- Email: [email protected]
Relationship between masticatory function, dental arch width, and bucco-lingual inclination of the first molars
orthodontic waves 65 (2006) 120–126
available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/odw
Research paper
Relationship between masticatory function, dental arch width, and bucco-lingual inclination of the first molars Ryosuke Hayashi *, Akira Kawamura, Kazutaka Kasai Department of Orthodontics, Nihon University School of Dentistry at Matsudo, 2-870-1 Sakaecho-nishi, Matsudo, Chiba 271-8587, Japan
article info
abstract
Article history:
The aim of this study was to clarify the influence of masticatory function on dental arch
Received 12 May 2006
forms. We evaluated the relationship between the masticatory movement path and occlusal
Received in revised form
force (as masticatory function) and the dental arch width and first molar bucco-lingual
9 August 2006
inclination. The subjects were 60 healthy adult females (mean 23.4 years; S.D. 1.6 years)
Accepted 10 August 2006
without previous orthodontic treatment or functional abnormalities in the temporoman-
Published on line 5 September 2006
dibular joint. Furthermore, the subjects were divided into a wide group (W-group) and a narrow group (N-group) based on mean maxillary inter-molar width in Japanese females.
Keywords:
The masticatory path was recorded using gnathohexagraph system. Maximum occlusal
Masticatory function
force was measured using a simple type occlusal force meter. And subjects’ arch width and
Masticatory movement
bucco-lingual inclination of the first molars was measured. W-group showed larger arch
Occlusal force
width and the first molar was more upright on the buccal side compared with N-group.
First molar inclination
Furthermore, the lateral component of masticatory movement and maximum occlusal force
Dental arch width
was large in W-group compared with N-group. In the group which strong occlusal force and grinding type mastication had wide arch width and the mandibular first molars upright on the buccal side. # 2006 Published by Elsevier Ltd.
1.
Introduction
The formation of dental arch morphology is influenced by jaw bones, muscles surrounding the mouth, and masticatory function. We have investigated dental arch form and molar tooth inclination from the perspective of orthodontics. Our evaluation of the relationship between first molar buccolingual inclination and maxillo-facial morphology [1,2] showed that the mandibular first molars were more upright on the buccal side, the mandibular cortical bone was thicker, and the dental arch width was larger in short facial type subjects in contrast to the long facial type. Comparing the dental arch form in Jomon period Japanese and that in modern * Corresponding author. Tel.: +81 47 360 9410; fax: +81 47 360 9410. E-mail address: [email protected] (R. Hayashi). 1344-0241/$ – see front matter # 2006 Published by Elsevier Ltd. doi:10.1016/j.odw.2006.08.003
Japanese [3], we reported that the molars were more upright on the buccal side and the dental arch width was larger in Jomon period Japanese. In these reports, we concluded that differences of masticatory function especially occlusal force and direction of occlusal force which applied to molars in the occlusal terminal phase influenced dental arch form and tooth inclination of the first molars. Furthermore, by a comparison of changes in dental arch form in crowding-improved and crowding-aggravation groups for 6 years until completing the permanent dental arch [4], the level of first molar buccal inclination and increases in the arch width were larger in the crowding-improved group than in the crowding-aggravation group. We speculated that masticatory function was involved
orthodontic waves 65 (2006) 120–126
121
Fig. 1 – An experimental view of a subject with wearing a head frame and a face bow of Gnatho-Hexagraph. Six degrees of freedom consisted of a head frame, a face bow, light-emitting diodes (LEDs), optical cameras, and a personal computer (Gnathohexagraph system, Ono Measurement Apparatus Co., Kanagawa). The sampling frequency was 89.3 Hz. The mean measurement error of the system was 150 mm (S.D. = 10 mm) [6]. Each subject was seated in an upright but relaxed position with the head unsupported and naturally oriented. A head frame and a face bow, each with three light-emitting diodes, were set securely onto the head and the dental clutch, which was bonded to the labial surfaces of lower incisors, respectively. The clutch was bent to ensure that the movement of the mandible and lip was inhibited as little as possible [7]. Two CCD cameras were placed approximately 1.2 meters in front of the subject.
in these differences, and increases in masticatory function caused first molar positional changes and increased the arch width. Therefore, we considered that masticatory function influences the tooth inclination of the first molars and arch width, and increases in malocclusion in modern Japanese are related to decreases in masticatory function. However, we have not investigated the relationship between masticatory function and dental arch form in detail, and there have been few other previous reports. In this study, to clarify the influence of masticatory function especially occlusal force and direction of occlusal force which applied to molars in the occlusal terminal phase on dental arch form and molar inclination, we evaluated the relationship between the masticatory movement path and maximum occlusal force and the dental arch width and first molar bucco-lingual inclination.
2.
Materials and methods
2.1.
Subjects and selection conditions
The subjects were 60 healthy young adult females (mean 23.4 years S.D. 1.6 years) without previous orthodontic treatment and functional abnormalities in the temporomandibular joint, and with the induction induced canine teeth, in whom normal overlap was noted without marked maxillo-mandibular antero-posterior disharmony, the amount of crowding was less than 2.0 mm, all permanent teeth excluding the maxillomandibular third teeth had erupted, and no restorations were inserted in the maxillo-mandibular bilateral first molars. All subjects’ informed consent was obtained prior to the investigation. And this study was conducted according to a
protocol reviewed by the Board of Nihon University School of Dentistry at Matsudo. Furthermore, setting the mean maxillary arch width which was defined as the distance between the bilateral mesio-buccal cusp tips of the maxillary first molars in Japanese females as the reference value [5], the subjects were divided into a wide group (W-group) whose maxillary arch width was higher than the reference value, and a narrow group (N-group) whose value was lower than the reference value.
