Dentoalveolar, skeletal, pharyngeal airway, cervical posture, hyoid bone position, and soft palate changes with Myobrace and Twin-block: a retrospective study

doi:10.21203/rs.3.rs-2131812/v1

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Dentoalveolar, skeletal, pharyngeal airway, cervical posture, hyoid bone position, and soft palate changes with Myobrace and Twin-block: a retrospective study

https://doi.org/10.21203/rs.3.rs-2131812/v1

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published 30 Jan, 2023

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Background: The primary aim of this study was to evaluate the dentoalveolar, skeletal, pharyngeal airway, cervical posture,hyoid bone position, and soft palate effects of myobrace and twin block appliances. The second aim was compare the appliances in terms of ease of use by assessing the factors that may influence patient compliance.

Methods: : The study included thirty-six Class II division 1 patients (19 females, 17 males; mean age, 12.14 ± 1.23) who had previously been treated in the Orthodontic clinic at Sivas Cumhuriyet University Faculty of Dentistry. The patients were divided into two groups: Group 1: myobrace (n=18), Group 2: twin block (n=18). The effects of the appliances on the skeletal, dentoalveolar, soft tissue, craniocervical, and other anotomic structures were assessed using 46 measurements, 22 linear and 24 angular, on pre and post-treatment cephalometric radiographs. AudaxCeph 5.0 software (Ljubljana, Slovenia) was used for the analysis. To analyze the changes after one year of treatment, a paired sample t-test and Wilcoxon signed-rank test were used. Intergroup comparison was performed by using the Student t-test and the Mann–Whitney U test.

Results: In the myobrace and twin block groups, there was a significant increase in SNB⁰(p=0.004, p=0.001), IMPA⁰ (p=0.005, p=0.001), and a significant drop in U1/SN⁰ (p=0.021, p=0.005). The lengths of Cd-Gn (mm), Go-Pg (mm), and Cd-Go (mm) increased significantly in the twin block group (p=0.003, p=0.010, p=0.001), whereas there was no change in the myobrace group. Similarly, there was no significant difference in pharyngeal and soft palate measurements in the Myobrace group, but there was a statistically significant decrease in SP length and SP angle in the twin block group (p=0.001, p=0.006). Increases in SN/OPT⁰ (p=0.032, p=0.001) and SN/CVT⁰ (p=0.012, p=0.001) were statistically significant in both groups. Myobrace was more difficult to use while sleeping, whereas twin block caused more nausea.

Conclusions: Both appliances can be used for mandibular advancement. The twin block appliance, on the other hand, was more effective and patient-friendly.

Functional orthodontic appliances

Myobrace

Twin block

Class 2 div 1 malocclusion

Functional orthopedic appliances are used to manage mandibular retrognathia in Skeletal class 2 cases by stimulating condylar growth [1]. Since the first functional appliances were introduced by Robin in 1902 and Andresen in 1908, a wide range of new functional appliances have been designed by other clinicians [2-5].

Following conventional functional appliances such as bionator and activator, a new device called Pre-Orthodontic Trainer for Kids^TM was developed in 1992 at the Myofunctional Research Center in Australia. It is now claimed that the trainer guides tooth eruption in the early mixed dentition, stimulates mandibular growth, and corrects abnormal myofunctional habits [6,7]. In 2004, the same company launched the Myobrace System, which was developed as a different version of the first introduced trainer. This system, which has different appliance designs based on age groups, is available on the market in a variety of sizes. The myobrace, unlike the first type of trainer appliance, facilitates dental arch development by applying light forces to the teeth via its dynamicore structure. The dynamicore structure is claimed to improve the arch shape and expand the dental arch [8].

Functional appliances increase oropharyngeal dimensions by forcing the mandible, tongue, soft palate and hyoid bone forward [9,10]. Early orthodontic treatment of mandibular retrognathia has been reported to improve insufficient airway dimension in previous studies [11,12]. Some researchers discovered that both the myobrace and twin block appliances have improvement effects on airway dimensions [1,13,14]. However, there are very limited clinical studies in the literature comparing the skeletal, dental, soft tissue and airway effects of these two appliances. On the other hand, clinicians are hesitant about the use of the Myobrace appliance, since its effectiveness is controversial and there are some difficulties in its use.

The primary aim of this retrospective study was to compare the effects of twin block and myobrace appliance on skeletal, dental, soft tissue and changes in hyoid bone, cervical posture, soft palate and airway. The secondary goal was to compare the appliances in terms of ease of use by assessing the factors that may influence patient compliance.

