Dental Concepts Article in the journal of Indian Orthodontic society
Indian Board of Orthodontics Case Report: Management of a Skeletal Cl II Malocclusion Using Two-phase Treatment with a Standard Twin Block Appliance

Hrushikesh Aphale


NK, a 12-year-old male patient, presented with a Class II division 1 incisor relation on Class II skeletal base with a decreased maxillomandibular plane angle and decreased the face-height ratio. He had a convex profile, incompetent lips, lip trap, deep Mentolabial Sulcus, everted lower lip and a positive VTO (Visual Treatment Objective). Intraorally, he presented with bilaterally Angle’s Class II molar relation and canine relation, scissor bite in the region of first premolars bilaterally, a closed bite and a 13 mm overjet. He presented with mild spacing in the upper arch and mild crowding in the lower arch with a pronounced curve of Spee. This was further complicated as the LR6 was Endodontically treated and temporarily restored; also, enamel hypoplasia was seen in all permanent first molar region. The treatment was carried out in two phases, Phase I involved growth modulation done with a twin block appliance, and Phase II was the post functional orthodontic phase for dental corrections and finishing and detailing of occlusion, which was done with a pre-adjusted edgewise appliance (0.022 × 0.028˝ slot) with MBT (McLaughlin, Bennett, Trevisi) prescription. The posttreatment results were highly satisfactory, showing improvement in facial esthetics and occlusal traits as well as good long-term stability as was evident in the 3-year retention records.


Class II malocclusion, Indian Board of Orthodontics case report, twin block appliance, functional appliance, two-phase treatment


The most common skeletal problem in orthodontics is the Class II malocclusion characterized by mandibular deficiency.1-5 Many methods for the orthodontic management of skeletal Class II malocclusion are published in the literature. However, when conducive growth is available, with respect to the timing of treatment and growth vector, growth modulation is the most favored modality of treatment. Out of the array of the removable functional appliances available, “the Standard Twin Block appliance” is preferred by many clinicians due to the ease of use by the patient and ease of management of the appliance. It was first introduced by Clark in 19886 and consists of two separate, upper and lower, removable plates with acrylic blocks trimmed to an angle of 70°. These separate plates make the twin block appliance different in comparison with other removable functional appliances, which are basically monoblocks. Theoretically, this plus a less bulky appearance would increase patient acceptance of the appliance. Patients would also have more freedom in their mandibular movements. All these considerations could conceptually produce different treatment results compared with the removable functional monoblocks.7 The following case, the report illustrates the use of a standard twin block appliance for skeletal correction of a Class II division 1 malocclusion in a 12-year-old male patient.

Case Report

Section I

Pretreatment assessment: History and clinical examination NK, a 12-year-old boy, came with a chief complaint of forwardly placed upper front teeth and presented with a Class II division 1 incisor relation on Class II skeletal base with a decreased maxillomandibular plane angle and decreased face-height ratio. He had a convex profile, incompetent lips, lip trap, deep Mentolabial sulcus, everted lower lip and a positive VTO (Visual Treatment Objective).

Relevant Dental History

The patient had a history of root canal treatment of the lower right, first molar.
He also had a history of orthodontic consultation. Clinical examination: Extraoral features

Figure 1. Pretreatment Extraoral Photos.

Figure 2. Pretreatment Intraoral Photos.

Skeletal Assessment

The patient shows an acceptable facial symmetry and balance on frontal examination. He shows convex profile due to Class II skeletal pattern, progenia due to prominence of chin button, low clinical FMA and reduced lower anterior facial height proportion.

Soft Tissues

Upper and lower lips are incompetent at rest, showing severe lip strain observed with oral seal. The lower lip is everted with a lip trap and a deep Mentolabial sulcus and a decreased nasolabial angle. Clinical examination: Intraoral features (Figures 2 and 18)

General Dental Condition

The general dental condition showed an occlusal composite resin restoration on lower left first molar. History of Endodontically treated lower right first molar with a blue-colored composite resin temporary restoration. Non-fluoride enamel opacities resembling enamel hypoplasia was seen on all the first molars. Improper contact (post-restoration) was noted between the lower right second premolar and lower right first molar.

Maxillary arch:

– Ovoid arch form
– Mild spacing in the upper anterior region
– Proclined upper anterior
– Mesial out rotations of all premolars and distal in
rotations of canine
Mandibular arch:
– Ovoid arch form
– Mild crowding in the anterior with a pronounced curve
of Spee
Other features:
– lingually tipped lower right canine, distal out the rotation of
lower left first premolar and second premolar, and mesial
out the rotation of lower right second premolar
– Improper contact of restored lower right first molar and
the rotated second premolar

Occlusal Features

Incisor relationship: Class II Overjet: 13 mm Overbite: Closed bite with upper anterior covering more than 100% of lower incisors. Left buccal segment relationship: Full unit Class II Image

Figure 3. Pretreatment Radiographs

Right buccal segment relationship: Full unit Class II Other occlusal features: Scissor bite (buccal non-occlusion) seen with upper first premolars with respect to the lower canines and premolars bilaterally and a deep curve of Spee on both sides. General radiographic examination (Figure 3) Pretreatment radiographs taken were panoramic radiographs, a lateral cephalogram along with IOPAs (Intra Oral Periapical) of the lower first molars. Panoramic
radiographic examination revealed the presence of unerupted second and third molars in all four quadrants. The alveolar bone levels and root morphologies of the teeth were normal. Temporomandibular joint space appeared optimal with normal size, shape, and position of condyle heads. The IOPAs and the panoramic radiograph also showed Endodontically treated lower right first molar (obturation filling short of apex in both the roots) and recurrent caries with lower left first molar.

The cephalometric evaluation revealed skeletal Class II jaw bases, horizontal growth pattern, decreased lower anterior facial height and facial height ratio, mild Proclination of the maxillary incisors, increased overjet and overbite, convex profile and acute nasolabial angle. Skeletal maturity was assessed using the cervical vertebral maturation index (CVMI) staging, which showed Stage 2 of skeletal maturation (acceleration stage, with more than 65%–80% pubertal growth still remaining). The timing of peak mandibular growth was assessed by using the cervical vertebral maturation staging. The findings indicate the CS3, that is, peak in the mandibular growth can occur during the year after this stage.

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