Biting strength wearers

and chewing

forces

in complete

denture

Cecile G. Michael, D.D.S.,* N. S. Javid, D.D.S., M.Sc., M.Ed.,** F. A. Colaizzi, D.M.D.,*** and C. H. Gibbs, Ph.D.**** University

of Florida,

College

of Dentistry,

Gainesville,

Fla.

Most studies concur that denture wearers have only about one fifth to one fourth the bite strength and masticatory force of natural dentition subjects. There appears to be a wide range of acceptable chewing forces, as evidenced by the wide variation in bite strength of natural dentition subjects. However, bite strength and masticatory forces in denture wearers fall below the natural dentition range and therefore it is concluded that denture wearers are handicapped in bite force. The occlusal form of the posterior denture teeth did not significantly influence masticatory force. (J PROSTHET DENT 1990;63:549-63.)

Studies have shownthat when comparedwith natural dentition subjects,denture wearerssuffer a significant lossin masticatory performance.’ Despitethis loss,denture wearers often do not prefer anatomic over nonanatomic posterior teeth and many cannot tell the difference when anatomic and nonanatomic posterior tooth forms are interchanged on their dentures.2-4 This study compared occlusal forces during chewing in denture wearers having two interchangeable occlusal schemesof artificial posterior teeth-teeth without cuspal inclinesand teeth with 30-degreecuspalinclines.A second purposewasto comparechewingforces and the maximum biting strength of complete denture wearersto corresponding measurementsin natural dentition subjects.

MATERIAL

AND

METHODS

Five edentulous subjectshaving previous denture experience ranging from 10 to 21 years were selectedfor this study. Each subject had residual ridgesof favorable morphology, firm mucosa,and a classI skeletal jaw relationship. Completedentures with interchangeableposterior teeth were madefor eachpatient. The posterior interchangeable segmentswere30-degreeteeth (Trubyte Pilkington-Turner Posterior Teeth, Dentsply International, York, Pa.) and teeth without cuspalinclines5(Trubyte Rational Posterior Teeth, Dentsply International).

This study was supported by NIDR grant No. DE04157 and by a grant from the Egyptian Cultural and Education Bureau. *Visiting Professor, Department of Prosthodontics; Currently Professor, Department of Removable Prosthodontics, Faculty of Dentistry, Cairo University, Cairo, Egypt. **Professor, Department of Prosthodontics. ***Associate Professor and Chairman, Department of Prosthodontics. ****Associate Professor, Department of Oral Biology.

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Force

measurement

Forces during biting and chewing were measuredwith four strain gaugediaphragmpressuretransducersplacedat the denture-mucosainterface. Thesefour diaphragmtransducerswere placed in the maxillary denture at the crest of the ridge, adjacent to the first molarsand canines(Figs. 1 and 2). The transducersadjacent to the first molar and canine on the right side were wired into opposite arms of a four-arm bridge so that the outputs were additive. Likewise,the transducersadjacent to the first molar and canine on the left side were wired to opposite arms in a second bridge so that their outputs were additive. This arrangement provided two channelsof force data, one for the right side and one for the left side. The diaphragmpressuretransducerswere constructed in our laboratory following the designdescribedby Kelsey et al.6Hard, T-6 aluminum wasmachined into a thin-walled cylindrical casewith a base (diaphragm) 0.08 mm (0.003 inch) thick. A miniature strain gauge (William T. Bean, Inc., Detroit, Mich., No. BAE-09-015 CC-120LE) was cemented to the center of the interior surface of the diaphragm. Wires were attached to the gauge and the gaugeswere coated. The top of the cylindrical casewas covered with a thin aluminum disk and was sealedwith epoxy cement; this formed an enclosedair chamber that remained approximately at atmospheric pressure. The completed transducer measured3.4 mm (0.130inch) in diameter and was 2 mm (0.08 in) tall. The four diaphragm transducerswere cementedin position in the maxillary denture with modeling compound (Kerr, Romulus, Mich.). The two wires from each transducer were placed through a smallhole drilled through the buccal flange and were connected to a small four-wire cable. The two four-wire cables, one to each side, were wrapped to the clutch, which supported the face-bow, and were brought outside the corner of the mouth (Figs. 1 and 3). The transducerswere moved betweendentures by softening the modeling compound in 160° F water. A total of three sets (12)O F transducers were used in this study. 549

Fig. 1. Maxillary denture with four strain gauge-equipped diaphragm transducers, two on right and two on left. Clutch was cemented to buccal flange well below teeth.

