periov&>ntics restohative dentistry...esthetic, and maintainable occlusion is the primary...

Special reprint from

THEINTERNATIONALJOURNALOF

PERIOV&>NTICSRESTOHATIVE

DENTISTRYVol'. 23

Copyright @ 2003 by Quintessence Publ Co, Inc

3

03

Occlusion-Based Treatment Planning forComplex Dental Restorations: Part 1

"\;~

Bernard Keough, DMD, CAGS*

Successful treatment of patients requiring complex dental restoration requires acomprehensive evaluation of their existing occlusion. Using a systematic and

ordered sequence for relating this occlusion to a physiologic standard greatly

facilitates the treatment planning process of reconstruction. Reconstructing the

occlusion in this same orderly sequence then significantly enhances the control

and predictability of the procedures performed by all practitioners involved in

management of the case. Six closely inter-related elements of an occlusion must

be evaluated and frequently modified in treatment. Part 1 of this article will dis- .cuss two elements of the occlusion, in the order of their evaluation-centric rela-

tion position of the mandible and vertical dimension of occlusion.

(lnt J Periodontics Restorative Dent 2003;23:237-247.)

*Private Practice Limited to Prosthodontics, West Palm Beach, Florida.

Reprint requests: Dr Bernard Keough, 2521 North Flagler Drive, WestPalm Beach, Florida 33407.

237

Successful reconstruction and long-

term maintenance of patients withextensive dental disease are highlydependent upon making the correctdiagnosis of the nature of the prob-

lems and developing a proper treat-ment plan for the implementation ofsolutions. However, the extent of

problems for many of these patientsfrequently makes diagnosis and suc-cessful treatment planning a very dif-ficult task. Patients with skeletal and

dental abnormalities, severe occlusal

disease, or extensive periodontaldisease coupled with multiple miss-ing teeth, collapsed occlusions, andyears of dental neglect and/or inad-

equate dental care can present withan extremely complicated and ini-tially confusing set of circumstances.

Add in the increasing complexity oftreatment procedures and tech-

niques used to solve various prob-lems, and it becomes very easy for.the clinician to lose sight of the full

extent of a patient's needs and pos-sible treatment solutions. It is

mandatory that practitioners be ableto assess the entire situation and

plan treatment based on the overall

needs of the patient, without first

Volume 23, Number 3, 2003

238

getting caught up in planning intri-cate procedures that may be avail-able for solving specific problems.

Therefore, it is imperative that a con-sistent and systematic approach to

planning treatment for the complexreconstruction patient be used.

Although these patients require mul-tidisciplinary treatment, the most

logical and orderly approach to plan-ning is through an evaluation of theexisting occlusal condition and a

comparison of that condition to anocclusal scheme that would be con-

sidered physiologic, protective, andmaintainable. From this comparison,

a plan for reconstructing a finalocclusal scheme that meets these

requirements can be developed, and

the final treatment plan will evolve.This is a reasonable approach, as the

establishment of a physiologic,esthetic, and maintainable occlusion

is the primary goal in the recon-struction of a patient's dentition.

Using a step-by-step approachto first evaluate, then design, and

subsequently construct a patient'socclusion not only facilitates the

treatment planning process, but also

the sequencing of therapy duringtreatment. Realization ofthe require-ments necessary to construct andthen maintain an occlusion will

greatly aid the practitioner in deci-sions regarding the possible needfor orthodontic therapy or the nature

of potential periodontal therapy.Decisions regarding the use of endo-dontically treated teeth, root-re-sected teeth, or the number and

position of dental implants that maybe used to support the prosthesiscan be made more intelligently once

the occlusal scheme has been previ-sualized. The ultimate long-term suc-

cess of the prosthesis is dependentupon force control, and occlusaldesign and construction are allabout

force control. Equally important arethe control and distribution of forces

acting on the supporting abutments,

periodontium, and temporo-mandibular joints (TMJ).This is alsodone through the occlusion; there-

fore, careful planning of the occlusal

scheme is the first step in theprocess.

