NBSIR 78-1452

An Evaluation of Children's

Biting Strength for Toy Safety

Criteria

Yung-Chi Wu

Product Safety Technology Division

Center for Consumer Product Technology

March 1978

U S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

NBSIR 78-1452

AN EVALUATION OF CHILDREN'S

BITING STRENGTH FOR TOY SAFETY

CRITERIA

Yung-Chi Wu

Product Safety Technology Division

Center for Consumer Product Technology

March 1978

Report To

Consumer Product Safety Commission

5401 Westbard Avenue

Bethesda, MD 20016

U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Dr. Sidney Harman, Under Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Introduction

siting is a natural function of human beings. Children start to bite

when their teeth begin to develop. They use their teeth to cut or incise

with the anterior teeth bite size pieces from apples and corn, and to grind

with the posterior teeth the bite sized pieces. The more hard foods they

eat, the stronger the biting force they develop V and 2/. As they

advance in age, their biting activity and their biting force increase.

They use their teeth not only for biting and chewing foods, but

unfortunately, also as tools with which to manipulate or operate toys and

other objects that they encounter.

Children play with toys in imaginative ways. Any toys with hazards

induced by "foreseeable and reasonable abuse" are prohibited by law. The

hazard of broken toys induced by children's biting falls into such a category. Since children cannot be prevented from biting on toys, biteinduced hazards can be avoided if the stress rupture strength of

materials used for toys is greater than the biting strength that children

would typically exert on the same materials. In the interest of toy safety

it is necessary to find out what the maximum biting strength would be for a given age group of children, so that the minimum compression failure

strength of a toy can be predetermined (for example, to accommodate the

maximum biting forces exerted by any, or say by 90%, of the population of

anticipated users) and the unnecessary hazard of broken toys can be

avoided. The pertinent parameters of these relative strengths are discussed.

Bite Induced Fracture of Toys

All toys are made of materials which have an intrinsic property known

as fracture or stress rupture strength. This property is determined by the

stress-strain relationship. The rupture stress strength is the stress at

which the material fractures (called the fracture point). Elastic

materials fracture when the applied stress exceeds the ultimate yield

strength of the material 3/ & 4/.

The phenomenon of failure by stress rupture is very complicated,

particularly for non-elastic materials. Among other factors, they involve

the test (or use) conditions, e.g., temperature, time, rate of application

of stress and nature of tested material, i.e. brittle or ductile, all of

which influence test results. No detail will be given here. However, the

applied stress, say the biting force over some constant occlusal area (which is the contact surface of the cusps in the teeth), to induce

fracture involves the relative strengths of both teeth and toy. It has

been reported that the tooth enamel has an approximate hardness of Brinell

No. 285 5/, which corresponds to~the hardness of carbon steel with a tensile strength of 9.7 X 10° N/rn (140,000 psi) 4/. This value of

strength is greater than that of most of the materials used for toys,

except some metals. High temperature and long periodsof loading can cause

plastic deformation (creep) and lower the yield strength and fracture point

of materials. Since biting action occurs at room or body temperature, the
- 2 -

effect on the strength of material is negligible. The duration of applied

stress, however, may affect the creep of materials 4/. Therefore, the

primary concern for the bite induced fracture of toys is the maximum biting

force children could exert, the area of occlusion, and the duration of

sustaining such force.

Biting Strength and Force

The biting strength is the biting force acting on the occlusal area of

the biting Diane; the occlusal area is the contact surface of the cusps in

the teeth. The number and radii of cusps vary from tooth to tooth.

Because of the complexity of the topology of the surface of the teeth,

biting forces, instead of biting strengths, are commonly reported in the

literature.

The biting force is the total force exerted by the biting muscles

which move the lower jaw upwards. In this upward movement, the lower jaw

acts like a lever 6/. For this reason, the biting force of an individual

tooth increases with its position, from anterior to posterior, and reaches

a maximum at the first molar (+6 or 6+) (+6 denotes the sixth tooth in the

left jaw counted from the first incisor; 6+ denotes the sixth tooth in the

right jaw) W & 7/. The biting force on anterior teeth is about one quarter or less of the posterior biting force W. Apparently, the bite

opening that limits the size of an object to be bitten, affects the biting

force. The maximum biting force measured is not at the maximum opening of

the jaws, and this led to the belief that "there is a critical state of

contraction in the muscles of mastication at which the force exerted by

them is at its maximum'’ 8/. For this reason, Worner and Anderson have

suggested that, owing to the development of the jaws, the optimum molar

bite opening of children increases with age, and is about 10 mm at age six,

and 18 mm at age ten and older. For children younger than six years, it is

often less than 7.5 mrn, and in the incisal region the optimum bite opening

is in the neighborhood of 20 mm 7/.

