Maximum bite force after the replacement ofcomplete dentures

Frauke Miiller', M. Robin Heath' and Rudolf Ott̂' Sl B.iriholonicw's and lhe Kiiy;il LDIKIOII School ol McJainc iind IX-nlisliy, London. UK; ^Llnivcrsily of Eriangcn, Department ofPmslhclic Dciuisin, Kriangcn. GcriiKiiu

Abstract

Objective: The aim of the present study was to investigate whether the maximum bite force (MBF) can

be improved by the replacement of complete dentures for elderly people. Design: Nine edentulous

volunteers, mean age 74,2 (± 5.5) years and average denture experience 19,4± 19.5 years (1 to 50 years)

had replacement dentures made. After a rehearsal session, MBF was recorded with the old dentures, and

with the new dentures immediately at insertion, at 3, 8 days, 2-3 weeks, 1, 2, 3 and 6-10 months post

insertion (p-i.). MBF was recorded with the central bearing point method using a full-bridge strain gauge

load cell. Data were analysed ofl-line using the mean of two peak readings per patient per session. Results:The results indicate that MBF tended to be impaired when replacement dentures were first fitted (n.s.).

How e\ er. this trend reversed during the first month p-i. for patients with a "moderate" lower ridge resorption

of Atwood grade 3 or 4 (n = 5), Patients with more severe lower ridge resorption Atwood grade 5 or 6

(n = 4) showed a significantly lower MBFo\er the entire observation period (p<0.05) and took longer to

regain bite strength. Only patients with moderate bone resorption exceeded their pre-insertion level of

MBF within the observation period of 6-10 months p-i.. Conclusion: The present pilot study suggests

that, at leasl for elderly patients with severe bone resorption, delayed improvement of MBF should be

expected w ith replacement complete dentures.

Key words: eomplete dentures, ma.ximum bite force, adaptation

IntroductionOne ofthe major concerns in geriatric dentistry isthe functional performance of complete denturesas a replacement for natural teeth. Functionalrehabilitation therefore contributes essentially tooral health and the quality of life in edentate elderlypeople.

It is well known, that complete denture wearersshow a lower chewing efficiency in comparisonto dentate controls' '. The same functionalimpairment applies to the maximum bite force(MBF) which was described to be five to six timeslower than in dentate subjects^ Muscular strengthand cross-seetional area are subject to ageing'' andare further affected by loss of teeth^ However,MBF might also be limited by sensitivity of themucoperiosteum covering the alveolar ridge and

thus the individual threshold for discomfort'^"'".Further impairment might be attributed to theageing properties of the load bearing mucosa'".However, there is still limited evidence on theinfiuence of denture fit and adaptation followinginsertion of new prostheses in elderly people.

Aim

The aim of the present study was therefore toinvestigate whether MBF can be improved by thereplacement of complete dentures.

Material and MethodsStudy subjeets

Nine edentulous volunteers - six men and threewomen - with a mean (± SD) age of 74.2 (± 5.5)years took part in the study. They had been

© The CiLroddnicilogy Associiilion 2001Gerodontology

MuxiinuiTi bile lorcc allcr lhe replacement ol complclc dentures

edentulous and wearing complete dentures for amean (± SD) of 19.4 ± 19.5 years (min. I to max.50 years). One patient did not wear her old lowerdenture. New replacement dentures were made forall subjects prior to the experiments. Functionalimpressions were taken using zinc-oxide eugenolpaste after border moulding. The verticaldimension remained unchanged in only one subjectand was modified slightly (0 - 1 mm) in two,moderately (1 -2 mm) in another two and clearly(>2 mm) in four patients. Acrylic teeth were setup in balanced occlusion. Denture fit was checkedand if necessary adjusted in a previous separateclinical session.

Experimental set-up and protoeolMBF was recorded with the central bearing point(CBP) method (Fig. I) using a custom made loadcell equipped with a full-bridge strain gauge' witha confirmed linearity from 1 to 1000 N and anaccuracy of ±1 N'*. This was mounted on Gerberregistration plates'" using Impression Compound'.The CBP was placed in the centre of gravity oftheupper denture. When inserted, the measuringdevice created an average incisal separation of4 mm. Data were amplified, digitised with a 1401

A/D converter' and stored for analysis using theprogramme Spike 2 .

