journal of prosthodontic research 58 (2014) 237–242
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/jpor
Original article
Gender differences in masticatory movement path and rhythm in dentate adults Kyoko Tamura DDS, Hiroshi Shiga BEng, DDS, PhD* Department of Partial and Complete Denture, School of Life Dentistry at Tokyo, The Nippon Dental University, 1-9-20 Fujimi, Chiyoda-ku, Tokyo 102-8159, Japan
article info
abstract
Article history:
Purpose: The purpose of this study was to clarify whether there might be a gender difference
Received 30 April 2014
in masticatory movement path and rhythm in dentate adults.
Received in revised form
Methods: Thirty healthy males and 30 healthy females were asked to chew softened chewing
5 June 2014
gum on their habitual chewing side for 20 sec, and the movement of the mandibular incisal
Accepted 7 June 2014
point was recorded using mandibular kinesiograph. For 10 cycles from the fifth cycle, the
Available online 1 August 2014
spatial and temporal parameters (spatial: amounts of vertical and lateral movements; temporal: opening, closing, occluding, and cycle times) of masticatory movement path
Keywords:
and rhythm and the parameters representing the stability of masticatory movement path
Masticatory movement
and rhythm were calculated and compared between males and females.
Gender difference
Results: The values of the spatial parameters were significantly greater for males than for
Masticatory path
females. The values of the temporal parameters were smaller for males than for females,
Masticatory rhythm
and significant differences were found in all parameters except occluding time. However, there was no statistically significant difference in the parameters representing the stability of masticatory movement path and rhythm. Conclusion: From these results it was suggested that although there were no differences in the stability of masticatory movement path and rhythm between genders, there were gender differences in the spatial and temporal parameters of masticatory movement path and rhythm. # 2014 Japan Prosthodontic Society. Published by Elsevier Ireland. All rights reserved.
1.
Introduction
One of the main purposes of dental practice is to restore and maintain masticatory function. In order to objectively evaluate masticatory function, many attempts have been made to investigate parameters such as occlusal force [1–3], masticatory performance [3–5], muscular activity [6,7], and masticatory
movement [2–4,8–13] and so on. Among these analyses, investigation of masticatory movement could be expected to be useful for quantitatively and objectively evaluating masticatory function. Therefore, several attempts have been made to analyze the amounts of vertical and lateral movements [6,7,14–19] and the rhythm [6,7,12–20], velocity [14– 16,19–21], variances [21,22], and patterns of masticatory movements [23–25].
* Corresponding author. Tel.: +81 3 3261 5729; fax: +81 3 3261 8464. E-mail address: [email protected] (H. Shiga). http://dx.doi.org/10.1016/j.jpor.2014.06.001 1883-1958/# 2014 Japan Prosthodontic Society. Published by Elsevier Ireland. All rights reserved.
238
journal of prosthodontic research 58 (2014) 237–242
It is necessary to clarify the presence of gender differences in masticatory movement for evaluating masticatory function using different parameters. However, gender differences in the amount and rhythm of masticatory movement have not been elucidated till date. In addition, gender differences in the stability of masticatory movement have also not been investigated. Masticatory movement may be affected by exogenous factors [9,20,26,27], such as test food, chewing methods, and section selected for analysis, and can vary, even among healthy subjects. Therefore, when evaluating masticatory movement, it is necessary to minimize the intra-individual variations arising from these factors. It is necessary to study this further by focusing on the masticatory condition and gender differences. Therefore, this study aimed to clarify the presence of gender differences in masticatory movement by investigating quantitative parameters of masticatory movement in healthy males and females.
2.
Materials and methods
2.1.
Subjects
Thirty healthy males (age range, 20–34 years; average age, 27.8 years) and thirty healthy females (age range, 20–35 years; average age, 27.6 years) participated in this study. None of the subjects had any clinical abnormalities in the masticatory system. The following selection criteria were used for inclusion: absence of complaints regarding bite; presence of a full set of teeth, excluding the third molars; absence of major dental restorations; and no history of orthodontic treatment. All experimental procedures were approved by the Ethics Committee of the Nippon Dental University (NDU-T2012-29). Informed consent was obtained from all subjects after they were provided with an explanation of the general nature of the study.
