INTRODUCTION

Class II malocclusion or skeletal distocclusion significantly impacts function and facial aesthetics. The prevalent diagnostic finding in this type of malocclusion is mandibular skeletal retrusion, which is challenging to treat and has a high risk of relapse.¹

Various functional/orthopedic devices for treating this malocclusion, among which the Herbst and the Twin-Block, stand out and have shown remarkable effectiveness ². In a systematic review, Cozza et al. reported substantial variabilities in the results of class II treatments attributed to the type of device used, duration of treatment, patient cooperation, time of intervention, and the inherent characteristics of the patient ³. Similarly, Canut and Arias report that patients’ response to this malocclusion treatment varies significantly. Moreover, the nature of the variations that induce the resolution of Class II with functional devices is still unclear ⁴. Petrovic et al., in addition to other authors, affirm that the effects of Class II therapy are much more effective when carried out during the peak of mandibular growth ^5-7. Saadia and Valencia report that if the therapy is applied when biological events occur during growth and craniofacial development processes, it will have a more effective impact and less tendency to relapse ⁸. The success in treating skeletal malocclusions is determined by the extent to which the correction is stable in the long term ^8,9. Al Yami et al. reported variable results between good and moderate stability in 10-year post-treatment follow-ups ¹⁰. Likewise, Bondemark et al., in a study on the post-treatment stability of Class II orthopedic therapies with Herbst-type appliances in patients who received the treatment during the pubertal growth peak, reported good stability regarding facial characteristics; however, they found recurrence regarding the molar and canine relationship ¹¹.

Ruf and Pancherz report that the correction of skeletal Class II is more effective if the Herbst appliance is combined with multibracket treatment; in this way, a more significant occlusal correction is achieved, and they report stability for two years’ post-treatment ¹². Tulloch et al. reported that in younger patients treated, less recurrence was observed than in those who received treatment at an older age ¹³. Failure can occur individually to different treatments and similar protocols, even in patients who receive treatment under ideal conditions ^8,9. The possibility of predicting with greater certainty the prognosis of the results of a skeletal Class II treatment and its long-term stability could be an invaluable tool for the clinician.

Previous studies have tried to find specific predictors to anticipate a successful treatment; however, they have yet to be systematically validated ^14-16. Some authors affirm that a Class II patient at the peak of pubertal growth with a closed gonial angle of the mandible will react successfully to functional orthopedic treatment ^7,17. In this regard, Baccetti and Franchi proposed a cephalometric model to predict individually the response to treatment of a skeletal Class II malocclusion with functional jaw orthopedics. They analyzed various cephalometric parameters, noting that only the angular relationship between the ramus and the mandibular body represents the indicator with predictive power ¹⁸.

This work aimed to report the prediction of the response to treatment of a skeletal Class II malocclusion and its long-term stability using the Baccetti and Franchi cephalometric model ¹⁸.

CASE PRESENTATION

This is the case of a 13-year-old male patient who attended the orthodontic service at the Piezzo Dental Clinic in Zacatecas, Mexico. Informed consent to participate in the study was obtained from the patient and his representatives, and the authorization to publish his photograph in this study. He presented with no medical history of interest, euryprosopic facial type, a symmetrical, slightly enlarged lower facial third, convex profile, short chin-neck distance, lip incompetence, open nasolabial angle, and closed mentolabial angle (Fig. 1a). Permanent dentition, Class II molar and bilateral canine, 14 mm overjet, and 30% overbite. A triangular symmetric upper dental arch; square asymmetric lower arch, upper and lower crowding; a severe curve of Spee (Fig. 2a); and cervical vertebral maturation stage CS3 ¹⁹.

Fig. 1 Front and profile photographs: (1a) pre-treatment at 13 years and three months of age; (1b) after Herbst therapy at 14 years and eight months of age; (1c) at the end of bracket treatment at 15 years and eight months of age; (1d) 16 years after treatment completion at 31 years and nine months of age. 

Fig. 2 Intraoral photographs, Right Lateral, Frontal, and Left Lateral Views: (2a) Pre-treatment at 13 years and three months of age; (2b) after Herbst therapy at 14 years and eight months of age; (2c) at the end of bracket treatment at 15 years and eight months of age; (2d) 16 years after treatment completion at 31 years and nine months of age. 

The cephalometric analysis determined a skeletal Class II mandibular hypoplasia²⁰ (Fig. 3a). The value of the predictive angular measurement (Co-Go-Me°) was 122°; therefore, according to the model, the patient would have a “great response” to treatment¹⁸ (Fig. 4).

Fig. 3 (3a) Initial Cephalometry; (3b) After treatment; (3c) 16 years post-treatment… 

Fig. 4 Tracing of the Condylion, Gonion, Menton (Co-Go-Me) planes to form the predictive angle according to Baccetti and Franchi’s individual prediction cephalometric model. 

The patient was treated with a fixed Herbst-type mandibular anterior projection appliance with bands for one year and five months to position the mandible in a molar and canine Class I (Fig. 2b) and a straight profile until the end of the mandibular growth peak CS4 and the beginning of CS5¹⁹, at 14 years and eight months of age (Fig. 1b). In the second phase, complete brackets were placed for one year, and Class II intermaxillary ligatures were used for four months (Fig. 2c). The profile and facial harmony were further improved at the end of this phase (Fig. 1c). Finally, a containment period was carried out for one year with Hawley-type removable retainers, worn 24 hours a day for six months, followed by six months of only night use, and the patient was discharged. Appointments were held every three years to monitor the stability of the results.

