Effects of Open Bite Activator and Skeletal Anchorage-Supported Vertical Elastics on the Masseter Muscle

This prospective clinical study investigates the dentofacial and muscular effects of a combined orthopedic treatment method in patients with skeletal open bite. The intervention includes the use of an open bite activator appliance along with anterior skeletal anchorage-supported vertical elastics. The study was conducted at Ankara University Faculty of Dentistry, Orthodontics Department, and received ethical approval (Approval No: 36290600/78).

A total of 24 growing individuals (14 females, 10 males) with increased vertical facial pattern (GoGn/SN ≥ 36°) were treated over a 12-month period. Patients received custom-made open bite activators designed to eliminate occlusal contact in the anterior region and redirect functional forces posteriorly. Miniscrews were placed between the lateral and canine teeth in both the maxilla and mandible, and vertical elastics were applied between these skeletal anchorage points with a force of 150 grams on each side, worn for 20-22 hours daily.

Masseter muscle changes were assessed using ultrasonography and sonoelastography at three time points: baseline (T0), interim (6 months, T1), and end of treatment (12 months, T2). Muscle thickness and stiffness (elasticity) were measured bilaterally during rest and maximal clenching. Cephalometric radiographs were obtained at T0 and T2 to evaluate skeletal and dentoalveolar changes, including SNA, SNB, ANB angles, overbite, U1-PP, L1-MP, and other relevant vertical and angular measurements.

Statistical analysis revealed significant increases in masseter muscle thickness during the treatment period, especially between T0 and T1. Stiffness values peaked at T1 and slightly decreased at T2, but remained higher than baseline. Cephalometric findings showed improvements in overbite and reductions in vertical growth tendencies, including significant changes in GoGn/SN and PP-MP angles.

This study demonstrates that combined functional appliance and skeletal anchorage-based vertical control therapy can positively influence muscle structure and dentofacial morphology in hyperdivergent skeletal open bite cases. Ultrasonography and sonoelastography proved to be reliable, non-invasive methods for assessing soft tissue changes in orthodontic treatment.

Inclusion criteria

• GoGn/SN angle ≥ 36°
• Decreased overbite (dental open bite)
• In active growth phase (confirmed by hand-wrist radiograph)
• Good oral hygiene
• No prior orthodontic or orthognathic treatment

Exclusion criteria

• Presence of systemic disease or craniofacial deformity
• Poor oral hygiene
• Non-compliance with appliance wear
• Previous use of skeletal anchorage devices