Criteria for Optimum Functional Occlusion

"Tlli' clinician tile needs to understand basic orthopedic

-JPO

1)or/and's Ii/ustrated Medical Dictionar~! defines occlude as "to close as to the mandibular teeth into contact with the

teeth in the maxilla "I In dentistry, occlusioll refers the relationship of the maxil and mandibu­

lar teeth when are in functional contact dur­activity of the mandible The that

3rises is What is the best functional

\~

.11 :::r occlusion of the teeth? This ~... :

stimulated much discussion and debate, ,ears, several concepts of occlusion have been

(it' _~eveloped and have varying degrees of It might be interesting to follow the

of these concepts

HISTORY OF THE STUDY OF OCCLUSION

of the occlusal relationships made by Edward in 1899,'

=:clusion became a topic of interest and much years of modern

and replacement of teeth 2came more feasible. The first

to describe functional occlu­"ll was called bellallced OCclHSiof1. This concept

- ,ocated bilateral and balancing tooth contacts .' ,-,ng all lateral and movements ::: ~ "nced occlusion was primarily for

dentures. with the rationale that this

-

of bilateral contact would aid in the mandibular movement The

concept was accepted, and with advances in dental instrumentatio~ and it carried over into the field of fixed prosthodontics.))

As total restoration of the dentition became more feasible controversy arose regarding the

of balanced occlusion in the natural dentition After much discussion and debate, the concept of unilateral eccentric contact was subse­quently the natural dentition 67 This theory suggeste

contacts) as well as protrusive contacts, should occur only on the anterior teeth It was during this time that the term was first used The study of has come to be known as the exact science of mandibular movement and resultant occlusal contacts. The con­cept was popular not for use in restoring teeth but also in attempting to eliminate occlusal It was accepted so

that with any other occlusal configuration were considered to have a malocclu­sion and often were treated because their occlusion did not conform to the criteria to be ideal.

In the late 1970s the concept of individ­ualocclusion . This concept centers around the health and function of the and not on any If the structures of the system are

and without pathology, the is considered physiologic and of specific tooth contacts.

95

.,.".

96 Functional Allatollllj

Therefore no in the occlusion is indicated Afte, examiration of m.;merous with a

of occlusal conditions and no apparent occl~sa;-related the merit of this con­cept becomes evidert.

The :aci ng derti stry is apparent when a with the and symptoms of occlusal-related comes to the dentai

The dentist must determine

inate th

time) \Vhat is the optir,lum func­tional occlusion) the study of occlusion so

have not been sa(sfactorily answered to determine which conditions to cause any

examines certain aratomic and features of the system f\n accu­

mulation of these features wiii represent the functional occlusion. wh:ch. although it

may not have a h incidence in the ulation. ShOl.;ld represent to the clin ment Is when ng to either eliminate occlusion-related disorders or restore mu:ilated dentition.

CR.ITERIAFOR1HE .9PTlMUM FUNCTIONAl··OCClUSION

As discussed, the system IS an interrelated system of

bones. I ~eeth and nerves To si a discussion of th system difficult necessary oefore the basic concepts that influence the function and health of al the components can beJ nderstood.

The mandible bone that is at:ached to the skull and It' a muscular sl irg When the elevator muscles I the masseter. the medial otemwid, and the temnoral I func­lion, their contraction raises the that contact is made and torce the skull in three areas: the two

IIMls) and the teeth I these muscles have the pabil

Fig.5-1 When the mandible is elevated, force is applied tc the cranium in three areas: (I and 2) the temporomandibu­lar joints and (3j the teeth.

for to . Thus tl~ese areas need:

to determine the IC relationst11p that wilt prevent, mini'T1izc

or eliminate ar.y oreakdown or trauma, The and teeth wili De exam;ned

OPTIMUM ORTHOPEDICALLY STABLE JOINT POSITION

The ten" celltric rt'latioll [CRI been used dentistry for many years ever the year:­

l'ad a of definitions. considered to designate the ~andibie when the

stable CR as the most retruded Because this is the I men~s of the

. It

the const; tior of CO~ dentures l\t the time it considered the most reliable reference pc obtainable ~n an edentu:Clus natient for accurat recoraing the oetween the mand:­and maxilia and u for contro

usa I contact pattern

'H,mr"'"

Ij~~~~i!Rlm"k'

(Ptl:H:I',

-

97

The popula of CR grew and carried over into the field of fixed useful­ness in fixed both its ity and ~esearch

studies associated with muscle function Conclusions from tne Ic

iE\1G) studies that the muscles of mas­tication function more harmon and with less

when the in C!;: at the time :hat the teeth are in maximum i

dental I)' that CR

.'.as a sound More ~ecent

~r~derstandjng of the biomechanics and ~unction -: the TM] however, has questioned the retruded

ly

confusing ::-:rcause the definition

--:r in tneir most : ~sae Some clinicians' that none of

: - -:rse definitions of CR ton and that the tioned downward and for'ward on the articular ~:ences. The ng the most

0' the wil continue - conclusive evidence exists tha: one

than the others ertheless. in the midst of this controversy

. sts must needed treatment for thei r ::'lts The use stable,

-:~cential to treatment. Therefore:t necessary ·c,mine and evaluate all available mfmmation

to draw intel conclusions on \\-hich treatment.

establishing the criteria for the optimum stable joint the anatomic

:: J of the TM) must be exarm ned described. the articular is

dense fibrous connective tssue de\'Oid and blood vessels" This ailows it wii'l­~eavy forces without damage or the induce­

nful stimuli The purpose disc --:c;ate. protect and stabilize ,he In

lar during functional movements

-

Criteria for OptimulII FUI1(/iollat Oa/llsiol1

Positional stabll of the jomt however, is not determined the articular disc

nt stabi is determined muscles that pull the loint and prevent dis­location the articular surfaces The directional

'mum

Muscles stabilize joints Therefore each mobile nthasa stobielMSI When pursuing most stable

'Hvlls, the muscles that Dull across the nts must be considered The ma muscles that stabil the P,Als are the elevators. The direction the

on the

t he tern pora I m usc!es have fi bers that are oriented nevertheless pre, dom in a superior These three rruscle groups

ble for joint and however, the inferior lateral

a make contribution In the postural without any influence

from the occlusal condition, the are sta­bilized muscle tonus of the elevators and the inferior :ateral Dter\20ids The temperal muscles

Fig. 5-2 The directional force of che primary elevator muscles (temporaliso masseter, and medial pterygoid) is to seat the condyles in the fossae in a superoanterior posicion,

98 Functional Anatoll1Y

position the condyles superiorly in the fossae. The masseters and medial pterygoids the

superoanteriorly. Tonus in the inferior lateral pterygoids the condyles against the slopes of the articular eminences.

By way of summary then, the most orthopedi­cally stable joint as dictated bv the muscles is when the are located in their most superoanterior in the articular fos­sae, fully seated and resting against the posterior slopes of the articular eminences. This description is not however, until the position of the articular discs is considered. rela­tionship is achieved only when the articular discs are interposed between the and the articular fossae The of the discs in the

joints is influenced by the interart:cular pressures, the morphology of the discs them­selves, and the tonus in the lateral ptery­goid muscles. This last causes the discs to be rotated on the condyles as far forward as the discal spaces (determined by interarticular pressure) and the thickness of the border of the discs will allow

The complete definition of the most orthopedi­cally stable position therefore is when the condyles are in their most superoanterior in the articular fossae. against the

of the articular with the discs properly inter-The assume this position when

the elevator muscles are activated with no occlusal influences. This position is therefore considered to be the most MS position of the mandible

In this MS position, the articular surfaces and tissues of the joints are such that forces applled the musculature do not create any dam­age When a dried skull is examined, the anterior and superior roof of the mandibular fossa can be seen to be quite thick and able to withstand loading forces. ing rest and function, this is both anatom­ically and physiologically sound.

The MS position is now described in the Glossary of Prostnodontic Terms as CR 2i earlier defi­nitions9ll of CR emphasized the most retruded position of the condyles, most clinicians have come to appreciate that seati ng the condvle in the

superoanterior is far more orthopedically acceptable

The controversy arises as to whether there an anteroposterior range in the most superior tion of the condyle Dawson l6 that there

not. which that if the condyles move either anteriorly or posteriorly from the most supe­rior position, they will also move inferiorly This may be accurate in the young, healthy but one must realize that not all joints are the same Posterior force applied to the mandible is resisted in the joint the inner horizontal fibers of the temporomandibular (TM) I superoposterior of the is there­fore, by definition. a ligamentous position If this ligament is tight, little difference may exist among the most superior retruded position, the most

position (ie Dawsons ), and the superoanterior (MS) position However, if the Tl\l ligament is loose or elongated an anteroposterior range of movement can occur while the remains in its most position The more posterior the force placed on the mandible, the more of the will occur and the more posterior will be the condylar . The degree of anteroposterio~

Fig.5.3 The most superoanterior position of the condy e (solid line) is musculoskeletally the most stable positic­of the joint. However, if the inner horizontal fibers of [C~ temporomandibular ligament allow for some posteric­movement of the condyle, posterior force will displace tr mandible from this to a more posterior, less stable positic­(dotted line).The two positions are at the same superior leve

,f ( \~

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i

5

It ~

d

5t e-

is ig 5t he 'M or

\'Ie

he

"nt the 'jor

dyle tion the

lrior the

ition eve!.

to the health of the nt appears to permit

movement from the MS position the health of the may be difficult to clinically assess.

Studies of the mandibular demonstrate that in

portion of Therefore some

movement to the [CP is normal during function In most this move­ment is small (I mm or occur in the structures of the

However, if joint

of the TM ligament. joint posterior range of movement can be increased. The clinician should note that the most and posterior (or retruded) condyle is not a sound (Fig '5-4). [n this :)e to the aspect of the -ior retrodiscal lamina, and retrodiscal tissues. 3ecause th.e retrodiscal tissues are h vascular­2ed and well sUDDlied with sensory nerve fibers,

are not structured to accept "rce. Therefore when force is aDDlied to this area, -ere is a great for eliciting and/or

:'iusing breakdown. 24•28

l=ig.5·4 Posterior force to the mandible can displace the : : - :yle from the musculoskeletally stable position.

