Palate Expansion
For decades, most dentists believed that palate expansion in adults was impossible; because they assumed that all the expansion occurs by separation of the maxillary bones at the midline suture, and therefore it must stop when the suture ossifies in the late teenage years. Now we know that palates can be expanded at any age using light steady forces, because the ossified suture and the rest of the midface adapt to a reshaping and unfolding of the maxillary bones, and the expansion can be maintained post-treatment by a stable bite and a retainer with a stable raised bite table that employs the forces of nocturnal bruxism to broadly load the expanded structure.
NATURAL PALATE EXPANSION
The upper jawbone and upper dental arch are designed to grow wide enough to fit around the tongue so the tongue can rest up high in the palate with its tip just behind the upper front teeth. The upper jawbone is a framework of two paired (right and left) maxillary bones, and they expand by spreading apart, like unfolding a pair of wings, in two directions.
In one direction, the two maxillary bones spread apart by rotating outward and upward due to growth at the midpalatal suture, seen from left to right in the illustration below. As biting forces drives these two maxillary bones upward, they also flatten the palate. In our ancestors, very strong chewers always had very shallow wide palates.
In another direction, the two maxillary bones swing out around their front-most connection, as can be seen from left to right in the illustration below, which flattens the midface. In our ancestors, very strong chewers also had very flat faces.
However, this natural upper jawbone expansion depends on jaw muscle forces, and the forces we apply with our jaw muscles have changed radically in the last couple of centuries due to our soft food diets. As a result, in modern humans, many upper jawbones do not fully expand and remain narrow. Instead of growing wide enough to fit around the tongue, they only grow wide enough to fit around the thumb or a pacifier.
One cause of narrow upper jawbones is weak jaw muscles. In fact, similar narrow upper jawbones can be produced in monkeys and other animals experimentally raised on soft diets. Our jaw muscles are about half as strong as they were just a couple of hundred years ago before processed foods came to provide most of our nutrition. Without sufficient forces to unfold the upper jawbone, it grows vertically rather than horizontally. When it can't grow out, it grows down. The downward growth then lowers the posture of the mandible, which tightens the cheeks and thereby causes them to push inward on the sides of the upper jawbone, further limiting natural palate expansion. The role of the tight cheeks in maintaining the narrow upper jawbone can be seen in the effectiveness of Frankel appliances, which expand palates simply by employing lip bumpers that hold the lips and cheeks away from the teeth.
Another cause of narrow upper jawbones is steeply cusped unworn teeth that connect the upper and lower jawbones like a cranial suture. The lower jawbone grows by translating rather than expanding, because it is made of one thick piece of cortical bone that gets driven forward by growth from behind. When it is locked to the upper teeth by a steeply interdigitated bite, it prevents those upper teeth from shifting to accommodate expansion of their underlying bones, which restricts the growth of those bones.
EFFECTS OF NARROW PALATES
When the upper jawbone cannot expand properly, the nasal airway just above it also remains narrow; because the roof of the upper jawbone (the palate) is the floor of the nose. People with very narrow palates are usually obligate mouth breathers. When their faces are at rest, their lips are slightly parted to allow an oral airway. People with slightly narrow palates become obligate mouth breathers whenever their nasal passages swell due to colds or allergies. Habitual mouth breathers have enough space for a nasal airway, but they don't use it.
MOUTH BREATHING - causes significant health problems. It prevents the nose from moistening, filtering, and warming the air before it hits the throat - making mouth breathers prone to upper respiratory problems. It prevents the release from the paranasal sinuses of nitric oxide; which has antibacterial properties, a vasodilating effect, and a role in endothelial health. It also impairs the effectiveness of respiration, because the nose acts like a little lung. In one study, volunteers who wore nose clips to force mouth breathing for a couple of hours developed lowered arterial oxygen levels. Sleep studies show that mouth breathing increases airway resistance and decreases sleep quality.
Mouth breathing also sustains itself by the way it alters facial growth. Mouth breathing lowers mandibular posture to create space for an oral airway passage, which causes vertical instead of horizontal facial growth, which prevents the nose from growing wide enough to allow normal nasal breathing. In monkeys forced to mouth breathe by experimentally plugging their nostrils, the mandible grows straight downward, resulting in a long narrow face. In humans forced to mouth breathe by an insufficient nasal airway, the mandible grows by rotating down and back, resulting in a long, narrow, and retrusive face (recessed chin).
MECHANICALLY ASSISTED PALATE EXPANSION - can increase the cross-sectional area of the nasal cavity at any age. The mechanical forces delivered transversely across the palate do not simply move the two maxillary bones apart in parallel in a manner that can be measured by the increase of distance across the suture, because this is biology not mechanics. The suture does not just widen, it remodels to allow an unfolding of the maxillary bones, which lowers the center of the palate; and the rest of the midface adapts by simultaneously remodeling its structural elements to accommodate the pattern of delivery of jaw muscle forces.
