from the literature.

 Sample Size and Selection

• Concern: The final sample consists of 18 participants, reduced from an initial target of 38. Although the power calculation was based on 14 participants, the reasons for dropout and the potential for bias (such as incomplete data and non-random loss) are not addressed.
• Suggestion: Provide additional information on the exclusion of participants and analyze how it could have influenced the outcomes.

 

 Overinterpretation of Findings

• Concern: The writers attribute noted changes to the effects of appliances without adequate caution. For example, increases in mandibular length might be partially due to normal growth during puberty.
• Suggestion: Soften causal terminology, particularly in relation to changes in skeletal and soft tissue, unless it is directly compared with a control or growth-standard dataset.

A professional English language edit is required. Streamline background information and focus on key rationales.

Comments on the Quality of English Language

Needs professional edit

Author Response

Thank you for your comments.

Comment: Lack of a Control Group; Concern: The lack of a control or untreated group weakens the capacity to ascribe changes solely to the Twin Block appliance as opposed to natural growth. Suggestion: This limitation should be examined more thoroughly. If feasible, compare the findings to established normative growth data or controls from the literature.

Response: Other studies that had control group and compared to the treated group were added. In text: Although the present study did not include a control group, previous research incorporating a control cohort found no statistically significant differences in skeletal discrepancy or overjet which could be contributed to the growth alone in control subjects [15]. Additionally, another study reported an average mandibular length increase of only 0.3 mm due to natural growth, an amount that was not statistically significant, particularly when compared to the treatment group managed with the Twin Block appliance, which exhibited a statistically significant increase in mandibular length [16], similar to our findings. Furthermore, the study of maxillomandibular growth in untreated class II showed that mandibular deficiency will not self-correct during pubertal peak growth [33].

Comment: Sample Size and Selection; Concern: The final sample consists of 18 participants, reduced from an initial target of 38. Although the power calculation was based on 14 participants, the reasons for dropout and the potential for bias (such as incomplete data and non-random loss) are not addressed. Suggestion: Provide additional information on the exclusion of participants and analyze how it could have influenced the outcomes.

Response: There was detailed explanation and Figure 1 about the sample added. We addressed it in text: Two participants declined to participate in the study, further three were non-cooperative (discontinued treatment), and remaining 33 finished the treatment. Unfortunately, it was established that further 15 participants had missing either one of the facial scans, or they were not suitable for analysis, even after inspection upon scanning. Therefore, the final sample consisted of 18 participants (Figure 1).

Comment: Overinterpretation of Findings; Concern: The writers attribute noted changes to the effects of appliances without adequate caution. For example, increases in mandibular length might be partially due to normal growth during puberty. Suggestion: Soften causal terminology, particularly in relation to changes in skeletal and soft tissue, unless it is directly compared with a control or growth-standard dataset. A professional English language edit is required. Streamline background information and focus on key rationales

Response: In article effective mandibular length was changed to soft tissue mandible length and also, we added studies that had control group and showed differences that occurred in growth versus with treatment with functional appliances. Also, it is clearly stated that this is a major limitation of our study. In text: Although the present study did not include a control group, previous research incorpo-rating a control cohort found no statistically significant differences in skeletal discrepancy or overjet which could be contributed to the growth alone in control subjects [15]. Additionally, another study reported an average mandibular length increase of only 0.3 mm due to natural growth, an amount that was not statistically significant, particularly when compared to the treatment group managed with the Twin Block appliance, which exhibited a statistically significant increase in mandibular length [16], similar to our findings. Furthermore, the study of maxillomandibular growth in untreated class II showed that mandibular deficiency will not self-correct during pubertal peak growth [33].

Reviewer 3 Report

Comments and Suggestions for Authors

I thank the editor for giving me the opportunity to review this manuscript. Here are some suggestions that would help for better presentation of the study:

Summary       

 Line 15-16 : ‘increase in position of the lower incisors to the apical base of the mandible :  is not clear what the authors mean, so please define the specific measurment

Line 17: … and in effective: Sentence should be rephrased

Line 19: “position of upper incisors to the apical base of the maxilla’’: please indicate the exact measurement

 

Introduction :

Dental characteristics of Skeletal Class II patients may also be the retrusion of upper incisors and decreased overbite (Class II/2 patients)

 

Line 48:  “The goal of the therapy ..” should be added: depending on the dental and skeletal characteristics of the patient is to...

 

Updated literature should be added on facial scan methods

 

Methods:

Please define if all the subjects were Class II, division 1 and what were the vertical characteristics of the patients. Was there a decreased or increased lower facial height in all subjects? What was the purpose of the therapy in regard to that? This should be discussed in regard to the findings of the study.

 

Authors should describe the appliance and the registration bite

 

Authors should add a relative photo of the facial scan. Light conditions during the scanning procedure should be mentioned

 

Line 168 : Authors should describe in detail the protocol for visual and metric inspection. What were the actions taken if the inspection revealed a non-satisfying registration?

 

3.2. Soft tissue analysis:

A relative figure for the measurements that were made from point tragus to point pogonion should be added

 

Discussion

 

Sentence 301-302 :  Vertical cephalometric parameters did not change significantly after therapy, and as such, did not contribute to masking or emphasizing the sagittal changes. The authors should discuss why there was not significant vertical changes as usually the advancement of the mandible is accompanied by increase of the lower vertical height.

Author Response

Thank you for your review

Comment: Line 15-16 : ‘increase in position of the lower incisors to the apical base of the mandible :  is not clear what the authors mean, so please define the specific measurment.

