It's not unusual for a tooth to be fairly stubborn in terms of its color. You can change aligners or have a wire adjustment, but the mirror still shows pretty much the same smile. What's going on underneath the gumline is the supporting tissue doing its part. Ortho treatment relies on that tissue doing its job: the bone has to make a path in front of the moving root and then rebuild the support behind it.
Bio-stimulation is the term for techniques that have an effect on the local response. Micro-osteoperforation is one such technique which is associated with the regional acceleratory phenomenon (RAP), a temporary increase in bone activity following a controlled stimulus. The appliance still moves the tooth, but it's the biology around the root that dictates how smoothly the movement can occur.
Bones Have to Shift
Every tooth is in alveolar bone and is connected to it via the periodontal ligament. That ligament is a thin layer of tissue containing connective tissue, nerve endings, blood vessels and cells which are capable of sensing pressure and tension. When a brace or clear aligner applies force the ligament transduces that mechanical loading into a biochemical signal.
On the pressure side the ligament is compressing. Osteoclasts are receiving the signal to resorb a very thin layer of mineralised bone from the surface which is facing the direction of movement. On the opposite (tension) side, the stretched cells are signalling the osteoblasts to lay down collagen and form new bone matrix. Resorption and formation occur in sequence with the ligament and the bone around it all adjusting as the tooth moves.
Bone is organised into small functional units which balance resorbed bone with formed bone. Cortical bone provides much of the outer strength of the jaw, cancellous bone has a more open internal structure. Both respond to mechanical stress. The nature of the response is dependent on local anatomy, the type of movement and the support available around the root.
That's why treatment speed is going to vary. Bone turnover is a response to mechanical loading, blood flow, local growth factors and signals from the immune cells. Age, bone quality, gum health, previous dental work and the amount of movement in your treatment plan will all have an effect. Two people could be wearing exactly the same appliance and still end up with very different timescales.
The Signal Behind Tooth Movement
The body doesn't move a tooth by pushing it through solid bone. It generates a controlled inflammatory response in the periodontal ligament. That is the process of mechanotransduction whereby the cells take the pressure and tension and convert it into cellular activity.
Compressed ligament cells release signals which attract osteoclast precursors. Those cells then mature, attach to the bone surface and commence the resorption phase. On the tension side osteoblasts and other local cells start to form collagen and lay down new bone. Blood vessels and the connective tissue provide the medium through which oxygen, nutrients and waste products are exchanged during the cycle of remodelling.
The changes take time. Bone removed from one area isn't replaced in the same instant, and a tooth can actually slow right down while the surrounding tissue catches up. An aligner can appear virtually unchanged for several days as the bone and ligament are all active underneath the gumline. More force doesn't necessarily equate to better movement. The appliance has to work within the limits of the tissue.
Why RAP Enters the Conversation
The Regional Acceleratory Phenomenon (RAP) is the term used to describe a short-term increase in local bone turnover following a controlled injury or surgical stimulus. It was first described by Harold Frost in skeletal bone. In orthodontics, it provides a mechanism to explain why a small localised stimulus can result in increased activity of the bone in the immediate vicinity for a short period of time.
Micro-osteoperforations create little holes in the cortical bone adjacent to the teeth being moved. The body interprets that as a repair stimulus, and the response is a local one. There's a change in blood flow, immune cells come in, and local cells release the cytokines and growth factors that are involved in the repair process. The response is very local and doesn't result in any change to the overall bone metabolism of the body.
The sequence involves a number of cell types. Immune cells are involved in initiating the response. Osteoclasts are involved in bone resorption. Mesenchymal cells and other local cells can be involved in the production of collagen and the extracellular matrix, which supports the new tissue. Osteoblasts then go on to be involved in bone formation. The length and intensity of the sequence will of course be dependent on the patient's anatomy, the stimulus and the orthodontic mechanics that are present at the same time.
What the Research Can Tell Us
Cytokines are the messenger proteins that mediate inflammation, tissue repair and bone turnover. TNF alpha is one of the inflammatory signals that has been studied in the context of orthodontic force. Other signals modulate the receptor activator of nuclear factor kappa-B ligand pathway, which is involved in the maturation of osteoclast precursors and their attachment to bone. TGF-beta is also involved in tissue repair and matrix regulation.
These signals form a network. The PDL cells, bone cells, blood vessels, osteoblasts, osteoclasts and the immune system all communicate at the sites of bone remodelling around the root. A measured inflammatory response is required for orthodontic movement. An overzealous inflammatory response, poor oral hygiene, untreated periodontal disease or insufficient bone support can all alter the clinical picture.
Research into micro-osteoperforations is inconclusive. Some papers have reported faster tooth movement or shorter intervals between appointments. Others have found a smaller effect or no real acceleration at all. The studies in question have used a variety of appliances, at various stages of treatment, with different perforation depths, different follow-up periods and different types of movement. You can't therefore draw any one conclusion as to how long the treatment will take.
The technique doesn't eliminate the need for sound mechanics. Perforation depth, location, number, timing and spacing all have an effect on the tissue response. Root position, cortical bone thickness, bone mechanical competence, gum health and the force of the appliance all play a part. A technique which may be very useful for one movement may be of very little value for another.
Light-based treatments use different wavelengths and protocols than micro-osteoperforation. Greenberg's laser treatments are a separate issue from the surgical stimulus discussed here. Photobiomodulation is being studied in terms of its effect on cellular energy, inflammation and tissue repair, but the parameters and the evidence in no way transfer from one treatment to another.
The Part Your Plan Plays
Your records give the orthodontist a far better view of the situation around each tooth. Root position, the thickness and shape of the supporting bone, the bite, the gums and any previous dental treatment all have an effect on the mechanics that can be used safely.
