Functional orthopedic magnetic appliance (FOMA) II-Modus operandi

A new functional appliance (FA) to correct Class II dentoskeletal malocclusions is introduced. The functional orthopedic magnetic appliance (FOMA) II uses upper and lower attracting magnetic means (Nd₂Fe₁₄B) to constrain the lower jaw in an advanced sagittal posture. In vitro, a special gauge transducer measured the magnetic attractive path and forces. In vivo, 13 prepubertal female Macaca fascicularis monkeys received facial implants and were treated for 4 months with the following appliances: conventional FA (four subjects), FOMA 11 (five subjects), a combined FOMA II + FA (two subjects), and sham (control) appliance (two subjects). The in vitro results showed the following: vertico-sagittally displaced upper and lower magnets attracted ultimately along an oblique line with a terminal horizonal slide to become fully superimposed; the functional performance improved when the magnetic interface acted as a magnetic inclined plane; and the magnetic force was able to guide and constrain the mandible toward the constructive protrusive closure position (CPCP) (1.2 mm, F = 570 gm) from levels below the habitual rest positon (3 mm, F = 219 gm) and the electromyographic (EMG) relaxed position (8.5 mm, F = 45 gm). The in vivo results demonstrated the following: functional performance increased in FOMA II (22%) and in the combined FOMA II + FA (28%) over the conventional FA; mandibular length increased significantly in the treated animals (X = 2.83 ± 0.70 mm) over the_ control animals (X = 0.43 ± 0.08 mm); incisor proclination was lower in magnetic appliances (X = 4.57 ± 1.76°) than in the conventional FA (X = 8.75 ± 1.85°); mandibular elongation and condylar posterior inclination resulted from posterosuperior endochondral growth (increased cell proliferation and/or hyperplasia of functional chondroblasts) and by bony remodeling of the condylar neck (apposition posterior border, resorption anterior border), respectively; virtually no anterior displacement of the postglenoid spine (X = 0.19 ± 0.68 mm) nor the articular eminence (X = 0.36 ± 0.69 mm) was found. Increased lower posterior alveolar height (X = 1.71 ± 0.82 mm) is a major impediment in the correction of excessive lower anterior facial height. The results of the study highly recommend the exploration of the clinical application of the FOMA II.