Step 1: Diagnosis (Establishment of Treatment Goals)

Individualized treatment goals in Sendai SF are established at the initial time of treatment.^1–3 This process is led by examining and analyzing the problem list developed for each patient. In our case example, a 37-year-old female presented with a prognathic profile and long face with facial asymmetry, an anterior open bite, and significant retroclination of the lower incisors (Fig. 22-1). According to the posteroanterior (PA) cephalometric radiograph, she had clear mandibular asymmetry. Cephalometric analysis to evaluate skeletal discrepancies was conducted based on five parameters: cephalometric template analysis (CDS analysis),⁸ McNamara analysis for points A and B, the A point nasion B point (ANB) angle, Wits appraisal,⁹ and Harvold analysis (Fig. 22-2). Results of the cephalometric analysis revealed her mandibular excess and excessive lower facial height due to vertical maxillary excess. These findings indicated her need for surgical correction with mandibular setback and reduction of lower facial height.

Based on the results of the cephalometric analysis, the patient’s treatment goals were established (Fig. 22-3). The amount of mandibular setback and the extent of decompensation of the incisors were evaluated as well. The amount of mandibular setback was predicted to be 10-mm on average and her denture relationship changed from Class III to Class II with open bite. In postsurgical orthodontics, 3-mm intrusion of upper molars and 5-mm protraction of lower dentition were needed to achieve the successful decompensation of her lower incisors and good Class I occlusion.

If using conventional surgical orthodontics, the patient would have been a candidate for two-jaw surgery since she had vertical problems in conjunction with anteroposterior and transverse problems. By using the SAS to intrude the maxillary posterior teeth, the need for two-jaw surgery was eliminated; the less invasive one-jaw surgical approach was all that was required.

At least 1 week before surgery, brackets were bonded indirectly and passive rectangular wires for stabilizing dentition and bone segments were prepared by a dental technician in a laboratory. The brackets and archwires were 0.022-inch and 0.016-inch × 0.022-inch stainless steel, respectively. Surgical hooks were soldered on the archwire (Fig. 22-4).

Step 2: Model Surgery

Model surgery is an essential step in Sendai SF and leads to the fabrication of the surgical splint that will maintain the transit occlusion postsurgically.

The facebow transfer process is used to transfer the maxillary model followed by the mandibular model onto a semiadjustable articulator. Based on the cephalometric prediction, the surgical movement is simulated. The patient needed mandibular setback of 13-mm on the right and 7-mm on the left (Fig. 22-5, A–C). The surgical simulation of mandibular movement should be parallel to the functional occlusal plane so that the posterior facial height is maintained (Fig. 22-5, D). As a result, many Class III cases will show Class II open bite immediately after surgery due to the occlusal interferences at the molar regions.

Other groups that promote SF treatment recommend establishing three-point contacts in model surgery to acquire stable occlusion and Class I molar relationships immediately after orthognathic surgery.^5,10,11 This is not necessarily required in Sendai SF. The surgical movement is aimed to correct the skeletal disharmony. It is the role of the SAS to achieve the proper occlusion postsurgically. Aymach and Kawamura described the attempt to achieve a three-point contact occlusion and close the open bite by counterclockwise rotation of the mandible will extend the pterygomasseteric sling due to the increase of posterior facial height. Such extension of the sling is closely associated with the postsurgical relapse seen with open bite.^12,13 Therefore other SF groups must apply more invasive two-jaw surgery in order to avoid the increase in posterior facial height.

With the surgical movement simulated, a surgical splint with four ball hooks and a lingual bar is fabricated (Fig. 22-5, E–G). Using a splint is essential to maximize the occlusal contact and to stabilize posterior support. Even though the molars cause occlusal interferences at this point in the treatment process, no cusp grinding of the molars is performed.

Since distalization of the maxillary molars and constriction of the maxillary dentition are needed at the early stage of postsurgical orthodontics, the surgical splint is usually placed at the mandibular dentition in Class III cases.

