Inside Dentistry
September 2013, Volume 9, Issue 9
Published by AEGIS Communications
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Understanding Occlusion
Frustration and confusion still reign over this complicated topic, but
experts agree that the differing philosophies of occlusion are slowly
finding common ground.
Jackie Syrop
For more than 100 years, dentists have debated the role of occlusion in
dental practice. Unlike most aspects of dentistry, there is a lack of
unified theory and practice regarding occlusion. In fact, the very
definition of the term has been a source of contention. The result has
been that occlusion is associated with a great deal of dogma and
division into “camps” of different occlusion philosophies. The camps
have changed somewhat over the years, but the debate—some would say
controversy—over occlusion has remained.
Five years ago, Inside Dentistry investigated the occlusion controversy in dentistry.1
Revisiting the topic of occlusion today, it is apparent that although
some divisive aspects of the debate remain, some of the differences have
narrowed. We interviewed a group of occlusion experts to gain insight
about the current state of occlusion. The good news is that although
divisions still exist, there appears to be a less dogmatic approach and a
greater willingness to concede that no single philosophy works for all
cases.
Yes, there is still “occlusion frustration,” but proponents of the main
occlusion philosophies agree on larger issues: the importance of
occlusion in dentistry and the acknowledgment that only a minority of
dentists are educated about occlusion in their practices; the negative
effects of not considering occlusion; and the need for solid
postgraduate training in occlusion. There are still differences of
opinion about which occlusion philosophy and training should be
embraced, but some of our experts espouse a more inclusive approach to
occlusion philosophies that acknowledges the possibility that more than
one way can work.
Finally, the occlusion experts were unified in hoping to see more
emphasis on effectively integrating occlusion into dentistry as the next
generation of dentists comes into its own.
Defining Occlusion
In discussions of this nuanced subject, even the definition of
occlusion isn’t cut and dried. “Unfortunately, the definition of
occlusion can range from the static ‘way teeth fit together’ to what
people do with their entire system: vital functions, such as chewing,
breathing, speaking, swallowing, and parafunctional behaviors,” says
John Kois, DMD, MSD, director of the Kois Center in Seattle, Washington.
The narrow definition of occlusion—how the teeth fit together—helps
create some of the confusion we see today, says Jim McKee, DDS, a
dentist in private practice in Downer’s Grove, Illinois, and a visiting
faculty member at the Piper Education and Research Center in St.
Petersburg, Florida. “If we were to talk about occlusion in terms of how
the mandible fits to the maxilla, it would allow us to have a
conversation that focuses on both the front end of the system—the
teeth—as well as the back end of the system—which is the TM joints,” he
notes. Dr. McKee points out that if we always talk about occlusion
relating only to the teeth, it is a problem, because bite forces aren’t
only transferred to the teeth, they’re also transferred to the
temporomandibular joints (TMJs).
Most dentists who have studied occlusion in depth concur that any
definition of occlusion should not be limited to tooth-contact
relationships, but rather should take into account the dynamic
morphologic and functional relationships among all components of the
masticatory system—not just teeth and supportive tissues but also the
neuromuscular system, TMJs, and the cranioskeleton.2
It is beyond the scope of this article to explain details about individual occlusion philosophies (see
sidebar
for basic definitions), or to come to definitive conclusions about
their pros and cons. But to understand the roots of occlusion
frustration, it makes sense to present summations of what of our
occlusion experts consider to be the main philosophies of occlusion so
that we are—as much as possible—speaking the same language.
Why is Occlusion Important?
“Occlusion is the ‘big picture’ in dentistry,” explains Dr. McKee.
“It’s the most important discipline in dentistry that there is to
learn.” As he explains, there are two root causes for most dental
problems: bacteria, which lead to decay or periodontal breakdown, and
bite forces. “Occlusion needs to be evaluated in every patient, just as
we evaluate other areas of the system,” he says. “It impacts every
dentist’s and every specialist’s practice.”
