Download Occlusal Adjustment via Selective Cutting of Natural Teeth.* (Part 1)

Survey
yes no Was this document useful for you?
   Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Document related concepts

Gear wikipedia, lookup

Machine (mechanical) wikipedia, lookup

Transcript
Original Article
McHorris - Occlusal Adjustment via Selective Cutting of Natural Teeth 1
Occlusal Adjustment via Selective
of Natural Teeth.* (Part 1)
Cutting
William H. McHorris
A well-planned, precise occlusal adjustment of
natural teeth has some distinct advantages over
other forms of occlusal therapy. It should be emphasized, however, that an occlusal adjustment is
an irreversible, "take away" procedure and has
definite contraindications in some mouths. Before
discussing types of treatment, it would be worthwhile to review the indications for any type of occlusal therapy.
Although much controversy and confusion have
surrounded the etiologic factors leading to occlusalrelated problems, dentistry has recognized that
there are two etiologic factors that must be dealt
with in treatment. The first is emotional or psychological stress; the second is existing occlusal interferences or maloccluding teeth. Their combined
effect leads to periods of parafunctional activity.
The parafunctional acts would include any use of
the teeth other than the functional activities of
chewing, swallowing, and speaking. Parafunctional
activities result in much greater forces over a longer
period of time than do functional activities. Such
activities as bruxism and clenching can result in
forces that exceed the gnathic system's ability to
resist.
Although the psychological stress factor must be
recognized and dealt with, it is worrisome that
dentistry is drifting toward increasing treatment of
this factor. The intent of this article is to deal with
the second etiological factor, occlusal interferences,
and how to systematically eliminate them. The term
occlusal interferences implies that the occlusion is
interfering with something or that something is interPresented to the American Academy of Restorative Dentistry. Chicago .
Illinois. February 1983.
The Journal of Gnathology . Volume 16. Number 1. 1997
fering with the occlusion. In the stomatognathic system the term must be assumed to mean the obstruction of normal functional usage or the hampering of certain anatomical components from obtaining positions or postures that they were intended to
be able to assume. The teeth are the interfering elements that must be dealt with. The postures or positions desired must first be defined and then a technique must be formulated to eliminate occlusal interferences that prevent the system from obtaining
them.
The objective of an occlusal adjustment, as with
any form of occlusal therapy, is to correct or remove
the occlusal interferences, or premature contacts,
on the occluding parts of the teeth that prevent
a centric relation closure of the mandible. It would
require removal of the parts of posterior teeth that
contact during working, nonworking, protrusive,
and lateroprotrusive movements. During these
movements, the only contacting surfaces should be
related to the anterior teeth in general and to the
mandibular anterior teeth in particular.
So that a systematic, disciplined approach can be
followed in treatment, the objectives should be listed. They are:
1. Centric relation occlusion of the posterior teeth
2. Proper "coupling" of the anterior teeth
3. An acceptable disclusive angle of the anterior
teeth in harmony with the condylar movement
patterns
4. Stability of the corrected occlusion
5. Resolution of the realted symptoms
The options available to accomplish these objectives are:
37
2 McHorris - Occlusal Adjustment via Selective Cutting of Natural Teeth
1. Occlusal adjustment of the existing natural teeth
2. Use of removable orthopedic repositioning appliances
3. Orthodontics
4. Full or partial reconstruction of the dentition (fixed
or removable denture)
5. Orthognathic surgical procedures
6. Any combination of the above
The choice of treatment should always be based on
the least offensive approach. The end result should
be the resolution of the symptoms.
Centric Relation Occlusion
of the Posterior Teeth
An occlusal correction should result in simultaneous
contact of all posterior teeth in centric relation
closure of the mandible. Centric relation occlusion
is the most important determinant of mandibular
stability. Consideration must be given to the
anatomical components that participate in this important posture.
Anatomical Considerations
In healthy, well-functioning temporomandibular
joints, the two mandibular condyles relate to the
articular discs to form the condyle-disc assembly.
It is important to recognize that these two components work as a unit.
The temporomandibular joint is classified as a compound joint. By definition, a compound joint requires the presence of at least three bones, yet the
temporomandibular joint has only two. The articulator disc functions as a "nonossified bone." Its
superior and inferior surfaces are true articular
facets. Therefore, the articular disc of the temporomandibular joint is not a meniscus at all. Considerable misunderstanding has resulted from the inaccurate use of this term. An anatomical meniscus
(from the Greek meniskos, meaning crescent) is a
crescent-shaped fibroartilaginous structure having
one edge attached to the articular capsule and the
other extended freely into the joint cavity.1
38
Original Article
Thus a true meniscus does not separate the joint
cavity or isolate the synovial fluid, but it functions
passively to facilitate movement between the bony
parts. Typical meniscuses are those of the knee
joint, where hinge action is the principal movement.
