| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Scientific Section |
Tokyo Medical and Dental University, Japan
Dr T. Kameyama, Orthodontic Science, Department of Orofacial Development and Function, Division of Oral Health Sciences, Graduate School, Tokyo Medical and Dental University, 1–5–45 Yushima, Bunkyo-ku, Tokyo, 113-8549, Japan. E-mail:
kame.orts{at}tmd.ac.jp
Abstract
Aim: To examine the effects of inactive periods of force on the amount of tooth displacement and root resorption during experimental tooth movement in rats.
Sample: Sixty 11-week-old male Sprague-Dawley rats.
Method: The maxillary first molar (M1) was moved mesially using a removable titanium-nickel alloy closed coil spring for 14 days. The rats were divided into four groups with, 0, 1, 4, and 9 hours of inactivation per day.
Results: Tooth displacement in the 0- and 1-hour groups was significantly greater than that in the 9-hour group. The area of root resorption in the 4- and 9-hour groups was significantly less than that in the 0- and 1-hour groups. There was no significant difference in root resorption between 0- and 1-hour groups, and also between 4- and 9-hour groups.
Conclusion: The distance of tooth displacement gradually decreased as the inactive period increased, whereas root resorption suddenly decreased between 1 and 4 hours of inactive orthodontic force.
Introduction
It is generally accepted that tooth pain, widening of periodontal ligament (PDL) space, and root resorption are produced less frequently by light forces.1,
2 However, it is still not known whether the optimal orthodontic force should be, continuous, intermittent, or interrupted. Some studies have demonstrated that light continuous forces produce effective tooth movement with minimum tissue damage.3–7 Reitan8,9 suggested that hyalinized tissues are resorbed more rapidly if a given force is applied intermittently, rather than in a continuously.
In addition, some studies have observed less root resorption in tooth movement produced by interrupted forces. For example, Levander et al.10 demonstrated that the amount of root resorption is significantly less in patients treated with a pause of 2–3 months compared to those treated without interruption. Moreover, Rygh11 reported that when the orthodontic force is discontinued, any root resorption is repaired.
In recent studies of intermittent forces, Igarashi et al.12 reported that the application of 20gf of force with a resting period of 12 hours per day in rats produces more effective movement than full time forces. Konoo et al.13 found that the application of 40gf of force for 1 hour per day in rats is ineffective at moving teeth. These studies, however, did not examine the effect of force duration on tooth movement. In the experiments reported here, we improved the tooth movement model developed in our previous study. The appliance comprised a nickel-titanium (Ni-Ti) alloy closed coil spring and a titanium screw implant.14
The aim of this study was to examine the effects of force duration, that is, inactive periods of force application on the amount of (i) tooth displacement and (ii) root resorption during experimental tooth movement.
Materials and methods
Animals
Sixty 11-week-old male Sprague–Dawley rats (body weight 360 ± 36; 18 g) were used. All rats were fed a solid diet and given water ad libitum during the period of the experiment. To assess whole-body effects, the animals were weighed before each treatment. All procedures followed the guidelines of the Tokyo Medical and Dental University for Animal Research. The experimental protocols had the approval by the local Ethics Committee.
Experimental tooth movement
We improved the method of tooth movement from our previous report.14 Eleven-week-old rats were intraperitoneally anaesthetized with ketamine hydrochloride (Ketalar 50, Sankyo Co. Ltd, Tokyo, Japan) containing 20% xylazine hydrochloride (Celactal 2% injection, Bayer-Japan Co. Ltd., Tokyo, Japan) as a muscle relaxant, after inhalant anaesthesia with diethyl ether. A titanium screw implant, 1.0 mm in diameter and 4.0 mm in length (Shioda Co. Ltd, Tochigi, Japan), with a titanium plate was placed just behind the right maxillary incisor for anchorage (Figure 1). Tooth movement was started after the implant had been allowed to stabilize for 1 week. The titanium plate and molar clamp allowed the easy removal of the a nickel-titanium (Ni-Ti) alloy closed coil spring14 (diameter: 0.015 mm; lumen: 0.9 mm; length: 2.0 mm; load: 10 gf; Figure 2), and the maxillary left first molar (M1) was moved in four patterns of continuation and intermittence for 14 days.