Fig. 2 – The measurements of masticatory widths (MW). Setting the intercuspal position to level 0, and mean maximum mouth opening position to level 10, we measured the distance corresponding to levels 1–9 on the mouth opening and closing paths, and the mean value was calculated as the masticatory width.
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orthodontic waves 65 (2006) 120–126
Fig. 3 – The measurements of chewing angle. (1) Chewing angle of closing path (close); (2) chewing angle of opening path (open); total chewing angle (CA). After obtaining coordinate points of the mouth opening and closing paths corresponding to level 1 in the mean masticatory movement path, angles formed by the Y-axis and lines connecting these coordinate points and the origin were set as the mouth opening path angle and mouth closing path angle, respectively. And we defined the masticatory angle as the sum of the mouth opening path angle and mouth closing path angle.
2.2.
Measurement methods
Regarding masticatory function, the masticatory movement path (Figs. 1–3) and maximum occlusal force (Fig. 4) were measured. Furthermore, after collecting maxillo-mandibular dental arch models from the subjects, the arch width and angle of bucco-lingual inclination of the first molars were measured (Figs. 5–7).
2.2.1.
Masticatory movement path
The masticatory movement path during masticating chewing gum on the subjects’ main masticatory side was recorded for 30 s using a movement measurement apparatus with 6 degrees of freedom consisted of a head frame, a face bow, light-emitting diodes (LEDs), optical cameras, and a personal computer (Gnathohexagraph system, Ono Measurement Apparatus Co., Kanagawa). The sampling frequency was 89.3 Hz. The mean measurement error of the system was 150 mm (S.D. = 10 mm) [6]. Each subject was seated in an upright but relaxed position with the head unsupported and naturally oriented. A head frame and a face bow, each with three light-emitting diodes, were set securely onto the head
and the dental clutch, which was bonded to the labial surfaces of lower incisors, respectively. The clutch was bent to ensure that the movement of the mandible and lip was inhibited as little as possible [7]. Two CCD cameras were placed approximately 1.2 meters in front of the subject (Fig. 1.) Chewing Brushing Gum (LION Co.) was used for mastication. The masticatory movement path during 10 strokes from the 5th to 14th stroke was analyzed after initiating mastication on the main first molar masticatory side. The masticatory width and angle of mouth opening and closing paths on the frontal plane during 10 strokes were measured, and mean values were calculated. Only when the main masticatory side recognized at the subjects’ interview accorded with the main masticatory side at the first stroke and many side in a ratio of right and left of the free mastication of chewing gum, did we consider it as the main masticatory side. Calculation methods of each measurement value are as follows [8]: (1) Masticatory width (Fig. 2) Setting the intercuspal position to level 0, and mean maximum mouth opening position to level 10, we
Fig. 4 – Occlusal force meter and an experimental view of a subject biting in first molar. Maximum occlusal force on the main masticatory side of the subjects was measured using a simple type occlusal force meter (GM10, Nagano Measurement Apparatus Factory). Each subject was seated in an upright but relaxed position with the head unsupported and naturally oriented.
orthodontic waves 65 (2006) 120–126
Fig. 5 – Reference plane and the X, Y, Z axes. Reference planes were designated between the incisive papilla, and the right and left papilla between the second premolars and first molars. Reference planes were set mathematically horizontal with the two related to the right and left lingual interdental papillae between the second premolars and first molars were aligned parallel to the x axis, and the y axis antero-posterior. For each plane, the origin of axes (0, 0, 0) was set at middle points of right and left lingual interdental papillae between the second premolars and first molars.
measured the distance corresponding to levels 1–9 on the mouth opening and closing paths, and the mean value was calculated as the masticatory width [8]. (2) Mouth opening and closing path angles (Fig. 3) After obtaining coordinate points of the mouth opening and closing paths corresponding to level 1 in the mean masticatory movement path, angles formed by the Y-axis
123
Fig. 7 – Bucco-lingual inclination of the first molars formed by the Z-axis and the vector passing 2 points, which were a shifting point from the buccal groove to buccal surface groove and that from the lingual groove to lingual surface groove of the first molar.
and lines connecting these coordinate points and the origin were set as the mouth opening path angle (open) and mouth closing path angle (close), respectively [8]. (3) Total chewing angle (CA) (Fig. 3) We defined the total chewing angle as the sum of the mouth opening path angle and mouth closing path angle.
2.2.2.
Maximum occlusal force
Maximum occlusal force on the main masticatory side of the subjects was measured using a simple type occlusal force meter (GM10, Nagano Measurement Apparatus Factory). GM10 has few burdens to a subject and can measure stable occlusal force [9]. Each subject was seated in an upright but relaxed position with the head unsupported and naturally oriented, and was asked to bite with maximum bite force three times in succession, resting 2 or 3 s between each bite. The largest value was chosen as the maximum occlusal force (Fig. 4).
2.2.3.
Fig. 6 – Arch width measurements. Inter-canine width was defined as the distance between the bilateral canine crests and inter-molar width was defined as the distance between the bilateral first molar mesio-buccal crests.
