The importance of occlusal balance in the control of complete dentures Anna 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 wiis assessed. Method and materials: The complete dentures of five patients who were having difficult) controlling tiicir prostheses were accurately duplicated. The artificial teeth were replaced with occhisally balanced teeth. No other 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 all patients. 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
Adaptation to dentures Clinical relevance Basker et al' described the function of m echan o receptors This study suggests that occlusal balance and re- in the oral mticosa when new dentures are fitted. moval of occlusally induced denture movements is Impulses arising from these receptors, which record as important to efflcient complete denture control touch and pressure, are transmitted to the sensory cortex, as fitting accuracy to underlying tissues, peripheral with the result that the patient can "'feel" tbe dentures. extension, or accurate recording of centric relation. However, continuous stimulation of these receptors does not result in a corresponding stream of impulses. The receptors adapt to the new environment, so that the patietit begins to lose conscious awareness of the new t is often assumed that patients provided with com- dentures in tbe mouth. Iplete dentures made without occlusal balance will, Furtber stimulation arises when force.s from tooth after a period of time, become accustomed to their den- contacts are transmitted to the underlying tissues. The tures and be able to control tbem during mastication. pattern of the stimulation of the mecbanoreceptors Some of tbese patients, however, cannot control their enables the patient to recognize food between the teeth prostheses, especially tbe mandibular ones, despite long and the presence or absence of occlusal disharmony. perseverance. Basker et al' reported tbat after new dentures were fitted, 60^ of experienced complete-denture patients were able to speak and eat satisfactorily within a week. A furtber 20% required tip to 1 month to become profi- * Teacher in Dental Sciente, Department of Neurology and Oro- cient. Tbese authors also recognized that some patients mandibular Dysfunction. Institute of Denlistry. Medical University. never become proficient denture wearers. ' Lodz, Poland. Grant et al- concluded that a lack of occlusal balance " Senior Lecturer, Department of Restorative Dentistry, Sehool of Clinical Dentistry, Llniverâty of Shettkid, Sheffield, Etjgland. causes dentures to tilt on their supporting tissues, dis- •—Lecturer, Department of Prosthodontics, Itistitute of Dentistry. rupting the retentive seal. They also thought that many Medical Universily, Lodz, Poland patients could successfully wear dentures without Reprint requests: Dr Graham E. White, KCOM, Department ot occlusal balance but that as retentive factors decrease Restorative Dentistry, School of Clinical Dentistry, Claremont Creseent. SliefTield SIO 2TA, England. E-mail: [email protected] (ie, as supporting tissues resorb), displacing forces gen-
Quintessence International 389 Duboiska et ai erated by lack of balance assume greater significance. po.sterior teeth to the flatter ridge parts and not allowing Furthermore, difficult-to-wear dentures made witbout teetb to be placed over inclined ridge parts. occiusal balance will often bave inaccurate maxillo- The aim of tbe present investigation was to assess the mandibular relationships together with fitfing errors and importance of occiusal balance in the control of com- inadequate peripheral extension. plete dentures during function.