|
|
). Zero-hour means continuous force. In 1-, 4-, and 9-hour groups, Ni-Ti alloy closed coil springs were set and removed everyday under ether anaesthesia. A previous study showed that under physiological conditions, both bone formation and resorption are more intense in the day-time than in the night time,15–17, and these are the resting and active periods for rats, respectively. Therefore, we set the inactive period at night to evaluate the most effective bone remodelling within the diurnal rhythm. The inactive periods were 22:00–23:00 in the 1-hour group, 20:00–24:00 in the 4-hour group, and 22:00–7:00 in the 9-hour group. During inactive periods, the Ni-Ti alloy closed coil spring was removed and no orthodontic force was applied. Non-treated rats were used as the control group.
|
7 The interproximal spaces between M1 and second molar (M2) of the models were measured five times by each of the four investigators at intervals of 1 hour using a non-contact digital microscopic gage (MS-214; Fusoh Co., Ltd, Tokyo, Japan) and the mean value within the groups was taken as the tooth displacement.7
Histological and histomorphometric examination
On day 14 of tooth displacement, the rats were sacrificed by decapitation and the maxillae were immediately removed, fixed in a solution of 10% neutral buffered formalin (Wako Pure Chemical Co. Ltd, Osaka, Japan) at 4°C overnight; decalcified in 10% EDTA solution at 4°C for 6 weeks; and embedded in paraffin with conventional methods. Seven-micrometre thick horizontal serial sections of the M1 were made with a microtome (RM2155, LEICA Co. Ltd., Nussloch, Germany). The mesial sides of distobuccal roots of M1 were selected for observation. They were stained with H&E for histomorphometric study. To identify osteoclasts and odontoclasts for active bone and root resorption, TRAP activity according to a previous method.18 The sections were counterstained with haematoxylin. The observation area was the mesial pressure side, 0.90–1.10 mm from the furcation of distobuccal and mesiobuccal roots of M1 (Figure 4). Consequently, we defined a TRAP-positive multinucleated cell on the bone surface as an osteoclast and on the root surface of resorption lacuna as an odontoclast. The area of the root resorption lacuna, in which odontoclasts were recognized in a serial section, was measured five times by each investigator at intervals of one hour at the pressure side of the root using a computer image analysis software (Image-Pro Plus, Media Cybernetics, Maryland, USA); (Figure 5).19 The mean root resorption area for each animal was the average of the values obtained from three sections selected at 70-µm intervals.
|
|
Results
Animals
The weight in the experimental group did not increase during the week after the implantation, in addition, there was no significant difference in weight between the control and the experimental groups over the whole experimental period (Figure 6).
|
shows the amount of tooth displacement in the animals of each group on days 7 and 14. The tooth movement distance of the 0- and 1-hour groups was significantly greater than that of the 9-hour group (P < 0.05). There was no significant difference between 0- and 1-hour groups, or between the 1- and 4-hour groups.
|
). In the 0- and 1-hour groups hyalinization of PDL and undermining bone resorption were found (Figure 8a,b). The root surface facing opposite the area of undermining bone resorption was resorbed by odontoclasts. Some of the root resorption occurred not only in cementum, but also in dentine. Observation of 4- and 9-hour groups revealed that hyalinized tissue and undermining bone resorption were rarely found and direct bone resorption was recognized as the duration of forces become short (Figure 8c,d). Less root resorption was found in the 4- and 9-hour groups. Figure 9 shows the mean area of root resorption lacunae. There was a significant difference in the area of root resorption lacunae between 0- and 1-hour groups, and 4- and 9-hour groups. On the other hand, there was no significant difference between the 0- and 1-hour groups, and also between 4- and 9-hour groups.
|
|
Discussion
We focused on differences for inactive periods of 10 gf of orthodontic force in rats and found two main results regarding the amount of tooth displacement and root resorption. First, the tooth displacement for 14 days increased proportionately to the increase in the active period of orthodontic force application. Igarashi et al.12 found that the application of orthodontic forces for 12 hours per day during the rat’s rest period moved teeth almost as much as full-time force, and the teeth did not move during the rat’s active period at night. In our pilot study, the intermittent application of 2 gf, which seems to be a near to optimal force for continuous application, could not move the rat molar. Taken together with our results, the magnitude of orthodontic force, duration, and period of the day are mutually related, and appear to be involved in determining the efficiency of tooth movement obtained with an intermittent orthodontic force.
