From Volume 14, Issue 2, April 2021 | Pages 90-96
In today's fast-paced world, reducing the duration of orthodontic treatment has become a priority for patients seeking treatment. There are now several approaches and devices available that are reported to accelerate orthodontic tooth movement (OTM) and, fortunately, there has been an increase in the amount of research in this area in recent times.
Orthodontic treatment with fixed appliances can be a lengthy process. Comprehensive treatment takes from 24 to 36 months, on average, and duration of treatment is one of the main concerns for patients.1 Approaches to accelerate orthodontic tooth movement (OTM) are, therefore, welcomed by orthodontists and patients alike. Numerous techniques have evolved over time. Some aim to reduce the treatment duration by accelerating the velocity of OTM, whereas other methods aim to make the mechanical force delivery system more efficient.
Figure 1 illustrates the available surgical and non-surgical methods for accelerating OTM. Surgical techniques on the whole, aim to facilitate tooth movement by inducing a regional acceleratory phenomenon (RAP).2,3 Regional acceleratory phenomenon, as described by Harold Frost (1983), is a tissue reaction to noxious stimuli that increases healing capacity.4 However, the use of surgical approaches is limited given the invasiveness of some techniques and the low quality of evidence to support their use. In light of this, the majority of research has focused on non-surgical approaches, which can be further subdivided into physical, biological and/or mechanical methods.
The aim of this article is to provide the orthodontic practitioner with an overview of the available methods for accelerating OTM, and to summarize the available evidence for their use.
Since their introduction, self-ligating brackets (SLB) have been reported to reduce friction and lead to a decrease in treatment duration. There are two main SLB designs: active SLBs (can apply force on the archwire, owing to the spring clip) and passive SLBs (do not exert active force and do not encroach on the slot lumen). Examples of self-ligating systems include Damon (Ormco, USA) (Figure 2), Speed (Strite, Canada), or In-Ovation (Dentsply, USA). The potential benefits of SLBs include reduced treatment time (reported to be due to the reduced friction between the archwire and bracket slots), reduced plaque build-up (given that there are no elastic modules, which can make plaque removal more difficult) and reduced chairside time (reported to be because ligation of the archwire does not involve the transfer of modules).
The first published clinical studies (retrospective design) on treatment efficiency became available in 2001 and concluded that the use of SLBs resulted in shorter treatment duration.5,6 However, subsequently, prospective clinical trials and a number of systematic reviews of randomized controlled trials (RCTs) have concluded that there is no difference between conventional brackets and self-ligating brackets with regard to treatment duration, efficiency of space closure, speed of alignment or transverse changes.7–13
A recent meta-analysis concluded that there was no difference between SLBs and conventional brackets in terms of rate of space closure (MD 0.13 mm, 95% confidence interaval (CI) 0.09–0.35) or efficiency of alignment (MD -4.69 days, 95% CI -22.28–12.91.13 However, this meta-analysis did conclude that active SLBs appear to be more efficient for alignment compared to passive SLBs, and conventional brackets (MD -10.24 days, 95% CI -17.68–-2.80). Given the confidence interval, this is likely to be a clinically insignificant difference.
Brackets customized to individual tooth surfaces are created and bonded indirectly using placement guides. Examples include SureSmile (OraMetrix, USA), which uses 3D scans to provide robotically bent wires to move the teeth into their desired positions. The system compensates for errors in bracket placement. In contrast with other systems, SureSmile customization takes place in the finishing stages of orthodontic treatment, ie by customizing the archwires and not the brackets. In some systems, for example Insignia (Ormco Corporation, USA), bracket bases are standard; slots are custom-created to produce the desired tooth movement via archwire progression to a straight final archwire. The aim of the aforementioned systems is to increase precision, and eliminate human error in archwire bending and bracket placement. The proposed advantages of such systems include:
To date, there is only one published RCT investigating the difference in treatment duration between a customized fixed appliance system (Insignia, Ormco, USA) and a non-customized system (Damon Q). The authors concluded that ‘the customized group had more loose brackets, a longer planning time, and more complaints (P <0.05). The customized orthodontic system was not associated with significantly reduced treatment duration, and treatment quality was comparable between the two systems.'14 Currently, there are no other published trials on this topic. The existing knowledge around the efficiency of customized labial appliances has consisted mostly of expert opinion, case reports and a retrospective studies.
Owing to the limitations of the available knowledge base at the time of writing, no conclusion can be made regarding the effectiveness of customized labial appliances in terms of treatment efficiency and speed of alignment.
