Growth modulation therapy in skeletal class II malocclusion

Abstract

A male child in his early adolescence was referred to the orthodontist to correct the proclined maxillary anterior teeth. Investigations concluded an excess maxilla, deficient mandible and remaining growth potential. The patient was treated with Twin Block functional appliance in combination with a high-pull headgear and later fixed pre-adjusted edgewise appliance to detail the occlusion. The total treatment duration was 18 months. The positive motivation and compliance exhibited by the patient were important.

Background

Various skeletal and dental component combinations may contribute to a skeletal class II discrepancy. Identifying the aetiology and understanding the manifestation of class II malocclusion are subsequently advantageous in correcting the discrepancy and selecting treatment modalities. Myofunctional appliances are used in the growing stage to control or alter the growth of the maxillomandibular skeletal components in the anteroposterior, vertical and transverse directions. An extraoral force applied through a headgear can restrict the forward and downward growth of the maxilla. The current case best describes the effects of myofunctional appliances, extraoral force and a fixed orthodontic appliance in treating a skeletal class II malocclusion considering the patient’s age and innate growth potential.

Case presentation

A male patient in his early adolescence presented with forwardly positioned upper front teeth. The history of the presenting illness shows that the patient’s mother first noticed the inclination 1 year ago. There was no relevant medical history, and the dental history revealed that this was the patient’s first dental visit. Extraoral examination showed a class II skeletal pattern, backwardly placed mandible, average growth pattern, convex profile, normal nasolabial angle, incompetent lips, protrusive upper and lower lip, and deep mentolabial sulcus. Intraoral examination showed Angle’s class II malocclusion, proclined upper anterior, upper and lower anterior crowding, overjet of 10 mm, overbite of 5 mm and curve of Spee of 3 mm. The objectives of the treatment included correction of the skeletal base, upper proclination, crowding, overjet and overbite.

Investigations

Facial photographs show the patient’s appearance, natural smile and convex profile. A clinical visualised treatment objective photograph was taken to confirm the facial improvement after advancing the lower jaw. Intraoral photographs show Angle’s class II molar and class II canine relation, upper and lower arch crowding, and an excess overjet (figure 1).

Figure 1.

Pretreatment facial and intraoral photographs.

In assessing the cephalometric radiograph (figure 2), the ANB value of 5° suggested a mild class II skeletal pattern. The vertical proportions were within the normal value. The upper incisors were proclined at 114°, and the lower incisors were inclined at 98°. The interincisal angle was reduced to 117°. The lower incisor to A-Po and the lower lip to E line were within normal values (table 1).

Figure 2.

Pretreatment radiographs.

Table 1.

Pretreatment cephalometric analysis

	Normal values	Patient values	Inference
SNA (Sella–Nasion–A point angle)	82±2°	82°	Normally placed maxilla
SNB (Sella–Nasion–B point angle)	80±2°	77°	Backwardly placed mandible
ANB (A point–Nasion–B point angle)	2°	5°	Class II skeletal pattern
Effective maxillary length	92.1±4.1mm	95 mm	Normal for age
Effective mandibular length	114.4±4.3mm	114 mm	Normal for age For a 95 mm maxilla, the mandible should be 122–125 mm, according to McNamara’s growth prediction. Hence, mandibular length is short by 8 mm for that maxilla.
FMA (Frankfort-mandibular plane angle)	17°–28°	26°	Average growth pattern
SN-GoGn (Sella-Nasion to Gonion-Gnathion angle)	32°	32°	Average growth pattern
Y-axis	53°–66°	62°	Average growth pattern
U1–SN (Upper incisor-Sella-Nasion angle)	102°	114°	Proclined upper incisors
U1–NA (Upper incisor-Nasion-Point A angle)
Linear	4 mm	10 mm	Forwardly placed upper incisors
Degree	22°	33°	Proclined upper incisors
L1–NB (Lower incisor-Nasion-Point B angle)
Linear	4 mm	7 mm	Forwardly placed lower incisors
Degree	25°	27°	Proclined lower incisors
L1–A-Pog (Lower incisor to Point A-Pogonion angle)	2 mm	2 mm	Normally placed lower incisors
U1–L1 (Upper incisor-Lower incisor angle)	135°	117°	Bidental proclination
IMPA (Incisor mandibular plane angle)	90°	98°	Proclined lower incisor
Cant of occlusion	1.5°–14°	8°	Normal
Nasolabial angle	90°–110°	100°	Normal
Lip strain		4 mm	Lip strain of 4 mm

The dental panoramic tomogram reveals an endodontically treated lower left first molar; restoration was done on the upper left first molar and the presence of all permanent teeth, including the erupting upper and lower third molars. A hand-wrist radiograph confirmed the remaining growth left in the patient (Fishman’s skeletal maturity index 6) (figure 2).

