03 - Accelerated Tooth Movement

Principles of Orthodontic Tooth Movement

Objectives

From a broad perspective, there are two ways to speed up orthodontic tooth movement: (1) improve the engineering of orthodontic materials and appliances, so that orthodontic force is delivered more efficiently, and (2) modify the underlying biology of tooth movement, which has the potential both to delay and accelerate it—so you would want to be sure the modification was on the acceleration side.

Faster treatment with better orthodontic appliances was the “hot topic” in recent years for the companies that manufacture brackets, wires and other supplies. New materials, especially brackets, were marketed aggressively as making treatment faster and easier, unfortunately with claims that were well beyond reality. Dentists, and the orthodontists with whom they work, have no choice but to critically evaluate new materials and appliances—a subject that we covered in an earlier module in this course and will review now.

Modification of the biology of tooth movement now is becoming the hot topic, again with aggressive marketing of new methods and devices to produce faster tooth movement. It is difficult to evaluate things that you don’t understand. The objectives of this module are to:

• Review and clarify the principles of conventional tooth movement
• Review changes in orthodontic appliances that can contribute to faster tooth movement
• Discuss the possible ways to accelerate tooth movement by changing the biologic response
• Provide information as to currently marked treatment modalities, drugs and devices to accelerate or, in some instances, decrease the rate of tooth movement.

Sequence of Events in Tooth Movement (light force)

Tooth movement is primarily a periodontal ligament (PDL) phenomenon, in the sense that the bone remodeling necessary to allow tooth movement is created by sustained pressure that compresses the PDL in some areas while stretching it in others. By now you should be familiar with the sequence of events when a spring that delivers light force is activated to remove a tooth:

• immediately, the alveolar bone bends and a short-acting piezo-electric signal is created
• in 1-2 seconds, the bone springs back (one more piezo-electric signal) (Figure 1) and the PDL is compressed on the side opposite to the spring and stretched on the side adjacent to it. After that, piezo-electric signals are inhibited. They are not part of the process that leads to tooth movement.
• in 3-5 seconds, changes in pressure and tension in affected areas of the PDL alter blood flow, and cells and fibers are mechanically distorted
• within a minute or so (Figure 2) blood flow decreases in the compressed area and increases in the stretched area
• chemical signals, especially prostaglandins and cytokines, are released from mechanically distorted cells in both areas
• in about 4 hours, secondary messengers (m-RNA) appear as differentiation of monocytes into osteoclasts (on the compressed side) and osteoblasts (on the stretched side) begins within the PDL (Figure 3)
• within 2-3 days, remodeling of the alveolar bone adjacent to the tooth begins
• over the next days (how many days depends on how quickly the force from the spring declines as the tooth moves), the tooth moves at a rate of about 1 mm/month

Image 1	Image 2
Image 3

Sequence of Events (heavy force)

If the force is heavy enough to totally cut off blood flow in the compressed area, the sequence changes after the first few seconds:

• within 30-60 seconds, blood flow stops in the compressed area (the increase in the stretched area is about the same as with light force)
• within an hour or so, cell death is occurring in the compressed area, so there are no viable cells to respond to the prostaglandins and cytokines that were released, no secondary messengers appear in that area and there is no cell differentiation to produce osteoclasts and osteoblasts
• over the next days, viable cells in the PDL adjacent to the necrotic area are stimulated by initial messengers that diffuse from the necrotic area and remodeling begins at the edge of the necrotic area, but osteoclast differentiation in the bone marrow beside the necrotic area requires diffusion of chemical signals all the way through the lamina dura of the adjacent bone, which can take a 5-7 days
• eventually, osteoclast differentiation in the bone marrow leads an attack on the underside of the lamina dura, and tooth movement begins 10-14 days after the heavy pressure was applied.

Perhaps this would be a good time to go back to Level III, Module 3 and look at the text and figures there, which present this material in greater detail.

Importance of Force Magnitude

It is obvious that light force for tooth movement is more physiologic and more desirable. Unfortunately, it is very difficult—in fact, almost impossible—to prevent the development of at least some small necrotic areas in the PDL even when light force is used. If that is true, is the magnitude of the force really important?

The answer is yes, for two reasons: (1) the amount of pain associated with tooth movement is linked to the size of the necrotic areas, and the heavier the force, the larger the area of necrosis; (2) heavy force becomes a greater stress on the anchor teeth that shouldn’t move. So using heavy force both increases the amount of pain and makes it harder to control the tooth movement. You have already seen the graph below in the context of controlling anchorage—but you need to remember its importance in determining the amount of tooth movement.

Orthodontic Mechanics as a Factor in the Rate of Tooth Movement

Importance of Force Duration

In Level III, you have already seen that the amount of tooth movement will be a function of how quickly the force from a spring declines as tooth movement occurs. Let’s review that concept. What does it mean, exactly?

There is no such thing as a perfect spring—the force any spring delivers will decline as the tooth moves and the stretch or compression of the spring changes. You have seen the graphs below before. Now look at them again as you think about force duration as a factor in the speed of tooth movement.

If there were a perfect spring, the force it delivered would not change as tooth movement occurred (the dashed green line in Figure 1). A good spring would show some reduction in force as a tooth moved, but would still produce a continuous force the force that would not decline to zero between activations. If a poorer spring produced no force soon after it was activated (Figure 2), this would be described as interrupted force. And if the force was produced by a removable appliance (remember, any appliance that can be removed will be) (Figure 3), the force would be described as intermittent. Light continuous force, not surprisingly, produces the fastest tooth movement.

Image 1: Continuous force	Image 2: Interrupted force
Image 3: Intermittent force

Sequence of Orthodontic Appointments: Repair Time

In clinical practice, orthodontic patients usually are seen no more frequently than once a month. Why? Couldn’t you move teeth faster if you saw them every two weeks to re-activate springs and archwires? In fact, you probably could move teeth faster with more frequent appointments, but that would not be good judgment. At least a few necrotic areas in the PDL are almost inevitable, so it is prudent to give enough time for repair of injured and inflamed areas.