Arch width and first molar inclination
Maxillo-mandibular dental arch models were scanned using a contact-type three-dimensional measurement apparatus (3DPicza, Roland Co.), setting the plane passing 3 points, which were the interpapillary crest between the bilateral central incisors and bilateral interpapillary crests between the second premolar and first molar, as the reference plane (Fig. 5). Using three-dimensional morphological analysis software (3DRUGLE, Medic Engineering Inc.), we measured the distance between the bilateral first molars and that between the bilateral canines as the dental arch width, and the buccolingual inclination of the first molars [4] (Figs. 6 and 7). Calculation methods of each measurement value are as follows:
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orthodontic waves 65 (2006) 120–126
Table 1 – Comparison of arch width and first molar inclination between W-group and N-group Variables
W-group (N = 31)
N-group (N = 29) Mean
t-Test
Mean
S.D.
S.D.
Maxilla Inter molar (mm) Inter canine (mm) R6 B-L inc. (8) L6 B-L inc. (8)
54.28 35.99 83.96 85.75
1.12 1.43 7.32 5.32
51.16 33.59 82.86 84.83
1.53 1.43 5.45 8.82
Mandible Inter molar (mm) Inter canine (mm) R6 B-L inc. (8) L6 B-L inc. (8)
45.67 28.18 101.88 103.58
1.78 1.46 7.88 8.98
43.86 26.05 107.26 109.08
2.39 1.77 8.64 8.92
** *
N.S. N.S. ** * ** **
N: sample size, S.D.: standard deviation. *P < .05, **P < .01, N.S.: not significant.
(1) Inter-canine width (Fig. 6) The distance between the bilateral canine crests was measured. (2) Inter-molar width (Fig. 6) The distance between the bilateral first molar mesiobuccal crests was measured. (3) Bucco-lingual inclination of the first molars (uB-L inc.) (Fig. 7) The angle formed by the Z-axis and the vector passing 2 points, which were a shifting point from the buccal groove to buccal surface groove and that from the lingual groove to lingual surface groove of the first molar. Each measurement item was compared between W-group and N-group using Student’ t-test.
3.
Results
Regarding dental arch morphology measurement, W-group showed a significantly larger maxillo-mandibular inter-canine width and mandibular arch width, compared with N-group. Although no significant differences in the first molar buccolingual inclination were found between the two groups in the maxillary arch, the tooth inclination in the mandibular arch was significantly smaller in W-group than in N-group.
Table 2 – Comparison of masticatory measurements between W-group and N-group Variables
MW (mm) Close (8) Open (8) CA (8)
W-group (N = 31)
N-group (N = 29)
Mean
S.D.
Mean
S.D.
3.59 47.68 22.04 69.72
1.14 11.59 20.52 22.59
2.11 33.57 12.10 45.66
0.84 9.53 22.14 25.64
t-Test
(Table 1). Regarding the measurement of the masticatory path, W-group showed a significantly larger masticatory width, mouth closing path angle, and total chewing angle, compared with N-group (Table 2). Furthermore, the maximum occlusal force was significantly larger in W-group than in Ngroup (Table 3). Therefore, the mandibular first molar was more upright on the buccal side and the dental arch width was larger in W-group, compared with N-group. Regarding masticatory function, the lateral component of the masticatory movement path and maximum occlusal force were larger in W-group than in N-group.
4.
Discussion
Previous reports on the relationship between occlusal force and maxillo-facial morphology suggested that maxillo-facial morphology was more frequently the short facial type when maximum occlusal force was larger [10,11]. Investigating developmental changes in normal and long facial types, it has been reported that since muscles related to occlusion were not strengthened in the growth period in the long facial type, occlusal force was weak in this type, the molars erupted to excess, and the anterior growth of the mandible was facilitated [12,13]. Furthermore, it has been reported that when masticatory training was performed on long facial type children, the anterior growth of the mandible was facilitated, and occlusal force was increased [14]. In these circumstances, occlusal force and maxillo-facial morphology affect it closely. Kanazawa et al. [15] reported that lingual inclination of mandibular molars of ancient people was less than that of modern people, and the mandibular cortical bone of ancient people was thicker than that of modern people to support
*
Table 3 – Comparison of maximam occlusal force (MF) between W-group and N-group
N.S.
Variables
**
*
N: sample size, S.D.: standard deviation. *P < 0.05, **P < 0.01, N.S.: not significant; MW: masticatory widths; Close: chewing angle of closing path; Open: chewing angle of opening path; CA: total chewing angle.
MF (kgN)
W-group (N = 31)
N-group (N = 29)
Mean
S.D.
Mean
S.D.
