ArticlePDF Available

Abstract and Figures

Maximum bite force is a useful indicator of the functional state of the masticatory system and the loading of the teeth, and its recordings can be performed in a relatively simple way in the clinic. However, because maximum bite-force levels vary with method, sex and age, it is important that the measurements are compared against the appropriate reference values. The level of bite force is a result of the combined action of the jaw elevator muscles modified by jaw biomechanics and reflex mechanisms. Pain limits the maximum bite force and may thus impede the measurements, but this factor may also be useful in treatment control. The maximum bite force increases with the number of teeth present. The number of occlusal tooth contacts is an important determinant for the maximally attainable bite force, explaining about 10% to 20% of the variation. The association between maximum bite force and the amount of occlusal contact is closest in the posterior region, and as a consequence, loss of molar support results in reduction of force. In contrast, malocclusions defined solely on the basis of molar and canine relationships have less influence on the level of bite force.
Content may be subject to copyright.
Bite Force and Occlusion
Merete Bakke
Maximum bite force is a useful indicator of the functional state of the
masticatory system and the loading of the teeth, and its recordings can be
performed in a relatively simple way in the clinic. However, because maxi-
mum bite-force levels vary with method, sex and age, it is important that the
measurements are compared against the appropriate reference values. The
level of bite force is a result of the combined action of the jaw elevator
muscles modified by jaw biomechanics and reflex mechanisms. Pain limits
the maximum bite force and may thus impede the measurements, but this
factor may also be useful in treatment control. The maximum bite force
increases with the number of teeth present. The number of occlusal tooth
contacts is an important determinant for the maximally attainable bite force,
explaining about 10% to 20% of the variation. The association between
maximum bite force and the amount of occlusal contact is closest in the
posterior region, and as a consequence, loss of molar support results in
reduction of force. In contrast, malocclusions defined solely on the basis of
molar and canine relationships have less influence on the level of bite force.
(Semin Orthod 2006;12:120-126.) © 2006 Elsevier Inc. All rights reserved.
Maximum bite force is one indicator of the
functional state of the masticatory sys-
The force results from the action of the
jaw elevator muscles (in turn, determined by the
central nervous system and feedback from mus-
cle spindles, mechanoreceptors, and nocicep-
tors) modified by the craniomandibular biome-
Bite-Force Measurements
Bite force is most often recorded with one or two
transducers placed between pairs of opposing
teeth during clenching.
This is a simple, direct
method for clinical use, but it increases the bite
height and leaves the rest of the dentition sepa-
Pressure-sensitive sheets, thin force-sens-
ing resistors, and strain gauges in dental recon-
structions do not disturb the dental occlusion as
much, but their recordings need far more prep-
aration or computer calculation.
Recording Technique
The recorded force during maximal clenching
varies with the location of the measurement
within the dental arch and the number of teeth
included. Also, the use of coverage, splints, and
other means of protecting teeth and transducers
may influence the measurements.
bite force is highest in the molar region.
lateral measurement of maximum bite force in
the molar region averages between 300 and 600
Newtons (N) in healthy adults with natural
With the transducer placed on the an-
terior teeth the measured force is about 40% of
the unilateral force recorded in the molar re-
gion, and with the transducer in the premolar
region it is about 70%. If the force is measured
bilaterally in the molar region, the recorded
force is about 40% higher than the unilateral
Department of Oral Medicine, Clinical Oral Physiology, Oral
Pathology & Anatomy, School of Dentistry, University of Copenha-
gen, Copenhagen, Denmark.
Address correspondence to Merete Bakke, DDS, PhD, Department
of Oral Medicine, Clinical Oral Physiology, Oral Pathology &
Anatomy, School of Dentistry, University of Copenhagen, 20 Nørre
Allé, DK-2200 Copenhagen, Denmark. Phone: 45-35 326 554; Fax:
45-35 326 569; E-mail:
© 2006 Elsevier Inc. All rights reserved.
120 Seminars in Orthodontics, Vol 12, No 2 (June), 2006: pp 120-126
With thin pressure-sensitive sheets that cover
the whole dental arch, the total bite force is
twice the unilateral molar bite force.
In addi-
tion, measuring the bite force on a splint cover-
ing all six anterior maxillary teeth (as opposed
to a single anterior tooth) increases the maxi-
mum bite force about 25%.
Even though the
force level varies systematically with measuring
technique, the values recorded with different
methods are generally significantly correlated,
and the method errors are small and the repro-
ducibility is good. However, for clinical evalua-
tion it is necessary to consult reference values
obtained with the technique used.
Measurements of maximum bite force are de-
pendent on the motivation and cooperation of
the subject. Concern about damage to the teeth
during the measurement, or ongoing pain and
tenderness in the teeth, supportive structures,
temporomandibular joint or masticatory mus-
cles have a negative influence on the bite-force
measurements. Pain limits the maximum bite
force due to reflex mechanisms and impedes
maximum bite-force measurements, but this fac-
tor may also indicate a patient’s actual func-
tional capacity and, therefore, provides useful
information for the control of treatment.
For example, pain in the temporomandibular
joints from chronic arthritis and temporoman-
dibular disorders (TMD) reduces the maximum
bite forces by 40% compared with control val-
ues, probably because the pain is associated with
a reflex “splinting” reaction that limits the ability
to work against heavy loads.
Maximum bite
forces have also been shown to decrease with
increased tenderness of the temporomandibular
joint in patients with arthralgia (Fig 1).
addition, biting on a transducer may in itself
provoke or aggravate pain.
Jaw Elevator Muscles
The highest voluntary force generated by the jaw
elevator muscles is during maximal clenching.
Bite-force levels increase when clenching is per-
formed with increased jaw opening until about
15 to 20 mm of interincisal distance, probably
corresponding to the optimum length of the
jaw-elevator muscle sarcomeres; bite force then
decreases with further opening.
This so-
called length-tension relationship should be
considered when assessing maximum bite force
with a bite-force meter that increases bite height
and jaw separation.
There is a close positive relationship be-
tween the bite force and the electromyo-
graphic activity of the jaw elevator muscles
(the temporal, the masseter, and the medial
pterygoid muscles) during isometric contrac-
Due to the jaw biomechanics, a
higher level of elevator activity is required in
the anterior part of the dental arch than in the
posterior part in order to produce the same
bite force.
For the same individual, during
the same recording session, the level of elec-
tromyographic activity fairly accurately reflects
the level of bite force during submaximal iso-
metric contractions (Fig 2).
