Fatty acid composition and arachidonic acid concentrations in alveolar bone of rats fed diets with different lipids

Summary The purpose of the present study was to determine if the type of dietary fat can modify the fatty acid composition and arachidonic acid levels in the alveolar bone phospholipids. Three groups of rats were fed nutritionally adequate semipurified diets containing different lipids: 10% corn oil (control, group 1, rich in n-6 fatty acids); 9% butter + 1% corn oil (experimental, group 11, rich in saturated fatty acids); and 9% ethyl ester concentrate of n-3 fatty acids + 1% corn oil (experimental, group 111, rich in n-3 fatty acids). After 10 weeks of feeding the various diets, rats were killed, maxillae and mandibles were dissected out, and the soft tissue was removed. Bone was frozen in liquid nitrogen and pulverized. Powdered bone was extracted for total lipids, and phospholipids were isolated by column chromatography. The fatty acid composition and arachidonic acid concentrations were determined in total phospholipids after the addition of an internal standard, octadecatetraenoic acid (18: 4n-3), and subsequent gas chromatography. The type of dietary lipids had a profound influence on the fatty acid composition of bone lipids. Arachidonic acid concentrations were significantly lower in total phospholipids of mandibles and maxillae of rats fed the experimental diets than in those fed the control diet. Because arachidonic acid is a precursor of prostaglandin E₂ and leukotriene C₄, a significant reduction in its concentration may result in reduced levels of these eicosanoids in the alveolar bone.Presented in part at the International Association for Dental Research Meeting, Glasgow, Scotland, July 1–4, 1992     

正畸力作用下大鼠炎性牙周组织牙槽骨改建的研究

目的：通过观察正畸力及炎症条件下大鼠牙槽骨高度的变化,研究正畸力和炎症对大鼠牙周组织改建的作用。方法：将60只sD大鼠随机分为加力对照组（P1组）和炎症对照组（P2组）各30只。施加50g近中向正畸力于P1组大鼠的左上第一磨牙;同时建立实验性牙周炎模型于P2组大鼠双侧上颌第一磨牙,2周后去除双侧牙周炎性刺激物,设右上第一磨牙为炎症对照组（P2组）,并施加50g近中向正畸力于左上第一磨牙,为炎症加力组（P3组）。运用组织形态测量法观测各组大鼠上颌第一磨牙加力或去除炎症刺激物后各时点牙槽骨的吸收量。结果：P1组大鼠近中牙槽骨未见明显丧失,P2、P3组可见近远中牙槽骨的丧失,但当去除炎症刺激物后加力,P3组大鼠近中牙槽骨未见明显丧失。结论：只要彻底清除炎性刺激物正畸力不会导致牙槽骨的明显丧失。     

Effects of Essential Fatty Acid Deficiency on Periodontal Tissue Adaptation to Spontaneous Tooth Migration

Essential fatty acids (EFAs) play a significant role in bone metabolism. Herein we studied the adaptation of alveolar bone to physiologic tooth drift in young rats deprived of essential fatty acids from birth. Reductions in femur size and trabecular bone volume reflected body growth impairment. Along the alveolar wall, osteoclastic resorption and bone formation were depressed, disrupting the adaptive deformation of the tooth socket to ongoing migration. As a result, the periodontal ligament narrowed considerably, and further adaptation was achieved through root resorption. Essential fatty acid deficiency (EFAD), did not affect precursor recruitment or differentiation in the periodontal ligament (PDL), but caused redistribution of nonspecific-esterase (NSE)–positive osteoclast precursors and tartrate-resistant acid phosphatase (TRAP)–positive preosteoclasts between the bone compartment (which was depleted) and the root compartment (which was enriched). EFAD had also a marked effect on the PDL vasculature; the number of vessels was reduced, whereas their size was markedly increased. As a whole, our results show that EFAD disturbs alveolar bone adaptation to drift, but that a reaction (detrimental to root integrity) prevents root collision with the bone surface, thereby preserving the PDL as a source of precursor cells for bone and cementum homeostasis. Moreover, our results confirm that although alveolar bone resorption is arachidonic acid–dependent, the factors activating root resorption are different.     

ω-3 fatty acids suppress inflammatory cytokine production by macrophages and hepatocytes

Objective

Long-term total parenteral nutrition (TPN) in children is often complicated by parental nutrition–associated liver disease and may even lead to liver failure. Recently, the addition of ω-3 fatty acids to TPN has been shown to reduce the risk of parental nutrition–associated liver disease. The purpose of this study was to explore the anti-inflammatory effects of ω-3 fatty acids (eicosapentaenoic acid [EPA]) to demonstrate the protection of the liver against hepatic steatosis and damage.