Then after all masticatory cycles recorded were separated into individual cycles, for 10 cycles from the fifth cycle, the spatial and temporal parameters (spatial: amounts of vertical and lateral movements; temporal: opening, closing, occluding, and cycle times) and the parameters representing the stability of masticatory movement path and rhythm were calculated.
2.4.1. Spatial and temporal parameters and parameters representing stability of masticatory movement path Using the centric occlusion (CO) position in each cycle from the fifth cycle to the fourteenth cycle as a standard, the coordinates for each cycle were determined by vertically dividing the opening and closing paths into 10 equally spaced sections in the frontal view (Fig. 1A–C). From these coordinates, the average path and standard deviation (SD) were calculated (Fig. 1D and E). The opening distance (OD, amount of vertical movement) and masticatory width (amount of lateral movement) were the indicators representing the amount of masticatory movement (Fig. 1F). The masticatory width was applied to the average of width from level 1 to 9 (Table 1). The SDs of lateral opening, lateral closing, and vertical components were calculated as indicators representing variations of the masticatory path. The averages of 11 SDs from level 0 to 10 in the horizontal direction during opening movement, in the horizontal direction during closing movement, and in the vertical direction were taken as the lateral opening component, lateral closing component, and vertical component, respectively (Table 1). These values were then divided by the opening distance, and the value (SD/OD) was used as the index representing the stability of masticatory movement path.
2.4.2. Temporal parameters and parameters representing stability of masticatory movement rhythm
A piece of chewing gum (Trident1, USA) was used as the test food, which weighed approximately 2 g. The chewing gum was sufficiently softened before recording masticatory movement.
As to masticatory rhythm, each starting point of the opening phase, closing phase and occluding phase of each cycle were first identified using our own method [9]. Next, for 10 cycles from the fifth cycle, the opening time, the closing time and the occluding time, and the sum of all the three times were calculated. And then the coefficient of variations (CVs) were obtained from the mean time of the ten cycles and its standard deviation (Table 2), and the mean values were used as temporal parameters, and the CVs were used to represent the stability of masticatory movement rhythm.
2.3.
2.5.
2.2.
Test food
Recording of masticatory movement
Analyzing method
The subjects were asked to sit in a chair so that their Frankfurt plane was parallel to the floor with the head not fixed in a relaxed state, and were asked to chew softened chewing gum on their habitual chewing side for 20 sec. Incisal point movement during mastication was recorded by mandibular kinesiograph (K6I, Myotronics, USA) using a data recorder (XR5000, TEAC, Tokyo).
The spatial and temporal parameters, and the parameters representing the stability of masticatory movement path and rhythm were compared between males and females using statistical software (SPSS for Windows 10.0J, SPSS, Chicago, IL, USA). The comparison was investigated by an independent ttest. A P value of 0.05, Table 3).
4.
Discussion
During mastication, a rhythmic pattern is maintained by the pattern generator in the brain stem [28]. The regulation of this movement is also derived on the basis of feedback information from the periphery, such as the teeth, masticatory muscles, and temporomandibular joints [9,20,27]. It has been reported
240
journal of prosthodontic research 58 (2014) 237–242
Table 1 – Numerical data of the average path of subject 1. Level
Lateral opening (mm) Mean
0 1 2 3 4 5 6 7 8 9 10 Mean SD/OD (%)
0.0 1.6 1.7 1.5 1.2 0.8 0.3 0.1 0.5 1.1 2.3
Lateral closing (mm)
SD
Mean
SD
0.0 0.3 0.5 0.6 0.6 0.8 0.8 0.8 0.8 0.7 0.6
0.0 2.0 2.7 3.3 3.9 4.2 4.4 4.4 4.2 3.7 2.3
0.0 0.2 0.3 0.4 0.5 0.5 0.5 0.5 0.6 0.7 0.6
0.65 3.87
0.48 2.86
Width (mm)
3.6 4.4 4.8 5.1 5.0 4.7 4.3 3.7 2.6
4.2
Table 2 – Numerical data of the opening, closing, occluding, and cycle times of subject 1.