Balanced occlusion and denture stability Method and materials
There are tbose who have questioned the validity of Patients who were having difficulty controlling com- occiusal balance on the grounds that wben food has plete dentures had their prostbeses accurately duplicated been introduced between the teeth, occiusal balance and the artiflcial teeth replaced witb occlusally balanced is lost at precisely tbe time it is most needed, ie, ieetb. No other changes were made. Fitting accuracy, "enter food—exit balance." Mindful of this problem, peripheral extension, and possible errors in maxillo- Tbompson' recommended that patients divide mouth- mandibular relafionsbips, whether apparent or not, were fuls of food and chew it on both sides of the mouth, ignored. The patients' reactions to the experimental den- simultaneously. tures were then assessed after 1 week, after 3 weeks, In justifying the need for occiusal balance, Hobkirk-' and after 6 weeks of use. concluded that the artificial teeth come into contact for a total of about 20 minutes a day during swallowing and Test group briefly during mastication. When a bolus of food is placed between the teeth, they will be held apart; as the Pafients attending the Prostbodontic Clinic at the Insti- pafient begins to penetrate the food, the denture will be tute of Dentistry in Lodz, Poland, for new complete inclined to move. This will be resisted by the retention dentures formed tbe test group. From this number five of the denture and the pafient's own muscular control. patients wbo bad worn complete dentures for at least 2 Furtber into the masticatory cycle, however, the teeth years without success were selected. From an examina- come closer to each other or may momentarily touch. tion of the dentures of all five pafients, it was evident Should there be any interfering contacts at tbis stage, that occiusal balance had not been provided and that a instability will result. Because of tbese intermittent simple hinge ariiculator had almost ceriainly been used. tooth contacts, Hobkirk'' believed that complete den- The mandihular molar teeth were set over a .sloping tures should have balanced occlu,sion. part of the lower residual ridge and the curve of the Hickey et al,-' in contrast, thought that dentures make occiusal plane of the posterior teeth was not related to several thousand contacts a day in both centric and the condylar path angles. During protrusive jaw move- eccentric positions with no food in the mouth and that, ments and edge-to-edge incisor tooth contacts, these even while chewing, the teeth cut through to contact combined factors allowed a space to exist between the every few fracfions of a second. Because of this, bal- posterior teetb; tbis space produced mandibular denture anced occlusion is desirable to ensure even pressure in filting (Fig 1). When the pafients were que.stioned ahout all parts of the arch to maintain the stability of the den- their problem dentures, typical complaints were, "The tures while tbe mandible is in centric and eccentric dentures move when I eat," and "I get sore spots under posifions. my dentures." Two pafients indicated that they removed In considering denture stability, Gerber* concluded their dentures to eat. that it is necessary to occlusally balance teeth placed in positions that would avoid instability, ie, to occlusally Fabrication of the experimental prostheses balance already stable dentures. Denture stability is achieved in this metbod by arranging the posterior teetb The patients' existing dentures were duplicated by on a curve that follows the curve of the residual ridges, direcfiy investing them in a denture-processing flask. Occiusal forces are transmitted at 90 degrees to the The dentures were then removed, and the resulting underlying bone, promoting a high level of stability mold cavity was packed in heat-cured acrylic resin (Fig even in resorbed residual ridges. This limitation of 2). The dentures were then polymerized by wet heat fol- occlusally induced denture movement prevents the lowed by slow overnight cooling to room tetnperature. mouth soreness observed by Hickey et al,-^ which is After careful trimming and very light polishing, the caused by denture movement along the slopes of the resuUing dentures were an accurate copy of the original residual ridges during deflective tooth contacts. For flat prostheses, except that the arfificial teeth were repro- residual ridges, Gerber" recommended restricting the duced in pink resin (Fig 3).
390 Volume 29, Number 6, 1993 DL bo i ska et al
Fig 1 Patient making a protrusive ¡aw move- Fig 2 Two-part denture mold made by investing and then remov- ment, showing a lack of posterior tooth contact. ing a resin denture.
Fig 3 An ali-pink resin, dupiicated denture Fig 4 Gothic Arch tracing plate fixed to the duplicated mandibu- seated on a casi made Irom its investment stone. lar denture with impression compound.
TABLE 1 Sagittal condylar path angles for patients in the study (degrees)
Patient Left joint Right joint 1 32* 40- 2 33* 33 3 23 32 4 37 35 5 30 35 Fig 5 Facebow lollowmg the protrusive move- ment of a patient's left condyle to produce a •The tracir g was stiort and/or confLsed, so tliat only an incomplete pari tracing of its sagittal path angle. •f the Irac rg was used.