The level of the biting force, as discussed by Carlsson V, is

governed by the neuromuscular control mechanism activated by the afferent

impulses from the masticatory system. These impulses are balanced in such

a way as to give the greatest comfort in biting action. Therefore, a sensation of pressure in the joints, muscles, tendons, periodontal tissues

and teeth which indicate that any further increase in biting force may

cause pain is one of the important factors limiting the maximum biting

force.

The physiological function also limits the duration of sustaining the

maximum biting force to 2 to 3 seconds. Heinroth 9/ reported that "A

measurement lasting 15 seconds was illustrated by a diagram (not shown).

The curve rises during the first two seconds up to about 30 kgf (300 N),

whereafter the force lessens during the following two seconds down to about

1 kgf (10 N). This weak condition lasts barely three seconds, whereafter

the curve rises in two seconds to a maximum of about 40 kgf (400 N), only

to fall rapidly to zero." Linderholrn and Wennstron 10 / have shown that

their subjects can produce the maximum biting forces for about 3 seconds.
- 3 -

It should be noted that the above measurements were performed on adults.

Children may have a lower tolerance limit for pain or discomfort (no data

available), so that one second for such duration is suggested.

Force is a vector quantity, and biting force, F, as generally

determined, is not normal to the biting plane. Therefore, the vertical

(normal) component, F , of the biting force, F, exerted by teeth will be:

6 / & VW

F

n

= F cos 9 ( 1

where 9 is the angle between the direction of the applied force of

occlusion and that normal to the occlusal plane of the tooth. Because of

the complex surface topology of the tooth cusps, the angle 9 is difficult

to measure and results in a wide range of values. However, its maximum

value is estimated to be 20 to 40 degrees 1 1/. The lowest value of F , then, will be greater than 75% of the biting force measured. n

Since the strength of a material is defined in terms of force per unit

area, and biting forces are generally reported in force alone, the occlusal

area needs to be considered.

The total occlusal area for a given tooth depends on the material

being bitten. If it is a hard and brittle material, it will make

essentially point contact with the cusps and the contact area is difficult

to assess. If the material is not so hard and is deformable under the

compression of biting force, the surface contact area may be estimated from

the number and curvature radius of cusps of a given tooth. Thus, in

mastication, it has been reported t^at the lower first molar of an adult

has an occlusal area of about 50 mrn 11/. Furthermore, Strenger 12/ has

measured the curvature radii of the cusps of the molars and premolars and

reported a mean value of 1.07 mm. He also reported the mean number of

impressions (the number of cusps of each tooth varies, so that the mean

value was taken) on the biting plane by cusps of individual premolar and

molar teeth as shown in Table 1

Table 1

Number of Impressions by Cusps of Individual Tooth

Tooth Position +7 +6 +5 +4 4+ 5+ 6+ 7+

+X, left; X+, right

No. of Impressions 532 12243

Both values for the radii and the number of cusps are statistically

significant (over 200 measurements 12/) . In assessing the occlusal area,

these statistical values are used because the variation of both the number

(table 1) and the curvature radii (0.3 mm to 2.1 mm) is so great; from cusp

to cusp in the same tooth, also from tooth to tooth and from person to
- 4 -

person. The total occlusal area for a given tooth, assuming a semispherical surface of each cusp is estimated as follows:

A = 2-nr^n (2)

where r = mean radius of curvature of cusps

n = number of cusps

Using the values cited above, the^estimated^maximum occlusal area for a molar tooth would be (51(2tt ) ( 1 .07^) = 36 mm. This value agrees reasonably

with the value of 50 mrn given above. It should be noted that this

occlusal area was obtained from teeth of adults. Since the deciduous teeth, are smaller, smaller occlusal areas would have been obtained if experiments

had been performed on children prior to the erupting of the first permanent

molar.

The Biting Force of Children

The development of human teeth, within broad limits of variability in

both order and eruption age, may be surrsnarized in table 2 13 /.

