Dentofacial orthopaedics for class II malocclusion with vertical maxillary excess in growing children

Introduction

The skeletal class II malocclusions with vertical maxillary excess (VME) exhibit an excessive gummy smile and a long face. These patients have a vertical growth pattern of the face with greater contribution from mid face. The craniofacial growth pattern is established early in childhood. Besides having a familial tendency, vertically growing class II children may also be adversely affected by the superimposed oral mode of respiration, leading to a lowering of the tongue and backwards rotation of the mandible. The maxillary buccal segments tend to compensate for the backwards rotation of the mandible by supra eruption of the molars to maintain occlusion contacts.

In addition to anterior maxillary excess, the patients with VME show maxillary vertical and maxillary descent features in the buccal region. Consequently, the palatal plane on the cephalogram shows an upward tilt in the region of the anterior nasal spine, a long dento-alveolar segment, but inclined downward in the molar region. The mandible is retrognathic, with a thin recessive chin. The growth of the ramus is inadequate; the gonial angle is large, leading to backward growth rotation and an increase in anterior face height ( Fig. 65.1.i ).

Image, AltText currently not available — Figure 65.1.i

These vertical grower patients with unique skeletal patterns are likely to benefit from a therapy which, in addition to encouraging sagittal mandibular advancement, can also restrain the vertical descent of the buccal segments of the maxilla, thereby allowing mandible and the chin to rotate in a counterclockwise fashion. These cumulative benefits improve the facial skeleton and soft tissue profile.

The rationale of combined headgear activator appliance therapy

The conventional functional activator therapy in class II growing patients brings significant dentoalveolar changes in the mandible and maxilla. ^, With distal inclinations of maxillary buccal teeth, the mesial and vertical eruption of mandibular buccal teeth combined with anterior displacement of the mandible, sagittal correction in maxilla-mandibular relations is achieved. The activator therapy restrains the sagittal growth of the maxilla and increases buccal maxillary vertical height.

The maxillary growth can be restrained effectively with cervical headgear but not without side effects of molar extrusion, which are not desirable in high-angle cases. Most of the fixed appliance orthodontic mechano-therapies are extrusive on anchorage molars. The extrusion of buccal segments is more prominent, particularly when the vertical chains of the jaw muscles are weak. The masticatory forces are unable to counter orthodontic extrusive forces, which cause an opening of the mandibular plane angle. With each millimetre of extrusion of the molars, the mandibular plane angle opens by 2.5 degrees, which has detrimental effects on the chin profile.

Therefore, a high pull facebow attached to the activator or such an appliance is expected to provide greater cumulative skeletal growth adaptation than when treated alone with an activator or headgear appliance. Class II division 1 malocclusion correction in high angle growing children is desired using high-pull headgear-activator combination therapy to produce restriction of forward maxillary growth, inhibition of the mesial and vertical displacement of the maxillary teeth, simultaneous improvement of the buccal occlusion and condyle glenoid fossa remodelling.

The main purpose of the headgear attached to the activator is to enhance the effectiveness of the sagittal correction by inhibiting vertical growth of the maxilla, restraining the growth of the maxilla in the sagittal and vertical direction, which helps in autorotation of the mandible. This phenomenon eliminates the ill effects associated with the extrusion of molars and benefits by encouraging further forward mandibular posture and an upward/anti clockwise rotation. ^, ^,

Concepts and desired effects

The problems of vertical control of the maxilla have been overcome in part by the utilisation of high-pull vectors of extraoral traction with the Kloehn type of facebow. Nonetheless, the creation of an acceptable facial profile for patients presenting with a divergent facial pattern continues to pose significant treatment challenges. When used alone, the headgear can transfer distally directed headgear forces from the maxilla via dentition to the mandible, which might prevent its forward relocation.

Ullrich Teuscher has described a combined activator-headgear therapy in 1978. He advocated the use of a high-pull headgear with the activator to counteract the undesired maxillary side effect of headgear alone. His therapy is also called headgear-activator Teuscher appliance (HATA). The objectives of combined activator headgear therapy are :

Maxilla

1.
Inhibition of the maxillary sagittal and vertical growth vectors of the dentoalveolar process and dentition.
2.
Restraint on the maxillary basal structures counter to the line of development.
3.
Restrain of maxillary dentition.

Mandible

1.
Unlocking the occlusion.
2.
Selective vertical management of mandibular molar eruption.
3.
Stimulation and redirection of condylar growth.
4.
Inducing a downward remodelling pattern of the glenoid fossae.

A case treated with combined activator headgear therapy is depicted in Fig. 65.1 .

Case NS, age: 10 years, class II division I malocclusion, with a maxillary protrusion, large overjet showed a vertical growth pattern. After a year of combined activator headgear therapy, class I molar and canine relations and normal overjet were attained. A fixed appliance was used to detail the occlusion. A significant improvement in profile and lip seal improved the patient’s confidence. The upper and lower molars have a superclass I relationship with normal overjet, and overbite was maintained. Cephalogram showed improved inclination of the palatal plane and sagittal skeletal relations. Although the case shows an increase in anterior face height for such a severe case, the results are acceptable.

Research on determining the centre of resistance for the application of extra-oral force

Determining the centre of resistance: According to Teuscher and Stockli and Teuscher, the centre of resistance (C _Res) of the nasomaxillary complex corresponds to a point just below the zygomatico-maxillary buttress, and that of the maxillary dental arch lies somewhat between roots of upper premolars. By directing the extraoral force between the respective centres of resistance, differential reaction patterns of the maxilla and dentition are observed ( Fig. 65.2 ).

There are differing research studies on the exact location of the centre of resistance of the nasomaxillary complex. ^, Finite element analysis (FEM) studies concluded that the centre of resistance of the nasomaxillary complex lies on the posterosuperior ridge of the pterygomaxillary fissure.

