This case report describes the lingual orthodontic treatment of an adult patient with Angle Class I malocclusion, agenesis of mandibular right central incisor, severe overjet and deep overbite, excessive proclination of maxillary and mandibular incisors, and midline discrepancy. Because of unique presentation, symmetric extraction could not be performed in the lower arch of this 34-year-old patient. She was treated with three premolar extractions and absolute anchorage with temporary anchorage devices for maximum retraction of upper anterior teeth. To correct the midline deviation and Bolton tooth-size discrepancy, the mandibular right lateral incisor, canine, and premolars were reshaped to reduce the mesiodistal width. The treatment approach greatly improved the patient’s facial and dental appearance and provided a stable occlusion.
Since their first introduction in 1979, lingual appliances have become popular as more adult patients are seeking esthetic orthodontic treatment [ ]. Lingual appliances are preferred by adults because of their invisible nature [ , ]; however, because of limited visibility, uncomfortable working posture, sensitive technique, long chairside time, and short interbracket span, they pose difficulties for orthodontists [ ]. Recent advances in lingual appliances, such as transition from mushroom archwire to straightwire concept and the application of multislot lingual brackets, have reduced these difficulties and improved the efficiency of lingual orthodontic treatment [ ]. The multislot lingual brackets have two slots with different directions: one horizontal and one vertical. The main advantage of multislot brackets over single-slot brackets is the better control of both rotation and tipping without using double overtie. In cases of excessively proclined incisors requiring maximum retraction, lingual appliances may have the advantage of strong molar anchorage and the consequent large amount of incisor uprighting [ ]. In addition, with labial appliances, the amount of lip protrusion increases during treatment because of bracket thickness, and this may affect the esthetics and cause lip incompetence [ , ].
Temporary anchorage devices have expanded the scope of both labial and lingual orthodontics [ ]. Miniscrews provide absolute anchorage without mesial movement of upper molars, and are particularly effective on East Asian patients who have severe overjet and require maximum retraction of upper anterior teeth [ ]. Miniscrews are also used to protract mandibular molars in adult patients, who have narrow alveolar width in the premolar region resisting mesial movement of lower molars [ ]. Protraction of mandibular molars is sometimes required to achieve a centered midline, especially in asymmetric extraction cases.
The causes of tooth agenesis include heredity, abnormal development of the mandibular symphysis, evolutionary reduction of dentition, and local jaw inflammation [ ]. The most common congenitally missing teeth are third molars, maxillary lateral incisors, and mandibular second premolars. Missing mandibular incisors is less common, and may pose many problems such as lower midline deviation, lower anterior spacing, excessive overjet, and overbite due to Bolton tooth-size discrepancy [ , ]. In these situations, it is challenging to have a good orthodontic treatment result with Class I occlusion, optimum overbite and overjet, and correct midline.
This case report portrays management of an adult patient with a missing mandibular right central incisor with multislot straight wire lingual appliances and miniscrews. The patient was managed with asymmetric extraction of three first premolars to correct severe overjet, excessive maxillary and mandibular incisor proclination, and lower midline deviation. Miniscrews were used for maximum retraction of severely proclined upper anterior teeth and the protraction of mandibular left molars to correct lower midline.
Diagnosis and etiology
The patient was a 34-year-old woman, with the chief complaint of protrusive lips, proclined maxillary and mandibular incisors, and excessive overjet. She was concerned about esthetics while undergoing orthodontic treatment and strongly desired an invisible treatment appliance. Extraorally, she had a convex profile with an acute nasolabial angle and strain on circumoral muscle while closing her mouth ( Fig. 1 ). No symptom of temporomandibular joint disorders was detected.
Intraorally, the patient had Class I molar and canine relationship on both sides. The upper and lower arch forms were slightly narrow, especially in the lower arch because of the lingually inclined mandibular molars. In the lower arch, she had agenesis of mandibular right central incisor, mild crowding, and deep curve of Spee ( Fig. 2 ). Despite the molar and canine relationships being in Class I relationship, the missing mandibular incisor created Bolton tooth size discrepancy (anterior ratio, 68.5%) and consequent excessive overjet of 7 mm and overbite of 3.5 mm (50%). The upper midline was coincident with the facial midline, but the mandibular midline was deviated 2.5 mm to the right. The gingival biotype is thin-scalloped.
The lateral cephalometric analysis showed a skeletal Class I jaw relationship with normally placed maxilla and mandible (sella nasion point A, 81.6°; sella nasion point B, 79.5°; A point, nasion, B point, 2.1°), and reduced lower facial height (Frankfort mandibular plane angle, 21.4°). The maxillary and mandibular incisors were proclined (upper central incisor to sella nasion line, 116.2°; lower central incisor to mandibular plane, 106.8°). Both the upper and lower lips were in front of the E-line ( Fig. 3 ). The panoramic radiograph confirmed the missing mandibular incisor; all other teeth were present.
