Orthodontics and TMJ Disorders
Orthodontics can control bites, and bites affect how faces grow, so orthodontics should be able to improve how faces grow; but most orthodontics in the US today just aligns the teeth for esthetics. During the last few decades of the twentieth century, researchers tried to understand facial growth, but it turned out to be too complex, and attempts to improve it by pushing on the bones with springs and wires usually relapsed. Researchers identified some of the mechanisms involved in the growth processes that build the upper and lower jawbones, but they failed to recognize the important role of bite forces in stimulating those growth mechanisms and the adaptive systems needed to coordinate them, and they did not realize that jawbone growth continues slowly during adulthood.
Since then, due to the enormous demand for esthetics, funds for studying facial growth have been replaced by research to study faster and more efficient mechanisms for straightening teeth. Dentists in school only learn about esthetic orthodontics, which employs braces (metal brackets and wires) or pre-formed plastic shells (clear aligners such as invisalign) to realign all the teeth. It does not address the alignment of the jawbones, which is the root problem in most TMJ disorders. It can align all the teeth while the face grows crooked.
Functional orthodontics has been popular in Europe for decades, and it is preferred by most TMJ specialists, because it is less concerned with the straightness of the teeth and more concerned with alignment and development of the jawbones. It employs removeable oral appliances containing expansion screws, springs, and inclines designed to shape and position the jawbones. It can also align the teeth, but not as perfectly as braces can. The appliances can be removed for cleaning, eating, and important social functions; but they must be worn most of the time during active treatment.
Both of these orthodontic techniques, (esthetic and functional), have advantages and disadvantages in different situations. Therefore, if you are considering orthodontics, the following information should help you and your dentist understand your options. The first half explains and contrasts these two different orthodontic styles, and the second half describes how the most common orthodontic problems are treated by each. The goal is to enable parents to look at their children and judge the type of orthodontics they will need.
ESTHETIC ORTHODONTICS
BRACES - In the 1950s, dentists believed that the shapes and positions of the jawbones are determined by genetics, and therefore the goal of orthodontics was simply to straighten the teeth within the existing bone structure. Dentists in the United States developed a clever system of metal brackets glued to the exact center of each tooth and connected by a series of pre-fabricated precisely curved arch wires to align all the teeth until they conform exactly to the curve of the arch wires. The technique provides excellent control of every aspect of each tooth's position, and it does not require patient cooperation. The teeth can be straightened as long as there is sufficient underlying jawbone and the child can be brought in for regular adjustments. If the jawbones are too small to accommodate all the teeth, permanent premolar teeth are removed, and the rest of the teeth are rearranged to fit within the small jawbones.
More than half a century later, we know that the shapes and positions of the jawbones are very much affected by the jaw muscles. Strong jaw muscle activity expands the upper jawbone and advances the tooth-containing front half (the corpus) of the mandible (the lower jawbone). When jaw muscle activity is weak, the upper jawbone remains narrow; and the lower jawbone does not advance properly.
Unfortunately, braces can inhibit jaw muscle development, because the pressure they apply to the teeth keeps them tender, which causes the jaw closing muscles to fire weakly and carefully, which can prevent them from gaining the strength they need to regulate facial growth. In addition, this inhibition of jaw muscle development usually occurs at the worst possible time, because orthodontists wait to place braces until the second molars have erupted in order to include them in the alignment, which is also about the time of the pubertal growth spurt, when jaw muscle development should be most rapid, and when inhibiting it has the most damaging effects.
CLEAR ALIGNERS employ a series of removable computer generated plastic shells to align the upper and lower teeth in a manner very similar to braces but with more convenience and less control. The appliances cannot easily open or close spaces between teeth or expand the dental arches; but they can be removed for brushing, and they are usually worn for a shorter time period.
RETENTION - is needed after esthetic orthodontics to prevent relapse. If the teeth are not "retained", they tend to return to where they came from. One cause of this post-orthodontic relapse is the "neutral zone" which holds the teeth in a balance between forces from the lips, cheeks, tongue, and bite, as shown below. If a tooth moves outside of its neutral zone, these forces will move it back in. Esthetic orthodontics was not designed to take neutral zone forces into account.
The other cause of relapse, especially crowding of the lower front teeth, is continuing adult jawbone growth. Esthetic orthodontics usually leaves the upper and lower teeth steeply interdigitated, because it was developed before we realized that the jawbone growth continues during adulthood. When the upper and lower jawbones are effectively locked together by a steeply interdigitated bite, the upper jawbone cannot expand normally, because it is locked to a lower jawbone that cannot expand; and the lower jawbone cannot translate normally, because it is locked to an upper jawbone that can only expand. Then the natural elongation of the mandible drives the lower front teeth into the overlapping upper front teeth at the anterior overbite, which splays those upper front teeth and compresses the front of the lower dental arch. The compression of the front of the lower arch typically causes buckling of the lower front teeth. To prevent that buckling, most orthodontists now use "forever" retainers, made of wires bonded behind those teeth, which is not really a sustainable solution.