Criteria for Optimum FUl1ctiOflal Occ/usioll 99

When the dried skull is examined from an anatomic the aspect of the mandibular fossa is seen to be quite thin and

This fea­not meant for stress the fact that the

as discussed in participate in

does not appear to be of the joint

t, liga­function.

exist to act as limiting structures for certain extended or border nt movements

as the idea of using this bcnder

an um functional was discussed Such a

border relationship would not be considered um for any other nt would this ortho­princi be any different for the TMI')

Because it is sometimes clinically difficult to determine the extracapsular and i condition of the it is advisable not to

force on the mandible when to locate the 'v1S of the joint The major

should be on guiding or directing the to their most in

the fossae This can be accomplished either a bilateral mandibular ng or by the musculature itself (as discussed in later For the remainder of this text CR will be defined as the most superoanterior of the

the articular fossae with the discs [t can thus be seen that CR are the same. This definition

of CR is becoming Another concept of mandibular stabil;tyl~ sug­

gests that a different is optimal for the are described

of the articular eminences iFig '5-5}l\s the downward and

the disc bone are d Examination of the dried skul; reveals that this area of the articular eminence is quite thick and able to

withstand force. Therefore tbis like the most 5uperoanterior appears be anatomically of forces. in fact this a normal orotrusive movement of

CLARK COLLEGE UBkARY

100 Functional Anatomy

Fig. 5-5 Forward movement of the mandible brings the condyles down the articular eminences. Increased muscle activity is likely.

the mandible. The major differences between this position and the 1\1S lie in muscle func­tion and mandibular stability

To position the condyles downward and forward on the posterior slopes of the articular eminences, the inferior lateral pterygoid muscles must con­tract. This is compatible with a protrusive move­ment. However, as soon as the elevator muscles are contracted, the force applied to the condyles by these muscles is in a superior and slightly ante­rior direction. This directional force will tend to drive the condyles to the superoanterior position as already described (i.e., MS position). If the max­imum ICP were developed in this more forward position, a discrepancy would exist between the most stable occlusal position and the most stable joint position Therefore in order for the patient to open and close in the ICP (which is, of course, necessary to function), the inferior lateral ptery­goid muscles must maintain a contracted state to keep the condyles from moving up to the most superoanterior positions Therefore this position represents a "muscle-stabilized" position. not an MS position Assuming that this position would require more muscle to maintain mandibu­lar stability is logical Because muscle pain is the most common complaint of patients with

masticatory disorders, it would not seem favorable to deveiop an occlusal condition that may actually increase muscle activity. Therefore it does not appear that this position is compatible with mus­cular rest,29 and it cannot be considered the most physiologic or functional position.

Another concept that has been proposed to help the dentist locate the most optimal condylar position is through the use of electrical stimula­tion and subsequent relaxation of elevator mus­cles. In this concept the elevator muscles are electrically pulsed or stimulated at regular inter­vals in an attempt to produce relaxation. This tech­nique has been used by physical therapists fOl years with good success in reducing muscle tension and pain. Therefore there may be good rationale to use electrical stimulation to reduce muscle pain, even though data are scarce (see Chapter II). The followers of this concept believe that if this pulsation is done in an upright-head position, the elevator muscles will continue to relax until their EMC activity reaches the lowest level possible, which they describe as rest. This rest represents the point at which the forces of gravity pul down on the mandible equal the elasticity of the muscles and ligaments that sup­port the mandible (viscoelastic tone) In mos[ cases this means that the mandible is positioned downward and fOf\vard to the seated superoante­rior position. The fact that this is the position of lowest EMC does not mean this is a reasonable position from which the mandible should function. /\s discussed in this text. the res~ position (lowest EMC activity) may be found a: 8 to 9 mm of mouth opening. whereas the postura position is located 2 to 4 mm below the ICP ir readiness to function 30JI Assuming that the idea mandibular position is at the lowest point of EMC

is a naive thought and certainly not sut· stantiated with data. However. followers of thl:,

believe that it is at this position the:: occlusion should be established.

At least three important considerations que~· tlon the likelihood that this position is an ide~

mandibular pOSition. The first is related to the fa.:' that this position is almost always found to downward and forward to the seated position. jf the teeth are restored in this

3nd the elevator muscles contract. the condyles !.dl be seated superiorly. leaving only posterior :eeth to occlude. The only way the occlusal posi­.. on can be maintained is to maintain the inferior 3~eral pterygoid muscles in a partial state of con­

--action bracing the condyles the posterior of the articular eminences. This, of course.

'e::lresents a "muscle-braced" position and not an ','5 as previously discussed.

-"nother consideration in a desirable ~. :;'ldibular position by pulsing the elevator mus­• e3 is that this position is almost always found to

an increased vertical dimension. The highest that can be by the elevator mus­

:5 at 4 to 6 mm of tooth separation 32 It is at =iistance that the elevator muscles are most

c': =2nt in breaking through food substances, the teeth into maximum intercuspation at

.ertical dimension would cause a great --:::se of forces to the teeth and periodontal

. _::Jres, increasing the for breakdown. ~ :~.ird consideration in using this technique is

~: : ~~ce the muscles are relaxed, the mandibular can be greatly

:·re the patient's head ::::uired maxillary/mandibular

influenced by

=~:ent moves his or her head forward or back ~ ~- tilts it to the right or left, the mandibular : : :- will change It would not appear

,ype of variation is reliable when restoring

:- er concern with this is that basi­_::::.- individual. whether healthy or with a :: ~.ar disorder, will assume an open and for­==~tion of the mandible following muscle

Therefore this technique is not helpful patients from normal healthy

·.'.'hen this occurs, individuals considered for unnecessary therapy,

_. ~',,' 8e quite extensive, '., -'ary, from an anatomic standpoint one -' ,je that the most superior and anterior

the condyles resting on ~he discs slopes of the articular em

most orthopedically sound position 3:e standpoint it also appears that this - of the condyles is mal, An addi­

.-: is that it also has the

Criteria for Optimum Functional Occlusion 101

of reproducible, Because the condyles are in a superior border position, a repeat­able terminal movement can be executed (see Chapter

OPTIMUM FUNCTIONAL TOOTH CONTACTS

just described has been consid­ered in relation to the infl factors of the joint and muscies. As previously discussed. the occlusal contact pattern influences the muscular control of mandibular When closure of the mandible in the MS position creates an unstable occlusal condition, the neuromuscular system quickly feeds back muscle action to locate a mandibular position that will result in a more stable occlusal condition. Therefore the MS of the joints can be maintained

when it is in harmony with a stable occlusal condition. The stable occlusal condition should allow for effective functioning while minimizing

to any components of the masticatory system The clinician should remember that the musculature is capable of much greater force to the teeth than is necessary for function Thus it is important to establish an occlusal condi­tion that can heavy forces with a minimal likelihood of and at the same time be

effici en t. The optimum occlusal condition can be deter­

mined by the following situations I. A patient has only the right maxil and

mandibular first molars present. As the mouth these two teeth provide the only occlusal

for the mandible (Fig. 5-6) Assuming that 40 Ib of force is applied d function. it can be seen that all this force will be applied to these two teeth. Because contact is only on the right the mandibular position will be unstable and the forces of occlusion provided by the musculature will likely cause an over­closure on the left side and a shift in the mandibular position to that side This con· dition does not the mandibular stabil ­ity necessary to function effectively instability) If forces are applied to ~he teeth and ioints in this situation breakdown to

"~

102 Functional AnatomlJ

Fig. 5-6 When only right-side occlusal contacts are present, activity of the elevator muscles tends to pivot the mandible using the tooth contacts as a fulcrum, The result is an increase in joint force to the left temporomandibular joint (TMJ) and a decreased force to the right TMJ.

tre teeth, and supporting structure is a significant risk

2. Another patient has only the four first molars present. When the mouth is closed, both right and left side molars contact lFig. 5-7L This occlusal condition is more favorable than the

because wr,en force is applied

the musculature, the bilateral molar contacts a more stable mandibular

only minimal tooth surfaces accept the 40 lb of force provided during function, the additlona I teeth lessen force appl ied to each tooth (20 lb per tooth) Therefore this type of occlusal condition provides more mandibular stability wr,i1e decreasing force to each tooth

3. A third patient has only the four first molars and four second premolars present When the mouth is closed In the .r-AS position, all eight teeth contact evenly and simultaneously ( 5~8)

The additional teeth provide more stabilization of the mandible. The increase in the number of teeth also decreases the Forces to each tooth, thereby potential (The 40 lb of force during function are now distributed four of teeth, reSUlting in 10 Ib on each tooth I Understanding the of these illustra~

tions leads to the conclusion that the occlusal condition during mandibular closure \vould be provided even and simultaneous contact of all possible teeth This type of occlusa

furnishes maximum for the mandible while minimizing the amount of force

!lIlr'.!l':~:: "''' If

Fig. 5·8 Bilateral occlusal contacts continue to maim2 ~

Fig. 5-7 With bilateral occlusal contacts, stability of the mandibular stability. As the number of occluding tee:­mandible is achieved. increases, the force to each tooth decreases.

::aced on each tooth during function Therefore ~;.,e criteria for optimum functional occlusion =2\'eloped to this point are described as even and

multaneous contact of all possible teeth when :~,e mandibular are in their most

peroanterior position, resting against the poste­slopes of the articular eminences, with the

::scs properly interposed In other words, the MS ~sjtjon of the (ie, CR ) coin~ jes with the maximum ICP of the teeth. This is

~ :nsidered orthopedic stabU Stating that the teeth must contact evenly and

is not descriptive enough to ~2,elop optimum occlusal conditions The exact . ~'~tact pattern of each tooth must be more closely '.amined so that a precise description of the

.: :::;mum relationship can be derived. To evaluate s better, the actual direction and amount of

.. "::e applied to each tooth needs to be =,,,mined.

Direction of Force Placed on Hie Teetft . ~en studying the supportive structures that sur­': ,,;nd the teeth, it is possible to make certain ~ servations:

First, osseous tissues do not tolerate pressure -"::eslG2340 In other words, if force is applied to

:-:e, the tissue will resorb. Because the :",,,,:h are constantly receiving occlusal a :,~:odontalligament ( is present between the

" -t of the tooth and the alveolar bone to help :: :,trol these forces The PDL is of col­~;:2nous connective tissue fibers that suspend the

'th in the socket. Most of these fibers run : ='c;uely from the cementum, extending occlusally

'ittach in the alveolus ( 5_9)40 When force : a::Jplied to the tooth, the fibers support it and

sion is created at the alveolar attachment. - '2::sure is a force that osseous tissue cannot

~2Pt, but tension (pulling) actually stimulates : c::eous formation. Therefore the PDL is capable of .: ~ ,erting a destructive force (pressure) into an ~eptable force (tension). [n a general sense it

be thought of as a natural shock absorber .: ~ :rolling the forces of occlusion on the bone.