Table 2

Development of Dentition

Deciduous dentition

Lower central incisors

Upper incisors

Lower lateral incisors and

Canines

2nd molars

Permanent dentition

1st molars

Central incisors

Lateral incisors

1st premolars

2nd premolars

Canines

2nd molars

3rd molars

6-9 months

8-10 months

1st molars 15-21 months

16-20 months

20-24 months

6th year

7th year

8th year

9th year

10th year

11

12th year

12-

1 8th year

17-26th year

The deciduous teeth number 20, viz., 2 incisors, 1 canine, and 2

molars, on each side of each jaw. These deciduous teeth, 20 in number,

begin to be replaced by permanent teeth around the fifth year. It should
5

be noted that premolar teeth never erupt in the deciduous dentition. The

permanent teeth number 32 when they are fully erupted. They are: 2

incisors, 1 canine, 2 premolars, and 3 molars on each side of each jaw.

The development of biting force follows the development of jaw bones

and biting muscles. This general trend, in turn, follows the advancement

of age but it may differ from individual to individual. Therefore, in

order to determine the biting force, experimental measurements are necessary. The measurement of biting force has been recorded as far back

as the 17th century 1/, 6/ & ]2J and has continued. There are several

review articles W

F/ & 12/ in the literature that give evaluations of

measurements of biting forces of human subjects ranging from 3 to 30 years

of age. Some of the early recorded values are generally assessed as inaccurate because of poor designs of the measuring instrument and

inadequate assessments of the biting mechanism. Nevertheless, the relative

value of different age groups is of interest; from these the rate of growth

of biting force for children may be projected. It is generally observed

that the biting force increases with age up until the late teens and then

levels off. In particular, Brawley and Sedwick 14/ have reported that

biting force increases over 22N (5 lbf) per year from 6 to 17 years of age.

The maximum biting forces may differ widely among the same age groups

for children as well as for adults. Thus, some younger children have shown

a strong biting force compared with older children. Some children of * kindergarten age have demonstrated biting force values of 400 N (88 lbf) V 0

, which are almost the same as that of adults. This variation of biting

force is apparently due to the state of dentition.

The most influential factors on the biting force, in addition to the

eating habits, and the development of jaw bones and muscles, are the health

condition of teeth and their surrounding tissues W. Thus, Worner and

Anderson 7/ reported that "the estimated average molar biting forces for

the children of all ages in this state (Australia) appear to be much lower

than those recorded for American children. It is suggested that this may

be attributed to the general lack of dental consciousness in this community

and to the fact that a large number of Victorial children are 'lazy

eaters'." The authors further stated that "the average biting pressures on the first permanent molars of the girls at the boarding school were above

those of the hospital patients, and these results were in turn above those

of children at a State school (Australia) in an industrial suburb. . . The

lower molar biting strength of the former scholars (state school children)

is thought to be due to a lack of dental consciousness and very poor oral

health." Krogman 15 / recently has reported the biting forces of children 3

to 6 years of age in Oakland, Calif, and in Philadelphia, Pa. The maximum

biting force of American children is comparable to those in Western Europe

and is much higher than those in Australia as the Australian authors

stated. All of these results are summarized in the accompanying figures.

Figures 1 and 2 show the mean values of the maximum biting forces in

the molar regions, which were computed by Worner and Anderson 16 / from

earlier investigations. Figure 3 is reproduced from Linke and Dette 17 /

for the maximum biting force of the deciduous molars (+6 or 6+) of
- 6 -

individual children. Figure 4 is plotted for the highest values taken from

Krogrnan 15/

.

It can be seen from these figures, that the measured values for biting

force are highly scattered. There is no available means to evaluate what

is the best value for the biting force of a given age group. Because the

measuring techniques varied among all the authors, the results cannot be

statistically compared with each other. However, in the interest of child

safety, some safety factors are required for the evaluation of the bite

induced hazards. It is reasonable to consider the highest values of the

biting force of each age group.

Figures 1 and 2 show only mean values which, if chosen as the force

for testing the bite resistance of toys, might protect the majority of

children but would not protect those whose biting force is higher than

average. The values shown in figure 3 are particularly interesting. The

data covers not only the age range of interest, but also gives the month of

each age group. The highest biting forces of a given age (including month)

are replotted in figure 5. As pointed out previously, the biting force

increases with age, and assuming that the increase is linear, a straight

line is fitted to those highest values as the maximum biting forces for

this age group (3-7 years). Although Krogrnan 's highest values as shown in

figure 4 are higher than those shown in figure 5, Krogrnan did not show

whether his results were obtained from biting with an opposing single or with two adjacent teeth. In view of his measuring instrument and the

instructions that were given to his test subjects, it appears that some of

his results could have been the biting force exerted by two adjacent teeth.

