Skeletal and dental discrepancies cause asymmetric malocclusions in orthodontic patients. It is difficult to achieve adequate functional occlusion and guidance in patients with congenital absence of a mandibular incisor due to the tooth-size discrepancy. Here, we describe the orthodontic treatment of a 22-year-old woman with an asymmetric Angle Class II malocclusion, mandibular deviation to the left, and 3 mandibular incisors. The anterior teeth and maxillary canines were crowded. We used an improved superelastic nickel-titanium alloy wire (Tomy International, Tokyo, Japan) to compensate for the asymmetric mandibular arch and an asymmetrically bent archwire to move the maxillary molars distally. A skeletal anchorage system provided traction for intermaxillary elastics, and extractions were not needed. We alleviated the crowding and created an ideal occlusion with proper overjet, overbite, and anterior guidance with Class I canine and molar relationships. This method of treatment with an asymmetrically bent nickel-titanium alloy wire provided proper Class I occlusion and anterior guidance despite the mandibular deviation to the left and 3 mandibular incisors, without the need for extractions.
Highlights
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A Class II patient had mandibular deviation and 3 mandibular incisors.
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We used an asymmetrically bent improved superelastic nickel-titanium alloy wire (ISW) in an asymmetric mandibular arch, without extractions.
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Proper Class I occlusion and anterior guidance were achieved.
The presence of only 3 mandibular incisors and, in particular, the congenital absence of a mandibular lateral incisor, is more prevalent in the Japanese population than in other populations. In these patients, it is difficult to establish a proper occlusion, due to morphologic and esthetic issues. Previous clinical studies have reported various treatment plans for achieving good occlusion in patients with 3 mandibular incisors. However, the conventional treatment methods increase overbite and overjet, due to insufficient stripping (ie, interproximal reduction) of the maxillary anterior teeth, and both anterior and lateral guidance are impaired. If a mandibular incisor is not extracted in these patients, 6 anterior teeth in the maxilla would have to match 5 anterior teeth in the mandible. Although such occlusions are regarded as unesthetic, due to the discordance of the maxillary and mandibular midlines, ideal occlusion and anterior guidance during mandibular movement can be achieved with appropriate dental compensation, despite nonextraction of a mandibular incisor.
In previous reports, the improved superelastic nickel-titanium alloy wire (ISW) (L&H Titan; Tomy International, Tokyo, Japan) has been used as a working archwire for clinical orthodontic treatment, by incorporating bends that were achieved with a heated bending machine.
We here describe the treatment of a patient with an asymmetric Class II mandibular deviation to the left and 3 mandibular incisors. We discuss a new method for achieving proper dental compensation of the asymmetric mandible by using an asymmetrically bent ISW without extraction. Such a wire can be skewed horizontally to the opposite side of mandibular shift and facilitates incorporation of asymmetric torque.
Diagnosis and etiology
The patient was a 22-year-old woman with chief complaints of crowding of the mandibular anterior teeth and the maxillary high canines. Pretreatment facial photographs showed a straight profile and mild protrusion of the upper and lower lips, both of which exceeded the E-line (upper lip, 1.9 mm; lower lip, 2.8 mm) ( Fig 1 ). The mandibular right lateral incisor was congenitally missing, and the center of the mandibular left central incisor was consistent with the facial midline. The maxillary midline deviated to the left by 2.0 mm from the facial midline. The left molar relationship was Class I, whereas the right molar relationship was Class II. The patient had an overjet of 3.0 mm and an overbite of 4.0 mm. Dental cast analysis showed arch length discrepancies of −8.0 mm in the maxilla and −3.5 mm in the mandible ( Fig 2 ).
Panoramic and lateral and posteroanterior (PA) cephalometric radiographs were taken before treatment ( Fig 3 ).
Cephalometric analysis showed a skeletal Class II relationship (ANB angle, 5.6°) with maxillary protrusion (SNA angle, 87.0°). The inclinations of the maxillary and mandibular incisors were within the normal ranges ( Table I ). The occlusal cant was inclined 2° upward to the left, and the mandible deviated by 3.0 mm to the left of the facial midline in the PA cephalometric analysis.
| Japanese norm | Pretreatment | Posttreatment | Retention | |
|---|---|---|---|---|
| SNA (°) | 82.3 ± 3.5 | 87 | 86.6 | 86.6 |
| SNB (°) | 78.9 ± 3.5 | 81.4 | 81.4 | 81.4 |
| ANB (°) | 3.4 ± 1.8 | 5.6 | 5.2 | 5.2 |
| FMA (°) | 28.8 ± 5.2 | 27.5 | 27.5 | 27.5 |
| U1 to SN (°) | 104.5 ± 5.2 | 106.7 | 108.6 | 108.6 |
| IMPA (°) | 96.3 ± 5.5 | 99.7 | 98.4 | 98.4 |
| Interincisal angle (°) | 124.1 ± 7.6 | 118.7 | 118.1 | 118.1 |
Based on these findings, we diagnosed the patient as skeletal Class II with an asymmetric molar relationship, mandibular deviation to the left, and 3 mandibular incisors.