The subjects sat upright on a wooden cliair andwere instructed to bite three times for 2 to 3 secondsas hard as possible and relax betweenmeasurements. During loading, they were exhortedto bite as hard as possible.

After a session with the old dentures, MBF wasrecorded immediately at in,sertion and at 3 and 8days, between 2 and 3 weeks, 1,2,3 and between6 and 10 months p-i. of the new prostheses.

Statistieal analysisData were analysed off-line using the mean of twohighest peak readings per patient per session(Fig. 2), For statistical analysis non-parametrictests, Wilcoxon for paired samples and Mann-Whitney for unpaired samples, were employed(StatView'').

ResultsThe mean (±SE) MBF dropped from 142,9 N(± 13,6) when replacement dentures were firstfitted to 102,2 N (±21,4), and thus a marked butnon-significant trend was recorded (Fig. 3).However, this trend reversed rapidly during the first

Figure 1. A load cell was mounted on Gerber-plates torecord the MBF using the central bearing point method.

3 0 ? 5 7 5 10 C U 5 15 0 17 ' ao 0 ;.'

Figure 2. Recording of .3 maximum bites. MBF wascalculated as average from the two highest forces.

IMI II131

i,;i

III

l U I

9081

7(± S E n ^ 9 i

12 Mioiith.--

Figure 3. Progressive changes in MBF over the observationperiod: Mean values (± SE) ot all suhjects.

175-

150-

125-

100 -

70

50-

er' •• of rpig'- resorption iAUsc<jdi

-»- 3 / Un = 4)- » • " . / H (n = 151

t.t •denture

K .1,1'' 3 . lays

Insertion'

' 1 h i o r i t h 2 m o n t h s 3 m o n t h s O K i2.tH.- , .ks months

Figure 4. Progressive changes in MBF over the obscr\ aimnperiod: Mean values (± SE) tor subjects with moderate(Atwood grade 3/4) and for se\ ore (Atwood grade 5/6) ridgeresorption.

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month p-i, and progressively thercaller. It wasnotable thai this reeo\ei\ was more favourable forpatients w ith a "moderate" lower ridge resorptiimol ,\i\\ood grade 3 or4". Patients with more severelower riilge resoi|ilion (Atwood grade > or6) tooklonger to regain bite strength (Fig, 4), Only patientsw ith moderate bone resorption showed ii trend toexceed their pre-insertion level of MBI within theobservation period of (vIO months p-i,(n,s,). Themean (± SM) age of this group (75.0 ± 2,2 years)w as not significantly different from the age of thosepatients with more se\ere bone resorption(73,3±.S,5 years).

Contrasts ean be seen in the data averaged overthe entire observation period. Patients withmoderate bone resorption showed a signifieantlyhigher MBF than those with severe resorption(p<0,05). Furthermore the present data indicate agender and an age association with MBF (althoughthis was not significant). Older and female subjectsdid less well (Fig, 5),

P'igure 5. Mean MBF (± Shj in relation to subjects' ridge

resorption. gender and age. Error bars are shown despite

the sample size as an indication tor the \ariabilil\ within

these data.

Discussion

Critique of method

Although muscle strength is a physiologicalattribute, clinical measurements of MBF areinfiuenced by the method of loading and by thesubjects' compliance and determination to bite ashard as possible. Furthermore pain thresholds ofthe denture bearing tissues vary betweenindividuals. Although the inevitable inter-occlusalseparation w as kept constant during the observationperiod, it has to be bom in mind that the verticaldimension and thus the sacromere length hadinitially been altered both by the new dentures andthe experimental set-up. Careful positioning ofthemeasuring device minimised variation betweensessions.