Whichever occlusion philosophy dentists follow, the bottom line is that
they all believe that occlusion underlies all dentistry. “Creating a
stable occlusion of the dentition helps provide a healthy masticatory
system,” explains Michael R. Sesemann, DDS, a dentist in private
practice in Omaha, Nebraska. A healthy masticatory system is an
effective chewing machine and has long-term stability because it
effectively manages functional forces, he says. But he cautions that as
dentists make changes to the system through dental restoration, they
have to do it in a way that ensures harmony of its essential elements: a
stable TMJ, a physiologically balanced musculature, a structurally
strong dentition, and a healthy periodontium. If that is not done, the
problems that ensue could include breakdown and failure of any one, or
all, parts of the masticatory system.
“Occlusion matters because our physiology dictates it,” says William G.
Dickerson, DDS, founder and chief executive officer of the Las Vegas
Institute for Advanced Dental Studies (LVI), in Las Vegas, Nevada. Our
teeth occlude thousands of times a day, and proprioceptive input is sent
to the brain from the periodontal ligament through the trigeminal
nerve. With more than half of the total neural input to our brain coming
from the trigeminal nerve, he says, nature has clearly placed a great
deal of importance on the sensory information from this region. “If the
occlusion is not balanced and in harmony, an avoidance reflex develops
to prevent injury from noxious input,” says Dr. Dickerson, and if the
noxious stimulus is chronic, such as occlusive interference from a
“high” filling or crown, the reflexes designed to protect become
harmful. Chronic avoidance reflexes can affect the posture of the jaw,
the head, neck, and body, leading to fatigue and chronic pain.
“Eliminating interferences in function is a critical part of
understanding occlusion,” Dr. Dickerson concludes.
Occlusion is important because dentists use it to help maintain their
patients’ teeth by controlling the forces placed on them, says Glenn E.
DuPont, DDS, who practices in St. Petersburg, Florida, and lectures at
the Dawson Academy. Certain forces are extremely detrimental to
particular teeth or the whole dentition, causing teeth to break, wear
out, or get loose, and leading to general discomfort, headaches, muscle
pain, and TMJ inflammation and discomfort. Any dentistry done for a
patient that does not fit into a well-designed or adjusted occlusion has
the potential to result in these same problems, cautions Dr. DuPont. describes the potential causes and consequences of malocclusion.
“In some patients, occlusion probably doesn’t matter very much, while
in others it is critical,” says Frank M. Spear, DDS, MSD, a
periodontist/prosthodontist and founder/director of Spear Education in
Seattle, Washington. “One of the biggest challenges of occlusion is
that, unlike most things we do in dentistry, occlusion is not at all
predictable. Some patients have significant malocclusion and have no
symptoms whatsoever but are fine; others seem to have ideal occlusions
but have symptoms, pain, or signs of tooth grinding,” he says.
By improving a patient’s occlusion, you are not only improving the
longevity of the patient’s own teeth, but you also improve the longevity
of your dentistry, Dr. Kois explains. Although we have come to accept
significant wear on teeth as being a “normal” adaptation, people are
adapting at accelerated rates because of compromises in occlusion. If we
can learn to harmonize occlusion, from even a younger age, the rate of
adaptation would be slowed down and the compromises people have to live
with would not be the same.
Fundamental, Yet Rare in Practice
One of the most difficult things to explain is the fact that although
all the experts with whom we spoke consider occlusion to be absolutely
fundamental to all dentistry, only a small percentage of practicing
dentists have a significant knowledge of the subject or effectively use
occlusion in their practices.
Teasing apart the reasons behind this discrepancy reveals important
clues as to why there’s so much controversy about occlusion: occlusion
is controversial because there is no unified theory and there’s no
agreement because there are too many controversial elements. Occlusion
isn’t studied in dental school because there is no definitive approach,
which makes it impossible to teach within a 4-year curriculum. The most
cited reasons for the small number of dentists practicing occlusion
dentistry follow.
Complex Subject Matter
Dentists who embrace occlusion believe that it underlies everything
dentists do, but the fact that occlusion is so basic does not negate how
complex and difficult a subject it is. “The execution of many of these
protocols is very difficult to master,” Dr. Kois acknowledges. A lot of
dentists don’t feel confident about occlusion, particularly newly
practicing dentists.