Materials and Methods

Lipopolysaccharide (LPS) and prostaglandin E₂ (PGE₂) were used to stimulate human macrophages and hepatocytes (THLE-3) to induce in vitro inflammatory condition. The cells were then incubated with either ω-3 (EPA) or ω-6 (arachidonic acid) fatty acids. Supernatants were collected at different time points for the measurement of tumor necrosis factor α (TNF-α), interleukin 6 (IL-6), and interleukin 10 (IL-10) using enzyme-linked immunosorbent assay. Furthermore, pretreated macrophages by LPS stimulation and after incubation with EPA were added to prestimulated hepatocytes for the subsequent measurement of cytokine response.

Results

Eicosapentaenoic acid effectively reduced LPS-induced or PGE₂-induced TNF-α and IL-6 expression, and increased IL-10 expression significantly when compared with arachidonic acid. Furthermore, supernatant collected after co-culturing EPA with macrophages also suppressed the levels of TNF-α and IL-6 in hepatocytes. This would suggest that EPA not only had an anti-inflammatory effect on macrophages and hepatocytes directly, it could indirectly reduce hepatocyte inflammation through activated macrophages.

Conclusions

The addition of ω-3 fatty acids in TPN suppresses the inflammatory response via direct and indirect routes. The findings may help explain the clinical benefits of EPA in pediatric patients receiving long-term TPN.     

Effects of low-energy laser irradiation on bone remodeling during experimental tooth movement in rats

BACKGROUND AND OBJECTIVE: Low-energy laser irradiation has many anabolic effects such as the acceleration of bone formation. However, its effects on tooth movement, performed by bone resorption and formation, have not been well characterized. STUDY DESIGN/MATERIALS AND METHODS: A total of 10 g of orthodontic force was applied to rat molars to cause experimental tooth movement. A Ga-Al-As diode laser was used to irradiate the area around the moved tooth, and after 12 days, the amount of tooth movement was measured. Calcein was injected subcutaneously to label the newly formed alveolar bone for quantitative analysis. Immunohistochemical staining of proliferating cell nuclear antigen was performed to evaluate cellular proliferation. TRAPase staining was also performed to facilitate the identification of osteoclasts. RESULTS: In the laser irradiation group, the amount of tooth movement was significantly greater (1. 3-fold) than that of the nonirradiation group in the end of the experiment. The amount of bone formation and rate of cellular proliferation in the tension side and the number of osteoclasts in the pressure side were all significantly increased in the irradiation group when compared with the nonirradiation group (P < 0. 01). CONCLUSION: These findings suggest that low-energy laser irradiation can accelerate tooth movement accompanied with alveolar bone remodeling.     

Local injection of 1,25-dihydroxyvitamin D<Subscript>3</Subscript> enhanced bone formation for tooth stabilization after experimental tooth movement in rats

The present investigation evaluated the effect of 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) on alveolar bone formation during tooth movement in rats. Orthodontic elastics were inserted between the maxillary first and second molars on bilateral sides in male rats. 1,25(OH)₂D₃ was injected locally, at the concentration of 10^–10M, once every 3 days in the submucosal palatal area of the root bifurcation of the molar on the right side. Histomorphometric analysis revealed that tooth movement without application of 1,25(OH)₂D₃ decreased the mineral appositional rate (MAR) on the compression area at 7 days. Repeated injections of 1,25(OH)₂D₃ in the orthodontically treated animals distinctly stimulated alveolar bone formation on the mesial side at 14 days. There was a significant increase in MAR associated with elevated osteoblast surface (Ob.S/BS) value on the tension surface. These findings suggest that local application of 1,25(OH)₂D₃ enhances the reestablishment of supporting tissue, especially alveolar bone of teeth, after orthodontic treatment.     

Metrical and histological investigation of the effects of low-level laser therapy on orthodontic tooth movement