Therefore, Krogrnan' s highest values are high compared to those with single

opposing molar teeth. However, based on Mansour's observations on adults,

the biting force of the first molars (+6 or 6+) is higher than that of the

second premolars (+5 or 5+) by about 40% 6/. Assuming the same relative

biting strength for children's two deciduous molar teeth, then Krogrnan 's highest values will be reduced (X/ 1.6) and would be compatible with those

values shown in figure 5.

It is interesting to note that most values referred to above are measurements of the biting force of the deciduous or the first permanent

molars (+6 or 6+) of children. There appears to be no quantitative data on the biting force of two adjacent deciduous molar teeth reported in the

literature. However, it has been observed that the resultant biting force

of the two incisor teeth for adults is approximately additive 19/. If the

resultant biting force of these two deciduous molar teeth is additive and

the relative biting forces are 1:0.6 as observed for adults, the resultant

force will be greater by a factor of 1.6 than the maximum biting force of

the second deciduous or the first permanent molar (+6 or 6+). However, the

occlusal area of the two teeth together is also approximately 1.6 times

that of the second deciduous molar (+6 or 6+) as estimated from the values

in Table 1. In this case, the biting force increases with the occlusal

area, but the biting strength of the two adjacent deciduous molars remains

approximately the same as that of the second deciduous molar. Thus, this

relationship may be approximately formulated as follows:
R = F/A = F’/A’ (3)

- 7

-

where B = biting strength

F, F' = biting force of single and adjacent teeth, respectively

A, A* = the corresponding occlusal areas of single and adjacent

teeth, respectively.

Toy Safety Aspect of Biting Force

The maximum biting forces reported in the literature, with the

possible exception of Krogman’s, were measured on the second deciduous or

the first permanent molar (+6, 6+) of children. Therefore, the occlusal

area was estimated for these teeth. It should be noted that the occlusal

area as discussed in the preceding section depends on the material being

bitten. It may be a point contact for hard and brittle materials and,

therefore, no area could be estimated. If the materials used for toys are deformable under the compression of biting force, the estimated occlusal

area may be used. There is no data available from which to simulate the

actual biting actions of children. Variables include the number and

location of teeth that are used, the occlusal area involved, and the size

of the mouth opening. However, it has been pointed out in the preceding

section that the maximum biting strength of two adjacent deciduous molar

teeth is about the same as that of the second deciduous molars. Therefore,

the following assessment of the maximum biting force is based on the values

for the second deciduous or the first permanent molars.

There appear to be six factors which influence the safety aspect of

bite induced toy failure; namely, the optimum molar teeth bite opening, the

biting force, the biting angle, the occlusal area, the duration of

sustaining the maximum biting force, and the hardness of the enamel of

teeth. The first four factors are related to the biting strength, and the

last two factors are pertinent to the ultimate yield strength of materials

used in toys that may be subjected to biting actions. Furthermore, the

values for the last four factors are taken to be constant for all ages of

children, whereas the first two biting factors vary from age to age, and

among the same age group.

Since children have very limited knowledge of what is hazardous, in

their play with toys, they require maximum protection. Further, although

toys are generally intended for children in a given age group (0-18 months,

18-36 months, and 36-96 months), there can be no assurance that they will

be used only by the intended age user, especially if there are older

siblings in the home. Therefore, in the interest of protecting children

from the hazards of bite-broken toys, the highest biting strength (biting

force; area, molar bite opening) of the upper age group in a given age

bracket is recommended for the evaluation of the minimal required fracture

strength of materials used in toys.
- 8 -

The bite opening has certain effects on the biting force. However,

the optimum opening to yield the maximum biting force of an individual, has

been disputed and has not been measured experimentally W. Furthermore,

Worner et. al. themselves have used a measuring pad of size (18 mm) which

is greater than their suggested optimum opening limits for measurements on children of ages 4 to 18, and their recorded biting forces show no drastic

change for the age range due to such openings. It appears that there is

insufficient data on the optimum opening to determine the size limit of

objects that may be bitten on by children. On the other hand, there is a criterion for "small objects" hazards, which requires a size greater than

32 mm ( 1 1/4") in diameter. For the sake of maximum protection of

children, it is suggested that toys and their external parts with size of

32 mm and smaller should be required to withstand the maximum biting

strength of children. The other five factors are evaluated as follows:

Constant Factors

1 . The biting angle - this angle is taken as 30 degrees which is the mean of the highest (33°) and the lowest (22°) values reported.

