Dentoskeletal changes following mini-implant molar intrusion in anterior open bite patients

Abstract

Objective: To evaluate skeletal and dental changes after intrusion of the maxillary molars in subjects with anterior open bite.

Materials and methods: This retrospective cephalometric study evaluated skeletal and dental changes resulting from the use of maxillary orthodontic mini-implants in 31 consecutively treated patients. Radiographs were taken at the start and end of maxillary molar intrusion to evaluate the associated changes. Statistical analysis was performed using a one-sample t-test.

Results: The mean treatment observation time was 1.31 years (SD = 2.03). The maxillary first molars (P = 0.0026) and second molars (P = 0.039) were intruded. However, the mandibular first molars (P = 0.0004) and second molars (P = 0.003) erupted in adolescent patients. Both the maxillary and mandibular first molars inclined distally (P = 0.025 and P = 0.044, respectively). The mandibular plane angle decreased (P = 0.036), lower facial height decreased (P = 0.002), and the occlusal plane angle increased (P = 0.009). The overbite increased (P < .0001). The ANB angle decreased (P < .0001). Mandibular dental and skeletal changes were more apparent in adolescents, while adults tended toward maxillary changes.

Conclusions: Vertical traction from orthodontic mini-implants reduces the maxillary posterior dentoalveolar height, thereby assisting orthodontic closure of anterior open bite. However, simultaneous eruption or extrusion of the mandibular molars should be controlled. Adolescent patients tend to demonstrate more favorable effects of mandibular autorotation than do adults.

Keywords: Anterior open bite; Mini-implant; Molar intrusion.

Figures

Figure 1.

Elastomeric traction applied from bilateral palatal (alveolar) mini-implants to a quad helix appliance. The maxillary second molars have been bonded as part of bilateral sectional fixed appliances.

Figure 2.

Elastomeric traction applied from a single midpalatal mini-implant with a dumbbell attachment to a transpalatal arch and second molars.

Figure 3.

Angular cephalometric measurements (degrees): 1  =  SNA, 2  =  SNB, 3  =  ANB, 4  =  FH-NA, 5  =  U1-FH, 6  =  L1-MP, 7  =  U1-L1, 8  =  MP-FH, 9  =  PP-SN, 10  =  OP-SN, 11  =  U6-FH, 12  =  L6-MP. Not shown: U7-FH, L7-MP.

Figure 4.

Linear cephalometric measurements (mm): 1  =  LFH (ANS-Me), 2  =  TFH (N-Me), 3  =  PLFH (ANS-MP), 4  =  PTFH (SES-MP), 5  =  U6-PTM, 6  =  L6-PTM, 7  =  OB, 8  =  OJ, 9  =  U6-PP, 10  =  U6-Ba, 11  =  L6-MP. Not shown: U7-PTM, L7-PTM, U7-PP, U7-Ba, L7-MP.