However, the re-
lationship between maximum bite forces
measured in different subjects and the corre-
sponding elevator muscle activities is much
more variable, due to differences in electrode
placements in relation to fiber direction, as
well as different anatomical and morphologi-
cal relations in terms of muscle thickness and
craniofacial dimension.
Analogous to the limb muscles, the volume
and cross-sectional thickness, the muscle fiber
distribution, and the training state are all corre-
lated with the maximum force of the jaw elevator
Based on ultrasonography, com-
Figure 1. Positive, linear correlation between maxi-
mum unilateral molar bite force (in Newtons) and
tenderness of the temporomandibular joint (TMJ) in
terms of the pressure-pain threshold (PPT in kPa).
Data from 26 female patients with unilateral arthral-
gia (y55.57 2.64x). Low threshold, correspond-
ing to a high level of tenderness and pain of the
temporomandibular joint, was associated with low
maximum bite force. kPa kilopascals. Reprinted
from Hansdottir and Bakke 2004
with permission.
121Bite Force and Occlusion
puted tomography, and magnetic resonance im-
aging, the thickness of the resting masseter
alone explains 55% of the variation of maximum
bite forces.
Anthropometric Factors and Craniofacial
Age, sex, and probably stature account for a part
of the variation of the maximum bite force. The
jaw closing force increases with age and
stays fairly constant from about 20
years to 40 or 50 years of age, and then de-
(Fig 3). The maximum bite force is
generally higher in men than in women because
of men’s larger jaw dimensions.
In addi-
tion, the muscle fibers may also differ between
the sexes, as the greater bite force in men seems
to correspond with a greater diameter and cross-
sectional area of the type II fibers in the masse-
ter muscle.
The maximum bite force also varies with skel-
etal craniofacial morphology, decreasing with
increasing vertical facial relationships, the ratio
between anterior and posterior facial height,
mandibular inclination, and gonial angle.
has been proposed that bite force reflects the
geometry of the lever system of the mandible.
That is, the elevator muscles appear to have
Figure 2. Positive, linear correlation between unilateral, molar bite force (in Newtons) at submaximal contrac-
tions (12.5, 25, 37.5, 50, 62.5, 75 and 87.5% of maximum bite force) and ipsilateral and contralateral anterior
temporalis (above) and superficial masseter (below) activities, recorded by surface electromyography (in
Average values from seven healthy control subjects. The elevator activities increased with increasing levels of bite
force. Reprinted from Bakke et al., 1989
with permission.
122 M. Bakke
greater mechanical advantage when the ramus is
more vertical and the gonial angle relatively
However, the interaction is probably
more complex because craniofacial form seems
to be determined, at least in part, by the biome-
chanics of the masticatory muscles. Thus, analy-
ses of structures by computed tomography have
shown that the jaw elevator muscles exert influ-
ence on their adjacent local skeletal sites by
mechanical stresses,
and that the maximum
electromyographic activity in the jaw elevator
muscles during clenching is highest in subjects
with a square facial type.
Occlusal Factors
There is a significant positive correlation be-
tween the maximum bite force and the number
of teeth present.
With increasing levels of
clenching, the occlusal tooth contact between
the maxillary and mandibular dental arches be-
comes closer. For example, with an increase of
the clenching level from 30% to 100% the oc-
clusal contact area is doubled.
Due to the bio-
mechanics of the jaw elevator muscles and the
lever system of the mandible, the occlusal force
is greater on the molars than on the incisors
(Table 1). Correspondingly, occlusal tooth con-
tacts are most frequent in the posterior re-
The number of occlusal contacts is a stronger
determinant of muscle action and bite force
than the number of teeth present.
The occlu-
sal contacts have been shown to determine 10%
to 20% of the variation of maximum bite force
in adults, and the association between maximum
bite force and contacts is higher in the posterior
region (r, 0.40-0.60) than in the anterior re-
One way to explain the correlation
between occlusal contacts and bite force is that
“good” occlusal support (ie, force distributed
over many teeth) may result in stronger or more
active jaw elevator muscles that can develop
higher bite force. Another explanation could be
Figure 4. Linear correlation between maximum bilat-
eral bite force (in Newtons) and number of posterior
teeth in the mandibular arch without opposing tooth
contact. The maximum level of clenching force de-
creased with loss of occlusal support. Data from 39
adults with one or more missing teeth distal to the
canines. The transducer, consisting of four strain
gauges in an electrical bridge, was positioned for max-
imum molar support on both sides. Reprinted from
Gibbs et al. 2002
with permission from The Editorial
Council of the Journal of Prosthetic Dentistry.
Figure 3. Relation between unilateral molar bite
force, age and gender in 122 healthy subjects (59
males and 63 females) with full complement of teeth
(fourth order polynomial regression lines). The max-
imum bite force (in Newtons) was lower in women
than in men and it increased until the second decade
and decreased again, especially after the fifth decade.
Redrawn after the data in Bakke M, Holm B, Jensen
BL et al. 1990.
Table 1. Relative Distribution of Maximum Bite
Force and Occlusal Tooth Contact in the Maxillary
Dental Arch*
Mean SD
Occlusal Force (On all
teeth in the group, in
percentage of the total
bite force)
Occlusal Tooth Contact
(Percentage of teeth
with contact, of all
teeth in the group)
Incisors 3 33230
Canines 4 27931
Premolars 12 7 100 0
Molars (third
78 8 100 0
*Values for tooth group on both sides in 17 healthy young
adults. Data from Shinogaya et al.
123Bite Force and Occlusion
that strong elevator muscles, with resulting
harder biting and vigorous function, cause bet-
ter occlusal support and increased number of
contacts. Both explanations are probably rele-
vant. However, we cannot be sure which is the
cause and which is the effect. Not unexpectedly,
strong correlations (r, 0.60-0.70) occur between
the number of occlusal contacts and the ampli-
tude of the electromyographic activity in the
masseter muscle during maximum voluntary
contraction and in the occlusal phase during
Dental Status, Prostheses, and Implants
Reduced bite force has often been ascribed to
deficiencies in the dentition, but neither re-
duced periodontal attachment nor tooth decay
seem to influence maximum bite force.
However, even moderate loss of posterior tooth
support results in loss of clenching force
4). Because the amount of occlusal contact on
the posterior teeth is the most important of the
occlusal parameters, tooth loss in the molar re-
gion has a greater influence on the level of
maximum bite force than loss in the anterior
part of the dental arch.