NASAL AIRWAY RESISTANCE - can be reduced by palate expansion, which is usually the goal of the treatment. The roof of the mouth is the floor of the nose, and a small increase in the width of the palate, which forms the base of the triangular nasal cavity, can significantly increase its cross sectional area. In particular, the upper premolar area, where most modern upper jawbones are especially narrow, is just below the front portion of the nasal cavity where the airway is most commonly restricted.
Expansive forces can increase the cross-sectional width of the palate, however they also push on the teeth, which tips those teeth to an extent that depends on the mechanics used to provide the forces. Bent wire appliances, such as quad helix appliances, bionators, Crozats, and ALF (advanced lightwire functional) appliances; employ a framework of wires and springs soldered to metal bands; and they can be relatively unobtrusive; but they tend to do more tipping of teeth and less expansion of the bones. Expansion screw appliances; such as Schwartz, Haas, Biobloc, Homeoblock, DNA, RNA, and Hyrax appliances; employ a powerful turnbuckle which can significantly move the maxillary bones, but they still cause some tipping of teeth. Recently some orthodontists have been using fixed (glued in) palate expanders with TADs (temporary anchorage devices), which are tiny lag screws temporarily implanted in the palate, to minimize tipping of the teeth.
OUR PALATE EXPANSION APPLIANCES are traditional expansion screw appliances that we have redesigned for adults by using a thin metal expansion framework and avoiding bulk in the front of the palate where it would interfere with tongue posture and speech. Whether finger springs or orthopedic inclines are added depends on patient needs. Our fee is $2,000 for the basic expansion screw appliance. If more widening or further tooth straightening is needed, a second stage of expansion can be made for half price. At the end of treatment, you'll need to wear a retainer at night on a long-term basis. That retainer can have various orthopedic features, like a front flat bite plate, and also various orthodontic features, like minor tooth straightening with clear aligners.
Although the palate expansion devices usually come with instructions to perform two turns weekly, we recommend making frequent turns that are as small as possible, because light steady forces shape bones. If the expansion produces pain, you are going too fast and triggering localized inflammation, which prevents smooth remodeling of bone. You can take your appliance out for meals and important social functions, but it cannot be worn only at night unless the bite is very flat or continually adjusted to fit the expansion, because the interdigitation of upper and lower teeth will shift the palatal bones back to their pre-treatment positions every day.
COMBINING PALATE EXPANSION WITH A SLEEP APNEA APPLIANCE - When a patient has both a narrow palate and obstructive sleep apnea, we can combine treatment for sleep apnea with palate expansion by using an upper palate expansion appliance to which the telescopic components and the lower member of the mandibular advancement appliance can be added every night. The process requires dexterity, but most people have no trouble with it.
GAPS BETWEEN TEETH - can result from palate widening. If the teeth were crowded before treatment due to insufficient space, simply straightening the teeth can close the gaps and align the teeth into a structural arch, which is incompressible and thereby helps retain the expansion. In people with some front teeth that are unusually narrow, the gaps can be shifted to the sides of those teeth and then closed by widening those teeth using composite resin or porcelain veneers.
RETENTION - After the expansion process, the palatal width needs to be maintained by wearing a removeable retainer every night and ensuring the presence of a solid stable natural bite table, which functions as an effective retainer during the day. If needed, the bite table can be stabilized by shaving down high spots, building up low spots, or using elastics to shift individual teeth. The night retainer should also provide a stable bite table, because people will clench or grind during sleep, and distributing the forces generated along the newly established upper jawbone structure acts to stabilize that structure.
Stabilizing the natural bite may or may not require directly treating the lower teeth. The lower dental arch is generally V shaped, and it typically advances along with any kind of TMJ treatment, thereby bringing a wider part of the lower dentition opposite the directly widening part of the upper dentition can maintain bite stability. However, if the teeth are steeply interdigitated, any change in their relative positions can cause uncomfortable collisions between opposing teeth. In such cases, flattening the steeply interdigitated teeth slightly by either reducing the steepest cusps (mountain peaks) or temporarily bonding composite resin into the deepest valleys can greatly facilitate treatment.
If flattening is not an option, the lower teeth may need to be uprighted to recreate a steep interdigitation. In most cases, the lower teeth were tipped inward to interdigitate with narrow upper teeth anyway. The lower teeth can be uprighted during palate expansion by making the palatal expander include flanges that reach down along side the inner edges of the lower teeth, or they can be uprighted after palate expansion by wearing a small unobtrusive removeable "spring" type of appliance, a series of clear aligners, or by pulling individual pairs of teeth into proper alignment using orthodontic elastics attached to tiny buttons temporarily glued to the sides of the involved teeth.