Vertical (mm)
Cycle
Mean
SD
0.0 1.5 3.0 4.6 6.1 7.6 9.1 10.6 12.2 13.7 15.2
0.0 0.1 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0.46 2.74
Opening (msec)
Closing (msec)
Occluding (msec)
Cycle (msec)
5 6 7 8 9 10 11 12 13 14
190 210 200 200 210 240 220 230 230 200
210 240 230 210 200 220 230 200 220 210
180 180 160 180 180 180 180 180 180 160
580 630 590 590 590 640 630 610 630 570
Mean SD CV (%)
213 16.4 7.7
217 13.4 6.2
176 8.4 4.8
606 25.0 4.1
Table 3 – Means (standard deviations) for the values of the spatial parameter, temporal parameter, stability of path, and stability of rhythm.
Spatial parameter (mm) Vertical movement Lateral movement Temporal parameter (msec) Opening time Closing time Occluding time Cycle time Stability of path (%) Lateral opening component Lateral closing component Vertical component Stability of rhythm (%) Opening time Closing time Occluding time Cycle time
Male
Female
P value
18.2 (3.4) 3.2 (1.0)
15.4 (2.7) 2.7 (0.8)
0.001 0.048
180.0 182.1 179.7 541.7
(33.5) (34.1) (28.6) (76.1)
201.6 205.7 187.8 595.2
(47.6) (39.9) (38.0) (93.2)
0.046 0.017 0.351 0.018
4.0 (1.6) 4.3 (1.5) 4.1 (1.3)
4.4 (1.6) 4.4 (1.3) 4.4 (1.3)
0.305 0.899 0.395
9.7 8.5 8.7 4.3
9.8 8.3 8.6 4.5
0.903 0.795 0.836 0.528
(2.5) (3.6) (2.8) (1.1)
that healthy subjects show a regular and stable masticatory movement path and rhythm [8]. However, masticatory movement may be affected by exogenous factors [9,20,26,27] such as masticating conditions, including food type or chewing methods, and can vary, even among healthy subjects. Therefore, it is recommended that such exogenous factors should be excluded when recording masticatory movement [10,11]. In this study, softened chewing gum was used as the test food because it does not change much in either hardness or size during the chewing sequence. Further, unilateral chewing was recommended instead of free chewing to eliminate any variations in chewing method [18,20,25,26]. We have previously observed that variations in masticatory movement can be minimized by employing softened chewing gum as the test food, the habitual side as the chewing side, and 10 cycles after the fourth to sixth cycle as the section selected for analysis [10]. Therefore, in this study, after considering the masticatory condition, the presence of gender differences in masticatory movement path and rhythm were investigated.
(3.2) (3.1) (2.6) (1.3)
Gender differences in masticatory movement have been previously investigated by many researchers. Neill and Howell [14] investigated quantitative parameters of mandibular movement when chewing various foods and found that with all food types, the cycle time was shorter for males than for females and that both vertical and lateral movements were greater for males than for females; the differences were statistically significant between genders. However, Kiliaridis et al. [15] reported that although there were significant differences in vertical and lateral movements between genders, there were no significant differences in cycle time. Youssef et al. [6] reported results different from those of Kiliaridis et al. [15], stating that significant differences were present in cycle time between males and females, with no significant differences in vertical and lateral movements. Further, Buschang et al. [16] showed that although there were no significant differences in lateral movement between genders, there were significant differences in vertical movement and cycle time. A study by Peyron et al. [7] reported that
journal of prosthodontic research 58 (2014) 237–242
cycle time tended to be shorter and that movement tended to be greater for males than for females. Salsench et al. [18] reported that although there were no significant differences between genders in the right vertical movement, there were significant differences in the left vertical movement and ambilateral cycle time. In addition, Lepley et al. [19] reported that although there were no significant differences in vertical movement and cycle time between genders, there was significant difference in lateral movement. As for the reasons that Buschang et al. [16] were able to detect gender difference, they listed the fact that they were able to select the 10 most representative cycles for each subject, who were instructed to masticate on one side; furthermore, they