Sadamori et al.

Int Chin J Dent 2007; 7: 43-47.

Quantitative analysis of occlusal force balance in intercuspal
position using the Dental Prescale system in patients withtemporomadibular disorders
Shinsuke Sadamori, DDS, PhD,a Hiroo Kotani, DDS, PhD,b Hitoshi Abekura, DDS,PhD,a and Taizo Hamada, DDS, PhDaa

Department of Prosthetic Dentistry, Programs for Applied Biomedicine Division of CervicoGnathostomatology, Hiroshima University Graduate School of Biomedical Sciences, andbKotani Dental Office, Hiroshima, Japan
Purpose: This study evaluated the quantitative analysis of occlusal data (occlusal contact areas, maximum
pressure, mean pressure, occlusal force, and occlusal force balance) in intercuspal position in both healthy
subjects and patients with temporomadibular disorders (TMD).
Materials and Methods: The occlusal data in intercuspal position were measured using the Dental Prescale
system in 15 healthy persons and 16 patients with TMD, i.e., myofascial pain dysfunction syndrome (MPDgroup; eight patients) and disorders of the temporomandibular joints (TMJ group; eight patients). Forceasymmetry index (force AI) was calculated to evaluate the occlusal force balance of the right and left sides.
Results: The value of the force AI of MPD patients was higher than that of healthy subjects. The mean ofpressures and force AI of TMJ patients were higher than those of healthy subjects. The values of occlusal
contact areas and occlusal force in TMJ patients were lower than those in healthy subjects, while the values ofocclusal contact areas and occlusal force in MPD patients were higher than those in TMJ patients.
Conclusion: These data in this study suggest that the force asymmetry index is suitable as the parameter of TMD.
(Int Chin J Dent 2007; 7: 43-47.)
Key Words: asymmetry index, Dental Prescale system, occlusal force balance, temporomadibular disorders.

Introduction
Improper occlusion is one of the important etiologic factors in temporomadibular disorders (TMD).1
Unilateral tooth clenching may alter the mechanical relationship of jaw closure; it produces strain a single
muscle unlike bilateral tooth clenching and therefore, contributes to more severe damage to the stomatognathicsystem.2 Furthermore one aim of treatment of trauma from occlusion and bruxism is to achieve simultaneous
bilateral contact in both the intercuspal (centric occlusion) and the retruded position (centric relation). It is thus
necessary for stability of occlusion to achieve balance of right and left side of dental arch.
Occlusal forces and balance in intercuspal position have been examined by various methods.3-13 A recently
developed photo-occlusion technique allows simultaneous quantitative optical recording of occlusal contacts.
The Dental Prescale system consists of pressure sensitive sheets and an analyzing computer. The sheet is 0.098
mm thickness and flexible.

This system analyses occlusal contact areas, mean pressure, occlusal forces,percentage of areas within a limit of pressure measurement, and occlusal force balance in near inter-cuspal
position.

Occlusal histories can become a permanent part of the patient's record because this recorded

information can be printed or stored in the computer with the software program.
The purpose of this study was to evaluate occlusal contact areas, maximum pressure, mean pressure, occlusal
forces, and occlusal force balance were examined in both healthy subjects and patients with TMD, using theDental Prescale system.

Materials and Methods
Subjects
Healthy subjects consisted of 15 volunteers without clinical evidence of dysfunction of the stomatognathic

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Int Chin J Dent 2007; 7: 43-47.

system and with class I molar relation with stable occlusions in the intercuspal position (ICP). The patients weredivided into the MPD group (eight patients with muscle symptoms of myofascial pain dysfunction syndrome),
and the TMJ group (eight patients with disorders of the temporomandibular joints) according to the previous
study.14 The MPD patients had moderate or severe symptoms of MPD syndrome and the TMJ group wascomposed of patients with disorders of the TMJs, such as TMJ internal derangement with and without reduction
and degenerative joint disease. The patients were classified by the history and condition of present illness andradiographs. Table 1 shows the gender distribution of the subjects.
Table 1.

