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ORIGINAL HYPOTHESIS |
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Year : 2014 | Volume
: 5
| Issue : 3 | Page : 98-102 |
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Mechanical vibration may be a novel adjuvant approach to promoting stability and retention following orthodontic treatment
Chunxiang Zhang1, Linkun Zhang1, Xiaomei Xu2, Peipei Duan3, Hongmei Wu4
1 Department of Orthodontics, Tianjin Stomatological Hospital of Nankai University, China 2 Department of Orthodontics, Stomatological Hospital of Luzhou Medical College, Luzhou, China 3 Department of Orthodontics, West China Hospital of Stomatology, Sichuan University, Chengdu, China 4 Department of Stomatology, The Fifth Central Hospital of Tianjin, Tianjin, China
Date of Web Publication | 15-Jul-2014 |
Correspondence Address: Xiaomei Xu No.2, Jiangyang Nan Road, Luzhou, Sichuan - 646 000 China
 Source of Support: This study is supported by the Luzhou Science and
Technology Planning Project (Grant No. 2011-S-44 (3/3)) and the Natural
Science Foundation of Luzhou Medical College (Grant No. 48)., Conflict of Interest: None  | Check |
DOI: 10.4103/2155-8213.136751
Introduction: Orthodontic tooth movement occurs as a consequence of paradental tissue remodeling in response to applied mechanical forces. Retention is a necessary procedure to prevent relapse when orthodontic appliances are removed. Developing new methods to promote stability and retention following orthodontic treatment has always been desired. Recent studies have demonstrated the favorable effects of low magnitude, high frequency (LMHF) mechanical vibration on bone homeostasis through an ability to stimulate cell metabolism and to enhance osteoblast proliferation, osteoblastic gene expression and bone formation. The Hypothesis: In this paper, we propose that LMHF mechanical vibration is a viable adjuvant method to accelerate bone and periodontal tissue remodeling, thereby promoting stability and shortening retention time. Evaluation of the Hypothesis: Much effort has been made to explore therapies to prevent relapse and shorten orthodontic retention time with limited success. LMHF mechanical vibration may be a promising approach to accelerate alveolar bone remodeling, ultimately promote stability and shorten retention time. Keywords: Orthodontic treatment, retention, stability, vibration
How to cite this article: Zhang C, Zhang L, Xu X, Duan P, Wu H. Mechanical vibration may be a novel adjuvant approach to promoting stability and retention following orthodontic treatment. Dent Hypotheses 2014;5:98-102 |
How to cite this URL: Zhang C, Zhang L, Xu X, Duan P, Wu H. Mechanical vibration may be a novel adjuvant approach to promoting stability and retention following orthodontic treatment. Dent Hypotheses [serial online] 2014 [cited 2023 Jun 8];5:98-102. Available from: http://www.dentalhypotheses.com/text.asp?2014/5/3/98/136751 |
Introduction | |  |
Orthodontic tooth movement (OTM) is generated by the coupling of bone resorption on the compressed side of the periodontal ligament (PDL) and bone formation on the stretched side of the PDL, as a consequence of therapeutic mechanical stress. The PDL is both the medium of force transfer and the means by which alveolar bone remodels in response to the applied force. Therefore, OTM is mediated by the PDL. Since the periodontal tissues affected by OTM require time for reorganization when the appliances are removed, [1] retention is necessary to maintain the teeth in the ideal aesthetic and functional position. Many patients desist from wearing a retainer after 2-years of orthodontic treatment. This has prompted orthodontists to develop strategies to promote bone conversion in order to combat the periodontal relapse force, and to shorten retention time. [2] The promotion of stability and shortening of retention time is therefore a worthy area of study in the field of orthodontics. [2],[3],[4],[5],[6],[7],[8]
The Role of Retention Following Orthodontic Treatment | |  |
Retention is one of the most difficult challenges facing orthodontists. Although the patient may feel that treatment is complete when the tooth has moved to an ideal position and the appliances have been removed, it is at this point that the important stage of retention begins. [1],[2],[3]
The PDL and bone remodeling that occur throughout the orthodontic treatment are not fully complete when a tooth is moved into the correct position. Both the cellular elements including undifferentiated mesenchymal cells and their progeny in the form of fibroblasts, osteoblasts, osteoclasts, and other types of cells, and the tissue fluids in the PDL play an important role in normal function and in allowing OTM to occur. Remodeling changes in paradental tissues, including alveolar bone, PDL, and gingiva, are considered essential in effecting OTM and are also important factors affecting the stability. [2],[3]
Bone resorption is crucial to OTM by removing alveolar bone. Following frontal or undermining resorption, OTM begins. Meanwhile, bone and PDL remodeling takes place at a specific rate. The end of bone resorption and the start of bone formation occur through a coupling mechanism, which ensures that an equivalent amount of bone is laid down after the previous resorption. Widening of the PDL space and disruption of the collagen fiber bundles that support the tooth are normal responses to orthodontic treatment. Indeed, these changes are necessary to allow OTM to occur. Paradental tissue reorganization is important for stability because of the periodontal contribution to the equilibrium that normally controls tooth position. After the application of force, the general trend is towards preservation of the width of the PDL. This involves precisely controlled osteogenic resorption and deposition at specific sites in the paradental tissues. Even if OTM ceases before the orthodontic appliance is removed, recovery of the normal periodontal architecture will not occur. The disruption of the PDL produced by OTM is unlikely to have an effect on stabilization against occlusal forces. However, it does reduce or eliminate the process of active stabilization. This means that immediately after orthodontic appliances are removed, teeth will be unstable in the face of occlusal and soft tissue pressures, underlining the need for retention. The disturbed gingival fiber networks which can still exert forces capable of displacing a tooth after removal of orthodontic appliances, must remodel to accommodate the new tooth position. This provides a further reason for retention. [3]