The aim of this study was to evaluate the effects of 820-nm diode laser on osteoclastic and osteoblastic cell proliferation-activity and RANKL/OPG release during orthodontic tooth movement. Thirty-eight albino Wistar rats were used for this experiment. Maxillary incisors of the subjects were moved orthodontically by a helical spring with force of 20 g. An 820-nm Ga-Al-As diode laser with an output power of 100 mW and a fiber probe with spot size of 2 mm in diameter were used for laser treatment and irradiations were performed on 5 points at the distal side of the tooth root on the first, second, and 3rd days of the experiment. Total laser energy of 54 J (100 mW, 3.18 W/cm², 1717.2 J/cm²) was applied to group II and a total of 15 J (100 mW, 3.18 W/cm², 477 J/cm²) to group III. The experiment lasted for 8 days. The number of osteoclasts, osteoblasts, inflammatory cells and capillaries, and new bone formation were evaluated histologically. Besides immunohistochemical staining of PCNA, RANKL and OPG were also performed. No statistical difference was found for the amount of tooth movement in between the control and study groups (p > 0.05). The number of osteoclasts, osteoblasts, inflammatory cells, capillary vascularization, and new bone formation were found to be increased significantly in group II (p < 0.05). Immunohistochemical staining findings showed that RANKL immunoreactivity was stronger in group II than in the other groups. As to OPG immunoreactivity, no difference was found between the groups. Immunohistochemical parameters were higher in group III than in group I, while both were lower than group II. On the basis of these findings, low-level laser irradiation accelerates the bone remodeling process by stimulating osteoblastic and osteoclastic cell proliferation and function during orthodontic tooth movement.     

Lipid mediated modification of rat heart allograft survival

The effect on allograft survival of intravenous fat emulsions that differed in the ratio of functionally important n-3 and n-6 fatty acids was studied in a heterotopic cardiac transplant model in rats. Twenty percent fat emulsions were administered by continuous infusion at a dosage of 9 g fat/kg body weight per day, starting immediately after transplantation and continuing until complete rejection. The n-6 and n-3 fatty acids represent 75%, 43%, 60%, and 59% of all fatty acids in safflower oil, fish oil, soybean oil, and a 1:1 mixture of safflower and fish oil, respectively. The n-6 fatty acids predominate in safflower oil (370/1) and soybean oil (6.5/1), while the n-3 fatty acids dominate in the fish oil (7.6/1). The 1:1 mixture of safflower and fish oil has the balanced composition (n-6/n-3=2.1/1) recommended by Kinsella and served as oil-treated controls. Continuous infusion of safflower oil, fish oil, and soybean oil prolonged graft survival time to 13.3, 12.3, and 10.4 days, respectively, compared to 6.8 days in the oil-treated controls (P<0.01 for all comparisons). Another control group infused with saline rejected the allografts after 7.8 days (P=NS compared to oil-treated controls; P<0.01 for all other comparisons). The data suggest that intravenous administration of polyunsaturated fat emulsions results in an immunosuppressive effect that seems to be dependent on the n-3/n-6 fatty acid ratio of the fat emulsion. The n-6 fatty acids turned out to be just as immunosuppressive as the n-3 fatty acids if each fatty acid family was applied as the main polyunsaturated fatty acid source. Soybean oil with a n-3/n-6 fatty acid ratio, coming closer to the ratio of the oil-treated controls, was significantly less immunosuppressive than safflower oil.     

Endogenously produced n-3 fatty acids protect against ovariectomy induced bone loss in fat-1 transgenic mice

Aging is associated with bone loss, leading to increased risk of fractures. Recently, there is growing interest in identifying nutritional supplements that can prevent bone loss with minimum side effects. There is increasing evidence for the beneficial effects of n-3 fatty acids in the prevention of bone loss. A transgenic mouse model (fat-1) that produces n-3 fatty acids endogenously and its wild type counterpart were used in this study to determine the effects of endogenously produced n-3 fatty acids on serum bone turnover markers, long bones, and lumbar vertebrae. Serum alkaline phosphatase and P1NP levels decreased significantly in wild type mice after ovariectomy. No significant changes were seen in osteocalcin. Cancellous and cortical bone mass were higher in the femur of fat-1 mice. In wild type mice, there was significant loss of bone after ovariectomy in the distal femur, femoral neck, proximal tibia, and fourth lumbar vertebra. However, in fat-1 mice, there was no, or significantly less, bone lost after ovariectomy in all the sites studied. We conclude that endogenously produced n-3 fatty acids can attenuate ovariectomy induced bone loss in the different bone sites studied, mainly as a consequence of decreased bone resorption at the endosteal surface.     

Extracorporeal shockwave treatment impedes tooth movement in rats

Background

Accelerated tooth movement has been a topic of interest for orthodontic research recently. Surgically facilitated orthodontic treatment has been shown to be an effective approach to accelerate tooth movement; however, it remains invasive, requires additional surgery, and may increase post-operative complications. In this study, we evaluate the effects of extracorporeal shockwave treatment (ESWT), a non-invasive approach to regenerate alveolar bone, on orthodontic tooth movement in rats.