Misinformation
Dentists have also been scared away from adjusting the occlusion
because of misinformation, states Dr. DuPont. The National Institutes of
Health has contributed to the confusion with its publication for
patients that advises them not to allow dentists to adjust their bite
because it may cause a TMJ problem, he says.3 The same
publication states that occlusion is not related to TMJ problems, which
Dr. DuPont terms “ridiculous” and in contradiction to every tenet of
evidence-based research.
Success Practicing Conformative Dentistry
Most dentists see little reason to learn more about and use the
principles of occlusion because conformative dentistry is working for
them. “Most people walking around do fine with whatever occlusion nature
gave them, and nature doesn’t generally create an occlusion in centric
relation,” Dr. Spear points out. It’s only when you need to treat a lot
of teeth, or the patient has muscle or jaw joint symptoms, that
occlusion becomes an issue.
Dr. Sesemann agrees. “Dentists can have good restorative knowledge and
not much occlusal knowledge and be able to do many things in dental
practice,” he says. “But if they need to do something outside of the
patients’ adaptability, that’s when complex issues can arise.”
Lack of “Hard” Science
Critics maintain that there is no real science supporting the various
occlusion philosophies. Dr. Dickerson points out that neuromuscular
occlusion dentistry uses electromyography techniques to measure
neurologic and muscular physiology. This helps quantify the best
neutral, balanced, and rested position of the muscles, which helps to
reach a physiologic state from which the best position to build the bite
will be in harmony with that patient’s physiology. Still, there aren’t
double-blind, randomized clinical trials in occlusion that would provide
solid evidence upon which to base decisions about occlusion treatments.
“The science is still trying to refine and resolve so many issues
pertaining to the human system,” says Dr. Kois.
Dental Schools Don’t Teach Occlusion
Without scientific evidence, it has not been proved definitively that
treatment planning with any one philosophy is better than using the
patient’s own occlusion. Each approach has worked in many people, so we
can’t say that there’s only one thing that works. Thus, dental school
faculty question why a great deal of curriculum time should be devoted
to teaching conflicting theories about occlusion.
Without consensus, dental schools have not addressed occlusion
comprehensively. Most of our experts don’t criticize schools of
dentistry, however. “Dental school provides a beginning for what we do
in dentistry, it’s not the endpoint,” says Dr. Kois. The lack of
occlusion curriculum is justified when you start to realize the
variability that humanity has, he says. It simply can’t be covered in
dental school.
“Four years is a short time to teach everything there is to know about
dentistry,” Dr. Sesemann agrees, “so choices have to be made as to what
to include or not include in a curriculum. A student cannot master
occlusal theory in dental school. It is a place to learn anatomical
facts and how to do basic, single-tooth dentistry in a conformative
occlusal scheme.” One attains higher-level knowledge of the masticatory
system and ways of providing complex dentistry only after graduation.
Individual Initiative and Self-Study Required
Unable to rely on dental school education in this case, dentists must
pursue postgraduate education about occlusion on their own initiative,
necessitating a substantial investment in both time and money.
Therefore, before they even decide which postgraduate institution to
attend, dentists must spend time researching the possibilities—itself a
time-consuming prospect. “Understanding occlusion takes deliberate
learning and years of experience,” says Dr. Kois, and it is an arduous
journey.
“Occlusion is probably our weakest area of training because of the
profession’s inability to come to a consensus on how to evaluate an
occlusion and how to treat occlusal problems,” says Dr. McKee.
Unfortunately, most dentists are lacking in postgraduate education and
stop intensive course work after finishing dental school, says Dr.
Dickerson. He suggests that they should instead view graduation from
dental school as a license to learn more about dentistry.
Why the Controversy?