.:. second observation is how the PDL accepts ::us directions of occlusal force. When a tooth

, ::;ntacted on a cusp tip or a relatively flat surface

Criteria for OptimulI1 Frtnctionai Occ/usion 103

Fig. 5-9 PERIODONTAL LIGAMENT. Most fibers run obliquely from the cementum to the bone, (The width of the periodontal ligament has been greatly enlarged for illustrative purposes.)

Fig. 5-1 0 When cusp tips contact flat suriaces, the result­ant force is directed vertically through the long axes of the teeth (arrows), This type of force is accepted well by the periodontal ligament.

such as the crest of a ridge or the bottom of a fossa the resultant force is directed vertically through its long axis. The fibers of the PDL are aligned such that this type of force can be well accepted and dissipated (Fig. 5-10 I When a tooth

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104 Functional Allatomy

A---l~-- I:J--+- B

'.::::1 ,i/fjB A

Fig. 5-11 When opposing teeth contact on inclines, the direction of force is not through the long axes of the teeth. Instead. tipping forces are created (arrows) that tend to cause compression (A) of certain areas of the periodontal ligament and elongation (B) of other areas.

contacted on an incline. however. the resultant force is not directed its axis. Instead. a horizontal component i incorporated and tends to cause tipping ( 5-1 II There'ore when horizontally directed forces are ied to a tooth. many of the fibers of the POL are not properly al to control them. As the tooth some

of the POL are \vhile others are pulled or elongated Overall. the forces are not

dissipated to the bone.: 1

A

The clinician should remember that vertical forces created tooth contacts are well

the POL. but horizontal forces cannot be ef'ec­dissipated ~2 These forces may create bone responses or even elicit neuromuscular

reflex activity in an attempt to avoid or guard against incline contacts.

way of summary. then if a tooth is contacted such that the resultant forces are directed

. the POL is quite efficient and breakdown is less

in such a manner that horizontal forces to the structures. likelihood of pathologic effects's greater.

The process of directing occlusal forces through the axis of the tooth is known as axial ioadifW Axial loading can be achieved two methods 1 The first method is the

tooth contacts on either cusp flat surfaces that are lar to the axis of the tooth These flat surfaces can be thE: crests of marginal or the bottoms

With this type of contac: the resu]ta;~-forces vd] be direcced the long axis the tooth iFig 5-12. Al

2 The second method (called tripodization) requirf: o

that each cusp contacti ng an fossa such :hat it three contac c

the actual cusp tip. When this c

the resultant force directed throw::' axis of the tooth ( 12.

Both methods eliminate the POL to accept

ng forces to the bone and essenti2. reduce them

B

.t~. t .... ~

J.

Fig. 5-12 Axial loading can be accomplished by (A) cusp tip-to-flat surface contacts or (B) reciprocal incline contacts (called tripodization).

Amount of Force Placed on the Teeth The criteria for um occlL:sion have now been

Criteria for OptimullI FUllctiollal Oce/usion 105

it is closer likelihood of its

the fulcrum to increase the cracked This demonstrates

that greater forces can be to an oblect as its nears the fulcrum The same can be

inences

First. even and simultaneous contact of teeth shoL:ld occur when the mandibu­

::econd, each tooth should contact in such :or that the forces of closure are directed

-~e

aspect that has been left undis­~3sed relates to the of the TMI The

-'.:1 permits lateral and excursions, -ch allow the teetn to contact during different

of eccentric movements. These lateral excur­1S allow horizontal forces to be to the

-22-C; As alreadv stated, horizontal forces are not the su structures and tne

-"_:omuscular system, yet the of the .-~ requires that SOr,le teeth bear the burden of

-:oe forces, Thus several factors 0- be considered wnen identifying which tooth

- -2eth can best accept these horizon:al forces --e lever system of the mandible can be com­

with a nutcracker When a nut is being ':':- ed it is between the levers of tile nut­

:'.2r and force is aPDlied It it is extremelv hard

said of the 5-1 '31 If a hard nct is to be cracked between the teeth, the mcst desirable is not between the anterior teeth but between the teeth, beca use as the nut is closer to the fulcrum (the TMII and the area of the force vectors (tne mas­seter and medial muscles), greater force can be ied to the Dosterior than to the anterior teeth . .)(,-;'

The however, more fulcrum of the nutcracker is

system is free to move. As a when forces are to an on the poste­

rior teeth the mandible ;s of downward and forward obtam the occlusal rela­

that wiil best the desired task This snifting of the mandibular Additional r,luscle groups such as the inferior and and the temporals are then called on

lateral pterygo to stabil

the fT~andib!e resulti in a more com than that of a nutcracker. th concept and realizing that

Whereas the

I Fig. 5·13 The amount of force that can be generated between the teeth depends on the distance from the temporomandibular joint and the muscle force vectors. Much more force can be generated on the posterior teeth (A) than on the anterior teeth (B).

A B

~

106 Fundional Anatomy

applied to the teeth can create pathologic changes lead to an obvious conclusion: The damaging hor­izontal forces of eccentric movement must be directed to the anterior teeth, which are positioned farthest from the fulcrum and the force vectors. Because the amount of force that can be applied to the anterior teeth is less than that which can be applied to the posterior teeth, the likelihood of breakdown is minimized 4850

When all the anterior teeth are examined. it becomes apparent that the canines are best suited to accept the horizontal forces that occur during eccentric movements}' They have the longest and largest roots and therefore the best crown/root ratio. They are also surrounded by dense compact bone. which tolerates the forces better than does the medullary bone found around posterior teeth Another advantage of the canines centers on sensory input and the resultant effect on the muscles of mastication. Apparently. fewer muscles are active when canines contact during eccentric movements than when posterior teeth contact. 5556 Lower levels of muscular would decrease forces to the dental and joint structures, minimizing pathosis, Therefore when the mandible is moved in a right or left laterotru­sive excursion. the maxillary and mandibular canines are appropriate teeth to contact and dissi­pate the horizontal forces while disoccluding or disarticulating the posterior teeth. When this con­dition exists. the patient is said to have canifle 9l1id­ance or canine rise ( 5-14).

Many patients' canines, however. are not in the proper position to accept the horizontal forces other teeth must contact during eccentric move­ments. The most favorable alternative to canine guidance is called group fltftction In group function. several teeth on the working side contact during the laterotrusive movement. The most desirable group function consists of the canine, premolars, and sometimes the mesiobuccal cusp of the first molar (Fig. 5-15) Any laterotrusive contacts more posterior than the mesial portion of the first molar are not desirable because of the increased amount of force that can be created as the contact gets closer to the fulcrum (TM])

The clinician should remember that the buccal cusp-to-buccal cusp contacts are more desirable

A t"

l B ~

Fig. 5-14 CANINE GUIDANCE. A, Laterotrusiv€ movement, a, Clinical appearance.

:-c; :" 1: •

:~~:

during laterotrusive movements than are :.....::::r.i.::

cusp-to-lingual cusp contacts (lingual to working) ( 5-16, Aj ir~

The laterotrusive contacts Ieither canine gu i I. cc,··",,"

ance or group function] need to provide adequa-c. :'J ~:lil~::.::;;rJguidance to disocclude the teeth on the

side of the arch lmediotrusive or nonworking sic" immediately I Fig 5-\6. B) Mediotrusive contac

A

B

Fig. 5-15 GROUP FUNCTION GUIDANCE A, Laterotrusive movement. B, Clinical appearance.

-

A B

L

B L

B

Fig. 5-16 A, Posterior teeth during a laterotrusive move­-;:'1t. Contacts can occur between opposing buccal (B) and - gJalIL) cusps. When group function guidance is desirable.

buccal-to-buccal contacts are used. Lingual-to-lingual :: -:aces are not desirable during eccentric movement. B. ::>osterior teeth during a mediotrusive movement. - --tactS occur between the lingual cusps of maxillary teeth : - :he buccal cusps of mandibular teeth.

~~estructive to the system because ::::'lount and direction of the forces trat can

.;:; to t'le joint and dental structures. * Some 5 trat mediotrusive contacts :;ciled by the neuromuscular system differ­

rn other of occlusal contact. EMC demonstrate trat all to()th contacts are

In other words. the presence :::ontacts tends to shut down or inhibit

This results from the in the POL. which when stim'

";cate responses Yet other EMC 5uggest that the presence of mediotru·

teeth increases muscle the increase in muscle

::Jnstrated. the rationa for its presence These concepts are discussed in more

13 47.52.57.58

Criteria for Optill1t11ll Functionai Ocdusioll 107

Fig. 5-17 Protrusive movement with anterior gUidance.

detail in 7.1 What however, is that mediotrusive contacts should be avoided in devel·

ar optimum fUicctional occlusion. When the mandible moves forward into protru,

sive contact. horizontal forces ca n ied to the tee,h /\s with !atera movements,

the anterior teeth can best receive and dissipate these forces.)0 Therefore the arterio y and not the teeth should contact

5-171 The anterior teeth shadid contact or to disarticulate the

contacts appear to unfavorable forces to the system because of the amount and direcion of the force that *

Our'ne this discussion it has become evident teeth fJnction

closure of the accept these forces wei!, I)

because their the arch is such trat the force can their axes

so axial loading is nearly

The anterior teet h. well in the arches

anterior teeth receive occlusal contacts du closure, there is a great Ilkeiihood that their suooort;ve structures will not be abe

forces and wi II be common finding in

tooth support I.

I 47 52 57. 58

108 Functional Anatomy

A '''If.....

B

Fig. 5-18 A, Heavy occlusal contacts on the anterior teeth can occur when posterior tooth support is lost. The maxillary anterior teeth are not aligned properly to accept the mandibular closing forces. These contacts often lead to labial displacement or flaring of the maxillary anterior teeth. B, Posterior bite collapse. The posterior teeth have been lost, resulting in flaring of the anterior teeth. The labial flar­ing has led to increased interdental spacing proximal to the maxillary lateral incisor.

Anterior unlike posterior teeth. are in Droper position to accept the forces of eccentric mandibular movements. Generally. therefore it may be stated that posterior teeth function most

in stopping the mandible during clo­sure, whereas anterior teeth function most effec­

ir gu the mandible during eccentric :llovements. With an appreciation of these roles it :)ecomes apparent that posterior teeth should ~ontact sl more than anterior teeth .. hen the teeth are occluded in the lCP This condi­~ion is described as mutlwlly vratected accilJsion.

