22.1 Indications
Key words: alternative to premolar extraction and mandibular advancement, chin hypoplasia and mandibular anterior protrusion are indications, combination with mandibular osteotomy, fitting anterior mandible height of 40 to 45 mm, mandibular retrognathia and anterior protrusion
Two initial criteria indicate anterior mandibular block rotation: horizontal chin hypoplasia and protrusion of the mandibular anterior teeth (Figs 22-1a and 22-1b).
Since the extent of the pubertal growth spurt is not always predictable, initial orthodontic treatment in childhood is often followed by secondary treatment after the end of skeletal growth. The orthodontic adjustment of a normal occlusion is aimed at even in cases of minor mandibular retrognathia and mandibular anterior crowding, which is accompanied by pronounced protrusion (Fig 22-1c). of the mandibular anterior teeth after resolution of the crowding and may occasionally show a tendency towards an open bite. Chin hypoplasia is not subjectively evaluated negatively, and mandibular retrognathia is ignored. In early adulthood, surgical intervention is readily avoided.
Figs 22-1a to 22-1c Diagrams of the surgical method of anterior mandibular block rotation. (a and b) Typical form of the mandibular anterior region with protruded incisors, chin hypoplasia, and anterior vertical mandibular height less than 45 mm. The osteotomy line is dotted, frontal and lateral view. (c) Anterior movement of the chin to augment the chin tip and compensate the incisor protrusion. The center of rotation is the mandibular central incisor, which moves in the occlusal splint. (Modified from Krüger1)
Early premolar extraction, orthodontic shaping of congruent dental arches, and surgical enlargement of the mandible after the end of the pubertal growth spurt could have been a target-oriented treatment path.
The alternative treatment path after this history is integration of a mandibular block rotation into the malocclusion correction. The orthodontic treatment result achieved so far can only be influenced by tilting the mandibular anterior teeth.
The aim of this adjuvant method is:
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to adjust the mandibular anterior teeth axially with the alveolar process and thus orthograde
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to improve the chin prominence individually at the same time
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to increase the anterior mandibular height.
Anterior mandibular block grafting can also be an adjuvant treatment measure for mandibular advancement. Since the geniohyoid muscles are also tightened in the process, a positive effect on the widening of the pharyngeal airway is also achieved.
Anterior mandibular block rotation is also suitable as an adjunctive measure at the end of a maxillomandibular osteotomy for malocclusion correction if the initial criteria are the same.
Very precise treatment planning is required to successfully perform surgical advancement of the mandible with simultaneous premolar extraction and subsequent orthodontic gap closure to establish a normal sagittal anterior step in the case of mandibular retrognathia with an Angle Class II and orthodontically induced mandibular anterior protrusion (Fig 22-1c).
In selected individual cases of mandibular retrognathia with juvenile arthrosis deformans of both temporomandibular joints (TMJs), the predisplacement distance of the receded mandible can be distributed between the sagittal cleft and the block rotation so that the resulting tension of the mandibular soft tissue mantle is reduced and the pressure on the TMJs is slight. TMJ pain, resorption, or dislocation can thus be minimized.
The ideal anterior mandibular height for block rotation is 40 to 45 mm from the incisal edge of the anterior teeth to the gnathion. Even with lower anterior mandibular heights, a harmonious facial profile can be achieved depending on the size of the mandibular body. A larger mandibular height often requires a secondary vertical chin reduction, and vice versa, a lesser height may require a vertical chin augmentation.
In cases of larger anterior mandibular height, the bony continuity of the mandibular body can be preserved. This can via a segmental osteotomy/distraction for correction of mandibular anterior protrusion, and simultaneous chin augmentation (genioplasty) for contour improvement should be considered.
Krüger2 described in 1976 the anterior mandibular segmental osteotomy to close a skeletal anterior open bite (Figs 22-2a and 22-2b).
Figs 22-2a and 22-2b Anterior mandibular segmental osteotomy to close a skeletal anterior open bite (modified from Krüger2).
22.2 Surgical planning
Key words: LCR analysis, model surgery with splint adjustment, periodontal disease rehabilitation
Before planning for anterior mandibular block rotation, periodontal disease in the anterior mandibular vestibule should first be treated by improving oral hygiene, recession coverage, or mucosal grafts. Periodontal disease is common at this site because protrusion of the mandibular anterior teeth and hyperfunction and hyperplasia of the mentalis muscles complicate daily oral hygiene measures.
After orthodontic pretreatment, the mandibular symphysis with the mandibular central incisor is drawn through in the lateral cephalometric radiograph (LCR). In case of protrusion of the mandibular anterior teeth, the angle between the mandibular margin and the incisor axis (L1-MEGo) is increased. By rotating the block of symphysis and incisor, the inclination can be normalized to 90 to 100 degrees, and the chin prominence can be increased. If the anterior teeth are elongated, the entire anterior block can also be positioned more caudally, thus improving the curve of Spee. Prerequisites are an anterior mandibular height ≥ 40 mm and a mandibular MeGo angle ≤ 120 degrees.
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