Underbite (Class III)
An underbite refers to a Class III malocclusion where the upper front teeth bite behind the lower front teeth. The back teeth
are usually in crossbite as well. Class III malocclusion is usually skeletal in origin and can be due to a normal upper jaw with a protrusive lower jaw, or a small upper jaw
with a normal lower jaw. The most severe case exhibit a small upper jaw with a protrusive lower jaw and those cases will require jaw surgery after cessation of growth.
Treatment is best undertaken during pre-puberty, especially if the problem has been identified as due to a small upper jaw. The wearing of a facemask is the treatment of choice
at age 8 or 9. In the adolescent years, facemask and Class III elastics can still be used, but success can be limited. Extractions may be indicated when dental crowding is
present. It is not uncommon to delay treatment of Class III patients till after complete cessation of jaw growth, at which time, an orthodontic-surgical approach will be
undertaken.
Problem: Class III malocclusion with severe dental crowding in both arches and right posterior crossbite.
Treatment: Upper and lower braces with extractions of 4 bicuspid teeth,
Hyrax appliance for correcting the crossbite and Class III elastics to correct the bite.
Treatment time is 2 yrs 7 mos.
Problem: Class III malocclusion in a 10 year old child.
Treatment: Phase I treatment with upper partial braces for 13 months. Patient wore a
facemask 12-14 hours per day for 8 months. Patient never
needed Phase II treatment.
Problem:
Class III malocclusion in a 7 years 10 month old boy. Maxilla is narrow resulting in a right crossbite and an end-on bite on the left side. The anterior teeth are also in
crossbite.
Treatment:
Phase I treatment with a Hyrax expander to correct the crossbite. Posterior bite plates were cemented onto the lower molars to open the bite so that
the upper braces would stay on and the upper front teeth can 'clear' the lower front teeth during correction. A facemask
is worn daily for 12 - 14 hours for a total of
12 months. Total treatment time for Phase I is 14 months. A Phase II treatment may be needed whenever all the permanent teeth has erupted.
Problem: Class III malocclusion in a 10y 8m old Chinese boy.
Treatment: Non-extraction treatment with full braces for 2y 10m. Patient wore a
facemask to protract the upper teeth. The lower teeth were
distalized with a lip bumper and the front teeth were tipped back with Class III elastics.
Problem: Class III dental malocclusion with crossbite of upper front teeth and presence of lower dental spacing due to multiple missing teeth in an adult
female.
Treatment: Non-extraction treatment with full braces for 21 months. All lower dental spaces were successfully closed.
Problem: Class III malocclusion in an adult male who had braces with removal of four bicuspid teeth as a teenager from age 14-17. However, his lower jaw continued to grow and the
upper and lower teeth became crooked again. Patient did not want to have jaw surgery to correct the problem.
Treatment: Removal of four wisdom teeth and a lower incisor with full braces for 23 months. Treatment resulted in dental compensation for the
skeletal jaw discrepancy with a very esthetic smile and a functional bite.
Problem: Class III open bite malocclusion with bilateral crossbite and crowding of upper and lower teeth in an adult female.
Treatment: Non-extraction treatment with full braces and upper jaw surgery to correct the skeletal Class III open bite and crossbite.
Treatment time was 19 months.
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