Postural Considerations and Functional Tootfl Contacts ~c ,)iscussed in Chapter 4, the postural of

ncandible is that which is maintained during of inactivitv. It is generally 2 to mIT:

below the lCP and can be influenced to some head position. The degree to which it is

affected by head position and the resulting occlusal contacts must be considered when devel­oping ar. optimum occlusal condition 6261 In the 'lormal upright head position. as well as the alert

position (head forwa rd approxi matel:, I the posterior teeth should contact

than the anterior teeth (mutuall" protected occlusion) If an occlusal condition is established with the patient reclined in a dental chair. the mandibular postural position and result­ant occlusal condition may be slightly posteriori" oriented \Vhen the patient sits up or assumes the alert feeding , any change in the postural

and its effect on occlusal contacts mLiS~ be evaluated If in the upright head or the alert feeding the patient's mandible assumes a sl anterior postural position

of the elevator muscles will result in heav, anterior tooth contacts. When this occurs, the anterior contacts must be reduced until the poste­rior teeth again contact more heavily durin{; normal closure. This concept is called the cmteril" envelope af f,melior! When this slight ir mandibular not considered, the resu ing anterior tooth contacts can lead to thE development of functional wear patterns on the anterior teeth This is not true for all patients. bu­it is difficult to predict which patient will show th!:, response This is especially important to thi:: restorative dentist who wants to minimize force, to anterior restorations, such as porcelain crowns Failure to understand and evaluate this positio:­can lead to crown fractures.

SUMMARY OF OPTIMUM FUNCTIONAL OCCLUSION

On the basis of the concepts presented in th' a summary of the most favorable func­

tional occlusal conditions can be derived The fc'­lowing conditions appear to be the least pathogen: for the greatest number of patients over tr

time When the mouth closes, the their most superoanterior !\' ­

on the

tJ "'"

11'1,

~~:e articular eminences with the discs properly ~terposed In this position there is even and

;:::multaneous contact of all posterior teeth. The ~.terior teeth also contact but more lightly

~:' an the posterior teeth. . I tooth contacts provide axial loading of =:clusal forces '.. :",en the mandible moves into laterotrusive

:: ~sitions, adequate tooth-guided contacts on ::: laterotrusive (working) side are present to

:::3occlude the mediotrusive (nonworking) side The most desirable guidance is

: -'·.ided by the canines (canine guidance), en the mandible moves into a protrusive

, ~ sition, adequate tooth-guided contacts on anterior teeth are present to disocclude all

: ~~erior teeth immediately ,:-:e upright head position and alert feeding

_ : sc:or., posterior tooth contacts are heavier -- - anterior tooth contacts,

_____________________~~_.M;'t':-tnces

-,;·:.15 illustrated medical dictionary, ed 30, Philadelphia, ~ Saunders, p 1298.

'_' ~ ~ HI: Classification of malocclusion, Dem Cosmos _. ~~::',-264, 1899,

:-,'~; \'1-/: Balanced occlusions, J :1m Dent Assoc 12:

: .. 33, 1925. _~,;: IL: Physiologic occlusion, J Am Dent Assoc 13:

:,v)3, 1926.

~~ FS: Cast bridgework in functional occlusion. J Am

~_','lY 20:1015·1019.1933 '.,c:r C: Correction of occlusion: disharmony of the

.~"; dentition. N Y Dent J 13:455-463. 1947, H. Stuart C: Concepts of occlusion, Dent Clin

~'n "iovember:591-601, 1963. - -- ,'rd SP, Ash MM: Occlusion, ed 3, Philadelphia, 1983. ... :2rs pp 129-136. _:.'a CO: Current clinical dental terminology, 5t Louis, : \!osby.

"~.: U Studies in the mobility of the human mandible, . ;.-n[O! Scand lO(Suppl): 19-27, 1952.

::,c CO: Swenson's complete den tH res, St Louis, 1970, 112.

. ~d SP: Dysfunctional temporomandibular joint and o pain, J Prostltet Dent 11 :353-362, 1961.

-:- ~d S' Bmxism: a clinical and electromyographic \m Dent AsSN 62:21-28, 19G1.

" Int1uence of occlusal patterns on movement of the - :.c'c J Prostltet Dem 12:255-261, 1962

Criteria for Optimum FrmclionalOcciusion 109

1.5. Posselt ll: of ('cciusion and re/t,liJiiit,l1ion, Philadelphia, 1968, FA Davis, p 60.

16. Dawson Pl.: El'aluation, diagnosis and treatment of occlusal problems, St Louis, 1989. \1osby, pp 28·34.

17. Jankelson B, Swain CW: Physiological aspects of mastica torv muscle stimulation: the myomonitor, Quime5sence lilt 3:57-62. 1972,

18, Gelb H: Clinical management of IWild, ned? and T\1J paill and Philadelphia, 1977, Saunders

19. DuBml EL: Sieller's oral anatomy, St Louis, 1980, Mosby, P 178.

20. Moffet BC: Articular remodeling in the adult human temporomandibular joint, Am) Anilt 115:119-127,1969,

21. Van B1arcom CW, Campbell SD, Carr AB et al: The glossary of prostltodontic terms, ed 7. St Louis, 1999, ,\-losb", P 58.

22. Wu CZ. Chou SL. Ash MM: Centric discrepancy associated with TM disorders in young adults, J Delli Res 69:.'\34-337,

1990. 23. DuBml EL: Sieher'" ora! anatom,o St Louis, 1980, Mosby. 24. lankelson B, Adib F: Effect of variation in manipulation

force on the repetitiveness of centric relations registration: a computer-based study, I Am Dent Assae 113:59-62, 1987,

25, Isberg A, Isacsson G: Tissue reactions associated with internal derangement of the temporomandibular joint. A radiographic, crvomorphologic, and histologic study, Acta Odontol Scand 44:160-164,1986,

26. Farrar WB, McCarty WL: A clinical outline of temporo­mandibular joint diagno:;is llnd treatment, Momgomerv, /\Ia, 1983, r-;ormandie Publications,

27, Dolwick MF: Diagnosis and etiology of mtemal demngemenfS of the temp(lromandibular joint: Presitieni's COIlFerence on tile Examination, Diagnosis, <lnd ;\janagement of 'Dyj Disorder" Chicago, 1983. American Dental Association, pp 112-117.

28. Stegenga B, de Bont lG, Boering G: Osteoarthrosis as the cause of naniomandibular pain and dysfunction: a unif)'­ing concept, J Oral A,jaxillofilc Surg 47:249-256, 1989.

29. '\1amyama T, r-;ishio K. Kotani :VI, Miyauchi S, Kuroda T: The effect of changing the maxillomandibular relationship by a bite plane on the habitual mandibular opening and closing movement, J Oral Rehabil 11 :455·465, 1984,

30. Rugh ID, Drago C): Vertical dimension: a study of clinical rest position and jaw muscle activity. I Prosthet Dent 45 :670-675, 1981.

31. Manns A, Zuazola RV, Sirhan mvL Quiroz M, Rocabado .\1: Relationship between the tonic elevator mandibular activ­ity and the vertical dimension during the states of vigilance and hypnosis, Crania 8: 163-1 70, 1990,

32. Manns A, 1'.1iralles R, Santander It Valdivia J: Influence of the vertical dimension in the treatment of myofascial pain-dysfunction syndrome, J Proslhet Dent 50: 70()-709. 1983 .

33. Gibbs CH, ,>"1ahan PE, Lundeen He. Brehan K: Occlusal forces during chewing: influence on biting strength and food consistency, JProsrl1er Dem 46:561-567, 198:,

3 .. , Bates IF: l\IasticatOlY function-a review of the liter.llure. I L Speed of movements of the mandible. rate of and forces developed in chewing. JOral Rehal>i12:24'l-256. 1

II

I

Determinants of Occlusal Morphology

teet(! that s[<ccessfull[J permit efficient mas­ticatory function is basic to dentistry and survival.'

-,PO

I n health the occlusal anatomy of the teeth func­,ions in harmony with the structures controlling :he movement patterns of the mandible The

..:ctures that determine these patterns are the -,,~-:Joromandibular joints I,TM]s) and the anterior -,,:':", During any given movement the unique

- ::::omic relationships of these structures com­~ -:' to dictate a precise and repeatable pathway - ~.a!ntain harmony of the occlusal the

- _ ~:erior teeth must pass close to but must not : . - :sct their opposing teeth during mandibular

.:':T',ent. Importantly, the clinician should exam­- - :,sch of these structures carefully and appreci­

, :' .- 2W the anatomic form of each can determine - -: :::::c1usal morphology necessary to achieve an _::-:-um occlusal relationship The structures that

mandibular movement are divided into two _:'3 I; I those that infl uence the movement of the . ~::,~ior portion of the mandible and (2) those ~-:-"fluence the movement of the anterior por­- _: the mandible. The TMjs are considered the

.:r controlling factors (PCFs). and the anterior . ­ are considered the anterior controlling factors

- ~:- '; The posterior teeth are positioned between ::0:' :\\'0 controlling factors and thus can be

::,::i bv both to varying degrees

POSTERIOR CONTROLLING FACTORS (CONDYLAR GUIDANCE)

As the condyle moves out of the centric relation position, it descends the articular eminence of the mandibular fossa. The rate at which it moves inferiorly as the mandible is being protruded depends on the steepness of the articular emi­nence. If the surface is quite steep. the condyle will take a steep. vertically inclined path If it flatter. the will take a path that is less vertically inclined The at which the condyle moves away from a horizontal reference plane is referred to as the condylar guidance angle.

Generally, the condylar guidance angle gener­ated bv the orbitin2 condyle when the mandible

than when the mandible protrudes straightforward This is because the medial wall of the mandibular fossa is generally steeper than the articular eminence of the fossa directly anterior to the condyle

The two TMJs provide the guidance for the pos­terior of the mandible and are responsible for determining the character of mandibular movement posteriorly They have therefore been referred to as the PCFs of tfte mandibttiC!r movement. The condylar guidance is con­sidered to be a fixed factor because it is unaJter­able in the healthv patient. It can be altered,

III

"111__--­

I 12 FUilctiolwl Ana/omy

however, under certain conditions (trauma. or a surgical procedure)

ANTERIOR CONTROLLING FACTORS (ANTERIOR GUIDANCE)

lust the TMls determine or control the manner in which the posterior portion of the mandible moves, the anterior teeth determi how the

or laterally the incisal mandibular teeth occlude with the of t he maxi I iary anterior The steepness of these lingual surfaces determines the amount of vertical movement of the mandible. It the surfaces are quite steep the anterior aspect of the mandible will take a steep-incline If the anterior teeth have little vertical will provide little vertical guidance during mandibular movement.