Interpretation of data

Measurements of MBF have a long history indental research, which was extensively reviewedby Carr and Laney'^ in 1987. MBF is thought tobe infiuenced by the dental state, chewing musclestrength and length, mucoperiostial sensitivity andvarious mechanical limitations, particularlydenture tilting, and psychological factors. Moststudies have found a mean MBF for completedenture wearers of either around or clearly under100 N' " " ^ The high MBF of 143 N, which wasrecorded with the old dentures in the present study,might be attributed to the central bearing pointmethod used. This has two major advantages: a)the interocclusal separation can be kept limited incomparison to bulky biting force gauges and b)the dentures are 'self-centred" by the CBP so thatthe load is distributed evenly onto the denturebeai ing tissues. Denture tilting or slipping, as mightoccur with unilateral biting or bilateral biting awayfrom the chewing centre, is thus avoided as longas the CBP is mounted in a central position.Michael et al'* used mucosal transducers formeasuring the MBF without any additional gapeand recorded in their edentate subjects MBFs ofup to 157 N (16 kg). A rather less mechanicalexplanation for the high MBF as measured withthe old dentures could be the patient's motivationwhilst biting as hard as possible. However, therewas good rapport with the operator who hadprovided the replacement dentures and the verbalexhortation during the recordings might haveplayed a role. The relationship of the MBF togender and age does conform to reports from theliterature'" '̂ . The present study also confirms bothclinical experience as well as scientific evidencethat a lower MBF occurs in patients withprogressive ridge resorption" \

Despite the limitations of this clinical pilot studythere is a clear indication of a reduction in MBFfollowing the insertion of replacement dentures,which reversed during the following observationperiod. Hardtmann and co-workers"* investigatedthe MBF and after an increase in occlusal verticaldimension they also found a reduction in force ofaround 259f in all subjects". Changes in verticaldimension have both, short term and lessimmediate effeets on the capacity of muscles toexert maximum tension. The immediate effect is afunction of the optimal working length of thesarcomeres. The less immediate effect results fromthe capacity of muscle to 'graft in' new sarcomeres"in series' on elongated muscles, thus restoring theoptimal sarcomere length'". It is plausible thatchange in vertical dimension contributed to the

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Maxiimim hilc force filler the replacement ol complclc dcniiircs

changes seen in this study. Although it should bestressed that all patients were unconscious of anychange, indeed were pleased with their newdentures, the immediate effect ofthe raised verticaldimension ofthe new dentures would be expectedto result in some reduction of MBF. The ability ofmuscle to add new sarcomeres will thenprogressively restore optimal working length andthus MBF, The speed at which such change occursis important both in research and clinical care.Many follow-up studies are concluded at threemonths on the assumption that adaptation will thenbe complete. The relevant "Muscle Growth Factor"has been shown in stretched medial pterygoidmuscle in man, within one week with a 5 mmincisal increase'"; but it is not known how fast thestructural change is achieved in man, nor howmuch slower this may be in older people.

A previous study has shown an increase ofinterocclusal tactile sensibility during theadaptation to replacement dentures-". Because asimilar improvement was not found in subjectswearing implant-supported overdentures, it wasconcluded, that mucosal settling (effecting a moreintimate contact to the denture bearing tissues) hadcontributed to the effect. Besides the neuro-muscular adaptation, the mucosal settling mightalso have contributed to the changes in bite forcedescribed in the present sample of edentatesubjects. Having used zinc-oxide eugenol pastesfor the functional impressions, the fit surface ofthe denture presented noticeable mucosal detail.Although all the subjects were free fromdiscomfort, subconscious periosteal stimulationmight have initially limited the MBF that thesepatients achieved: a negative correlation of MBFwith mucoperiosteal sensitivity has previouslybeen reported** '̂.

An opposite shift was shown in a recent studyby Leyka et a^' that described an immediate andprogressive increase of "bite-strength" afterrelining or insertion of new dentures. However,these authors used silicone impression materials.Lundquist, Carlsson and Hedegard'-* re-evaluatedthe MBF with a two and six month adaptationperiod respectively after the replacement oroptimising of complete dentures. After a two-month adaptation period they found a significantincrease of MBF in the "best biting position" butfor the group, which was re-examined after a six-month period, they found a non-significantdecrease of MBF. Haraldson, Karlsson andCarlsson' re-assessed the MBF in six edentatesubjects after they had been wearing their denturefor one year. They too failed to show a significant

improvement of the maximum bite force.Improvement of MBF in complete denture wearersis therefore not eonsistent after the renewal oroptimisation of the prostheses.

ConclusionsThe present pilot study therelore suggests that, atleast for elderly patients with severe boneresorption, an initial deterioration and subsequentdelayed improvement of MBF should be expected.

AcknowledgementsThe authors wish to express their gratitude to MrA M Ferman for his assistance during theexperiments. Professor Dr G Hommel providedstatistical advice. Further thanks are due to theDeutsche Forschungsgemeinschaft (DFG) forsupporting this study by grant No. Mu 991/1-3.