Participants

The current study involved thirty-six (19 females, 17 males; mean age, 12.14 ± 1.23) class 2 growing patients who had been treated at the Orthodontic department of Sivas Cumhuriyet University Dentistry Faculty. Written and verbal informed consent were obtained from the patients and their legal guards separately, and approval was obtained from the Clinical Research Ethics Committee of Sivas Cumhuriyet University (ID: 2020-02/05). This study was prepared in accordance with the Declaration of Helsinki. The sample size calculation using the G Power software revealed that at least 32 patients were required (effect size = 0.8, α = 0.05, and 1-β = 0.90) [15].

The inclusion criteria were as follows: [16,17] overjet > 4 mm, ANB>4, class 2 molar and canine relationships, normal or decreased lower facial height, C3 cervical vertebral maturation stage, no previous orthodontic treatment history. The exclusion criteria were as follows: post-pubertal growth period [18], lack of cooperation. The orthodontic archive provided information on 87 patients. Patients who did not meet the inclusion criteria (21), had radiograph artifacts (14), or had missing form data (16) were excluded from the study. Data from 36 patients treated with twin blocks and myobraces (18 in each group) who met the inclusion criteria were analyzed in this study.

The upper and lower parts of the twin block, whose effects were evaluated and routinely used in the orthodontic clinic, had labial bows and adams clasps. Slow expansion screws were added to the upper part of the appliances in 16 patients with relative maxillary narrowness.

Lateral cephalograms taken in the natural head position using the Orthoceph OC200D (Instrumentarium Dental, Tuusula, Finland) device were evaluated. AudaxCeph Version 5X software was used to perform cephalometric measurements (Ljubljana, Slovenia) (Table 1), (Figure 1, Figure 2, Figure 3).

Patients undergoing functional treatment are routinely asked to complete a form called the 'Pain and Discomfort Level Determination.' The data on this form, which the patients filled out at the first week, first month, third month, and sixth month of treatment, were analyzed in the current study.

Measurements were performed by a single investigator (Hasan Camcı) without knowing which group each x-ray belonged to.

Error of the method

The measurements of ten randomly selected patients were repeated 15 days later by the same investigator (Hasan Camcı). Repeated measurements were compared with the intra-correlation test. Correlation coefficient values for all measurements were greater than 0.762.

Statistical analysis

SPSS statistical software (version 21.0; IBM Corp, Armonk, NY) was used for all analyzes. The homogeneity of the data was evaluated with the Shapiro-Wilk test. Paired-sample t-test and the Wilcoxon signed-rank test were used for intra-group comparison of pre- and post-treatment data. The Student's t-test and the Mann–Whitney U test were used for inter-group comparison of data at T0 and T1. A p value <0.05 was considered statistically significant.

The standard deviations and mean values of the T0 and T1 periods of the patients in both groups were calculated. Pre-treatment and post-treatment cephalometric values, intra-group and inter-group comparisons were presented in Table 2 and Table 3.

Skeletal and Dental Measurements

In the myobrace group's skeletal and dental measurements, there was a statistically significant increase in SNB⁽⁰⁾, L1/NB ⁽⁰⁾ and L1-NB (mm), IMPA⁽⁰⁾ (p=0.004, p=0.003, p=0.026), and a significant decrease in U1/NA⁽⁰⁾ and U1-NA (mm) (p=0.020, p=0.020). U1/SN⁽⁰⁾and overjet showed statistically significant decreases (p=0.021, p=0.001) while NAPg⁽⁰⁾ and SNPg⁽⁰⁾ showed statistically significant increases (p=0.042, p=0.003).

In the twin-block group, skeletal and dental measurements showed a statistically significant decrease for SNA⁽⁰⁾ and ANB⁽⁰⁾ (p=0.001, p=0.001), and a statistically significant increase for SNB⁽⁰⁾ (p=0.001). IMPA showed statistically significant increase (p=0.001). Increases in SN/GoGn (⁰), FMA (⁰) were significant (p=0.001, p=0.001). A statistically significant decrease was observed in the interincisal angle (p=0.010). The increase in the lengths of Cd-Gn (mm), Go-Pg (mm), Cd-Go (mm) was statistically significant (p=0.003, p=0.010, p=0.001).