Furthermore, the results demonstrate that damage such as hyalinization of PDL and root resorption markedly decreased when the inactive period exceeded 4 hours per day. Root resorption lacunae measured in this experiment were related to the experimental tooth movement because no root resorption was seen on the mesial side of the root in the control group. In general, orthodontic root resorption is known to occur at the periphery of hyalinized tissue.20–23 Root resorption involves differentiation, fusion, and activation of odontoclasts that are recruited and activated by increased production of local inflammatory cytokines in the periodontal ligament due to mechanical stress or necrosis of the PDL24–28. In this study, the 0-hour group, which received a continuous load of 10 gf, presented with root resorption, which we related to continuous mechanical stress and hyalinization of the periodontal ligament. Results from the 1-hour group were similar to those of the 0-hour group because the active period was almost the same and the inactive period was too short. By contrast, the 4- and 9-hour groups showed less root resorption because of a decrease in mechanical stress and hyalinized tissue, recovery of form and function of the blood vessels, reduction of cytokine production and subsequent odontoclast formation. The threshold for the appearance of hyalinized tissue and root resorption may occur in the 1- and 4-hour inactivation period.
Figure 10 shows the relation between tooth displacement and root resorption area to the inactivation periods. The amount of tooth displacement gradually decreased as the inactivation periods were increased, whereas the amount of root resorption decreased between the 1- and 4-hour inactivation period of orthodontic force. Comprehensive analysis of this figure revealed that the optimal orthodontic force duration to move the rat M1 mesially with 10 gf comprised a 4-hour period of inactivation each day during the biological active period at night. The root surface area of the human maxillary first molar and canine teeth are 20 and 10 times larger than the rat M1.29,30 If we extrapolate our findings to the clinical situation, if orthodontic forces equivalent to a 200 or 100 gf are used to move a first molar or canine, respectively, a 4-hour inactivation period during the human active period in daytime may reduce the risk of root resorption and move teeth effectively, without compromising tooth movement efficiency.
|
Acknowledgments
This research was supported in part by Grants-in-Aid for Scientific Research (No. 10771169, 12671988, 12771271, 19671989) from the Ministry of Education, Culture, Sports, Science and Technology, Japan. Part of this work was presented at the 60th Annual Meeting and 3rd International Congress of the Japanese Orthodontic Society (October 2001, Tokyo, Japan).
References
Storey E, Smith R. Force in orthodontics and its relation to tooth movement. Aust J Dent 1952; 56: 11–18.
Burstone CH. The biomechanics of tooth movement. In Kraus BS, Riedel RA (Eds) Vistas in Orthodontics. Philadelphia: Lea & Febiger, 1962: 202–214.
King GJ, Fischlschweiger W. The effect of force magnitude on extractable bone resorptive activity and cemental cratering in orthodontic tooth movement. J Dent Res 1982; 61: 775–779.
Kirino Y, Tsuchiya T, Kurihara S, Chiba M, Miura F. A study of tooth movement with super-elastic force. J Jpn Orthod Soc 1991; 50: 315–324.
Kono H., Tsuchiya T, Warita H., Kubota M, Iida J, Mogi M, et al. A histological studies on tooth movement with super-elastic force (part.1). J Jpn Orthod Soc 1991; 50: 126–136.
Warita H, Iida J, Yamaguchi S, Matsumoto Y, Fujita Y, Domon S, et al. A study on experimental tooth movement with Ni-Ti alloy orthodontic wires: comparison between light continuous force and light dissipating force. J Jpn Orthod Soc 1996; 55: 515–527.
Kohno T, Matsumoto Y, Kanno Z, Warita H, Soma K. Experimental tooth movement under light orthodontic forces—rates of tooth movement and changes of the periodontium. J Orthod 2002; 29: 125–132.
Reitan K. Some factors determining the evaluation of forces in orthodontic. Am J Orthod 1957; 43: 32–45.[CrossRef]
Reitan K. Effects of force magnitude and direction of tooth movement on different alveolar bone types. Angle Orthod 1964; 34: 244–255.