“If there was only one approach that worked, we would say this is the
way it should be done, and that nothing else works,” says Dr. Spear. But
with occlusion, there are multiple approaches that will work. You can
use one approach with one patient and it works, and yet the same
approach doesn’t work when used on a different patient. “Everyone has
their own philosophy or belief about how occlusion should be done, and
can point to the fact that they’ve been successful—which is true. But at
other times those same approaches may not be successful,” he says.
It is important to acknowledge that whether one is a proponent of a
centric relation, joint-based, or neuromuscular-based occlusal
philosophy, those in the respective camps sincerely believe that there
are reasons why one reference point is better than the other. Each can
point to successful treatment of many patients. But the division into
camps has sometimes been described as “almost religious,” with “gurus
and disciples.”4 There is also a paradigm effect, in which
one filters all available data, valuing only data that support a growing
belief while discounting or dismissing opposing opinions.
“The controversy can become quite emotional, taking on a life of its
own as loyal followers defend hallowed ground,” says Dr. Sesemann. “The
TM joint versus muscles ‘battle’ is a factor that can be strongly
differentiated for philosophical as well as commercial objectives,” he
cautions. “Problems arise when, in the process of emphasizing that
difference, marketing rhetoric and heated debates can spin out of
control, becoming disrespectful and hurtful.”
Main Sources of Disagreement
At the heart of much of the controversy in occlusion is which reference
position—the muscles or TMJ—one should use to build a healthy
masticatory system. “If the teeth don’t currently fit together, you can
no longer use the teeth as your reference for occlusion. You then need
to use two other systems to rebuild the occlusion: the joint as a
reference position (ie, centric relation) or the muscles to orient the
lower jaw as a reference point (ie, neuromuscular),” Dr. Kois explains.
According to Dr. McKee, the joint-based occlusion philosophy grew out
of the realization that a significant number of patients have
unrecognized structural damage to the TMJs. The ability to image the TMJ
with computed tomography illuminated the true prevalence of joint
damage, especially among women, who are more prone to ligament injuries.
Further complicating matters, there are differing views within the
centric relation philosophical camp as to where centric relation
actually is, with many instructors differing in terms of techniques and
final position of centric relation.
Differences also exist with regard to treating bruxism. Neuromuscular
proponents believe that bruxism is related to the bite and can be
stopped with changes to the occlusion. Most dentists in other occlusal
camps believe bruxism is a central nervous system function related to a
certain sleep stage, and that people are going to grind their teeth
whether they are balanced occlusally or not. “We can’t necessarily stop
patients from bruxing, but we can change the impact the muscles are
having on the jaw joint and the teeth by changing the way the bite
fits,” Dr. Spear says.
Areas of Agreement
There are actually multiple areas of agreement among the different
occlusal philosophies. As Dr. DuPont points out, most of the different
occlusion schools of thought have more in common than not in common.
There is consensus among all the experts interviewed that occlusion
should be a routine part of every patient assessment and every
procedure.
The teeth should hit evenly and with equal intensity so that no one tooth is taking all the force.
The anterior teeth should guide the posterior teeth when the patient takes their teeth in any movement or excursive pathway.
All the teeth should fit within the confines of the muscle forces for the best stability.
Eliminating interferences is important.
Functional movements should allow for access to maximum intercuspation
without interferences occurring in the posterior teeth or anterior
teeth.
The shapes and positioning of the anterior teeth influence healthy
guidance patterns (though there is disagreement as to whether anterior
teeth contact in functional movements).
Although there is general agreement that posterior teeth must have
equal, simultaneous, bilateral contact in an unstrained joint position,
what experts don’t agree about is the way you arrive at the solution
when a patient presents with less than ideal contacts.
Occlusion as an Obligation
Any time a significant amount of dentistry is being contemplated, it is
paramount that practitioners know what they are proposing to change,
why they are proposing the change, and how to go about doing it while
exercising a responsible clinical acumen. “To not have occlusion as part
of any initial diagnostic dialogue is a recipe for potential disaster,”
asserts Dr. Sesemann.
Dentists need to learn all they can about occlusion because they can’t
diagnose what they can’t see—and they can’t see what they don’t know.