0.41
0.13
0.29
0.11
N: sample size, S.D.: standard deviation. **P < .01.
t-Test
**
orthodontic waves 65 (2006) 120–126
strong bite force and masticatory function. Furthermore, Kasai et al. [16] reported that Fijians with a strong occlusal force had the wide dental arch and the mandibular first molar upright on the buccal side in contrast to Japanese. In this study W-group had the wide dental arch and the mandibular first molar upright on the buccal side. The results agreed with those of Kanazawa et al. [15] and Kasai et al. [16] Regarding maxillary, Okano [17] reported main lateral growth of maxillary arch was not change of tooth inclination but growth of a palate. In addition, a strong racial palate of occlusal force was larger than modern Japanese. Masumoto et al. [18] reported maxillary first molar inclination was not affected by a masticatory function than mandibular first molar. And maxillary first molar inclination and maxillary arch width did not have correlation. In this study, it speculated W-group with strong occlusal force had wide maxillary arch width was affected not change of first molar tooth inclination, but growth of a palate. Regarding the masticatory movement path, although there have been reports in which the normal masticatory movement path was classified [19,20], ideal masticatory movement was considered [21,22], and the influence of the size of food and differences in eating style on the masticatory movement path were evaluated [23,24], there have been few reports of the relationship between the masticatory movement path and dento-facial morphology. The lateral component of the mandibular movement during mastication was larger in Wgroup than in N-group in this study. Regarding grinding teeth during mastication, it has been reported that grinding contact of the maxillo-mandibular molars increased with increases in the lateral component of masticatory movement [25]. Investigating kinetics during first molar functioning, Ishida and Soma [26] reported that the maxillo-mandibular first molars received lateral force in the buccal direction in the position near the occlusal terminal position. Comparing masticatory movement in modern Japanese and that in Australian aborigines with developed masticatory function, Aboshi et al. [27] reported that modern Japanese showed chopping type mastication, whereas Australian aborigines showed grinding type mastication. Fujino [28] described that the round bone of the mandibular molar region had a structure resistant to torsional moments. Nakajima [29] described that the buccal cortical bone thickness of mandibular molars was influenced by masticatory muscle and mandibular movement. Sato et al. [30] reported that the bone density and cortical bones thickness more increase when occlusal force resulting from mastication is added. It considered that since strong occlusal force was always applied to the molar area in the buccal direction in Australian aborigines due to grinding type mastication,their bone density and cortical bone thickness on the buccal side increased, and the first molars were more upright on the buccal side and stable. In this study grinding type mastication group had wide mandibular arch width and the mandibular first molar upright on the buccal side. Therefore, it was speculated that when the lateral component of mandibular movement during mastication is larger as in the grinding type, the lateral force applied to the molars increases, and the mandibular first molars show buccal positional changes, leading to increases in the dental arch width. In addition, Schwartz [31] reported aborigine with strong masticatory function have helicoidal plane of occlusal
125
characteristics of functional cusp of heavy attrition and mandibular molar too much upright on the buccal side. This feature stand for maxillary molar was hard to be affected by inclination condition of the mandibular molar. In this study, it considered bucco-lingual inclinaton of mandibular first molar did not influenced of bucco-lingual inclination of maxillary first molar. The results agreed with that of Schwartz [31]. In the group which strong occlusal force and grinding type mastication had wide arch width and the mandibular first molars upright on the buccal side. Therefore, it was speculated that reinforce of occlulal force and masticatory training to obtain grinding type masticatory movement cause positional changes in the mandibular molar and increase the dental arch width. However, further examination is necessary about this point.
reference
[1] Tsunori M, Mashita M, Kasai K. Relationship between types and bone characteristics of the mandible obtained by CT scanning. Angle Orthod 1998;68:557–62. [2] Kawamura A. Relationship between buccolingual inclination of mandibular molars and dentofacial morphology. Nihon Univ J Sci 1999;25:339–49. [3] Kasai K, Kawamura A. Correlation between buccolingual inclination and wear of mandibular teeth in ancient and modern Japanese. Arch Oral Biol 2001;46:269–73. [4] Hayashi R, Knazawa E, Kasai K. Three-dimensional changes of the dental arch form and the inclination of the first molars—comparison between crowding-improvement and crowding-aggravation groups. Orthod wave 2006;65:21–30. [5] Fukuzawa H. Multivariate analysis of dental arch size in south pacific populations. Nihon Univ J Oral Sci 1998;24:1–9. [6] Tokiwa H, Miura F, Kuwahara Y. Development of a new analyzing system for stomatognathic functions. J Jpn Soc Stomatognath Funct 1996;3:11–24. [7] Miyawaki S, Ohkochi N, Kawakami T, Sugimura M. Effect of food size on the movement of the mandibular first molars and condyles during deliberate unilateral mastication in humans. J Dent Res 2000;79:1525–31. [8] Chujo M, Sugawara J, Tomoyose Y, Kawamura H, Mitani H. Effects of functional training with chewing gum after surgical orthodontic treatment on masticatory system in jaw deformity patients. Jpn J Jaw Deform 2004;14:170–9. [9] Usui T, Satoh Y, Uematsu S, Kurihara S. Application to clinical of the occlusal force meter. J Kouhokushineths Orthod Soc 2001;9:67–74. [10] Kiliaridis S, Kjellberg H, Wenneberg B, Engstrom E. The relationship between maximal bite force,bite force endurance, and facial morphology during growth. A crosssectonal study. Acta Odontol Scand 1993;51:323–31. [11] Ingervall B, Minder C. Correlation between maximum bite force and facial morphology in children. Angle Orthod 1997;67:415–24. [12] Proffit WR, Fields HW, Nixon WL. Occlusal forces in normal-and long-face adults. J Dent Res 1983;62:566–71. [13] Proffit WR, Fielda HW. Occlusal forces in normal-and longface children. J Dent Res 1983;62:571–4. [14] Ingervall B, Bitsanis E. A pilot study of the effect of masticatory muscle training on facial growth in long-face children. Eur J Orthod 1987;9:15–23. [15] Kanazawa E, Kasai K. Comparative study of vertical sections of the Jomon and modern Japanese mandibles. Anthrop Sci 1998;106:107–18.