Materials and methods

Seventy-two male rats, aged 10 weeks old, were subjected to 10-cN closed-coil nickel-titanium springs for unilateral maxillary first molar tooth movement. One group of rats received a single treatment of extracorporeal shockwave treatment at 500 impulses at energy flux density 0.1 mJ/mm², with a pulse rate of 5 pulses per second immediately after spring installation while the non-ESWT-treated group served as a control group. The rats were sacrificed at day 3, 7, 14, 21 and 28 for tooth movement evaluation and sample analyses. Faxitron radiography, histological, double bone labeling and gene expression analyses were performed. Serum biochemistry was evaluated at day 3, 7 and 28 of the study. Kruskal-Wallis analysis of variance was used to determine the mean difference among groups, and multiple comparisons were analyzed by Mann-Whitney-U tests with a significance level?=?0.05.

Results

The results demonstrated that tooth movement in the ESWT-treated rats (0.11 ± 0.07 mm) was impeded compared to the tooth movement in the non-ESWT-treated rats (0.44 ± 0.09 mm). ESWT up-regulated several osteoblastic and osteoclastic gene markers and cytokines; however, the effects on osteoclasts were only transient. Double-fluorescence bone labeling demonstrated that osteoblastic activity increased after ESWT treatment. There was no difference in systemic RANKL/OPG ratio between groups.

Conclusions

ESWT at 500 impulse at energy flux density 0.1 mJ/mm² increased osteoblast and osteoclast activities and imbalanced bone remodeling resulting in impeded tooth movement in rats.

     

The interaction of the macrophage and the osteoblast in the pathophysiology of aseptic loosening of joint replacements

Macrophage phagocytosis of cement particles with production of inflammatory mediators is a component of the underlying mechanism of aseptic loosening of joint prostheses. Prostaglandin E₂ (PGE₂), a bone resorbing mediator, has been implicated in the loosening process. Investigations have shown that macrophage phagocytosis of cement particles leads to production of bone-resorbing mediators other than PGE₂. In this study, conditioned medium from macrophages exposed to crushed simplex cement particles stimulated osteoblasts to release radiolabeled arachidonic acid and metabolites. Incubation of osteoblasts in conditioned medium from macrophages exposed to cement particles small enough to be phagocytized increased PGE₂ release 80-fold over unexposed osteoblasts (P<0.001). Incubation of osteoblasts in conditioned medium from macrophages exposed to particles too large to be phagocytized, or to bone cement filtrate, did not stimulate PGE₂ release. We propose that the role of the macrophage in aseptic loosening is primarily to recognize the mechanical failure of the cement mantle by phagocytosis of cement particles and subsequent production of small amounts of specific mediators. These mediators stimulate surrounding osteoblasts to secrete PGE₂, which then amplifies the inflammatory response and ultimately results in bone resorption and aseptic loosening.     

单侧完全性唇腭裂患者自体骨移植修复牙槽突裂后早期牙移入的CT评价

目的 应用螺旋CT评价早期移动裂隙两侧的牙齿给予植骨区适当的功能刺激能否减少牙槽突裂植骨术后植入骨的吸收,增加新骨的形成,从而提高植骨手术成功率及植骨效果.方法 牙槽突裂患者12例,年龄9～13岁,分为两组：正畸牙移动组（A组）,在牙槽突裂植骨术后早期进行正畸牙移动;对照组（B组）只是行自体骨牙槽突裂植骨术.在植骨前后和正畸治疗后进行三维CT扫描,并对获得数据进行重建分析,观察正畸牙移入植骨区域后,正畸牙位置及牙槽骨的形态及体积变化.结果 两组在术前裂隙宽度及牙槽突裂体积均未见明显差异.术后6个月A组的新骨成骨体积为（0.98±0.23） mm3,显著大于B组的（0.73±0.15） mm3.新骨形成率在A组为（72.5±11.9）％,显著大于B组的（53.2±9.7）％.牙槽突裂患者自体骨植骨术后,早期正畸牙移动可顺利使裂隙侧牙齿移入植骨区域,正畸牙的牙根尖位置发生明显的位移,CT断面未见明显牙根吸收.结论 早期正畸牙移动可明显减少牙槽突裂植骨术后植入骨的吸收,其对植入骨的改建有明显的积极作用.     