It’s a moral issue as much as a legal one, says Dr. McKee. It’s one of
the things that should be included in the dialogue with every patient.
“Every dentist needs to understand all aspects of occlusion in order to
have a better understanding of what can happen if dentistry is done in
an occlusionless vacuum,” says Dr. Dickerson. Not having sufficient
knowledge about occlusion to recognize the signs and symptoms of harmful
occlusal forces leads to a failure to diagnose a patient’s root
problems and instead focuses treatment on only the signs and symptoms.
Making occlusion treatment more affordable is an obligation for Dr.
Kois, and he is working to create entry points to make treatment
available to more people. The focus of occlusion, he believes, should be
on children. They are wearing down their teeth by the time they are
teens, and the goal is to keep them from needing significant dentistry
in their 50s and 60s. “Occlusion is the next frontier that is left
virtually untapped by most of the profession because most dentists,
including me, are so highly trained that we have priced ourselves out of
what most people can afford,” says Dr. Kois.
What’s Changing?
As part of a trend toward an individualized approach to occlusion, the
concept of an “ideal occlusion” is now questioned. A rigid, dogmatic
approach to therapy that implies that one fixed, predefined concept
should be applied to all patients, in all situations, holds much less
sway. There is a greater appreciation that the concept of ideal is
something like “infinity,” in that it can be approached but never
actually reached.2
In the past decade, there has been a shift toward a greater
appreciation of the individuality of each patient as an important
determinant of the occlusion method used. “The masticatory system must
be viewed within the context of the overall physical and emotional
health of the patient,” notes Dr. Kois, who advocates moving away from
treating symptoms toward understanding the causes for symptoms.
Functional or parafunctional forces in one person may produce a tissue
response, sign, or symptom that is different than that produced in
another individual. Deciding on what you’re trying to do should be based
on the diagnosis of what is wrong, not a dogmatic philosophy.
“Some schools of occlusion are increasingly comfortable with not
choosing a side, in talking about the successes and/or failures of
different approaches, and illustrating places where those different
approaches are possibly the best way to go,” says Dr. Sesemann. Things
have been moving in that direction for 10 to 15 years. Prior to that,
the camps were a lot more divided. “You either believed their way or you
were doing something detriwwmental to the public,” he notes.
“It’s a very different way of looking at occlusion now than it was when
I trained 35 or 40 years ago,” says Dr. Spear. His approach is
“diagnostically driven,” and “anti-one approach,” because he believes
any one philosophy is too narrow. Each occlusal philosophy wants to
present itself as the answer, the way to do it, he says, but when you
treat a human being, there isn’t just one answer. You have to examine
the patient’s joints, muscles, and teeth looking for wear, fractures,
and other problems, and you can decide what your options are to design
the occlusion based on those findings.
Change will come quickly as Baby Boomer dentists retire and are
replaced by a new generation of dentists who grew up with computers and
are trained in 3D imaging in dental school, Dr. McKee predicts. They
will be more comfortable with the technology and better metrics that are
being developed in occlusion treatments.
There is an evolution in continuing education as well. In the past,
there simply wasn’t the array of resources available today, particularly
in terms of user-friendly online and printed educational information on
occlusion that can enable more dentists to continue their education.
There are more opportunities for face-to-face meetings, which used to be
rare. In years past, there was a controlled amount of information, and a
few printed journals. With so much more information available, there is
a good chance that the future of occlusion philosophy will move toward
more cohesion.
Choosing Education in Occlusion
The best way to explore post-graduate education in occlusion is to
start by getting exposed to all the concepts involved so that you can
decide why you would develop one occlusion over another in a particular
case. Become familiar with the various options and choices. It is
important to seek out feedback from colleagues about their experiences.
Try to learn about the different occlusal philosophies through the
various programs offered online, on DVDs, and through videos, and
familiarize yourself with the various institutes and schools by
attending their meetings or taking online courses. Eventually you need
to get comfortable through hands-on workshops and repetition.
lists the expert sources mentioned in this article and provides a good
starting point to help you move into the next phase of your dental
education in occlusion. Renew your license to learn and you can reap the
rewards of better treatment planning and a higher level of care for
patients.