Esthetic orthodontics with braces or clear aligners can sometimes help treat TMJ disorders that are caused by jaw muscle tightness by deprogramming the jaw muscles, like a FRONT FLAT PLATE APPLIANCE does. Basically it can disrupt a strained bite situation and thereby interrupt the pain generating cycle in which it plays a part. Then, if the jaw muscles can hold the mandible in a better location for the duration of the treatment, the teeth will end up fitting there. Physical therapy and exercises can help the postural muscles maintain a healthy mandibular position during the treatment.
However, braces and clear aligners cannot be considered treatments for TMJ disorders, because TMJ disorders are caused by the malpositioning of the jawbones rather than the straightness of the teeth. Therefore, esthetic orthodontics is a good tool for people who want very straight teeth and already have well developed jaw muscles, good jawbone structures, and a healthy symmetrical facial growth pattern.
FUNCTIONAL ORTHODONTICS
While American orthodontists were developing more efficient methods for aligning the teeth, European orthodontists were developing more efficient methods for expanding and realigning the jawbones using removeable oral appliances. Their appliances have certain advantages in regard to airway management and preventing TMJ disorders.
EARLY TREATMENT – While esthetic orthodontics waits until age 12, when the second molars arrive; functional orthodontics can begin early, when it has a greater effect on craniofacial growth. Even before the adult teeth have begun to erupt, young children can chew for short periods of time on specially molded rubber appliances, such as the Myobrace or the Myomunchie to help develop their jawbones. Beginning at age 6, when the permanent first molars arrive, functional appliances can be used to develop the jawbones and make room for the teeth so they don't come in crooked due to lack of space. Bones and teeth move easily in children.
ADULT TREATMENT - In adults, everything moves more slowly, but the effects are still significant. Lower jawbones can be advanced and/or repositioned more symmetrically, and upper jawbones can be expanded. Recently, some old functional orthodontic treatments have been repackaged for marketing to adults. ALF (advanced lightwire functional) appliances, which are made of wires soldered to bands glued onto the teeth, are thin and easy to wear; but they must be worn for a long time, making it hard to keep the gums healthy. DNA, RNA, and HOMEOBLOCK APPLIANCES are traditional screw type palate expansion appliances that are sometimes marketed as treatments for obstructive sleep apnea, and they can facilitate nasal breathing; but the expansion in the nasal cavity occurs too far from the obstruction to have much effect on sleep apnea. These appliances are also marketed as, "epigenetic orthodontics"; which is misleading; because there is no evidence or likelihood that straightening the teeth or widening the palate of an adult will lead to straighter teeth or wider palates in their offspring.
ORTHOTROPICS - is a style of functional orthodontics that also incorporates tongue exercises and stretches, based on the belief that tongue strength is the key to wide palates and healthy facial growth. The tongue naturally helps guide the erupting teeth into place, and people who are born without tongues develop narrow collapsed palates; but that does not mean the tongue is responsible for providing the forces that expand the palate. Bite forces expand palates. Bottle fed infants get much less tongue exercise early in life than breast fed infants, and they can be expected to have weaker tongues; but they do not have narrower palates. In fact, there are several devices for measuring tongue strength (such as the tongue digital spoon), but tongue strength has never been correlated to palate width. The tongue muscles are part of a network of craniofacial and neck muscles which all work together. To strengthen one requires strengthening them all.
HEALTHY CHEWING - is the ideal functional orthodontic treatment and myofunctional therapy. Tribal cultures that chew tough food don't have orthodontic problems or horizontal facial growth restrictions. Babies need to nurse forcefully; and they need to transition from breast milk to food with consistency rather than baby food, (baby led weaning), so their jaw muscles keep developing as the teeth are erupting. Once all the baby teeth are in, tough foods like dried fruit, whole nuts, and jerky act like a gym for the jaw muscles, because they prevent the opposing teeth from making physical contact, which immediately shuts down the jaw muscles by activating the jaw opening reflex. In healthy jaw muscle exercise, the jaw muscles fire in long smooth strokes uninterrupted by protective reflexes, and the mandible pivots and slides on the bolus without allowing the opposing teeth to penetrate it.