Response: Specific measure was named. In text: Dependent t-test results showed significant increase in protrusion of the lower incisors (p < 0.001), proclination of the lower incisors (p = 0.021)

Comment: Line 17: … and in effective: Sentence should be rephrased

Response: Line changed, in text: and in soft tissue mandible length

Comment: Line 19: “position of upper incisors to the apical base of the maxilla’’: please indicate the exact measurement

Response: Exact measurement was indicated, in text: and retrusion of upper incisors (p=0.002).

Also, changes were made in all tables mentioning cephalometric parameters.

Comment: Dental characteristics of Skeletal Class II patients may also be the retrusion of upper incisors and decreased overbite (Class II/2 patients)

Response: Added in text: Dental characteristics often include the relationship of the upper first permanent molars and canines with their antagonists in Class II, protrusion of the upper incisors and increased overbite, retrusion of upper incisors and decreased overbite and a narrow maxilla with a high palate, which can result in a bilateral crossbite.

Comment: Line 48:  “The goal of the therapy ..” should be added: depending on the dental and skeletal characteristics of the patient is to...

Response: Added into the text, in text: The goal of the therapy, depending on the dental and skeletal characteristics of the patient, is to is to create more harmonious skeletal and soft tissue relations.

Comment: Updated literature should be added on facial scan methods

Response: Literature updated. In text: Combined with artificial intelligence (AI)-based analysis, facial scanning is emerging as a powerful approach for early disease detection [10]. Beyond internal structural and func-tional abnormalities, many diseases are associated with distinctive craniofacial features. These facial phenotypes can serve as clinically relevant biomarkers, particularly in the diagnosis of genetic syndromes, metabolic disorders and neuromuscular conditions [10]. Compared to conventional imaging techniques, 3D facial scans capture the entire face without radiation exposure or angular distortion, enabling precise quantification of linear and angular distances, area superimposition and volumetric analysis [11, 12]. High degree of precision and accuracy is making 3D facial scans suitable for monitoring in orthodontic practice. This method enables the evaluation of facial morphological changes in pediatric patients, the analysis of craniofacial pathologies and asymmetries, as well as the detailed assessment of soft tissue structures in individuals undergoing oral surgery [11, 13].  

Comment: Please define if all the subjects were Class II, division 1 and what were the vertical characteristics of the patients. Was there a decreased or increased lower facial height in all subjects? What was the purpose of the therapy in regard to that? This should be discussed in regard to the findings of the study.

Response: All subjects were class II, division 1; six of them had horizontal growth pattern (SN:GoGn ≤ 26°), 10 had neutral growth pattern (SN:GoGn > 26° < 37°), and two exhibited vertical growth pattern (SN:GoGn > 37°). Treatment choice for functional appliance was made upon performing the Fränkel manoeuvre.

Comment: Authors should describe the appliance and the registration bite.

Response: Described in methods, in text: Appliance described in methods. In text: Twin Block appliance consist of the upper and lower plates with occlusal ramps and hooks that retain the appliance on the dental arch. Registration of the constructional bite is most important in the design and final fabrication of the functional appliance. It de-termines the new sagittal, vertical and horizontal relationships of the lower jaw to the upper jaw. Activation of the lower jaw must sufficiently stretch the masticatory muscles and allow a positive proprioceptive response, while also staying within the physiological limits of the muscles and joints [4].

Comment: Authors should add a relative photo of the facial scan. Light conditions during the scanning procedure should be mentioned

Response: Light conditions mentioned in text: Facial scanning was performed under illumination provided by a ring light with a correlated color temperature (CCT) of 3000K. Pictures of typical facial scans before and after therapy, and as used for analyses were added.

Comment: Line 168 : Authors should describe in detail the protocol for visual and metric inspection. What were the actions taken if the inspection revealed a non-satisfying registration?

Response: Described the protocol for capturing 3D facial scans with NHP. In text: Natural head position (NHP) was used to ensure consistency in image capture as it is proven to be reproducible [21]. Participants were seated on a height-adjustable stool and instructed to align their eyes with the level of the front-facing camera. Seating height was modified as needed to facilitate proper NHP alignment. Prior to scanning, subjects were asked to maintain a relaxed jaw posture with their mouths gently closed. Scans were repeated in cases where any irregularities or deviations from the required positioning were observed.

Comment: A relative figure for the measurements that were made from point tragus to point pogonion should be added

Response: Figure is added.

Comment: Sentence 301-302 :  Vertical cephalometric parameters did not change significantly after therapy, and as such, did not contribute to masking or emphasizing the sagittal changes. The authors should discuss why there was not significant vertical changes as usually the advancement of the mandible is accompanied by increase of the lower vertical height.

Response: Cephalometric data supports the above-mentioned statement, there was addition in the text: Figure 3 shows typical example of a case before and after treatment with Twin block from our study. Superimposed analyses before and after treatment show downwards and forwards displacement of the lower facial third, but no change in vertical relations in terms of the change of the mandibular plane angle (p = 0.283, visible in results from Table 3).

Also: Other variables did not show significant changes, including maxillary and mandibular plane angles, and intermaxillary angle, indicating no change in vertical dimensions.

The increase in the lower facial third is a favourable response to therapy in class II patients, and it is mostly attributed to the vertical growth in the condyle and mandibular ramus, without opening of mandibular plane angle [7].

The downside is that we didn’t measure the increase in lower facial third, as it would be interesting to see if the faces became more harmonious, as compared to lower facial heights before therapy.

In text: Also, it would be interesting to see in future research, whether the increase in lower facial third would contribute to the more harmonious relations, as compared to lower facial heights before therapy.

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

thank you for the modifications

all the best and much appreciated