eliminated large differences among cycles. In this study, we analyzed masticatory movement with focus on masticatory conditions similar to those used by Buschang et al. [16] and found that the cycle time was significantly shorter for males than for females; both vertical and lateral movements were significantly greater for males than for females. Therefore, we were also able to detect gender difference. This result may also indicate that exogenous factors should be excluded when analyzing masticatory movement. Buschang et al. [16] used softened chewing gum with a texture that does not considerably change with mastication. In other experiments, peanuts whose size and hardness changed while chewing and relatively hard gummy that was a bit difficult to chew were used. This could perhaps be the reason why the other experiments could not detect gender differences. However, even in these studies, when looking at the values of the result, almost all of them showed that in compared with females, males had a shorter cycle time and larger movements. From these results it might be concluded that the amount of masticatory movement was greater and that the cycle time was shorter for males than for females. Also it could be contemplated that in general male masticates faster than female. In either way, the fact that differences were found between genders in both spatial and temporal parameters, it then would be necessary to evaluate male and female separately. With regard to the stability of masticatory movement during mastication, as far as we know, although there are no previous investigations on which we can compare, the results of this study did not find statistically significant differences in indicators representing the stability of masticatory path and rhythm between males and females. These results showed that, regardless of gender, normal healthy adults have regular and rhythmic masticatory movement. In other words, it could be said that for the stability of masticatory movement there is no need to pay special attention to gender differences. The results of paying attention to the chewing condition and looking for gender differences were that in normal healthy adults, although gender differences were found for the amount and rhythm of masticatory movement, there were no differences between genders in the stability of masticatory movement. It was clarified that when analyzing masticatory movement, there are indicators that need paying attention to gender difference and there are indicators that did not need such attention.
5.
241
Conclusion
It was suggested that although there were no differences in the stability of masticatory movement path and rhythm between genders, there were gender differences in the spatial and temporal parameters of masticatory movement path and rhythm.
Conflict of interest statement The authors declare no competing financial interests.
references
[1] Owais AI, Shaweesh M, Abu Alhaija ESJ. Maximum occusal bite force for children in different dentition stages. Eur J Orthod 2013;35:427–33. [2] Shimada A, Yamabe Y, Torisu T, Baad-Hansen L, Murata H, Svensson P. Measurement of dynamic bite force during mastication. J Oral Rehabil 2012;39:349–56. [3] Fueki K, Yoshida E, Igarashi Y. A structural equation model to investigate the impact of missing occlusal units on objective masticatory function in patients with shortened dental arches. J Oral Rehabil 2011;38:810–7. [4] Endo T, Komatsuzaki A, Kurokawa H, Tanaka S, Kobayashi Y, Kojima K. A two-colored chewing gum test for assessing masticatory performance: a preliminary study. Odontology 2014;102:68–75. [5] Ikebe K, Matsuda K, Kagawa R, Enoki K, Yoshida M, Maeda Y, et al. Association of masticatory performance with age, gender, number of teeth, occlusal force and salivary flow in Japanese older adults: is ageing a risk factor for masticatory dysfunction? Arch Oral Biol 2011;56:991–6. [6] Youssef RE, Throckmorton GS, Ellis 3rd E, Sinn DP. Comparison of habitual masticatory patterns in men and women using a custom computer program. J Prosthet Dent 1997;78:179–86. [7] Peyron MA, Blanc O, Lund JP, Woda A. Influence of age on adaptability of human mastication. J Neurophysiol 2004;92:773–9. [8] Mongini F, Tempia-Valenta G. A graphic and statistical analysis of the chewing movements in function and dysfunction. J