References
1. DiMatteo AM, Pounding on the occlusion pulpit—wherein lies all the controversy? Inside Dentistry. 2008:4(3).
2. Turp JC, Greene CS, Strub JR. Dental occlusion: a critical reflection on past, present, and future concepts. J Oral Rehabilitation. 2008;35:446-453.
3. National Institute of Dental and Craniofacial Research/Office of
Research on Women’s Health. National Institutes of Health. Less is often
best in treating TMJ disorders.
www.nidcr.nih.gov/oralhealth/topics/tmj/lessisbest.htm. Accessed July 10, 2013.
4. Neiburger E. The evolution of human occlusion: ancient clinical tips for modern dentists. Chairside. Winter 2008.
www.glidewelldental.com/dentist/chairside/issues/winter 0809/clinical-techniques3.aspx. Accessed July 10, 2013.
Philosophies of Occlusion
Centric Relation:
Uses the temporomandibular joint (TMJ) as a reference position from
which to build occlusion. When the teeth fit together, the joint should
fit completely in its socket. Centric relation (CR) proponents believe
it is most important to structure the condyle/disk/fossa assembly to
distribute the bite forces more evenly, but vary in how to determine CR
and how to achieve it.
Note: Within the CR category, there are several “schools,” including
the gnathologic and bioesthetics philosophies. Gnathologic uses CR in
the intercuspal position along with canine guidance. The amount of
anterior overbite/overjet is related to the TMJ. Bioesthetics uses
specific anterior tooth size and specific overbite/overjet to develop
occlusion that would, proponents say, prevent bruxism, wear of the back
teeth, and damage to front teeth. Like gnathology and bioesthetics, the
Pankey and Dawson schools use CR for intercuspal position to build
occlusion in CR but differ
in ways of addressing front teeth and overbite/overjet.
Conformational Occlusion:
Not so much a philosophy itself, conformational occlusion makes
everyone’s list simply because so many dentists practice conformational
dentistry and don’t follow one of the other theories. A conformational
occlusion approach basically allows patients to function with whatever
bite they currently have. Experts pointed out that this may be
appropriate as long as there are no problems with the occlusion, but if
there are problems, the dentist is forced to choose between building
into an occlusion with known instability or to use one of the other
theories.
Neuromuscular-Based Occlusion:
Uses the muscles of mastication as a point of reference. Dentists use
electronic stimulation of muscles with an electromyogram to find the
most relaxed state, and in this position, resting muscle length will
determine condylar position. The role of the trigeminal nerve is
important. This school of thought says that when the muscles are in
physiologic harmony, the patient is not coping with pathologic muscle
forces and you can create long-term bite stability.
Joint-Based Occlusion:
Uses the condition and position of the condyle and disk within the
glenoid fossa to determine condylar position during maximum
intercuspation. Unlike CR, joint-based occlusion does not assume that
the joint is structurally intact. TMJ imaging using magnetic resonance
imaging and cone-beam computed tomography is performed to evaluate
dimensional changes in the joint.
A second newer school of thought is represented by neuromuscular dentistry,
established on the knowledge that the TMJ is in a physiologic resting
position primarily based on direction provided by muscles and stabilized
by an occlusional relationship between the upper and lower teeth. Here
the focus is on a physiologic posture of the mandible correlated to the
skull, along with physiology of the muscles in supporting a position of
occlusion for stabilization of all involved entities: the TMJ, muscles
and teeth.
Advancement
of dental technology has greatly enhanced understanding of the
mastication system and it accompanying structures. Dr. Bernard Jankelson
led a new movement using scientific instrumentation to obtain
objective, quantifiable data that can be documented to evaluate
mandibular movements both during functional motion and at rest. A
variety of systematic studies have been published in medical journals
helping to reveal the dynamics of mandibular functionality, as well as
muscle activity through both active and resting modes. Paths of
mandibular motion can effectively be registered by neuromuscular dentistry in six different plains to distinguish pathological from physiological activity: