Prosthodontics

The importance of occlusal balance in the controlof complete denturesAnna M. Dubojska, MSc, MCGI*/Graham E. White, KCOM, PhD, MMedSci, FCGI. CGIA**/Slawomir Pasiek, DDS,

Objeclive: The importance ofocclu.sal balance to the control of complete dentures during function wiisassessed.Method and materials: The complete dentures of five patients who were having difficult) controlling tiicirprostheses were accurately duplicated. The artificial teeth were replaced with occhisally balanced teeth. Noother changes were made. Patients were asked to report their experiences with the new dentures afier 1 week.3 weeks, and 6 weeks.Results: By the end ufó weeks, improvements in denture stability and eating comfort were reported by allpatients.Conclusion: Improvements occurred when the occlusion was balanced, despite existing jaw relationship errors.fitting inaccuracies, and peripheral e.xtension errors. (Quintessence Int 1998;29:389-394)

Key words: complete denture, denture stability, ocelusal balance

Clinical relevance

This study suggests that occlusal balance and re-moval of occlusally induced denture movements isas important to efflcient complete denture controlas fitting accuracy to underlying tissues, peripheralextension, or accurate recording of centric relation.

It is often assumed that patients provided with com-plete dentures made without occlusal balance will,

after a period of time, become accustomed to their den-tures and be able to control tbem during mastication.Some of tbese patients, however, cannot control theirprostheses, especially tbe mandibular ones, despite longperseverance.

* Teacher in Dental Sciente, Department of Neurology and Oro-mandibular Dysfunction. Institute of Denlistry. Medical University.Lodz, Poland.

" Senior Lecturer, Department of Restorative Dentistry, Sehool ofClinical Dentistry, Llniverâty of Shettkid, Sheffield, Etjgland.

•—Lecturer, Department of Prosthodontics, Itistitute of Dentistry.Medical Universily, Lodz, Poland

Reprint requests: Dr Graham E. White, KCOM, Department otRestorative Dentistry, School of Clinical Dentistry, Claremont Creseent.SliefTield SIO 2TA, England. E-mail: G.E.White@Shefneld.ai.-.uk

Adaptation to dentures

Basker et al' described the function of m echan o receptorsin the oral mticosa when new dentures are fitted.Impulses arising from these receptors, which recordtouch and pressure, are transmitted to the sensory cortex,with the result that the patient can "'feel" tbe dentures.However, continuous stimulation of these receptors doesnot result in a corresponding stream of impulses. Thereceptors adapt to the new environment, so that thepatietit begins to lose conscious awareness of the newdentures in tbe mouth.

Furtber stimulation arises when force.s from toothcontacts are transmitted to the underlying tissues. Thepattern of the stimulation of the mecbanoreceptorsenables the patient to recognize food between the teethand the presence or absence of occlusal disharmony.

Basker et al' reported tbat after new dentures werefitted, 60^ of experienced complete-denture patientswere able to speak and eat satisfactorily within a week.A furtber 20% required tip to 1 month to become profi-cient. Tbese authors also recognized that some patientsnever become proficient denture wearers. '

Grant et al- concluded that a lack of occlusal balancecauses dentures to tilt on their supporting tissues, dis-rupting the retentive seal. They also thought that manypatients could successfully wear dentures withoutocclusal balance but that as retentive factors decrease(ie, as supporting tissues resorb), displacing forces gen-

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erated by lack of balance assume greater significance.Furthermore, difficult-to-wear dentures made witboutocciusal balance will often bave inaccurate maxillo-mandibular relationships together with fitfing errors andinadequate peripheral extension.

Balanced occlusion and denture stability

There are tbose who have questioned the validity ofocciusal balance on the grounds that wben food hasbeen introduced between the teeth, occiusal balanceis lost at precisely tbe time it is most needed, ie,"enter food—exit balance." Mindful of this problem,Tbompson' recommended that patients divide mouth-fuls of food and chew it on both sides of the mouth,simultaneously.

In justifying the need for occiusal balance, Hobkirk-'concluded that the artificial teeth come into contact fora total of about 20 minutes a day during swallowing andbriefly during mastication. When a bolus of food isplaced between the teeth, they will be held apart; as thepafient begins to penetrate the food, the denture will beinclined to move. This will be resisted by the retentionof the denture and the pafient's own muscular control.Furtber into the masticatory cycle, however, the teethcome closer to each other or may momentarily touch.Should there be any interfering contacts at tbis stage,instability will result. Because of tbese intermittenttooth contacts, Hobkirk'' believed that complete den-tures should have balanced occlu,sion.