Soft Tissue Measurements

Gla-Sub-Pg⁽⁰⁾and labiomental angle increased statistically in the myobrace group (p=0.011, p=0.005). The nasolabial angle, as well as the Gla-Sub-Pg ⁽⁰⁾and Mentolabial angles, increased significantly in the twin block group (p=0.001, p=0.002, p=0.003).

Pharyngeal and Soft Palate Measurements

In the myobrace group, no statistically significant differences in pharyngeal and soft palate measurements were found (p>0.05). In the twin block group, the decrease in SP length and SP angle⁽⁰⁾ was statistically significant (p=0.001, p=0.006).

Craniocervical and hyoid measurements

In both the myobrace and twin block groups, the increases in SN/OPT⁽⁰⁾ (p=0.032, p=0.001) and SN/CVT⁽⁰⁾ (p=0.012, p=0.001) were statistically significant. CVT/HR ⁽⁰⁾ and Hi-HR (mm) in the twin block group showed statistically significant increases (p=0.001, p=0.001).

When the alterations that occurred in the T0-T1 interval were compared between groups, the changes in FH/MP⁽⁰⁾ and PNS-AD1 (mm), and CVT/HR⁽⁰⁾measurements were found to be statistically significant (Table 4) (p=0.041, p=0.009, p=0.038).

Findings of the questionnaire

The 1st week, 1st month, 3rd month and 6th-month survey data mean, standard deviations, and intergroup comparison results of the groups were shown in Table 4.

In the first week, there was a significant difference between the groups in terms of speech disorder and nausea (p=0.020, p=0.001). When the first month data were analyzed in terms of nausea, difficulty using while sleeping, pain, and speech impairments, the difference between the groups was statistically significant (p=0.014, p=0.019, p=0.027, p=0.035). Variations such as using in sleep, appliance discomfort, and gingival bleeding showed a significant difference in the third month (p=0.003, p=0.001).

The present study was quite comprehensive as it simultaneously evaluated skeletal, dental, soft tissue, pharyngeal airway, soft palate, craniocervical posture, and hyoid bone effects of twin block and myobrace appliances. In addition, the two appliances were compared in terms of ease of use. To the best of our knowledge, no comprehensive research on the effects of these two appliances has ever been conducted.

At the end of the treatment, both groups showed statistically significant changes in skeletal and dental measurements, but the twin block treatment appeared to be more effective in several categories. [15,20]. In the twin block group, the increase in SNB angle, decrease in ANB, and changes in mandibular length were more noticeable. Ghodke et al. [13] found comparable results in terms of twin block effectiveness. In the current study, no significant change in mandibular length was seen in the myobrace group, similar to the findings of Idris et al. [17] and Ushumez et al. [21]. There was a significant increase in the lower incisor angle in both groups, consistent with the study results of Elhamouly et al. [15] However, several studies found that using a trainer or activator had little effect on the angle of the lower incisors [17]. Twin block was a more effective mandibular advancement technique compared to myobrace. While previous research showed the ability of myobrace in mandibular advancement to be limited, the current study found that it plays an active role in mandibular advancement. In general, the Myobrace appliance is made of a more flexible material than the twin block. This may make it difficult for patients to keep their mandibles in a forward position [17]. The medium hard form of the myobrace was used in the current study to make it easier for patients to hold their mandible forward.

Unlike previous studies [17,22], soft tissue measurements of mybroce showed a significant improvement (Gla-Sub-Pg and mentolabial angle). The improvement in the twin block group, on the other hand, was greater than in the mybroce group.

The widening of the nasopharyngeal and hypopharyngeal regions after mandibular advancement using orthopedic appliances indicates that the airway is affected by the mandibular position [9]. Pavoni et al. [23] found that using a conventional functional appliance for mandibular advancement increased the dimensions of the pharyngeal airway, PNS-AD1 and PNS-AD2. However, in this study, they found a significant decrease in upper adenoid dimensions (AD2-H). Myobrace has been shown to have similar airway widening effects by some researches [14]. In the current study, both groups showed an increase in airway measurements, which was not statistically significant. The discrepancies in the results could be attributed to a variety of factors, including the severity of the malocclusion, age variations, treatment periods, and appliance type.

Chewing, breathing, and phonation are all influenced by the relationships between soft palate and pharyngeal airway diameters. Similar to the findings of the current investigation, Ghodke et al. [13] observed that the SP angle in the twin block group decreased significantly. Jena et al. reported that SP length and angle decreased significantly in both groups in their study comparing two different mandibular advancement devices, whereas SP thickness increased in the twin block group. In the current study, no significant change was observed in soft palate measurements in neither the twin bock group nor the myobrace group.