2

2. The occlusal area - this area is taken to be 50 mm .

3. The duration of biting - the duration of sustained maximum biting

force is taken to be one second.

4. The hardness of the tooth enamel - this is taken to be

approximately Brinell #285, which is equivalent to the hardness of

carbon steel with a tensile strength of 140,000 psi (9.7 X 10

N/m )

.

Biting Force

The highest maximum biting forces of children from age 3 to 7 years

are shown in figure 5. There appears to be no value reported in the

literature for children younger than three years of age. Above age seven,

the reported mean values are shown in figures 1 and 2. To be consistent,

the extrapolated values for ages 18 months and 8 years from figure 5 are

taken. They are:

0-18 months - 177 N (40 lbf)

18-36 months - 255 N (57 lbf)

3-8 years - 540 N (121 lbf)

It should be noted that these biting forces are not the vertical

(normal) forces to the biting plane, which are needed for the evaluation of

the bite induced hazard. In order to obtain normal forces, equation 1 is

used, and a biting angle of 30 degrees is employed. Furthermore, according

to Table 2, children at ages of 18 months and under do not have their

second deciduous molar teeth which exert the highest biting force before

the permanent molars are erupted. If the relative biting force of the
- 9 -

first deciduous molars is taken to be 40% less than that of the second as discussed previously, and if the occlusal area is assumed to be

approximately 20% less than that taken in the above section, the estimated

maximum vertical force for age of 18 months will be:

(177)(1-.4%)(cos30)/(1-.2%) = 115 N (26 lbf)

Children of ages 36 months and up already have their second deciduous

molars whose area is taken to be a constant as 50 mm. The estimated

maximum vertical forces for these age groups are:

18-36 months (255) (cos 30) = 221 N (50 lbf)

3-8 years (540) (cos 30) = 468 N (105 lbf)

Conclusions and Recommendations

In view of the foregoing discussions and the information presented, it

is suggested that the following criteria be considered in evaluating the

bite induced hazards of toys.

1. The duration of sustained maximum biting force is 1 second.

2. The upper size limit of toys subject to evaluation is 32 mm (1

1/4") for all ages.

3. The maximum vertical biting forces for different age groups are:

0-18 months - 111 N (25 lbf)

18-36 months - 222 N (50 lbf)

3-8 years - 445 N (100 lbf)

2

4. The occlusal area is 50 mm .

It should be noted that the above criteria for force level and

occlusal area are based on measurements cited for single molar teeth and

that the mean radius of curvature for molar cusps is 1.07 mm. It is

suggested that any rational device which is chosen for testing the bite

resistance of toys should have a radius of no less than 1 mm (rounded

number) on the test edges. Furthermore, assuming that the occlusal area is

the same as the contact surface area, the test force should be chosen in

accordance with equation 3, above.
-

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BOYS

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F

inure

1.

Mean

values

of

first

molar

bitinq

forces

for

boys

of

anes

6

to

18,

reproduced

from

Worner

and

Anderson
GIRLS

CD O

IT) O o

co o

CM

AGE,

YEARS

!

Figure

2.

Mean

values

of

first

molar

biting

forces

for

girls

of

ages

6

to

18,

reproduced

from

Worner

and

Anderson
1

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°

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Maximum

bitinq

forces

of

the

deciduous

molars

(+6,

6+)

of

individual

children

of

aqes

3

to

7,

reproduced

from

Linke,

Dette

and

Hoppman

(ref.

17).
BITING

FORCE,

Lb

0 1 2 3 4 5 6

ri'niro 4

.