When the function of the masticatory system
is reduced due to loss of occlusal support, re-
movable prostheses do not compensate enough
to maintain the previous level of maximum bite
(Fig 5). However, if complete dentures
are converted into implant-supported overden-
tures the maximum bite force is almost doubled,
corresponding to about two thirds of the value
obtained for dentate subjects.
Because re-
ceptors in the periodontal ligament modify the
activity of the masticatory muscles, and thus the
bite force, their function in the edentulous jaw
and with implants must be taken over by other
receptors, such as mucosal and periosteal mech-
anoreceptors, as well as intraosseous nerve end-
Most bite force studies have been comprised of
subjects with a full complement of teeth, Angle
Class I molar occlusions, and no dysfunction.
However, there has long been an interest in how
maximum bite force influences the develop-
ment of facial morphology and malocclusions
(eg, the overeruption of posterior teeth in the
development of anterior open bite) and in the
planning of orthodontic treatment.
It has
also been shown that both bite force and occlu-
sal tooth contact most often are reduced tempo-
rarily during orthodontic treatment.
Malocclusions are often associated with re-
duced maximum bite force.
orthodontic treatment may be needed to im-
prove function.
However, the bite force does
not seem to vary between Angle malocclusion
At the same time children with unilat-
eral posterior cross bites have been reported to
have both lower maximum bite forces and lower
numbers of occlusal contacts than children with-
out malocclusions.
The same difference of bite
force and occlusal contact is found between
adults subjects with anterior open bite and sub-
jects without malocclusion, but not in young
Generally, there is not the same
systematic relation between malocclusion and
maximum bite force as with occlusal contact and
maximum bite force. In subjects with malocclu-
sion the reduced maximum bite force is proba-
bly related more to the effect of occlusal contact
Figure 5. Maximum bite force in different states of
dentition and with dental prostheses. Good dentition:
normal posterior occlusal support; Compromised
dentition: loss of posterior support and no removable
prosthesis, Partial denture: either upper or lower par-
tial denture; Complete dentures: both upper and
lower complete dentures. The maximum bite-force
values from the groups with compromised dentition,
partial denture and complete dentures are shown in
percentage of the recorded values in adults with good
dentition (100%). The fewer the natural teeth
present, the lower the maximum bite force. Drawn
after the data in Miyaura et al. 2000 (thin pressure-
sensitive sheets in 500 adults
) and Shinkai et al.
2001 (bilateral force transducer in 731 adults
124 M. Bakke
and the biomechanics of the jaws and mastica-
tory muscles than to the classification of mor-
phological occlusion per se. As a consequence it
may be useful to routinely assess the occlusal
contact together with the morphological occlu-
sion of the teeth, and also take both into con-
sideration when planning and evaluating orth-
odontic treatment.
1. Hagberg C: Assessments of bite force: a review. J Crani-
omandib Disord 1:162-169, 1987
2. Bakke M, Michler L, Han K, et al: Clinical significance of
isometric bite force versus electrical activity in temporal
and masseter muscles. Scand J Dent Res 97:539-551,
3. Julien KC, Buschang PH, Throckmorton GS, et al: Nor-
mal masticatory performance in young adults and chil-
dren. Arch Oral Biol 41:69-75, 1996
4. Hatch JP, Shinkai RS, Sakai S, et al: Determinants of
masticatory performance in dentate adults. Arch Oral
Biol 46:641-648, 2001
5. Okiyama S, Ikebe K, Nokubi T: Association between
masticatory performance and maximal occlusal force in
young men. J Oral Rehabil 30:278-282, 2003
6. Bakke M: Mandibular elevator muscles: physiology, ac-
tion, and effect of dental occlusion. Scand J Dent Res
101:314-331, 1993
7. Shinogaya T, Bakke M, Thomsen CE, et al: Bite force
and occlusal load in healthy young subjects—a method-
ological study. Eur J Prosthodont Restor Dent 8:11-15,
8. Fernandes CP, Glantz PO, Svensson SA, et al: A novel
sensor for bite force determinations. Dent Mater 19:118-
126, 2003
9. Helkimo E, Carlsson GE, Helkimo M: Bite force and the
state of dentition. Acta Odontol Scand 35:297-303, 1977
10. Shiau YY, Wang JS: The effects of dental condition on
hand strength and maximum bite force. Cranio 11:48-
54; discussion 54, 1993
11. Ferrario VF, Sforza C, Serrao G, et al: Single tooth bite
forces in healthy young adults. J Oral Rehabil 31:18-22,
12. Tortopidis D, Lyons MF, Baxendale RH, et al: The vari-
ability of bite force measurement between sessions, in
different positions within the dental arch. J Oral Rehabil
25:681-686, 1998
13. Waltimo A, Kononen M: Bite force on single as opposed
to all maxillary front teeth. Scand J Dent Res 102:372-
375, 1994
14. Braun S, Bantleon HP, Hnat WP, et al: A study of bite
force, part 1: relationship to various physical character-
istics. Angle Orthod 65:367-372, 1995
15. Wenneberg B, Kjellberg H, Kiliaridis S: Bite force and
temporomandibular disorder in juvenile chronic arthri-
tis. J Oral Rehabil 22:633-641, 1995
16. Tortopidis D, Lyons MF, Baxendale RH: Bite force, en-
durance and masseter muscle fatigue in healthy edentu-
lous subjects and those with TMD. J Oral Rehabil 26:321-
328, 1999
17. Ahlberg JP, Kovero OA, Hurmerinta KA, et al: Maximal
bite force and its association with signs and symptoms of
TMD, occlusion, and body mass index in a cohort of
young adults. Cranio 21:248-252, 2003
18. Hansdottir R, Bakke M: Joint tenderness, jaw opening,
chewing velocity, and bite force in patients with tem-
poromandibular joint pain and matched healthy control
subjects. J Orofac Pain 18:108-113, 2004
19. Stohler CS: Muscle-related temporomandibular disor-
ders. J Orofac Pain 13:273-284, 1999
20. Stegenga B, Broekhuijsen ML, de Bont LG, et al: Bite-
force endurance in patients with temporomandibular
joint osteoarthrosis and internal derangement. J Oral
Rehabil 19:639-647, 1992
21. Manns A, Miralles R, Palazzi C: EMG, bite force, and
elongation of the masseter muscle under isometric vol-
untary contractions and variations of vertical dimension.
