Cephalometric Analysis of Growing Patients with Class II Malocclusion Treated with Prefabricated Myofunctional Appliance
Article information
Trans Abstract
The study aimed to evaluate the skeletal, dentoalveolar, and soft-tissue effects of prefabricated myofunctional appliances in pediatric patients with Class II malocclusion. Twenty-three patients (12 boys and 11 girls; mean chronological age 9.03 ± 1.90 years) with Class Ⅱ malocclusion who were treated with Éducation Fonctionnelle (EF line®) (Orthoplus, Igny, France) were assessed. Radiographic analysis using lateral cephalograms was conducted at treatment initiation and following a 12-month intervention period, with an average monitoring duration of 14.13 ± 2.82 months. Cephalometric evaluation was performed using V-ceph™ (Osstem, Seoul, Korea), and the Wilcoxon signed-rank test was employed for data analysis. The results demonstrated significant improvements in sagittal relationships, including decreased ANB angle and Wits appraisal, as well as increased SNB angle. Mandibular growth was evident through increases in mandibular length measurements (Co-Go, Co-Gn, and Go-Gn). Vertically, backward and downward rotation of the mandible was observed, as evidenced by increases in FMA, SN-MP, and Y-axis angles, resulting in significant increases in facial height. Dentoalveolar changes were characterized by lingual inclination of the maxillary incisors and labial tipping of the mandibular incisors, with significant reductions in both overjet and overbite. Soft tissue analysis revealed enhanced facial esthetics through increases in the nasolabial and mentolabial angles, accompanied by reduced upper lip protrusion. In conclusion, this study validated the clinical efficacy of prefabricated myofunctional appliances in managing Class II malocclusions.
Introduction
Class II malocclusion presents as a sagittal discrepancy, in which the mandible is positioned posteriorly relative to the maxilla [1]. According to McNamara, mandibular retrognathia was found to be the primary skeletal characteristic of Class II malocclusions in growing children [2]. Furthermore, this dentoskeletal disharmony tends to persist with growth, and without intervention, may further compromise mandibular development in terms of both mandibular length and ramus height [3]. Based on this understanding, functional appliances have been developed, which induce a remodeling response at the condyle, thereby promoting mandibular growth while allowing the surrounding muscles to adapt to the new position [4,5].
While activators represented early approaches to functional therapy [6], a new era began in 1975 with the introduction of the Eruption Guidance Appliance (EGA) (ORTHO-TAIN, Inc., Bayamon Gardens, Puerto Rico) [7]. The EGA is unique in combining functional appliances with eruption guidance [7,8]. Subsequently, the Pre-Orthodontic Trainer for Kids (T4K™) (Myofunctional Research Co., Helensvale, Queensland, Australia) was developed in 1992 [9]. Since then, various prefabricated myofunctional appliances (PMAs) have been introduced, including the LM-Activator™ (LM-dental, Pargas, Finland), Myobrace® (Myofunctional Research Co., Helensvale), PreOrtho® (Biomaterials Korea Inc., Hanam, Korea), and Éducation Fonctionnelle (EF line®) (Orthoplus, Igny, France) [10,11].
PMAs are noncustomized, removable devices made of soft elastomeric materials, designed to function similarly to traditional functional appliances [10,12]. Their prefabricated nature eliminates the need for impressions and laboratory work, making them cost-effective [13,14]. Furthermore, the flexible material properties of PMAs minimize the risk of breakage, unlike conventional functional appliances [14]. Most importantly, PMAs are designed to address the underlying etiological factors of malocclusion by correcting orofacial muscle dysfunction and tongue posture, while simultaneously providing tooth eruption guidance and alignment [15,16]. By targeting these fundamental soft-tissue issues, PMAs aim to achieve stable treatment outcomes [17].
Therefore, PMAs are indicated for cases such as Class I crowding, Class II malocclusion, anterior open bite, deep bite, and various oral habits including mouth breathing, tongue thrusting, and thumb sucking. However, PMAs are generally not indicated for conditions such as dolichofacial patterns, complete nasal obstruction, and reluctant children or parents [18].
Among these PMAs, the EF line incorporates several distinctive design elements that distinguish it from other myofunctional appliances. The raised molar area promotes condylar remodeling and facilitates forward mandibular growth. The twin splint guides the teeth to the proper position by eliminating adverse buccal and lingual muscle pressures. The lip bumper component helps reduce excessive lower lip tension by stretching the lip muscles, thereby eliminating unfavorable lip pressure. Additionally, the appliance features a tongue ramp that guides the tongue toward the palate during swallowing, promoting lateral palatal development. These integrated design features work synergistically to achieve both skeletal and dentoalveolar corrections while addressing underlying myofunctional issues [18].
