Assessment of Borderline Patients

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In determining if a patient can be treated without extraction, the primary question is whether the mandibular arch crowding can be resolved while the anterior teeth are maintained in acceptable positions. This decision is based partly on the extent of the mandibular tooth size-arch length discrepancy. In general, 4-6 mm of arch length can be "controlled" with good mechanics. This additional 4-6 mm of space can be gained by slightly advancing the incisors and uprighting the molars. More space can be gained if the posterior transverse dimensions can be expanded.

In my experience, approximately 15% to 20% of patients are definitely extraction cases. Another 50% definitely do not require extraction. The critical area is the other 30% or so of patients who are borderline cases. In our practice, nearly all of these borderline patients are treated without extraction. Five factors allow the use of nonextraction therapy and enable the mandibular incisors to remain positioned upright over basal bone:

1. Space gained by transverse expansion with rapid palatal expanders and lip bumpers. Studies by Adkins et al1 and Chung and Font2 show that there is a 0.6-0.7 mm perimeter increase for every millimeter of posterior expansion.

2. The -5 degrees of torque built into the mandibular incisor brackets maintains proper uprighting, while, at the same time, the -6 degrees of angulation in the mandibular first molar brackets will upright the mandibular molars, creating more arch length in the distal segments.

3. The use of rectangular flexible archwires such as braided stainless steel, nickel, copper, and titanium wires allows mandibular anterior torque control, beginning with the initial archwire.

4. Judicious use of class 3 elastics with the initial arch-wire can prevent the mandibular incisors from excessive labial tipping. The elastics can also increase available space by helping to upright the molars.

5. Interproximal enamel reduction of the dentition can create several extra millimeters of space in each arch. At least 0.25 mm of enamel can be removed from each interproximal surface of the mandibular anterior teeth. If the teeth are large, even more enamel can be safely removed.

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