During machining of the cylindrical case, the base (diaphragm) was bowed in slightly. Therefore the strain gauge that was cemented on the inner surface of the diaphragm was placed in tension during biting. During attempts to elevate the denture from the ridge, the diaphragm andstrain gauge were placed in compression. Therefore both biting forces and forces tending to lift the denture off the ridge could be measured. Measurement of maximum bite strength and calibration of the diaphragm pressure transducers were performed on each subject for bilateral and unilateral biting with a strain gauged gnathodynamometer of our own design.l Two stainless steel plates 57 mm long and 19 mm wide were separated by a steel sphere and were loosely held together with two machine screws. The steel sphere allowed forces to balance across the denture during, bilateral biting. During unilateral calibration, one side of the gnathodynamometer was clamped and the opposite end was placed between the teeth. The gnathodynamometer was installed with four resistance-type strain gauges, two on top of the baseplate and two on the bottom, and was wired in a four active-arm .bridge circuit so that their outputs were active during bending of the baseplate with biting and offsetting during elongation from changes in temperature. This gnathodynamometer was calibrated in an Instron testing machine (Model No. 1125, Instron Corp., Canton, Mass.) over a range of 0 to 300 lb and was found to be linear and its measurements were repeatable within 2.3%. The bite opening at the posterior teeth with the gnathodynamometer was approximately 10 mm. First premolars and first and second molars bilaterally usually contacted the gnathodynamometer. During each experiment, the gnathodynamometer was loaded with a 45 lb (20.4 kg) dead weight to calibrate the recorded force data.

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Fig. 2. Closeup of two right-sided strain gauge-equipped diaphragm pressure transducers cosal interface.

Jaw movement

located at denture-mu-

measurements

Movements of the entire lower jaw were recorded during chewing by the replicator systema*g (Fig. 3). Jaw movements were measured with six incremental, photo-optical transducers mounted between maxillary and mandibular face-bows. The total weight and frictional force applied to the mandible was only 100 gm. Overall measurement error was 0.125 mm. The head was unrestrained and the subject sat upright during the chewing recordings. The clutches, which attached the measuring instrument to the dentures, were cemented to the facial surfaces of the dentures, well below the chewing surfaces. The clutches were designed to minimize interference to lip sealing at closure1

Electromyography

measurements

Electromyography (EMG) data were recorded with surface electrodes over right and left masseter, anterior temporalis, and anterior digastric-mylohyoid muscles. The EMG data will be discussed in a subsequent article.

Recording

sessions

Each subject participated in two recording sessions. The subject wore either the 0- or 30-degree posterior denture teeth for at least 2 weeks before the first recording session. Following the first recording session, .the posterior teeth were exchanged and worn a minimum of 2 weeks before the second recording session. During the recording sessions, the patient sat upright. The head was unrestrained. For each recording a standardsized portion of food was placed on the right side posterior teeth and the subject was instructed to chew and swallow. After swallowing, a similar portion of food was placed on the left side posterior teeth where it was chewed and swallowed. Two soft foods (cheese) and two hard foods (one peanut and one carrot) recordings were made at each ses-

MAY

1990

VOLUME

68

NUMBER

5

BITING

STRENGTH-CHEWING

FORCES

IN DENTURE

WEARERS

Table I. Mean peak force in denture wearersin lb (kg) (n = 4) 1 Bite

strength

35 lb (16 kg) Range 22-47 lb

2 Chewingforcesaveragedover soft andhard foods,andworkingand nonworkingsides a. Forceduringclosure,unilateralchewing 4.6 (2.1) b. Forceat occlusion,unilateralchewing 9.8 (4.4)

sion.An averageof 225chewswereanalyzed for eachof four subjects.In the fifth subject (RJ), a portion of the chewing data were lost becauseof an electrical failure and therefore chewingforce for only four subjectsis reported. Maximum biting strength values, measured with the gnathodynamometer are reported for all five subjects.

Statistical

methods

Bite strength data were compared with the Student’s ttest. Two independent samples,natural dentition subjects versus denture wearers,were compared. The chewing data were analyzed with a repeated measuresanalysisof variance (ANOVA). The format of the repeated measuresdesignwas two sides,working and nonworking; by two foods, soft and hard; by three mandibular positions, closing,closed,and opening; and by two types of posterior tooth forms, 0 and 30 degrees.All combinations were administered in each of the subjects.

RESULTS Bite strength The maximum bite strength of the five denture wearers averaged 35 lb (16 Kg), with a range of 22 to 47 lb.