The importance of doing that is magnified by the fact that it’s not just adjacent alveolar bone that’s being remodeled. Cementum on the tooth root adjacent to a necrotic PDL area also is marked in some way, so that it is attacked by the clast cells that are part of the remodeling process. Cementum, like alveolar bone, is repaired as part of the remodeling process, so there’s no permanent damage to the side of the root unless repair is inhibited—but you would not want to apply new force that would do just that until the repair process is complete.

The attached figure, from human autopsy material, is a coronal section through the root of a premolar that is being moved to the left. Remodeling of alveolar bone can be seen on both sides. Note the areas of root resorption on the left side of the root that will be repaired by later deposition of cementum. In some places, resorption has penetrated through the cementum into the dentin, leaving craters that will filled with cementum and would not be visible unless the root was sectioned as this one was.

Sequence of Appointments (cont.)

You might say, “Enough time between appointments for repair makes sense if heavy force is used, but with light force, would that be necessary?” It’s correct that when heavy interrupted force is used, a month or even 6 weeks for repair is important to prevent permanent damage to bone and teeth. But flexible springs or wires can be active over a period of a month or longer, and there is no need to re-activate them at shorter intervals. In fact, longer appointment intervals are quite feasible if modern NiTi or TMA wires are used, simply because they can provide light continuous force. That doesn’t necessarily move teeth faster, but it does reduce the number of appointments, which benefits both the patient and the doctor.

Now you know that light continuous force is best because it produces less damage to soft tissue (PDL) and hard tissues (tooth, alveolar bone). Heavy intermittent force is acceptable, but only if re-activation is not done until there has been time for repair. Heavy continuous force is not acceptable. There has to be time for repair.

Summary, Orthodontic Mechanics and Speed of Tooth Movement

Let’s summarize the relationship between orthodontic mechanics and the speed of tooth movement.

1. It’s important to remember that wires and springs move teeth. In contrast, brackets just provide an attachment to the tooth, and excellent evidence now shows that the way a wire is held in a bracket is not a major influence on the speed of movement.
2. Light continuous force is ideal for tooth movement. Superelastic nickel-titanium (NiTi) and beta-titanium (TMA) wires and springs, which are more flexible than stainless steel wires, do allow faster tooth movement because they provide light force with a considerable range of activation;
3. Stiffer wires and springs generate heavier force that is likely to decay quickly. This makes it particularly important to provide enough time between appointments for repair of damaged soft and hard tissues. More frequent adjustments of stiff wires might produce faster tooth movement, but at too high a risk of damage to the teeth and their bony support.

Effect of Electro-Magnetic Fields and Drugs on Tooth Movement

Electro-Magnetic Fields

We have already noted that piezo-electricity is critical for maintenance of bone but does not seem to be important for orthodontic tooth movement. It has been observed in orthopedics that small electric currents applied to casts over a fractured bone can increase the rate of healing, but how this effect is mediated remains unclear. In orthodontics, delivering an electric current to the alveolar bone is difficult, and to this point, experiments have not shown any increase in the speed of tooth movement.

Electrical currents create an electro-magnetic field in the area, and the reverse also is true: imposing an electro-magnetic field (EMF) creates electrical current flows. So perhaps creating an EMF around the teeth and alveolar bone would alter the response to orthodontic force. How could you do that? One way would be to place magnets close to the targeted area of the jaws.

Small magnets that produce a relatively large EMF now can be produced using rare earth elements (ytterbium, etc.). For intraoral use they must be carefully packaged to insure that corrosion products are not ingested, and that can be accomplished. If such magnets are attached to an orthodontic appliance and placed in attraction or repulsion, they can generate enough force to move teeth (Figures 1 and 2). But the non-linear force system is far from ideal—the amount of force changes as the square of the distance between the magnets. Nonetheless, magnets would be potentially valuable in orthodontics if the magnetic fields changed the biology.

Unfortunately, the best evidence shows little if any effect of these small fields on the biologic response. So from an orthodontic perspective, magnets can be best viewed rather simply as bad springs. They have essentially disappeared from modern orthodontic treatment.

Image 1: Magnets in attraction: Small rare-earth magnets can be bonded to teeth to produce tooth movement.	Image 2: Magnets in attraction, progress: Note the space closure as the magnets moved together. Magnets now have been positioned to move the root of the mandibular canine distally into contact with the first premolar.

Drugs to Accelerate Tooth Movement: Prostaglandin?

Orthodontists rarely use drugs, even local anesthetics—but the possibility of drug therapy to accelerate the rate of tooth movement is intriguing. Think back to the cascade of events when sustained force is applied to a tooth. What are the chemical agents involved in that? That’s right, prostaglandins and cytokines are the initial signals. Could you increase their amount and thereby get faster tooth movement?

Prostaglandins have the almost unique ability to simultaneously stimulate differentiation of both osteoclasts and osteoblasts, and of course an increase in both is needed for bone remodeling. The drug would have to be delivered locally, because prostaglandins have a wide range of effects beyond bone remodeling. Could you increase the rate of tooth movement by injecting prostaglandin E or one of its chemical cousins into the PDL space? Interestingly, there is some evidence that you could.

Then why isn’t prostaglandin injection used for that purpose? There are two problems: (1) the PDL space is small, and injecting anything into it hurts; and (2) prostaglandins create intense and painful inflammation when injected. When a wasp or bee stings you, what it really does is inject prostaglandin subcutaneously. So injecting prostaglandin into the PDL would be quite painful, and certainly wouldn’t be a practice builder.

Drugs to Accelerate Tooth Movement: Relaxin?

Another drug possibility for moving teeth faster is Relaxin, a hormone discovered in the 1980s that increases collagen breakdown and decreases collagen synthesis, both of which are needed in bone remodeling. Relaxin is considered a pregnancy hormone because it facilitates birth by softening the cervix and loosening the pelvic symphysis. It almost surely is involved in more than that, because in pregnant women its blood levels are highest well before birth, but its larger role has not been well defined.

Preliminary animal experiments indicated that Relaxin injected near teeth that were being moved did increase the rate of tooth movement. That led to a double-blinded human randomized clinical trial at the University of Florida, in which one maxillary central incisor was moved with a clear aligner, and Relaxin or a saline control was injected mesial and distal to the tooth. Although there were differences between patients in the rate of movement of the tooth, there was no difference between the control and experimental teeth (McGorry SP et al, Am J Orthod Dentofac Orthop, Feb. 2012). Future clinical trials have been delayed.