Treatment

After critical evaluation, we proceeded with a two-phase treatment to introduce the patient to simple appliances and reduce the complexity of the treatment while keeping in mind the less extensive therapy required later. The first phase of treatment included a Twin Block appliance with a high-pull headgear and facebow to correct the skeletal discrepancy by growth modulation (figure 3). In class II patients with increased lower facial height, high-pull headgear is used. Teuscher proposed that the downward and forward growth of the maxilla could be altered and that the mandible could also change its growth direction to a more forward and upward position with condylar adaptation using the high-pull headgear.¹ The objectives were to restrict the growth of the maxilla, enhance that of the mandible and control the eruption of the molars, thus correcting the skeletal class II relationship and improving his profile. Meanwhile, correction of the lip-biting habit, functional training of lip muscles and psychological counselling were necessary. In phase 2 treatment, a pre-adjusted edgewise appliance (0.022-inch slot brackets) was used to align and level the dentition and achieve a neutroclusion (figure 4).

Figure 3.

Phase 1 treatment showing headgear and Twin Block.

Figure 4.

Phase 2 treatment with pre-adjusted edgewise appliance.

Extraction was not required since the space to correct the mild crowding and proclination was achieved through expansion and interproximal reduction. The treatment duration of myofunctional therapy and fixed appliance therapy was 9 months each.

Outcome and follow-up

Post-treatment, we achieved a skeletal class I relation, pleasing profile, Angle’s class I normal occlusion and competent lips (figure 5). Radiographs confirm the skeletal and dental values towards the normal limits and exhibit root parallelism (figure 6; tables 2 and 3). The retention phase included a removable upper retainer and a lower fixed retainer.

Figure 5.

Post-treatment facial and intraoral photographs.

Figure 6.

Post-treatment radiographs.

Table 2.

Post-functional cephalometric analysis

	Normal values	Patient values	Inference
SNA (Sella–Nasion–A point angle)	82±2°	82°	Normally placed maxilla
SNB (Sella–Nasion–B point angle)	80±2°	79.5°	Backwardly placed mandible
ANB (A point–Nasion–B point angle)	2°	2.5°	Class II skeletal pattern
Effective maxillary length	92.1±4.1mm	95 mm	Normal for age
Effective mandibular length	114.4±4.3mm	117 mm	Normal for age For 95 mm maxilla, the mandible should be 122–125 mm, according to McNamara’s growth prediction. Hence, mandibular length is short by 8 mm for that maxilla.
FMA (Frankfort-mandibular plane angle)	17°–28°	23°	Average growth pattern
SN-GoGn (Sella-Nasion to Gonion-Gnathion angle)	32°	33°	Average growth pattern
Y-axis	53°–66°	65.9°	Average growth pattern
U1–SN (Upper incisor-Sella-Nasion angle)	102°	114°	Proclined upper incisors
U1–NA (Upper incisor-Nasion-Point A angle)
Linear	4 mm	6.7 mm	Forwardly placed upper incisors
Degree	22°	25.7°	Proclined upper incisors
L1–NB (Lower incisor-Nasion-Point B angle)
Linear	4 mm	8.3 mm	Forwardly placed lower incisors
Degree	25°	35.6°	Proclined lower incisors
L1–A-Pog (Lower incisor to Point A-Pogonion angle)	2 mm	5.9 mm	Normally placed lower incisors
U1–L1 (Upper incisor-Lower incisor angle)	135°	116°	Bidental proclination
IMPA (Incisor mandibular plane angle)	90°	105.8°	Proclined lower incisor
Cant of occlusion	1.5°–14°	8°	Normal
Nasolabial angle	90° –110°	100°	Normal
Lip strain		2 mm	Lip strain of 2 mm

Table 3.