In the temporomandibular joint, the articular disc
not only divides the joint compartment into parts; it
separates the joint into two distinct and quite different units, thus converting a simple joint into a
compound joint. Both compartments, contain synovial fluid which lubricates the actions of the parts.
The upper joint remains a freely movable sliding
joint (arthrodial) while the lower functions as a pure
hinge joint (ginglymoid). The synovial fluid also
fulfills the metabolic requirements of the nonvascularized and noninnervated portions of the temporomandibular joints.
The confinement of the synovial fluid to the articular
surfaces requires encapsulation in a fibrous connective tissue bag which is attached at the circumferential peripheries of the articulating surfaces
(Fig 1).
This encapsulating structure is well vascularized
and innervated and thus provides the blood and
nerve supply to the joint. Its inner lining is the
specialized synovial membrane which secretes the
vital synovial fluid that provides nourishment to the
joint.
Furthermore, the temporomandibular articular disc
is not a passive structure. It enters actively into joint
function, being independently powered to make it
capable of its own movements quite separate from
those of the bony structures of the joint.2 The nonvascularized articular surfaces of the temporomandibular joint are composed of dense fibrous
tissue rather than the hyaline cartilage found in all
other synovial joints except those of the clavicle.
This results in two unique advantages:
1. Since fibrous tissue is not as susceptible to
the effects of aging as hyaline cartilage, these
joints are less vulnerable to degenerative joint
disease.
2. Since fibrous tissue is more capable of repair
and regeneration than hyaline cartilage, these
joints enjoy healing characteristics that have
significance in treatment planning and prognosis.1
The Journal of Gnathology. Volume 16. Number 1. 1997
Original Article
McHorris - Occlusal Adjustment via Selective Cutting of Natural Teeth 7
attached to the tympanic plate or posterior wall of
the glenoid fossa (Fig 8). This retrodiscal or retroarticular attachment is also referred to as the bilaminar zone.5 The elastic connective tissue found
in this attachment is primarily in the top layer of the
two-layered (bilaminar) zone.6
The elastic properties of the retrodiscal attachment
prevent excessive anterior and medial displacement of the articular disc . The attachment is thus
the antagonist to the superior head of the lateral
pterygoid muscle, which contracts during closure.
This makes it a very active muscle during bruxing
activities.
Centric Relation
The condyle-disc assembly is bodily seated against
the fibrous-covered posterior slope of the articular
eminence at the centric relation closed position
(Fig 9).
This relationship is a result of contractions of the
closure muscles. The ability of the condyles to attain the seated posture, however, is dependent
upon three important conditions. First, the inferior
heads of both lateral pterygoid muscles, which are
attached to the condyles, must be bilaterally relaxed. Second, there must not be an excessive
amount of synovial fluid in the upper or lower compartments of the temporomandibular joint. An increased amount of synovial fluid in these compartments is not an uncommon finding in patients who
chronically "brux" their teeth and who suffer from
temporomandibular joint disorders. Third, and by
far the most common deterrent, are the fittings of
the occlud ing parts of the teeth. If the occlusal surfaces of the teeth, at maximum intercuspation, prevent the condyles from seating against the disc, the
condyles must accommodate to an eccentric posture. This tooth-dictated, eccentric posture that the
condyles are forced to assume is usually inferior and
anterior to the desired seated, centric relation position.
The posterior teeth should allow the condyles to
assume their seated position against the articular
disc. The inclines of posterior teeth should never
have contacts that would force the condyle's seated
closure position in a distal, inferior, or anterior direcThe Journal of Gnathology, Volume 16. Number 1. 1997
tion. Once the seated position is obtained, the
posterior teeth must support and protect it. It is
important to note that mandibular "rest position" of
the condyles would be nearly the same as the
centric relation occluded position, but it would not
and does not result from muscular contraction
(Fig 10). It is a posture in which the teeth are not
occluded or touching and would require muscular
rest or relaxation. By nature's law of "conservation
of energy" the rest position of the condyles is not
a seated position against the articular disc - the
condyle-disc assembly is in a nonstress bearing or
uncompressed relationship. Rest position would
have to be considered the most therapeutic position for the mandible.
Knowledge and understanding of these physiologic
principles should be utilized in taking centric relation registrations for mounting diagnostic casts in
an articulator. The principles should also be utilized
in marking occlusal interferences that prevent
the mandible from closing to a centric relation occluded position.