Crowding may well require a different sequence to space closure after an extraction. A bite correction which involves movement across several planes of the mouth will have very different demands on the supporting bone than a simple small alignment change. Consistent aligner wear, elastic use, appliance care and regular monitoring all give the tissue the best chance of responding as intended. Smoking, active periodontal disease, certain medications, and untreated inflammation can all complicate the healing and bone turnover.
During treatment, your ortho will be looking out for the sign that a tooth is approaching the edge of its available support. All sorts of things can be assessed in this respect (diagnostic imaging, root position, recession, mobility, changes in the bone around the root) and will all have an influence on what the next step is. It may be that a slower sequence is required or that the mechanics are altered in some way to protect the result.
A Tooth’s Support Is Three-Dimensional
Tooth movement is frequently described as the root moving along a flat track. That's not how the jaw works. Bone is all around each root in multiple directions, and the available support can vary considerably from the front to the back, from the cheek to the tongue side of the tooth. The cortical plate may be quite thick in one area and very thin in another.
A small movement at the crown can have a significant effect on the root. Uprighting, rotation, intrusion, extrusion and root translation all place different demands on the periodontal ligament. The orthodontist has to take that into account when working out how much force to use and how long to leave between the brackets.
A 'healthy-looking' smile doesn't necessarily tell the whole story. The crown may look perfectly aligned, whilst the roots are still in the process of settling into their final position. The bone support is only really assessable via radiographic and clinical examination.
The surrounding bone also has an effect on stability post-treatment. The teeth obviously need time to settle into a position that the periodontal ligament and bone can support. Retainers are used to maintain that position as the tissue reorganises. The active phase will still be relatively short and a sensible retention programme is required.
Age and Dental History Change the Conversation
Adult bone is fully formed but is still capable of remodelling. It may respond at a different rate to younger bone, particularly in the presence of gum recession, bone loss, crowns, implants, missing teeth or previous orthodontics. Age in itself is not the determining factor. The actual condition of the teeth, roots, gums and the supporting bone is what matters.
Previous dental work can alter the biomechanics. A tooth with a large restoration may require protection from certain forces. A missing tooth will alter the position of the adjacent roots. A history of periodontal disease may necessitate periodontal treatment and more intensive monitoring prior to the commencement of orthodontic movement.
These details don't make treatment impossible at all. They just make the planning even more important. The safest sequence of events might involve more gradual activation, smaller movements, further imaging and/or co-management with another dental professional. The adjunctive treatment should be part of that plan rather than the plan itself.
Bone loss is something that requires special consideration. A tooth in a situation of reduced support may still move, but the margin for error is much smaller. The ortho may well be constrained as to the direction or amount of movement that can be achieved, may well have to use much lighter forces or may well need to deal with the periodontal inflammation first. Moving teeth through thin or compromised bone carries an increased risk of recession, mobility and an ultimately unstable result.
What You May Notice During Treatment
Most patients will notice the appliance before they will notice the biology. A new aligner will probably feel a bit tight for a day or two. Braces can, of course, create pressure around a bracket and can make a tooth feel sore during an adjustment. All of that will generally settle as the periodontal ligament adapts.
The rate of movement is also very much visible and can be quite uneven. One tooth may move quite rapidly whilst the tooth next to it seems to be holding its position. Roots can move at a different rate to crowns and spaces can close unevenly prior to the bite coming into equilibrium. The progress photos and scans will often show changes which are extremely difficult to see from day to day.
Some patients will be concerned when their aligner still looks pretty much the same after a few days. That appearance in no way tells you what is happening to the bone. The movement may be very small, or the tissue may simply be in a phase of reorganisation which is not yet visible. The only way the ortho can get any information is by having the patient wear the appliance for the prescribed number of hours and by having the monitoring appointments. A mirror is of no use at all in this respect.
Call the office if the discomfort is severe, getting worse, or is accompanied by swelling, fever, a loose appliance or a change in the gums. Those are signs that require attention for reasons which go beyond the normal degree of soreness you'd expect with orthodontic force.
A consultation is where these questions become concrete. The orthodontist can go through the amount of movement required, the quality of the supporting bone, and the factors that may slow or impede the response. That conversation gives you a very realistic idea of what an adjunctive treatment could do and what it simply couldn't do.
How the Decision Is Made
A bio-stimulatory recommendation begins with the biomechanics of the case. The clinician will be looking at the tooth or teeth in question, the direction of movement required, the amount of bone available, the state of the gums, and the appliance that will be used to deliver the force. The technique employed in a canine retraction scenario may well have a very different role in an alignment or bite correction situation.
The timing is also important. A local stimulus may or may not be considered before a particular stage of movement, may be considered during a period of active remodelling or may be considered at no stage at all. Repeating a treatment doesn't necessarily lead to a better response. Tissue healing, patient comfort and the evidence for the particular protocol are all factors that need to be taken into account.
A considered plan will include a discussion of the various alternatives. Traditional braces and clear aligners can both generate the force required for many types of tooth movement. A light-based treatment may be an option for a different indication than micro-osteoperforation. In certain cases, the optimal approach is simply to use the ortho appliance and let the bone respond to the force at its own rate.
That's a personal decision, but it should be based on anatomy and evidence rather than a promised percentage. The time it takes to treat is going to be dictated by the initial position of the teeth, the complexity of the bite, the health of the supporting tissues, and the degree of compliance at home.
Dr Vickie Greenberg can go through the various options that would be appropriate for your case (traditional braces, clear aligners etc). If you have any questions about bone support or are considering ortho treatment, then your initial appointment is the opportunity for the team to go through your records and assess the movements you require. You can also arrange a consultation with Greenberg Orthodontics & TMJ Airway. Your timeline is dictated by the interplay between the appliance, the bone and the way your body responds.