The stone plaster used as investing material in the ments. Writing styli positioned over each joint were processing flask was required to accurately flow into the used to make left and right tracings of sagittal condylar fitting surface of the original dentures. After it vi-as care- inclination on a card resting on the side of the patient's fully recovered from the flask and trimmed, this invest- face (Fig 5), A protractor was then used to determine ment material formed the future working casts (Fig 3). the angles of the tracings. Softened impression compound was used to fix Patient I had difflculty producing both the left and maxillary and mandibular Gothic Ari:h tracing plates right tracings, and patient 2 had difficulty producing the (Condylator-Service) to the old dentures (Fig 4) and to left condylar tracing. These patients could not easily connect a Condyiator facebow (Condylator-Service) to tTiake protrusive jaw movements (Table 1), the mandibular transfer plate. After the height of the The composition material joining the transfer plate to upper stylus was adjusted to just separate the artificial the mandibular denture produced accurate imprints of teeth and tracing plates during mandihular movements, the posterior teeth. These imprints were used as locators the patient was asked to make protrusive jaw move- to position the duplicated mandibular denture, with hard
Quintessence Internationai 391 Dubojska et al
Fig 6 Duplicated denlure and cast related to an aa¡ustat:le artic- Fig 7a Masiiiary and mandibular duplicated dentures fixed uiator by means of a lacebcw. together in maximai intercuspation, ready to mount tiie maxillary denture and cast pn the articuiator.
sides of the tnandibular cast. For cotnparison, the curve of the occlusal plane of the original dentures was also drawn (Fig 7b). After the duplicated pink resin teeth were ground away, new resin anterior and posterior teeth (Mifatn Super Lux) were set up in occlusal balance according to the methods described by Gerber^ (Fig 8a). Especially important, the posterior teeth were restricted to the flat- ter parts of the residual mandibular ridge to promote stahility in the dentures when separated hy food—under loading situations (Fig 8b), In all five patients, this meant that the maxillary and mandibular second molar teeth were not used. In some patients, other tooth sub- Fig 7b Mounted dupiicated dentures. The top line tracing follows stitutions were also necessary (Fig 8c). ttie ourve of the residuai mandibuiar ridge. The bottom line shows the ocolusal plane pf the ppsteiipr leeth of the original dentures. After the trial experimental dencures were assessed in the mouth for appearance and occlusion, accurate stone overcasts were made to attach the artificial teeth to the duplicated bases with autopolymerizing resin (Vertex wax, on its cast in the transfer plate, Imrnediately after Castapress, Dentimex Zeist). The polytnerized dentures this, the facebow record was used to mount the dupli- were returned to the Condylator articuiator, and occlusal cated mandihular denture atid its cast otito a Condylator prematurities affecting occlusal balance were removed Itidividual articuiator (Fig 6), White and Duhojska^ with stones and ahrasive paste. showed that different tnodels of adjustable articiulators, programtned with idetitical condylar path angles and Placement of the experimental prostheses incisai guidaitce settings, produce different paths of mandibular movement. Among the articulators tested, Immediately after placement, the experimental dentures the Condylator articuiator (Condylator-Service) was were assessed for occlusal balance. The patients were found to produce correctly formed cusp groove angles, instructed to make protrusive jaw movements (Fig 9a), so this instrntnent was chosen to provide balanced as well as lateral and protrusive jaw movements, while occlusion in the pre.sent study. keeping the maxillary and mandibular posterior teeth in The duplicated dentures were then waxed together contact. The same occlusal contacts observed in the lab- in their position of maxirnum intercuspation to mount oratory were found in the mouth (Fig 9b), The lack of the maxillary model in the articuiator (Fig 7a), The posterior tooth contact in protrusion of one patient's measured left and right condylar path angles were then original dentures (Fig 9c), for example, was eliminated transferred to the articuiator. Left and right mandibular on the articuiator and in the mouth by the new denture residual ridge profile lines were then drawn on the (Figs 9a and 9h).
392 Voiuma29, Number6, 1998 Dubcjska et ai
Fig 8a New setup, showing protrusive looth contacts. Tiie incisai Fig eb Poslerior teeth set up to loilow the curve ol the residuai rod is not contacting the incisai guidance tabie, reprodtjcing the mandibular ndge, thereby promoting a high degree of stabiiity situation in the mouth. Note the bottom iine, which shows the aimost tiat occlusal piane of the originai dentures.
Fig Sc Dentures with reduced occiusal table Note the use ot a Fig 9a Patient making a protrusive jaw move- premolar instead of a mandibuiar second molar and the use ot ment with Ihe new dentures. The posterior teeth only one maxiliary molar. The distal mandibular premoiar aids sta- are still in contact. bility when It contacts the maxiiiary moiar during protrusion.