It has been reported that vibration leads to stimulation of cell differentiation and maturation, thereby increasing the rate of bone remodelling and turnover. From that perspective, the effect of vibratory appliances appears to be linked to local injury (ie inducing microfractures in the alveolar bone). An example of this approach is the AcceleDent device (OrthoAccel Technologies Inc, USA). AcceleDent was first introduced in 2009 (Figure 3). It provides low-frequency vibratory forces (30 Hz) that produce around 25 grams of force with the view to stimulating cell differentiation and maturation, thereby accelerating bone remodelling and hence tooth movement.7
A systematic review published in 201715 assessed the effectiveness of vibrational stimulus. Eight prospective clinical trials, with an overall sample of 305 patients, were included, and the authors stated that: ‘weak evidence indicates that vibrational stimulus is effective for accelerating canine retraction but not for alignment.’ However, the heterogeneity in methodology and non-comparability of outcome measures used in the studies prevented a quantitative synthesis from being performed.
The general consensus in the literature at the time of writing is that microvibration does not cause clinically significant increase of OTM in terms of initial alignment phase or rate space closure.7,16–18
Pharmacological agents have been used in an attempt to alter the biological response to orthodontic force.7 Most of the data comes from animal rather than human studies and, although an insight to their effects is provided, the results must be interpreted with caution.
A recent meta-analysis of 27 animal studies found that the rate of orthodontic tooth movement increases after the administration of diazepam, vitamin C and pantoprazole, while simvastatin, atorvastatin, calcium compounds, strontium ranelate, propranolol, losartan, famotidine, cetirizine and metformin decreased the rate of orthodontic tooth movement.19 Additionally, a number of pharmacological agents may reduce the rate of OTM (eg drugs that block the action of prostaglandins, such as aspirin and NSAIDs). Common pharmacological agents and systemic factors, and their effect on OTM are summarized in Table 2.
| Study | Type of trial | MOP device | Methodology | Tooth movement | Findings |
|---|---|---|---|---|---|
| Alkebsi et al 201835 | RCT Split-mouth design | Miniscrew (Aarhus Mini-Implant System) |
|
|
There was no statistically significant difference in the rates of tooth movement between the MOP and the control sides at all time points. Mean difference between the two groups: 0.05–0.2 mm |
| Sivarajan et al 201836 | RCT Three-arm parallel design | Miniscrew (using Orlus screw) |
|
|
MOP can increase overall mini-implant supported canine retraction over a 16-week period of observation, 4.16 (±1.62) mm with MOP and 3.06 (±1.64) mm without |
| Attri et al 201837 | RCT Two-arm parallel design | Propel |
|
|
MOP appears to enhance the rate of tooth movement with no differences in pain perception. The monthly rate of space closure was 0.73–0.89 mm in the MOP group and 0.49-0.63 mm in the control group |
| Alikhani et al 201338 | RCT Two-arm parallel design | Propel |
|
|
MOP appears to enhance the rate of tooth movement with no differences in pain perception. Canines moved by 0.5 mm after 28 days in the control group and 1.4 mm in the MOP group |
| Drugs | Effects on bone metabolism | Effects on tooth movement |
|---|---|---|
| Non-steroidal anti-inflammatory drugs (NSAIDs) | ||
| Aspirin | Decrease bone resorption | Decrease tooth movement |
| Diclofenac | Decrease bone resorption | Decrease tooth movement |
| Ibuprofen | Decrease bone resorption | Decrease tooth movement |
| Indomethacin | Decrease bone resorption | Decrease tooth movement |
| Celecoxib | Decrease bone resorption | No influence |
| Acetaminophen analgesics | ||
| Paracetamol | Unproven | No influence |
| Miscellaneous drugs | ||
| Prostaglandins | Stimulate bone resorption | Increase tooth movement |
| Corticosteroids | Increase bone resorption | Increase tooth movement |
| Leukotrienes | Stimulate bone resorption | Increase tooth movement |
| Bisphosphonates | Decrease bone resorption | Decrease tooth movement |
| Interleukin antagonist | Reduced bone remodelling | Decrease tooth movement |
| Fluorides | Inhibit osteoclastic activity | Decrease tooth movement |
| Systemic factors | ||
| Parathyroid hormone | Increase bone resorption | Increase tooth movement |
| Thyroid hormone | Increase rate of bone remodelling | Increase tooth movement |
| Vitamin D | Increase rate of bone remodelling | Increase tooth movement |
| Relaxin | Increase bone resorption | Increase tooth movement |
| Oestrogen | Decrease bone resorption | Decrease tooth movement |
| Calcitonin | Inhibit bone resorption | Decrease tooth movement |
The practical use of these exogenous molecules/medications is limited because of the need for regular administration (as frequently as every week) and the anxiety and discomfort associated with injections.