Craniomandibular Pract 1984;2:125–34. [9] Shiga H, Stohler CS, Kobayashi Y. The effect of bolus size on the chewing cycle in humans. Odontology 2001;89:49–53. [10] Shiga H, Kobayashi Y, Arakawa I, Shonai Y. Selection of food and chewing side for evaluating masticatory path stability. Odontology 2003;91:26–30. [11] Wintergerst AM, Buschang PH, Hutchins B, Throckmorton GS. Effect of an auditory cue on chewing cycle kinematics. Arch Oral Biol 2006;51:50–7. [12] Sakaguchi K, Maeda N, Yokoyama A. Examination of lower facial skin movements during left- and right-side chewing. J Prosthodont Res 2011;55:32–9. [13] Komagamine Y, Kanazawa M, Minakuchi S, Uchida T, Sasaki Y. Association between masticatory performance using a colour-changeable chewing gum and jaw movement. J Oral Rehabil 2011;38:555–63. [14] Neill DJ, Howell PGT. A study of mastication in dentate individuals. Int J Prosthodont 1988;1:93–8. [15] Kiliaridis S, Karlsson S, Kjellberg H. Characteristics of masticatory mandibular movements and velocity in
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growing individuals and young adults. J Dent Res 1991;70:1367–70. Buschang PH, Hayasaki H, Throckmorton GS. Quantification of human chewing-cycle kinematics. Arch Oral Biol 2000;45:461–74. Throckmorton GS, Ellis III E, Hayasaki H. Masticatory motion after surgical or nonsurgical treatment for unilateral fractures of the mandibular condylar process. J Oral Maxillofac Surg 2004;62:127–38. Salsench J, Martı´nez-Gomis J, Torrent J, Bizar J, Samso´ J, Peraire M. Relationship between duration of unilateral masticatory cycles and the type of lateral dental guidance: a preliminary study. Int J Prosthodont 2005;18:339–46. Lepley CR, Throckmorton GS, Ceen RF, Buschang PH. Relative contributions of occlusion, maximum bite force, and chewing cycle kinematics to masticatory performance. Am J Orthod Dentofacial Orthop 2011;139:606–13. Bhatka R, Throckmorton GS, Wintergerst AM, Hutchins B, Buschang PH. Bolus size and unilateral chewing cycle kinematics. Arch Oral Biol 2004;49:559–66. Throckmorton GS, Buschang BH, Hayasaki H, Phelan T. The effects of chewing rates on mandibular kinematics. J Oral Rehabil 2001;28:328–34.
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Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/jpor
Original article
Gender differences in masticatory movement path and rhythm in dentate adults Kyoko Tamura DDS, Hiroshi Shiga BEng, DDS, PhD* Department of Partial and Complete Denture, School of Life Dentistry at Tokyo, The Nippon Dental University, 1-9-20 Fujimi, Chiyoda-ku, Tokyo 102-8159, Japan
article info
abstract
Article history:
Purpose: The purpose of this study was to clarify whether there might be a gender difference
Received 30 April 2014
in masticatory movement path and rhythm in dentate adults.
Received in revised form
Methods: Thirty healthy males and 30 healthy females were asked to chew softened chewing
5 June 2014
gum on their habitual chewing side for 20 sec, and the movement of the mandibular incisal
Accepted 7 June 2014
point was recorded using mandibular kinesiograph. For 10 cycles from the fifth cycle, the
Available online 1 August 2014
spatial and temporal parameters (spatial: amounts of vertical and lateral movements; temporal: opening, closing, occluding, and cycle times) of masticatory movement path
Keywords:
and rhythm and the parameters representing the stability of masticatory movement path
Masticatory movement
and rhythm were calculated and compared between males and females.
Gender difference
Results: The values of the spatial parameters were significantly greater for males than for
Masticatory path
females. The values of the temporal parameters were smaller for males than for females,
Masticatory rhythm
and significant differences were found in all parameters except occluding time. However, there was no statistically significant difference in the parameters representing the stability of masticatory movement path and rhythm. Conclusion: From these results it was suggested that although there were no differences in the stability of masticatory movement path and rhythm between genders, there were gender differences in the spatial and temporal parameters of masticatory movement path and rhythm. # 2014 Japan Prosthodontic Society. Published by Elsevier Ireland. All rights reserved.
1.