Fig 9tj Dentures in Fig 9a, showing Ihe same tooth oontacts in Fig 9c Original dentures cf the patient in Fig 9a Note the the iaboralory as lound in the mouth. absence ot tooth contacls.
Quintessence Inter nation ai 393 DubO}Ska el al
The two patients who had earlier difficulty in pro- Snmmary truding the mandible were not able to make lateral jaw movements, and side-to-side head movements were Wben difficult-to-wear complete dentures without made instead. It was speculated that the patients bad occlusal balance were duplicated and new teeth with accomtnodated to tbeir original dentures' incorrect max- occlusal balance were substituted, all five participating illotnandibular relationships to an extent that prevented patients reponed an improvement in denture stability lateral movements. and chewing comfort. Tbe reduction of the occiusal Functional mandibular denture stability was assessed table, produced by confining tbe posterior teeth to by the application of alternate finger tip pressure on the those parts of the residual ridge table to support den- most distally placed posterior teeth on each side of the ture loads without denture movement, bad a strong mouth. The dentures were observed not to move utider denture-stabilizing effect. This could be demonstrated tbese occlusal loads despite tbeir universally poor adap- by applying occlusal loads witb a finger tip on the tation to tbe underlying tissues. distal-most tnandibular molar teetb, a pressure that dis- The patients were told not to wear their original den- placed dentures with these teeth set over sloping resid- tures after they had been provided with their experimen- ual ridge parts. tal pro.stheses. To ensure compliance, the investigators These improvements were made despite remaining retained the patients" original dentttres for the duration jaw registration errors and poor adaptation of the den- of the experiment. tures to their underlying tissues. From tbese results, it may be tbeorized that occlusal balance and the removal Resnlts of occlusally induced denture movements is as impor- tant to efficient denture control as fitting accuracy to Patients were recalled for a.ssessment after I week. underlying tissues, peripheral extension, or accurate 3 weeks, and 6 weeks of wearing their experimental recording of centric relation. prostheses. After I week, two patients reported much improved denture stability and chewing comfort, but References three patients did not notice much difference. After 3 weeks, four patients reported much improved denture 1. Basker RM, Davenport JC. Tomlin HR. Prosthetic Treatment of stability and greater comfort during eating. The two the Edentulous Patient, ed 3. London: Macmillian, 1992. patients who previously could not make lateral man- 2. Grant AA, Heath JR, McCord JF. Complete Prosthodonties, Problems, Diagnosis and Management. London: Wolfe, 1994. dibular movements could now demonstrate this function 3. Thompson H. Occlusion, ed 2. London: Wright, 1990. without difficulty. After 6 weeks, all five patients 4. Hobkirk JA. Complete Denture.s: Dental Practitioners Handbook reported much improved denture stability and greater 1Î. Bristol, England: Wright, 1986. comfort of their dentures during eating. All patients 5. Hickey JC, Zarb GA, Bolender CL. Boucher's Prostliodontic demonstrated tbat tbey could make lateral and protru- Treatment for Edentulous Patients, ed 9. St Louis: Mosby. 1985. sive jaw movements without difficulty. 6. Gerber A. Complete dentures. Color atlas. Quintessence Int The patients reported that the itiiprovements occurred 1974;5(121:3.1-38. without them being required to "'do anything different," 7. White GE, Dubojska AM. System konstrukeji protez ealkow- itych w oparciu o artykiilalor Gerbera-Condylator. Qumtesienee and they were at a loss to explain bow this had occurred. Int (Polish ed) l99î;4:219-238. Tbe increase in stability during eating was particularly commented on. together with what was described as the "better fitting" of tbe mandibular denture. The absence of second molar teeth and/or the existence of tooth sub- stitutions was noted by tbe patients, but they did not adversely comment on tbe unconventional appearance. When the original dentures were returned to tbe mouth, protrtisive jaw movements were observed to produce a space between the maxillary and mandibular occlusal surfaces of tbe posterior teeth. This lack of contact produced mandibular denture tilting when the maxillary and mandibular incisors were in edge-to-edge contact. All five patients reported tbat their original dentures now felt "strange" and that they would not like to return to them.
394 Volume 29, Number 6, 1998