AGE, YEARS

Highest bitinn forces of children. Data taken from Kronman

(ref. 15). The solid line indicates the mean values.
Fiqure 5. The hiqhest bitinn forces of

a qiven ane taken from finure 3 (•) and f inure 4 ( 0 , see text ) 

References

1. E. Carlsson, Front. Oral Physiol., 1, 265 (Krager, Basel 1974).

2. G.N. Jenkins, Physiology of the Mouth, Blackwell Scientific

Publications, Oxford, England (1966)

3. S. Timoshenko, Strength of Materials, 3rd Ed., D. Van Nostrand Co.,

New York, NY (1955).

4. J.H. Faupel , Engineering Design, John Wiley and Sons, Inc., New York,

NY (1964)

5. Wilmer Souder and G.C. Paffenbarger , Physical Properties of Dental

Materials, NBS Circular No. 433 (1942).

6. R.M. Mansour, Drexel Tech. Jour., 34, 32 (1972).

7. H.K. Worner and M.N. Anderson, Austral. J. Dent. 48, 1 (1944).

8. R.H. Boos, J.A.D.A., 27, 1192 (1940), cited by Worner et. al. (ref.

7).

9. Hans Heinroth, cited by F. Strenger, Biting Force in Man, Stockholm,

Sweden (1949).

10. H. Linderholm and A. Wennstrom, Acta Odont. Scand. 28, 679 (1970).

11. R.S. Ledley, Engineering Analysis of Dental Forces, Theory and

Application, National Biomedical Research Foundation, Silver Spring,

MD (1969).

12. F. Strenger, Biting Force in Man, Stockholm, Sweden (1949).

13. M.F. Ashley Montagu, Anthroplogy: Physical, Methods in Medical

Physics, Vol. 2, Ed. 0. Glasser, The Year Book Publishers, Inc.,

Chicago, 111. (1950).

14. R.E. Brawley and H.J. Sedwick, Int. J. Orthodontia, 24, 256 (1938),

cited by Worner, et. al. (ref. 7).

15. W.M. Krogman, "The Manual and Oral Strengths of American White and

Negro Children, Ages 3-6 years" A Report to Glass Container

Manufacturers Institute, Inc. (1971).

16. Literatures cited by Worner and Anderson, ref. 7.

17. P.G. Linke, K.E. Dette and I. Hoppmann, Aertzliche Jugenkunde,

Leipzig, 62, 338 (1971).

18. K.E. Dette, I. Hoppmann and P.G. Linke, Deutsche Zahn-, Mund-Und

Kieferheilkunde, 59, 399 (1972).

19. Yoshihide Maeda, J. Tokyo Dent College Soc. 73, 434 (1973).

..1I4A ("tv. 7-7*>

"u.S OEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLIC ATION OR REPORT NO.

NBSIR78-1 452

2. Gov’t Accession

No.

3. Recipient’s Accession No.

TITLE AND SUBTITLE

An Evaluation of Children's Biting Strength

for Toy Safety Criteria

5. Publication Date March 1978

6. Performing Organization Code

AUTHOR(S)

Yung-Chi Wu

8. Performing Organ. Report No.

PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 4401422

11. Contract /Grant No.

Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Consumer Product Safety Commission

5401 Westbard Avenue

Bethesda, MD 20016

13. Type of Report Si Period

Covered

14. Sponsoring Agency Code

SUPPLEMENTARY NOTES

ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.)

Children's biting strength (biting force over the occlusal area) is one

of the major parameters in evaluating the bite induced broken-toy hazard.

The estimation of biting strength includes the assessments of controlling

factors that influence the maximum biting force and the occlusal area.

Values for biting strength are discussed accordingly. Since only the

maximum biting forces (over a constant area of measuring device) of the

deciduous molars or the first permanent molars are given in the literature,

and since the biting strength of single opposing molars is approximately

equal to that of two adjacent opposing molars, the maximum biting forces

for single molars are evaluated. In the interest of child safety, the

highest biting strength (biting force and area) of upper age group in a given age bracket is recommended. Other parameters, such as molar bite

opening, time for sustaining maximum biting force, and the hardness of

the enamel of teeth are also discussed.

. KEY WORDS (six to twelve entries; alphabetical order; capitalize only die first letter of the first key word unless a proper name; separated by semicolons)

Bite opening; biting force; biting strength; cusps; dentitions; duration

of sustained maximum biting force; hardness of enamel; occlusal area.

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(THIS PAGE)

22. Price

1 1 Order From National Technical Information Service (NTIS)

Springfield, Virginia 22151 UNCLASSIFIED

USCOMM.DC 29042* P74
.