Relaxin may not be the drug that becomes useful as an accelerator of tooth movement, but it seems likely that such a drug will be discovered and used in the future—probably in your professional lifetime.

Drugs to Impede Tooth Movement: Prostaglandin Inhibitors

Drugs are almost never used to deliberately impede tooth movement, but widely used medications can do that. You need to understand this because patients and parents are going to ask you about it, whether or not you are doing any orthodontics.

Most current over-the-counter analgesics (aspirin, ibuprofen, naprosyn) are prostaglandin inhibitors, and of course if increasing the amount of prostaglandin increases the rate of tooth movement, inhibiting it certainly could slow treatment down. There is an alternative pain reliever that isn’t a prostaglandin inhibitor: acetaminophen (paracetomol in Europe), which acts centrally rather than peripherally. Acetaminophen has no anti-inflammatory action, however, and inflammation in the PDL is a component of orthodontic pain.

Fortunately, orthodontic pain is (usually) not severe, and medication is needed for only 3-5 days after activation of springs or wires. Clinical data show that low doses of both ibuprofen and acetaminophen are effective in managing orthodontic pain, and which one you choose makes no difference in the rate of tooth movement.

If there is a problem due to prostaglandin inhibitors, it occurs in adults who are taking large doses day after day, usually to control pain from arthritis. Both the strength of the inhibitor and the duration of use are important factors, but if orthodontic treatment is to succeed, these adults will need another approach to pain control.

Drugs to Impede Tooth Movement: Bisphosphonates

Osteoporosis becomes a problem for many post-menopausal women and, less frequently, for aging men. Estrogens were used to treat this until recent studies showed a risk of cardiovascular and related problems; now, bisphosphonates of moderate potency are widely used to control osteoporosis, and adults seeking orthodontic treatment often have been exposed to these drugs.

Bisphosphonates are osteoclast inhibitors, and it is easy to see how this could help to control osteoporosis. Bone remodeling occurs all the time, and inhibiting osteoclasts but not osteoblasts would change the equilibrium between bone formation and resorption toward a net increase in the amount of bone and bone quality.

Active bisphosphonate treatment, even with the less potent drugs used to treat osteoporosis (Fosamax, Actonel, Atelvia, several others), makes tooth movement essentially impossible. Bisphosphonates are incorporated into bone, and so have the potential to inhibit tooth movement for some time after they were first used. Fortunately, most of the drug remains on the surface of bone, where it can be “washed out” after treatment is discontinued. The best guideline is that tooth movement will be very difficult for the first 3 months after a bisphosphonate is discontinued, and teeth will begin to respond, perhaps still slowly, after that.

Orthodontics in Bisphosphonate Patients

It must be remembered that treatment for osteoporosis can’t be just discontinued when the patient wants orthodontics. A hip fracture during orthodontic treatment would be too high a price to pay for straight teeth and a better bite. There is an alternative to bisphosphonates: replacing them with an estrogen like Evista, which has a maximum effect on bone and minimal estrogenic side effects. Consulting with the patient’s physician to see if bisphosphonates can be discontinued temporarily may make orthodontics possible (Figure 1).

Extraction of mandibular teeth in some bisphosphonate patients has led to progressive necrosis of bone around the extraction site. Fortunately, that is much more likely in patients taking the potent bisphosphonates that are used in patients with metastatic bone cancer—but elective extractions for orthodontic purposes after any bisphosphonate exposure carries a high (and probably unacceptable) risk with it (Figure 2).

Guidelines for orthodontic treatment of patients with a history of bisphosphonate treatment are shown in Figure 3.

Image 1	Image 2
Image 3

Non-Bisphonate Drugs

Newer drugs that can have adverse effects on tooth movement, not classified as bisphonates, have recently been introduced to fight osteoporosis.

Prolia (Denosumab) is a RANK ligand inhibitor. As you already know, RANK ligand plays a significant role in osteoclast development and function. The clinical effect of Prolia on tooth movement has not been well explored yet, but the biologic basis for the interaction of this drug with tooth movement is essentially the same as bisphosphonates: inhibition of the osteoclast activity needed for teeth to move.

It is important to ask your patients about all the medications they might be taking for bone health, not just bisphosphonates.

Alveolar Bone Injury to Accelerate Tooth Movement

Development of Corticotomy

The idea that making cuts into the bone between teeth would make it possible to move them faster is an old one. It was tried in the early 20th century and abandoned as too dangerous (that was, after all, the pre-antibiotic era).

The German surgeon Kὃle in the late 1950s proposed doing rapid orthodontics in an interesting way that he called corticotomy. The method was to make cuts into the alveolar bone between and around the teeth so that each tooth was supported on a relatively small bony pedicle, then use heavy force from stiff orthodontic archwires to green stick-fracture the remaining bony support for each tooth and pull it into position against the arch wire. That was instant orthodontics, if you saw no need to reposition the roots. Fortunately, the blood supply to teeth is so good that the teeth usually didn’t lose pulp vitality. This approach was briefly advocated in the American northwest at that time, but again abandoned as not worth the morbidity and risk.

Corticotomy (Images 1 and 2) was revived in the US in the 1990s, originally with only a slight modification of the Kὃle approach. It was heavily promoted by periodontist-orthodontist brothers who gave courses on how to do this. As you can see in these images, large flaps are reflected both facially and lingually to expose the alveolar bone, and cuts are made almost all the way through the interdental bone are made. (All images in this section of the module, courtesy Dr. S. Dibart)

Image 1: Maxillary corticotomy: After reflection of a gingival flap, cuts have been made through the interdental alveolar bone adjacent to each tooth to be repositioned. The bone over the roots has been scored to induce remodeling there—that was not part of the original technique.	Image 2: Maxillary corticotomy, lingual: Cuts also are made lingual to the involved teeth.

