periov&>ntics restohative dentistry...esthetic, and maintainable occlusion is the primary...
TRANSCRIPT
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
The International Journal of Periodontics & Restorative Dentistry
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.
Volume 23, Number 3, 2003
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
The International Journal of Periodontics & Restorative Dentistry
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,
Volume 23, Number 3, 2003
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
The International Journal of Periodontics & Restorative Dentistry
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.
Volume 23, Number 3, 2003
246
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