Step 3: Orthognathic Surgery

Accurate surgical technique has a major role in the success of Sendai SF. Achieving an appropriate osteotomy design, splitting, fixation technique, and proper condyle seating are key in conferring stable results.

The surgeons on the Sendai SF team use a modified design of a bilateral sagittal split osteotomy (BSSO) combined with a T-shaped bone mini-plate fixation.^14–16 The design has a buccal step laid adjacent to the mandibular second molar area. This design prevents condylar dislocation and therefore minimizes relapse (Fig. 22-6). Aymach and Kawamura have shown that for mandibular setback or advancement surgery, a modified BSSO and buccal step, combined with a T-shaped bone mini-plate fixation, optimizes the resistance and stability of the fixation when compared to a standard BSSO fixed with a single straight bone mini-plate.

The authors suggest avoiding the use of positional screws for osteotomy fixation, as they confer a high potential for torquing the condyle and consequentially shifting the occlusion. Using bone mini-plates provides a sufficient semirigid fixation that allows functional stability under minimal bone movement.^14,17,18

The patient underwent modified BSSO for mandibular setback. Her maxillary right second molar was extracted because of root fracture. This problem was caused by her general dentist prior to treatment. During the operation, Y-type and L-type orthodontic mini-plates were implanted at the zygomatic buttress and the mandibular body, respectively (Fig. 22-7). Immediately after surgery, the patient showed Class II profile and Class II denture with open bite. Although her profile appeared Class II, her skeletal relationship changed to skeletal Class I. Her mandible was maintained in the proper position using a surgical splint and training elastics at the canine regions (Fig. 22-8). No extraoral appliance, such as a chin cap, was required for maintenance.

Cephalometric superimposition of images at initial presentation and 9 days after surgery showed a 10-mm setback on average, in line with the treatment goal (Fig. 22-9).

Step 4: Orthodontic Treatment

Orthodontic treatment commonly starts 17 days after surgery. Usually 3 to 4 weeks are allowed for recovery and to enhance nutrition. However, in most Sendai SF cases postsurgical treatment begins 2 to 3 weeks after orthognathic surgery.

In the patient, leveling of upper and lower dentition started using 0.016-inch nickel-titanium (Ni-Ti) archwires (Fig. 22-10). The surgical splint was placed at the mandibular posteriors and modified to an occlusal splint by flattening the occlusal surface. It was used in order to not disturb the tooth movement of the upper dentition and to help with eating. Two months after surgery, rectangular Ni-Ti archwires were engaged and intrusion and distalization of maxillary molars and protraction of mandibular dentition were carried out (Fig. 22-11). The occlusal splint was discontinued at that time. In combination with intrusion and distalization of the maxillary posterior teeth and protraction of the mandibular dentition using SAS biomechanics, correction of her Class II denture was started. In addition to correction of the anteroposterior and vertical problems, transverse correction was needed. Constriction of the maxillary arch with buccolingual archwires was performed to allow for transverse decompensation.

Copper-nickel-titanium (Cu-Ni-Ti) archwires (0.019-inch × 0.025-inch) for mandibular use were engaged buccally and a 0.032-inch × 0.032-inch TMA lingual arch was placed (Fig. 22-12). In the lower arch, a 0.019-inch × 0.025-inch Cu-Ni-Ti archwire for maxillary use was engaged for expansion of the mandibular arch, as the mandibular posteriors showed excessive Wilson curve. In most Class III cases, occlusal interferences between the functional cusps of the upper and lower molars occur immediately after mandibular setback osteotomy because of transverse dental compensation. To remedy this problem, transverse decompensation by constriction of the upper arch and expansion of the lower arch is required (Fig. 22-13, A). With SAS biomechanics, the cusp to fossa relationship at the posterior teeth is corrected significantly and counterclockwise rotation of the mandible is then induced (Fig. 22-13, B). Anterior open bite is improved and rigid intercuspation is established (Fig. 22-13, C).