Journal of Oral Rehabilitation 1996 23; 321-329

Studies of changes in occlusion after the insertion ofcomplete dentures. PartK . - H . U T Z University of Bonn, Dental School, Department of Prosthetic Dentistry I, Bonn, Germany

SUMMARY. The present study aims to investigatechanges in the occlusion of complete dentures aftertheir insertion. A total of 85 edentulous patients wereprovided with new complete dentures. Their indi-vidual hinge axes were determined using mechanicalaxiography and the upper finished dentures weretransferred by facehows to Dentatus articulators.The lower dentures were mounted according toan intraoral central hearing point (CBP) registrationand equilibrated in terminal hinge position. Anarticulator specially modified for measurements inthe condylar area was used. The differences betweenthe positions of the condylar balls with CBPregistration and those after equilibrating the occlusionwere determined. On average, 19 days after insertion.

71 patients took part in a follow-up examination.As in the first session, the terminal hinge positionwas registered with the CBP method using theapex of the Gothic arch. Thus, the positions of thecondylar balls immediately after the new registrationcould be compared with those in equilibrated in-tercuspation 3 weeks earlier. The differences werefound to be 0-5 0-4 mm (0-2-9 mm) in the three axes(sagittal, coronal and horizontal). They are thoughtto result from settling into the denture bearingtissues and also from neuromuscular adjustmentof the masticatory system. Compulsory remountingof complete dentures after insertion is thereforerecommended.

IntroductionThe occurrence of complete denture malocclusion postinsertion has been reported by several authors, e.g.Bergman, Carlsson & Hedegard (1964), Brigante (1965),Tallgren (1969), Goebel (1980), Taege & Stoica (1982)and Berg & Knudsen (1983). In theory, occlusai changesoccurring shortly after insertion could have two maincauses: first, the settling of the dentures into thedeformable denture-bearing tissues; and second, thechanges in the afferent input from the oral cavity. Tallgrenet al. (1980) provided evidence that the electromyogramchanges after the insertion of new dentures, which mightwell lead to a different position of the lower jaw. On theother hand, when dentures have been worn for many

* These studies are dedicated to Prof. Dr Lorenz Hupfauf on his 70thbirthday.

years, resorption of the alveolar ridges is unlikely to causemalocclusion within a few weeks of insertion of newdentures. ^ : :

The aim of the present study was to discover andquantify any shifts between upper and lower denturesoccurring after insertion. Furthermore, the most favour-able time for remounting was to be determined. ;

Materials and methods

First session . . .

Forty-one female and 44 male edentulous patients tookpart in the study. Their ages ranged from 25 to 87 withan average of 65 10 years. The mean duration of theiredentulism was 13 10 years (0-1-40 years).

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322 K . - H . UTZ

New dentures were constructed by students during theirfinal examinations. On the day of insertion, the patients'individual hinge axes were determined. The lower jawclamp from the Lauritzen set*, the mandibular face-bow and a modified flagbow from the SAM-AxiographNo 2+ were used for this. The new upper dentureswere transferred with Dentatus AEK-facebows* to newDentatus-ARL articulators. For recording the mandibularposition, removable stainless steel Gerber (1986) CBPplates^ were located on the dentures with light curingacrylic''. The writing pin was positioned on the palate insuch a way that both upper and lower dentures wereloaded centrally (Utz, 1990; Utz et al., 1991). The gapduring recording was kept as small as possible and wason average 3-8 0-9 mm (2-7 mm) in the incisal areaand 5 1 mm (3-8 mm) at the articulator's incisalindicator pin. The Gothic arch was recorded under themoderate manual guidance of the operator, its apexmarked with a crosshair and checked twice forcongruence. A pierced acrylic plate** was then attachedwith sticky wax onto the apex of the Gothic arch in orderto lock the lower jaw. The upper and lower dentures werethen keyed with impression plaster++ and removed fromthe mouth assembled (Fig. 1, record 1). The lowerdenture was mounted in two stages with impressionplaster. The mounted dentures were then transferred toa special measuring articulator**, which has beendescribed previously (Utz et al., 1991, 1993). Thearticulator mounting plates were unscrewed andrescrewed twice, the upper part of the measuring devicewas loaded with 10 N and the position of the condylarballs recorded electronically in three dimensions (Fig. 1,measurement 1). The dentures were then returned tothe original articulator, equilibrated in terminal hingeposition using Hanel Foil^ of 8 |j.m thickness with specialemphasis on the depth of pits and grooves and thereforethe definition of the intercuspation (Fig. 1, equilibra-tion 1) and then transferred back to the measuring device.