Photobiomodulation, also known as low-level light therapy (LLLT) uses low-energy lasers or light-emitting diodes (LED) in an attempt to modify cellular biology. The theory is that exposure to light in the red to near-infrared range (600–1000 nm) induces a photochemical reaction at the cellular level. Light energy is absorbed by cellular photoreceptors and converted into adenosine triphosphate by mitochondria.7 This subsequently increases cellular activities such as DNA, RNA and protein synthesis, thereby potentially accelerating OTM. It is suggested that a 10-second exposure to a diode laser emitting light for 20 mW once a week is required to induce a potentially clinical effect.20
The first published RCT investigating the effect of LLLT on OTM was reported in 2004.20 This was a split-mouth trial and concluded that LLLT does accelerate the rate of canine retraction. However, the rate of acceleration was clinically insignificant. After 60 days, the canine retraction was 4.39±0.27 mm for the intervention group and 3.30±0.24 mm for the control group. Since 2004, several RCTs have been carried out. The most recent trial (split-mouth design investigating the rate of canine retraction in premolar extraction cases) found that LLLT may accelerate OTM after 10 irradiations.21 In this study, the canines moved 1.1 mm more on the intervention side than the control side after 84 days. However, the reduction in treatment time was not clinically significant.
A recent meta-analysis of six RCTs suggests that the application of LLLT may accelerate OTM.22 After 21 days and 4.5 months, orthodontic tooth movement was statistically significantly increased in the LLLT group compared with the control group (21 days: MD 0.74 mm; 95% CI 0.17–1.31, P=0.01; 4.5 months: MD 1.53 mm, 95% CI 0.92–2.14; P<0.001). The authors concluded that ‘the LLLT can speed up the rate of tooth movement of human canine and consequently decrease the treatment time.’ However, these changes are unlikely to be clinically significant. Also, given the small sample sizes of the included RCTs, the effect of LLLT on rate of OTM should be interpreted with caution.
In light of the above, there is limited evidence to suggest that the application of LLLT may enhance the rate of OTM. This is an area that requires further research before clinical recommendations can be made.
The proposed mechanism of action is that electromagnetic fields affect the activity of intracellular cyclic adenosine monophosphate and cyclic guanosine monophosphate. This may subsequently lead to an acceleration of bone remodelling and, hence, OTM. A circuit and watch battery is used to generate approximately 1 Hz of electric current in a removable appliance.
A single trial (non-randomized prospective design) assessing the effect of electromagnetic fields on OTM was identified. This trial showed an increase in OTM of 0.3 mm/month in relation to canine retraction and space closure.23
Given the lack of evidence associated with the application of electromagnetic fields and direct electric currents, its clinical use cannot be recommended at present.
Micro-osteoperforation (MOP) refers to localized bone trauma in the region where acceleration of OTM is required. Trauma to bone subsequently induces RAP. Micro-osteoperforation is a relatively minimally invasive procedure, as there is no need to raise a full thickness flap, or to make separate soft tissue incisions prior to the osteoperforation. Propel (Propel Orthodontics, USA) is an example of one device that can be used (Figure 4). It has a pointed surgical stainless steel tip of 1.6 mm in diameter at its widest aspect and a usable length of up to 7.0 mm. It is used to create small MOPs, usually three, in the extraction spaces directly through the gingival tissue into bone.
There are currently four RCTs investigating the effectiveness of this method. The findings of these trials are summarized in Table 1.
The findings from these four trials demonstrate an average reduction in time for canine retraction of up to 3 months in MOP groups. However, despite the statistically significant increase in rate of canine retraction, the authors were unable to identify any published studies evaluating the effects of MOPs over the whole course of orthodontic treatment.
This procedure adopts the principles of MOP in terms of mechanism of action; however, it is more invasive. It involves creating incisions in the buccal/labial gingiva parallel to the long axes of teeth, followed by incisions in the buccal cortical plates using a piezo surgical knife under local anaesthetic.
Two systematic reviews based on RCTs have concluded that there is weak evidence to suggest that this procedure is a safe adjunct to accelerate OTM, and it is up to two times faster than use of a conventional method.24,25 However, in one of the systematic reviews only two RCTs investigating the effects of piezocision were included, both with very small sample sizes (10 and 20 patients), which may not be representative. These results therefore need to be interpreted with caution.
Given the limitations of the existing evidence, further high-quality clinical trials are needed to determine the long-term effects, and optimal protocol for piezocision, prior to drawing more definitive conclusions. Well-designed RCTs are required to confirm the rate of acceleration, risk–benefit ratio, patient perception, long-term follow-up and relapse after corticotomy and piezocision.
A corticotomy is defined as a surgical procedure whereby cortical bone is cut, perforated or mechanically altered. Kole was the first to describe modern-day corticotomy-facilitated orthodontics. He used the term ‘bony block’ to describe the suspected mode of movement after corticotomy.26 Selective alveolar corticotomy can be used in most cases in which traditional fixed orthodontic therapy is used. Unlike MOP and piezocision, which penetrate the cortical bone through the overlying tissue, corticotomy requires raising a full thickness mucoperiosteal flap. The procedure is usually carried out under local anaesthesia, vertical incisions are made between the roots of the teeth horizontally, 2–3 mm above the apices (in order not to damage nerve and blood supply). Trauma to bone subsequently induces RAP and may therefore accelerate OTM.