However, despite these potentially advantageous design features and the growing interest in using the EF line as interceptive orthodontic treatments in the mixed dentition stage, scientific validation of their clinical effectiveness remains limited. This gap in scientific evidence underscores the need for comprehensive research on the efficacy of the EF line. Therefore, the objective of this study was to assess the effect of the EF line on skeletal, dentoalveolar, and soft tissue changes during the treatment of Class II malocclusion. By analyzing cephalometric radiographs, this retrospective study seeks to contribute to the contemporary discussion on the efficacy of PMAs and provide clinicians with evidencebased insights for treatment planning in growing Class II patients.
Materials and Methods
1. Ethics approval
This study was approved by the Institutional Review Board (IRB) of Wonkwang University Dental Hospital (IRB number: WKDIRB202404-01).
2. Patient selection
This retrospective study included participants diagnosed with Class II malocclusion and treated with an EF line at the Department of Pediatric Dentistry, Wonkwang University Dental Hospital, from January 2021 to September 2023. A detailed flowchart of patient selection, including the inclusion and exclusion criteria, is summarized in Fig. 1 [12,19-21].
Flow chart of patient selection in this study.
Class II molar and canine relationships for inclusion criteria were assessed as follows: A Class II molar relationship was determined when the mesiobuccal cusp of the maxillary first molar was occluded anterior to the mesiobuccal groove of the mandibular first molar. In cases with incompletely erupted permanent first molars, a distal step relationship between the distal surfaces of the maxillary and mandibular primary second molars was used. A Class II canine relationship was established when the cusp of the maxillary (primary) canine was occluded anterior to the embrasure between the mandibular (primary) canine and the first premolar (or primary first molar).
3. Intervention
The study population exhibited Class II malocclusion characterized by mandibular retrognathism, along with multiple concurrent issues including deep bite, hyperactive mentalis muscle, mouth breathing, or lip sucking habits. PMA therapy was selected due to its therapeutic efficacy in improving sagittal relationships while simultaneously addressing deep bite tendencies and intercepting dysfunctional oral habits [11,18].
The type of EF line (T Slim, Class II Slim, Class II Standard, or Class II 2 steps) was selected based on the patient’s plaster model analysis and the manufacturer’ s guidelines. Specifically, appliance selection was determined by the severity of the overjet: EF T Slim for patients with overjet < 6 mm, EF Class II Slim or Class II Standard for patients with overjet between 6 and 10 mm, and EF Class II 2 steps for patients with overjet > 10 mm. During treatment, when a patient’s overjet was reduced to < 6 mm, the EF T Slim appliance was prescribed in accordance with the manufacturer’s guidelines [22].
To achieve optimal treatment outcomes, manufacturers recommend wearing appliances for a minimum of one hour during the daytime and while sleeping [23-25]. While explicit guidelines for nighttime wear duration are not standardized, specific protocols such as those for the LM-Activator™ recommend wear from 8 PM until the next morning, and previous studies have recommended nocturnal wear of 10 – 12 hours [14,24]. Following these guidelines, the patients were advised to wear the appliance during sleep and for a minimum of 2 hours during the daytime. Bimonthly follow-up appointments were conducted to encourage consistent use of the appliances. Clinical assessments were performed to verify proper appliance fit and compliance with the daily wear duration.
4. Cephalometric analysis
Cephalometric analysis was conducted based on lateral cephalometric radiographs recorded at the commencement of treatment (Time 0, T0) and 12 months after treatment (Time 1, T1). All cephalometric measurements were performed by a single-blinded investigator. Radiographs from both time points (T0 and T1) were coded and randomized prior to analysis to ensure unbiased assessment. All measurements and analyses were performed using the V-ceph™ software (version 8.5; Osstem, Seoul, Korea). The cephalometric landmarks are illustrated in Fig. 2, and the definitions of the landmarks and reference planes are provided in Table 1. Table 2 presents the definitions of cephalometric measurements.
Illustration of landmarks used in the lateral cephalometric analysis in this study.
N: Nasion; S: Sella; Po: Porion; Or: Orbitale; ANS: Anterior nasal spine; PNS: Posterior nasal spine; A: A point; B: B point; Pog: Pogonion; Gn: Gnathion; Me: Menton; Go: Gonion; Co: Condylion; Ar: Articulare; U1: Upper central incisor tip; U1R: Root apex of upper central incisor; L1: Lower central incisor tip; L1R: Root apex of upper central incisor; G: Glabella; PRN: Pronasale; Cm: Columella; Sn: Subnasale; Ls: Labialis Superior; Li: Labialis inferior; ILS: Inferior labial sulcus; Pog’: Soft tissue pogonion.