Centric Registration Technique
The technique preferred by this author when taking
centric relation registrations is the one utilizing a
"leaf gauge ." 7 The gauge consists of 15 to 20
leaves of acetate, vinyl, or some other plasticlike
material held together by rivets or brass brads
(Fig 11). The gauge is placed between the anterior
teeth, and the patient is asked to close in a retruded position. The interocclusal space is observed
and leaves are added or subtracted to secure the
vertical relation desired to obtain the registration
(Fig 12).
A dependable plasticized wax in two separate
strips is softened in hot water and then placed on
the maxillary posterior teeth, one strip on each side
of the arch. The leaf gauge is replaced between the
anterior teeth, the mandible is retruded, and the
patient is asked to apply moderate biting pressure
on the leaf gauge until the wax is hardened or set
(Fig 13). Only cusp tip indexing of the wax is preferred. If the indentions in the wax are too deep or
too shallow, leaves can be added or subtracted
43
Original Article
McHorris - Occlusal Adjustment via Selective Cutting of Natural Teeth 9
and the technique repeated to obtain the desired
registration. The leaf gauge between the anterior
teeth aids the patient in retruding the mandible
while the biting force of the closure or elevator
muscles will seat the condyle-disc assembly against
the posterior slope of the articular eminence. This
eliminates the operator error often encountered
in attempts to manipulate a patient's mandible to
centric relation. Since the patient is applying all of
the pressures, the seated position of the condyledisc assembly is not likely to exceed the physiologic limits of the system. In the case of end-to-end
or Class Ill relationships of anterior teeth, or in the
case of the absence of anterior teeth, a downward
or "resistance-to-closure force" is applied against
the patient's chin at the midline as closure into the
wax is occurring.
Centric Relation Occlusion (Objective 1)
The centric relation occluded position can be maintained through the proper distribution of the forces
exerted by the interocclusal contacts. The interocclusal contacts between opposing posterior teeth
should occur on the occluding surfaces in such a
way that they will provide mesiodistal and buccolingual stability of the teeth and mandible.
Closure stoppers* and equalizers, when equal
and opposite, assure mesiodistal stability (Fig 14).
A, B, and C contacts, when equal and opposite,
assure bucculingual stability (Fig 15).8
all the forces in eccentric bruxing attempts. They
will be the only teeth contacting in any movement
of the mandible away from the centric relation occluded position. If there is proper coupling, anterior
contact will take place within one-half thousandth of
an inch (.0005) or within the first degree of rotation
of the mandible away from the centric relation
occluded position. This resultant "dis-occlusion" of
the posterior teeth is called disclusion. 10 Disclusion
can exist only through the efforts of the anterior teeth
working in harmony with the condyles if posterior
eccentric interferences are to be prevented.
Natural teeth resemble gothic pyramids because
they are rounded or spheroidal in all three dimensions. Two rounded surfaces meet at a point and,
if either surface is moved along a tangent to the
radius of the curvature, the two surfaces will
immediately separate or disclude. This is the
mechanical principle utilized in obtaining disclusion
of posterior teeth (Fig 16 and 17).
In the gnathic system, the angle of movement can
be determined through mandibular recordings or
approximated by carefully obtained lateral checkbites. Thus articulators can become a mechanical
likeness of patient's existing maxillomandibular relationship and allow diagnosis and treatment of their
occlusal relationships.
0
Proper "Coupling" of the Anterior Teeth (Objective 2)
Equal and opposite distribution of forces on the
posterior teeth will stop the hinge closure of the
mandible without deflection and prevent hard contact to the more sensitive, more vulnerable anterior
teeth. The "together," almost touching, relationship
of the anterior teeth to each other is known as
"anterior coupling." 9 This coupling relationship of
the anterior teeth will enable them to quickly assume
•
Closure stoppers are any interocclusal contact found on the distal inclines
of maxillary teeth and the mesial inclines of mandibular teeth.
•• Equalizers are any interocclusal contact found on the mesial inclines of
maxillary teeth and the distal inclines of mandibular teeth.
The Journal of Gnathology, Volume 16. Number 1. 1997
Acceptable Disclusive Angle of the Anterior Teeth
(Objective 3)
The angle of thrust of the mandibular anterior teeth
against their maxillary opponents can be controlled
so as not to be too restrictive. The less restrictive,
the less friction, and therefore the less tooth movement and wear. The dictating factor is the angle of
the articular eminentia. These vertically inclined
slopes dictate the condyles' angle of thrust or disclusive movement. This is particularly true when the
condyle-disc assembly is held in forceful contact
against the eminence during periods of bruxism.
This angle can be approximated through instrumentation to serve as a guide to approximate what the
anterior disclusive angle should be. It is the likeness of the condylar disclusive angles and the
anterior disclusive angles that facilitates harmonious, effortless mandibular movement. This harmony
45