Treatment objectives
The treatment objectives for this patient included (1) eliminating crowding, (2) creating an ideal occlusion with proper overjet and overbite, (3) achieving proper anterior and lateral guidance with Class I canine and molar relationships, and (4) aligning the midline of the maxillary incisors with the facial midline and with the center of the mandibular left central incisor. Thus, we planned to distalize the maxillary molars (right, 2.5 mm; left, 1.0 mm), strip a total of 2.7 mm in the 6 maxillary anterior teeth, and expand the dental arches (maxillary canine width, −3.0 mm; maxillary first molar width, +1.0 mm; mandibular canine width, +2.0 mm; mandibular first molar width, +2.0 mm).
Treatment objectives
The treatment objectives for this patient included (1) eliminating crowding, (2) creating an ideal occlusion with proper overjet and overbite, (3) achieving proper anterior and lateral guidance with Class I canine and molar relationships, and (4) aligning the midline of the maxillary incisors with the facial midline and with the center of the mandibular left central incisor. Thus, we planned to distalize the maxillary molars (right, 2.5 mm; left, 1.0 mm), strip a total of 2.7 mm in the 6 maxillary anterior teeth, and expand the dental arches (maxillary canine width, −3.0 mm; maxillary first molar width, +1.0 mm; mandibular canine width, +2.0 mm; mandibular first molar width, +2.0 mm).
Treatment alternatives
First, we considered the PA position of the mandibular incisors. Because the patient had a slightly protrusive facial profile, a mandibular deviation to the left, and 3 mandibular incisors, we discussed incisor extraction or premolar extraction on the nonaffected side. However, no extraction of the mandibular tooth was indicated, because the discrepancy was minor. On the other hand, it was difficult to gain space for prosthetic treatment of the missing lateral incisor. Therefore, mandibular crowding required improvement by extraction of the third molars, expansion of the mandibular arch, and uprighting of the molars.
Two approaches were considered for the maxillary arch. One was extraction of the right first premolar and the left second premolar. The other was asymmetric molar distalization, with extraction of the third molars. Finally, we selected the latter plan, to consider the patient’s wish for no extraction of premolars.
Treatment progress
Before orthodontic treatment, 4 impacted third molars were extracted, and a Y-shaped anchor plate (Orthoanchor SMAP; Dentsply-Sankin, Tokyo, Japan) was inserted between the maxillary right first and second molars to reinforce anchorage and to move the molars distally. In addition, an orthodontic miniscrew (Dualtop; Jeil Medical, Seoul, Korea) was inserted between the maxillary left second premolar and first molar to reinforce anchorage and to move the molars distally.
Orthodontic tooth movement was performed with 0.018 × 0.025-in slot preadjusted brackets (Dentsply-Sankin and Tomy International, Tokyo, Japan) and 0.016 × 0.022-in ISW in all treatment stages.
First, nickel-titanium open-coil (100 gf) springs (Tomy International) were placed between the second premolars and first molars on both sides to move the first and second molars distally, while concurrently leveling the posterior teeth. On the right side, we ligated the mesial end of the open-coil spring directly to the anchor plate, without touching the second molar, to prevent a reciprocal reaction. On the left side, we ligated the second premolar to the miniscrew to prevent a reaction of the open coil and reinforce the anchorage. Canine and premolar distalization were performed (Pro-Chain; Dentsply-Sankin) concurrent with first and second molar distalization in the maxilla ( Fig 4 , A ). After molar distalization, anterior retraction toward the right side and intrusion of maxillary incisors progressed, with stripping to correct the tooth-size discrepancy and to align the midline of the maxillary incisors with the facial midline.
In the mandible, crowding was improved by expansion and uprighting the molars using the ISW with a reverse curve and the intermaxillary Class III elastics (3/16 Medium-Light; 3M Unitek, Monrovia, Calif) ( Fig 4 , B ). At the same time, the maxillary second premolars were tied with the skeletal anchorage system to prevent downward and forward reactions. The mandibular archwire had to be adjusted by skewing it to the right side to maintain the arch form adequately. This asymmetrically bent ISW was used to establish proper tooth contacts, because of excessive lateral overjet on the right side due to the mandibular deviation to the left and the presence of 3 incisors in the mandible. The mandibular arch showed dental compensation of unilateral expansion and torque control of the right side. The excessive offset was bent between the right central incisor and canine, and excessive crown-buccal torque was applied for the right canine and molars. Furthermore, caplin hooks were bonded to the lingual sides of the mandibular right second premolar and the first molar. A combination of intermaxillary cross elastics was used on the right side to facilitate change in the mandibular arch form with the ISW. At the same time, the mandibular left canine and molars were tilted by means of the excessive crown-lingual torque ( Fig 5 ). After achieving dental compensation with the asymmetrically bent ISW, the mandibular arch form was gradually adjusted toward an ideal arch form in the detailing stage.