The primary treatment objectives were to eliminate the excessive overjet, reduce maxillary and mandibular incisor proclination, and reduce lip protrusion. Additional objectives were to align and level the dental arches, correct lower midline deviation, and maintain Class I molar and canine relationship with normal overjet and overbite.
According to the treatment objectives, three potential treatment options were considered for this patient. The first option was nonextraction treatment, correcting the Bolton tooth size discrepancy and severe overjet by reducing mesiodistal width of upper anterior teeth and proclining the lower anterior teeth. However, this option would increase lower incisor proclination, and would limit retraction of protruding upper incisors and lips. The patient refused this plan as she needed a straight profile with maximum retraction of anterior teeth and lips. In addition, the lower midline deviation would not be corrected with this option. The second alternative involved extraction of upper first premolars and the remaining lower left central incisor to reduce incisor proclination and correct lower midline. Mandibular first premolars would substitute as canines. Centered lower midline would be achieved more easily with this option. However, as a teacher, the patient had high esthetic demand and could not accept a visible gap in the anterior segment after removing the lower left central incisor. A temporary esthetic prosthesis could be bonded to the adjacent tooth and be progressively reduced, but a small gap would still remain to allow space closing. The third option was an asymmetric extraction treatment approach with removing two maxillary first premolars and the mandibular left first premolar, so the extraction space would not be visible during the treatment. To reduce excessive overjet and maximize retraction of maxillary incisors, miniscrews were used in the maxillary arch. The mandibular right first premolar would substitute as the canine, and the mandibular canine would substitute as the lateral incisor, making interproximal reduction (IPR) necessary in the lower right quadrant. Even after informing the difficulty in midline correction due to the asymmetric extraction in the lower arch and the need to incorporate miniscrews in the lower arch, considering the amount of dentoalveolar protrusion reduction and the esthetics during treatment, the patient chose the third option with a lingual fixed appliance.
The treatment was initiated by bonding all teeth with a 0.018 × 0.018-inch preadjusted edgewise multi-slot lingual appliance (CLB brackets; Hubit, Gyeonggi-do, Korea) using indirect bonding with thermoplastic trays in both arches. The brackets were bonded on initial malocclusion models without set-up. Nickel-titanium archwires (0.014, 0.016, 0.016 × 0.016 and 0.018 × 0.018 inch) were placed for initial alignment and leveling. After 1 month, the maxillary first premolars and mandibular left first premolar were extracted under local anesthesia. The chosen archwire form was slightly wider than the patient’s arch form so that both upper and lower arches would be expanded by uprighting molars.
After 6 months of treatment, the space closure stage was initiated. In the initial space closure stage, the upper anterior teeth were retracted with absolute anchorage from miniscrew to correct the overjet. In the final space closure stage, when the overjet was corrected, upper molar mesialization was allowed. When the archwire progressed to 0.018 × 0.018-inch stainless steel in both the arches with 10° lingual root torque for upper anterior teeth, two miniscrews (diameter, 1.6 mm; length 8 mm; Jeil Medical, Seoul Korea) were inserted on the palatal alveolar bone between first and second molars. The upper anterior teeth were retracted with NiTi coil springs (Hubit, Gyeonggi-do, Korea) exerting a force of approximately 150 g each side from miniscrews to crimpable hooks on the main archwire to avoid mesialization of the upper molars. The crimpable hooks helped to maintain force vector approximately to the upper anterior segment’s center of resistance. In the lower arch, the space closure force was initiated from lower left molars to lower left canine, both labially and lingually to prevent rotation and consequent transverse bowing effect. Second molar tubes were bonded to the labial surface for operator convenience and patient comfort without affecting esthetics ( Fig. 4 ). The labial force is applied from the bondable molar tube to a clear composite button placed in the canine. The main archwires in both arches were straight to facilitate sliding mechanics.
After 16 months of treatment, the extraction space was almost closed in the upper arch. But in the lower arch, the space in the left quadrant remained, and the lower midline was coincident with the upper midline. Therefore, a miniscrew was placed distally to the lower left canine to mesialize the lower left molars. The closed coil spring in the upper right quadrant was removed so that the upper midline could be shifted to the left to compensate with the lower midline shift due to space closing in the lower left quadrant. The lower right lateral incisor, canine, and first premolar were mesiodistally reshaped to correct Bolton tooth size discrepancy. The Bolton anterior ratio was 83.8% when the lower right first premolar was included in the lower anterior teeth, so the interproximal reduction of 2.2 mm was needed in the lower right quadrant to achieve the anterior ratio of 79%. The interproximal stripping procedure was performed with Contacez IPR System (DynaFlex, St. Ann, MO), and the surfaces were polished by Super-Snap Polystrips (Shofu, Kyoto, Japan). After 18 months of treatment, all extraction spaces were closed, and the lower midline was centered. The remaining spaces were closed by forward movement of molars. Elastic chains were used both lingually and labially to close minor spaces opened in the upper anterior region and interproximal stripping spaces in the lower arch ( Fig. 5 ). These elastic chains also helped avoid unwanted rotation of canines. The duration of the space-closure stage was approximately 15 months.