Gender distribution of the subjects.
Healthy group

MPD group

TMJ group

Total

MaleFemale

9644171417

Total

158831

Recording procedure
Occlusal forces and balance were measured by a Dental Prescale system (Fuji Photo Film, Tokyo, Japan)
consists of the pressure sensitive sheets (Dental Prescale, Fuji Photo Film, Tokyo, Japan) and an analyzing
computer (Occluzer, GC Corp., Tokyo, Japan). All subjects were asked to sit upright and occlude on the Dental
Prescale (50H, type R), in ICP with maximum clenching level for one second. After the Dental Prescale wasremoved, Occluzer was used to evaluate the occlusally recorded colorations (pattern).
Denal Prescale consists of color-developing materials and various sizes of microcapsules containingcolor-producing materials which are coated on the polyethylene-terephthalate (PET) resin film, and wrappedwith PET films on both sides. The foil shows coloration depending on pressure. According to the level of thepressure applied (occlusal pressure and force), color formation occurs in different densities. Formed colors on
the sheets are read out by an Occluzer-contained color image scanner, the identified color density and area data
can be used to estimate the magnitude of the occlusal pressure and force.15 To evaluate the occlusal force
balance of the right and left sides, the asymmetry index (AI), advocated by Naeije et al.16 was modified for thisstudy as follows:force Asymmetry Index (AI) = ｜Occlusal force (Right) - Occlusal force (Left) ｜ x 100
x ｜Occlusal force (Right) + Occlusal force (Left) ｜-1 (%)
Statistical evaluation was based on Mann-Whitney U-test. The results were analyzed by the StatView Version
4.0 software (Abacus Concepts, Inc., Berkeley, CA, USA).

Results
Table 2 shows data of occlusal contact areas, maximum pressure, mean pressure, occlusal forces, and occlusal
force balances (force AI) of healthy subjects and p values analyzed by Mann-Whitney U-test. There is nosignificant difference (p>0.05) between the occlusal data of male and female. However the values of occlusal
contact areas and occlusal forces in males tended to be greater than those in females.
Table 3 shows data of healthy subjects and MPD patients. MPD patients demonstrate difference from thehealthy subjects in the force asymmetry index (force AI). The value of the force AI of MPD patients is higher

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Int Chin J Dent 2007; 7: 43-47.

than that of healthy subjects (p=0.0141).
Table 2.

Means and SDs of occlusal data in healthy subjects.

SubjectOcclusal contact areas
(mm2)
Mean
SD

Maximum pressure
(MPa)
Mean
SD

Mean pressure(MPa)
MeanSD

Occlusal force(N)
MeanSDforce AI(%)
MeanSD

Male
Female

21.5
16.7

112.6
113.2

40.0
41.4

861.5
687.0

3.4
7.0

p-value

0.1255

5.2
5.5

8.4
7.3

0.85703.6
3.0

0.3458

219.5
213.4

0.19494.1
4.2

0.0582

Subject number: Male=9, Female=6. The p-values were analyzed by Mann-Whitney U-test.

Table 3.

Means and SDs of occlusal data in MPD patients and healthy subjects.

SubjectOcclusal contact areas
(mm2)
Mean
SD

MPD group
21.7
Healthy group 19.6
p-value

7.8
5.7

0.4577

Maximum pressure(MPa)
MeanSD

Mean pressure(MPa)
MeanSD

Occlusal force(N)
MeanSDforce AI(%)
MeanSD

116.3
112.8

42.9
40.6

896.9
791.7

18.5
4.9

7.3
7.7

0.15096.9
3.3

0.4578

274.1
227.2

0.366218.5
4.40.0141

Subject number: MPD group=8, Healthy group=15. The p-values were analyzed by Mann-Whitney U-test.

TMJ patients demonstrated differences from healthy subjects in occlusal contact areas, mean pressure,occlusal forces, and the force AI (Table 4). There are significant differences (p=0.0108, 0.0453, 0.0332, and0.0012) in occlusal contact areas, mean pressure, occlusal forces, and force AI, respectively.
Table 4.

Means and SDs of occlusal data in TMJ patients and healthy subjects.

SubjectOcclusal contact areas(mm2)
MeanSD

TMJ group
12.5
Healthy group 19.6
p-value

5.1
5.7

0.0108Maximum pressure(MPa)
MeanSD

Mean pressure(MPa)MeanSD

Occlusal force(N)
MeanSDforce AI(%)
MeanSD

117.7
112.8

43.5
40.6

538.3
791.7

27.9
4.9

6.3
7.7

0.06481.7
3.3

0.0453

204.3
227.2

0.033216.5
4.4

0.0012

Subject number: TMJ group=8, Healthy group=15. The p-values were analyzed by Mann-Whitney U-test.

Table 5.

Means and SDs of occlusal data in MPD and TMJ patients.