The anterior gUidance is considered to be a variable rather than a fixed factor It can be altered by denta I proced u res sLlch as restorations, ortho­dontia. and extractions. It can also be a:te;ed by pathologic conditions such as caries, habits and tooth wear,

UNDERSTANDING THE CONTROLLING FACTORS

To understand the infl of mandibular move­ment on the occlusal of posterior teeth, one must consider the factors that influence mandibular movement. As discussed in Chapter 4.

mandibular movement is determined by the anatomic characteristics both of the TMJs posteri­

and of the anterior teeth anterioriy Variations in the anatomv of the TMls and the anterior teeth

in the movement pattern of If the criteria fOe optimum functional

occlusion to be fulfilled the morphologic char­acteristics of tooth must be in har­mony with those of its opposing tooth or teeth during II tric mandibular movements, Therefore the exact morphology of the tooth influenced the it travels

ng tooth or teeth

The relationship of a tooth to the con­trolling factors influences the D;ecise movement c: that tooth, This means that the nearer a tooth is L:

the TM!. the more the nt anatomy will influenc~ its eccentric movement and the less the anatorr of the anterior teeth will influence its movemel-: Likewise. the nearer a tooth is to the ante~ rior teeth. the more the anatomy of the anteri,' teeth will influence its movement and the less t;"~ anatomy of the TMls will influence that mover::er:

The occlusal surfaces of teeth consj~-of a series of cusps with both vertical and horize tal dimensions. are made up of com ridges that vary in steepness (vertical dimensic­and direction (horizontal dimension)

Mandibular movement has both a vertical an,~ horizontal component and it is the relations!­between these com ponents or the ratio that

in the of mandibular moveme'-­The vertical component is a function of the sur=~ oinferior movement. and the horizontal com:: nent a function of the anteroposterior moveme'-­If a condyle moves downward two units as it IllC. C'

forvvard two units. it moves away from a horiZOI-­reference an of 4S degrees I' moves downward two units and forward one it from this plane at an ang

64 The angle of devia­horizontal reference plane is what

ill mandibular movement the mandible as it me

horizontal plane and zero unite resulting in a deviation

from horizontal of 0 degrees Fig 6-2 shows mandible four units in the horizonta; four units in the vertical plane. The result here deviation away from horizontal of 4'5

In 6-3 the mandible moves four units ir horizontal plane, but in the vertical the moves four units and the l'\CF moves six units resUlts in a movement of the rCF

movement of the ACE Points bet\,. the factors will deviate by different amounts

plane depending on the:r factor The nearer a is to the

the more its movement will appr: (because of the greater influenCe:

the PCF on its movement) Likewise the

"~i""';:-;::~ _,'

I!,;'

+1111

.'

Determinants of Occlusal Morphology 113

PCF 4 units forward ounits downward

Units of -- ~ ___ vertical

HRP

movement

HRP ACF 4 units forward ounits downward :--­ Units of J

vertical movement --=:___ iTI'n i I ! I

~ Units of ~ horizontal movement

Fig. 6-1 Horizontal reference plane (HRP) of the mandible at both the posterior (PCF) and the anterior (ACF) controlling factor. The mandible moves horizontally four units from a position marked by the dotted line. No vertical movement occurs. The solid line represents the position of the mandible after the movement has taken place.

::lCF 4 units forward ounits downward

HRP

HRP ACF 4 units forward

Fig. 6·2 Movement of the mandible four units horizontally and four units vertically at both the posterior (PCF) and the anterior (ACF) controlling factor. When the mandible moves four units down. it moves four units forward at the same time. The net result is that it is at a 45-degree angle from the horizontal reference planes. Because both the PCFs and the ACFs are causing the mandible to move at the same rate. each point on the mandible is at a 45-degree angle from the horizontal reference plane at the end of a mandibular excursion.

ITU

the ACF the more its movement wiil .~ 57 (because of the greater :nflu­

.-\CF on its movement I. A the factors will move a'way from

of

ounits downward

45°

one that 259c closer to the ACF than to the PCF will move away from horizontal at an of 54 (one fourth of the way between 57 a:'d 45 i

To examine the influence of any anatomic varia­tion on the movement pattern of the mandible.

114 FUI1cti011lli Al1alolH!J

PCF 4 units forward ounits downward

HRP

HRP ACF 4 units forward

" _R;~"do""wacd x y ~

••••••••••••••••'\}••••••••••••••••~ •••••••••••• -. I I _~r' 54' ==' I

Fig.6-3 RESULTANT MOVEMENT OFTHE MANDIBLEWHEN THE CON­TROLLING FACTORS ARE NOT IDENTICAL. The posterior controlling factor (PCF) causes the posterior portion of the mandible to move four units forward (horizontally) and four units downward (vertically). However, the anterior controlling factor (ACF) causes the anterior portion of the mandible to move four units forward and six units downward. Therefore the posterior portion of the mandible is moving away from the reference plane at a 45-degree angle, and the anterior por­tion is moving away at a 57-degree angle. A point (x) that is equidistant from the controlling factors will move at a 51-degree angle from the reference plane. Another point (y) that is one fourth closer to the ACF than to the PCF will move at a 54-degree angle. Thus it can be seen that the nearer the point is to a controlling factor, the more its movement is influenced by the factor.

_ necessary to control all factors except the one distance it extends into the depth of an ng examined Remember that the fossa are determined three factors

the anterior and guidances lies in how I. The ACF of mandibular movement (ie anter,:' ; nfl uence tooth Because the guidance)

. cclusal surface can be affected in two manners 2. The PCF of mandibular movement (i.e, and width\. it is to separate the guidance)

~~ructural influence on mandibular movement into 3. The nearness of the cusp to these control:,­that influence the vertical components and factors

that influence the horizontal components The centric cusps are de\ anatomy of the occlusal surface is also influ­ to disocclude eccentric mandibu

ced by its relationship with the tooth that movements but to contact in the intercuspal pc< :asses across it during movement. Therefore the tion. For this to occur, they must be enoug~ , . cation of the tooth to the center of rotation is contact in the i position but not so Ie .

discussed. that thev contact dunng eccentric movements

EFFECT OF CONDYLAR GUIDANCEVERTICAL DETERMINANTS (ANGLE OF THE EMINENCE) ONOF OCCLUSAL MORPHOLOGY CUSP HEIGHT

=actors that influence the of cusps and the As the mandible is protruded, the desce:' of fossae are the vertical determinants 0: the articular eminence. Its descent in rela~

:::c;usal morphologv. The len2th of a cusp and the to a horizontal reference plane is determined

,ill,

---,.

""'" t

-

~---

Deterl11i1wnts of occlusal Morphology I 15

'.""''''1 41311. I,., :"Uiil;;;MMl,1I11l!f" '·::"!ii\ft~:.."

steepness of the eminence. The steeper the emi­nence, the more the is forced to move

as it shifts anteriorly This results in sreater vertical movement of the :llandible, and mandibular teeth.

In Fig 6-4 the moves away from a hori ­:)ntai reference at a To c mplify visualization, anterior guidance is i Ilus­--ated at an equal angle The cusp of .~. ,,'.ill move away from a horizontal reference ~- a 45-degree To avoid eccentric contact ::2tween premolar A and premolar B in a protrusive ~- ;::vement, cuspal inclination must be less than

in Fig 6-5, and anterior ~ ::e are presented as bei ng 60 degrees to the hor­

_. - ntal reference pia nes With these steeper "":Ical premolar A will move away

from 8 at a 60-degree in longer cusps. Therefore a steeper of the eminence guidance) allows for steeper

cusps.

EFFECT OF ANTERIOR GUIDANCE ON CUSP HEIGHT

Anterior guidance is a function of the relationship between the maxillary and mandibular anterior teeth. As presented in Chapter 3. it consists of the vertical and horizontal of the anterior teeth To illustrate its influence on mandlbu!ar movement and thereFore on the occlusal of posterior teeth, some combinations of vertical and horizontal appear in 6-6.

Parts A. B. and C present anterior relationsh that maintain ecwai amounts of vertical

j') A cr

A

/'// /

/I I, \

\ \ ~ , \ ,

' ..... _­

8

Fig. 6-4 A, The posterior and anterior controlling factors are the same, causing the mandible to move away from the reference plane at a 45-degree angle. B. For premolar A to be disoccluded from premolar B during a protru­sive movement. the cuspal inclines must be less than 45 degrees,

116 Functional Arlalomy

A

(? U,{<\-WFig. 6-5 A, Posterior and ante­rior controlling factors are identi­cal and cause the mandible to move away from the reference plane at a 60-degree angle. B, For premolar A to be disoccluded from premo­lar B during a protrusive move­ment, the cuspal inclines must be

Bless than 60 degrees. Thus it can be seen that steeper posterior and anterior controlling factors allow for steeper posterior cusps.

•

\ \ \

A

the in horizontal one can see that as the horizontal overlap increases, the anterior decreases

Parts 0, E, and F present anterior that maintain equal amounts of horizontal but varying amounts of vertical overlap By com­

the changes in vertical overlap, one can see that as the vertical overlap increases, the anterior guidance angle increases.