For many years, clinicians havebeen evaluating and treating occlu-

sions as part of the reconstructionprocess. Beyron1 stated that one ofthe most important phases of thereconstructive procedure is the plan-ning of occlusal therapy. Others2,3have attributed the success of fixed

bridgework in patients with reducedperiodontal support to an occlusal

design that precludes the concen-tration of undue stress in the remain-

ing periodontal tissues. More

recently, the success of implant-sup-ported restorations has also beendirectly attributed to a control of the

forces placed on these prostheses,which are managed, according tosome,4,S in large part through thedesign of the occlusion. Currently,

with the profession's heightened in-

terest in esthetics and cosmetic pro-cedures, the occlusal condition of a

patient may frequently be over-looked, but this is to the detriment

ofthe patient. Much ofthe wear andbreakage seen in teeth requiringcosmetic enhancement is the direct

result of occlusal dysfunction and

parafunctional habits.6 Miller7 has

also reaffirmed the interdependenceof the II esthetic zone/' the anteriorteeth, with the rest of the masticatorysystem. It is clear that an adherence

to the requirements of a physiologicocclusion is applicable to all patientsrequiring restorative endeavors (Fig1). The concept that the dictates of

esthetics and the requirements of aphysiologic occlusion may be in con-flict with one another is totally un-founded. Successful esthetic treat-

ment of many patients cannot beaccomplished without considerationand modification of various elementsofthe occlusion. The metal-free res-

torations that many practitioners arenow using simply do not withstandocclusal forces as well as the metal-

based restorations of the past.Dawson8 has stated that with

regard to treatment planning forocclusal problems, restorative pro-cedures should not be undertakenunless the end result can be visual-

ized. However, there has frequentlybeen controversy and confusion asto what that end result should be,

what therapy should consist of, andhow the occlusion should be estab-

lished. Taylor et al9 stated thatalthough anatomic occlusal charac-

teristics for implant-supportedrestorations have been empiricallydescribed, they have not beenexamined scientifically. Further,

E:usp height, angulation, type ofexcursive contact, occlusal tablewidth, and other considerationshave. . . . never been examined sci-

entifically as they apply to naturalteeth either. The generation of suf-ficient data for making meaningfulconclusions will require studies of

The International Journal of Periodontics & Restorative Dentistry

~

239

Fig 1a Patientrequesting cosmetic den-tal procedures to restore worn andchipped maxillary and mandibular incisors.Patient is unaware of parafunctional habits.

such magnitude and expense thatthey will never likely be done, andhuman occlusion will remain in the

realm of anecdote and empiricism.

In today's environment of lIevi-

dence-based therapy," the reliance

upon empirical long-term observa-tion and evaluation is discounted.

However, ifTaylor et ai's assessmentof the situation is accurate, one is

forced to look at those concepts ofocclusal design that have had suc-

cess over time, in spite of their empir-ical nature. Since the design of an

occlusion is a complicated and elu-sive area, decades of treatment andobservation are not without value.

Many of these successful occlusal

concepts have been described forthe so-called periodontal prostheticpatient2,10,11; however, they have

been just as applicable to patientswith occlusal disease,12 implant-sup-ported restorations,13 restorative

procedures for anterior estheticproblems,? and even nonextensiverestorations.14

Fig 1b Mounted models demonstrateinitial contact in centric relation of the

molars only. Premature oce/usal contacts in

centric, which may result in parafunctionalhabits and tooth wear, must be addressed

prior to cosmetic procedures.

A successful physiologic occlu-sion may be described as one that

enables the patient to function withefficiency and comfort, and one that

is well-tolerated by the periodon-tium, teeth, and TMJs.15 It acts to

minimize activity of the muscles C?fmastication, creating neuromuscu-lar harmony, and it does not create

any pathologic symptoms in thesemuscles. There are several generally

accepted criteria for this occlu-sion 16:

1. Stable, simultaneous bilateral

maximal intercuspation of theteeth with the mandible in the

centric relation orterminal hinge

position; no interferences to clo-sure between maximal intercus-

pation and the terminal hingeposition of the mandible.

2. Freedom of mandibular move-

ment in lateral and protrusivemovement to and from the maxi-

mal intercuspation position, with-

out posterior or anterior interfer-ences.

Fig 1c Prognosisforsuccess of ceramicveneers is greatly enhanced when forcesare controlled and a physiologic oce/usionis established as part of therapy.