SubjectOcclusal contact areas(mm2)
MeanSD

Maximum pressure(MPa)
MeanSD

Mean pressure(MPa)MeanSD

Occlusal force(N)
MeanSDforce AI(%)
MeanSD

MPD group
TMJ group

21.7
12.5

116.3
117.7

42.9
43.5

896.9
538.3

18.5
27.9

p-value0.0208

7.8
5.1

7.3
6.3

0.89030.3442

6.9
1.7

274.1
204.3

0.011718.5
16.5

0.2936

Subject number: MPD group=8, TMJ group=8. The p-values were analyzed by Mann-Whitney U-test.

The data of MPD and TMJ patients was shown in Table 5. There are significant differences (p=0.0208, andp=0.0117) in occlusal contact areas and occlusal force, respectively.

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Int Chin J Dent 2007; 7: 43-47.

Discussion
Several methods have been employed for the evaluation of occlusal data. New diagnostic devices such as
Photocclusion8 and T-scan system (Tekscan, Boston, MA, USA)9 have been developed. The Photocclusion
system is difficult to measure the acting occusal force precisely because of using a rather rigid material for
occlusal examination.15 Patyk et al.9 stated that the T-Scan-sensor-foil was too thick and too inflexible andtherefore created an uncontrollable shift of the mandible when biting. It may misreading the qualitative analysisof the occlusion. The thickness of the Dental Prescale sensor (0.098 mm) is similar to that of the T-Scan systemsensor (0.1 mm). However, the Dental Prescale sensor is more flexible than the T-Scan system sensor. It iseasier to control the shift of the mandible when closing the bite and may achieve improvement in quantifying
and simplifying the analysis of occlusion. Another advantage is that occlusal data are recorded easily, withresulting comparing with other data.
There were not significant differences of occlusal data between male and female, although the values ofocclusal contact areas and occlusal forces in males tended to be greater than those in females. This is inagreement with the previous report that studies of static closing force report no correlation between force and sex,weight, height, or body build of the subjects.17 The force AI in both of male and female indicated low values. It
is not surprising that there is no significant difference between the force AIs in male and female. There isgeneral agreement concerning this.
TMD is a frequent clinical problem and its pathophysiologic characteristics are complicated, but can beseparated into masticatory muscle disorders and disorders of the temporomandibular joints.18-20 TMD in thisstudy was separated into MPD and TMJ groups, and evaluated. The force AI of TMD patients was higher thanthat of healthy subjects (Tables 3 and 4). The absolute asymmetry index (aAI) of the masseter muscles during
intercuspal maximal clenching was higher in TMD patients than the healthy subjects.14 This is in agreementwith the results in this study. This result might indicate that the greater occlusal imbalance, namely the highvalue of the force AI, relate to TMD. However it cannot be denied that the increase of the force AI was theresult that the symptoms such as pain in TMD are commonly unilateral. However, determination of occlusal
force balance (force AI) is a reliable index of TMD.
MPD syndrome is believed to be a stress-related disorder21-23 and starts as a functional disorder. It ishypothesized that centrally induced increases in muscle tension, frequently combined with the presence ofparafunctional habits such as clenching or grinding of the teeth, result in muscle fatigue and spasm that produce
the pain and dysfunction. There were no significant differences between the values of occlusal contacts area andocclusal force in MPD patients and in healthy subjects (Table 3). This result is in agreement with the fact thatthe occlusions in some cases of MPD patients are stable.
The occlusal data in TMJ patients were different from those in healthy subjects, except for the data ofmaximum pressure. TMJ patients had the high value of force AI and mean pressure, and low value of contact
areas comparing with the values in MPD patients (Table 4). These data in TMJ patients might indicate that there
were not only imbalance between left and right of occlusion but also unstable occlusion due to the interfering
occlusal contacts.
The Dental Prescale system has potential as a clinical device to diagnose and treat occlusion because it offersa greater variety and accuracy of occlusal data and because it uses time as the diagnostic variable.

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Int Chin J Dent 2007; 7: 43-47.

Acknowledgment
This study was supported in part by Grant-in-Aid for Scientific Research (16390617) from the Japan Society for thePromotion of Science.

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Correspondence to:
Dr. Shinsuke Sadamori
Department of Prosthetic Dentistry, Programs for Applied Biomedicine Division of Cervico-Gnathostomatology,
Hiroshima University Graduate School of Biomedical Sciences
1-2-3 Kasumi, Minami-ku, Hiroshima 734-8553, Japan
Fax: +81-82-257-5684 E-mail: tsada@hiroshima-u.ac.jp
Received April 17, 2007. Accepted May 18, 2007.
Copyright ©2007 by the International Chinese Journal of Dentistry.

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