The most common retention measure to overcome relapse is the use of a retainer. Essentially, full-time retention is required for the first 6 months, except during meals, and night wear is required for at least 12 months. Orthodontic patients frequently complain about the long duration of their active treatment (1.5-2.0 years), in addition, a 2-year retention time typically leaves the patient dissatisfied. Many patients reject or cease wearing the retainer, leading to relapse. Retention is one of the most difficult challenges facing orthodontists. [1]
Stimulation of alveolar bone formation or inhibition of alveolar bone resorption in the retention phase should effectively prevent relapse and promote stability since the relapse pressure persists until alveolar bone remodeling is complete. In recent years, many studies have proposed that pharmacologic therapy might control OTM and prevent relapse. These therapies have included systemic administration of bisphosphonate, [4] simvastatin, [5] and osteoprotegerin (OPG) gene transfection. [6],[7] However, these strategies have some significant drawbacks. Systemic drug administration and gene transfection are non-specific, and long-term studies are required to detect potential side effects on other systems in the human body.
A recent report highlighted that, following OTM, occlusal forces were major factors in fostering and expediting periodontal recovery. [8] During the recovery period, the return of periodontal dimensions to normal values is regulated by the rate and direction of alveolar bone turnover. [9] Therefore, how to promote the alveolar bone turnover to ultimately shorten retention time and promote stability is a valuable area of research.
The influence of low-magnitude mechanical vibration on bone remodeling
It is well known that mechanical stimuli have an important role in bone tissue metabolism. [10],[11],[12] Consequently, research has been focused on developing novel types of loading that can promote bone formation. Recently, the application of low magnitude, high frequency (LMHF, acceleration less than 1 × g, where g = 9.81 m/s 2 , at 20-90 Hz) mechanical vibration has been proposed. [13],[14] Studies have shown that such mechanical stimulation can positively influence skeletal homeostasis in animals and humans. LMHF signals appear to be important contributors to bone adaptation. [15],[16],[17] LMHF mechanical vibration has been shown to enhance new trabecular bone formation in sheep, [13] prevent bone loss and reductions in bone strength in ovariectomized rats, [18],[19] increase bone-specific gene expression, [20] increase callus formation in a rabbit osteotomy model, [21] prevent osteoporosis from disuse, [22] increase bone mass in female sheep without undesirable side effects, [13],[23] and inhibit some of the deleterious consequences of glucocorticoids on bone structure in rats. [24] Judex observed that whole-body vibration resulted in greater trabecular and cortical bone formation rates in ovariectomized rats, as well as enhanced trabecular bone morphology. [25] Tanaka showed that LMHF vibration enhanced the expression of osteoblastic genes associated with bone formation and remodeling [26] and increased new cortical bone formation in the mouse ulna. [27] Several clinical findings have also indicated that LMHF mechanical signals may play a role in the regulation of skeletal structure. [28],[29],[30] These results indicate that LMHF vibration can enhance bone modeling and may affect osteoblastic and osteoclastic activity, resulting in greater bone mass. The technique therefore has the potential to be a non-pharmacological method for recovering osteogenic stimuli. [31]
However, the way by which a stimulus is transformed from a mechanical signal to a biological signal is still controversial. The molecular pathways mediating mechanical signaling in bone are not yet well established. [32] Some previous research has indicated that LMHF mechanical stimulations favorably influence osteoblasts and their precursors. LMHF mechanical vibration could enhance osteoblast proliferation and the expression of osteoblastic genes involved in bone formation and remodeling. [26],[33] Mechanical stimulation can direct the differentiation of bone marrow stromal cells (BMSC) into osteoblast lineage, [34],[35],[36],[37] by biasing cell fate in favor of osteogenesis over adipogenesis. There appears to be a generality in cell responses to mechanical force. Stromal cells, osteoblasts, and osteocytes, as well as alveoloblasts all have similar basic machinery for responding to mechanical signals. However, differential responses arise out of site-specific and temporal-specific gene patterns associated with the target cell. Zhou showed that extracellular-signal-regulated kinases (ERK) 1/2 pathway plays an important role in mechanical vibration induced osteogenesis in BMSC cellular scaffolds. [38] In addition, the increase in bone formation secondary to mechanical stimulus may be associated with a simultaneous decrease in bone resorption activity. [19],[25] Kulkarni reported that mechanical vibration inhibits osteoclast formation by reducing dendritic cell-specific transmembrane protein (DC-STAMP) receptor expression in osteoclast precursor cells. [39] Wu showed that LMHF vibration inhibits receptor activator of nuclear factor kappa-B ligand (RANKL)-induced osteoclast differentiation. [40]
The Hypothesis | |  |
LMHF mechanical vibration has not previously been reported as a non-invasive treatment for orthodontic retention. We put forward a hypothesis that LMHF mechanical vibration may be applied clinically to accelerate the remodeling of alveolar bone and PDL in order to induce faster and more stable orthodontic retention. This hypothesis is based on the following four points:
- Previous research has shown that LMHF mechanical vibration can positively influence bone homeostasis in animals and humans, which may act through promoting bone formation, [41],[42] enhancing bone morphology, [14] increasing bone strength, [43] and attenuating bone resorption. [42] LMHF mechanical vibration is a form of non-invasive and biophysical intervention, confirmed as a potential therapeutic approach to osteoporosis. [41],[42] It has been reported that LMHF stimuli can benefit implant osseointegration. [44] Therefore, LMHF mechanical vibration may accelerate alveolar bone remodeling by means of increasing cellular signaling and activity.