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[16] Kasai K, Kanazawa E, Aboshi H, Tuisuva J, Takahashi M, Matsuno M. Comparative study of craniofacial morphology and bite force in Fijians and Japanese. Am J Hum Biol 1998;10:63–72. [17] Okano M. A growth pattern of bucco-lingual inclination and arch width of first molar—a comparison with Japanese and 2 group of South Pacific populations. Orthod Wave Jpn Ed 2006;65:112–21. [18] Masumoto T, Hayashi I, Kawamura A, Tanaka K, Kasai K. Relationships among facial type, bucco-lingual molar inclination, and cortical born thickness of the mandibule. Eur J Orthod 2001;23:15–23. [19] Proschel P. An extensive classification of chewing patterns in the frontal plane. J Craniomandibular Pract 1987;5:56–63. [20] Wilding RJC, Lewin A. A computer analysis of normal human masticatory movements recorded with a sirognathograph. Arch Oral Biol 1991;36:65–75. [21] Yamashita S, Hatch JP, Rugh JD. Does chewing performance depend upon a specific masticatory pattern? J Oral Rehabil 1999;26:547–53. [22] Wilding RJC, Lewin A. A model for optimum functional human jaw movements based on values associated with preferred chewing patterns. Arch Oral Biol 1991;36:519–23. [23] Pro¨schel P, Hofmann M. Frontal chewing patterns of the incisor point and their dependence on resistance of food and type of occlusion. J Prosthet Dent 1988;59:617–24.
[24] Shiga H, Kobayashi Y, Arakawa I, Shonai Y. Selecton of food and chewing side for evaluating masticatory path stability. Odontology 2003;91:31–6. [25] Stanley R, Charles H, Steven T. Study of gliding tooth contacts during mastication. J Periodontol 1976;47:331–4. [26] Ishida T, Soma K. Stress analysis of the space between the upper and lower first molars during the final stage of occlusion. J Jpn Orthod Soc 1993;52:161–72. [27] Aboshi H, Kasai K, Ozaki T, Kanazawa E. Relationship between masticatory function and standing position of mandibular molars. Anthropol Sci 1999;107:82. [28] Fujino A. Studies on the mechanism of stress–strain distribution in mandibles. Part 1: an analysis of stress– strain distribution in human dry mandible. J Osaka Odont Soc 1983;46:513–42 (in Japanese). [29] Nakajima K. A study on the internal structure of the Japanese mandible. J Tokyo Dent Coll Soc 1995;95:229–38 (in Japanese). [30] Sato H, Kawamura A, Yamaguchi M, Kasai K. Relationship between masticatory function and internal structure of the mandible based on computed tomography findings. Am J Orthod 2005;128:766–73. [31] Schwartz GT. Enamel thickness and the helicoidal wear plane in modern human mandibular molars. Arch Oral Biol 2000;45:401–9.
available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/odw
Research paper
Relationship between masticatory function, dental arch width, and bucco-lingual inclination of the first molars Ryosuke Hayashi *, Akira Kawamura, Kazutaka Kasai Department of Orthodontics, Nihon University School of Dentistry at Matsudo, 2-870-1 Sakaecho-nishi, Matsudo, Chiba 271-8587, Japan
article info
abstract
Article history:
The aim of this study was to clarify the influence of masticatory function on dental arch
Received 12 May 2006
forms. We evaluated the relationship between the masticatory movement path and occlusal
Received in revised form
force (as masticatory function) and the dental arch width and first molar bucco-lingual
9 August 2006
inclination. The subjects were 60 healthy adult females (mean 23.4 years; S.D. 1.6 years)
Accepted 10 August 2006
without previous orthodontic treatment or functional abnormalities in the temporoman-
Published on line 5 September 2006
dibular joint. Furthermore, the subjects were divided into a wide group (W-group) and a narrow group (N-group) based on mean maxillary inter-molar width in Japanese females.
Keywords:
The masticatory path was recorded using gnathohexagraph system. Maximum occlusal
Masticatory function
force was measured using a simple type occlusal force meter. And subjects’ arch width and
Masticatory movement
bucco-lingual inclination of the first molars was measured. W-group showed larger arch
Occlusal force
width and the first molar was more upright on the buccal side compared with N-group.
First molar inclination
Furthermore, the lateral component of masticatory movement and maximum occlusal force
Dental arch width
was large in W-group compared with N-group. In the group which strong occlusal force and grinding type mastication had wide arch width and the mandibular first molars upright on the buccal side. # 2006 Published by Elsevier Ltd.
1.