Cephalometric landmarks and planes used in this study
Definitions of cephalometric measurements used in this study
5. Intra-examiner reliability
All lateral cephalometric radiographs were subjected to repeated measurements at a one-month interval to determine intra-examiner reliability. An analysis using the intraclass correlation coefficient (ICC) revealed excellent reliability, with all measurements showing values greater than 0.86.
6. Statistical analysis
All data analyses were conducted using SPSS (version 29.0; IBM, Chicago, IL, USA). The Shapiro-Wilk test was used to assess data normality. Based on the normality results, comparisons between parameters at T0 and T1 were conducted using the Wilcoxon signed-rank test. The significance level was established at p < 0.05.
Results
1. Sample characteristics and growth stage distribution
The study sample consisted of 23 subjects (12 boys and 11 girls) with a mean chronological age of 9.03 ± 1.90 years at T0. The mean observation period was 14.13 ± 2.82 months. Detailed demographic data are presented in Table 3.
General characteristics of the study participants
Regarding cervical vertebral maturation (CVM) stages, four participants were in CVM1, 11 participants were in CVM2, and eight participants were in CVM3. None of the participants in the CVM4 met both inclusion and exclu-sion criteria. To evaluate the treatment effects of the EF line according to growth stage, participants were divided into prepubertal (CVM1 and 2) and pubertal (CVM3) stages for subgroup analysis [26].
2. Overall treatment effects
Statistical comparisons of the 35 measurements between T0 and T1 for all 23 participants are presented in Table 4. Skeletal sagittal measurements showed favorable changes, characterized by increases in the SNB angle and maxillomandibular differential and decreases in the ANB angle, A-B to mandibular plane angle, and Wits appraisal. Mandibular length parameters (Co-Go, Co-Gn, Go-Gn, Ar-Go, and Ar-Gn) showed significant increases, indicating mandibular elongation. The vertical dimension showed significant increases in anterior facial height, lower anterior facial height, and posterior facial height, aligned with increased angular measurements. With regard to dentoalveolar changes, the upper incisors showed significant retroclination, whereas the lower incisors demonstrated proclination. Both overjet and overbite were significantly reduced. Improvements in the soft tissue profile were characterized by increases in both the nasolabial and mentolabial angles, along with a decrease in the distance from the upper lip to the E-line.
Cephalometric changes after treatment with prefabricated myofunctional appliances
3. Comparisons between growth stages
Cephalometric measurements and statistical analyses according to growth stage are described in Table 5. When comparing the prepubertal and pubertal stages, findings were similar to those of the overall analysis of the 23 participants. However, changes in the vertical growth pattern were more pronounced in the pubertal stage than in the prepubertal stage, whereas facial height increased significantly in both groups. Furthermore, in the prepubertal stage, no significant increase in mandibular length was observed, except for Ar-Gn length. Additionally, the pubertal stage demonstrated a significant increase in the facial convexity angle.
Cephalometric changes after treatment with prefabricated myofunctional appliances according to growth stage
4. Treatment compliance and appliance usage
While patient compliance was monitored through regular check-ups, there was a limitation of relying on subjective patient reporting rather than using a standardized method to quantitatively track the actual wearing time. Throughout the treatment period, no appliances were lost; however, 17 out of 23 patients required appliance replacement, either due to appliance tearing or progression to a different appliance type. On average, each patient used 1.96 appliances throughout the treatment period.
Discussion
Previous research has shown that traditional functional appliances generally demonstrate greater skeletal effects, including improvements in mandibular growth and anteroposterior relationships, than PMAs [10,14,27]. This enhanced skeletal response can be attributed to the fundamental characteristics of traditional functional appliances: their custom-made design enables precise anterior mandibular repositioning, and their rigid material composition provides better stability in holding the mandible forward than the flexible material of PMAs [10,19]. Both appliance types have proven effective in reducing overjet and overbite [10,28], while PMAs offered practical advantages, including cost-effectiveness and reduced chair time [10,13].
Additionally, PMAs may be more effective than no treatment in managing Class II malocclusions in growing patients. Significant improvements were observed in dental relationships, including overjet, overbite, and molar relationship [8,14,29]. Although the magnitude of the skeletal changes showed some variability, favorable outcomes were typically observed, including improvements in sagittal relationships [28]. This evidence supports PMAs as a viable treatment option compared with no intervention, although the magnitude of the effect varies across different parameters.