3. Occlusal forces are distributed

as widely as possible, with at-

tempts made to minimize hori-zontal forces on both posteriorand anterior teeth.

Establishment of a physiologicocclusion encompasses much morethan just evaluation and use of a

specific condylar position or modi-fication of the restored anatomy of

the posterior teeth. Sixseparate butclosely inter-related elements must

be evaluated and frequently altered.Through an understanding of the

significance, inter-relationship, andworkings of these various elements,a functional and esthetic treatment

plan can be achieved. Orderly andsystematic comparison of thoseaspects of a patient's occlusion to a'physiologic and esthetic standardmakes treatment decisions mucheasier.

The first step is an evaluation ofthe centric relation position of the

mandible. Most patients must berestored with this position coincident

Volume 23, Number 3,2003

240

with maximal intercuspation. Se-cond, the vertical dimension of

occlusion (VDO)must be evaluated.The joints, muscles, and teeth must

be placed at an acceptable VDO in

the final restoration. Third, the pa-tient should be restored with an ap-

propriate posterior occlusal plane.This has a direct effect on posterior

cusp height and vertical overlap ofthe anterior teeth. Study modelsmounted in centric relation by

means of a facebow allow proper

evaluation of both the VDO and pos-terior occlusal plane. The fourth ele-ment to evaluate is the maxillary

anterior incisal edge location, which

represents an extension of the max-

illary posterior plane of occlusion.This is important in both functional

and esthetic treatment planning.Fifth, in conjunction with the lingualcontours of the maxillary anterior

teeth, the incisal edges of the man-dibular incisors function as the ante-riordeterminant of occlusal function.

This isa most important relationship.

Finally,a protective posterior oc-clusal surface design must be estab-lished. The occlusal anatomy of the

posterior teeth is modified to fit thefunctional and esthetic dictates of

the previous five components of theocclusion. Ifapproached in this se-

quence, acomplicated set of dentalproblems becomes much easier to

resolve. Once problems have beenfullyrecognized, solutions are easierto devise. This, in turn, facilitates

communication among the differentmembers of the team.

Elements of an occlusion

Centric relation

Several condylar positions havebeen used as a reference or starting

position from which to establish an

occlusion. The centric relation posi-tion has been described and advo-

cated by many authors.17-19Centricocclusion has also been used, andstill others have recommended the

use of the patient's neuromuscularcentric occiusion.2Q,21However, the

preponderance of evidence doesnot support the use of the latter posi-

tions; neither has proven to be phys-iologic.22

Centric relation may be definedas "the maxillomandibular relation-

ship in which the condyles articulatewith the thinnest avascular portion oftheir respective disks with the com-

plex inthe anterior-superior positionagainst the shapes of the articular

eminences."23 The first step in thediagnostic phase of therapy is toanalyze the relationship between thisdefined centric relation position ofthe condyle-disc assemblies and the

maximal intercuspation position ofthe teeth.24 This relationship mustbe understood to both evaluate andtest the current state of health of the

patient's TMJs, as well as to relatethe intercuspal position of the teeth

to the terminal hinge position.

Normal, properly aligned, and func-tioning condyle-disc assemblies can

be functionally loaded without painand support an occlusion, and theyare the most stable in the long term.This is of utmost importance, as the

TMJs are the foundation upon which

we build the occlusion. Many TMJshave undergone structural changes

and adapted through remodeling ofthe soft tissues,25 but they may also

accept firm loading in function with-out discomfort. Condylar movementof these joints, however, may not be

as reproducible overtime,26 and theocclusion may require additional

adjustment as the case iscompleted,but they will support a properlydesigned occlusal scheme. Defini-

tive treatment of patients whoseTMJs cannot be maximally loaded

without pain should not be under-

taken until the cause of the pain hasbeen determined and resolved.27

One must be able to freely

locate the terminal hinge position, asit is the reference of the condyles towhich the restored maximal inter-

cuspal position will be established(Fig 2). The terminal hinge, centricrelation position is used for several

important reasons. It is reprodu-cible28over a fairlynarrow range andstable over the length of time re-

quired to complete the reconstruc-tion process. This is an important

consideration, for many complexcases take months to a year or more

to complete. Centric relation is alsoa border position on the envelope offunction, and the mandible willfunc-

tion from this position if there areno interferences preventing closure

into it. From this position, all man-di~ular movement begins. Its use inreconstruction will ensure that allmovements of the condyle from this

position act to separate the posteriorteeth.