* Almorc hiternational Inc., PO Box 252 14, Portland, OR 97225, U.S.A.+ SAM, Taxisstr. 41, D - 80637 Munich, Germany.' Dcniatus, Jakobsdalvagen 14-16, S - 12653 Hagersien, Sweden.*> Set No 105 and 110, "^Gerber 1986, Condylalor Service, Switzerland." Convertray, Wilde GmbH, D - 65396 Walluf, Germany.** Condylator Service, Bellariastrasse48, CH-8038 Zurich, Switzerland.tt Snow while plaster No 2, Kerr GmbH, Wiststr. 28, D - 76185Karlsruhe, Germany.' Ulrich Wegmann, University of Bonn, Dental School, Dept. ofProsthetic Dentistry II, Welschnonnenstr. 17, D-53111 Bonn, Germany.'''' Hanel GmbH, Herman-Lons-Str. 120, D - 72622 Niirtingen, Germany.

Measurement 2 was taken with the dentures in maximumintercuspation (Figs 1 & 2) so that the difference incondylar position between the CBP registration and theequilibrated dentures could be calculated. The den-tures were then delivered to the patient. Patients wereinstructed to wear the dentures day and night duringthe first 3 weeks. The mounted upper support cast andthe registration plates were kept and stored.

Second session

1st SessionRegistration 1 0-98 0 - 5 5

0-253-37

The data represent the shift between upper and lower dentures in a time period of 19 4 days (71 subjects, method 1;

50.

mm

Fig. 4. The histogram depicts the amount of shift of the condylarballs (mm) after 19 4 days depending on the number of patients(right and left side) (n = 142).

errors in equilibrium are to be considered as source oferror when interpreting the results.

For this investigation the fixation of the mandibularposition on the apex of the Gothic arch was chosen toachieve the best reproducibility of the CBP registration.Although not measured in this study, its reproducibilitywas recently described in three independent studies for

a total of 112 complete denture patients who had threeregistrations each as 0-26 0-22 mm (0-0-56 mm) (Utzet al., 1991, 1993, 1995). An even settlement of thedentures on the denture-bearing tissues, which is a purerotatory settlement around the hinge axis, cannot bedetected by the present method. Also the position of thedentures in relation to the bony denture bed cannot beassessed. Therefore, the experimental set-up does notallow the distinction between settlement of the denturesand a shift in mandibular position, which would haveprovided additional information for the interpretationof the present results.

The summation of the different sources of error isunlikely as the scatter of data in all measurements wasequal for the different room directions. Also those patientswho had the biggest differences after equilibrationwere not identical with those patients whose denturesdemonstrated the greatest shifts, the five maxima of eachindividual measurement were checked. Despite the smalldistances measured, the results seem reliable as method2 (the comparison of the position of the condylar ballsin maximum intercuspation in the first and secondsession) shows similar results to method 1. Seven out of10 patients with extreme denture shifts were detectedby both methods independently. However, either methodhas advantages and disadvantages: in method 1 the mainsource of error are inaccuracies in equilibration (0-33 mm)whereas in method 2 the inductive measuring deviceswere not checked for any changes after the 3-weekinterval.

General comments . : : ; : : '

The methodological reproducibility of the CBP regis-tration (0-26 mm) and the reproducibility of mounting

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326 K . - H . UTZ

Change in the positionof the condylar spheres

after 19 daysright, mm (n =71)

lateral-I-3

Transversal plane

1 1 , X U '3 2 l\ . \ ^

cranial3

2

2

3caudal

"

medial2 3

Horizontal plane

ventral

2

3medial Fig. 5. Differences in position of the

right (a) and left (b) condylar ballsbetween the terminal hinge positionrecorded after 19 days (coordinatecross) and the maximumintercuspation in the first session(method 1). For complete denturewearers the depicted differences ofcondylar balls positions are inevita-bly not identical with changes in thepatients' condylar position.

Table 4. Differences in position of the condylar balls between the equilibrated occlusion in the first session and theintercuspal position in the second session (not newly equilibrated)

MeanStandard deviationMinimumMaximum

Sagittal(mm)

0-560-430-002 2 5

Right

Vertical(mm)

0-600-500-022-52

Transversal(mm)

0-480-370-041-89

Left

Sagittal(mm)

0-540-450-001-78

Vertical(mm)

0-560-430-001-73

Total displacementRight -t- left(mm)

1-050-55.0-152-82

The data represent the shift between upper and lower dentures in a time period of 19 4 days (71 subjects, method 2).

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INSERTION OF COMPLETE DENTURES. PART I 327

(b)

Sagittal plane Change in the positionof the condylar spheres

after 19 daysleft, mm (n= 71)

ventral

medial3

Horizontal plane

dorsal

Fig. 5. (continued)

the lower denture (0-20 mm) have to be borne in mindwhen interpreting the data. Yet the results of this study(0-5 0-4 mm) were found in a higher range and gainin importance considering that about 50% of the differ-ences measured after 3 weeks were greater than 0-5 mm(Fig. 4). Therefore the occlusion of half the patientschanged more than the range of error of the method.The visual assessment of the apex of the Gothic arch alsoindicated that about half of the patients did not have acongruent horizontal denture position on the first andthe second visit (Fig. 3). As this amount of denture shifthas not been observed in various recent studies on thereproducibility of the CBP registration, the present resultsseem to be different as a result of denture adaptation

between recordings, and factors other than reproducibilityseem to be involved. Features of the denture material,such as further polymerization, water saturation ordeformation of the denture during chewing, are mostlikely of minor influence in this respect, as is the closingmovement of the articulator. The resorption of thealveolar ridge within the 3-week time span of the experi-ment should also be negligible as the average period ofdenture wearing was 13 years. Thus the settlement ofthe dentures on the denture-bearing tissues and a neu-romuscular adjustment of the masticatory system shouldbe considered as an explanation for the denture shift.