Hickey et al,-' in contrast, thought that dentures makeseveral thousand contacts a day in both centric andeccentric positions with no food in the mouth and that,even while chewing, the teeth cut through to contactevery few fracfions of a second. Because of this, bal-anced occlusion is desirable to ensure even pressure inall parts of the arch to maintain the stability of the den-tures while tbe mandible is in centric and eccentricposifions.

In considering denture stability, Gerber* concludedthat it is necessary to occlusally balance teeth placed inpositions that would avoid instability, ie, to occlusallybalance already stable dentures. Denture stability isachieved in this metbod by arranging the posterior teetbon a curve that follows the curve of the residual ridges,Occiusal forces are transmitted at 90 degrees to theunderlying bone, promoting a high level of stabilityeven in resorbed residual ridges. This limitation ofocclusally induced denture movement prevents themouth soreness observed by Hickey et al,-̂ which iscaused by denture movement along the slopes of theresidual ridges during deflective tooth contacts. For flatresidual ridges, Gerber" recommended restricting the

po.sterior teeth to the flatter ridge parts and not allowingteetb to be placed over inclined ridge parts.

The aim of tbe present investigation was to assess theimportance of occiusal balance in the control of com-plete dentures during function.

Method and materials

Patients who were having difficulty controlling com-plete dentures had their prostbeses accurately duplicatedand the artiflcial teeth replaced witb occlusally balancedieetb. No other changes were made. Fitting accuracy,peripheral extension, and possible errors in maxillo-mandibular relafionsbips, whether apparent or not, wereignored. The patients' reactions to the experimental den-tures were then assessed after 1 week, after 3 weeks,and after 6 weeks of use.

Test group

Pafients attending the Prostbodontic Clinic at the Insti-tute of Dentistry in Lodz, Poland, for new completedentures formed tbe test group. From this number fivepatients wbo bad worn complete dentures for at least 2years without success were selected. From an examina-tion of the dentures of all five pafients, it was evidentthat occiusal balance had not been provided and that asimple hinge ariiculator had almost ceriainly been used.

The mandihular molar teeth were set over a .slopingpart of the lower residual ridge and the curve of theocciusal plane of the posterior teeth was not related tothe condylar path angles. During protrusive jaw move-ments and edge-to-edge incisor tooth contacts, thesecombined factors allowed a space to exist between theposterior teetb; tbis space produced mandibular denturefilting (Fig 1). When the pafients were que.stioned ahouttheir problem dentures, typical complaints were, "Thedentures move when I eat," and "I get sore spots undermy dentures." Two pafients indicated that they removedtheir dentures to eat.

Fabrication of the experimental prostheses

The patients' existing dentures were duplicated bydirecfiy investing them in a denture-processing flask.The dentures were then removed, and the resultingmold cavity was packed in heat-cured acrylic resin (Fig2). The dentures were then polymerized by wet heat fol-lowed by slow overnight cooling to room tetnperature.After careful trimming and very light polishing, theresuUing dentures were an accurate copy of the originalprostheses, except that the arfificial teeth were repro-duced in pink resin (Fig 3).

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Fig 1 Patient making a protrusive ¡aw move-ment, showing a lack of posterior tooth contact.

Fig 2 Two-part denture mold made by investing and then remov-ing a resin denture.

Fig 3 An ali-pink resin, dupiicated dentureseated on a casi made Irom its investment stone.

Fig 4 Gothic Arch tracing plate fixed to the duplicated mandibu-lar denture with impression compound.

Fig 5 Facebow lollowmg the protrusive move-ment of a patient's left condyle to produce atracing of its sagittal path angle.

TABLE 1 Sagittal condylar path angles for patientsin the study (degrees)

Patient

12345

•The tracir•f the Irac

Left joint

32*33*233730

Right joint

40-33323535

g was stiort and/or confLsed, so tliat only an incomplete parirg was used.

The stone plaster used as investing material in theprocessing flask was required to accurately flow into thefitting surface of the original dentures. After it vi-as care-fully recovered from the flask and trimmed, this invest-ment material formed the future working casts (Fig 3).