Finally, one of the tenets

of a physiologic occlusion is


241

Fig 2a Patientrequesting dental recon-structionafter many years of neglect.Evidence of prior occlusalparafunctionisdemonstrated by extensive wearofremainingmandibularincisors.

'--- Fig 2b (right) Radiographicsurveydemonstrates extent of tooth damage andloss.

Fig 2c Basic concepts of denture tech-nique may also be used with completely orpartially dentate patients. For this patient,a maxillary wax rim is useful in establishingthe plane of occlusion and incisor position.

'\\j

Fig 2d Teeth positioned on maxillarywax rim establish desired position for finalprosthesis. Wax rims are used to recordcentric relation position of the mandible,which must be located prior to therapy.

Fig 2f (left) Diagnostic information isconverted into initial treatment proceduresthrough the formation of processed acrylicresin provisional restorations.

Fig 2g (right) Facial view of final prosthe-sis. Shallow incisal guidance and level

occlusal plane facilitate accommodation of

patient's parafunctional habits.

Fig 2e Toothposition transferred tostudy models mounted in centric relation.Maxillary occlusal plane also used to facili-tate location of mandibular implants. Class1/position of mandible dictates final incisalguidance and posterior occlusal anatomy.


242

\

neuromuscular harmony. Therefore,

a goal of reconstruction is to create

the lowest level of muscle activity

during both function and parafunc-

tion. Complete seating of the con-

dyles into centric relation during

maximal intercuspation results in

minimal electromyographic activityof the inferior head of the lateral

pterygoid muscle.29,3oAny other ref-

erence position, which places the

condyle-disc assembly down and for-

ward on the slope of the eminence

during maximal intercuspation, will

require activity of the inferior head to

Fig 2i (left) Lateral view of prosthesisdemonstrates extent of overjet requiredfor lip support and facial esthetics.

Fig 2j (right) Final case closely followsocclusal and functional dictates estab-

lished by wax rims.

maintain this position. The resultingantagonistic activity between the lat-

eral pterygoid and elevator musclesacting to seat the condyles results in

heightened and uncoordinated

activity of all of these muscles31,32

and frequent pain in the pterygoids.Although there is controversy over

the direct relationship between pre-mature occlusal contacts to centric

closure and occlusal muscle disor-

ders, or temporomandibular disor-ders, clinicians have long recognized

that many patients do demonstrate

a direct relationship, and every effort

Fig 2h Radiographic survey of final pros-thesis.

should be made to prevent these

interferences to minimize the possi-

bility of muscle pain or dysfunction.Increased muscle activity will

also act to create greater load on

the TMJs. Under load, the superior

head of the lateral pterygoid is

thought to become most active,30

and hyperactivity of this muscle may

disrupt the normal relationship ofthe condyle-disc assembly, resulting

in transitory or permanent disc

derangement. This is an important

consideration in patients with para-functional habits, where the joints


243

may be under heavy loads manyhours a day. Some investigators have

shown that interfering contactsbetween centric relation and maxi-

mal intercuspation are a prime factortriggering the initiation of bruxism,33although the role of defective oc-clusal contacts is still controversial.

Although the causes are not fullyknown, the destructive nature ofthese forces is well-documented.12

Thus, every effort should be made to

prevent centric interferences and anyparafunctional habits that may con-sequently result, and to minimizemuscle activity should these habits

persist following reconstruction.The relationship between cen-

tric relation of the condyles and max-

imal intercuspation can only bedemonstrated with axis-oriented

casts mounted on an articulator.

Mounted casts willshow which pairsof teeth contact prematurely on thearc of centric closure. The effect

these contacts have on the magni-

tude and direction of condylar dis-

placement down the slope of theeminences may then be quantified

to begin to provide a basis for for-

mulating a treatment plan.