The settling process can be defined as the differencebetween the position of the denture to the cast and the

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328 K . - H . UTZ

denture-bearing tissues, which adapt to the fitting surfaceof the denture (Boucher, 1940; Lytle, 1962; Stephens,Cox & Sharry, 1966), the settling of the post dam (Nergiz,Proschel & Niedermeier, 1992) and any further slightshifts of the denture position that are not due toresorption (Hanau, 1929; Brigante, 1965; Niedermeier,1980; Tuncay et al., 1984; Sassen, 1989). However, itseems out of the question that the amount of shiftobserved in the present study is due exclusively to theabove-mentioned phenomena. It is therefore most likelythat neuromuscular adjustments of the masticatorysystem contribute. With the insertion of new dentures,the stimuli to peripheral receptors in the mucosa, themuscles, the tendons and the temporomandibular jointschange (Brill, 1957; Tallgren et al., 1980). For example,if the patient had an eccentric occlusion for many years,the new dentures will first lead to disorientation. Throughthe altered peripheral input the muscles relax and themandible changes position as it is held and moved bythe muscles. Altered pressures on the joint might resultin a change in condylar position. The effect of the newdentures on the stomatognathic system is thereforesimilar to a splint (Jarabak, 1956; Calagna, Silvermann& Garfinkel, 1973; Kowaleski & De Boever, 1975; Roura& Clayton, 1975; Tallgren et ai, 1980; Serrano, NichoUs& Yuodelis, 1984; Singh & Berry, 1985; Akerman,Nordstrom & Hansson, 1986; Carossa etal., 1990). How-ever, the results of the present study do not relate onlyto changes in mandibular position. If one assumes thatthe position of dentures in relation to denture-bearingtissues, and therefore to the bone, does not change,condylar deviations and the displacement of the mandiblemust occur in the same room direction. Consequently, agothic arch, which is in the second session recordedfurther dorsally than in the first session, would beidentical to a ventral shift of the mandible. In a non-arcon articulator this is identical to a dorsal shift of theupper part. However, a dorsal displacement of the upperpart of the measuring device did not coincide with aGothic arch located further distally. Nor could thiscorrelation be found for the other room directions ofarticulator displacement, as would have been the casewhen the measured shifts in denture position were dueexclusively to an altered mandibular position. It cantherefore be concluded that the measured denture shiftsare based on a combination of the mentioned reasons.

Direct comparisons with other studies are not possiblebecause of methodological differences, but clinicalhints that the relation between upper and lower dentures

does change after insertion were given by Jakstat &Wegmann (1990), Lenz & Goebel (1982), Nergiz et al.(1992), Sonntagbauer & Sassen (1982) and Taege & Stoica(1982). These studies, as well as the present study,emphasize that the occlusion in complete dentures ismore a changeable than an unchangeable relation.

Conclusions

Within the first weeks after insertion of complete denturesadaptive processes in the area of the denture-bearingtissues and the masticatory system lead to a change inrelation of the upper to the lower denture.

The amount of occlusal changes in the course of timevaries considerably between individuals. Completedentures should be inserted.with clinically even occlusalcontacts, and sophisticated remounting should becompulsory after only 1-3 weeks.

AcknowledgmentsThis study is part of the habilitation thesis of the authorand was supported by the 'Deutsche Gesellschaft fiirZahn-, Mund- und Kieferheilkunde'. The author is deeplyindebted to DipL- Math. Wolfgang Huntebrinker forcomprehensive data analysis and graphical display (Figs4 and 5). Statistical advice was gratefully received fromDipL- Math. Dr Konrad Oettershagen. Many thanks aredue to Ms Gabi Reppert for fabrication of the registrationplates. Dr Axel Malchau designed Figs 1, 3 and 4.Numerous fruitful discussions with Dr Norbert Bernardand Professor Dr Lorenz Hupfauf as well as criticalcomments on the manuscript from Dr Frauke Miiller andDr John Besford are greatly appreciated.

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Correspondence: Priv.-Doz. Dr K.-H. Utz, Zentrum fiir Zahn-, Mund-und Kieferheilkunde, Poliklinik fiir Zahnarztliche Prothetik I derUniversitat Bonn, Welschnonnenstrasse 17, 53111 Bonn, Gerniany.

1996 Blackwell Science Ltd, Journal of Oral Rehabilitation 23; 321-329