Introduction
One of the main purposes of dental practice is to restore and maintain masticatory function. In order to objectively evaluate masticatory function, many attempts have been made to investigate parameters such as occlusal force [1–3], masticatory performance [3–5], muscular activity [6,7], and masticatory
movement [2–4,8–13] and so on. Among these analyses, investigation of masticatory movement could be expected to be useful for quantitatively and objectively evaluating masticatory function. Therefore, several attempts have been made to analyze the amounts of vertical and lateral movements [6,7,14–19] and the rhythm [6,7,12–20], velocity [14– 16,19–21], variances [21,22], and patterns of masticatory movements [23–25].
* Corresponding author. Tel.: +81 3 3261 5729; fax: +81 3 3261 8464. E-mail address: [email protected] (H. Shiga). http://dx.doi.org/10.1016/j.jpor.2014.06.001 1883-1958/# 2014 Japan Prosthodontic Society. Published by Elsevier Ireland. All rights reserved.
238
journal of prosthodontic research 58 (2014) 237–242
It is necessary to clarify the presence of gender differences in masticatory movement for evaluating masticatory function using different parameters. However, gender differences in the amount and rhythm of masticatory movement have not been elucidated till date. In addition, gender differences in the stability of masticatory movement have also not been investigated. Masticatory movement may be affected by exogenous factors [9,20,26,27], such as test food, chewing methods, and section selected for analysis, and can vary, even among healthy subjects. Therefore, when evaluating masticatory movement, it is necessary to minimize the intra-individual variations arising from these factors. It is necessary to study this further by focusing on the masticatory condition and gender differences. Therefore, this study aimed to clarify the presence of gender differences in masticatory movement by investigating quantitative parameters of masticatory movement in healthy males and females.
2.
Materials and methods
2.1.
Subjects
Thirty healthy males (age range, 20–34 years; average age, 27.8 years) and thirty healthy females (age range, 20–35 years; average age, 27.6 years) participated in this study. None of the subjects had any clinical abnormalities in the masticatory system. The following selection criteria were used for inclusion: absence of complaints regarding bite; presence of a full set of teeth, excluding the third molars; absence of major dental restorations; and no history of orthodontic treatment. All experimental procedures were approved by the Ethics Committee of the Nippon Dental University (NDU-T2012-29). Informed consent was obtained from all subjects after they were provided with an explanation of the general nature of the study.
Then after all masticatory cycles recorded were separated into individual cycles, for 10 cycles from the fifth cycle, the spatial and temporal parameters (spatial: amounts of vertical and lateral movements; temporal: opening, closing, occluding, and cycle times) and the parameters representing the stability of masticatory movement path and rhythm were calculated.
2.4.1. Spatial and temporal parameters and parameters representing stability of masticatory movement path Using the centric occlusion (CO) position in each cycle from the fifth cycle to the fourteenth cycle as a standard, the coordinates for each cycle were determined by vertically dividing the opening and closing paths into 10 equally spaced sections in the frontal view (Fig. 1A–C). From these coordinates, the average path and standard deviation (SD) were calculated (Fig. 1D and E). The opening distance (OD, amount of vertical movement) and masticatory width (amount of lateral movement) were the indicators representing the amount of masticatory movement (Fig. 1F). The masticatory width was applied to the average of width from level 1 to 9 (Table 1). The SDs of lateral opening, lateral closing, and vertical components were calculated as indicators representing variations of the masticatory path. The averages of 11 SDs from level 0 to 10 in the horizontal direction during opening movement, in the horizontal direction during closing movement, and in the vertical direction were taken as the lateral opening component, lateral closing component, and vertical component, respectively (Table 1). These values were then divided by the opening distance, and the value (SD/OD) was used as the index representing the stability of masticatory movement path.
2.4.2. Temporal parameters and parameters representing stability of masticatory movement rhythm
A piece of chewing gum (Trident1, USA) was used as the test food, which weighed approximately 2 g. The chewing gum was sufficiently softened before recording masticatory movement.
As to masticatory rhythm, each starting point of the opening phase, closing phase and occluding phase of each cycle were first identified using our own method [9]. Next, for 10 cycles from the fifth cycle, the opening time, the closing time and the occluding time, and the sum of all the three times were calculated. And then the coefficient of variations (CVs) were obtained from the mean time of the ten cycles and its standard deviation (Table 2), and the mean values were used as temporal parameters, and the CVs were used to represent the stability of masticatory movement rhythm.