Because mandibular movement is determined to a great extent by anterior changes in the vertical and horizontal overlaps of the anterior teeth cause changes in the vertical movement patterns of the mandible. An increase in horizonta: leads to a decreased anterior vertical component to mandibular movement, and flatter posterior cusps. An increase in vertical over­

produces an increased anterior guidance

a more vertical component to mandibular me. ment and steeper posterior cusps

EFFECT OF THE PLANE OF OCCLUSION ON CUSP HEIGHT

The of occlusion is an imaginary line tOL~ ing the incisal edges of the maxillary anterior te",­and the cusps of the maxillary posterior teeth

of the plane to the angle of the nence influences the steepness of the cusps. \\ the movement of a mandibular tooth is vie.­in relation to the plane of occlusion rather t~, in relation to a horizontal reference plane -­i nfl uence of the plane of occl usion can be see:­

In Fig 6-7, condylar guidance and anterior ance are combined to a 45-degree m. ment of a mandibular tooth when compared

Determinants of Oalt/sal Morp{lO{ogy I 17

B c

I I

HO

D

HO , I

Fig. 6-6 The anterior gUidance angle is altered by variations in the horizontal and vertical overlap. In A to C the horizontal overlap (HO) varies, whereas the vertical overlap (VO) remains constant. When the HO increases, the anterior guidance angle decreases. In D to F the VO varies, whereas the HO remains constant. As VO increases, the anterior guidance angle increases.

reference plane. However. when the with the of occlusion ( it can oe ~'ovement is compared with one plane hat the movement av/ay from this plane

_- I it can be seen that the tooth is 60 Therefore the posterior tee:h can have .. 'i\ from plane at only a ;onger cusps and we have determined that the

- =~, results in the need for flatter poste- plane of occlusion oecomes more nearlv Ilel 0::, that tooth contact wil! be to the angle of the eminence. the ~en the tooth movement is compared must be mace shorter.

i

- -

I 18 Fun(tional AnatolllY

Fig. 6·7 A, The anterior and poste­rior controlling factors create a (JA 45° from the horizontal reference plane. B, The tooth moves at a 45-degree angle from the reference plane (HRP). However. if one plane of occlusion (POA! is angled. the tooth will move away from the reference plane at only 25 degrees. Therefore the cusp must

mandibular movement of 45 degrees

,. POsbe relatively flat to be disoccluded ........during protrusive movement. When - - - .... the angle at which the tooth moves 15°

HRPduring a protrusive movement is com­60°

pared with another plane of occlusion -,".. ....(POs). a much greater discrepancy is evident (45 + 15 = 60 degrees). This -allows for taller and steeper poste­ ;- ­81 ,V' - PO;rior cusps. 25°

of Spee. Given a short radius. the angle at wi­EFFECT OF THE CURVE OF SPEE the mandibular teeth move away from the me'ON CUSP HEIGHT

teeth will be greater than with a radi~,

When viewed from the the curve of Sree is an The orientation of the curve of as dE~~' curve from the of the mined by the of its radius to a !­

mandibular canine the buccal cusp of will also influence hm\ ­the mandibular teeth Its curvature can of an individual toot-be described in terms of the of the radius of 6-10, A the radi us of the the curve. With a short the curve will be forms a with a constant horizc. more acute than with a longer radius ( 6-81. reference plane Molars Iwhich are located d 0'

The of curvature of the curve of Spee to the radius I will have shorter cusps. whereas' influences the height of the cusps that molars (located mesial) will have cusc: will function in ,;vith mandibular move­ 6- 10. B. the radi us forms a 60-degree d­

ment. In Fig. 6-9 the mandible is moving away from (

a horizontal reference plane at a 45-degree curve Of more the (, Movement away from the maxi teeth more forward with respect to the horizontal p will vary depending on the curvature of the curve one can see that all the teeth Iprem'

-I ----,

-. •

:---::::- JF ..,': ~ .. '" S....!.. TI(

':.~,:: -E!Ct

..

A

~

-:,'",rence plane c:, - sced more

:::,:ior teeth . - ·",r cusps

~~-::-ECT OF MANDIBULAR LATERAL --;:'l. 'SLATION MOVEMENT ON =--_ SP HEIGHT

Determinants of Occlusal Morphology I 19

B

Fig. 6·8 CURVE OF SPEE. A, A longer radius causes a flatter plane of occlusion. B, A shorter radius causes a more acute plane of occlusion.

B

45°

Fig. 6·9 The mandible is moving away from a horizontal reference plane at a 45-degree angle. The flatter the plane of occlusion (A), the greater will be the angle at which the mandibular posterior teeth move away from the maxillary posterior teeth and therefore the taller the cusp can be.The more acute the plane of occlusion (B), the smaller will be the angle of the mandibular posterior tooth movement and the flatter the teeth can be.

:S I will have shorter cusps In Fig. 6-10. C. lateral movements ( ca IIed Bennett line from the constant hori- mOVel11/,fltj During a latera excursion the

rotated (curve moves downward and inward in one can see that the mandibular fossa around axes located in the

(especially the molars) can ( The of inward movement of the orbiting condyle determined

two factors 1.11 of the medial wall of the mandibular fossa and (2)

of the which attaches to the lateral. condyle If the T!v1 I of the

··:Jular lateral translation movement is a is tight and the medial wall is close to the orbiting ::' shift of the mandible that occurs during a pure arcing movement wili be made

·-li

120 FUllaiollal Allatomy

~ •

" ""

A

cB ~ :­

Fig. 6-10 ORIENTATION OFTHE CURVE OF SPEE. A, Radius perpendicu­lar to a horizontal reference plane. Posterior teeth located distal to the radius will need shorter cusps than those located mesial to the radius. B, If the plane of occlusion is rotated more posteriorly. it can be seen that more posterior teeth will be positioned distal to the perpendicular from the reference plane and can have shorter cusps. C, If the plane is rotated more anteriorly. it can be seen that more posterior teeth will be positioned mesial to the perpendicular and can have taller cusps.

around the axis of rotation in the rotating \\hen this condition exists, no late:al translation

the rnandiole occurs therefore no mandibu­r lateral translation movement} I 6-111 Such condition occurs, Most often :here some

of tne TM I ment, and the medial \\lall the rnandibclar fossa lies medial to an arc

round the axis of the !Fig 6-12) i1en this occurs, the orbiting is moved

to the medial wall and uces a Tandibuiar lateral translation moven'ent.

The lateral translation movement has three c,ltributes: amount, timing, and direction The ;;;,0"111 and are determined in part the ~:egree to which the medial wall of the mandibular

medially from an arc round the alsc determined

'ng

../ Fig. 6· I I With proximity of the medial wall and a : , temporomandibular (TM) ligament, there is no lateral t-· ­

lation movement.

•

-:.-.

~"

,

'I'.'.'"

1\'1,,\1:1111

Ii

./ Fig.6·12 When there is distance between the medial wall -: 11edial pole of the orbiting condyle and the temporo­

-3ndlbular (TM) ligament allows some movement of the -: :3.ting condyle, a lateral translation movement occurs.

~he TM I . ,:al the wall from the media!

The more of the orbit-

the greater tne amount of latera! c ~'ation movement ( 6-13) and the looser ~ -\1 ligament attached to the

./ =g_ 6·13 The more medial the medial wall is from the

. : - e. the greater will be the lateral translation movement. -. '=:ore when the medial walt is in position 3, It witl allow

.'~ ateral translation of the mandible than in position I.

fr \\,

\

Drlenili;wllts of Occ/usal Mor~hology '2'

./ Fig. 6·14 The direction of the lateral translation move­ment is determined by the direction taken by the rotating condyle. When the rotating condyle follows pathway I. the central fossa of the teeth will need to be wider than pathway 2 to disengage the opposing teeth.

the greater trle lateral translation movement. The dirccticn of latera I translation movement

the direction taKen by the the bodilY move:nent i Fie. 6-14:

Effect of tfle AmoUtlt of Lateral Translation Movement on Cusp Height As iust stated the amount Of latera! translation movement determined the tightness of the inner horizontal attached to the rotating

to \,l/hich ;:he medial wall of the :nanciibu1ar from the :ned:al of the

and the greater the greater the amoum mandibu­

lar translation movement .As tile lateral transla, tion movement increases, the shift of the mandible dictates that the cusps be shorter;:o perr.lit lateral translation \vithout creat,

con~act between the maxil and :nandibular teeth ( 6-151

Effect of the Direction of the Lateral Translation Movement on Cusp Height The direction of shift of the du a iateral translation movement is determined the fl'orDholoev and iJea:ner'tou5 attachments of

122 Functional Analolll/j

,./

Fig. 6-15 The greater the lateral translation movement, the shorter is rhe posterior cusp. Pathway 3 will require shorter cusps chan pathway I.

the I'M joint ng rotation The movemen' occurs within a (or less) cone. the apex of wh ich is located at the aXIs of rotation ( 6-16) Therefore in addition lateral movement, the

may also move in (I) a superior ( ) an inferior. (3) an anterior, or (4) a direction. comb:nations of these can occur. In other words, shifts

and so on

,./

Fig. 6·16 The rotating condyle is capable of moving larer­ally within the area of a 60-degree cone during lateral trans­lation movement.

1

2 3

,./

Fig.6·17 The more superior the lateral translation move­ment of the rotating condyle (I), the shorter the posterior cusp. The more inferior the lateral translation movemen: (3), the taller the cusp.

as a determinant of cusp is the vertical movement of

a lateral translation mo'. e:

movement of :­re shorter

lateral movement; likewise

c.

lateroinferior movement will p05~

rior cusps than will a straight lateral movement

Effect of the Timing of the Lateral Translation Movement on Cusp Height

of the lateral translation movement function of the medial wall to the orb:

and the attachment of the TM I to the These two condit determine when this movement occurs durj!' 'ateral excursion. Of the three attributes ateral translation movement (amount, direc

and timing)' the last has the greatest influenc:­the occl usa I of the te c

If the tim:ng occurs late and the maxillar) n"Landibular cusps are functional range amount and direction of the lateral transl,,' movement will have I if any, influenCe: occiusal morohol02v f-Iowever. if the timing C

-

-'i :- :: 'T .....r.-- ::,"'- ,.

i

Determinal1ts of Oce/usal Morphology 123

./ Fig. 6·18 TIMING OF THE LATERAL TRANS· LATION MOVEMENT. /, Immediate lateral transla­: :on movement (immediate side shift): 2, progressive lateral :-~nslation movement (progressive side shift). The more -1iediate the lateral translation, the shorter the posterior :_sp.

- .ement occurs in the laterotrusive move-the amount and direction of the lateral

:ation movement will influence Jsal .r:e'1 the lateral translation movement occurs

a shift is seen even before the ns :-;,nslate from the fossa This is ca:ied an imil1e­':lieral translation movemf'flt or irnmedwte side

6-18). If it occurs in with eccen­~:ovement, the movement is known as a pro­

_,' latera! tra 115/,1 ti011 mOVP111e11t or side -'le more immediate the side shift the shorter i'sterior teeth.

HORIZONTAL DETERMINANTS OF OCCLUSAL MORPHOLOGY

- - _ital determinants of ocC:usal relationships that influence the direction of

3'ld grooves on the occlusal surfaces. Because oetween and over grooves

--c movements. the horizontal determinants : uence the of cusps.

_. centric cusp generates both lat­~·.e and mediotrusive oathwavs across

yi ~ \ \

).... CJ?

.., (

'~Al ;/

Fig. 6·19 The pathway that the cusp of a tooth follows in passing over the opposing tooth is a factor of its distance (radius) from the rotating condyle. Mediotrusive pathway (A) and laterotrusive pathway (B).

ng tooth. Each tion of the arc formed the rotating condvle (

be on the relationship of the

to certain anatomic structures.