- Some studies have indicated that LMHF vibration favorably influences osteoblasts and their precursors. LMHF vibration could enhance osteoblast proliferation and the expression of osteoblastic genes associated with bone formation and remodeling. [26],[33] LMHF vibration has the ability to direct the lineage commitment of BMSCs by biasing cell fate in favor of osteogenesis over adipogenesis. [36],[37],[45]
- The retention stage of orthodontic treatment is a periodontal tissue and bone remodeling process involving a variety of cells, such as bone marrow mesenchymal stem cells, PDL stem cells, osteoblasts, osteoclasts, and fibroblasts. There is evidence that LMHF vibration promoting bone remodeling and cell differentiation is anabolic to the bone. [26],[27] Due to the similarity between bone remodeling and periodontal tissue remodeling, we speculate that LMHF vibration can not only enhance bone formation but also accelerate periodontal tissue reconstruction following the removal of an orthodontic appliance, shortening retention time, and promoting stability as a consequence.
- Low-magnitude mechanical vibration can be applied both clinically and in practice. Given the current advanced electronic technology, it is feasible to produce a small instrument to deliver LMHF mechanical vibration. The handheld appliance can consist of a mouthpiece and activator. The activator delivers the mechanical vibration forces via the mouthpiece to the patient's teeth. The small mouthpiece can be an independent entity or be integrated into retainers for convenience of operation.
Evaluation of the Hypothesis | |  |
Retention is a necessary procedure in orthodontic treatment and is often prescribed for long periods of time, particularly in adults and patients with periodontitis. Relapse is a major concern in orthodontics in terms of the goals for successful orthodontic treatment. Since the relapse pressure persists until alveolar bone remodeling is complete, stimulation of alveolar bone production or inhibition of bone resorption after orthodontic tooth movement should serve as effective protection against the relapse of moved teeth. We have observed that that LMHF mechanical vibration promotes human multipotent stem cells derived from periodontal ligaments (PDLSC) osteogenic differentiation. [46] According to above mentioned theory, we propose that mechanical vibration may potentially represent a viable method to stabilize moved teeth, reduce the occurrence of relapse, and to shorten the retention time.
Recent studies have shown that LMHF mechanical vibration can positively influence skeletal homeostasis in animals and humans, enhance bone modeling, direct differentiation of BMSCs into osteoblast lineage, and affect osteoblastic and osteoclastic activity, resulting in greater bone mass. [13],[21],[23],[25] Consequently, we hypothesize that LMHF mechanical vibration may be applied to accelerate the remodeling of alveolar bone and PDL, leading to a faster and more stable period of orthodontic retention. According to our data, [19],[24],[38],[46] patients will be able to operate the vibration instrument in combination with conventional retention method themselves periodically throughout the day. While the patients use the appliance for 30 minutes daily during retention, they can go about their other daily activities - doing homework, watching TV, using the computer, reading, or doing housework, at the advantages of being a convenient and non-pharmacological method, leading to a faster and more stable retention, and shortening the duration of retention.
Although LMHF mechanical vibration may be adjunctive method to enhance stability, the precise mechanical parameter(s) that is most critical for controlling the cellular response is yet to be identified. The safety of mechanical vibration depends on their frequency, magnitude, amplitude and duration, as overloading may induce a bone resorption response. However, it is known that frequencies ranging from 15-90 Hz can be strongly anabolic. [13] Further research is necessary to test the ideal intensity and frequency of the LMHF mechanical vibration in order to optimize the clinical application protocol to stimulate bone and PDL tissue remodeling effectively and safely.
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