Comparison of mouth opening angle between dentate and edentulous subjects.
Article Type:
Dentition (Health aspects)
Dentition (Research)
Temporomandibular joint (Health aspects)
Temporomandibular joint (Research)
Temporomandibular joint disorders (Causes of)
Temporomandibular joint disorders (Research)
Gokce, Bulent
Destan, Umut Iyiyapici
Ozpinar, Birgul
Sonugelen, Mehmet
Pub Date:
Name: CRANIO: The Journal of Craniomandibular Practice Publisher: Chroma, Inc. Audience: Academic Format: Magazine/Journal Subject: Science and technology Copyright: COPYRIGHT 2009 Chroma, Inc. ISSN: 0886-9634
Date: July, 2009 Source Volume: 27 Source Issue: 3
Event Code: 310 Science & research
Geographic Scope: Turkey Geographic Code: 7TURK Turkey

Accession Number:
Full Text:
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 disease. (15)

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 range.

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 performed.

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 values.

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.



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).



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 was insignificant.


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 mandibular goniometer.

Manuscript received October 22, 2008; revised manuscript received February 10, 2009; accepted May 5, 2009


(1.) Dijkstra PU. De Bont LGM. Stegenga B, Boering G: Angle of mouth opening measurement: reliability of a technique for temporomandibular joint mobility assessment. J Oral Rehabil 1995: 22:263-268.

(2.) Dijkstra PU. Hof AL. Stegenga B. De Bont LGM: Influence of mandibular length on mouth opening. J Oral Rehabil 1999: 26:117-122.

(3.) Dijkstra PU. Kropmans JB, Stegenga B: Ratio between vertical and horizontal range of motion. J Oral Rehabil 1998:25:353-357.

(4.) Agerberg G: Maximal mandibular movements in young men and women. Swed Dent J 1974:76:81-100.

(5.) Agerberg G, Osterberg T: Maximal mandibular movements and symptoms of mandibular dysfunction in 70-year-old men and women. Swed Dent J 1974; 67:1-18.

(6.) Mezitis M, Rallis G, Zachariades N: The normal range of mouth opening. J Oral Maxillofac Surg 1989; 47:1028-1030.

(7.) Dworkin SH, Leresche L. Derouen T. Von Korff M: Assessing clinical signs of temporomandibular disorders: Reliability of clinical examiners. J Prosthet Dent 1990: 63:574-579.

(8.) Westling L, Helkimo E: Maximum jaw opening capacity in adolescents in relation to general joint mobility. J Oral Rehabil 1992: 19:485-494.

(9.) Wright V, Hopkins R: The temporomandibular joint. Clin Rheum Dis 1982: 8:715-722.

(10.) Widmalm SE, Larsson EM: A new method for the recording temporomandibular joint sounds electrical jaw muscle activity in relation to jaw opening degree. Acta Odontol Scand 1982; 40:429-434.

(11.) Pullinger AG, Shu P, Ao LIU. Low G. Tay D: Differences between sexes in maximum jaw opening when corrected to body size. J Oral Rehabil 1987: 14:291-299.

(12.) Brooks SV, Faulkner JA: Skeletal muscle weakness in old age: underlying mechanisms. Med Sci Sports Exerc 1994; 26:432-439.

(13.) Ikebe K, Nokubi T, Morii K. Kashiwagi J, Furuya M: Association of bite force with ageing and occlusal support in older adults. J Dent 2005:33:131-137.

(14.) Newton JP, Yemm R, Abel RW. Menhinick S: Changes in human jaw muscles with age and dental state. Gerodontology 1993: 10:16-22.

(15.) Tallents RH, Macher DJ, Kyrkanides S. Katzberg RW. Moss ME: Prevalence of missing posterior teeth and intraarticular temporomaudibular disorders. J Prosthet Dent 2002: 87:45-50.

(16.) Stipeti J, Celebi A. Katunari M, Valenti-Peruzovi M, Stipeti D: Influence of aging and the loss of teeth on some variations of TMJ. Acta Stomatol Croat 1990; 24:185-196.

(17.) Huang Q, Opstelten D, Samman N, Tideman H: Experimentally induced unilateral tooth loss: expression of type 11 collagen in temporomandibular joint cartilage. J Oral Maxillofac Surg 2003; 61:1054-1060.

(18.) Swanljung O, Rantanen T: Functional disorders of the masticatory system in southwest Finland. Community Dent Oral Epidemol 1979: 7:177-182.

(19.) Wilding RJ, Owen CP: The prevalence of temporomandibular joint dysfunction in edentulous non denture wearing individuals. J Oral Rehabil 1987: 14:175-182.

(20.) Kraus SL: TMJ disorders: Management of the craniomandibular complex. New York: Kraus SL. Churchill Livingstone: 1988.

(21.) Helkimo M: Studies on function and dysfunction of the masticatory system. IV. Age and sex distribution of dysfunction in the masticatory system in Lapps in the north of Finland. Acta Ododntol Stand 1974; 32:1-13.

(22.) Carlsson GE. Egermark-Eriksson I, Magnusson T: Intra and inter-observer variation in functional examination of the masticatory system. Swed Dent J 1980; 4:187-194.

(23.) Dijkstra PU, De Bont. LGM. Van Der Weele LTH. Boering G: Joint mobility measurements: reliability of a standardized method. J Craniomandib Pract 1994: 12:52-56.

(24.) Winkler S: Essentials of complete denture prosthodontics. London: W.B. Saunders Co., 1979.

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

Ege University

School of Dentistry

Dept. of Prosthodontics

35100 Bornova

Izmir, Turkey


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 journals.

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 implantology.
Table 1
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]

                 AMO ([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)

Table 2
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)

Table 3
Pearson Correlation Between Age and AMO

                            Age mean
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]

                    AMO ([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

(b) Unsignificant

(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)
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