Changing Rationale for Corticotomy

The rationale for corticotomy, and the technique for doing it, changed as three things were realized: fracturing the teeth into position often did not give satisfactory occlusion; teeth could be moved orthodontically after corticotomy (and perhaps more quickly); and loss of alveolar bone height often occurred in corticotomy patients. The concept became that faster tooth movement could be achieved if remodeling of the bone around the teeth was stimulated by the bone healing in adjacent areas, i.e., no more bone fracture as part of the tooth movement, and if application of a bone graft slurry was added to the technique. The current corticotomy technique, now called AOO (Accelerated Osteogenic Orthodontics) is illustrated in the images here.

The method now uses bone cuts as previously, with the addition of scoring of the bone facial to the roots to induce remodeling there (Images 1 and 2). Light (normal orthodontic) force instead of heavy force is used for the tooth movement. The theory is that remodeling associated with bone healing at the osteotomy sites will lead to faster remodeling of the bone immediately adjacent to the teeth.

A bone graft slurry now is placed over the facial surface before the gingival flaps are sutured back into position (Images 3 and 4). The slurry contains ground-up human cadaver bone, bovine bone or synthetic bone mineral. It has two purposes: to (1) prevent loss of alveolar bone height, and (2) facilitate dental arch expansion and prevent fenestration of the alveolar bone with expansion. How well it accomplishes either of these goals has not been verified.

For this patient, treatment was completed in 6 months, with good healing (Image 5).

Image 1: Just before corticotomy to accelerate tooth movement.	Image 2: Maxillary corticotomy surgery: After reflection of the maxillary gingival flap, interdental cuts and scoring of the facial bone can be seen.
Image 3: Mandibular surgery (same patient): Similar cuts and scoring of facial bone surfaces in the mandibular arch.	Image 4: Maxillary bone graft: A bone graft slurry is placed over the surgical area.
Image 5: Mandibular bone graft: As in the maxillary arch, a bone graft slurry is placed over the surgical area.	Image 6: Surgical area 11 months later: Orthodontic treatment for this patient was completed in 6 months. The surgical area shows excellent healing.

Outcomes of Corticotomy and AOO

Although corticotomy and AOO have been advocated since the 1990s, there is a remarkable dearth of outcome reports. The published literature consists almost totally of before and after photographs and the amount of time needed to align crowded teeth in selected cases. Based on that, one can conclude that faster tooth movement soon after the surgery does occur (always? sometimes?). No data from a series of consecutive patients has been made available, and there is no good information as to the prevalence of problems related to the surgery or the percentage of patients with good / fair / poor outcomes. In short, the advocates of corticotomy and AOO offer no good evidence to support the claims of greatly reduced treatment times and no complications or problems. A complete report of at least 25 consecutive cases, including all patients and data for occurrence and management of problems, is badly needed.

It is apparent, however, that this is not incidental surgery. The large flaps and extensive bone cuts require one-two hours of surgery, and there is enough morbidity to mean that there is an effect on quality of life (for how long?). An obvious question is whether this extent of injury to the alveolar bone is necessary to obtain faster movement, and many clinicians have thought about possibilities to decrease the amount of injury and associated morbidity.

Piezocision as a Less Invasive Alternative

In recent years, piezocision has been offered as an alternative to corticotomy by both Japanese and American periodontists. Piezocision is based on cuts through the interdental gingiva that penetrate into the bone, without raising extensive soft tissue flaps and with significantly less bone injury. The American technique has four steps:

• “micro-incisions” instead of reflecting the gingiva (Image 1)
• use of a piezo-electric (vibrating) knife to penetrate into the interdental bone (Image 2)
• tunneling beneath the gingiva in preparation for a bone graft (Image 3), and
• use of a syringe to inject a bone graft slurry over the facial alveolar bone (Images 4 and 5).

In contrast to AOO, there is minimal morbidity, but orthodontic treatment does not start for 1-2 weeks with both methods. There are no good comparative data, but it appears that orthodontic treatment time with piezocision is similar to corticotomy / AOO.

Image 1: Gingival “micro-incisions”: Piezocision incisions are made only on the facial, without reflecting flaps.	Image 2: Piezo-electric knife: A piezo-electric knife, which vibrates, is used to penetrate into the alveolar bone.
Image 3: Tunneling in preparation for bone graft: A tunnel beneath the facial gingiva is created for placement of a bone graft.	Image 4: Syringe to inject the bone graft slurry: The bone graft material is injected into the tunnel, from both ends.
Image 5: End of procedure: Appearance immediately after surgery and injection of bone graft material.	Image 6: 10 months later: Appearance 4 months after end of orthodontic treatment, with good healing. Orthodontic retainers are needed—the gingival fibers that contribute to relapse were not sectioned during the surgery.

Propel: A Commercial System for Bone Injury

The most recent (2013) approach to bone injury as way to speed up tooth movement is to screw a device (which is about the size of a typical bone screw for skeletal anchorage) into the interdental bone and then immediately remove it, leaving a bone defect to heal. This is done at 3 locations adjacent to each tooth (near the alveolar bone crest, at the middle of the root and near the root apex). A sterile kit with the removable equivalent of a bone screw and a driver for the device are provided.

As with the other bone injury approaches described above, the marketing for Propel has greatly outstripped the data (Image 1,2). Does it work? Probably. Is it as effective as piezocision or corticotomy? There are simply no data to provide information of that type.

Image 1: Propel ad [upper half]	Image 2: Propel ad [lower half]

Treatment Time with Bone Injury Techniques

The critical question about the bone injury techniques is “How much time does it really save?” The answer, of course, would come from data for total treatment time, not for time to initial alignment, but some insight comes from considering the rate of time for healing after injury more generally.

How long does it take for bone to heal after a fracture? That depends on the extent of the injury and the age of the patient, but for a typical uncomplicated fracture of a limb in an adolescent or young adult, there is enough formation of new bone in about 6 weeks that casts can be removed, and bone in the healing area is relatively mature in another 6 weeks or so. Remodeling is essentially complete in 4 months.

Based on that, you would need to accomplish essentially all the tooth movement in 3-4 months after the bone injury in order to obtain an acceleration. If treatment took longer than that, the latter part would be at the usual speed. So if movement was twice as fast in those four months, you would expect to reduce total treatment time by 2 months. Is the benefit of saving that amount of time worth the expense and morbidity of the surgery?