2.3.
2.5.
2.2.
Test food
Recording of masticatory movement
Analyzing method
The subjects were asked to sit in a chair so that their Frankfurt plane was parallel to the floor with the head not fixed in a relaxed state, and were asked to chew softened chewing gum on their habitual chewing side for 20 sec. Incisal point movement during mastication was recorded by mandibular kinesiograph (K6I, Myotronics, USA) using a data recorder (XR5000, TEAC, Tokyo).
The spatial and temporal parameters, and the parameters representing the stability of masticatory movement path and rhythm were compared between males and females using statistical software (SPSS for Windows 10.0J, SPSS, Chicago, IL, USA). The comparison was investigated by an independent ttest. A P value of 0.05, Table 3).
4.
Discussion
During mastication, a rhythmic pattern is maintained by the pattern generator in the brain stem [28]. The regulation of this movement is also derived on the basis of feedback information from the periphery, such as the teeth, masticatory muscles, and temporomandibular joints [9,20,27]. It has been reported
240
journal of prosthodontic research 58 (2014) 237–242
Table 1 – Numerical data of the average path of subject 1. Level
Lateral opening (mm) Mean
0 1 2 3 4 5 6 7 8 9 10 Mean SD/OD (%)
0.0 1.6 1.7 1.5 1.2 0.8 0.3 0.1 0.5 1.1 2.3
Lateral closing (mm)
SD
Mean
SD
0.0 0.3 0.5 0.6 0.6 0.8 0.8 0.8 0.8 0.7 0.6
0.0 2.0 2.7 3.3 3.9 4.2 4.4 4.4 4.2 3.7 2.3
0.0 0.2 0.3 0.4 0.5 0.5 0.5 0.5 0.6 0.7 0.6
0.65 3.87
0.48 2.86
Width (mm)
3.6 4.4 4.8 5.1 5.0 4.7 4.3 3.7 2.6
4.2
Table 2 – Numerical data of the opening, closing, occluding, and cycle times of subject 1.
Vertical (mm)
Cycle
Mean
SD
0.0 1.5 3.0 4.6 6.1 7.6 9.1 10.6 12.2 13.7 15.2
0.0 0.1 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0.46 2.74
Opening (msec)
Closing (msec)
Occluding (msec)
Cycle (msec)
5 6 7 8 9 10 11 12 13 14
190 210 200 200 210 240 220 230 230 200
210 240 230 210 200 220 230 200 220 210
180 180 160 180 180 180 180 180 180 160
580 630 590 590 590 640 630 610 630 570
Mean SD CV (%)
213 16.4 7.7
217 13.4 6.2
176 8.4 4.8
606 25.0 4.1
Table 3 – Means (standard deviations) for the values of the spatial parameter, temporal parameter, stability of path, and stability of rhythm.
Spatial parameter (mm) Vertical movement Lateral movement Temporal parameter (msec) Opening time Closing time Occluding time Cycle time Stability of path (%) Lateral opening component Lateral closing component Vertical component Stability of rhythm (%) Opening time Closing time Occluding time Cycle time
Male
Female
P value
18.2 (3.4) 3.2 (1.0)
15.4 (2.7) 2.7 (0.8)
0.001 0.048
180.0 182.1 179.7 541.7
(33.5) (34.1) (28.6) (76.1)
201.6 205.7 187.8 595.2
(47.6) (39.9) (38.0) (93.2)
0.046 0.017 0.351 0.018
4.0 (1.6) 4.3 (1.5) 4.1 (1.3)
4.4 (1.6) 4.4 (1.3) 4.4 (1.3)
0.305 0.899 0.395
9.7 8.5 8.7 4.3
9.8 8.3 8.6 4.5
0.903 0.795 0.836 0.528
(2.5) (3.6) (2.8) (1.1)
that healthy subjects show a regular and stable masticatory movement path and rhythm [8]. However, masticatory movement may be affected by exogenous factors [9,20,26,27] such as masticating conditions, including food type or chewing methods, and can vary, even among healthy subjects. Therefore, it is recommended that such exogenous factors should be excluded when recording masticatory movement [10,11]. In this study, softened chewing gum was used as the test food because it does not change much in either hardness or size during the chewing sequence. Further, unilateral chewing was recommended instead of free chewing to eliminate any variations in chewing method [18,20,25,26]. We have previously observed that variations in masticatory movement can be minimized by employing softened chewing gum as the test food, the habitual side as the chewing side, and 10 cycles after the fourth to sixth cycle as the section selected for analysis [10]. Therefore, in this study, after considering the masticatory condition, the presence of gender differences in masticatory movement path and rhythm were investigated.