EFFECT OF DISTANCE FROM THE ROTATING CONDYLE ON RIDGE AND GROOVE DIRECTION

Because the of a tooth varies in relation to the axis ot rotation of the mandible li.e. rotat­ing variation \dl occur in the

the laterotrusive and mediotrusive The greater the distance of the tooth

from the axis of rotation i I. the wider the formed the laterotrusive and

6-20i. This is consis­tent regarcJless of whether maxil or mandibular

the are increased in size as the distance from the rotating

is increased because the ma'1dibular

are more distally [see Fig 6-20. BI

124 FWlCtionaf Anatomy

...

EFFEC ROTAT THE .\1 ~'D G

A B B

Fig. 6-20 The greater the distance of the tooth from the rotating condyle, the wider the angle formed by the laterotrusive and mediotrusive pathways. This is true for both mandibu­

~,

lar (A) and maxillary (8) teeth. A, Mediotrusive pathway; B, laterotrusive pathway.

EFFECT OF DISTANCE FROM THE MIDSAGITTAL PLANE ON RIDGE AND GROOVE DIRECTION

The relationship of a tooth to the midsagittal plane will also influence the laterotrusive and mediotrusive

Midsagittal plane

pathways generated on the tooth by an centric cusp l\s the tooth is positioned farthe' from the midsagittal plane the angles formed the laterotrusive and mediotrusive pathways \\ increase \ 6-21 )

Midsagittal plane

y~

!1B=-= ~ 'I~ =-a::BA

Fig. 6-21 The greater the distance of the tooth from the midsagittal plane, the wider ::111!11;r:1,9~" <~

the angle formed by the laterotrusive and mediotrusive pathways. This is true for both (A) mandibular and (8) maxillary teeth. A, Mediotrusive pathway; B, laterotrusive pathway .

.1 "'-'­

of the two determines the

Positioning the rotating

but nearer the midsagittal plane, would

angle between the

in the dental arch at and

the smallest teeth nearer to both

as the distance increases, its

decreases

than the

anterior region angles between

~eady been discussed as a vertical determ i-This movement also

and grooves /\S

pathways gener­

::Hrection that the rotating condyle shifts lateral translation movement influences

mediotrusive

Dftennil1allts of Occ/usal MorpflO/oqU 125

Midsagittal plane t?!J

B

Fig.6.22 The more anterior the tooth in the dental arch, the wider the angle formed by the (A) mediotrusive and (B) laterotrusive pathways.

pathways and resuitant angles (Fig 6-24) If the shifts in a lateral and anterior

between the laterotrusive and mediotrusive pathways will decrease on both max­illary and mandibular teeth If the condyle shifts laterally and posteriorly, the angles eenerated will increase,

EFFECT OF INTERCON DYLAR DISTANCE ON RIDGE AND GROOVE DIRECTION

In considering the influence of the intercondylar distance on the of laterotrusive and mediotrusive it is important to consider how a distance influences the relationship of the tooth to the rotating condyle and midsagittal plane As the inter­condylar distance increases, the distance between the and the tooth in a arch ration increases. This tends to cause wider between the laterotrus;ve and mediotrusive

However, as the distance increases, the tooth is placed nearer the midsagit­

relative to the rotating condyle-midsagittal distance. This tends to decrease the

EFFECT OF DISTANCE FROM THE ROTATING CONDYLES AND FROM THE MIDSAGITTAL PLANE ON RIDGE AND GROOVE DIRECTION

has been demonstrated that a tooths position in :elation to the rotating condyle and ~he midsagit­:31 plane influences the laterotrusive and medio­:-usive pathways The combination =:)sitional relationships is what e:\act pathways of the centric cusp --.e tooth a greater distance from

:~lJse the latter determinant to negate the influ­:e of the former. The

:;:erotrusive and mediotrusive pathways would be by teeth

·'eat distance from both the rotating '-e midsagittal plane

would be generated rotating condyle and the midsagittal plane

3ecause of the curvature of the dental arch, the can be seen: Generally

.. :; tooth from the rotating _ ::::1nce from the midsagittal plane - : ... ever, because the distance from the

- :::::Ie increases faster ~ :-ease in distance from the midsagittal

the teeth tovvard the premolars) will have

~terotrusive and mediotrusive pathways than teeth located more posteriorly

6·22)

::FFECT OF MANDIBULAR LATERAL TRANSLATION MOVEMENT ON RIDGE 1.." 0 GROOVE DIRECTION

-fjuence of the lateral translation movement

.': _ occlusal e- ::es the directions of -' :)unt of it increases, the angle between the

-' -'usive and mediotrusive - the centric cusp tips increases (Fig 6-23]

= :ection of laterotrusive and .3

126 Fwutiollal Al1atoll1~

-j A~ JJ

Fig. 6-23 As the amount of lateral translation movement increases, the angle between the (A) mediotrusive and (8) laterotrusive pathways generated by the centric cusp tips increases. This is true for both mandibular (A) and maxillary (B) teeth.

A B

A, B1A1 B· B2 A2 B2

B3 A2 A3

'" Ao

EA

B, B2 B3

_._rr/

Fig. 6-24 Effect of anterolateral and posterolateral translation movement of the rotating condyle. The more anterolateral the movement of the rotating condyle. the smaller the angle formed by the mediotrusive and laterotrusive pathways (Al and Bl).The more posterolateral the movement of the rotating condyle. the wider the angle formed by the mediotrusive and laterotrusive pathways (AI and BI)' This is true for both mandibular (A) and maxillary (8) teeth.

6-251 The latter factor negates the most often minimai and therefore the leas:: influence of the former to the extent that the net enced of the determinants. effect of increasing the distance is to A summary of the vertical and horizontal

between the laterotrusive and minants of occlusal morohologv can be fow" mediotrusive The decrease. however. is Tab'es 6-1 and 6-2.

.:

-:-~I

I'_~IZ::' ~

.l!jJ,J

~~

.!~I,.::&o

""""':~2

'~-;'Ir'

~":illll!JnI~~~,

h, IHji~,'II!Qj:r'

Determinal1ts of O((IL/SIII MorpFlOlo!JY 127

~Al\(-;-V·_A2).

\~i\..:-l\.-~:'~,\-.~.-Y' \ \ i 1\\ 1: \ \ \

I \ I \ \ \ I \ ~ •.. ~

A2 A,

Fig. 6-25 The greater the intercondylar distances, the smaller the angle formed by the laterotrusive and mediotrusive pathways. The greater the intercondylar distances. the smaller the angle formed by the laterotrusive and mediotrusive cusp pathways (AI and 8 1), The smaller the intercondylar distance. the wider the angle between the laterotrusive and mediotrusive cusp pathways (A2 and 82),

TABLE 6-1

Vertical Determinants of Occlusal Morphology (Cusp Height and Fossa Depth)

Factors Conditions Effects

:: :>ndylar guidance Steeper the guidance Taller the posterior cusps :'.lcerior guidance Greater the vertical overlap Taller the posterior cusps

Greater the horizontal overlap Shorter the posterior cusps ~ ~ ne of occlusion More parallel the plane to condylar guidance Shorter the posterior cusps :: J I've of Spee More acute the curve Shorter the most posterior cusps ...::c:eral translation Greater the movement Shorter the posterior cusps

'Tlovement More superior the movement of rotating Shorter the posterior cusps condyle

Greater t\\e immediate '.>ide '.>\\i1t S\\oner t\\e ?o'.>terior eu'.>?>

TABLE 6-2.

-: rizontal Determinants of Occlusal Morphology (Ridge and Groove Direction)

fM:tors Conditions Effects

- ::::~ce from rotating condyle Greater the distance Wider the angle between laterotrusive and mediotrusive pathways

_ ':::-ce from midsagittal plane Greater the distance Wider the angle between laterotrusive and mediotrusive pathways

_::~-:" translation movement Greater the movement Wider the angle between laterotrusive and mediotrusive pathways

-= -: ::>ndylar distance Greater the distance Smaller the angle between laterotrusive and mediotrusive pathways

E' of If

-...

.,.

Ie ':;"'5:

.;.~

128 FUllctiorwl Ana/oll1t}

lns~ead. studies seem to indicate that the the articular eminence is not related to any~~~1](C)NSH1PBETWEENANTERIOR occlusal relationshio ' . In otherAN[)P(C)STE~IOR.CONTR<pLlING

FACTORS

bave oeen made to demonstrate d'ctating mandibular movemeN. This

correlation between the vertica. and horizontal tant c(wcept because the .ACFs can be influence

of the with tre dental ures . .Alteration 0: the ,ACFs

lingual concavities of the rraxillary anterior an important

teeth ivertical and horizc'ntal relationshi of disturbances in the

anterior lOne suggests that consistent with

Cons'deration directed 'RtjerCllCeS ril} toward the PCFs that steepness of the

movement le.g. of the eminence and 1. Moffett BC: The joint. In Sham

editor Complete demure prosthodolllics, New York, 1·'lateral translation movement) This phi ,\!cGrdw-llilL pp 2J 3-230.

that moverrent becomes mere Ricketts R'\I: Variations of the temporornandihular jOiL:

horizontal in articular eminence rewaled by cephalometric laminagrarhy, :\m J 0,:' with increase in lateral translationi tr:e 'i :lG:R77-892, 1')50 .

concavities of the maXillary anterior teeth will •\nglc IL: ~dctorS in temporom':lIldibular form, Alii I ~:

83.223-234, J ')4S. increase reflect a similar movement characteristic However, scientific evidence to support a corre­

lation betvveen the .ACFs and rCFs IS

'hlI!!

...". .rje

mn'l'

l

--

Irhe

is present when lhere i of tissues without a local

A common location for Ip Patien~s who

pain will c~)mmon report that· Itle:r When ,he is ned. no local

54 FUIICliolllll Anatomy

Arother type of pain sensation that be expe­rienced wlen afferent inter:,eurons stimulated is >c Te understand tils condi tion. tle term must be broken dOWI) nd

raised or increased condition The in fact mea:-,')

painful s~imul '-';len increased

some I factm. such splinter in the finger .After a Fe'.'! hours the tissue

round the ;Iter becerres quire sensitive to toucl This primary because the

cause can found This is a fai situation in of heac; and neck

different from at

the sou rce of the symptoms Instead

may I for some time i 12 to olockade is administered. This clinical feature cause some confusion du

Until now Iy the effect a of svmptoms has consloerecL

is true when afferent Interneuron are involved. If the ce:ltral effect involves efferent interneurons. however. motor

One type of efferent effect the develoome:lt of a localized area hvpersensi­

called are discussed i:l I"'ore detail in Another com effere;~t

ttle ng muscles are activated while the elevator muscles Clre relaxed In the presence of in however ~;le

CNS to resoond differentlv Stohler< has

demonstraleo that when ta

to p:otE~ct

CO-COl1traction because of simultaneous contraction of antagonis­

m groups BeW' recognized this CNS response this conditi,jn is pain it can

mally

I Thus felt in a reflex musclE~

such in

lead to muscle pain if it Protective co-contraction Imuscle i

in the genera location lad to it 1101

ina muscles of mastication. Tilis condition is not unusual and unfortu fools mallY de:ltists

muscles of mastication the of the Hmvever. such treatment

alone cannot resolve the the co-contraction

pail: must De addressed for effec've elimination of the masticat,:;rv n'uscle

Understanding rhe effect on the muse! for

management Feat detail in later

n however must use it is vltaily i

usc;e pa in As has in input can ind

sou

Tris condition of Ilal

this condition cal 51',151115 r;;ecel:t stud ies however. feli 1

the that mare aCil spasms·' ':-hererore this condltic'i

T io.... __ ~.. ~ ..