Answers to several additional questions are needed:

• Are there specific indications for using injury to accelerate tooth movement? Should it be limited to mature adults, or is it useful in adolescents and perhaps even in children?
• Does the bone graft slurry really allow greater facial movement of teeth without creating bone dehiscence?
• How does long-term stability compare to stability without bone injury?

Bone Injury Conclusions

The bottom line on bone injury to speed up orthodontic tooth movement:

• Anecdotal case reports and selected patient samples indicate that the amount of time for alignment of crowded incisors decreases after corticotomy, piezocision and creation of empty bone screw sites
• The injury effect decreases as healing progresses, and any acceleration of tooth movement would be expected to disappear after 3-4 months
• The effect of injury with these techniques while a patient is still growing is unknown, but other types of injury do tend to decrease subsequent growth, so using this approach in adolescents should not be done until the end of the growth period
• If one assumes that the alignment phase of treatment in adults is cut in half by bone injury, and there is no decrease in time after that, the saving in total treatment time would be about 2 months. No data for actual treatment times in a controlled study are publicly available.

Non-Invasive Methods

Acceledent: High-Energy Vibration

As we noted earlier, piezo-electric current flow generated by bending of bone during function is a key element in maintaining bone health. For astronauts in reduced or zero gravity situations, there is less bone bending, and loss of bone is inevitable unless piezo-electric currents can be induced. At first this was done by vigorously pedaling an exercise bicycle. NASA scientists discovered that vibration could produce the same bone-sparing effect, and a bulky exercise bike in the space station has been replaced by a vibrating platform on which the astronauts can stand.

Based on this experience, the idea was advanced that faster tooth movement could be produced by high-energy vibration of the teeth, and a device to do this is now marketed as Acceledent (Images 1 and 2). Preliminary data suggested that with a regimen of 20 minutes of vibration every day, the teeth would move more quickly. A randomized clinical trial conducted at the Univ. of Texas-San Antonio showed faster closure of a maxillary premolar extraction site in patients who used the vibration device, and on that basis the US Food & Drug Administration approved its sale.

FDA approval rarely has been sought for an orthodontic device, and seeking and obtaining it certainly is a positive step. Based on this, an aggressive marketing program has moved forward. The clinical trial data, however, have not yet appeared in the orthodontic literature (as of mid-2013) because journal reviewers have expressed concerns about the interpretation of the outcomes.

It is interesting to note that although the focus of the clinical trial was the time to close an extraction space and malalignment was not quantified, claims of reduction in time for alignment and total treatment time are included in current advertisements. It is fair to say that the marketing is far ahead of the evidence to support it.

Image 1: Acceledent device: The device consists of a mouthpiece that is activated by batteries in the extra-oral part into which the mouthpiece is inserted.	Image 2: Acceledent in use: The recommendation is 20 minutes per day of vibration.

High-energy Vibration (cont.)

In comparison to bone injury methods, there is one great advantage of vibration as a way to accelerate tooth movement: no surgery is required, and the morbidity associated with it is avoided. Patients in the Acceledent trial did not report pain beyond what orthodontic patients normally experience—mild to moderate pain lasting only a few days after appliance adjustment.

There are, however, two types of problems. The first is that the mechanism of action with vibration is not understood. Is that important? As part of the reaction to the 2012 “discovery” of neutrinos moving faster than light (which was retracted after further evaluation of the data), the interesting cartoon shown in Image 1 accompanied a NY Times story about it. The astrophysicist’s comment was “No experiment should be believed until it has been confirmed by theory.” The orthodontic analogue would be “No experimental result should be completely accepted until the underlying mechanism is understood.” Why? Because if you don’t understand the mechanism, you have no way to identify exactly what outcomes you should be looking for.

What is the mechanism for high-energy vibration? We simply do not know—but especially since its effect seems to be similar to that of bone injury, one can wonder if the device is creating micro-fractures in the alveolar bone that lead to greater bone remodeling. If that is the mechanism, however, an appropriate concern would be the long-term effect of repeated injury during a year or more of treatment. The surgical bone-injury approaches produce injury once and then it is allowed to heal. What would repeated injury do? At this point that is not known.

Practical Considerations with Vibration

The other type of problem with vibration is best labeled a series of practical considerations. These include

• If you want to move only some of the teeth (which is the case for the great majority of orthodontic patients), can the vibration effect be restricted to only one part of the dental arch without altering the effect elsewhere?
• Is the frequency / intensity of the vibration optimal? The objective is to deliver enough vibrational energy to alter the response to orthodontic force, in 20 minutes per day. What happens if these variables change? Importantly, what happens if the patient uses the device more or less than 20 minutes per day?
• For adults, is there a maximum duration of safe use? Can it be used safely in adolescents? in younger patients who are still growing?
• Does the device work equally well with all types of appliances? It has been suggested that it may be particularly useful with Invisalign, and it seems reasonable that this might help in fully seating the aligners—but there are no data yet to support that idea.

High-Intensity Light

High-intensity light in the 800-900 nanometer range (just outside the visible range for humans) penetrates through soft tissues. It has been hypothesized that it could be used to activate cells in the PDL and alveolar bone and thereby lead to faster tooth movement. With vibration the mechanism could still be injury in the form of micro-fractures; with light, it is hard to see how the mechanism could be injury.

That leaves the same problem as with vibration: if you don’t know the mechanism, you don’t know what to look for as outcome parameters beyond the desired effect. It is known that light of this type can produce some tissue heating that would increase blood flow, and in studies of tooth eruption, it has been shown that increasing blood flow does affect the rate of eruption. So there is some reason to believe that the light could increase blood flow, and perhaps that would be a way to accelerate tooth movement.

At this point (mid-2013) Biolux, the company that is working with high-intensity light, has obtained encouraging preliminary data and a randomized clinical trial has just begun. The first efforts with humans used an extra-oral device like the one shown in Images 1 and 2, with illumination for 20 minutes per day. Although most of the light (97%, according to the company) was absorbed before it reached the alveolar bone, the remaining 3% was thought to be intense enough to affect cells there. Currently, an intra-oral device to supply the light (Image 3) is being used, with illumination for only 3 minutes per day.

Is light really going to accelerate tooth movement (Images 4,5,6)? If so, will patients be willing to wear a device like either of the ones in these images? That simply is not known at present, although the devices already are being promoted commercially. But light does seem to offer a non-injurious way to possibly affect tooth movement by increasing blood flow in the PDL and adjacent alveolar bone. Is the primary effect on the PDL or the bone? That also is not known.

Image 1: Experimental extra-oral device: With this device, light-emitting diodes are placed so that light penetrates through the cheeks to the gingival area of both arches.	Image 2: Infra-red image of light from extra-oral device: In this image from an infra-red camera, the nose is at the top and the lips in the center. Note that light does penetrate to (and presumably into) the PDL and alveolar bone adjacent to the teeth.
Image 3: Intra-oral device, high-intensity light: With the intra-oral device, tissue-penetrating light only has to go through gingival tissues to reach the PDL and alveolar bone. In the current clinical trial, the tissues are illuminated for only 3 minutes per day.	Image 4: Use of intraoral light device during treatment: The instructions were to use the light appliance daily for 3 minutes.
Image 5: Pretreatment incisor crowding: An early adolescent with crowding, before alignment with a fixed appliance and use of an intraoral device to supply 850 nm light.	Image 6: After incisor alignment: Alignment took 4 months, which is relatively quick but not a large change from what would be expected with a superelastic NiTi archwire. Is this normal individual variation or an acceleration due to the light? Only a randomized clinical trial will give a clear answer.

Therapeutic Ultrasound

There is no doubt that therapeutic ultrasound (which has much greater intensity than diagnostic ultrasound) can increase blood flow in targeted tissues. For that reason, therapeutic ultrasound is widely used in physical therapy, typically to increase blood flow in deep muscles that are contracted and painful.

A possible application of therapeutic ultrasound to orthodontics would be to increase blood flow in the PDL, as a way to decrease the formation of necrotic areas and the size of those that do form. That would have the potential to decrease the amount of root resorption, and if increasing blood flow leads to accelerated tooth movement, it might be another non-injury way to accomplish this also.

At this point, intra-oral devices to supply ultrasound to the teeth have been developed, and the possibilities of decreased root resorption and /or faster tooth movement are being evaluated. This technology has not yet been marketed.

Non-injury Methods: Summary

To summarize what is known about possible physical methods to accelerate tooth movement:

• High-intensity vibration has been shown to accelerate the rate of tooth movement in humans in closure of extraction spaces.
• Devices to supply high-energy vibration now are for sale in most countries, including the United States. The marketing claims go beyond the supporting evidence, and it is not yet clear whether this will become an important adjunct to orthodontic therapy.
• The mechanism of action for vibration is not known, but it may be a less invasive way to induce alveolar bone injury. The magnitude of change in tooth movement is similar to what is seen with more overt injury procedures.
• High-intensity light that penetrates soft tissues also seems to have the potential to increase tooth movement, and clinical trial data are being gathered now.
• The mechanism of action for light is not known, but does not seem to be another way to injure the bone, and may be related to its ability to increase blood flow in the PDL and alveolar bone.
• Therapeutic ultrasound definitely increases blood flow in areas targeted with it. It will be interesting to see if increased blood flow in the PDL and adjacent alveolar bone decreases root resorption and/or alters the rate of tooth movement.

Referral to Self-Test

At this point, review the assigned reading for this module (Chapter 8, pages 278-295, *Contemporary Orthodontics,*5th edition) (much of the information in this module is new, not in the 4th edition). Then take the self-test and use it to direct your re-examination of parts of the teaching module and the reading.

Copyright 2013, UNC Department of Orthodontics

Self-test

Question 1

Which of the following would not be an acceptable way to speed up orthodontic tooth movement?

1. more flexible archwires
2. shorter intervals between appointments ✓
3. better orthodontic brackets
4. NiTi auxiliary springs
5. all of these would be OK

Correct

That’s right, shorter intervals between appointments is not an acceptable way to speed up tooth movement. If force is heavy and interrupted, this would not allow time for repair of damaged areas of bone and tooth roots; if force is continuous, more frequent appointments would have little effect because movement was continuing anyway. But remember that heavy continuous force would maximize damage to tooth roots, so it’s not acceptable.

Incorrect

No, that’s incorrect. Shorter intervals between appointments is not an acceptable way to speed up tooth movement. If force is heavy and interrupted, this would not allow time for repair of damaged areas of bone and tooth roots; if force is continuous, more frequent appointments would have little effect because movement was continuing anyway. But remember that heavy continuous force would maximize damage to tooth roots, so it’s not acceptable.

Question 2

What is the first thing that happens when an orthodontic spring is activated against a tooth?

1. bending of alveolar bone ✓
2. displacement of the tooth in the PDL space
3. release of chemical agents from affected cells
4. interruption of blood flow to compressed areas
5. all of them happen simultaneously

Correct

That’s right, the first thing to occur when force of any magnitude is placed against a tooth is bending of the alveolar bone. The tooth moves relative to external landmarks, but not within the PDL space until fluid is squeezed out as the bone springs back and the tooth is held where the spring pushed it. So answers 1 and 2 occur in that order; items 3 and 4 do occur essentially simultaneously.

Incorrect

No, that’s wrong. The first thing to occur when force of any magnitude is placed against a tooth is bending of the alveolar bone. The tooth moves relative to external landmarks, but not within the PDL space until fluid is squeezed out as the bone springs back and the tooth is held where the spring pushed it. So answers 1 and 2 occur in that order; items 3 and 4 do occur essentially simultaneously.

Question 3

How long does it take for pain from heavy force against a tooth to develop?

1. a few seconds ✓
2. a few minutes
3. a few hours
4. about 24 hours
5. a few days

Correct

That’s right, heavy force causes pain almost immediately, after just a few seconds. It develops as the bone springs back after teeth are displaced. That’s why you don’t maintain heavy force as you eat your dinner—you bite down and then remove the force, maintaining the pressure for only a few seconds. It’s also one of the ways you can tell if too much force is being delivered by an orthodontic wire or spring—if it hurts immediately as the wire is tied into a bracket or when the spring is connected, the force is too great.

