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 orthodontists do not understand how to use control of the bite to improve facial growth patterns, so they just straighten teeth for esthetics. During the last few decades of the twentieth century, researchers tried to understand facial growth, but it turned out to be very complex, and attempts to improve it by pushing on the bones with springs and wires usually relapsed. They 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. As a result, although it is well known that certain facial growth patterns are much more likely to result in TMJ disorders and sleep apnea, conventional esthetic orthodontics ignores the developing facial growth problems and its limitation of airway passage development while straightening the teeth.
ESTHETIC ORTHODONTICS - Due to the enormous demand for esthetics, funds for studying facial growth have been replaced by research to study faster and more efficient mechanisms for straightening teeth; and dental schools only teach esthetic orthodontics, which employs braces (metal brackets and wires) or pre-formed plastic shells (clear aligners such as invisalign) to realign all the teeth. Esthetic orthodontics 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 jaws continue growing 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. The appliances can hold the mandible in an improved location while realigning the teeth to support it there. 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 today 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 treatment 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. The technique provides excellent control of every aspect of each tooth's position, but the process is slow, because the tooth roots can only be drawn through the bone slowly, or they resorb.
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 and expand the airway passage through the face. In addition, this inhibition of jaw muscle development usually occurs at the worst possible time, because orthodontists wait to place braces until the age of 12, so they can include the second molars in the alignment, which is also the time of the pubertal growth spurt, when jaw muscle development should be most rapid, and when inhibiting it has the most damaging effects. Treatment that locks the mandible posteriorly facilitates aligning the teeth, but it also strains jawbone growth and restricts airway passage. Academic orthodontists here still spend most of their effort trying to justify the use of premolar extraction and braces by claiming that there is no proof that they negatively impact facial growth. The problem is that they ignore the pathologically developing facial growth while straightening the teeth.
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 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. The locking together of the upper and lower teeth in the bite prevents the upper jawbone from expanding, because the upper jawbone is locked to a lower jawbone that cannot expand but can only advance; and it prevents the lower jawbone from advancing, because the lower jawbone is locked to an upper jawbone that cannot advance but can only expand. When the mandible cannot advance, continuing growth at the back of the mandible drives the front of the mandible and the lower front teeth into the overlapping upper front teeth at the anterior overbite. The resulting pressure can splay the upper front teeth, or it can compress the lower front teeth, which typically causes them to buckle, because an arch is incompressible. To try and prevent that buckling due to continuing adult jawbone growth, most orthodontists now use "forever" retainers, made of wires bonded behind the front teeth.
If the patient had an overbite before the orthodontic treatment was begun, the retainer should include a front flat bite plate (Hawley) to prevent a rapid return of the overbite, especially during the first year after the braces are removed when the posterior teeth are still mobile. At that stage, the teeth are easily intruded by bruxism, which is why displaced TMJ disks are especially common in teenagers who develop clicking within a year after their braces are removed.
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. 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. Esthetic orthodontics with braces or clear aligners can also disrupt a strained bite situation and thereby interrupt the pain generating cycle. Physical therapy and exercises can help the postural muscles maintain a healthy mandibular position during esthetic orthodontic 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 and good jawbone structures.
FUNCTIONAL ORTHODONTICS
While American orthodontists were developing more efficient methods for esthetically aligning the teeth, European orthodontists were developing more efficient methods for expanding and realigning the jawbones based on research showing 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 lower jawbone. When jaw muscle activity is weak, the upper jawbone remains narrow; and the lower jawbone does not advance properly. Their appliances have certain advantages in regard to airway management and preventing TMJ disorders. While esthetic orthodontics waits until age 12, so the second molars can be included in the alignment of the teeth; functional orthodontics can begin early, when it has a greater effect on craniofacial growth.
EARLY TREATMENT – The first effective functional orthodontic treatment is breast feeding. Squeezing on the nipple develops the jaw closing muscles, enabling babies to start making facial expressions, so we can know what they are feeling. Natural breast feeding also begins advancing the mandible as the baby moves it back and forth to improve the flow of milk, strengthening the superior lateral pterygoids. In contrast, bottle feeding primarily develops the lips and the front of the tongue.