Fundional NeuroanatolHij and Phijsiologij of tile Masticatorij System 55

is more called mLiscle This condition can become a diagnostic problem for the clinician because the patient continues to report suffering after the nal source of pain has resolved.

Because muscle pain is an important clin­ical problem to understand. the example is given to illustrate SOr:le considerations in its management

A third molar is extracted, and during the ensuing week a ;ocalized osteitis (dry socket) develops. This becomes a source of constant deep pain that, by way of the central excitatory effect, produces protective co-contraction I muscle splinting) of the masseter and medial pterygoid 'T1uscle. The patient returns in 5 days complaining of the Jainful condition. Examination reveals a limited range of "'1andibular opening, caused not by the infection but by the secondary muscle response. If the source of the deep pain s resolved quickly (Le., the local osteitis is eliminated). the :;rotective co-contraction is resolved and normal mandibu­?r opening will return. If the source is not quickly resolved. :-e protracted co-contraction may itself produce pain • ... .,ich then perpetuates the protective co-contraction and ",:s:ablishes a cyclic muscle pain condition. In such a case .

."inating the original source of pain (the osteitis) will not ~ ."inate the muscle pain. Treatment must now be directed :::ecificaily toward the masticatory muscle pain disorder. . , - ch has become wholly independent of the original source :: :Jain.

central effects involve the autonomic - _ '2ns. characteristic manifestations will be -~~ Because the autonomic system controls the

:::::n and constriction of blood vessels. variation 'cd flow will appear as reddening or blanching "" involved tissues. Patients may complain of

or a eye. Sometimes the the eye will redden Even

:::oms may be reported . a stuffy or runny -~ SOr:le patients may report a

the same side as the pain CI .,elling is rarely seen in

::~rs. yet this is commonly patients and may represent

to autonomic effects.

The key to determin whether these symp­toms are a result of the central effect is their unilaterality Clinicians should remember that central effects do not cross the r:lid­line in the trigeminal area. Therefore the ciinical manifestations will be seen only on the side of the constant deep pain. In other words. one eye will be red and the other normal. or one nostril may be

mucus and the other not If the source of the autonomic were le.g .. allergy). both eyes would be red and both nostrils discha rging.

Understanding these central basic to the management of facial pain The role that such conditions play in the diagnosis and treatment of temporomandibular disorders is discussed in detail in later chapters

Suggested 'Readin!ls

Hell \VE: Temporomandibular dis(1l'ders; classiflClltioll, dwgrwsis, lIIanagemenl. ed 3, Chicago, 1990, Year Book MedicaL

Okeson JP: Bell's oraj/Kial pains, I'd 6, Chicago, 2005, Quintessence.

'References

1. Okeson JP: Bell's orojaci(// pains, ed 6, Chicago. 2005, Quintessence .

2. Cuyton AC: Texlboo" of mediwl physiolog)" Philadelphia, 1991. Saunders, p 1013.

3. De Laat ;\: Reflexes elicitable in jaw muscles and their role during jaw function and dysfunction: a review of the I itcra­lUre. Part II. Central connections of oro facial afferent tlbers, Cranio 5:246-253. 1987.

4. Dubner R, Bennett GJ: Spinal and trigeminal mechanisms of nociception, Artrll1 ReI' Nellrosci 6:381-418, 1983.

5. Sessle Ill: The neurobiology of facial and demal pain: present knowledge, future directions, J Dent Res 66:962-981.

1987. 6. Hu J\V, Dostrovsky 10, Sessle IlJ: functional properties of

neurons in cat trigeminal subnucleus caudalis (meJulLuy dorsal horn). I. Responses to oral·facial noxious and nonnoxious stimuli and projections to thalamus and subnucleus oralis. I Neurophysiol 45: 1 73~ J92. 1981.

7. Sessle B): Recent insights into brainstem mechanisms underlying craniof.Kial pain, IDem Educ 66: 108-11 2. 2002.

8. Lund Jr, Donga R. Widmer CC, Stohler CS: The pajn~

adaptation model: a discussion of the relationship between

Functional Neuroanatomy and Physiology of the

Masticatory System

"You wl1not treat [wiess ~IOU wldfrsta ml functioll.··

-JPO

T he function of the system is , Discr:minatory contraction of

the various head an,d neck muscles is 'lec­2ssary to move the mandible ,;:ffective :unctioning A h neu :::ont:ol system coordi nates the "ctivities of the entire

rill' of nerves ~2rm l1eUrGI1Hj5CUfar 5&151011 ,A basic un.ders~anding of ~he anatomy and function of the neuromuscular

stem is essential to the in,fjuence -:lat tooth contacts as \'1ell as other conditions, -:'jV on mandibular movement.

This chaoter divided into :hree The :st section reviews In detail the basic

~'-d fU'lction of the neuromusCl;lar system The ~::::ond describes the basic aclvities of

3stication, swal and The third - Il reviews important concepts and mechanisms

are necessary to understand orofacia l

the concepTS in these three sections should enhance the clinicians abll to understand a

~~en,t's comolaint and orov:de effective

ANATOMY AND FUNCTION OF THE NEUROMUSCULAR SYSTEM

:~'urposes of discussion, the neuromuscL;lar sys­divided Into tViO maior comuonents ( I J the

..

neurologic structures and 12) the musc,es. The anatomy and function of each of components is reviewed in many instances It

difficult to separate function. With a'l understand­ing of these components, basic neuromuscula r func­tion can be revie\ved

MUSCLES

Motor Ullit The of the neuromuscular system is the rrotor unit. v.,hich consists of a nL;mber of mUSCle fibers that are innervated ore motor neuron. Each neuron with the muscle fiber at a motor When the r.euror is activated the motor amounts of which initiates depOlar­ization of the muscle fibers. causes the muscle fibers to shortell or contract.

The nJmber of muscle fibers in'lervated by one motor neuron according the fu'lc­tlon of the motor unit. The fewer the muscle fibers per motor 'leu ron, t he more the move­ment. /\ motor neuron may innervate only two or three rnuscle fibers, as in the cil muscles

control the lens of the eye). one motor neuron may innervate ~Ull­

dreds of muscle fibers, in any muscle (e.g. the rectus femoris in the l.... similar variatio'l exists in the number of muscle [ibers per motor neuron v:ithin the muscles of masticaton The inferior lateral muscle has a low muscle fj ber/motor neu ron ratio: therefore it is capable the fine adlustments in length needed

25 'i~ili

:'" !

Functional NeuroanatolllY mid PflysioloflY of the Masticatory System 31

The limbic structures function to control our emotional and behavioral activities. Within the limbic structures are centers or nuclei that are

for speci fic behaviors such as anger. The limbic structures also control

fear. or center apparently exists.

on an instinctive level. the individual driven toward behaviors that stimulate the side of the center. These drives are not generaly perceived at a conscious level but more as a basic nstinct The instinct will certain

behaviors to a conscious level For when an individual chronic pain behavior xiiI be oriented toward withdrawal from any stimu­us that may increase the pain. Often the sufferer .'.ill withdraw from life itself. and mood alterations 3uch as depression will occur. It is believed that

of the limbic structures interact and associations with the cortex, thereby coor­

::i;'ating the conscious cerebral behavioral func­-ons with the subconscious behavioral functions

: the deeper limbic system from the limbic system leading into

can anyone or all of the ~-any internal bodily functions controlled by the

Impulses from the limbic system into the midbrain and meduila can control

~ch behavior as wakefulness, excitement o.-.:J attentiveness. With this basic understanding .. I imbic function, one can quickly understand the _. oact it can have on the overall function of the indi­::Jal. The limbic system certainly a major role

. :Jain problems, as discussed in later chapters Cortex. The cerebral cortex represents the

. _.~er of the cerebrum and is made up • -"domi of gray matter. The cerebral cortex is -" portion of the brain most associated

the process, even though it cannot .ide thinking without simultaneous action of

c'::per structures of the brain The cerebral cortex - ·-e portion of the brain in which all

_ne's memories are stored, and it is also the -~~ most responsible for one's abil to ~ -.' muscle skills. Researchers still do not know

basic mechanisms which the -c'Jral cortex stores either memories or

. _. Jscle skills.

In most areas the cerebral cortex is about 6 mm th and all it contains an estimated 50 to 80 billion nerve cell bodies Perhaps a biilion nerve fioers lead away from the cortex. as well as

numbers into it. to other areas of the cortex. to and from deeper struc­tures of the brain. and some al the way to the

cord Different regions of the cerebral cortex have

been identified to have different functions A motor area is primarily involved with motor function. A sensory area receives somatosensory input for evaluation. Areas for I senses. such as visual and auditory areas. are also found.

If one were to again compare the human brain with a computer. the cerebral cortex wou:d represent the hard disc drive that stores all information of memory and motor function. Once one should remember that the thalamus keyboard) is the necessary unit that calls the cortex to function

Sensory Receptors are neurologlC structures or

organs located in all tissues that proVide information to the CNS way of the afferent neurons the status of these tissues. As in other areas of the body, various types of sensory receptors are located the tissues that make up the masticatory system Specialized sen­sory receptors information to the afferent neurons and thus back to the CNS. Some receptors are specific for discomfort and pain These are called Other receptors provide infor­mation regarding the position and movement of the mandible and associated oral structures. These are called that carry informa­tion regarding the status of the internal organs are referred to as Constant input received from all of these receptors allows the cortex and brainstem to coordinate action of individual muscles or muscle groups to create appropriate response in the individual

Like other s, the masticatory system uses four malor types of sensory receptors to mon:tor the status of its structures ( 1 ) the muscle which are receptor organs found in the muscle tissues (21 the tendon organs, located in the tendons: (3) the pacinian corpuscles

11­