This case report describes the treatment of a patient with congenital loss of both mandibular lateral incisors and severely retroclined maxillary incisors. The treatment included bilateral extraction of the maxillary first premolars, accurate 3-digital setup, a 2-stage torque control strategy, and intricate mechanic management. The dilemma of tooth-size discrepancy was solved by ideal torque control to avoid interproximal enamel reduction. An ideal Class I molar and canine relation, as well as canine guidance in the lateral excursion movement, was achieved with good stability.
Loss of 2 mandibular incisors was treated by extraction of maxillary premolars.
Torque of retroclined maxillary incisors was corrected by a 2-stage mechanic system.
Good intercuspation was achieved by adjusting the torque of maxillary incisors.
Accurate 3-dimensional diagnosis and effective mechanic management were performed.
A light force was used to achieve bodily movement of incisors.
Congenitally missing teeth is a common developmental dental problem. The most common missing teeth are the mandibular second premolars or the maxillary lateral incisors in white populations. , In contrast, mandibular lateral incisors are the most commonly missing teeth in China, affecting 58.7% of children with hypodontia in a southern Chinese population and comprising 59.2% of all congenital tooth loss in a northern Chinese population. The high incidence of congenital loss of mandibular incisors is similar to that in the Japanese population.
Orthodontic diagnosis and treatment planning require properly considering specific dimensional intermaxillary relationships to ensure ideal conditions of interdigitation, overjet, and overbite. Thus, ideal occlusion depends not only on proper skeletal jaw relation but also on a fine tooth-size ratio between the opposing maxillary and mandibular arches. Because the mandibular lateral incisor is about 1.6 mm smaller than the first premolar, tooth-size discrepancy (TSD) is an unavoidable dilemma in treating patients with loss or extraction of mandibular lateral incisors.
Despite the high prevalence of congenital loss of mandibular incisors in the Eastern Asian population, data regarding the treatment modalities for such anomalies are rare. In contrast to the space opening required for maxillary lateral incisors to achieve a harmonious smile, space opening in the mandibular arch has not been reported in the literature. Such differences in the clinical decision may arise from the differed anatomy in the front region of maxilla and the mandible. Thus, the extraction of 1 mandibular incisor has been advocated in patients with severely crowded mandibular arches or adults with mild Class III malocclusion and reduced overbite. It must be noted that if mandibular incisor extraction is performed without careful planning, the resulting occlusal discrepancy often cannot be resolved satisfactorily.
The extraction or congenital loss of 2 mandibular lateral incisors leads to a more severe TSD. Our present case report demonstrated that by proper diagnosis, treatment planning, and mechanic management, satisfactory occlusion could be achieved with maxillary first premolar extraction in patients with congenital loss of both mandibular lateral incisors. By bodily movement of maxillary incisors of up to 6 mm, fine torque control in the maxillary arch led to a Class I molar and canine relationship, canine guidance, and proper overjet without any interproximal reduction in the mandibular arch.
Diagnosis and etiology
A motivated woman, aged 21 years, came to the dental clinic with the chief complaint of irregular maxillary incisors. In the frontal view, she displayed a symmetrical facial appearance with no excessive exposure of maxillary teeth. She had a straight profile with upper and lower lips behind the esthetic line, a normal mandible, and deep mentolabial sulcus. In addition, the patient showed a normal nasolabial angle ( Fig 1 ).
Intraoral photographs and dental casts showed an Angle Class I canine and molar relationship with impinging deep overbite and reduced overjet. The maxillary central incisors were retroclined, whereas the lateral incisors were proclined. Straight mandibular arch could be observed with congenital loss of mandibular lateral incisors ( Figs 1 and 2 ). The maxillary midline was 1 mm shifted to the right. The patient showed normal mandibular movement and no signs of temporomandibular joint disorder.
The panoramic radiograph showed that the 4 third molars were in eruption. Cephalometric analysis indicated that the patient had a sagittal skeletal Class I pattern (ANB, 2.9°); the patient displayed a normal mandibular plane angle of 29.5°(MP-FH). Maxillary central incisors were in a retroclined inclination (U1-SN, 82.8°), whereas the lateral incisors were in a protrusive inclination (U2-SN, 107°). In addition, the mandibular central incisors showed slight lingual inclination (L1-MP, 86.8°) ( Fig 3 ; Table ). The cone-beam computed tomography (CBCT) showed that alveolar bone was thick at the central incisor, whereas thin at the lateral incisor.
|SNA (°)||82.8 ± 3.5||79.2||79.8|
|SNB (°)||80.9 ± 3.4||76.3||76.4|
|ANB (°)||2.6 ± 1.5||2.9||3.4|
|MP-FH (°)||27.6 ± 4.5||29.5||28.1|
|MP-SN (°)||33.0 ± 6.0||35.1||35.2|
|U1-SN (°)||102.0 ± 5.5||82.8||102|
|U1-NA (mm)||4.3 ± 2.7||−0.6||4.4|
|U1-NA (°)||22.8 ± 5.7||3.6||23.0|
|L1-NB (mm)||4.0 ± 1.8||1.4||1.4|
|L1-NB (°)||25.3 ± 6.0||23.2||25.0|
|L1-MP (°)||95.0 ± 6.0||87.8||89.7|
|UL′-EP (mm)||−2.7 ± 2||−1.8||−3.7|
|LL′-EP (mm)||−2.0 ± 2.0||−3.1||−1.6|
|Z angle (°)||75.0 ± 4.0||76.8||71.0|