COMPARATIVE ORTHODONTICS
The two different styles of orthodontics have very different applications. Braces are powerful esthetic tools. By dragging the roots through the bone in any direction desired, they can control every angle of a tooth's ultimate position. However, they have to move the roots slowly, or they can resorb. The process cannot do anything to prevent the development of a TMJ disorder later in life, because it cannot move big blocks of bone. Also, making the teeth tender for a long period of time can prevent jaw muscle development, which promotes vertical facial growth, so it should be used for people who already have a good horizontal facial growth pattern. In contrast, functional orthodontics should be used when the pattern of facial growth needs to be improved. Orthodontists worldwide agree that ideal treatment would start with functional orthodontics to shape and position the jawbones and then finish with braces to align the teeth, like framing followed by finish carpentry. The following text describes the way both of these different types of orthodontics deal with each of the common orthodontic problems that predispose a child to have TMJ disorders and airway problems later in life - the narrow upper jawbone, the downwardly and backwardly rotating lower jawbone, excessive vertical face length, and the deep or steep overbite.
COMMON ORTHODONTIC PROBLEMS
1. THE NARROW UPPER JAWBONE
The width of the upper jawbone is determined largely by the activity of the jaw muscles, and many modern children have narrow upper jawbones due to weak jaw muscle activity. Frequently the upper dental arch is more V-shaped than U-shaped. The upper teeth come in crooked due to lack of space, and the lower dental arch can get locked back behind them from where it cannot easily advance. The lower teeth tip inward to fit inside the narrowed line of upper teeth. The tongue cannot fit up in the front of the palate where it belongs, so it acquires a downward and backward resting posture, often resting on top of the lower teeth, which tips them further inward. The lowered tongue posture also lowers mandibular posture, which rotates its front end down and back into the space needed for the pharyngeal airway passage.
MOUTH BREATHING is the most damaging consequence of a narrow upper jawbone. The narrowing that results in the V-shaped upper dental arch typically occurs in the premolar area just under the anterior nasal airway, where the roof of the mouth (the palate) is the floor of the nose. When that area is too narrow to allow adequate nasal airway passage, people become obligate mouth breathers. Their lips are always parted to provide oral airflow. Many people with palates of borderline width become obligate mouth breathers whenever a cold or allergy causes swelling of their nasal passages.
CROSSBITE occurs when the upper jawbone is so much narrower than the lower jawbone that some of the lower teeth fit outside of the upper teeth instead of inside them. In bilateral crossbite, both sides have this reversed interdigitation. In unilateral crossbite, the lower jawbone shifts to one side to create a reversed interdigitation only on that side, while the other side fits normally.
TREATMENT of narrow upper jawbones can provided by widening them. Slow palate expansion can be performed with removeable appliances after the median palatine suture fuses in the late teens, because the whole upper jawbone unfolds and remodels in response to light steady forces at any age.
2. THE DOWNWARDLY AND BACKWARDLY ROTATING LOWER JAWBONE
Another problem that is correlated with TMJ disorders and has become common in modern children is a mandible that rotates down and back, as seen below left, rather than advancing and rotating forward to open the pharyngeal airway.
DOWNWARD AND BACKWARDLY ROTATING MANDIBLE FORWARD ROTATING MANDIBLE WITH DEEP OVERBITE
WEAK CHIN LONG FACE STRONG CHIN SHORT FACE
The backward rotation pattern, seen on the left side above and the right side below, can be contrasted with the forward rotation pattern seen on the right side above and the left side below.
FORWARD ROTATING MANDIBLE BACKWARD ROTATING MANDIBLE
However, in the forwardly rotating mandibles shown here in the strong chin short face and the forwardly rotating mandible, the mandible is still locked back (posteriorly displaced) behind a deep overbite; which is a different pathological facial growth process that is discussed in the next section.
The downwardly and backwardly rotating facial growth pattern can certainly be caused by weak jaw muscles. People with jaw muscle injury or disease show an extreme backward rotating facial growth pattern, as seen in the X-rays of a patient with muscular dystrophy below. The picture on the right below is a longitudinal study, and the picture on the left below compares the myotonic dystrophy face at late adolescence with a normal adolescent face, seen as a white line. In the myotonic dystrophy patient, the upper teeth have acquired a form that fits around the tongue, which has found a resting posture that maintains a pharyngeal airway, despite the front portion of the mandible (the corpus containing the teeth) pulling the rest of the face downward and backward around it. The vertical redirection of growth in the upper jawbone has prevented it from expanding normally.
Conversely, the pattern of backward rotation can be reversed by making the jaw muscles stronger and healthier. A study of children with downwardly and backwardly rotating facial growth patterns found that chewing exercise gum for a year reversed their facial growth to a forward rotating pattern, which reverted back to the backward rotating pattern again after the gum chewing stopped.
