Download Jaw and Order

SUMMARIES
ANNUAL SESSION
Jaw and
Order
Presented by Dr. John McDonald.
Summarized by Dr. Bruce P. Hawley, Northern Region Editor
EDITOR’S NOTE:
Dr. McDonald’s presentation was a remarkably clear review
of facial development and this review
is a must-read for clinical staff members.
there are problems if they are lost early.
Generally, lower teeth come in around
six months before the respective upper
teeth. The order of eruption involves
the front teeth first, back teeth second,
r. John McDonald addressed
and middle teeth last. In erupting, teeth
an audience of PCSO team
“slide” along the teeth in front of them
members on the effects of jaw
(except for the first teeth that erupt), and
growth and eruption on orthodontic
a panoramic x-ray allows us to track the
treatment. What we do in orthodontics
eruption pattern of teeth. We still do not
is miraculous. We change our patients,
know exactly why teeth erupt, but they
but the patients are changing themselves,
seem to “drop” in, with guidance from
DR. McDONALD
in essence a moving target. Growth and
the tooth in front. Panoramic x-rays
development is an area that we are really
allow us to count the teeth, see the path
only beginning to understand biologically. Our genes
of eruption and location of teeth, and identify missing
control our growth and development, including the size
or extra teeth.
and shape of our teeth, their location, and our skeletal
The AAO recommends an orthodontic examination by
classification. While growth is fairly predictable for large
age seven. As the permanent first molars and incisors are
populations, it varies considerably for individuals. The
frequently
in by that age, we can see evidence of crowdknowledge of growth and development distinguishes
ing
as
well
as malocclusion. With an accompanying
orthodontists from many other dental practitioners, and it
panoramic
x-ray,
Dr. McDonald feels he can often specuis important for the assistant to be able to communicate
late
on
the
entire
treatment
plan at an early age, even if
on this subject. We want our patients to have the best
treatment
may
not
be
needed
for several years. Teeth will
final occlusions and smiles, and by our knowledge we
erupt
straight
if
there
is
enough
room for them; the lips,
will distinguish ourselves. Braces are not the entire story,
tongue,
and
chewing
assist
in
this
process. Teeth erupt
as management of the jaw relationship is critical. While
until
they
hit
something,
such
as
opposing
teeth. When
many patients want the art of orthodontics, we work
space
is
adequate
and
teeth
are
still
not
straight,
we look
within the realm of physics, art, and biology, which create
for
other
perverse
infl
uences.
Insuffi
cient
space
can
result
boundaries related to treatment.
in crooked teeth, teeth that do not erupt, or a tooth becomWe want straight teeth but also would like for them to reing dissolved by an adjacent tooth. The panogram allows
main stable after treatment. We strive to achieve beautiful
us to count the teeth and check the path of eruption. A
smiles and a good bite relationship, reducing protrusion
permanent tooth should erupt relatively soon after the
without root resorption. Orthodontics does not hurt when
primary tooth exfoliates. When upper permanent lateral
it is done correctly. Employees are valuable for what is
incisors are missing, the permanent canines often move
in their fingertips as well as in their heads. Dr. McDonald
toward the central incisors and may impact. This can also
estimates that 25% to 30% of orthodontic residents chose
result with peg lateral incisors, since there is not a normal
orthodontics because they had a good personal orthodonroot surface to guide the eruption of the canines. Identic or dental experience.
tify submerged primary teeth without a successor. Teeth
develop in an orderly and predictable fashion, so learn
the differences between normal and abnormal situations.
RUPTION AND EVELOPMENT
Often simple intervention, sometimes with extractions,
OF THE ENTITION
can help enormously. Dr. McDonald looks at crowding
Eruption is the process of teeth coming into the mouth,
as a math problem. Let the lower permanent incisors get
and this happens generally when the root is 30% to
straight, even if the lower primary canines are extracted,
50% formed. Primary teeth are space holders, and
and move crowding to the back of the arch, where there is
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P C S O B U L L ET I N • S P R I N G 2 0 0 7
SUMMARIES
ANNUAL SESSION
leeway space. Early extraction does not necessarily solve
the crowding but rather allows management for later time
but with aligned incisors.
SKELETAL DEVELOPMENT
There are three major bones in the head: the cranium,
which houses the brain; the maxilla, which sits at the
base of the brain; and the mandible, which is completely
independent and has a joint. Different genes control
the maxilla and mandible, which are different types of
bones. In order for the teeth to fit together, the jaws have
to fit together and be lined up. Frequently in growth
modification we are working in the 2mm to 8mm range.
Maxillas can be changed, while mandibles cannot. The
length of the mandible cannot be altered, but the relative growth between the bones can be. The lower jaw is
analogous to a leg bone, but the way it grows is relative
to the maxilla. Mandibles grow more than maxillas, and
especially during the pubertal growth spurt. Like a long
bone, the mandible grows at the condyle at a cartilageonous growth center. Genetics determines lower jaw
growth, and chin cups have a negligible effect on the
mandible. Mesial to the permanent first molars, there is
virtually no increase for space for teeth in the mandible
after age seven, as the mandible grows mainly behind
or posterior to the dentition. The chin moves downward
and forward with condylar growth. Eruption takes place
while the bones are growing.
The maxilla is actually multiple bones with sutural
joints, which are modifiable by pressure or tension. The
bones of the maxilla can be pulled apart and bone fills
in, such as during rapid palatal expansion. They are not
as interlocked in children as in older individuals, and the
growth direction of the maxillary growth plate tends to
follow the mandible. Reverse pull headgear shifts the
maxilla forward on the sutures. The horizontal position of the maxilla and mandible determines the facial
profile. Growth expression manifests itself through the
teeth and their occlusion. Headfilms allow us to trace
around landmarks for measurement. A point and B point
are the forward-most horizontal points of the bases of
the maxilla and mandible, respectively. The anteroposterior position of point A and B differs for Class I, II, and
Class III patients, and the size of the chin affects
the appearance of the Class II individual.
In American orthodontic practices, we see around 50%
of our patients with a Class I malocclusion, while 45%
are Class II and 5% are Class III. The basis of Class
II correction is holding the upper jaw and letting the
mandible grow. This can be done with headgear, twin
block appliance, Herbst, or Class II elastics. If there is no
treatment in a Class II case, then nothing changes, as the
upper jaw grows along with the lower jaw. Children only
grow once, and if treatment is not done during growth,
the teeth will not spontaneously change their relationship. Boys grow later than girls, whose growth is usually
done within six months of the onset of menstrual cycle.
Pubertal growth only happens once, so don’t miss out on
it in rendering an essential orthodontic correction. Stress
to patient family who may be resistant to needed orthodontic treatment that you cannot recapture the growth
period and that “your teeth will otherwise stick out for
the rest of your life.” With a general knowledge of dental
and skeletal development, you will be able to better
communicate with patients and parents about orthodontic
treatment and assist in the management and success of
orthodontic cases you work with.
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COMPONENT REPORTS
Continued from page 6
They will present a comprehensive overview of “Self Ligation Appliances” from
an evidence-based perspective. The role
of indirect bracket placement, optimized
wire selections based on metallurgy,
and utilizations of 3-D models will be
discussed. (6 CE credits available).
The staff program features Ms. Carolyn
Friedman founder of Ortho Assist TM.
She will provide an encompassing
S P R I N G 2 0 0 7 • P C S O B U L L ET I N
discussion of insurance, marketing
efficiency, referrals, and optimal
utilization of the ortho team. (3 CE
credits available).
Additional course and registration
information can be found online at
www.oregondental.org.
Jay Schofield, President
Salem, Oregon
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