Introduction
The formation of dental arch morphology is influenced by jaw bones, muscles surrounding the mouth, and masticatory function. We have investigated dental arch form and molar tooth inclination from the perspective of orthodontics. Our evaluation of the relationship between first molar buccolingual inclination and maxillo-facial morphology [1,2] showed that the mandibular first molars were more upright on the buccal side, the mandibular cortical bone was thicker, and the dental arch width was larger in short facial type subjects in contrast to the long facial type. Comparing the dental arch form in Jomon period Japanese and that in modern * Corresponding author. Tel.: +81 47 360 9410; fax: +81 47 360 9410. E-mail address: [email protected] (R. Hayashi). 1344-0241/$ – see front matter # 2006 Published by Elsevier Ltd. doi:10.1016/j.odw.2006.08.003
Japanese [3], we reported that the molars were more upright on the buccal side and the dental arch width was larger in Jomon period Japanese. In these reports, we concluded that differences of masticatory function especially occlusal force and direction of occlusal force which applied to molars in the occlusal terminal phase influenced dental arch form and tooth inclination of the first molars. Furthermore, by a comparison of changes in dental arch form in crowding-improved and crowding-aggravation groups for 6 years until completing the permanent dental arch [4], the level of first molar buccal inclination and increases in the arch width were larger in the crowding-improved group than in the crowding-aggravation group. We speculated that masticatory function was involved
orthodontic waves 65 (2006) 120–126
121
Fig. 1 – An experimental view of a subject with wearing a head frame and a face bow of Gnatho-Hexagraph. Six degrees of freedom consisted of a head frame, a face bow, light-emitting diodes (LEDs), optical cameras, and a personal computer (Gnathohexagraph system, Ono Measurement Apparatus Co., Kanagawa). The sampling frequency was 89.3 Hz. The mean measurement error of the system was 150 mm (S.D. = 10 mm) [6]. Each subject was seated in an upright but relaxed position with the head unsupported and naturally oriented. A head frame and a face bow, each with three light-emitting diodes, were set securely onto the head and the dental clutch, which was bonded to the labial surfaces of lower incisors, respectively. The clutch was bent to ensure that the movement of the mandible and lip was inhibited as little as possible [7]. Two CCD cameras were placed approximately 1.2 meters in front of the subject.
in these differences, and increases in masticatory function caused first molar positional changes and increased the arch width. Therefore, we considered that masticatory function influences the tooth inclination of the first molars and arch width, and increases in malocclusion in modern Japanese are related to decreases in masticatory function. However, we have not investigated the relationship between masticatory function and dental arch form in detail, and there have been few other previous reports. In this study, to clarify the influence of masticatory function especially occlusal force and direction of occlusal force which applied to molars in the occlusal terminal phase on dental arch form and molar inclination, we evaluated the relationship between the masticatory movement path and maximum occlusal force and the dental arch width and first molar bucco-lingual inclination.
2.
Materials and methods
2.1.
Subjects and selection conditions
The subjects were 60 healthy young adult females (mean 23.4 years S.D. 1.6 years) without previous orthodontic treatment and functional abnormalities in the temporomandibular joint, and with the induction induced canine teeth, in whom normal overlap was noted without marked maxillo-mandibular antero-posterior disharmony, the amount of crowding was less than 2.0 mm, all permanent teeth excluding the maxillomandibular third teeth had erupted, and no restorations were inserted in the maxillo-mandibular bilateral first molars. All subjects’ informed consent was obtained prior to the investigation. And this study was conducted according to a
protocol reviewed by the Board of Nihon University School of Dentistry at Matsudo. Furthermore, setting the mean maxillary arch width which was defined as the distance between the bilateral mesio-buccal cusp tips of the maxillary first molars in Japanese females as the reference value [5], the subjects were divided into a wide group (W-group) whose maxillary arch width was higher than the reference value, and a narrow group (N-group) whose value was lower than the reference value.
Fig. 2 – The measurements of masticatory widths (MW). Setting the intercuspal position to level 0, and mean maximum mouth opening position to level 10, we measured the distance corresponding to levels 1–9 on the mouth opening and closing paths, and the mean value was calculated as the masticatory width.
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Fig. 3 – The measurements of chewing angle. (1) Chewing angle of closing path (close); (2) chewing angle of opening path (open); total chewing angle (CA). After obtaining coordinate points of the mouth opening and closing paths corresponding to level 1 in the mean masticatory movement path, angles formed by the Y-axis and lines connecting these coordinate points and the origin were set as the mouth opening path angle and mouth closing path angle, respectively. And we defined the masticatory angle as the sum of the mouth opening path angle and mouth closing path angle.
2.2.
Measurement methods
Regarding masticatory function, the masticatory movement path (Figs. 1–3) and maximum occlusal force (Fig. 4) were measured. Furthermore, after collecting maxillo-mandibular dental arch models from the subjects, the arch width and angle of bucco-lingual inclination of the first molars were measured (Figs. 5–7).
2.2.1.
Masticatory movement path
The masticatory movement path during masticating chewing gum on the subjects’ main masticatory side was recorded for 30 s using a movement measurement apparatus with 6 degrees of freedom consisted of a head frame, a face bow, light-emitting diodes (LEDs), optical cameras, and a personal computer (Gnathohexagraph system, Ono Measurement Apparatus Co., Kanagawa). The sampling frequency was 89.3 Hz. The mean measurement error of the system was 150 mm (S.D. = 10 mm) [6]. Each subject was seated in an upright but relaxed position with the head unsupported and naturally oriented. A head frame and a face bow, each with three light-emitting diodes, were set securely onto the head
and the dental clutch, which was bonded to the labial surfaces of lower incisors, respectively. The clutch was bent to ensure that the movement of the mandible and lip was inhibited as little as possible [7]. Two CCD cameras were placed approximately 1.2 meters in front of the subject (Fig. 1.) Chewing Brushing Gum (LION Co.) was used for mastication. The masticatory movement path during 10 strokes from the 5th to 14th stroke was analyzed after initiating mastication on the main first molar masticatory side. The masticatory width and angle of mouth opening and closing paths on the frontal plane during 10 strokes were measured, and mean values were calculated. Only when the main masticatory side recognized at the subjects’ interview accorded with the main masticatory side at the first stroke and many side in a ratio of right and left of the free mastication of chewing gum, did we consider it as the main masticatory side. Calculation methods of each measurement value are as follows [8]: (1) Masticatory width (Fig. 2) Setting the intercuspal position to level 0, and mean maximum mouth opening position to level 10, we
Fig. 4 – Occlusal force meter and an experimental view of a subject biting in first molar. Maximum occlusal force on the main masticatory side of the subjects was measured using a simple type occlusal force meter (GM10, Nagano Measurement Apparatus Factory). Each subject was seated in an upright but relaxed position with the head unsupported and naturally oriented.