(3.2) (3.1) (2.6) (1.3)
Gender differences in masticatory movement have been previously investigated by many researchers. Neill and Howell [14] investigated quantitative parameters of mandibular movement when chewing various foods and found that with all food types, the cycle time was shorter for males than for females and that both vertical and lateral movements were greater for males than for females; the differences were statistically significant between genders. However, Kiliaridis et al. [15] reported that although there were significant differences in vertical and lateral movements between genders, there were no significant differences in cycle time. Youssef et al. [6] reported results different from those of Kiliaridis et al. [15], stating that significant differences were present in cycle time between males and females, with no significant differences in vertical and lateral movements. Further, Buschang et al. [16] showed that although there were no significant differences in lateral movement between genders, there were significant differences in vertical movement and cycle time. A study by Peyron et al. [7] reported that
journal of prosthodontic research 58 (2014) 237–242
cycle time tended to be shorter and that movement tended to be greater for males than for females. Salsench et al. [18] reported that although there were no significant differences between genders in the right vertical movement, there were significant differences in the left vertical movement and ambilateral cycle time. In addition, Lepley et al. [19] reported that although there were no significant differences in vertical movement and cycle time between genders, there was significant difference in lateral movement. As for the reasons that Buschang et al. [16] were able to detect gender difference, they listed the fact that they were able to select the 10 most representative cycles for each subject, who were instructed to masticate on one side; furthermore, they eliminated large differences among cycles. In this study, we analyzed masticatory movement with focus on masticatory conditions similar to those used by Buschang et al. [16] and found that the cycle time was significantly shorter for males than for females; both vertical and lateral movements were significantly greater for males than for females. Therefore, we were also able to detect gender difference. This result may also indicate that exogenous factors should be excluded when analyzing masticatory movement. Buschang et al. [16] used softened chewing gum with a texture that does not considerably change with mastication. In other experiments, peanuts whose size and hardness changed while chewing and relatively hard gummy that was a bit difficult to chew were used. This could perhaps be the reason why the other experiments could not detect gender differences. However, even in these studies, when looking at the values of the result, almost all of them showed that in compared with females, males had a shorter cycle time and larger movements. From these results it might be concluded that the amount of masticatory movement was greater and that the cycle time was shorter for males than for females. Also it could be contemplated that in general male masticates faster than female. In either way, the fact that differences were found between genders in both spatial and temporal parameters, it then would be necessary to evaluate male and female separately. With regard to the stability of masticatory movement during mastication, as far as we know, although there are no previous investigations on which we can compare, the results of this study did not find statistically significant differences in indicators representing the stability of masticatory path and rhythm between males and females. These results showed that, regardless of gender, normal healthy adults have regular and rhythmic masticatory movement. In other words, it could be said that for the stability of masticatory movement there is no need to pay special attention to gender differences. The results of paying attention to the chewing condition and looking for gender differences were that in normal healthy adults, although gender differences were found for the amount and rhythm of masticatory movement, there were no differences between genders in the stability of masticatory movement. It was clarified that when analyzing masticatory movement, there are indicators that need paying attention to gender difference and there are indicators that did not need such attention.
5.
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Conclusion
It was suggested that although there were no differences in the stability of masticatory movement path and rhythm between genders, there were gender differences in the spatial and temporal parameters of masticatory movement path and rhythm.
Conflict of interest statement The authors declare no competing financial interests.
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