10 Levander E, Malmgren O, Eliasson S. Evaluation of root resorption in relation to two orthodontic treatment regimes. A clinical experimental study. Eur J Orthod 1994; 16: 223–228
11 Rygh P. Orthodontic root resorption studied by electron microscopy. Angle Orthod 1977; 47: 1–16.[Medline]
12 Igarashi K, Miyoshi K, Shinoda H, Saeki S, Mitani H. Diurnal variation in tooth movement in response to orthodontic force in rats. Am J Orthod Dentofac Orthop 1998; 114: 8–14.[CrossRef][Medline]
13 Konoo T, Kim YJ, Gu GM, King GJ. intermittent force in orthodontic tooth movement. J Dent Res 2001; 80: 457–460.
14 Kameyama T, Matsumoto Y, Warita H, Otsubo K, Soma K. A mechanical stress model applied to the rat periodontium. Using controlled magnitude and direction of orthodontic force with an absolute anchorage. Oral Med Pathol 2002; 7: 1–7
15 Shinoda H, Stern PH. Diurnal rhythms in calcium transfer into bone calcium release from bone and bone resorbing activity in serum of rats. Am J Physiol 1992; 262: R235–R240.
16 Simmons DJ, Menton DN, Russell JE, Smith R, Walker WV. Bone cell populations and histomorphometric correlates to function. Anat Rec 1988; 222: 228–236.[CrossRef][Medline]
17 Roberts WE, Klingler E, Mozsary PG. Circadian rhythm of mechanically mediated differentiation of osteoblasts. Calcif Tissue Int 1984; 36: S62–S66.
18 Domon S, Shimokawa H, Matsumoto Y, Yamaguchi S, Soma K. In situ hybridization for matrix metalloproteinase-1 and cathepsin K in rat root-resorbing tissue induced by tooth movement. Arch Oral Biol, 1999; 44: 907–915[CrossRef][Medline]
19 Sringkarnboriboon S, Matsumoto Y, Soma K. Root resorption related to hypofunctional periodontium in experimental tooth movement. [Abstract]. J Dent Res 2001; 80: 789.
20 Rygh P. Ultrastructural cellular reactions in pressure zones of rat molar periodontium incident to orthodontic tooth movement. Acta Odontol Scand 1972; 81: 467–480.
21 Brudvik P, Rygh P. The initial phase of orthodontic root resorption incident to local compression of the periodontal ligament. Eur J Orthod 1993; 15: 249–63.
22 Brezniak N, Wasserstein A. Root resorption after orthodontic treatment: part 1. Literature review. Am J Orthod Dentofac Orthop 1993; 103: 62–66.[Medline]
23 Brezniak N, Wasserstein A. Root resorption after orthodontic treatment: part 2. Literature review. Am J Orthod Dentofac Orthop 1993; 103: 138–146.[Medline]
24 Brudvik P, Rygh P. Root resorption after local injection of prostaglandin E2 during experimental tooth movement. Eur J Orthod 1991; 13: 255–263.
25 Birkedal-Hansen H. Role of cytokines and inflammatory mediators in tissue destruction. J Periodont Res 1993; 28: 500–510.[CrossRef][Medline]
26 Murakami S, Takayama S, Ikezawa K, Shimabukuro Y, Kitamura M, Nozaki T, et al. Regeneration of periodontal tissues by basic fibroblast growth factor. J Periodont Res 1999; 34: 425–30.[CrossRef][Medline]
27 Wu YM, Richards DW, Rowe DJ. Production of matrix-degrading enzymes and inhibition of osteoclast-like cell differentiation by fibroblast-like cells from the periodontal ligament of human primary teeth. J Dent Res 1999; 78: 681–689.
28 Kimoto S, Matsuzawa M, Matsubara S, Komatsu T, Uchimura N, Kawase T, et al. Cytokine secretion of periodontal ligament fibroblasts derived from human deciduous teeth: effect of mechanical stress on the secretion of transforming growth factor-beta 1 and macrophage colony stimulating factor. J Periodontal Res 1999; 34: 235–243.[CrossRef][Medline]
29 Sato T, Iida J, Kurihara S. A histological investigation on the periodontal tissue changes during molar depression in rats. J Jpn Orthod Soc 1984; 46: 361–372.
30 Proffit WR. The biological basis of orthodontic therapy. In: Rudolph P (Ed.) Contemporary Orthodontics. London: Mosby, 1999: 309.
Received February 14, 2002; accepted July 11, 2002
This article has been cited by other articles:
|
|
 |
|
  M. Sakata, Y. Yamamoto, N. Imamura, S. Nakata, and A. Nakasima The effects of a static magnetic field on orthodontic tooth movement J. Orthod., December 1, 2008; 35(4): 249 - 254. [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