Billiet et al. used holography to study the centre of resistance of the nasomaxillary complex and dentition with extraoral traction using a model of the macerated skull. They concluded that pure translation of the nasomaxillary complex and dentition occurred when a force vector passed by in the area of the key ridge. Their study could not distinguish between the centre of resistance of the nasomaxillary complex and upper dentition.

Jorge et al. studied the biomechanical effects of stresses transmitted to the maxilla and teeth by a Teuscher’s activator (TA) for different extraoral force lines of action. They created a FEM model on a CT scan of a skull and simulated activator headgear appliance using force at 0, 15, 30, 45 and 60 degrees to the occlusal plane. They concluded that 30 degrees is the most compatible with the objectives of the hyperdivergent class II malocclusion treatment in growing patients ( Fig. 65.3 ).

Case selection, ^, ^, ^, and bite recording

The selection of an appropriate case based on the nature of malocclusion, the assessment of the patient’s expected cooperation and the prediction of prognosis are critical steps before initiating therapy. This process relies on a thorough clinical examination analysis of records and clinical judgement based on experience in managing such cases of malocclusion.

Nature of malocclusion

The application of an activator headgear set-up is indicated if a skeletal class II malocclusion is present in growing subjects in which an anterior movement of the chin prominence is desirable and little posteriorly directed maxillary dentoalveolar reaction is acceptable. High angle cases with moderate vertical excess are indicated for combination therapy ( Fig. 65.1 ). ^, ^,

The activator-headgear combination can be utilised for class II correction in the deciduous, mixed or permanent dentition. The optimal developmental stage for this therapy is early mixed dentition, characterised by the eruption of all permanent incisors and the deciduous teeth still maintaining sufficient firmness to provide adequate anchorage.

The activator headgear is also well suited for retention of a corrected class II. When used for retention purposes, the construction bite is recorded with little sagittal advancement of the mandible combined with a vertical opening.

Contraindications

1.
Dental class II situations with a skeletal class I profile should not be treated with this appliance therapy.
2.
Class II horizontal growers are not prescribed to this type of appliance therapy.
3.
Patients with hypodivergent skeletal patterns such as class II division 2 and of the ‘Deckbiss’ type with severe vertical deficiencies.
4.
An unfavourable period for starting activator-headgear treatment is when the deciduous teeth in the buccal segment are loose, or most of them shed with little anchorage available in the buccal segment.

Bite recording

Before the activator headgear therapy is instituted in children with a narrow maxilla, these children can receive a short phase of maxillary expansion with W-appliance or rapid maxillary expansion. Two sets of working models are prepared with alginate impressions to record the bite. The first set of models is used for appliances, and the second for the records. The models should be diligently checked for the accurate reproduction of occlusal surfaces, palatal area and lower lingual flange area.

The bite is recorded with a moderate vertical displacement of the mandible slightly beyond freeway space and anterior displacement not exceeding 6 mm. In patients with large overjet, two step activations are performed.

A horseshoe-shaped wax rim is prepared on lower working models that do not distally extend beyond the last erupted tooth. The recorded bite should be rechecked in the patient’s mouth before it is mounted on an articulator. A greater vertical component of the bite is considered for vertically growing children.

Appliance design

In 1978, Teuscher presented a preliminary report on an activator design of a palatal bar, lower lip pads and torque-control auxiliaries for the upper incisors. Lip pads are not used now.

The appliance parts are (1) acrylic components, (2) metal framework and headgear tubes, (3) facebow and (4) high-pull headgear.

Acrylic components

The appliance is constructed with heat cure acrylic as a palate-free activator. The upper part of the appliance provides anchorage in the maxillary arch with coverage on all occlusal and incisal surfaces of the teeth. Laterally, the acrylic is extended to the buccal cusps. The acrylic is extended towards the palatal vault in the buccal segment from the mesial of the canine. The acrylic extends laterally to the buccal cusps while covering the incisor’s labial surfaces and canines by about 2 mm.

In the mandibular arch, the appliance on the lingual side is extended down as far as the floor of the mouth permits. The acrylic is extended to the buccal cusps of the posterior teeth, and all teeth touch the appliance on their lingual and buccal surfaces. The canines and incisors are covered labially with about 2–3 mm acrylic to secure good anchorage. Any undercuts, if present, are partly blocked before constructing the appliance. Adequate relief is provided to the lingual frenum. The lingual acrylic over the lower incisors must extend to the gingival level, and the occlusal details of the lower buccal segments must be retained where possible.

The acrylic base must cover one-third of the lower incisors, and the upper incisors should be covered on the palatal side up to one-half and on the labial side only up to the incisal edges.

Metal framework

The metal components of the appliance are (1) torque springs of maxillary incisors, (2) a coffin spring and (3) activator-headgear tubes.

Torque springs

With the activator-headgear assembly, the applied forces are transmitted eccentrically from the acrylic covering the occlusal and incisal portions of the teeth. The bodily control over the incisors is lacking, which is why incisor crowns tend to tip palatally because of the posteriorly directed component of the force vector. The torquing springs are attached to counteract the tendency of the interior crowns to tip palatal. The springs are fabricated from 0.5 mm (0.020 in.) resilient stainless-steel wire. The torquing springs provide palatal root tipping forces to the upper incisors. The springs at their gingival end contact the upper incisors, placed 1–2 mm short of the gingival margin. These are bent to provide a point of contact at their gingival end, while the rest of the springs remain out of contact with the clinical crown. Their free ends are retained in the inter-incisal wax block ( Fig. 65.4 ).

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Dentofacial orthopaedics for class II malocclusion with vertical maxillary excess in growing children

Introduction

The rationale of combined headgear activator appliance therapy