J Prosthet Dent 42:674-682, 1979
22. Paphangkorakit J, Osborn JW: Effect of jaw opening on
the direction and magnitude of human incisal bite
forces. J Dent Res 76:561-567, 1997
23. Pruim GJ, Ten Bosch JJ, de Jong HJ: Jaw muscle EMG-
activity and static loading of the mandible. J Biomech
11:389-395, 1978
24. Mao JJ, Major PW, Osborn JW: Coupling electrical and
mechanical outputs of human jaw muscles undertaking
multidirectional bite-force tasks. Arch Oral Biol 41:1141-
1147, 1996
25. Ferrrario VF, Sforza C, Zanotti G, et al: Maximal bite
forces in healthy young adults as predicted by surface
electromyography. J Dent 32:451-457, 2004
26. Van Eijden TM: Jaw muscle activity in relation to the
direction and point of application of bite force. J Dent
Res 69:901-905, 1990
27. Van Spronsen PH, Weijs WA, Prahl-Andersen B, et al:
Comparison of jaw-muscle bite-force cross-sections ob-
tained by means of magnetic resonance imaging and
high-resolution CT scanning. J Dent Res 68:1765-1770,
28. Bakke M, Tuxen A, Vilmann P, et al: Ultrasound image
of human masseter muscle related to bite force, electro-
myography, facial morphology, and occlusal factors.
Scand J Dent Res 100:164-171, 1992
29. Lamey PJ, Burnett CA, Fartash L, et al: Migraine and
masticatory muscle volume, bite force, and craniofacial
morphology. Headache 41:49-56, 2001
30. Raadsheer MC, van Eijden TM, van Ginkel FC, et al:
Human jaw muscle strength and size in relation to limb
muscle strength and size. Eur J Oral Sci 112:398-405,
31. Ringqvist M: Fibre sizes of human masseter muscle in
relation to bite force. J Neurol Sci 19:297-305, 1973
32. Thompson DJ, Throckmorton GS, Buschang PH: The
effects of isometric exercise on maximum voluntary bite
forces and jaw muscle strength and endurance. J Oral
Rehabil 28:909-917, 2001
125Bite Force and Occlusion
33. Bakke M, Stoltze K, Tuxen A: Variables related to mas-
seter muscle function: a maximum R2 improvement
analysis. Scand J Dent Res 101:159-165, 1993
34. Braun S, Hnat WP, Freudenthaler JW, et al: A study of
maximum bite force during growth and development.
Angle Orthod 66:261-264, 1996
35. Sonnesen L, Bakke M, Solow B: Bite force in pre-orth-
odontic children with unilateral crossbite. Eur J Orthod
23:741-749, 2001
36. Bakke M, Holm B, Jensen BL, et al: Unilateral, iso-
metric bite force in 868-year-old women and men
related to occlusal factors. Scand J Dent Res 98:149-
158, 1990
37. Miyaura K, Matsuka Y, Morita M, et al: Comparison of
biting forces in different age and sex groups: a study of
biting efficiency with mobile and non-mobile teeth.
J Oral Rehabil 26:223-227, 1999
38. Shinogaya T, Bakke M, Thomsen CE, et al: Effects of
ethnicity, gender and age on clenching force and load
distribution. Clin Oral Investig 5:63-68, 2001
39. Tuxen A, Bakke M, Pinholt EM: Comparative data from
young men and women on masseter muscle fibres, func-
tion and facial morphology. Arch Oral Biol 44:509-518,
40. Ingervall B, Helkimo E: Masticatory muscle force and
facial morphology in man. Arch Oral Biol 23:203-206;
discussion 423-424, 1978
41. Throckmorton GS, Finn RA, Bell WH: Biomechanics of
differences in lower facial height. Am J Orthod 77:410-
420, 1980
42. Proffit WR, Fields HW, Nixon WL: Occlusal forces in
normal- and long-face adults. J Dent Res 62:566-571,
43. Braun S, Bantleon HP, Hnat WP, et al: A study of bite
force, part 2: relationship to various cephalometric mea-
surements. Angle Orthod 65:373-377, 1995
44. Ingervall B, Minder C: Correlation between maximum
bite force and facial morphology in children. Angle
Orthod 67:415-424, 1997
45. Throckmorton GS, Ellis E, Buschang PH: Morphologic
and biomechanical correlates with maximum bite forces
in orthognathic surgery patients. J Oral Maxillofac Surg
58:515-524, 2000
46. Kitai N, Fujii Y, Murakami S, et al: Human masticatory
muscle volume and zygomatico-mandibular form in
adults with mandibular prognathism. J Dent Res 81:752-
756, 2002
47. Moller E: The chewing apparatus. An electromyographic
study of the action of the muscles of mastication and its
correlation to facial morphology. Acta Physiol Scand
Suppl 280:1-229, 1966
48. Tsuga K, Carlsson GE, Osterberg T, et al: Self-assessed
masticatory ability in relation to maximal bite force and
dental state in 80-year-old subjects. J Oral Rehabil 25:
117-124, 1998
49. Hidaka O, Iwasaki M, Saito M, et al: Influence of clench-
ing intensity on bite force balance, occlusal contact area,
and average bite pressure. J Dent Res 78:1336-1344, 1999
50. Bakke M, Michler L, Moller E: Occlusal control of mandibu-
lar elevator muscles. Scand J Dent Res 100:284-291, 1992
51. Morita M, Nishi K, Kimura T, et al: Correlation between
periodontal status and biting ability in Chinese adult
population. J Oral Rehabil 30:260-264, 2003
52. Gibbs CH, Anusavice KJ, Young HM, et al: Maximum
clenching force of patients with moderate loss of posterior
tooth support: a pilot study. J Prosthet 88:498-502, 2002
53. Miyaura K, Morita M, Matsuka Y, et al: Rehabilitation of
biting abilities in patients with different types of dental
prostheses. J Oral Rehabil 27:1073-1076, 2000
54. Shinkai RSA, Hatch JP, Sakai S, et al: Oral function and
diet quality in a community-based sample. J Dent Res
80:1625-1630, 2001
55. Shinogaya T, Toda S: Rehabilitation of occlusal support
by removable partial dentures with free-end saddles. Eur
J Prosthodont Restor 11:107-113, 2003
56. Fontijn-Tekamp FA, Slagter AP, van der Bilt A, et al:
Biting and chewing in overdentures, full dentures and
natural dentitions. J Dent Res 79:1519-1524, 2000
57. Bakke M, Holm B, Gotfredsen K: Masticatory function
and patient satisfaction with implant-supported mandib-
ular overdentures: a prospective 5.year study. Int J
Prosthodont 15:575-581, 2002
58. van Kampen FM, van der Bilt A, Cune MS, et al: The
influence of various attachment types in mandibular
implant-retained overdentures on maximum bite force
and EMG. J Dent Res 81:170-173, 2002
59. Yawaka Y, Hironaka S, Akiyama A, et al: Changes in
occlusal contact area and average bite pressure during
treatment of anterior crossbite in primary dentition.