Incorrect

No, that’s wrong. Heavy force causes pain almost immediately, after just a few seconds. It develops as the bone springs back after teeth are displaced. That’s why you don’t maintain heavy force as you eat your dinner—you bite down and then remove the force, maintaining the pressure for only a few seconds. It’s also one of the ways you can tell if too much force is being delivered by an orthodontic wire or spring—if it hurts immediately as the wire is tied into a bracket or when the spring is connected, the force is too great.

Question 4

How long does it take for piezo-electric signals to disappear after an orthodontic archwire is activated?

1. a few seconds ✓
2. a few minutes
3. a few hours
4. about 24 hours
5. a few days

Correct

That’s right. There would be a piezo-electric signal as the bone bends and when it bends back—and no further piezo-electric activity caused by the archwire, which would hold the tooth in position but would not cause further bone bending. So from a piezo-electric perspective, the action would be over in a few seconds—and that fits with what we know, that tooth movement has little or nothing to do with pizeo-electricity.

Incorrect

No, that’s wrong. There would be a piezo-electric signal as the bone bends and when it bends back—and no further piezo-electric activity caused by the archwire, which would hold the tooth in position but would not cause further bone bending. So from a piezo-electric perspective, the action would be over in a few seconds—and that that fits with what we know, that tooth movement has little or nothing to do with pizeo-electricity.

Question 5

With orthodontic force heavy enough to produce significantly large areas of necrosis in the periodontal ligament, how long does it take to get tooth movement?

1. a few hours
2. about 24 hours
3. about 2 days
4. 3-5 days
5. about 10 days ✓

Correct

That’s right, it would take about 10 days. Undermining resorption would be required because in the necrotic areas there would be no cells left to differentiate into osteoclasts and osteoblasts. Penetration of cells from adjacent PDL areas is slow, and activation of cells in the bone marrow beneath the lamina dura is necessary. It takes a few days for chemical signals to reach the bone marrow, and it takes another few days for the newly-formed osteoclasts in the bone marrow to remove the bone beneath the necrotic PDL area.

Incorrect

No, that’s wrong. It would take about 10 days. Undermining resorption would be required because in the necrotic areas there would be no cells left to differentiate into osteoclasts and osteoblasts. Penetration of cells from adjacent PDL areas is slow, and activation of cells in the bone marrow beneath the lamina dura is necessary. It takes a few days for chemical signals to reach the bone marrow, and it takes another few days for the newly-formed osteoclasts in the bone marrow to remove the bone beneath the necrotic PDL area.

Question 6

(A) Heavy orthodontic force causes pain because (B) heavy force causes greater stress on anchor teeth and more movement of anchor teeth. These statements are:

1. A true, B true, related
2. A true, B true, not related ✓
3. A true, B false
4. A false, B true
5. A and B false

Correct

That’s correct. A and B are true, but they have no cause and effect relationship. Heavy orthodontic force causes pain because of the necrotic areas and inflammation in the PDL that it produces. More movement of anchor teeth has to do with the differential in pressure between anchor teeth and those you want to move, whether or not pain is produced. So there’s no cause and effect relationship between the two true statements—except that both pain and loss of anchorage are undesirable effects of heavy force.

Incorrect

No, that’s incorrect. A and B are true but they have no cause and effect relationship. Heavy orthodontic force causes pain because of the necrotic areas and inflammation in the PDL that it produces. More movement of anchor teeth has to do with the differential in pressure between anchor teeth and those you want to move, whether or not pain is produced. So there’s no cause and effect relationship between the two true statements—except that both pain and loss of anchorage are undesirable effects of heavy force.

Question 7

Which of the following statements correctly describe magnets as orthodontic springs?

1. they produce more blood flow through the PDL
2. they exert particularly heavy force as they come closer together
3. piezo-electric signals are magnified by the presence of an electro-magnetic field
4. protecting against corrosion is a critical part of magnet design
5. a and b
6. a and c
7. b and c
8. b and d ✓
9. c and d

Correct

That’s right, the non-linear forces produced by magnets are a correct description, and so is the need to protect patients from potentially dangerous corrosion products if magnets are used intra-orally. They don’t change the biology, so they don’t affect blood flow and piezo-electric signals. Those characteristics indicate why magnets are not used much in modern orthodontics even though they can serve as orthodontic springs—they have poor spring characteristics, are potentially dangerous, and don’t affect the biologic response favorably (or unfavorably).

Incorrect

No, that’s incorrect. The non-linear forces produced by magnets are a correct description, and so is the need to protect patients from potentially dangerous corrosion products if magnets are used intra-orally. They don’t change the biology, so they don’t affect blood flow and piezo-electric signals. Those characteristics indicate why magnets are not used much in modern orthodontics even though they can serve as orthodontic springs—they have poor spring characteristics, are potentially dangerous, and don’t affect the biologic response favorably (or unfavorably).

Question 8

Which of the following drugs would be most likely to speed up tooth movement?

1. prostaglandin E ✓
2. Relaxin
3. ibuprofen
4. acetaminophen
5. Fosamax

Correct

That’s right, prostaglandin E stimulates both osteoclastic and osteoblastic activity, so it should speed up tooth movement and there is some evidence that it does—at the price of significant pain. Relaxin was not effective in a clinical trial; ibuprofen and Fosamax (a widely used bisphosphonate) can slow down tooth movement, and acetaminophen doesn’t affect it.

Incorrect

No, that’s wrong. Prostaglandin E stimulates both osteoclastic and osteoblastic activity, so it should speed up tooth movement and there is some evidence that it does—at the price of significant pain. Relaxin was not effective in a clinical trial; ibuprofen and Fosamax (a widely used bisphosphonate) can slow down tooth movement, and acetaminophen doesn’t affect it.

Question 9

Which of the following are correct about orthodontic treatments for patients who are taking a bisphosphonate for control of osteoporosis?

