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RESEARCH REPORT |
Orthodontic Science, Department of Orofacial Development and Function, Division of Oral Health Science, Graduate School, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8549, Japan;
*corresponding author, y.matsumoto.orts{at}tmd.ac.jp
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS & METHODSRESULTSDISCUSSIONREFERENCES |
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KEY WORDS: root resorption • periodontium • hypofunction • tooth movement
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS & METHODSRESULTSDISCUSSIONREFERENCES |
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Histologically, in the absence of occlusal function, teeth exhibit a hypofunctional periodontium (Kronfeld, 1931; Newman, 1975) characterized by loss of functional structures. The periodontal ligament space becomes narrow (Kronfeld, 1931), and atrophic changes such as the disappearance of the functional arrangement of Sharpey’s fibers and a decrease in fibroblastic proliferation activity (Koike, 1996) occur. Changes in vascularity (Tanaka et al., 1998) and distribution of Ruffini’s nerve endings and proteoglycans (Muramoto et al., 2000; Kaneko et al., 2001) have also been reported. Large marrow spaces and thinner outer shells of alveolar bone were observed in the mandibular teeth after extraction of the opposing teeth in rats (Lee and Nakamura, 1999). Based on these clinical and histological findings, an altered response to orthodontically induced mechanical stress could be expected in hypofunctional non-occluding teeth. Moreover, no histological investigations have been performed to examine the possible etiology of root resorption under hypofunctional conditions.
The aim of the present study was to compare the incidence and extent of root resorption in hypofunctionally non-occluding teeth with those in normally occluding teeth during experimental tooth movement in rats. We established the experimental hypofunctional periodontal condition by relieving the teeth from normal functional stress and measured orthodontically induced root resorption quantitatively. We hypothesized that non-occluding teeth would have a higher risk for orthodontically induced root resorption than would normally occluding teeth.
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MATERIALS & METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS & METHODSRESULTSDISCUSSIONREFERENCES |
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). The animals were fed with powder-form fodder (Rodent Diet CE-2; Japan Clea Inc., Shizuoka, Japan) and water ad libitum in separate cages, in a 12-hour light/dark environment at a constant temperature of 23°C. During the experimental period, the rats were weighed twice a week. The experimental procedures were approved by the Animal Ethics Committee of Tokyo Medical and Dental University. All procedures were carried out while the animals were under general anesthesia with ketamine hydrochloride (KETALAR 50, Sankyo Co., Ltd., Tokyo, Japan) and 20% xylazine hydrochloride (Celactel 2% injections, BAYER-Japan Co., Ltd., Tokyo, Japan) administered intraperitoneally.
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). We performed a preliminary experiment to verify the hypofunctional condition. Occlusal records were registered in the closed-jaw position by means of silicone impression material (Dent Silicone-V, regular type, Shofu Inc., Kyoto, Japan) prior to tooth movement. These records showed the contact area between maxillary and mandibular teeth, with a lack of impression material at the area of composite resin. The interocclusal space at the left mandibular first and second molars indicated a non-occluding condition. In addition, we examined paraffin-embedded sagittal sections histologically by staining them with hematoxylin and eosin to verify the hypofunctional periodontium.
Experimental Tooth Movement
When the rats were 8 wks old, the left mandibular first molars were moved mesio-occlusally for 15 days in both groups (Fig. 1A). Necessary anchorage was provided by a 3.5-mm-long titanium-screw implant with a diameter of 1.0 mm (Kameyama et al., 2002), fixed to the left body of the mandible, and a 1.2-mm-diameter cobalt-chromium (Co-Cr) alloy wire extending along the incisal axis. A 2-mm-long 50-gram-force super-elastic titanium-nickel (Ti-Ni) alloy closed-coil spring (Sentalloy® closed coil spring, EX Light, Tomy International Inc., Tokyo, Japan) (Tobiume et al., 2000), which delivered sufficient continuous heavy force to initiate root resorption (King and Fischlschweiger, 1982), extended from the tip of the Co-Cr alloy wire to the left mandibular first molar (Fig. 1B). This spring was attached to the tooth by a clamp at the mesial furcation and was reinforced by composite resin filling the gap between the clamp and the tooth surface.
