Orthodontic management of long face syndrome

Long face syndrome is among the most difficult problems encountered in the practice of orthodontics. And, unless orthodontic treatments are carefully monitored and controlled, patients with long face syndrome risk developing even more severe characteristics of the syndrome.' Characteristics of long face syndrome include excessive eruption of posterior teeth, large increases in vertical dimension, dental and skeletal open bite, and a retrusively positioned mandible-all of which have been major causes of poor orthodontic results.'

Monitoring for long face syndrome throughout treatment is an important part of the proper therapy for patients who are at risk. One of the best ways to measure whether long face syndrome characteristics exist is to measure the cephalometric MM angle-the angle between the palatal plane (ANS-PNS) and the mandibular plane (Go-Gn) (Fig. 1). The average MM angle is 26. Larger MM angles (more than 32) warn the clinician that further increases in this angle may result in an increase in long face syndrome characteristics. Frequent (every six to ten months) cephalometric radiography, to monitor changes in the MM angle, is necessary for patients who are at risk of developing characteristics of long face syndrome.

Fig. 1. The palatal plane to mandibular plane angle (MM) is a key diagnostic measurement in patients with long face syndrome.


Fig. 2. Relative material stiffness (which is directly proportional to load- deflection rate) of commonly used arch wires. For practical clinical purposes, the material stiffness can be used to determine the relative amount of force that a wire will provide per unit of activation."


Fig. 3. A transpalatal arch (TPA) can be used in patients with long face syndrome to restrict vertical descent of the maxillary molars.

Treatment alternatives There are various treatment mod- ifications that reduce the likeli- hood of the expression of long face syndrome characteristics. Premolar extractions have proved to be effective and should be care- fully considered. Also, closing space by moving molars forward reduces the vertical dimension of occlusion. This permits the mandible to rotate into a more closed position along its arc of clo- sure, resulting in a more forward positioned chin and a smaller MM angle.4 Conversely, procedures that result in bite opening, such as arch expansion and advancing teeth, should be avoided.

Long face syndrome also can be controlled by minimizing the extrusion of posterior teeth, particularly maxillary molars. They extrude more easily than mandibular molars for two reasons: the masticatory muscles restrict the posterior mandibular teeth more than their maxillary counterparts; and the thin cortices and trabecular bone of the maxilla provide less resistance to movement than the thick cortices and more dense trabeculae of the mandible."

Use of arch wires-Careful forc application helps to control extrusion of posterior teeth. Also, usin arch wires with a low load-deflection rate greatly reduces tooth extrusion. (The load-deflection rate of an arch wire is defined as the force that an arch wire produces per unit of activation.) Two characteristics, size and compositio of the wire, contribute to th wire's load-deflection rate.' Ever wire and bracket system exerts extrusive force upon the teeth, bu these extrusive forces are expressed differently in different patients. Figure 2 shows the relative load-deflection rates of commonly used arch wires." Since patients with long face syndrome have relatively weak masticatory muscles, high load-deflection rate arch wires (e.g., stainless steel) easily overpower their masticatory muscles, resulting in posterior tooth extrusion. Patients who do not have long face syndrome generally have stronger masticatory muscles, so the same high load-deflection rate arch wires will not cause as much posterior tooth extrusion in such patients.

As a rule, stainless steel arch wires should be avoided in patients with long face syndrome. Leveling and aligning can be done with low load-deflection rate arch wires, such as those made of nickel-titanium. However, these arch wires are too flimsy to be used for space closure and other mechanics. An intermediate load-deflection rate arch wire is needed for these procedures. TMA, a titanium-molybdenum alloy arch wire (Ormco, Orange, CA), is firm enough for these mechanics, and its load-deflection rate is low enough to prevent unwanted molar extrusion.

Anchorage enhancement is another way that maxillary molar extrusion can be prevented. The enhancement can be accomplished with transpalatal arches (TPA5).'1 TPAs are fabricated by attaching a heavy wire (.036 ss), with a 5 mm diameter loop at the midline, that has been secured to the mesiolingual surfaces of the maxillary molar bands. (Fig. 3). When a patient talks or swallows, the tongue exerts a palatally directed force against the loop. This, in turn, helps to overcome the extrusive force of most orthodontic mechanics." (Molar crown rotation and root torque can also be accomplished with the use of TPA5.) The more a patient exhibits the characteristics of long face syndrome, the more critical is the need to use a TPA.