Chewing

forces

No statistical difference in chewingforces wasfound between the two (0 and 30 degrees)posterior denture tooth types (p = 0.96). The data from both types were combined (Tables I through III). The meanpeak closingforce during chewingaveraged4.6 lb (2.1 kg) in the denture wearers.Mean peak force at occlusion during chewing averaged 9.3 lb (4.4 kg). Chewing forcesweregreater at closurethan during closing(p < 0.01) (Table I). In the denture wearers, chewing forces during closing and at closurewere much greater on the working sidethan on the nonworking side for both hard and soft foods @ < 0.01) (Table II). Nonworking sideforceswere low and were negative in someindividual chews,indicating a tendency for the denture to attempt to lift from the mucosaon the nonworking side. Mean peak chewing forces in the denture wearersweremore than twice ashigh for hard food (peanut and carrot) than for soft food (cheese)@ < 0.05) (Table II).

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3. Replicator face-bows for measuring jaw movement. Surface electromyogram (EMG) electrodes were placed over masseter,anterior temporalis,,and anterior digastric-mylohyoid muscles. Fig.

DENTISTRY

Forces were greater on the working than on the nonworking side (p < 0.01). During closure, the working side force was eight times greater than the nonworking side force. At closure,forceson the working sidewerefour times greater than forces on the nonworking side (Table III). On several occasions,an uncomfortable spot, created by a particle of food beneath the denture, resulted in greatly reduced chewing force.

DISCUSSION Bite strength The bite strength of natural dentition subjectsreported in previous articles,lopl1 162lb (74kg), was4.5 times greater than that of the denture wearers, 35 lb (16 kg) (Table I). The denture wearers and the natural dentition subjects were recorded with the samegnathodynamometer sothat values would be comparable.This finding of a ratio of 4.5 to 1 is in generalagreementwith the results of Haraldson et al.,12who reported a 5.5 to 1 difference and those of Worner,13who reported a 4 to 1 difference in bite strength

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HlCHAELETAL.

Table

II.

Mean peak chewing forces in denture wearers in lb (kg): Unilateral chewing (n = 4) Working side

Soft food Hard food

side

Closing

Closed

Opening

Closing

Closed

Opening

2.0 (0.9) 6.0

4.2 (1.9) 11.3 (5.1) 7.8 (3.5)

0.2 (0.1) 0.8 (0.4) 0.5

0.7 (0.3) 0.4

1.9 (0.9) 1.8

(0.2)

(0.8)

0.2 (0.1) 0.3 (0.1) 0.3 (0.1)

(2.7) Average of soft & hard foods

Nonworking

4.0

(1.8)

(0.2)

Au averageof 225 chews per subject were analyzed. III. Denture wearers--working ver8u8 nonworking side: lb (kg): Mean peak force unilateral chewing Table

Working

Force during closing Force closed (at IP)

side

4.0 (1.7) 7.9 (3.3)

Nonworking

0.5 (0.2) 1.9 (0.8)

side

Ratio

8:l 4:l

An averageof 225 chews of both hard and soft foodswere analyzed for each of four subjecta.

of natural dentition subjects over denture wearers. Although the ratio of magnitudesof bite strength for natural dentition subject8 and denture wearersof this study wa8 eimilar to those of Haraldson et all2 the absolute magnitudes of the present study were about twice a8great. Bite strength in complete denture wearersin the present study correspondedclosely to the 21 to 3’7lb, 29.3lb average,reported by Meng and Rugh.14 Disagreementis noted with Atkinson and Ralph,15who found no difference in bite strength between denture wearersand young dentate adults. Atkinson and Ralph16 measuredbite force betweena singlepair of opposingteeth rather than betweensegmentsof opposingteeth bilaterally a8 in this study. Apparently for this reason, their values were only about one third of the force values reported in this study. This would tend to reduce bite strength in natural dentition subject.8over denture wearers. In natural dentition subjects,all the load would be carried on onepair of teeth unilaterally and would not be distributed over the whole arch, whereasin denture wearersthe denture base distributes the load. There was a wide range of bite strength among both denture wearer8(22 to 47 lb) and in natural dentition subjects (55 to 280lb). The range8were not overlapping, however. The denture wearer with the greatest bite strength did not reach the bite strength of the lowest bite strength natural dentition subject. Haraldson et all2 reported similar results. It is apparent that although there must be a wide rangeof adequatebite strengths, denture wearersappear significantly limited. The limitation of bite strength probably results from tissue discomfort, especially in the lower arch. Sposetti et al. l6 found that by placing load-

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bearing attachment8 in the mandibular denture, without modifying the opposing complete maxillary denture, the bite strength increasedby 50%. Dorrough and Rugh* al80 observed an increasein bite strength after making overdenture attachments load-bearing.