Histochemical Analysis
After 15 days of tooth movement, the animals were anesthetized by diethyl ether and killed by cervical dislocation. The left half of mandible was dissected and immersed overnight in 10% neutral buffered formalin (pH 7.4) at 4°C. Before decalcification, the amount of horizontal tooth movement was determined from the space between the contact areas of first and second molars (Kohno et al., 2002). The specimens were then decalcified in 10% (W/V) ethylene diamine tetra-acetic acid for 4 wks at 4°C, dehydrated, and embedded in paraffin. Serial sections of 5.0-µm thickness were made along the sagittal axis. The sections that included the root canal were stained with hematoxylin and eosin for examination of root resorption at the compression area. Odontoclasts were detected by being stained with tartrate-resistant acid phosphatase (TRAP) (Domon et al., 1999). In brief, after fixation in citrate-acetone-formaldehyde solution for 30 sec, the sections were incubated in de-ionized water containing naphthol AS-MX phosphate (Sigma, St. Louis, MO, USA) as the substrate and Fast Red Violet LB salt (Sigma, St. Louis, MO, USA) for color reaction at pH 5.4 with 50 mM sodium tartrate. The reaction was stopped with distilled water. The sections were counterstained with hematoxylin and mounted with permanent aqueous mounting medium (Crystal/Mount, Biomeda Corp., Foster City, CA, USA). The newly formed resorption lacunae were identified by the presence of TRAP-positive multinucleated cells.
Quantitative Evaluation of Root Resorption
The disto-apical region of the distal root was observed as the compression area. All sections that included the root canal were examined. In both normal and hypofunctional periodontium groups, root resorption was approximately equal in dimension bucco-lingually, but differed occluso-apically. Hence, the buccal, middle, and lingual one-third sections were measured, and the mean value for each animal was calculated for statistical analysis.
Since the distal root has a stable conformation, the root-shape outline can be easily estimated by means of a template reference. The distal root was photographed by a digital camera (DXm1200, Nikon, Tokyo, Japan), and the resorption lacunar length, depth, and area were estimated three-dimensionally by image analysis software (Image-Pro Plus 4.0, Media Cybernetics, Silver Spring, MD, USA). Resorption lacunar length and area represent the lacunar surface area and volume, respectively (Kameyama et al., 1994), while resorption lacunar depth is the length of the deepest point from the simulated root surface to the resorption surface of the lacuna (Owman-Moll et al., 1995).
Statistical Analysis
The amount of tooth movement and dimensions of root-resorption lacuna were represented as the mean ± standard error of the mean (SEM) (n = 10). Comparisons between normal and hypofunctional periodontium groups were performed with the Mann-Whitney U test and the use of statistical analysis software (Statview 5.0, SAS Institute, Cary, NC, USA). The level of significance was set at 0.05.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS & METHODSRESULTSDISCUSSIONREFERENCES |
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Histological Examination of Hypofunctional Periodontium
When compared with normal periodontium, the hematoxylin/eosin-stained sagittal sections of the hypofunctional periodontium group demonstrated a narrow periodontal width, atrophic changes, and derangement of principal collagen fibers. Fibroblasts were also relatively few in the hypofunctional periodontium group (Fig. 2).
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Characteristics of Root Resorption
In all specimens of both the normal and hypofunctional periodontium groups, root resorption had occurred on the disto-apical third of the distal root facing the alveolar bone in the compression zone (Fig. 3). In the hypofunctional periodontium group, the roots were resorbed extensively into dentin after 15 days of orthodontic movement.
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).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS & METHODSRESULTSDISCUSSIONREFERENCES |
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The method used in the present study for quantitative assessment of root resorption has been widely used in histomorphometric studies (Kameyama et al., 1994; Owman-Moll et al., 1995). These procedures are performed to estimate the resorption three-dimensionally. The presence of TRAP-positive cells in the resorption lacunae confirms the resorptive activity. This is a standard method for the detection of active root resorption (Brudvik and Rygh, 1994; Baroukh et al., 2000).
In the present study, heavy and continuous orthodontic forces were applied to both groups. This force would naturally induce root resorption in teeth with normal periodontium (Brezniak and Wasserstein, 1993). However, root resorption was greater in the hypofunctional periodontium group. This implies that factors other than the applied force were responsible for root resorption.
Since the hypofunctional periodontium exhibited progressive atrophic changes in all functional structures, this might have accelerated the root destruction resulting from the mechanical stress of orthodontic force. Due to the narrow periodontal space in the hypofunctional periodontium, the applied force might concentrate in the compression area (Jeon et al., 1999). In addition, the narrow periodontal space and derangement of functional fibers would eliminate the normal cushioning effect of the periodontal ligament (Selliseth and Selvig, 1994), thus resulting in a high concentration of force. This would stimulate inflammation by the promotion of inflammatory mediators (Cooper and Sims, 1989) secreted from local cells to induce destruction of tooth and bone.