Fig. 4. (Top) Cephalometric x-ray shows the descent of PNS common in patients with long face syndrome. (Bottom) Cephalonietric x-ray of a patient with no symptoms of long face syndrome. Note the lack of vertical descent of PNS.

High-pull headgear - High-pull headgear (HPHg) prevents maxillary molar extrusion even more effectively than a transpalatal arch. In patients with long face syndrome, the masticatory muscles do not support the palate. This lack of muscular support causes the posterior half of the palate to tip downward and mesially, carrying the maxillary molars downward and mesially as well (Fig. 4)1213 The direction of force applied by the HPHg helps prevent this palatal tipping (Fig. 5). Clinically, it has been demonstrated that 14 hours of HPHg wear per day eliminates most maxillary molar extrusion.

HPHg is also used for Class II correction. Fourteen hours of HPHg wear per day helps correct Class II discrepancies in two ways: the maxillary restriction common to all types of headgear and repositioning appliances occurs, and, probably more important, the restriction of maxillary molar eruption allows the mandible to rotate into a more forward position as it grows-" A number of clinicians, including Terel Root in the 1970s, recognized the importance of maxillary molar vertica restriction as a method of Class I correction. According to Root, ' high-pull facebow is used in individuals in whom increases in vertical dimension are to be avoided. As a growth guidance appliance, it (HPHg) can decrease vertical development of the maxilla, thereby allowing for autorotation of the mandible, and maximizing the horizontal expression of mandibular growth."

Twin block appliance - Using a twin block appliance is an alternative method of Class II correction. It consists of repositioning the mandible by using removable maxillary and mandibular splints with acrylic ramps. The ramps measure 5 mm to 8 mm in thickness in the premolar region. This impinges on the patient's freeway space, which, in turn, results in increased masseter tension. This tension not only restricts vertical descent of the maxillary posterior teeth, but also produces a relative intrusion of the posterior aspect of the maxilla in growing patients." This phenomenon, which is called the bite-block effect, provides excellent vertical control. Although long-term studies documenting the results of this treatment are not yet available, the early results are promising.

Figure 6 shows the cephalometnic superimposition of a long face syndrome patient. Her Class II malocclusion was corrected with a twin block. Notice the excellent vertical control, highlighted by a 2 decrease in the MM angle. The MM angle was controlled due to the bite-block effect. No further tipping of PNS occurred during this treatment phase. The next phase of treatment involves fixed appliance therapy. Low load-deflection arch wires and a transpalatal arch will help control the MM angle. Premolar extractions will help reduce crowding, dentoalveolar protrusion, and the MM angle.

Fig. 5. High-pull headgear (left). The inner bow of the headgear is attached to the maxillary first molar. The direction of the force applied by the headgear (right) helps prevent the descent of the posterior portion of the palate.

Fig. 6. Initial cephalornetric (dotted lines and shaded teeth) and final cephalometric outline (continuous lines) of a patient with long face syndrome whose Class 11 malocclusion was corrected in 11 months with a twin block appliance.

Summary and conclusions

Long face syndrome has been recognized for many decades as one of the major problems in orthodontic treatment. A number of clinicians and lecturers warn against the indiscriminate use of heavy forces in patients in whom adverse side effects, such as long face syndrome, may be expressed. One of the most important duties of the orthodontic clinician is to avoid counterproductive side effects excess molar extrusion) even if their probability of expression appears low.' Orthodontic clinicians must be aware of the symptoms of long face syndrome, and, even if a small chance of excess molar eruption exists, must use a mechanical system that minimizes this side effect.

Dr. Prittinen practices general dentistry in Virginia, Minnesota, and is also an orthodontics instructor for the United States Dental Institute.

Address correspondence to:
Jim R. Prittinen, DDS
216 North Fifth Avenue
Virginia, MN 55792.

References

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General Dentistry, 1997 Vol. 45, No 6, pp. 568-572. Dr. Jim Prittinen, DDS