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In the event that incisal
overlap is <50%, consider making device on
the lower teeth. Doing so will minimize (practically eliminate)
the occurance of a lower
canine occluding of
the DE (Discluding Element) in aggressive excursive movements.
The fabrication sequence remains the same. When incisal overlap
is in excess of 50%, the use of a lower device tends to overly
translate the condyle(s) (by
increasing the vertical dimension of occluding in excursive movement).
The above images
show the use of the NTI-RV
(Reduced
Vertical) device to provide for Incisal
Guidance. The NTI-RV is typically used on the upper arch,
while the newer IG-NTI
is ideal for the lower.
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a)
b) 
- 
Confirm
a Standard
matrix fits passively over the (maxillary or mandibular) incisors (a)
(It may be necessary to
relieve
the internal of the device to so)
While
holding the matrix in place, have the patient tap on the matrix several
times, so that the mandible begins to reprogram. As the patient
gently
taps several times, the mandible's path of closure will begin to
stabilize
and replicate itself. If necessary, position the matrix laterally
so
that the two opposing central incisors contact the Discluding Element
upon
closure. If this ends up being off of the maxillary center,
mark
the matrix with a pencil line over a landmark (usually the central
midline)
so that placement during the reline can be easily replicated.
Confirm
the the occluding plane of the Discluding Element (DE) is parallel to
the
maxillary plane, and perpendicular to the lower incisors (b)
(some
occlusal schemes won't allow for this. The practitioner may need
to relieve the internals of the matrix to come as close as possible, or
may elect to place the NTI-tss on the opposite arch).
| If the patient has a relativley narrow mandibular
arch and the NTI
device as been adapted to the maxillary incisors, the lower canine(s)
may
easily occlude on the DE in excursive movement (there is a short
distance
to travel to get to the midline), thereby perpetuating clenching
intensity.
In this event, adapt the NTI device to the mandibular incisors, as in b
above.
See also: Excursive
clenching. |
c)
d) (e*
Load the matrix with
ethyl-methacrylate
(Parkell's SNAP clear and colorless acrylic for temporary
crowns
works best), in a damp, thick stage (c). (In a dappen dish, add
acrylic
powder to 1 to 2 cc's of liquid monomer, until the powder is no
longer
being readily absorbed. Do no stir the mixture, and do not "wet"
the matrix with monomer in advance...doing so will allow for
shattering
of the matrix!.) Remove the matrix with a snapping motion at two
minutes (d). Drop into a cup of hot tap water for 30 seconds
for rapid final cure, or let set undisturbed for another 4 or 5 minutes
to fully cure. Trim the internal embrasures with an Exacto knife
or finishing bur (e), ensuring to leave enough for a "snap in" and
"snap
out" retention.
For patients who can not
accommodate
to the cold cure acrylic, thermoplastic materials (*such
as the thermoplastic
matrix button) can be substituted, but with some limitations on
the sculpting of the final device.
(Now available: ThermoPlasticBeads are included in the Alternate
NTI Trial
Kit. (TPB
instructions for use) )
f) g)  h)
The finished sculpted and
polished NTI-tss
(f) will contact the two lower centrals in a functional arc of
closure.
In protrusive, the lower incisors will not be able to "get in front" of
the DE (g). The lower incisors will not able to "get behind" the DE (or
even within 1 millimeter of the anterior or posterior edges.)
Reduce the DE so as the
vertical
opening in not excessive.
Please
review the oversights (click here).
If the incisors are
considerably
flared:
Follow normal protocol for adaptation of matrix, without addressing
the relationship between the DE and the opposing incisors.
Reshape
and add acrylic to the DE to make the occluding surface parallel to the
maxillary occlusal plane. In extreme cases the long axis of the
lower
incisors may not be perpendicular to the DE. Doing so would slant
the DE in such a way that it would provide resistance to
protrusive
movement. Due to the patient's pre-existing adaptation, there are
usually no adverse effects.
DE parallel to maxillary occlusal
plane
(see also: Excessive
vertical in protrusion)
A general rule-of-thumb is to have the occluding surface of the
Discluding
Element
parallel with the maxillary occlusal plane...
(the below animation plays for 16 seconds and then repeats).
...the above photo on the
left was
sent by a patient, wondering if her NTI was adjusted properly.
The photo on the right was
altered
to show a more appropriate alignment.
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