Korean J Orthod.  2019 May;49(3):161-169. 10.4041/kjod.2019.49.3.161.

Cone-beam computed tomography-guided three-dimensional evaluation of treatment effectiveness of the Frog appliance

Affiliations
  • 1Clinical Research Center of Shaanxi Province for Dental and Maxillofacial Diseases, College of Stomatology, Xi'an Jiaotong University, Xi'an, China. sixinqin@mail.xjtu.edu.cn
  • 2Department of Orthodontics, Stomatological Hospital, Xi'an Jiaotong University, Xi'an, China.
  • 3Department of Orthodontics, Xi'an No.1 Hospital, Xi'an, China.

Abstract


OBJECTIVE
To evaluate the effectiveness of the Frog appliance in three dimensions by using cone-beam computed tomography (CBCT) images.
METHODS
Forty patients (21 boys and 19 girls), averaged 11.7 years old, with an Angle Class II division 1 malocclusion were included in our study. They had either late mixed dentition or early permanent dentition, and the maxillary second molars had not yet erupted. All patients underwent CBCT before and after the treatment for measuring changes in the maxillary first molars, second premolars, central incisors, and profile. Paired-samples t-test was used to compare the mean difference in each variable before treatment and after the first phase of treatment.
RESULTS
The maxillary first molars were effectively distalized by 4.25 mm (p < 0.001) and 3.53 mm (p < 0.05) in the dental crown and root apex, respectively. The tipping increased by 2.25°, but the difference was not significant. Moreover the teeth moved buccally by 0.84 mm (p < 0.05) and 2.87 mm (p < 0.01) in the mesiobuccal and distobuccal cusps, respectively, whereas no significant changes occurred in the root apex. Regarding the anchorage parts, the angle of the maxillary central incisor's long axis to the sella-nasion plane increased by 2.76° (p < 0.05) and the distance from the upper lip to the esthetic plane decreased by 0.52 mm (p = 0.01).
CONCLUSIONS
The Frog appliance effectively distalized the maxillary molars with an acceptable degree of tipping, distobuccal rotation, and buccal crown torque, with only slight anchorage loss. Furthermore, CBCT image demonstrated that it is a simple and reliable method for three-dimensional analysis.

Keyword

Non-extraction treatment; Molar distalization; Cone-beam computed tomography; Class II malocclusion

MeSH Terms

Bicuspid
Cone-Beam Computed Tomography
Crowns
Dentition, Mixed
Dentition, Permanent
Humans
Incisor
Lip
Malocclusion
Malocclusion, Angle Class II
Methods
Molar
Tooth
Torque
Treatment Outcome*

Figure

  • Figure 1 Structure of the Frog appliance (FORESTADENT Bernhard Förster GmbH, Pforzheim, Germany). A, Components of the Frog appliance, from top to bottom: screwdriver, preformed spring, and screw. B, Occlusal rest, one of the anchorage devices in the appliance. C, Fabrication of the complete appliance, each part of which is connected by an elastic band and Nance button. D, Activation of the appliance.

  • Figure 2 Intraoral view after treatment.

  • Figure 3 Cephalometric measurements performed in the study. A, B, Linear and angular measurements. C, Coronal measurements of the maxillary first molars. The upper two red dots indicate bilateral distobuccal root apices of the maxillary first molars; the lower two red dots indicate bilateral distobuccal cusps of the maxillary first molar. D, E, Position of the distobuccal cusp (D) and distobuccal root apex (E) of the right maxillary first molars in the coronal (left), sagittal (middle), and transverse (right) directions. N, Nasion; SN, sella-nasion; E line, esthetic plane; ANS, anterior nasal spine; OP, occlusion plane; Me, menton; Go-Gn, mandibular plane; PTV, pterygoid vertical; FH, Frankfort horizontal plane; PP, palatal plane.


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