Softened impression compound was used to fixmaxillary and mandibular Gothic Ari:h tracing plates(Condylator-Service) to the old dentures (Fig 4) and toconnect a Condyiator facebow (Condylator-Service) tothe mandibular transfer plate. After the height of theupper stylus was adjusted to just separate the artificialteeth and tracing plates during mandihular movements,the patient was asked to make protrusive jaw move-

ments. Writing styli positioned over each joint wereused to make left and right tracings of sagittal condylarinclination on a card resting on the side of the patient'sface (Fig 5), A protractor was then used to determinethe angles of the tracings.

Patient I had difflculty producing both the left andright tracings, and patient 2 had difficulty producing theleft condylar tracing. These patients could not easilytTiake protrusive jaw movements (Table 1),

The composition material joining the transfer plate tothe mandibular denture produced accurate imprints ofthe posterior teeth. These imprints were used as locatorsto position the duplicated mandibular denture, with hard

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Fig 6 Duplicated denlure and cast related to an aa¡ustat:le artic-uiator by means of a lacebcw.

Fig 7a Masiiiary and mandibular duplicated dentures fixedtogether in maximai intercuspation, ready to mount tiie maxillarydenture and cast pn the articuiator.

Fig 7b Mounted dupiicated dentures. The top line tracing followsttie ourve of the residuai mandibuiar ridge. The bottom line showsthe ocolusal plane pf the ppsteiipr leeth of the original dentures.

wax, on its cast in the transfer plate, Imrnediately afterthis, the facebow record was used to mount the dupli-cated mandihular denture atid its cast otito a CondylatorItidividual articuiator (Fig 6), White and Duhojska^showed that different tnodels of adjustable articiulators,programtned with idetitical condylar path angles andincisai guidaitce settings, produce different paths ofmandibular movement. Among the articulators tested,the Condylator articuiator (Condylator-Service) wasfound to produce correctly formed cusp groove angles,so this instrntnent was chosen to provide balancedocclusion in the pre.sent study.

The duplicated dentures were then waxed togetherin their position of maxirnum intercuspation to mountthe maxillary model in the articuiator (Fig 7a), Themeasured left and right condylar path angles were thentransferred to the articuiator. Left and right mandibularresidual ridge profile lines were then drawn on the

sides of the tnandibular cast. For cotnparison, the curveof the occlusal plane of the original dentures was alsodrawn (Fig 7b).

After the duplicated pink resin teeth were groundaway, new resin anterior and posterior teeth (MifatnSuper Lux) were set up in occlusal balance according tothe methods described by Gerber̂ (Fig 8a). Especiallyimportant, the posterior teeth were restricted to the flat-ter parts of the residual mandibular ridge to promotestahility in the dentures when separated hy food—underloading situations (Fig 8b), In all five patients, thismeant that the maxillary and mandibular second molarteeth were not used. In some patients, other tooth sub-stitutions were also necessary (Fig 8c).

After the trial experimental dencures were assessed inthe mouth for appearance and occlusion, accurate stoneovercasts were made to attach the artificial teeth to theduplicated bases with autopolymerizing resin (VertexCastapress, Dentimex Zeist). The polytnerized dentureswere returned to the Condylator articuiator, and occlusalprematurities affecting occlusal balance were removedwith stones and ahrasive paste.

Placement of the experimental prostheses

Immediately after placement, the experimental dentureswere assessed for occlusal balance. The patients wereinstructed to make protrusive jaw movements (Fig 9a),as well as lateral and protrusive jaw movements, whilekeeping the maxillary and mandibular posterior teeth incontact. The same occlusal contacts observed in the lab-oratory were found in the mouth (Fig 9b), The lack ofposterior tooth contact in protrusion of one patient'soriginal dentures (Fig 9c), for example, was eliminatedon the articuiator and in the mouth by the new denture(Figs 9a and 9h).

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Fig 8a New setup, showing protrusive looth contacts. Tiie incisairod is not contacting the incisai guidance tabie, reprodtjcing thesituation in the mouth.

Fig eb Poslerior teeth set up to loilow the curve ol the residuaimandibular ndge, thereby promoting a high degree of stabiiityNote the bottom iine, which shows the aimost tiat occlusal pianeof the originai dentures.

Fig Sc Dentures with reduced occiusal table Note the use ot apremolar instead of a mandibuiar second molar and the use otonly one maxiliary molar. The distal mandibular premoiar aids sta-bility when It contacts the maxiiiary moiar during protrusion.

