ABSTRACT: Angle of mouth opening provides information concerning
temporomandibular joint mobility. The aim of this study was to compare
angle of mouth opening of dentate and edentuluous subjects at similar
ages. Eighty (80) subjects, 24 women and 16 men (mean age 51.2 yrs.) for
the dentate group and 21 women and 19 men (mean age 52.3 yrs.) for the
edentuluous group participated in the study. The angle of mouth opening
measurements were performed with a mandibular goniometer at four
independent sessions of three measurements. The angle of mouth opening
values of the dentate group were significantly higher than that of the
edentulous group. The results of this study revealed that tooth loss
resulted in a decrease in angle of mouth opening values independent of
gender and age. The clinical implications of this finding is that oral
function might well be preserved with advancing age if dentition is
maintained in good condition.
Assesment of the mobility of temporomandibular joints (TMJ) and the
masticatory system by mouth opening (MO) during routine functioning of
the joints or the course of a treatment can provide data on the benefits
of the selected treatment. (1-3) Depending on age and gender, mouth
opening ranges from about 40 to 75 mm in healthy subjects and usually
decreases with age. (4-6) A severely restricted mandibular opening may
impede communication, oral hygiene, and food intake, whereas excessive
mandibular opening may indicate hypermobility of the TMJ. (3)
Mouth opening is measured as inter-incisal distance at maximal
mouth opening added to the vertical overbite, (l-3,7) which can be made
easily and reliably. However this method partially reflects TMJ mobility
as the MO is influenced by the length of the mandible). (8,9) A method
proposed by Dijstra, et al. enables reliable MO measurements, providing
adequate information concerning TMJ mobility independent of mandibular
length so called angle of mouth opening (AMO) and was defined as angular
displacement of the mandible relative to cranium. (1-2)
Teeth fixed goniometers, a complex registration apparatus, chin
positioned gonimeters, recording EMG activities, mandibular goniometer
(MG) or mathematical equations have been used to assess AMO. (1,8,10,11)
The clinical validity of these methods is questionable, considering the
discrepancies of the results. Some of these methods were too complex,
(10) whereas some were not sufficiently reliable. (9) It has been
suggested that AMO could reliably and easily be measured in clinical
circumstances with an MG. (1)
Skeletal muscle atrophy, declining strength, and physical frailty
are generally accepted as inevitable concomitants of ageing. (12) Bite
force for individuals of 75 years and over was reported to be 40% lower
than that for those of 35-44 years. (12) The main reason for the reduced
bite force was thought to be atrophy of the jaw-closing muscles. The
cross-sectional areas of these muscles showed a significant reduction
with age, with those in edentulous subjects showing a greater decrease
than in dentate subjects. (14)
The association between the effect of tooth loss on the TMJ has
been studied, (15,16) but the effect remains unclear. Changes in form or
shape of the condyles were age-related and could be correlated to the
number of teeth lost. (15,16) Histological findings also support the
changes in the TMJ following tooth loss. (17) Missing mandibular
posterior teeth might accelerate the development of degenerative joint
Studies of nonpatient populations do not provide sufficient
evidence of an association between changes in the TMJ and loss of molar
support, (18-19) even though loss of molar support has been correlated
with osteoarthritic changes in the TMJ. (15,17,18,20)
Previous investigations have shown that the range of mandibular
movement varies considerably from one individual to another. (4,20) Most
investigators used subjects of the same gender or within narrow ranges
of age. (1) Statistically significant differences in jaw mobility are
present between men and women, (4,11,20) as well as between young and
old people. (4,5,8)
Studies have shown that there can be pain and loss of motion in the
cervical region with increasing age, and TMJ pathology and
temporomandibular disorders may result in limited TMJ mobility
(2,7,12,21) which may lead to limited AMO and changes in opening
pattern. But the effect of tooth loss on AMO has not previously been
investigated. The aim of this study was to compare angle of mouth
opening in dentate and edentulous healthy subjects within a narrow age
Materials and Methods
Eighty (80) consecutive subjects, 24 women and 16 men (mean age: 51
[+ or -] 2.9, range 47-54 yrs.) for the dentate group and 21 women and
19 men (mean age: 52 [+ or -] 3.7, range 45-57 yrs.) for the edentuluous
group were recruited from the patients of Ege University School of
Dentistry Department of Prosthodontics. The subjects in the edentulous
group had worn complete dentures for 2-9 years. All participants were in
a good health. Subjects with limited mouth opening, a history of trauma
or local disorders of the masticatory system, reduced joint mobility,
with current neck pain and using pain medications, having major
illnesses, nervous tics, shoulder pain, as well as subjects with
trismus, pain during mouth opening and cervical range of motion,
pericoronitis or radiographic evidence of degenerative disorders of the
TMJ were not included in the study. Informed consent was obtained from
all participating subjects.