A recent systematic review concluded that this technique may be effective in accelerating OTM. The authors concluded that: ‘Corticotomy-facilitated orthodontics resulted in decreased treatment time. Few complications and low morbidity were found. More solid evidence-based research is required to support these results.'27
Another systematic review concluded that corticotomy resulted in greater acceleration of OTM than did conventional techniques. The rate of orthodontic tooth movement in corticotomy varied with an increase of 1.5–4 times that of the conventional rate of tooth movement, this varied depending on the surgical methods used.25
There certainly has been a growing interest in the use of corticotomies as an adjunct to orthodontic treatment owing to a deeper understanding of its effects and the emerging evidence base. However, this technique is more invasive that those previously described, is more costly as it often needs to be performed by an oral surgeon or periodontist, and arguably has a higher risk of morbidity compared with MOP and piezocision.
A segmental osteotomy may be performed by either distraction of periodontal ligament (involves reduction of the interseptal bone distal to the tooth to be retracted) or distraction of dento-alveolus (this involves a larger osteotomy to fully mobilize the dentoalveolar segment surrounding the tooth to be retracted). These procedures are limited to single tooth retraction, usually maxillary canine retraction after premolar extraction. Again, trauma to bone from this procedure subsequently induces RAP and hence, may accelerate OTM.
The application of this technique is very limited owing to the invasiveness of the surgeries. There is currently a low level of evidence to support its clinical use.28
In the studies reviewed, there were contradictory results regarding of the pulp vitality of the retracted canines. In one report nine of 26 teeth showed positive vitality,29 while another reported that seven out of 20 showed positive vitality after the sixth month of retraction.30 Therefore, there are still some uncertainties regarding this technique and there is a need for more research with additional attention paid to adverse effects and the cost–benefit ratio.
This concept was first introduced in Japan in 2009.31 A ‘surgery-first’ approach, preceding orthodontic treatment, has been suggested in cases requiring orthognathic correction as part of the overall comprehensive orthodontic/orthognathic treatment.31 Traditionally, prior to orthognathic treatment, orthodontic treatment is initiated to prepare the occlusion for surgery. However, in its purest form the surgery-first approach involves performing orthognathic surgery prior to orthodontic tooth movement. The types of cases best suited to this approach meet certain criteria:
The theory is that a region acceleratory phenomenon is initiated by the orthognathic surgery that allows for the subsequent OTM to be accelerated.
This approach has not been the subject of a prospective randomized trial7 and therefore, definitive conclusions cannot be drawn. A recent meta-analysis (12 observational studies including 498 participants) found that the pooled estimate suggested that the surgery-first group manifested less post-operative stability (moderate heterogeneity) than those in the traditional approach group.32 Therefore, patient screening and treatment planning should be reviewed carefully to compensate for possible post-operative relapse when adopting the surgery-first approach.
Further research and work relating to standardized treatment protocols is required prior to the potential wider implementation of this approach.
In recent times, there has been an increase in the number of approaches aimed at accelerating OTM. In this article, we have explored the majority of proposed surgical and non-surgical approaches proposed. A 2015 Cochrane review,33 summarizes the effectiveness of the non-surgical approaches as follows: ‘there is very little clinical research concerning the effectiveness of non-surgical interventions to accelerate orthodontic treatment. The available evidence is of very low quality and so it is not possible to determine if there is a positive effect of non-surgical adjunctive interventions to accelerate tooth movement.’ The updated literature search in this review continues to support this view.
Surgical approaches to accelerate OTM are more invasive in nature and thus less widely applied. Another Cochrane review34 summarizes the effectiveness of the surgical approaches as follows: ‘there is limited research concerning the effectiveness of surgical interventions to accelerate orthodontic treatment, with no studies directly assessing our prespecified primary outcome. The available evidence is of low quality, which indicates that further research is likely to change the estimate of the effect. Based on measured outcomes in the short-term, these procedures do appear to show promise as a means of accelerating tooth movement. It is therefore possible that these procedures may prove useful.’
Several studies published since the Cochrane reviews, including this review, have attempted to incorporate this additional evidence. Despite the availability of new trials the conclusions remain largely unchanged.
At present, there is insufficient evidence to support the use of the majority of approaches reported to accelerate OTM. Non-surgical approaches can be difficult to apply in everyday practice owing to the use of expensive and specialized equipment and the need for regular and repeated administration of the intervention. The evidence to support surgical approaches to accelerating OTM is limited and they are associated with significant invasiveness, exposing the patient to additional stress and post-operative pain. Of the surgical approaches reviewed, MOP seems to be most promising; however, more clinical trials are needed before clinical recommendations can be made.