Fig 9a Patient making a protrusive jaw move-ment with Ihe new dentures. The posterior teethare still in contact.

Fig 9tj Dentures in Fig 9a, showing Ihe same tooth oontacts inthe iaboralory as lound in the mouth.

Fig 9c Original dentures cf the patient in Fig 9a Note theabsence ot tooth contacls.

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The two patients who had earlier difficulty in pro-truding the mandible were not able to make lateral jawmovements, and side-to-side head movements weremade instead. It was speculated that the patients badaccomtnodated to tbeir original dentures' incorrect max-illotnandibular relationships to an extent that preventedlateral movements.

Functional mandibular denture stability was assessedby the application of alternate finger tip pressure on themost distally placed posterior teeth on each side of themouth. The dentures were observed not to move utidertbese occlusal loads despite tbeir universally poor adap-tation to tbe underlying tissues.

The patients were told not to wear their original den-tures after they had been provided with their experimen-tal pro.stheses. To ensure compliance, the investigatorsretained the patients" original dentttres for the durationof the experiment.

Resnlts

Patients were recalled for a.ssessment after I week.3 weeks, and 6 weeks of wearing their experimentalprostheses. After I week, two patients reported muchimproved denture stability and chewing comfort, butthree patients did not notice much difference. After 3weeks, four patients reported much improved denturestability and greater comfort during eating. The twopatients who previously could not make lateral man-dibular movements could now demonstrate this functionwithout difficulty. After 6 weeks, all five patientsreported much improved denture stability and greatercomfort of their dentures during eating. All patientsdemonstrated tbat tbey could make lateral and protru-sive jaw movements without difficulty.

The patients reported that the itiiprovements occurredwithout them being required to "'do anything different,"and they were at a loss to explain bow this had occurred.Tbe increase in stability during eating was particularlycommented on. together with what was described as the"better fitting" of tbe mandibular denture. The absenceof second molar teeth and/or the existence of tooth sub-stitutions was noted by tbe patients, but they did notadversely comment on tbe unconventional appearance.

When the original dentures were returned to tbemouth, protrtisive jaw movements were observed toproduce a space between the maxillary and mandibularocclusal surfaces of tbe posterior teeth. This lack ofcontact produced mandibular denture tilting when themaxillary and mandibular incisors were in edge-to-edgecontact. All five patients reported tbat their originaldentures now felt "strange" and that they would not liketo return to them.

Snmmary

Wben difficult-to-wear complete dentures withoutocclusal balance were duplicated and new teeth withocclusal balance were substituted, all five participatingpatients reponed an improvement in denture stabilityand chewing comfort. Tbe reduction of the occiusaltable, produced by confining tbe posterior teeth tothose parts of the residual ridge table to support den-ture loads without denture movement, bad a strongdenture-stabilizing effect. This could be demonstratedby applying occlusal loads witb a finger tip on thedistal-most tnandibular molar teetb, a pressure that dis-placed dentures with these teeth set over sloping resid-ual ridge parts.

These improvements were made despite remainingjaw registration errors and poor adaptation of the den-tures to their underlying tissues. From tbese results, itmay be tbeorized that occlusal balance and the removalof occlusally induced denture movements is as impor-tant to efficient denture control as fitting accuracy tounderlying tissues, peripheral extension, or accuraterecording of centric relation.

References

1. Basker RM, Davenport JC. Tomlin HR. Prosthetic Treatment ofthe Edentulous Patient, ed 3. London: Macmillian, 1992.

2. Grant AA, Heath JR, McCord JF. Complete Prosthodonties,Problems, Diagnosis and Management. London: Wolfe, 1994.

3. Thompson H. Occlusion, ed 2. London: Wright, 1990.

4. Hobkirk JA. Complete Denture.s: Dental Practitioners Handbook1Î. Bristol, England: Wright, 1986.

5. Hickey JC, Zarb GA, Bolender CL. Boucher's ProstliodonticTreatment for Edentulous Patients, ed 9. St Louis: Mosby. 1985.

6. Gerber A. Complete dentures. Color atlas. Quintessence Int1974;5(121:3.1-38.

7. White GE, Dubojska AM. System konstrukeji protez ealkow-itych w oparciu o artykiilalor Gerbera-Condylator. QumtesieneeInt (Polish ed) l99î;4:219-238.

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