Measuring AMO with Mandibular Goniometer (MG)
The subject was seated in a straight-back chair, knees slightly
flexed, head, thoracic, and lumbar spine against the back support of the
chair, but not fixed to the back support. All subjects were read
standardized instructions by the examiner before measurements were
The positioning of MG and AMO measurements was performed as
described in detail by Dijkstra, et al. (1) The mandibular goniometer
(Figure 1 a,b) was positioned with the L-shaped profiles held against
the inferior border of the mandible while the chin support rested
against the anterior aspect of the mandible was set to zero. The subject
was asked to close his/her mouth in maximal intercuspitation and then
open actively as far as possible (Figure 2). The values displayed by the
mandibular goniometer were recorded, to the nearest degree, as AMO
One operator performed four independent measurement sessions on
consecutive days. Within each measurement session, three measurements
were made. The mean AMO was calculated from the measurement results of
each session. The observer was blinded for the measurement results in
the former sessions.
The data were controlled for normality using the Kolmogorov-Smirnov
test and statistically analyzed using a t-test, Pearson Correlation, and
Multiple Linear Regression Analysis. The level of significance was
established as 0.05 for all statistical tests. Statistical analyses were
processed with the SPSS 15.0 software system (SPSS Inc., Chicago, IL).
The Kolmogorov-Smirnov (nonparametric and distribution free) test
was used to determine whether or not the data had a normal distribution.
The t-test was applied to show the significance of the difference
between the means of two populations. Pearson Correlation was used to
determine the degree of correlation between two related variables.
Multiple linear regression was adopted to model the relationship between
two or more explanatory variables and a response variable by fitting a
linear equation to observed data.
[FIGURE 1 OMITTED]
AMO values showed normal distribution according to the
Kolmogorov-Smirnov test. The minimum, maximum and the mean([+ or -] sd)
AMO values of dentate and edentulous subjects were summarized in Table
1. The mean AMO difference between dentate and edentulous subjects was
significant (p<0.05) with dentate subjects having higher AMO values
(Table 1). The t-test revealed that, although the intragroup and overall
mean AMO values for males were higher than the females, the difference
between gender and AMO was insignificant (p>0.05) (Table 2). No
significant correlation between age and AMO was determined according to
Pearson correlation analysis (p>0.05) (Table 3). Multiple linear
regression analysis revealed that the differences of AMO related to
gender and age were insignificant (p>0.05) (Table 4); whereas the
differences of AMO related to dental status were significant (p<0.05)
(Table 4). The mean ages between dentate and edentulous groups were
statistically insignificant (p>0.05).
[FIGURE 2 OMITTED]
Accurate measurement and interpretation of joint motions are
imperative to develop a treatment plan, monitor patient progress, and
evaluate treatment effectiveness. (22,23) Among various methods, mouth
opening is regarded as one of the most objective indicators of TMJ
status. Linear measurement of maximal active mandibular movement has
been thoroughly studied and accepted as an easy and reliable method to
evaluate TMJ mobility with great constancy. (4,5-7,22) But the maximal
range of mouth opening has its limitations since it is influenced by the
length of the mandible. (1,8-9) Measuring AMO with MG provides a
reliable measure for TMJ mobility, independent of the length of the
mandible. (1,2) Therefore, MG was used to measure AMO without the bias
of the mandibular length.
The recorded angles for AMO are relatively divergent ranging from
28[degrees] to 51[degrees]. (1,3) The AMO values measured in this study
were close to the lower ranges reported in the literature. This might be
attributed to the age range of the subjects in the current study.
The effects of tooth loss have been investigated by various
studies. (15-17) However, the effect of tooth loss on AMO has not been
investigated. The mean AMO values of the edentate group were
significantly less than that of the dentates, where various factors
should be taken into account.
Tooth loss has a direct effect on the alveolar process but not
necessarily on the other components of the mandible or maxilla. Any
changes that may occur elsewhere, i.e., the angular region and TMJ, are
indirect and are the result of modified function that may have been
required because of the edentuluous situation. (24)
Tooth loss is a deprivation of an important source of sensory
input, affecting intraoral perception, and other mandibular functions
such as mouth opening. The edentulous patients are more dependent upon
the sensory receptors located in the capsule and ligaments of the TMJ
than are dentulous individuals. These receptors play an important role
in the perception and the limitation of mandibular movements. (24) The
significant difference of AMO values between the groups in this study
could be attributed to this limitation.
Natural dentition carries most of the load relieving the joint from
undue compressive forces. (24) The tooth loss may place additional
forces on the TMJ, which is then required to adapt to these new
functional demands. Edentulous patients may be suspectible to
degenerative changes to the TMJ due to the increase in forces and as a
result of muscular activity, (24) which might also explain the lower AMO
values of the edentulous subjects as a result of protective mechanisms,
i.e., changing the limits of the border movements.