Vertical dimension of occlusion

Following evaluation of the centric

relation position, the VDO-the dis-

tance "between two points whenthe occluding members are in con-tact"23-is assessed. Clinicians tend

to relate the VDO to two fixed ref-

erence points of the anterior teeth.In reality, most patients present withtwo different vertical dimensions in

the anterior segment; one, with theoccluding surfaces of the teeth in

maximal intercuspation, does notconsider the location of the con-

dyles, and a second may be mea-sured with the condyles seated incentric relation and the mandibleclosed on the arc of closure until the

teeth first touch. However, in this

position, the anterior segments maynot be in contact. This second ante-

rior vertical dimension is usual!ygreater than the first, with the dif-

ference representing the vertical

component to the slide from contactin centric relation to maximal inter-

cuspation. With a few exceptions,34reconstruction should occur with the

mandible placed in centric relation,or the position of adapted centric

posture.24 Therefore, if the VDO ofmaximal intercuspation is accept-

able, an occlusal equilibration maybe performed, which eliminates theprematurities to closure, and oc-clusal contact in centric relation ismade coincident with maximal

intercuspation. Should the VDOwith the condyles already posi-

tioned in centric relation proveacceptable, the provisional restora-tions may be made with maximum

intercuspation at that position;

through provisionalization, thatVDO is established as the one VDO

for the patient.

Many patients, however, requirea VDO that is neither ofthese (Fig 3),and an alternative is needed, al-

though this has long been a topic ofcontroversy. For example, many

patients with "posterior bite col-lapse" do not present with enough

interarch space to accommodate anew prosthesis. Implant-supported

prostheses require adequate spacefor components, and restorative ma-terials require a certain dimensionfor strength and esthetics; it is fre-

quently necessary to increase theVDO. Second, gaining room for oc-

clusal thickness of posterior restora-tions by increasing the VDO mayalso minimize or eliminate the need

for clinical crown lengthening of the

posterior teeth. This may be espe-cially important inthe restoration ofbruxers with extreme posterior toothwear and diminished crown height,

and may also help reduce the neces-sity for endodontic therapy of theseteeth by reducing the amount of oc-clusal reduction that would be re-

quired if the VDO were not in-creased. A third and very importantreason to alter the VDO is to change

the overbite-overjet relationship ofthe anterior teeth.1o Patients with

posterior bite collapse, loss of pos-

terior teeth, or severely worn poste-

.rior teeth may present with an exces-

sively steep overbite that results in a

steep angle of incisalguidance. This,in turn, results in an increased hori-zontal vector of force on the anterior

teeth. Increasing the VDO will de-

crease the overbite relationship,


244

Fig 3a Patient requesting elimination of maxillary removable par-tial denture and restoration by means of fixed prostheses. Patientadmits to bruxism habits, as evidenced by wear on incisal edges ofmandibular incisors. Deep overbite and steep incisal guidancetransmit excessive horizontal forces to teeth and would diminish

prognosis for a fixed prosthesis.

allowing for the restoration of a shal-lower anterior guidance, whichallows for a reduction of the hori-

zontal forces acting on the anterior

teeth.35 This is very important for

patients with weakened anteriorteeth. Modification of the overbite

relationship is also significant forpatients with uncontrollable bruxinghabits. A diminished angle of incisalcontact not only reduces horizontalforces on teeth, but has also been

shown to minimize masticatory mus-cle activity.36

Although increasing the VDOcan greatly facilitate restoration of

some patients, this procedure maycause difficulties in managing the

overjet relationship of the anteriorteeth. Increasing the VDO also

increases the overjet relationship ofthe anterior teeth, which may makeestablishing contact of these teeth incentric relation difficult. Contact of

Fig 3b As part of the oce/usal reconstruction, VDO opened 3 mmwith the final restoration to diminish excessive overbite relationshipand shallow incisal guidance and decrease forces on the prosthesis.

the anterior teeth in centric relation,

and especially during excursivemovements, must occur if the pos-terior teeth are to be separated and

the phenomenon of proprioceptiveinhibition is to occur. A reduction of

activity in the muscles of mastica-tion through contact of the anteriorteeth has been documented37 and is

an important aspect of controlling

forces on the prosthesis throughcontrol of the occlusion. Instances

of excessive overjet will frequentlyrequire the building of lingual plat-forms on the maxillary canines toallow this contact.

A final benefit of altering theVDO is in creating esthetic change.