Despite these findings, there remains substantial controversy surrounding the capacity of PMAs to promote mandibular growth [12,14,20,27,30]. These conflicting results can be attributed to variations in appliance type, intervention timing, and patient compliance [21,31,32]. Critics have also questioned whether the observed changes represent true mandibular growth, suggesting that cephalometric measurements may have been influenced by noncentric relation positioning [33]. Specifically, the reported mandibular elongation could be the result of anterior mandibular positioning rather than the actual growth [8]. To address these methodological concerns, this study implemented two approaches: first, mandibular length and ramus height were measured using the condylion (Co) instead of the articulare (Ar) as reference points [5,19,34]. Second, specific precautions were taken before cephalometric imaging to prevent anterior mandibular positioning, which can occur because of neuromuscular reflexes that develop from prolonged appliance wear [8].
Our findings indicated an increase in mandibular length (Co-Go, Go-Gn, and Co-Gn) following EF line treatment, especially during the pubertal stage. These results align with those of Ravera et al. [11] who reported significant increases in mandibular measurements (GoCo, GnCo, and GoGn) in patients treated during the CVM3 stage. While a significant increase in the Ar-Gn length was observed in the prepubertal stage, this result should be interpreted with caution because of the potential influence of anterior mandibular positioning on these reference points, as previously discussed [5,19,34].
To differentiate treatment effects from natural growth, our findings (Ar-Go and Ar-Gn) were compared with the annual growth increments of Korean children aged 8 – 12 years in a previous semi-longitudinal study [35]. The observed increase induced by the EF line (1.69 mm for Ar-Go and 3.52 mm for Ar-Gn) exceeded the average growth rate (1.19 mm for Ar-Go and 2.00 mm for Ar-Gn), suggesting that the EF line facilitates mandibular growth. However, this comparison had a few limitations. First, while Co-based measurements are considered more reliable indicators of true mandibular growth as mentioned above, the comparison relied on Ar-based measurements (Ar-Go and Ar-Gn) because historical growth data using Co-based parameters were unavailable. Second, the two studies were conducted at different time points, which may reflect changes in environmental factors and nutritional status that affect growth patterns. Third, this simple comparison of mean values did not account for individual variations in growth timing and velocity, nor did it control for factors, such as sex distribution or skeletal maturity. Additionally, without an appropriate statistical analysis that considers sample sizes, standard deviations, and variances, the statistical significance of these differences cannot be determined. Therefore, future studies should include a properly matched control group to distinguish treatment effects from natural growth more accurately.
In terms of sagittal changes, there were no significant alterations in maxillary position, contrary to the “headgear effect” reported in previous studies [36]. The increase in the SNB angle suggests favorable changes in the mandibular position. This, combined with improvements in ANB, A-B to mandibular plane angles, Wits appraisal, and maxillomandibular differential, indicates an enhancement of sagittal relationships [14,27]. These findings suggest that compared to maxillary prognathism, the EF line may be more effective in managing mandibular retrognathism.
Regarding the vertical dimension, significant increases were observed in the FMA, SN-MP, and Y-axis angles, indicating a backward and downward rotation of the mandible. This vertical change manifested in two clinically relevant ways. First, it contributes to significant increases in facial height measurements (anterior, lower anterior, and posterior facial heights), which may be particularly beneficial for patients with hypodivergent facial patterns. Second, this rotation pattern influenced the expression of sagittal changes: while mandibular length measurements showed significant increases, clockwise rotation resulted in growth manifesting more vertically [37]. This explains our observation that despite significant increases in the SNB angle and mandibular length measurements, changes in the linear measurements of the B point and pogonion relative to the N-perpendicular line were less pronounced. Understanding this growth pattern is crucial for appropriate patient selection and treatment planning.
These findings contrast with those reported by Chen et al. [20], who found no statistically significant changes in most vertical measurements. This discrepancy might be attributed to their relatively small sample size, which may have constrained their ability to identify significant changes in vertical parameters. Additionally, while Chen et al. [20] included patients before CVM3, the precise distribution across the CVM stages was not specified, making it difficult to account for growth potential variations. Our findings support the observations of Ravera et al. [11], who demonstrated that vertical skeletal changes can vary significantly according to the CVM stage, with significant increases observed during CVM3, but not during CVM2.
Dentoalveolar changes include retraction of the maxillary incisors due to the labial shield and labial tipping of the mandibular incisors due to the lip bumper effect, which is consistent with previous studies [9,14,27]. These changes, combined with an improvement in the anteroposterior relationship, contribute to a reduction in overjet [8,14]. Additionally, a significant reduction in overbite was observed, which can be attributed to the intrusion of the upper incisors and vertical extrusion of the mandibular molars [8].