In many people, the downward and backward rotation of the mandible makes the framework of bones and teeth at the front of the face too long for the curtain of soft tissues hanging down from the top of the head to comfortably cover them, producing a characteristic gummy smile and visible strain in the muscles surrounding the mouth when they have to hold the lips closed to maintain a lip seal. The opening of the lips that occurs when the peri-oral muscles relax often results in habitual mouth breathing, because the open lips create an easy path for airway flow.
In some people with weak jaw muscles and downwardly and backwardly rotating lower jawbones, the tongue intervenes to prevent the upper jawbone from following the front of the lower jawbone down and back by holding the upper jawbone upward and forward to maintain an adequate airway passage, as can be seen above in the growth of the muscular dystrophy patient above. In about 5 percent of the population, an anterior tongue posture responds to a restrictive bite by placing itself between the teeth, which has caused an anterior open bite that prevents the front teeth from coming into contact and thereby makes it impossible to incise food or bite your fingernails. For decades, orthodontists assumed that these anterior open bites were caused by a retained infantile swallowing pattern, which included a tongue thrust during the swallow. However, studies using force sensors showed that it is the resting posture of the tongue, not its functional activity during swallowing, that determines tooth positions. Here again, it is the light steady types of forces, such as those produced by postural muscle tonus, that determine the shapes of bones. Tongue posture is steady, because it maintains the airway, so it shapes the bones effectively . Intermittent forces, like during swallowing, primarily determine the internal architecture of the bones to enable them to withstand the functional forces they will receive.
3. EXCESSIVE VERTICAL FACIAL GROWTH - A third facial growth pattern that is correlated with TMJ disorders and has become a common problem in modern children, primarily in those with weak jaw closing muscles, is excessive vertical lengthening of the whole face, both at the front and back of the mandible. It does not rotate down and back, it shifts downward.
TREATMENT
Excessive vertical facial growth has always been a difficult problem for esthetic orthodontics, because the only tool they have had to limit it is high-pull headgear; but that is still retractive in nature. In addition, by the time the second molars have erupted at 12 years, much of the vertical excess has already occurred, and reversing it would require maxillary impaction surgery to remove a wedge of bone from under the nose so the upper jawbone can be rotated upward, or intruding multiple teeth using springs or elastics attached to temporary anchorage devices (TADs) implanted in bones around the face.
Functional orthodontics treats excessive vertical growth by redirecting growth horizontally. The upper jawbone is expanded, and the lower jawbone is advanced.
4. DEEP OR STEEP OVERBITE
A fourth orthodontic problem that frequently causes TMJ disorders today is an overbite that is deep or steep enough to lock the mandible back and thereby prevent it from advancing. The overbite is the vertical overlap of the front teeth. When you bite all the way down on your back teeth, your upper front teeth should only cover a small portion of your lower front teeth, as shown on the right below, and you should be able to slide your bottom teeth easily forward onto your top teeth. If your lower front teeth are mostly covered by your upper front teeth, you have a large overbite, as shown on the left below. If your lower front teeth are completely covered by your upper front teeth, you have a 100% overbite. In some people, the overbite is even deeper, and the lower front teeth impact the soft tissues of the palate just behind the upper front teeth. In other people, the overbite is steep rather than deep, making it difficult or impossible to slide your lower front teeth up onto the backs of your upper front teeth.
DEEP OVERBITE SHALLOW OVERBITE
The trouble with a deep or steep overbite is that it can lock the mandible back behind the upper front teeth and thereby prevent it from advancing during adulthood to compensate for the weakening of the muscles that also occurs during adulthood. The upper front teeth have positions that are relatively stable, because they are controlled by the tension of the lower lip and its powerful contraction during swallowing. If the lower front teeth are locked behind stable upper front teeth, the mandible cannot advance, and the body compensates with forward head posture to keep its airway open.
TREATMENT of steep or deep overbite can be accomplished with braces or functional orthodontics. Braces can eliminate the overbite by arch leveling, especially if assisted by using TADs (temporary anchorage devices) to intrude super-erupted teeth, however the treatment needs to be followed up with retainers that maintain the corrected overbite, such as Hawley or front flat bite plate appliances. These appliances can gradually eliminate the overbite if worn at night for many years to redirect bruxism forces axially onto the anterior teeth, and the process can be accelerated by using finger springs to tip out some of the front teeth or orthodontic elastics on little buttons temporarily glued to the back teeth. One problem with treating deep or steep overbites is that most dentists and orthodontists have come to accept them as normal.
COSTS OF FUNCTIONAL ORTHODONTICS
The cost of single stage treatment involving a removable appliance is usually about $2000. A second stage is often added at about half that cost to refine tooth positions and to later function as a retainer to prevent relapse of the overbite.