A loss of VDO may result in a col-

lapse of midfacial height, alteringthe overall facial esthetics. In fact,the esthetic evaluation of the

patient's face has been used as aguideline in VDO assessment.38

Although an evaluation of facial pro-portions may be helpful in analyzingthe VDO, this should not be a pri-maryfactor in VDO alteration. This orother esthetic changes should not

be made without first consideringtheir functional ramifications. For

example, in the current literature,

many advocate that patients withseverely worn anterior and posteriorteeth-the typical horizontal brux-er-be restored with long anteriorteeth, a 3- to 4-mm overbite rela-

tionship, and the resulting steepanterior guidance as a means of

reestablishing optimum estheticsand eliminating the bruxing behav-ior. Establishing longer anterior teethfor esthetics may be desirable; how-

ever, establishing a steep anteriorguidance in the hope of eliminatinghorizontal bruxism is dangerous.

Although this approach may be suc-cessful for some, the behavior will


245

continue for many others. For these

patients, restorations with this incisalguidance will fail, just as their own

dentitions have failed. Consequent-ly,the clinician must determine with

each patient whether increasedanterior guidance will in fact mini-

mize the bruxing behavior.Once the decision that the VDO

must be altered has been made, the

appropriate increase must be deter-mined. Although various techniqueshave been recommended for deter-

mining an acceptable VDO, nonehave proven to be definitively accu-rate. The most commonly used

guideline, the 3-mm freeway space,

is particularly unreliable, being highlyvariable based on head position and

time of day and adaptable tochanges in the VDO itself.39 Theguideline isthat the minimal amountof anterior vertical increase neces-

sary to meet the objectives of recon-

struction should be used. Practically

speaking, this is generally from 1 to3 mm of opening inthe anterior seg-ment. The use of sibilant sounds, the

"closest speaking space," is a prac-tical if not totally accurate guide todetermine if the altered VDO may

have exceeded the adaptive rangeof the patient.4o However, this israrely a problem with this amount ofopening.

The stability of an altered VDOis a concern for many clinicians, and

it is speculated that any increase inthe contracted length of the mas-seter muscle willresult in an unstable

situation following restoration.41,42However, as a means of further as-

sessing the amount of increase,

Spear43 has described two posterior

dimensions of the VDO that directly

impact the stability of its alteration-

vertical positioning of the condylewithin the joint space itself andlength of the masseter muscle. Be-

cause of the geometry of the man-dible as a class III lever, a 3-mm in-

crease in opening in the anteriorsegment results in an approximate 1-

mm opening in the posterior seg-ment. This is also the location of the

masseter muscle. Therefore, a 3-mm

opening of the anterior VDO could

potentially result in a 1-mm increaseinthe length of the masseter muscle.However, the vast majority of

patients presenting for reconstruc-tion demonstrate a c'Ondylar slidefrom centric relation to maximal

intercuspation, and Spear43 has also

reported this discrepancy to aver-age approximately 1 mm in a verti-cal direction. Elimination of this slide

will therefore result in an approxi-mate seating of the condyles 1 mm

superiorly in the fossae, with theresult that the masseter muscles are

also shortened by 1 mm. Conse-

quently, for the average patient, a 3-mm increase in the anterior VDO,

with the condyles repositioned tothe most superior position in the fos-sae, will result in no change in thelength of the masseter muscles. It is

rare that an increase greater than 3mm would be done; however, it canoccu r.

Because of the rotation of the

condyles on the terminal hinge,

each additional millimeter of open-ing potentially results in only a 0.33-mm lengthening of the massetermuscles. Indeed, other researchers

have reported stable long-term

results following an increase in the

VDO.44There appears to be a range

of neuromuscular adaptability that ishighly individual and will allow for

some slight increase in musclelength, within limits. The objective,

then, is to prevent or minimizeincreasing muscle length when pos-sible; it is possible to do so,45 how-ever, with careful monitoring of thejoints and muscular function

throughout the course of therapy.

The inter-relationship of the cen-tric relation position ofthe mandible

and the VDO isunique and becomesmore significant if an alteration of

the VDO is contemplated. Theremaining elements of an occlusion

may be more precisely evaluatedand established once the locationof these two has been determined.


246

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