Since tooth loss is not physiological aging but pathological aging,
(12) lower AMO values can be expected as tooth loss is supposed to be
the most significant factor on reduction of functions such as bite force
(12) and TMJ mobility rather than aging itself. The maximal range of
mouth opening has been stated to be higher in males than in females in
several epidemiological studies. (4,11,20) Although the AMO values for
males were higher than the females in this study, the difference found
Based upon the outcome in the current study, a significant
relationship was found between AMO and dental status. Oral function
might well be preserved through advancing age if dentition is maintained
in good condition.
The authors wish to thank P.U. Dijkstra for supplying the
Manuscript received October 22, 2008; revised manuscript received
February 10, 2009; accepted May 5, 2009
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Bulent Gokce, D.D.S., Ph.D.; Umut Iyiyapici Destan, D.D.S., Ph.D.;
Birgul Ozpinar, D.D.S., Ph.D.; Mehmet Sonugelen, D.D.S., Ph.D.
Address for correspondence: Bulent Gokce
School of Dentistry
Dept. of Prosthodontics
Dr. Bulent Gokce received his D.D.S. degree from Ege University in
1998 and a Ph.D. degree in 2004 from the same university. His primary
areas of interest are prosthodontics, biomechanics, implantology, and
dental materials. Dr. Gokce has publications in many scientific
Dr. Umut Iyiyapici Destan received a D.D.S. degree in 1998 from Ege
University School of Dentistry and a Ph.D. in 2004 from the same
university. Her primary areas of interest are prosthodontics,
biomechanics, implantology, and dental materials.
Dr. Birgul Ozpinar received a D.D.S. degree in 1975 from Ege
University School of Dentistry. She has been a professor since 1988 and
received a Ph.D. in 1994 from Ege University School of Dentistry. Dr.
Ozpinar's primary areas of interest are prosthodontics, the
stomatognathic system, precision attachments, overdentures, and
implantology. She has authored several scientific articles.
Dr. Mehmet Sonugelen received his D.D.S. in 1981 from Ege
University School of Dentistry and a Ph.D. in 1988 from the same
university. Since 1996, he has been a professor. Dr. Sonugelen's
primary areas of interest are prosthodontics, biomechanics, and
Maximum, Minimum, and Mean ([+ or -] SD) AMO Values of Dentate
and Edentulous Subjects
AMO ([degrees]) AMO ([degrees])
Dental status N Minimum Maximum
Dentate 40 29 [degrees] 36 [degrees]
Edentulous 40 27 [degrees] 32 [degrees]
Dental status Mean [+ or -] SD t p
Dentate 33 [+ or -] 2.0 [degrees]
Edentulous 30 [+ or -] 1.5 [degree 5.424 * 0.000
AMO: angle of mouth opening; N number; SD: standard deviation
* Difference between dentate and edentulous subjects was
statiscally significant based on results of t-test (p<0.05)
Mean ([+ or -] SD) AMO Values for Female and Male
Gender N AMO ([degrees]) mean t p
[+ or -] SD
Female 45 31.3 [+ or -] 2.1 [degrees] -0.170 * 0.866
Male 35 31.5 [+ or -] 2.9 [degrees]
AMO: angle of mouth opening; N number;
SD: standard deviation
* Difference between dentate and edentulous subjects was
statiscally significant based on results of t-test (p<0.05)
Pearson Correlation Between Age and AMO
Group N [+ or -] SD
Dentate 40 51 [+ or -] 2.9 [degrees]
Edentulous 40 52 [+ or -] 3,7 [degrees]
Total 80 51 [+ or -] 8.3 [degrees]
Group mean [+ or -] SD r p
Dentate 33 [+ or -] 2.0 [degrees] -0.268 0.253
Edentulous 30 [+ or -] 1.5 [degrees] -0.278 0.236
Total 31 [+ or -] 6.7 [degrees] -0.273 0.214
AMO: angle of mouth opening; N: number; SD: standard deviation
* Overall and intragroup dentate and edentulous subject correlation
between age and AMO were statistically insignificant (p<0.05)
Table 4 Multiple Linear Repression Analysis
(a) Significant coefficients
predictors B Std. Error
(Constant) 36.100 0.918
Dentate/edentulous -3.150 0.581
(a) Significant coefficients
predictors Beta t p
(Constant) 39.316 0.000
Dentate/edentulous -0.661 -5.424 0.000
(b) Unsignificant Beta in t p
Gender 0.135 1.101 0.278
Age -0.278 -1.669 0.103
Dependent variable: AMO
AMO: angle of mouth opening
Results of the multiple regression analysis revealed that being
dentate or edentulous was responsible for significant AMO
differences (a) (p<0.05). Neither gender nor age had a significant
impact on AMO (b) (p<0.05)