References

1, Carlsson G E. Bite force and chewingefficiency. In: Frontiers of Oral Physiology, ed,Kawamura, Y, pp265-292, Basel: Karger 1974,

2 Helkimo E, Carlsson G E, Helkimo M. Biteforce and state of dentition. Aeta Odont Seand 1977:35: 297-303,

3. Heath M R. The effect of maximum bitingforce and bone resorption on masticatory function anddietary selection ofthe elderly, //;/ Dent J 1982; 32:345-356.

4. Michael C G, Javid N S, Colaizzi F A, GibbsD H. Biting strength and chewing forces in completedenture wearers. J Prosthet Dent 1990; 63: 549-553,

5. Haraldson T, Karlsson U, Carlsson G E. Biteforce and oral function in complete denture wearers.J Oral Rehabil 1979; 6: 41-48.

6. Newton J P, Abel R W, Robertson E M,Yemm R. Changes in human masseter and medialpterygoid muscles with age: a study by computedtomography, Gerodonties 1987; 3: 151-154,

7. Newton J P, Yemm R, Abel R W, MenhinickS. Changes in human jaw muscles with age and dentalstate. Gerodontology 1993; 10: 16-22,

8. O'Rouke J T. Significance of tests for bitingstrength, J Am Dent Ass 1949; 38: 627-633.

9. Slagter A P, Bosman F, Van der Glas H W,VanderBiltA. Human jaw-elevator muscle activityand food comminution in dentate and edentulousstate. Arch Oral Biol 1993; 38: 195-205.

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10, Yoshida M, Omiitsu M, Plquero K, SakiiraiK. Relationship between aging and recovery ot theunderlying nuieosa iininediately after removal ofpiessme: the lirst molar region in the mandible. BullTokyo Dent Coll 1999; 40: 61-69,

11, Atwood D A. Postextraction changes in theadult mandible as illustrated by microradiographs ofmidsagittal sections and serial cephalometricroentgenograms,7/'/uv/Zx/D('///1963; 13: 81()-S24,

12, Carr A B, Laney W R. Maximum occlusalforce levels in patients with osseointegrated oralimplant prostheses and patients with completedentures, //)/ J Oral Maxillofae impl 1987; 2: 101-108,

13, Lundquist L W, Carlsson G E, Hedegard B.Changes in bite foree and chewing efficiency afterdenture treatment in edentulous patients with dentureadaptation difficulties, y Ora//?f/!a/7/7 1986; 13: 21-29,

14, Eerikainen E, Kononen M. Forces requiredby complete dentures for penetrating food insimulated function, J Oral Rehabil 1987; 14: 607-613.

15, Tzakis M G, Osterberg T, Carlsson G E. Astudy of some masticatory functions in 90 year oldsubjects, Gerodontology 1994; 11: 25-29,

16, Tsuga K, Carlsson G E, Osterberg T,Karlsson S. Self-assessed masticatory ability inrelation to maximal bite force and dental state in 80-year-old subjects. J Oral Rehabil 1998; 25: 117-124,

17. Tortopldis D, Lyons M F, Baxendale R H.Bite force, endurance and masseter muscle fatigue inhealthy edentulous subjects and those with TMD. JOral Rehabil 1999; 26: 321-328.

18. Hardtmann G, Proschel P, Ott R W.Kaukriilte und maximale KieferschlieBkrafte vonTotalprothesentragern vor und nach BiBhebung.Dt.seh ZalmdrztlZ 1989; 44: 26-29.

19. Goldspink G. Cellular and molecular aspectsof muscle growth adaptation and ageing.Gerodontology 1998; 15: 35-43.

20. Mulier F, Hanke M, Herr H, Behneke N. Oralstereognosis and tactile sensibility in edentuloussubjects after the insertion of new replacementdentures. J Oral Rehabil 2000; 27: 447-448.

21. Leyka A, Ferger P, Wostmann B. (2000)Changes in bite force after renewal or relining of fulldentures. J Dent Res 2000; 79: 352.

Address for correspondence

Priv-Doz Dr. Frauke MulierUniversity of MainzDepartment of Prosthetic DentistryAugustusplatz 2; D - 55131 Mainz

e-mail: fmueller@mail.uni-mainz.de

Equipment and software suppliers

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d Cambridge Electronic Design Ltd,, Science Park. Milton Road, Cambridge CB4 4FE. UK

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