1. there is about a 3 month delay in tooth movement after a bisphosphonate is discontinued
2. extraction of teeth in orthodontics for a bisphosphonate patient is more likely to be necessary
3. temporary replacement of the bisphosphonate with Evista may facilitate treatment
4. heavier than normal orthodontic force is likely to be needed
5. a and b
6. a and c ✓
7. b and c
8. b and d
9. a, c and d

Correct

Yes, that’s right, there is about a 3 month delay, and replacing the bisphosphonate with Evista can maintain osteoporosis control during orthodontic treatment. Extractions in a bisphosphonate patient are not a good idea because of the possibility of severe bone healing problems, and heavier orthodontic force would not increase the rate of bone remodeling that is necessary for tooth movement.

Incorrect

No, that’s incorrect. The right answer is b and c. There is about a 3 month delay in response, and replacing the bisphosphonate with Evista can maintain osteoporosis control during orthodontic treatment. Extractions in a bisphosphonate patient are not a good idea because of the possibility of severe bone healing problems, and heavier orthodontic force would not increase the rate of bone remodeling that is necessary for tooth movement.

Question 10

Which of the following are disadvantages of 21st century corticotomy?

1. large gingival flaps
2. green-stick fractures of alveolar bone
3. major blood loss
4. long delay before initiating orthodontic treatment
5. a only ✓
6. b only
7. a and b
8. b and d
9. a, c and d

Correct

That’s correct. The large gingival flaps are a disadvantage because of the extensive surgery to elevate and reposition them, which increases morbidity compared to less invasive approaches. Green-stick fractures of alveolar bone are not part of current corticotomy techniques, and neither major blood loss nor a long delay in initiating orthodontic treatment would be expected.

Incorrect

No, that’s incorrect. The large gingival flaps are a disadvantage because of the extensive surgery to elevate and reposition them, which increases morbidity compared to less invasive approaches. Green-stick fractures of alveolar bone are not part of current corticotomy techniques, and neither major blood loss nor a long delay in initiating orthodontic treatment would be expected.

Question 11

Which of the following are potential advantages of the bone graft slurry used with corticotomy and piezocision?

1. prevention of loss of alveolar bone height
2. prevention of dehiscences in alveolar bone with orthodontic expansion
3. faster healing of the bone cuts
4. reduction in post-operative pain
5. a only
6. b only
7. a and b ✓
8. b and d
9. a, c and d

Correct

That’s right, the bone grafts are said by proponents of corticotomy and piezocision to prevent loss of alveolar bone height, and to decrease the possibility of bone dehiscence (breaks in the continuity of bone over the tooth roots) with subsequent orthodontic arch expansion. They aren’t used to increase the rate of healing of the bone cuts (which they would not be expected to affect) and have no effect on post-operative pain. The extent to which either of the potential advantages are real advantages has not been determined by evidence-based studies, and that must be kept in mind when evaluating these treatment procedures.

Incorrect

No, that’s incorrect. The bone grafts are said by proponents of corticotomy and piezocision to prevent loss of alveolar bone height, and to decrease the possibility of bone dehiscence (breaks in the continuity of bone over the tooth roots) with subsequent orthodontic arch expansion. They aren’t used to increase the rate of healing of the bone cuts (which they would not be expected to affect) and have no effect on post-operative pain. The extent to which either of the potential advantages are real advantages has not been determined by evidence-based studies, and that must be kept in mind when evaluating these treatment procedures.

Question 12

How much time in treatment should you expect to save with bone injury techniques during typical orthodontic therapy?

1. 2-3 months ✓
2. up to 6 months
3. 33% reduction in treatment time
4. 50% reduction in treatment time
5. 75% reduction in treatment time

Correct

That’s correct. Two months is the best answer in the above list—although there are no good data to support any of these answers. The effect of bone injury wears off in about 4 months, and if you moved the teeth twice as fast during that time, you would save about 2 months. There is no reason to expect that more rapid bone remodeling would occur after repair is complete, and no data to support that contention.

Incorrect

No, that’s incorrect. Two months is the best answer in the above list—although there are no good data to support any of these answers. The effect of bone injury wears off in about 4 months, and if you moved the teeth twice as fast during that time, you would save about 2 months. There is no reason to expect that more rapid bone remodeling would occur after repair is complete, and no data to support that contention.

Question 13

What is the mechanism of action for high-energy vibration to make teeth move faster?

1. activation of osteoclasts
2. increase in blood flow to the PDL
3. repair of micro-fractures in the alveolar bone
4. increased release of cytokines and prostaglandin in the PDL
5. the mechanism is unknown ✓

Correct

That’s right, the mechanism by which vibrating the teeth increases the rate of tooth movement (if it does) is unknown. That’s a problem because it is difficult to know what side effects and potential problems to look for without a firm biologic rationale. That is important when you are evaluating the claims from proponents for any new methodology. You have to look very carefully at the supporting data when the mechanism is really unknown.

Incorrect

No, that’s incorrect. The mechanism by which vibrating the teeth increases the rate of tooth movement (if it does) is unknown. That’s a problem because it is difficult to know what side effects and potential problems to look for without a firm biologic rationale. That is important when you are evaluating the claims from proponents for any new methodology. You have to look very carefully at the supporting data when the mechanism is really unknown.

Question 14

(A) The most likely mechanism by which high-intensity light accelerates tooth movement (if it does) is increased blood flow because (B) light chills the tissues it affects and cold is known to facilitate healing. These statements are:

1. A true, B true, related
2. A true, B true, not related
3. A true, B false ✓
4. A false, B true
5. A and B false

Correct

That’s right, A is true and B is false. Light energy is known to heat tissues, heating tissues is known to increase blood flow, and increased blood flow seems to facilitate tooth movement, so A is the most likely mechanism at present—though the mechanism is not understood.. Even though correctly-timed cold can facilitate healing after injury, light doesn’t chill tissues, so B is incorrect. What is the real mechanism for tissue-penetrating light? That’s still unknown.

Incorrect

No, that’s incorrect. A is true and B is false. Light energy is known to heat tissues, heating tissues is known to increase blood flow, and increased blood flow seems to facilitate tooth movement, so A is the most likely mechanism at present—though the mechanism is not understood. Even though correctly-timed cold can facilitate healing after injury, light doesn’t chill tissues, so B is incorrect. What is the real mechanism for tissue-penetrating light? That’s still unknown.