J Clin Pediatr Dent 28:75-79, 2003
60. Sonnesen L, Bakke M, Solow B: Malocclusion traits and
symptoms and signs of temporomandibular disorders in
children with severe malocclusion. Eur J Orthod 20:543-
559, 1998
61. Tsai HH: Maximum bite force and related dental status
in children with deciduous dentition. J Clin Pediatr Dent
28:139-42, 2004
62. Sonnesen L, Bakke M: Molar bite force in relation to
occlusion, craniofacial dimensions, and head posture
in pre-orthodontic children. Eur J Orthod 27:58-63,
63. Bakke M, Michler L: Temporalis and masseter muscle
activity in patients with anterior open bite and cranio-
mandibular disorders. Scand J Dent. Res 99:219-228,
64. Rentes AM, Gaviao MB, Amaral JR: Bite force determi-
nation in children with primary dentition. J Oral Rehabil
29:1174-1180, 2002
126 M. Bakke
... The significance of the vertical distance between the bite (mastication) pads during the measurements is explained [15,18]. The bite plate spacing was adjusted to 1.5 cm in accordance with the literature [15,44,45]. The pain threshold was lowered by coating the bite platforms with flexible epoxy resin. ...
... The presence and number of natural teeth in the mouth are essential, and tooth loss reduces mastication efficiency. It is reported that the mean mastication efficiency of individuals using prostheses is 24% [55], while in the posterior (premolar-molar) region of individuals with natural teeth, the mean masticatory forces can be between 300 and 600 N (30.5-61.1 kg) [44]. Some individuals habit unilateral mastication, and the interocclusal masticatory forces on the balancing side are half that of the functional side. ...
... The anterior segment (intercanine) findings in this study are consistent with the findings of Tortopidis and Gökcan [15,58]. The posterior segment (premolar-molar region) results are observed to be compatible with the results of Klatsky, Tortipidis, Gökcan, Brudevold, Klaffenbach, and Bakke [15,21,24,26,44,58] (Table V). ...
Full-text available
Objectives: Intraoral forces can be affected by several factors, including craniofacial dimensions, muscles, teeth status, and age. This study aims to reveal a possible correlation between maximum vertical interocclusal bite and masticatory forces and the total mandible length. Materials and methods: The law of the lever was used to elucidate the mastication function by recording the occlusion and phases of mastication movements. A total of 115 people, 18 females, and 97 males, participated in the study. The midpoints of Gnathion (Gn), and Condyle (Co) were selected on the digital radiographs, and line connecting these points were used. Bite, and masticatory forces were measured in the anterior (intercanine) and posterior (premolar-molar) segments. Pearson correlation and multiple regression analyses were performed to evaluate the relationship between mandibular measurements and masticatory force. Results: Total mandible length varied between 11.0 and 13.0 cm in females and between 10.3 and 13.9 cm in males. The bite force of the anterior segment was found to be 34.2–52.1 kg in females and 27.0–61.2 kg in males, whereas posterior segment masticatory forces were determined between 45.0 and 69.0 kg in females and 36.8–93.6 kg in males. A weak positive correlation was found between the posterior segment and total mandibular length (p = 0.016) in the study. However, no correlation was found between the anterior segment and total mandibular length (p = 0.733). Conclusion: The results of the current study point to the fact that, as the total length of the mandible increase, the posterior segment masticatory forces increase as well. However, this relationship is relatively weak.
... Maximum bite force (MBF) is an indicator of the functional state of the masticatory system [1]. Individual MBF has been used to evaluate jaw muscle functionality and activity and the therapeutic effect of prosthetic devices [2]; it is considered important in the diagnosis of the disturbances of the stomatognathic system. ...
... From the characterization of the device, if the distance R1 between the application point of F1 and the fulcrum of the device is greater than the distance R2 for F2, then the sensor momentum (Ms = Fs·Rs) is equal to the momentum at the upper incisal teeth (M1 = F1·R1) because the top element of the device works as a hyperstatic beam and the force F3 is equal to zero. Conversely, if R1 is smaller than R2, then Ms is proportional to the momentum at the upper lower incisal teeth (M2 = F2·R2), and F4 is equal to zero, see Equation (1). Therefore, the force recorded by the sensor depends on the distance between the sensor and the most distant incisal application point. ...
Full-text available
Assessing maximum voluntary bite force is important to characterize the functional state of the masticatory system. Due to several factors affecting the estimation of the maximum bite force, a unique solution combining desirable features such as reliability, accuracy, precision, usability, and comfort is not available. The aim of the present study was to develop a low-cost bite force measurement device allowing for subject-specific customization, comfortable bite force expression, and reliable force estimation over time. The device was realized using an inexpensive load cell, two 3D printed ergonomic forks hosting reusable subject-specific silicone molds, a read-out system based on a low-cost microcontroller, and a wireless link to a personal computer. A simple model was used to estimate bite force taking into account individual morphology and device placement in the mouth. Measurement reliability, accuracy, and precision were assessed on a calibration dataset. A validation procedure on healthy participants was performed to assess the repeatability of the measurements over multiple repetitions and sessions. A 2 % precision and 2 % accuracy were achieved on measurements of forces in the physiological range of adult bite forces. Multiple recordings on healthy participants demonstrated good repeatability (coefficient of variation 11 %) with no significant effect of repetition and session. The novel device provides an affordable and reliable solution for assessing maximum bite force that can be easily used to perform clinical evaluations in single sessions or in longitudinal studies.
... Bite force results from the action of the jaw elevator muscles, as modified by jaw biomechanics and reflex mechanisms, and may vary widely in magnitude and direction [1]. The determination of bite force is considered an important parameter in assessing the function and efficacy of dental prostheses and orthodontic treatments and in studying the effect of deformities and pathologies, such as malocclusion and over loading, on the masticatory system [2]. ...