Chewing

forces

No statistical difference in chewingforce8 wasfound between the 0- and 30-degreeposterior teeth. Thii supports the finding8 in previous report8 by Brewer et al.,2 Clough et aL3 and Woelfel et al.,4 who have reported that denture wearersoften do not prefer one form of posterior denture teeth over another and often cannot tell the difference when posterior teeth of different forms are interchangedon their denture. One might expect that lesschewing force would have been used with the 30-degreeposterior teeth compared with the O-degreeposterior teeth, especiallysincelessforce wasusedwith the soft food than with the hard food (Table II). However, perhapa the force neededfor chewing is the samefor both posterior tooth forms, especiallyin the final highest force phaseof chewingat the intercuspal poeterior. That is, even though cusp teeth may reduce chewingforce during the closing phasewhile shearingoccurs, they may have no advantage during the near motionless, occlusal phase,when the greatest force occurs. Chewing forces in denture wearer8 on the nonworking side were especially low and were negative in someindividual chews,indicating that at times the denture wasattempting to lift from the mucosaduring chewing.Negative forceswere alsoreported by Frechette17and in oneof three patients studied by Cutright et aLla Chewing forces in denture wearer8were of low magnitude when compared with those of natural dentition subjecta (Table I). The force during closure in chewing averaged4.6 lb (2.1 kg) in the denture wearerscomparedwith 18.2 lb (8.3 kg) in the natural dentition subjects,‘O* l1 a 1:4 ratio. Force at occlusionduring chewingaveraged9.8lb (4.4 kg) in the denture wearera,which wa8 six time8 less than the 58.7lb (26.7 kg) recorded in the natural dentition subjects. *Dorrough

BC, Rugh JD. Pesonal communications,

1985.

BITING

STRENGTH-CHEWING

FORCES

IN DENTURE

WEARERS

Previous studies of chewing forces in denture wearers have been reported. Howell and Brudevold,lg using strain gauges in one patient, reported that the mean forces on two premolars and on the first molar on the working side ranged from 8.1 to 10.8 lb (3.7 to 4.9 kg) for peanuts, coconut, and raisins. Yurkstas and Curby, in four complete and partial denture wearers, using a variety of foods, reported the most common maximum forces on the working side ranged from 13.2 to 17.6 lb (6 to 8 kg). Bearn,21 using a hydraulic device in 10 denture wearers with broad occlusal teeth, who chewed apples, biscuits, and gum, reported mean peak vertical forces on t.he working side ranging from 2.7 to 5.3 lb (1.2 to 2.4 kg). These values are of a similar magnitude to those reported in this study for the working side in the closed position, 4.2 lb (1.9 kg) for soft food and 11.3 lb (5.1 kg) for hard food (Table II). Using surface EMG electrodes over the superficial masseter muscles, Kapur and Garrett’ estimated that denture wearers applied 1:4.5 to 1:2.6 (22% to 39%) of the muscle force applied by natural dentition subjects to chew hard food (peanuts and carrots). These ratios are somewhat lower than the ratios of 1:4 at closing and 1:6 at occlusion measured in this study for an average of soft (cheese) and hard foods (peanuts and carrots) (Table I).

CONCLUSIONS 1. The maximum bite strength of the five denture wearers averaged35 lb (16 kg). 2. No statistical difference in chewing forces wasfound betweenthe two (0- and 30-degree)posterior denture tooth forms. 3. The closingforce during chewingaveraged 4.6 lb (2.1 kg). 4. The force at occlusionduring chewing averaged9.8 lb (4.4 kg). 5. Chewing forces during closing and at closure were much greater on the working sidethan on the nonworking side for both hard and soft foods. 6. Chewing forces were greater for hard food (peanuts and carrot) than for soft food (cheese)during closing and at closure. 7. Uncomfortable spots greatly reduced chewing force. We express appreciation to Dr. Charles C. Kelsey for providing technical advice and samples for fabrication of the force transducer used in this study. We also express appreciation to the Learning Resource Center, University of Florida for preparation of the illustrations and to Ms. Marilyn Lietz for typing of the manuscript. REFERENCES 1. Kapur KK, Garrett NR. Studies of biologic parameters for denture design. Part II. Comparison of masseter muscle activity, masticatory performance, and salivary secretion rates between denture and natural dentition groups. J PROSTHET DENT 1984;52:408-13.