orthodontic waves 65 (2006) 120–126
Fig. 5 – Reference plane and the X, Y, Z axes. Reference planes were designated between the incisive papilla, and the right and left papilla between the second premolars and first molars. Reference planes were set mathematically horizontal with the two related to the right and left lingual interdental papillae between the second premolars and first molars were aligned parallel to the x axis, and the y axis antero-posterior. For each plane, the origin of axes (0, 0, 0) was set at middle points of right and left lingual interdental papillae between the second premolars and first molars.
measured the distance corresponding to levels 1–9 on the mouth opening and closing paths, and the mean value was calculated as the masticatory width [8]. (2) Mouth opening and closing path angles (Fig. 3) After obtaining coordinate points of the mouth opening and closing paths corresponding to level 1 in the mean masticatory movement path, angles formed by the Y-axis
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Fig. 7 – Bucco-lingual inclination of the first molars formed by the Z-axis and the vector passing 2 points, which were a shifting point from the buccal groove to buccal surface groove and that from the lingual groove to lingual surface groove of the first molar.
and lines connecting these coordinate points and the origin were set as the mouth opening path angle (open) and mouth closing path angle (close), respectively [8]. (3) Total chewing angle (CA) (Fig. 3) We defined the total chewing angle as the sum of the mouth opening path angle and mouth closing path angle.
2.2.2.
Maximum occlusal force
Maximum occlusal force on the main masticatory side of the subjects was measured using a simple type occlusal force meter (GM10, Nagano Measurement Apparatus Factory). GM10 has few burdens to a subject and can measure stable occlusal force [9]. Each subject was seated in an upright but relaxed position with the head unsupported and naturally oriented, and was asked to bite with maximum bite force three times in succession, resting 2 or 3 s between each bite. The largest value was chosen as the maximum occlusal force (Fig. 4).
2.2.3.
Fig. 6 – Arch width measurements. Inter-canine width was defined as the distance between the bilateral canine crests and inter-molar width was defined as the distance between the bilateral first molar mesio-buccal crests.
Arch width and first molar inclination
Maxillo-mandibular dental arch models were scanned using a contact-type three-dimensional measurement apparatus (3DPicza, Roland Co.), setting the plane passing 3 points, which were the interpapillary crest between the bilateral central incisors and bilateral interpapillary crests between the second premolar and first molar, as the reference plane (Fig. 5). Using three-dimensional morphological analysis software (3DRUGLE, Medic Engineering Inc.), we measured the distance between the bilateral first molars and that between the bilateral canines as the dental arch width, and the buccolingual inclination of the first molars [4] (Figs. 6 and 7). Calculation methods of each measurement value are as follows:
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Table 1 – Comparison of arch width and first molar inclination between W-group and N-group Variables
W-group (N = 31)
N-group (N = 29) Mean
t-Test
Mean
S.D.
S.D.
Maxilla Inter molar (mm) Inter canine (mm) R6 B-L inc. (8) L6 B-L inc. (8)
54.28 35.99 83.96 85.75
1.12 1.43 7.32 5.32
51.16 33.59 82.86 84.83
1.53 1.43 5.45 8.82
Mandible Inter molar (mm) Inter canine (mm) R6 B-L inc. (8) L6 B-L inc. (8)
45.67 28.18 101.88 103.58
1.78 1.46 7.88 8.98
43.86 26.05 107.26 109.08
2.39 1.77 8.64 8.92
** *
N.S. N.S. ** * ** **
N: sample size, S.D.: standard deviation. *P < .05, **P < .01, N.S.: not significant.
(1) Inter-canine width (Fig. 6) The distance between the bilateral canine crests was measured. (2) Inter-molar width (Fig. 6) The distance between the bilateral first molar mesiobuccal crests was measured. (3) Bucco-lingual inclination of the first molars (uB-L inc.) (Fig. 7) The angle formed by the Z-axis and the vector passing 2 points, which were a shifting point from the buccal groove to buccal surface groove and that from the lingual groove to lingual surface groove of the first molar. Each measurement item was compared between W-group and N-group using Student’ t-test.
3.
Results
Regarding dental arch morphology measurement, W-group showed a significantly larger maxillo-mandibular inter-canine width and mandibular arch width, compared with N-group. Although no significant differences in the first molar buccolingual inclination were found between the two groups in the maxillary arch, the tooth inclination in the mandibular arch was significantly smaller in W-group than in N-group.
Table 2 – Comparison of masticatory measurements between W-group and N-group Variables
MW (mm) Close (8) Open (8) CA (8)
W-group (N = 31)
N-group (N = 29)
Mean
S.D.
Mean
S.D.