... In view of the studies that demonstrated higher occluding forces on teeth adjacent to dental implants [23] and a higher incidence of VRFs in endodontically treated teeth adjacent to implants [24], our findings could be interpreted as a psychophysical fear of damaging abutment teeth, implants, or prostheses. This concern about causing damage or generating pain and tenderness in the teeth, supportive structures, temporomandibular joint, or masticatory muscles during the measurements might have a negative influence on bite force measurements [1]. There are other possible reasons that can generate discomfort biting on a successful dental implant. ...
Full-text available
The aims of the current study were as following: (1) to evaluate the maximal bite forces in patients with dental implants versus patients without dental implants, as measured by a digital bite force transducer (GM10); (2) to evaluate the influences of sex, age, and sleep/awake bruxism on the maximal bite forces of the two groups. Forty patients recruited to the study were divided into two groups: test group (“implant”) if they had one or more posterior restored implants and control group (“no-implant”) without the presence of posterior dental implants. A digital bite fork (GM10) was used to measure the bite forces from three posterior occluding pairs in all participants. Differences in the mean values between the test and control groups and between different sexes were evaluated using one-way and two-way ANOVA tests. A cross-tabulation analysis was conducted to identify a trend line between the groups. There was no significant difference in the maximal bite force between the test and control groups (p = 0.422), but the cross-tabulation analysis revealed a clear trend of a stronger representation of the “no-implant” group at higher occlusal forces. A significant difference was detected between the maximal biting forces of male and female subjects (p = 0.030 in the implant group, p = 0.010 in the no-implant group), regardless of the experimental group. The presence of bruxism and clenching did not influence the bite force values (p = 0.953), and a significant difference was not found between the age groups (p = 0.393). Within the limitations of this study, it may be assumed that there was no significant difference between the maximal bite forces between patients with and without dental implants but that there was a trend line implicating a stronger representation of the “no-implant” group at higher forces. In addition, the results revealed a significant sex-related difference in the maximal occlusal force. Further studies with larger sample sizes are warranted.
... Patient's age and sex had no significant influence on the survival of single crowns. The magnitude of the biting force is higher in men than women [12][13][14]54] and decreases significantly after 50 years of age [13]. However, number of teeth has been reported as the most important factor affecting the magnitude of the biting force rather than patient's age and sex [13]. ...
The purpose of the study was to investigate the influence of multiple factors on the survival of tooth‐supported single crowns and assess the biological and technical complications. This retrospective study included patients rehabilitated with single crowns with a minimum follow‐up time of 6 months after delivery. The cumulative survival rate was calculated over the maximum period of follow‐up time and reported in a life‐table survival analysis. Univariate and multivariate Cox regression was used to evaluate the associations between clinical covariates and crown failure. The included cohort group consisted of 1037 single crowns delivered in 401 patients and followed for a mean of 134.8 ± 80.2 months. Cumulative survival rate was 89.9% and 80.9% after 5 and 10 years and 70.5% and 61.8% after 15 and 20 years, respectively. The main reasons for single crown failure were loss of retention, tooth loss, and fracture. Anterior placement, non‐vital abutments, and bruxism significantly influenced the survival of single crowns. The survival of single crowns was not influenced by patient's age and sex, location of the crowns in relation to the jaws, type of tooth, presence of post and core, and type of crown material, treatment providers, or smoking. Anterior placement, non‐vital abutments, and bruxism are factors suggested to increase the risk of single crown failure and the prevalence of technical and biological complications.
... In addition, the physiology of aging leads to atrophy of the masticatory muscles (sarcopenia, hypoactivity of the chewing muscles) [51]. This process is further intensified by tooth loss [52] and results in a decrease of the maximum jaw closing force [8,53,54]. Furthermore, impaired motor skills in people with dementia appear to contribute to a reduced chewing efficiency [49] and an overall impaired masticatory function [49,55]. The negative effect which reduced cognitive abilities have on motor skills is more pronounced than the negative influence of a poor dentition on the cognitive state [56]. ...
Full-text available
Until now, no study has investigated the effects of masticatory muscle training on chewing function in people with dementia. This study aimed to investigate whether physiotherapeutic exercises for the masticatory muscles have an influence on chewing efficiency and bite force in people with dementia. In a clinical trial with stratified randomization subjects were assigned to three groups based on the Mini Mental State Examination (MMSE: group 1—28–30, group 2—25–27, group 3—18–24). Each group was divided into an experimental (ExpG, intervention) and control group (ConG, no intervention). As intervention a Masticatory Muscle Training (MaMuT) (part 1: three physiotherapeutic treatments and daily home exercises, part 2: daily home exercises only) was carried out. Chewing efficiency and bite force were recorded. The MaMuT influenced the masticatory performance regardless of the cognitive state. Bite force increased in ExpG 1 and 2. Without further training, however, the effect disappeared. Chewing efficiency increased in all ExpG. After completion of the training, the ExpG 2 and 3 showed a decrease to initial values. Subjects of ExpG 1 showed a training effect at the final examination, but a tendency toward the initial values was observed. ExpG 3 seemed to benefit most from the physiotherapeutic exercises in terms of improving chewing efficiency by the end of the intervention phase. ExpG 1 showed the greatest gain in bite force. The MaMuT program is a potential method of improving masticatory performance in people with cognitive impairment or dementia when used on a daily basis.
... A useful indicator of the functional state of the stomatognathic system and the load on teeth is the maximum bite force. 5 So, considering the inadequate studies in the literature regarding comparison of various fixation techniques in the mandibular anterior region (interforamina) and its association with bite force, this study aims to compare the clinical outcome of the open reduction and internal fixation of symphysis fracture with conventional and perpendicular plating system along with changes in the bite force at varying intervals among both the groups. ...
Full-text available
In the conventional method of fixation of symphyseal fractures, 2 miniplates are fixed in the interforamina region of the mandible at the lateral cortex. However, with the better understanding of tension and compression areas defined according to the place of energy insertion, it is now possible to fix miniplates at the lower border of the mandible. In this study we assumed that the application of perpendicular miniplates, in contrast to the placement of the plates on the lateral surface of the mandibular cortex, will constrict the motion in horizontal as well as vertical planes leading to better functional outcomes, which can be evaluated by measuring bite forces. The results obtained were affirmative with the hypothesis.