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2. Brewer AA, Reibel PR, Nassif NJ. Comparison of zero degree teeth and anatomic teeth on complete dentures. J PROSTWET DENT 1967;17:28-35. 3. Clough HE, Knodle JM, Leeper SH, Pudwill ML, Taylor DT. A comparison of lingualized occlusion and monoplane occlusion in complete dentures. J PROSTHFZ DENT 1983;50:176-9. 4. Woelfel JB, Hickey JC, Allison ML. Effect of posterior tooth form on jaw and denture movement. J PROSTHET DENT 1962;12:922-39. 5. Colaizzi FA, Michael CG, Javid NS, Gibbs CH. Condylar and incisal border movements: a comparative study of complete denture wearers and natural dentition subjects. J PROSTHET DENT 198&59:453-g. 6. Kelsey CC, Reid FD, Coplowitz JA. A method for measuring pressures against tissues supporting functioning complete dentures. J PROSTHET DENT 1976;35:376-83. 7. Gibbs CH, Mahan PE, Mauderli A, Lundeen HC, Walsh EK. Limits of human bite strength. J PROSTHET DENT 1986;56:226-9. 8. Gibbs CH, Wickwire NA, Jacobson AP, Lundeen HC, Mahan PE, Lupkiewicz SM. Comparison of typical chewing patterns in normal children and adults. J Am Dent Assoc 1982;105:33-42. 9. Gibbs CH, Lundeen HC. Jaw movements and forces during chewing and swallowing and their clinical significance. In: Lundeen HC, Gibbs CH, eds. Advances in occlusion. Littleton, Mass: Wright-PSG Publishing Co, Inc, 1982:2-3‘2. 10. Gibbs CH, Mahan PE, Lundeen HC, Brehnan K, Walsh EK, Holbrook WB. Occlusal forces during chewing and swallowing measured by sound transmission. J PROSTHET DENT 1981;46:443-9. 11. Gibbs CH, Mahan PE, Lundeen HC, Brehnan K, Walsh EK, Sinkewiz SL, Ginsburg SB. Occlusal forces during chewing-the influences of biting strength aud food consistency. J PROSTHET DENT 1981;46:561-7. 12. Haraldson T, Karlsson U, Carlsson GE. Bite force and oral function in complete denture wearers. J Oral Rehabil 1979;6:41-8. 13. Worrier HK. Gnathodynamics-the measurement of biting force with a new design of gnathodynamometer. Aust J Dent 1939;43:381-93. 14. Meng TR, Rugh JD. Biting force in overdenture and conventional denture patients [Abstract]. J Dent Res 1983;62:249. 15. Atkinson HF, Ralph WJ. Tooth loss and biting force in man. J Dent Res 1973;52:225-8. 16. Sposetti VJ, Gibbs CH, Alderson TH, Jaggers JH, Richmond A, Conion M, Nickerson DM. Bite force and’muscle activity in overdenture wearers before and after attachment placement. J PROSTHET DENT 1986; 55:265-73. 17. Frechette AR. Masticatory forces associated with the use of various types of artificial teeth. J PROSTHET DENT 1955$x252-67. 18. Cutright DE, Brudvik JS, Gay WD, Selting WJ. Tissue pressure under complete maxillary dentures. J PROSTHET DENT 1976;35:160-70. 19. Howell AH, Brudevold F. vertical forces used during chewing of food. J Dent Res 1950;29:133-6. 20. Yurkstas BS, Curby WA. Force analysis of prosthetic appliances during function. J PROSTHET DENT 1953;3:82-7. 21. Bearn EM. Effect of different occlusal profiles on the masticatory forces transmitted by complete dentures. Br Dent J 1973;134:7-10. Reprint requests to: DR. CHARLES H. GIBBS Box J-424 JHMHC COLLEGE OF DENTISTRY UNIVEF~SITY OF FLORIDA GAINESVILLE, FL 32610

CONTRIBUTING

AUTHORS

D.D.S., D.D.Sc., Visiting Professor,Department of Prosthodontics, College of Dentistry, currently Department of Prosthodontics, School of Dentistry, University of Niigata, Niigata, Japan M. Conlon, Ph.D., Assistant ResearchScientist, Biostatistics Unit, J. Hillis Miller Health Center, Gainesville, Fla. R. Frier, B.SXE., ResearchAssistant, Department of Oral Biology, Collegeof Dentistry, Gainesville, Fla. S. Nomura,

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