Post-treatment cephalometric analysis

	Normal values	Patient values	Inference
SNA (Sella–Nasion–A point angle)	82±2°	82°	Normally placed maxilla
SNB (Sella–Nasion–B point angle)	80±2°	78.5°	Backwardly placed mandible
ANB (A point–Nasion–B point angle)	2°	2.5°	Class II skeletal pattern
Effective maxillary length	92.1±4.1mm	95 mm	Normal for age
Effective mandibular length	114.4±4.3mm	117 mm	Normal for age For 95 mm maxilla, the mandible should be 122–125 mm, according to McNamara’s growth prediction. Hence, mandibular length is short by 5 mm for that maxilla.
FMA (Frankfort-mandibular plane angle)	17°–28°	26°	Average growth pattern
SN-GoGn (Sella-Nasion to Gonion-Gnathion angle)	32°	33°	Average growth pattern
Y-axis	53°–66°	64°	Average growth pattern
U1–SN (Upper incisor-Sella-Nasion angle)	102°	106°	Proclined upper incisors
U1–NA (Upper incisor-Nasion-Point A angle)
Linear	4 mm	5.9 mm	Forwardly placed upper incisors
Degree	22°	26.3°	Proclined upper incisors
L1–NB (Lower incisor-Nasion-Point B angle)
Linear	4 mm	7.6 mm	Forwardly placed lower incisors
Degree	25°	28°	Proclined lower incisors
L1–A-Pog (Lower incisor to Point A-Pogonion angle)	2 mm	3 mm	Normally placed lower incisors
U1–L1 (Upper incisor-Lower incisor angle)	135°	119°	Bidental proclination
IMPA (Incisor mandibular plane angle)	90°	99°	Proclined lower incisor
Cant of occlusion	1.5°–14°	8°	Normal
Nasolabial angle	90°–110°	102°	Normal
Lip strain		2 mm	Lip strain of 2 mm

Discussion

The patient presented with a skeletal class II pattern due to an excess maxilla and a deficient mandible and growth potential indicated by the hand-wrist radiograph; therefore, it was essential to use a myofunctional appliance and extraoral forces for sagittal correction. Several studies show that a Twin Block, an Activator or a Herbst appliance can induce significant favourable growth modifications.

We used a Twin Block appliance, in this case, which Clark introduced in the 1980s.² The mode of action differs depending on the design. However, their effect is produced by the forces generated by stretching the muscles.³ There are several established advantages to the Twin Block functional appliance. It is durable, easy to repair, and suitable for permanent and mixed dentition.⁴ The Twin Block appliance has two advantages over the Herbst and Activator appliances. One advantage is that greater mandibular growth can be expected due to the duration and timing when the appliance is worn. Another advantage was the apparent lengthening of the mandibular ramus in our patient, which could be explained by greater vertical activation of the appliance (bite blocks must be at least 5–7 mm thick vertically).⁵

The mesialisation of mandibular molars was evident as a result of the Twin Block appliance, which led to an increase in the growth of the mandible. By decreasing the overjet with functional appliances, the patient’s confidence was established, and the risk of upper incisor injury was minimised.⁶ Even though the Twin Block appliance could provide a headgear effect, our experience showed unsatisfactory control of the maxilla. Therefore, a high-pull headgear was used to restrict the further growth of the maxilla and tip maxillary teeth distally and prevent posterior maxillary tooth eruption.⁷ In terms of soft tissue changes, the profile improved significantly.

Lower incisor proclination was not considered during the functional phase, as lower incisor capping in Twin Block appliances has proven ineffective.⁸ This was addressed during the fixed appliance phase, with interproximal reduction and expansion achieved. The appliances were removed after the patient’s satisfaction with the treatment outcome. Retainers were delivered, and the patient was instructed to wear them throughout the day. Furthermore, he was referred for regular check-up appointments.

Patient’s perspective.

My son had first complained to me about his forwardly inclined upper front teeth a year back when his friends had bullied him. This was the first time I had noticed. After a few days, we had an appointment with a dentist who thoroughly examined my child and explained the deformity and how it could be corrected easily with a few appliances.

We were then referred to an orthodontist for treatment. After the examination, we were instructed to take a few radiographs to find the underlying fault and remaining growth. The first stage of treatment began using a removable appliance called twin block, which was to posture the lower jaw forward along with a headgear appliance, a strap worn over the head attached to the appliance within the mouth. This was to restrain the unwanted growth of the upper jaw.

Initially, he had discomfort with the twin block appliance, and soon as he got adjusted, its removal caused mild pain after 3 months. We had monthly appointments with our orthodontist for supervision and to adjust the appliance. Although my son had shown a gradual loss of interest in wearing the appliance, the improvement in his lower jaw growth was a significant motivation to continue using it. He had only used the headgear appliance at home, fearing his peer group bullying him. He had shown a positive attitude for the entire treatment duration of 18 months. We are happy with the overall treatment results and how his face has improved significantly.

Learning points.

• This is the most prevalent case describing the correction of class II skeletal discrepancy in a growing patient.

• Two-phase therapy was required to treat this patient successfully.

• Timely intervention, strategic uses of appliances and utilisation of the innate growth potential are the key to a successful dentofacial orthopaedic therapy.

Ethics statements

Patient consent for publication

Parental/guardian consent obtained.