The interest to characterize texture‐modified foods (TMFs) intended for people with oropharyngeal dysphagia (OD) has grown significantly since 2011. Several instrumental and sensory techniques have been applied in the analysis of these foods. The objective of the present systematic review was to identify the most appropriate techniques, especially for the food industry and clinical setting. The search was carried out in three online databases according to the “Preferred Reporting Items for Systematic Reviews and Meta‐Analyses” (PRISMA). Across the multiple trials reviewed, Texture Profile Analysis and the Uniaxial Compression Test were most used as the instrumental technique for solid foods, and the Back Extrusion Test for fluid and semisolid foods. All trials used descriptive analysis as the sensory technique. However, the experimental conditions of the trials lacked standardization. Consequently, the results of the trials were not comparable. To properly characterize the texture of TMFs intended for OD by each technique, an international consensus is needed to establish standardized experimental conditions. Methods based on these techniques should also be validated by collaborative studies to verify repeatability, replicability, and reproducibility.
Background/purpose Rotating mandible backward downward is one of the treatment options in non-surgical skeletal class III malocclusion. The purpose of this study was to compare the true vertical changes after camouflage orthodontic treatment of adult patients with skeletal class III malocclusion categorized by vertical facial type. Materials and methods This retrospective study included 27 adult patients (age >18 years) with skeletal class III malocclusion (ANB<1°) who underwent nonsurgical orthodontic treatment at Taipei Veterans General Hospital. The patients were divided into the low-angle (SN-MP<28°), high-angle (SN-MP>36°), and normal-angle (28°≤ SN-MP ≤ 36°) groups according to the original vertical facial pattern. Pretreatment (T1) and post-treatment (T2) lateral cephalograms were superimposed and treatment changes were evaluated. Results In all cases, proper overjet and occlusion were achieved after treatment, and the lower anterior facial height increased with the backward rotation of the mandibular plane. Increase in vertical dimension was the most obvious in the high-angle group, while it was the least obvious in the low-angle group. Extrusion of both the maxillary and mandibular incisors was observed in the high-angle group; however, intrusion of the maxillary and mandibular incisors and decreased overbite were observed in the low-angle group. Conclusion Camouflage orthodontic treatment of skeletal class III malocclusion improves the facial profile by increasing the vertical dimension and clockwise rotation of the mandible. According to our results, patients with a high mandibular plane angle showed better response to vertical dimension increment treatment mechanics than those with low and normal mandibular plane angles.
Background: Bite is an important function of the human stomatognathic system. Despite this, it is commonly impaired in temporomandibular disorder (TMD) populations. The aim of this review is to evaluate the effectiveness of conservative interventions on self-reported and physical measures of bite function in individuals with TMD. Methods: This review was performed in compliance with PRISMA guidelines. An electronic search was performed on databases including Pubmed, CINAHL, Embase, and Cochrane Central. Inclusion criteria were journal articles evaluating the effect of any non-pharmacological conservative interventions on bite function in participants diagnosed with TMD. Risk of bias for individual studies was assessed using the Cochrane risk-of-bias v2 tool, and the NIH NHLBI pre-post tool. Data was synthesised based on outcome measures of bite function, and the quality of evidence was assessed using the Grading of Recommendations Assessment, Development and Evaluation approach. Results: Eleven studies were eligible for this review. Interventions included splinting, photobiomodulation, needling, exercise, manual therapy, and patient education; which were evaluated using mastication-related pain, self-reported chewing difficulty, and bite force/endurance outcome measures. Findings suggested manual therapy, needling, oral splinting, exercise and PBM interventions may improve bite function in TMD, although confidence in cumulative evidence ranged from moderate to very low. There was no evidence that patient education improved bite function. Conclusion: Conservative interventions may be helpful to address bite-related impairments associated with TMD, although further research is needed to improve the quality of evidence and direct clinical guidelines.
Full-text available
In spite of differences in embryologic origin, central nervous organization, and muscle fiber distribution, the physiology and action of mandibular elevator muscles are comparable to those of skeletal muscles of the limbs, back, and shoulder. They also share the same age-, sex-, and activity-related variations of muscular strength. With respect to pathogenesis, the type of muscular performance associated with the development of fatigue, discomfort, and pain in mandibular elevators seems to be influenced by the dental occlusion. Clinical research comparing the extent of occlusal contact in patients and controls as well as epidemiologic studies have shown reduced occlusal support to be a risk factor in the development of craniomandibular disorders. In healthy subjects with full natural dentition, occlusal support in the intercuspal position generally amounts to 12–14 pairs of contacting teeth, with predominance of contact on first and second molars. The extent of occlusal contact clearly affects electric muscle activity, bite force, jaw movements, and masticatory efficiency. Neurophysiologic evidence of receptor activity and reflex interaction with the basic motor programs of craniomandibular muscles tends to indicate that the peripheral occlusal control of the elevator muscles is provided by feedback from periodontal pressoreceptors. With stable intercuspal support, especially from posterior teeth, elevator muscles are activated strongly during biting and chewing with a high degree of force and masticatory efficiency, and with relatively short contractions, allowing for pauses. These variables of muscle contraction seem, in general, to strengthen the muscles and prevent discomfort. Therefore, occlusal stability keeps the muscles fit, and enables the masticatory system to meet its functional demands.
The type of attachment that is used in oral rehabilitation by means of implant-retained mandibular overdentures may influence the retention and the stability of the denture. In this study, we examined the hypothesis that a better retention and stability of the denture improve the oral function. Eighteen edentulous subjects received 2 permucosal implants, a new denture, and, successively, 3 suprastructure modalities. Maximum bite force and electrical activity of the masseter and temporalis muscles were measured. The maximum bite force nearly doubled after treatment for each of the 3 attachments. However, the average bite force after treatment was still only two-thirds of the value obtained for dentate subjects. No large differences in maximum bite force and muscle activity were found among the 3 attachment types. Temporalis activity was significantly lower than masseter activity when subjects clenched without implant support. There was no difference in activity when subjects clenched with implant support.
Although several investigators have reported associations between masticatory muscles and skeletal craniofacial form, there is no agreement on the association. We tested the hypothesis that masticatory muscle volume correlates with the size and form of the adjacent local skeletal sites. For this purpose, we investigated the morphological association of the cross-sectional area and volume of temporal and masseter muscles with zygomatico-mandibular skeletal structures using computerized tomography (CT) in 25 male adults with mandibular prognathism. Muscle variables significantly correlated with widths of the bizygomatic arch and temporal fossa but not with the cranium width. Masseter volume significantly correlated with cross-sectional areas of the zygomatic arch and mandibular ramus. Masseter orientation was almost perpendicular to the zygomatic arch and mandibular antegonial region. The zygomatic arch angle significantly correlated with the antegonial angle. The results of the study suggest that the masticatory muscles exert influence on the adjacent local skeletal sites.