The hyoid bone's position is clinically significant since it is essential for maintaining upper airway dimensions. Ozdemir et al. [24] found no change in hyoid bone position after fixed functional treatment of class II malocclusion. Rizk et al. [25] reported that mandibular advancement causes anterior movement of the hyoid bone. Bavbek et al. [10] observed that after forsus treatment, the hyoid bone moved forward significantly, but there was no significant change in the vertical direction. The hyoid bone moved significantly in the sagittal direction in the twin block group in the current study, however there was no significant change in the vertical direction. In the myobrace group, no significant movement was observed in the hyoid bone in the sagittal and vertical directions.

In the current study, a statistically significant increase was observed in the SN/OPT and SN/CVT angles in both the twin block and myobrace groups. In other words, both treatment methods resulted in a more upright craniocervical posture. According to Alsheikho et al. [26], functional orthopedic treatment had no effect on craniocervical posture. Kamal et al. [27] also suggested that functional treatment had no effect on cranio-cervical angles. Significant changes in the CVT/HR and OPT/CVT angles were detected in the twin block group in the current study, which is consistent with other cervical vertebral changes. Similarly, Aglarci [28] observed a significant change in mid-cervical posture (OPT-CVT) with the use of twin blocks.

The ease of use of orthodontic appliances is critical to patient compliance. Nausea was detected at a higher rate in the twin block group than in the myobrace group during the early stages of treatment (1st week and 1st month). This could be because the twin block appliance covers a larger area of the palate. In the first and third months of treatment, patients in the myobrace group had significantly more difficulty using it while sleeping than patients in the twin block group. In terms of retention, the customized produced twin block was already expected to outperform the myobrace.

Pain was found to be higher in the myobrace group in the first month of the current study. Idris et al. found moderate pain in both the trainer and activator groups during the first months of treatment, but the pain was greater in the activator group [16]. In this study, the medium hard form of the myobrace appliance was used. This could explain the increased level of pain.

Speech difficulty was significantly higher in the myobrace appliance than in the twin block appliance. Similarly, in a previous study, less speech difficulties were reported in the twin block group [16]. The myobrace contains a double barrier (lingual and buccal oral screens) and additionally includes tongue tag and tongue guard. The current study's authors suggest that the structure of the myobrace cause to the speech difficulty. There was no significant difference between the groups in terms of temporomandibular joint pain.

Limitations

In the current study, 3D structures were evaluated using 2D cephalometric X-rays. Three-dimensional image evaluations generate more reliable results. However, in terms of radiation dose, the use of 3D imaging techniques in children is debatable. Because of its low cost and low radiation dose, cephalometric X-ray is more convenient.

The results of myobrace and twin block appliances after a year were analyzed in the current study. Another limitations of the study include not knowing the long-term effects of the appliances and not being able to assess the possibility of relapse.

Both appliances can be used for mandibular advancement. However, the twin block appliance was more effective.
The twin block appliance was convenient to use and more widely accepted by patients.
Because the long-term effects of myobrace on mandibular advancement are unknown, generalizations should not be made based on the current study's findings.

None

Ethics approval and consent to participate

Written and verbal informed consent were obtained from the patients and their legal guards separately, and approval was obtained from the Clinical Research Ethics Committee of Sivas Cumhuriyet University (ID: 2020-02/05).

All experiments were performed in accordance with the Declaration of Helsinki.

Consent for publication

Not applicable.

Availability of data and materials

The datasets created and/or analyzed during the current study are not publicly available due to [Ethics committee decision], but are available from the corresponding author upon reasonable request.

Competing interests

The authors declare that they have no competing interests.

Funding

None

Authors' contributions

Zeynep Çoban Büyükbayraktar wrote the main manuscript text and Hasan Camcı prepared figures 1-3. Zeynep Çoban Büyükbayraktar collected the data. Hasan Camcı carried out the statistical analysis. The literature review was completed by Zeynep Çoban Büyükbayraktar. The critical assessments were completed by Hasan Camcı and Zeynep Çoban Büyükbayraktar.

Acknowledgement

None

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Updated tables can be found in the supplementary file section.

No competing interests reported.

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Dentoalveolar, skeletal, pharyngeal airway, cervical posture, hyoid bone position, and soft palate changes with Myobrace and Twin-block: a retrospective study

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