Intraorally, the molar and canine Class II changed to Class I (Fig. 2c). Post-treatment cephalometry, in general terms, showed a remarkable correction of skeletal Class II and harmonization in profile 20. Most notable was the 6° increase in angulation between the ramus and the mandibular body, thus increasing the total mandibular length by 10 mm (Fig. 3b).

At the age of 31 years, new records were taken: extra orally, greater harmony was observed in the facial contour, proportioned thirds, and straight and balanced profile (Fig. 1d). Intra orally, a Class I molar and canine occlusion with solid interdigitation on both sides, 2 mm overjet, and 30% overbite were observed (Fig. 2d).

Cephalometrically, a relevant value was the increase in total mandibular length of 3 mm in these 16 years after finishing the treatment, thus maintaining a balanced profile ²⁰ (Fig. 3c).

A superimposition shows us that 16 years after treatment, the total mandibular length alone increased by 3 mm more, reaching a total increase of 13 mm since the beginning of treatment (Fig. 5).

Fig. 5 Superimposition of the mandible (Continuous line: 13 years three months of age - Dotted line: 31 years nine months of age). 

DISCUSSION

This paper reports the prediction of the response to treatment and its long-term stability by applying the Baccetti and Franchi ¹⁸ model in an adolescent with skeletal class II malocclusion, treated with a Herbst-type fixed appliance and the use of brackets for the final detailing of the occlusion.

The study by Baccetti and Franchi ¹⁸ identified the Co-Go-Me angle with a predictive power of 80.4% reliability. According to this model, a Co-Go-Me angle between 124° and 128.5° will respond favorably to orthopedic therapy; a Co-Go-Me angle greater than 128.5° will react unfavorably to therapy; and those patients who initially present a Co-Go-Me angle of less than 124° will have a great response to treatment; however, these authors did not present long-term stability results. In the present report, this measure (122°) correctly predicted the largely favorable response to treatment.

This prediction model determines that the shape of the mandible, specifically the angular relationship between the ramus and the body, plays a more critical role as an indicator of treatment prognosis than the position of the mandible in relation to other craniofacial structures. Other authors report similar findings ^14,15.

Van Limborgh and Enlow ²¹ described that the mandible has growth control with a more significant genetic load than the maxilla; therefore, there is less possibility of changes under environmental influences. However, the rotations between the ramus and mandibular body and the redirection of condylar growth are susceptible to changes determined by environmental factors or therapeutic actions ²¹. In skeletal Class II malocclusion due to mandibular hypoplasia, the therapeutic solution is the elongation of the mandible to bring forward its body and the chin, and this can be achieved by generating, with the treatment, a descending intra-matrix rotation between the ramus and the mandibular body; that is, opening precisely the angle between these two structures, consequently increasing the distance between the condyle and the chin, and therefore increasing the total mandibular length². So, if the mandible initially presents an open angle between the ramus and the body, the prognosis could be unfavorable, since it would have less possibility of opening further and lengthening the mandible forward (it is as if a hinge were opening). Therefore, it is necessary that this angle initially be closed ⁵.

Cozza et al. suggest that a closed mandibular angle before treatment correlates with evidence of better responsiveness to orthopedic treatment to increase total mandibular length and vice versa. At the start of treatment, a patient with an open angle between the ramus and the mandibular body will be less likely to attain elongation through orthopedic therapy ³. Likewise, Petrovic et al. state that the potential responsiveness to orthopedic therapy aimed at stimulating growth in the mandibular condyle is significantly more significant in the presence of anterior growth rotation of the mandible than in a posterior growth rotation ⁵. In the case of the current study, the patient initially presented a significantly closed Co-Go-Me mandibular angle and a notable anterior rotation of the mandible. On the other hand, Proffit and Saadia define a good response to orthopedic therapy as one that is maintained in the long term ^8,9. Canut et al. state that there is a high risk of recurrence in skeletal Class II treatments; however, in some cases, it is possible to maintain stable long-term favorable treatment results, free of recurrence and containment ⁴.

In the case described in this report, after completing the comprehensive treatment, the patient only used removable retainers for one year with discontinuous use over time. The remaining time, the patient remained free of containment and relapse.

Ruf and Pancherz report good results in occlusal correction and stability of the treatment of skeletal Class II; they attribute this to the simultaneous application of full bracket and Herbst appliances ¹². In the patient of the present report, occlusal correction and excellent stability were achieved by combining complete brackets and Herbst. Ruf and Pancherz¹² made the stability evaluation two years after treatment, unlike in the case presented in this report, where the evaluation was performed 16 years after finishing the treatment.

Bondemark reports post-treatment stability in facial characteristics but not in occlusion or cephalometric data ¹¹. The present report maintained favorable facial, dental, and cephalometric changes; moreover, a better and more detailed occlusal interdigitation was achieved with time. This refinement was self-formed. Likewise, the facial profile reached a better balance and harmony, so it can be inferred that growth and development alone have the capacity for self-improvement in cases like this when they are helped at a specific moment through a treatment that creates a suitable scenario.

Tulloch et al. state that the earlier the age at which treatment is started, the more stable it will be, and vice versa ¹³. This statement sounds somewhat ambiguous since they do not mention the specific age. In our case, Herbst therapy was started at the beginning of the CS3 ¹⁹ mandibular growth peak.

In conclusion, Baccetti and Franchi’s prediction model for Class II malocclusion correction predicted the response to treatment in this particular patient, which was confirmed and resulted in long-term stable facial and dental skeleton changes.