As the teeth erupt, babies need to transition from breast milk to real food with consistency rather than baby food, (baby led weaning), to develop their jaw muscles. Forceful chewing is ideal exercise for the jaw muscles and for ensuring healthy facial growth. 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. Tribal cultures that chew tough food don't have orthodontic problems or horizontal facial growth restrictions. An exercise gum was shown in a study of schoolchildren to improve the direction of facial growth, but our commercial chewing gum is too soft to prevent the teeth from contacting through the gum. There is now an exercise gum available called Mastica from Greece.
There are also orthodontic devices to help jaw development in young children. Some dental companies produce molded silicone rubber appliances, such as the Myobrace or the Myomunchie, that young children can chew on to help develop their jawbones. Beginning at age 6, when the permanent first molars arrive; custom functional appliances can be made for use during sleep (when all facial growth occurs), 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, the facial growth pattern continues much more slowly, but its effects are still clinically significant. Horizontal jawbone growth is needed to increase airway passage space to reduce resistance in airway flow as muscle strength decreases about 5% per decade, so your respiratory muscles do not have to keep increasing their effort with age.
Recently, some 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 emphasizes tongue exercises, based on the belief that tongue strength is the key to wide palates, proper tongue posture, 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 the tongue is not responsible for providing the forces that expand the palate. Bite forces, not tongue forces, expand palates. 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.
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 do not even attempt to prevent the development of a TMJ disorder later in life. 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. Typically the upper dental arch is more V-shaped than U-shaped, the upper teeth come in crooked due to lack of space, the lower dental arch gets locked back behind the upper front teeth, and the lower teeth tip inward to fit 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 slow palate expansion, as explained in detail in PALATE EXPANSION under the tab TREATMENTS.
2. THE DOWNWARDLY AND BACKWARDLY ROTATING LOWER JAWBONE
Another problem that is correlated with TMJ disorders and sleep apnea is a mandible that rotates down and back, as seen below left, rather than advancing forward to open the pharyngeal airway. When the normal advancement of the mandible is blocked by the bite, the mandible can only rotate down and back, moving into the space needed for the pharyngeal airway.
DOWNWARD AND BACKWARDLY ROTATING MANDIBLE FORWARD ROTATING MANDIBLE WITH DEEP OVERBITE
WEAK CHIN LONG FACE STRONG CHIN SHORT FACE
The same two divergent facial growth patterns are contrasted with X-rays shown below. In the forwardly rotating mandible on the left side, the mandible is still prevented from advancing, because it is locked back (posteriorly displaced) behind a deep overbite. This is a facial growth pattern common in people with strong jaw closing muscles, as discussed later in common orthodontic problem # 4.
FORWARD ROTATING MANDIBLE BACKWARD ROTATING MANDIBLE
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.
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 then reverted back to the backward rotating pattern again after the gum chewing stopped.
The downward and backward rotation of the mandible can make 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 close the lips to swallow. The opening of the lips that occurs when the muscles are relaxed creates an easy path for airway flow, often resulting in habitual mouth breathing.
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. It can hold the upper jawbone as far upward and forward as needed to maintain an adequate airway passage. Such growth can be seen above in the muscular dystrophy patient illustrated above.
If the tongue acquires a rest position between the front teeth, it can produce an anterior open bite that makes it impossible to incise food or bite your fingernails. For decades, orthodontists assumed that such 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; because light steady types of forces determine the shapes of bones. 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. The mandible in these cases does not rotate down and back, it shifts straight downward, lengthening the whole face.
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 attempts to prevent 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 to compensate for the weakening of the muscles that occurs during adulthood. The upper front teeth have positions that are relatively stable, because they are controlled by the contraction of the lower lip during swallowing. If the lower front teeth are locked behind them, the mandible cannot advance, and the body compensates with forward head posture to keep its airway open, as summarized in THE ROLE OF POSTURE under the tab TMJ DISORDERS and explained in detail in BITES AND BODY POSTURE under the tab FOR DOCTORS.
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. Functional orthodontics uses front flat bite plate appliances to gradually eliminate the overbite by redirecting 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.
COSTS OF FUNCTIONAL ORTHODONTICS
The cost of single stage treatment involving a removable appliance is usually about $2500. 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.