Page 36 - Dental Practice South Asia 18-6

prosthodontic section

BITE
All dentists use marking ribbon to mark and adjust any high spots
to achieve equal contacts of the teeth when the patient bites (MIP).
However, if the patient has worn or broken teeth, periodontal
disease, muscle or TMJ dysfunction, then the patient’s bite (MIP) in
relation to their jaw position may not be working well and may be
one should consider changing the bite to a new jaw position.
• Maximal Intercuspal Position (MIP): the best fit of the teeth
regardless of condylar position.
• Centric Relation (CR): a maxillomandibular relationship inde-
pendent of tooth contact.
• Centric Occlusion (CO): the occlusion (first contact)of oppos-
ing teeth when the mandible is in centric relation.

It makes anatomical sense to have the jaw in a physiologic posi-
tion where the condyles are against the disc orthopedically aligned
FIG 10 in the fossa when all the teeth are occluded (CR+MIP=CO) with
normal neuromuscular function (Figure 9). It is important to con-
firm that the Centric Relation jaw position is a comfortable, stable,
and repeatable position. This should involve the use of an orthotic
device that incorporates an anterior deprogrammer (something
between the anterior teeth) which separates the posterior teeth,
relaxes the muscles, and allows the condyles to seat upward and for-
ward against the disc in the fossa (Figure 10) The orthotic device can
be adjusted periodically as healing and remodeling occurs until the
TM Joints have stabilized. Methods for registering a CR interoc-
clusal record usually incorporates the use of an anterior discluder
such as a Lucia Jig, leaf gauge, etc.
Since the articulator axis is not the true hinge axis of the patient
when using a facebow or Kois DFA, changing Vertical Dimension of
Occlusion (VDO) on the articulator can create positive errors or
discrepancies in the Bite. When changing VDO, it is highly recom-
mended to take an interocclusal record at the VDO that the restora-
tions, prostheses, or occlusal splint will be fabricated to reduce pos-
FIG 11 itive errors for less adjustments of the Bite.

CHEWING
It is important to understand incising and lateral chewing move-
ments (envelope of function) to simulate more accurate chewing
movements in an articulator. The protrusive pathway (downward
and forward movement of the condyles) together with incisal guid-
ance can have a discluding influence on the distal inclines of the
upper teeth and/or mesial inclines of the lower teeth in incising
chewing movements (Figure 11). Research shows that the angle of
o
o
the protrusive pathway ranges from 25 to 75 to an axis-horizon-
tal plane of reference. The protrusive pathway is the only discluding
factor that can be programmed into an articulator which can be
communicated with a protrusive interocclusal record to set the
articulator. If no protrusive record is taken, it is recommended to
o
set the articulator to a 25 protrusive pathway to create negative
errors in incising chewing movements.
The Bennett movement (inward movement of the condyles)
FIG 12
together with canine guidance can have a discluding influence on
the buccal and lingual cusps of the posterior teeth in lateral chewing
movements (Figure 12). Research shows that Bennett movement
ranges from 0.5mm to 2.5mm with approximately 90% of the

36 Dental Practice // November-December 2022 // Vol 18 No 6