Conventional orthodontic treatment normally takes two to three years. Prolonged orthodontic treatment impairs patient compliance and increases the risk of gingival inflammation, dental caries, pulpal reactions, and root resorption, all of which can have long-term, burdensome consequences [1, 2]. Several accelerated tooth movement approaches have been proposed to alleviate these issues, and can be categorized as biological, surgical, or physical . The biological methods aim to modify paradental tissue remodeling by injecting various key molecules into the periodontium; however, multiple painful injections are required and this approach increases the risk of root resorption . Surgical methods are based on the regional acceleratory phenomenon (RAP) theory and aim to increase tissue remodeling and decrease bone density. The drawbacks of this method are surgical complications such as pain, swelling, and loss of tooth vitality. Lastly, physical approaches include low-level laser illumination or vibration. While their efficacy is still controversial, physical approaches offer the unique advantages of being non-invasive, painless, and complication-free.
Vibration has two main effects on bone remodeling, as it can enhance both osteogenesis and osteoclastogenesis. Vibration is employed as a safe medical treatment to enhance osteogenesis in order to prevent bone loss and increase bone density in the long bones [5, 6]. However, the ability of vibration to enhance osteoclastogenesis and accelerate tooth movement during orthodontic treatment is still controversial . At the cellular level, high-frequency vibration increases secretion of inflammatory cytokines and the numbers of osteoclasts and has been shown to accelerate tooth movement in animal models [8–10]. However, low-frequency vibration does not affect tooth movement in animal models . Moreover, several in vitro studies have demonstrated that mechanical vibration promotes the expression of PGE2, RANKL, interleukin-6 (IL-6), and IL-8 in compressed human periodontal ligament cells [12–14]. In addition to, a previous clinical study demonstrated that light force with HFV can increase secretion of IL-1β in GCF and accelerate tooth movement .
Root resorption is a serious problem that can occur during orthodontic treatment, especially when exerting a heavy force [16, 17]. The optimal level of clinical force for maximizing orthodontic tooth movement while avoiding iatrogenic tissue damage and patient discomfort has been extensively researched [18–21]. According to the systematic review, the inability to quantify the distribution of stress and strain in the periodontal ligament (PDL), the lack of control over the kind of tooth movement, and the considerable inter-individual variation, no ideal magnitude of force could be identified in the clinic . Despite the fact that light force may lead to a slower rate of tooth movement than optimal force, previous study showed that it may help to prevent complications including hyalinization and root resorption [22, 23].
At lower force magnitudes, there is a positive correlation between the force magnitude and the rate of tooth movement. However, increasing the magnitude above the optimal force level does not further accelerate tooth movement . The association between tooth movement and the force magnitude in rats was shown to be linear up to a point (10 grams), beyond which tooth movement did not further increase . In addition, a range of magnitudes of light force below 10 grams (1.2, 3.6, 6.5, and 10 grams) were shown to promote bone remodeling via frontal bone resorption. However, a force magnitude of 1.2 grams did not effectively promote tooth movement, and led to significantly less tooth movement than other magnitudes of force . Thus, for this investigation, the optimal force was defined as 10 grams, while light force was defined as 5 grams.
To investigate an effective approach for orthodontic treatment with a shorter treatment duration and less complications, the high-frequency mechanical vibration (HFV) was considered as the adjunctive device for accelerated tooth movement. Then, the aim of the present study was to determine and compare the effects of high-frequency mechanical vibration (HFV) with light force and optimal force on the tooth movement and root resorption in rat model.