Piezoelectric force transducer and hand dynamometer were used for measuring the maximum bite force and hand grasp force on 2034 primary, middle, and high school students. Dental condition and body weight and height were also observed to relate to the force measurements. It was discovered that both forces increased relative to the increase of age, body weight, and body height. Boys had stronger bite force than girls at all age groups, while the grasp force of boys became significantly stronger only after the age of 13. Students who had dentition with decay and missing teeth tended to have weaker bite force, while hand force was not influenced. Bite force does not seem parallel to hand strength and is, instead, related to dental condition.
SUMMARY The present study reports the prevalence of the various traits of malocclusion, as well as the occurrence of associations between malocclusion, and symptoms and signs of temporomandibular disorders (TMD) in children selected for orthodontic treatment by the new Danish procedure for screening the child population for severe malocclusions entailing health risks. The sample comprised 104 children (56 F, 48 M) aged 7‐13. Malocclusion traits were recorded at the time of selection, symptoms and signs of TMD were recorded at recall. The most prevalent malocclusion traits were distal molar occlusion (Angle Class II; 72 per cent), crowding (57 per cent), extreme maxillary overjet (37 per cent) and deep bite (31 per cent). Agenesis or peg-shaped lateral teeth were observed in 14 per cent of the children. The most prevalent symptom of TMD was weekly headache (27 per cent); the most prevalent signs of TMD were tenderness in the anterior temporal, occipital, trapezius, and superficial and profound masseter muscles (39‐34 per cent). Seven per cent of the children were referred for TMD treatment. The Danish TMD screening procedure was positive in 26 per cent, while 20 per cent had severe symptoms (AiII), and 30 per cent had moderate signs (DiII) according to Helkimo (1974). Symptoms and signs of TMD were significantly associated with distal molar occlusion, extreme maxillary overjet, open bite, unilateral crossbite, midline displacement, and errors of tooth formation. The analysis suggests that there is a higher risk of children with severe malocclusions developing TMD. Errors of tooth formation in the form of agenesis or peg-shaped lateral teeth showed the largest number of associations with symptoms and signs of TMD; these associations have not previously been reported in the literature.
A multiple linear regression analysis, with stepwise maximum R2 improvement technique by forward selection and pair switching, was used to select the occlusal, morphologic, and histologic variables which explained most of the variation in bite force and electric masseter muscle activity. The variables comprised tooth contact and facial morphology together with thickness and fiber characteristics of the masseter muscle. The study included 13 healthy women, 21–28 yr of age, with a minimum of 24 teeth and no serious malocclusion. Significant exploratory models (R2: 0.55–0.85) were shown concerning bite force, and electromyographic amplitude during resting posture, maximal voluntary contraction (ICP), and unilateral chewing, as well as contraction time (chewing side). Muscle thickness and molar contact had a significant, positive effect on the level of forceful muscle contraction. The explorative model both demonstrated explicable relations, and offered better insight into interrelations than did univariate analysis.
Occlusal stability and mandibular elevator muscle function was studied in 25 women (20–30 yr of age). They had 27–32 fully erupted teeth with few treated occlusal surfaces, and craniomandibular function including mandibular mobility was normal. The aim was to analyze the influence of natural patterns of occlusal contact on electromyographic activity, unaffected by pain and functional disorders. Occlusal stability was assessed in the intercuspal and in lateral contact positions as the number of teeth with physical contact and the number of opposing pairs of teeth in contact. Electromyographic activity was recorded by surface electrodes over anterior and posterior temporalis and masseter muscles. In general, positive correlations were found between occlusal stability in intercuspal position and moderate to strong static and dynamic contractions, most significant in masseter muscles, indicating that forceful contraction of these muscles implies stable occlusion. Systematically, the duration of activity during chewing was negatively correlated with occlusal stability in the intercuspal position, most pronounced in working-side muscles. This pointed to shorter contractions with stable occlusion and is interpreted as the result of less need for stabilizing activity. It is concluded, that the correlations between occlusal stability and elevator muscle function are probably based on feedback mechanisms from periodontal pressoreceptors.
Abstract – Activity in temporalis and masseter muscles, and traits of facial morphology and occlusal stability were studied in 22 patients (19 women, 3 men; 15–45 yr of age) with anterior open bite and symptoms and signs of craniomandibular disorders. Facial morphology was assessed by profile radiographs, occlusal stability by tooth contacts, and craniomandibular function by clinical and radiological examination. Electromyographic activity was recorded by surface electrodes after primary treatment with a reflex-releasing, stabilizing splint. Maximal voluntary contraction was reduced compared to reference values, particularly in subjects with muscular affection, but maximal activity increased significantly when biting on the splint. Maximal voluntary contraction was positively correlated to molar contact and negatively to anterior face height, mandibular inclination, vertical jaw relation and gonial angle. Relative loading of the muscles was markedly increased during resting posture. It was concluded that reduced occlusal stability and long-face morphology were associated with weak elevator muscle activity with disposition overload and tenderness. The results also indicated that increase of occlusal stability might lead to increased muscle strength and possibly reduce risk of physical strain.
The relation between EMG activity, bite force, and muscular elongation was studied in eight subjects with complete natural dentition during isometric contractions of the masseter muscle, measured from 7 mm to almost maximum jaw opening. EMG was registered with superficial electrodes and bite force with a gnathodynamometer. In series 1, recordings of EMG activity maintaining bite force constant (10 and 20 kg) show that EMG is high when the bite opening is 7 mm, decreases from 15 to 20 mm, and then increases again as jaw opening approaches maximum opening. In series 2, recordings of bite force maintaining EMG constant show that bite force increases up to a certain range of jaw opening (around 15 to 20 mm) and then decreases as we approach maximum jaw opening. Results show that there is for each experimental subject a physiologically optimum muscular elongation of major efficiency where the masseter develops highest muscular force with least EMG activity.
A two-dimensional model which allows calculation of mechanical advantage of the human temporalis and masseter muscles is presented. The model is manipulated to demonstrate how selected differences in facial morphology affect the mechanical advantage of the muscles. The model is then used to evaluate the differences in mechanical advantage between patients with the long face syndrome and those with the short face syndrome. Differences in facial morphology between these two groups result in significant differences in the mechanical advantages of their muscles. Mechanical advantage may, in part, explain observed differences in bite force between the two groups. The model suggests that some surgical procedures used to correct facial disharmonies may have a significant effect on the mechanical advantage of the jaw muscles.