3.59 47.68 22.04 69.72
1.14 11.59 20.52 22.59
2.11 33.57 12.10 45.66
0.84 9.53 22.14 25.64
t-Test
(Table 1). Regarding the measurement of the masticatory path, W-group showed a significantly larger masticatory width, mouth closing path angle, and total chewing angle, compared with N-group (Table 2). Furthermore, the maximum occlusal force was significantly larger in W-group than in Ngroup (Table 3). Therefore, the mandibular first molar was more upright on the buccal side and the dental arch width was larger in W-group, compared with N-group. Regarding masticatory function, the lateral component of the masticatory movement path and maximum occlusal force were larger in W-group than in N-group.
4.
Discussion
Previous reports on the relationship between occlusal force and maxillo-facial morphology suggested that maxillo-facial morphology was more frequently the short facial type when maximum occlusal force was larger [10,11]. Investigating developmental changes in normal and long facial types, it has been reported that since muscles related to occlusion were not strengthened in the growth period in the long facial type, occlusal force was weak in this type, the molars erupted to excess, and the anterior growth of the mandible was facilitated [12,13]. Furthermore, it has been reported that when masticatory training was performed on long facial type children, the anterior growth of the mandible was facilitated, and occlusal force was increased [14]. In these circumstances, occlusal force and maxillo-facial morphology affect it closely. Kanazawa et al. [15] reported that lingual inclination of mandibular molars of ancient people was less than that of modern people, and the mandibular cortical bone of ancient people was thicker than that of modern people to support
*
Table 3 – Comparison of maximam occlusal force (MF) between W-group and N-group
N.S.
Variables
**
*
N: sample size, S.D.: standard deviation. *P < 0.05, **P < 0.01, N.S.: not significant; MW: masticatory widths; Close: chewing angle of closing path; Open: chewing angle of opening path; CA: total chewing angle.
MF (kgN)
W-group (N = 31)
N-group (N = 29)
Mean
S.D.
Mean
S.D.
0.41
0.13
0.29
0.11
N: sample size, S.D.: standard deviation. **P < .01.
t-Test
**
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strong bite force and masticatory function. Furthermore, Kasai et al. [16] reported that Fijians with a strong occlusal force had the wide dental arch and the mandibular first molar upright on the buccal side in contrast to Japanese. In this study W-group had the wide dental arch and the mandibular first molar upright on the buccal side. The results agreed with those of Kanazawa et al. [15] and Kasai et al. [16] Regarding maxillary, Okano [17] reported main lateral growth of maxillary arch was not change of tooth inclination but growth of a palate. In addition, a strong racial palate of occlusal force was larger than modern Japanese. Masumoto et al. [18] reported maxillary first molar inclination was not affected by a masticatory function than mandibular first molar. And maxillary first molar inclination and maxillary arch width did not have correlation. In this study, it speculated W-group with strong occlusal force had wide maxillary arch width was affected not change of first molar tooth inclination, but growth of a palate. Regarding the masticatory movement path, although there have been reports in which the normal masticatory movement path was classified [19,20], ideal masticatory movement was considered [21,22], and the influence of the size of food and differences in eating style on the masticatory movement path were evaluated [23,24], there have been few reports of the relationship between the masticatory movement path and dento-facial morphology. The lateral component of the mandibular movement during mastication was larger in Wgroup than in N-group in this study. Regarding grinding teeth during mastication, it has been reported that grinding contact of the maxillo-mandibular molars increased with increases in the lateral component of masticatory movement [25]. Investigating kinetics during first molar functioning, Ishida and Soma [26] reported that the maxillo-mandibular first molars received lateral force in the buccal direction in the position near the occlusal terminal position. Comparing masticatory movement in modern Japanese and that in Australian aborigines with developed masticatory function, Aboshi et al. [27] reported that modern Japanese showed chopping type mastication, whereas Australian aborigines showed grinding type mastication. Fujino [28] described that the round bone of the mandibular molar region had a structure resistant to torsional moments. Nakajima [29] described that the buccal cortical bone thickness of mandibular molars was influenced by masticatory muscle and mandibular movement. Sato et al. [30] reported that the bone density and cortical bones thickness more increase when occlusal force resulting from mastication is added. It considered that since strong occlusal force was always applied to the molar area in the buccal direction in Australian aborigines due to grinding type mastication,their bone density and cortical bone thickness on the buccal side increased, and the first molars were more upright on the buccal side and stable. In this study grinding type mastication group had wide mandibular arch width and the mandibular first molar upright on the buccal side. Therefore, it was speculated that when the lateral component of mandibular movement during mastication is larger as in the grinding type, the lateral force applied to the molars increases, and the mandibular first molars show buccal positional changes, leading to increases in the dental arch width. In addition, Schwartz [31] reported aborigine with strong masticatory function have helicoidal plane of occlusal
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characteristics of functional cusp of heavy attrition and mandibular molar too much upright on the buccal side. This feature stand for maxillary molar was hard to be affected by inclination condition of the mandibular molar. In this study, it considered bucco-lingual inclinaton of mandibular first molar did not influenced of bucco-lingual inclination of maxillary first molar. The results agreed with that of Schwartz [31]. In the group which strong occlusal force and grinding type mastication had wide arch width and the mandibular first molars upright on the buccal side. Therefore, it was speculated that reinforce of occlulal force and masticatory training to obtain grinding type masticatory movement cause positional changes in the mandibular molar and increase the dental arch width. However, further examination is necessary about this point.
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