Our results suggest that orthodontists should be cautious while applying orthodontic force to non-occluding teeth with a hypofunctional periodontium so as to avoid the occurrence of undesirable root resorption.
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ACKNOWLEDGMENTS |
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Received June 26, 2002; Last revision January 25, 2003; Accepted February 6, 2003
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REFERENCES |
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Bondevik O (1984). Tissue changes in the rat molar periodontium following alteration of normal occlusal forces. Eur J Orthod 6:205–212.
Brezniak N, Wasserstein A (1993). Root resorption after orthodontic treatment: Part 2. Literature review. Am J Orthod Dentofacial Orthop 103:138–146.[ISI][Medline]
Brudvik P, Rygh P (1994). Root resorption beneath the main hyalinized zone. Eur J Orthod 16:249–263.
Cooper SM, Sims MR (1989). Evidence of acute inflammation in the periodontal ligament subsequent to orthodontic tooth movement in rats. Aust Orthod J 11:107–109.[Medline]
Domon S, Shimokawa H, Matsumoto Y, Yamaguchi S, Soma K (1999). In situ hybridization for matrix metalloproteinase-1 and cathepsin K in rat root-resorbing tissue induced by tooth movement. Arch Oral Biol 44:907–915.[ISI][Medline]
Harris EF, Butler ML (1992). Patterns of incisor root resorption before and after orthodontic correction in cases with anterior open bites. Am J Orthod Dentofacial Orthop 101:112–119.[ISI][Medline]
Jeon PD, Turley PK, Moon HB, Ting K (1999). Analysis of stress in the periodontium of the maxillary first molar with a three-dimensional finite element model. Am J Orthod Dentofacial Orthop 115:267–274.[ISI][Medline]
Kameyama T, Matsumoto Y, Warita H, Otsubo K, Soma K (2002). A mechanical stress model applied to the rat periodontium: using controlled magnitude and direction of orthodontic force with an absolute anchorage. Oral Med Pathol 7:1–7.
Kameyama Y, Nakane S, Maeda H, Fujita K, Takesue M, Sato E (1994). Inhibitory effect of aspirin on root resorption induced by mechanical injury of the soft periodontal tissues in rats. J Periodontal Res 29:113–117.[ISI][Medline]
Kaneko S, Ohashi K, Soma K, Yanagishita M (2001). Occlusal hypofunction causes changes of proteoglycan content in the rat periodontal ligament. J Periodontal Res 36:9–17.[ISI][Medline]
King GJ, Fischlschweiger W (1982). The effect of force magnitude on extractable bone resorptive activity and cemental cratering in orthodontic tooth movement. J Dent Res 61:775–779.
Kohno T, Matsumoto Y, Kanno Z, Warita H, Soma K (2002). Experimental tooth movement under light orthodontic forces: rates of tooth movement and changes of the periodontium. J Orthod 29:129–135.
Koike K (1996). The effects of loss and restoration of occlusal function on the periodontal tissues of rat molar teeth—histopathological and histometrical investigation. J Jpn Soc Periodont 38:1–19.
Kronfeld R (1931). Histologic study of the influence of function on the human periodontal membrane. J Am Dent Assoc 18:1242–1274.
Lee M, Nakamura Y (1999). A histological study on the periodontal ligament during the experimental movement of hypofunctional teeth in rats—on the tension side. Orthod Waves 58:416–427.
Muramoto T, Takano Y, Soma K (2000). Time-related changes in periodontal mechanoreceptors in rat molars after the loss of occlusal stimuli. Arch Histol Cytol 63:369–380.[ISI][Medline]
Newman WG (1975). Possible etiologic factors in external root resorption. Am J Orthod 67:522–539.[ISI][Medline]
Owman-Moll P, Kurol J, Lundgren D (1995). Continuous versus interrupted continuous orthodontic force related to early tooth movement and root resorption. Angle Orthod 65:395–401.[ISI][Medline]
Selliseth NJ, Selvig KA (1994). The vasculature of the periodontal ligament: a scanning electron microscopic study using corrosion casts in the rat. J Periodontol 65:1079–1087.[ISI][Medline]
Tanaka A, Iida J, Soma K (1998). Effect of hypofunction on the microvasculature in the periodontal ligament of the rat molar. Orthod Waves 57:180–188.
Tobiume Y, Otsubo K, Soma K, Yoneyama T, Hamanaka H (2000). Improvement in the load changeability of super-elastic Ti-Ni alloy orthodontic closed coil spring by the two-step heat treatment. J Jpn Dent Mater Devices 19:170–178.
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