Modifications to the hard tissues of the perioral region can substantially influence the inferior facial third, including the labial, nasal, and mental areas [38]. Čirgić et al. [39] reported a significant improvement in lip seal following treatment with the Myobrace. Similarly, An et al. [40] observed decreased maxillary prominence as evidenced by a reduction in the upper lip to the E-line (mm). Despite these findings, little is known about soft tissue modifications induced by the EF line. In the current study, there was a significant decrease in the distance from the upper lip to the E-line and an increase in the nasolabial angle, likely due to the retroclination of the maxillary incisor [41,42]. Additionally, the substantial increase in the mentolabial angle can be attributed primarily to the reduction in overjet, which eliminated lower lip distortion and curling [42]. The necessity of lip closure while wearing the appliance also appears to be a contributing factor, as it intensifies lip strain and alters both the tone and position of the perioral muscles [42]. Furthermore, the pubertal stage showed a significant increase in the facial convexity angle, which was mostly due to the increased mandibular length resulting from EF line treatment [42].
Throughout the treatment period, material tearing was observed in several cases, necessitating appliance replacement. This finding can be attributed to the material properties of EF line devices, which are fabricated from plasticized polyvinyl chloride [43]. Previous research has shown that traditional polyurethane- and vinyl-based materials demonstrate significantly higher tear strengths than silicone materials [44]. However, while plasticization offers enhanced flexibility and patient comfort, particularly beneficial for younger patients, it may result in decreased mechanical properties [45]. Although there is currently a lack of published studies directly comparing the material durability of EF line appliances and other PMAs, these material characteristics suggest that the frequent tearing of EF line appliances can be attributed to their material properties.
In addition to material-tearing issues, appliance replacement is necessary in several other clinical scenarios to maintain optimal treatment effectiveness. Treatment progress often necessitates transitions between different appliance types based on overjet reduction, from EF Class II 2 steps (overjet > 10 mm) to EF Class II Slim/Standard (overjet 6 – 10 mm), and subsequently to EF T Slim (overjet < 6 mm). Additionally, dental arch development and molar eruption may require switching to appliances with distal extensions, such as the EF T Slim long or EF Guide. Transitioning to specialized EF Braces appliances is necessary for patients proceeding to fixed orthodontic treatment [22]. Regular clinical monitoring ensures appropriate timing of these replacements to maintain therapeutic momentum while adapting to the changing needs of patients.
Furthermore, the long-term effectiveness of PMAs remains a subject of ongoing research. Čirgić et al. [39] revealed that even patients who achieved successful overjet reduction to less than 3 mm experienced an increase in overjet at the 1-year follow-up, and sagittal molar relationship corrections showed relapse during the followup period. Similarly, Janson et al. [46] found a significant relapse of both overbite and mandibular anterior crowding after EGA treatment. These findings underscore the necessity of long-term follow-up. While definitive evidence on the optimal follow-up duration remains limited, research suggests that approximately 49% of total relapses occur during the first two years post-retention [47], indicating that a minimum follow-up period of 2 years is necessary. This consideration is particularly crucial for growing patients, in whom the residual growth potential can significantly influence the stability of orthodontic treatment outcomes [48]. Furthermore, extended followup protocols may be warranted in cases presenting with severe skeletal discrepancies or persistent oral habits.
In this study, although the EF line treatment in growing patients with Class II malocclusion yielded significant and multifaceted dentoskeletal and soft tissue changes, several limitations should be acknowledged. The relatively small sample size inherently limited the statistical power and generalizability of the findings. Additionally, the short observation period may not have been sufficient to fully evaluate the long-term treatment effects and stability. Another significant limitation was the lack of a matched control group, which made it challenging to distinguish treatment effects from natural growth. Furthermore, the retrospective nature of this study introduced a potential bias.
Conclusion
Despite these limitations, the present study suggests that treatment with the EF line in growing patients with Class II malocclusion may facilitate mandibular advancement and elongation, consequently improving sagittal relationships. Vertically, the clockwise rotation of the mandible resulted in an increased facial height. Notably, both mandibular growth and vertical changes were more pronounced during the pubertal stage. Moreover, significant reductions in overjet and overbite were observed, and these biomechanical modifications led to improvements in the soft tissue profile. Therefore, this study verified the clinical efficacy of the EF line as a promising therapeutic intervention for Class II malocclusion, particularly in patients presenting with a retruded mandible and a hypodivergent growth pattern.
Notes
Conflicts of Interest
The authors have no potential conflicts of interest to disclose.