A 21-year-old woman visited the outpatient orthodontic clinic of Okayama University Hospital with the chief complaint of a protruding maxillary right central incisor. She desired nonsurgical treatment with invisible appliance. Front and profile facial photographs showed a symmetrical face, convex profile and protruded and incompetent lips (Fig 1). Mentalis muscle strain was seen, and a slightly gummy smile was observed. An intraoral examination revealed an excessive 8.0-mm overjet (OJ), with Angle Class III molar relationships on both sides and bilateral congenitally missing mandibular canines. A Class II division 1 incisor relationship, with anterior open bite (AOB) and tongue thrusting habit was observed. She had no family history of the same open bite condition. Anterior mild crowding was also observed in maxillary and mandibular arches. The upper dental midline almost coincided with the facial midline; however, the lower dental midline was shifted 1.0 mm toward left. Panoramic radiograph confirmed the absence of mandibular canines on both sides, and two midline supernumerary teeth were detected at the maxillary central incisors region (Fig 1K). Cone-beam computed tomography showed no pathological problems in the root structure of maxillary central incisors on either side (Figs 1L to 1M). The patient reported clicking sounds in the temporomandibular joint without pain during maximum opening on the right side. The interincisal distance on maximum opening was 44 mm.
In comparison to the Japanese female norms, cephalometric evaluation showed a mild skeletal Class II jaw relationship (ANB = 4.5 ; SNA = 83.0 ; SNB = 78.5 ). Although her lower facial height ratio was normal (N-Me = 125.5 mm; Me-PP = 71.5 mm), with normal mandibular plane angle (FMA = 29.0 ) (Fig. 1J, Table 1), a decreased overbite of -1.0 mm was observed, since she had two distinct upper occlusal planes. The maxillary incisor angle was increased (U1-SN = 114.0 ), and the mandibular incisor angle was slightly reduced (L1-Mp = 87.5 ). The lower lip was slightly protruded against the aesthetic E-line (upper = 0.0 mm; lower = +2.5 mm). Given the above findings, the patient was diagnosed with a mild skeletal Class II jaw-base relationship; increased OJ, due to the bilateral congenitally missing mandibular canines; and Angle Class III malocclusion with AOB.
The primary treatment objectives were to correct the increased OJ with substitution of the mandibular canines by the first premolars, and the AOB without extruding the maxillary and mandibular incisors; create lip sealing and improve facial aesthetics. Additional objectives included Class III molar correction and establishment of functional occlusion. Based on the primary objectives, extraction of the maxillary first premolars was considered to correct the OJ. The use of temporary anchorage devices (TADs) was also planned to control the vertical relationship of maxillary molars.
Another conservative approach involves maxillary molar distalization using TADs, and extraction of the maxillary third molars. However, this option increases the risk of AOB, since vertical control is difficult. After a thorough discussion of these options, the patient agreed with the premolar extraction treatment plan, with lingual brackets in the maxillary arch and labial brackets in the mandibular arch.
After extraction of two supernumerary teeth, a transpalatal arch was inserted in the maxillary arch (Figs 2A - 2D). Two TADs were also implanted at the buccal side of the maxillary molar region of both sides, to control the vertical relationship of posterior teeth. Four weeks after implantation, a 0.018-in preadjusted Edgewise appliance (iPass , Dentaurum, Pforzheim, Germany) was placed, with sectional 0.016 x 0.022-in NiTi wires in the maxillary posterior segment. Two months after leveling and alignment, 0.016 x 0.022-in stainless steel (SS) archwire was installed to initiate the vertical anchorage control of the maxillary molars, using an elastomeric chain from the TADs to the segmental wires (Figs 2E - 2H). After 4 months of molar intrusion and bilateral maxillary first premolars extraction, the maxillary lingual brackets (STb , Ormco, Glendora, CA, USA) by indirect bonding system and the mandibular labial brackets (iPass , Dentaurum, Pforzheim, Germany) by direct bonding system were placed, then the alignment was initiated by inserting 0.014-in NiTi wires in both arches (Figs 2I - 2P).The wire size was increased to 0.016 x 0.022-in NiTi. For space closure and anterior teeth retraction of the maxillary arch, a loop mechanic with 0.017 x 0.025-in SS was used (Figs 2Q - 2T). Detailing and finishing were achieved using 0.016 x 0.022-in beta-titanium-molybdenum wire in both arches (Figs 2U - 2X). After 35 months of active treatment, a circumferential double retainer with a tongue crib in the maxillary arch and a lingual bonded retainer in the maxillary and mandibular arches were used as retention appliances. 
Compared to the pretreatment photographs, the posttreatment photographs showed retraction of the upper and lower lips, which subsequently improved the patient's facial profile and the relief of lip incompetence (Figs 3A-3I). Although the missing mandibular canines were substituted by mandibular first premolars, well-aligned arches and good interdigitation were achieved, with Angle Class I molar relation (Figs 3A-3I). By means of the extraction of maxillary first premolars and retraction of maxillary anterior teeth, an ideal overjet of 2.0 mm and an overbite of 2.0 mm were also achieved (Table 1). The posttreatment panoramic radiograph showed acceptable root parallelism, with no significant root resorption, except for slight apical root resorption of the maxillary right second premolar (Fig 3K). Superimposition of the pre- and posttreatment cephalometric tracings showed that the maxillary and mandibular incisors inclination was normalized (Fig 4). The mild skeletal Class II relationship was improved due to the slight reduction in the SNA angle (Table 1). The vertical dimension was maintained after orthodontic treatment. 
In the evaluation using a jaw movement recording system with six degrees of freedom (Gnathohexagraph System, version 1.31; Ono Sokki, Kanagawa, Japan), a smooth increase in the condylar movement was observed during protrusive or lateral excursion (Fig 5, Table 2).The interincisal distance on maximum opening without pain was maintained at 45 mm. Good facial aesthetics and acceptable occlusion were maintained after 29 months of retention (Figs 6 and 7). Occlusal force and occlusal contact area were also increased, compared with before treatment (Table 3). The patient was satisfied with treatment results.