Effects of two types of low-level laser wave lengths (850 and 630 nm) on the orthodontic tooth movements in rabbits

The effects of low-level lasers on bone cellular activity, bone structures, bone healing, fibroblasts activity and inflammation process have already been investigated. Considering orthodontic tooth movement, which is a complicated inflammatory process involving simultaneous bone apposition and resorption, the aim of this controlled study is to investigate the quantitative effects of a pulsed 850 nm laser (Optodan) and a continuous 630 nm laser (KLO3) on the orthodontic tooth movement in rabbits. This experimental study was conducted on 18 male albino rabbits divided into three equal groups of control, Optodan and KLO3. In all the groups, NiTi-closed coil springs were used on the first mandibular molars with 4-oz tension. The control group was not irradiated by laser, but the teeth in the laser groups were irradiated 9 days according to the periodontal therapeutic protocols. After 16 days, samples were sacrificed. The distance between the distal surface of the first molar and the mesial surface of the second molar was measured with 0.05-mm accuracy. The data were subjected to the statistical tests of Kolmogrov Smirnov and variance analysis. The mean orthodontic tooth movements of the first mandibular molars were 1.7 ± 0.16 mm in control group, 0.69 ± 0.16 mm in Optodan group and 0.86 ± 0.13 mm in KLO3 group. There were statistically significant difference between the control and the two other laser-irradiated groups (P < 0.001). The findings of the present study imply that the amounts of orthodontic tooth movement, after low-level laser therapy, are diminished. It could not be concluded that any low-level laser will reduce the speed of teeth movement in orthodontic treatments, and further studies with less or more energies may show different results.     

Evaluation of the effects of diode laser application on experimental orthodontic tooth movements in rats. Histopathological analysis

Purpose:To evaluate the effect of diode laser use on experimental orthodontic tooth movements.Methods:Thirty Rattus norvegicus albinus Wistar were divided into three equal groups (n = 10), two experimentals and one control. Applying 20 g orthodontic force were attached to the maxillary incisors of the rats in all groups. Low dose laser was applied to the surrounding tissues of the maxillary incisors of the rats in the experimental groups. Two exposure times for laser irradiation were used for seven days: t = 12 min (energy dose = 72 J) and t = 9 min (energy dose = 54 J) by a 0.1 W DEKA brand diode laser with wavelength of 980 nm.Results:Osteoclastic activation increased in the 72 J group when compared to control group and decreased in comparison to the 54 J group. Osteoblastic activation was decreased in the 72 J group when compared to the control group and increased in comparison to the 54 J group.Conclusions:Applying 54 J laser energy has been found effective to accelerate the orthodontic tooth movement.Key words: Tooth Movement, Techniques, Lasers, Semiconductor, Rats     

Effect of low-level laser therapy (LLLT) on orthodontic tooth movement

The aim of this study is to evaluate the effects of low-level laser therapy (LLLT) on (1) the velocity of orthodontic tooth movement and (2) the nitric oxide levels in gingival crevicular fluid (GCF) during orthodontic treatment. The sample consisted of 20 patients (14 girls, six boys) whose maxillary first premolars were extracted and canines distalized. A gallium-aluminum-arsenide (Ga-Al-As) diode laser was applied on the day 0, and the 3rd, 7th, 14th, 21st, and 28th days when the retraction of the maxillary lateral incisors was initiated. The right maxillary lateral incisors composed the study group (the laser group), whereas the left maxillary lateral incisors served as the control. The teeth in the laser group received a total of ten doses of laser application: five doses from the buccal and five doses from the palatal side (two cervical, one middle, two apical) with an output power of 20 mW and a dose of 0.71 J /cm². Gingival crevicular fluid samples were obtained on the above-mentioned days, and the nitric oxide levels were analyzed. Bonferroni and repeated measures variant analysis tests were used for statistical analysis with the significance level set at p ≤ 0.05. The application of low-level laser therapy accelerated orthodontic tooth movement significantly; there were no statistically significant changes in the nitric oxide levels of the gingival crevicular fluid during orthodontic treatment.     

Low-Magnitude Forces for Bone Modeling and Remodeling in Dentofacial Orthopedics

Purpose of Review

To examine the evidence in support of light continuous forces for enhancing bone adaptation (modeling and remodeling) in orthodontics and dentofacial orthopedics.

Recent Findings

Clinical evidence suggests that light continuous orthodontic force can achieve physiologic expansion of the maxillary arch, but the long-term stability and the biological effects of the procedure are unclear. Compared to conventional orthodontic appliances that deliver heavy interrupted forces for tooth movement, the application of low-magnitude forces in animal models leads to anabolic modeling and remodeling of the alveolar bone in the path of orthodontic tooth movement. This results in dental translation and expansion of the alveolar process.

Summary

Light continuous forces are preferable to heavy forces for more physiologic dentofacial orthopedics. The interaction of low-magnitude loads with soft tissue posture achieves therapeutic adaptation of the craniofacial skeleton. The increasing emphasis on genomic medicine and personalized treatment planning should focus on low-magnitude loads in orthodontics and dentofacial orthopedics.

     

Inferior alveolar nerve transection inhibits increase in osteoclast appearance during experimental tooth movement

To evaluate the role of sensory nerve innervation in alveolar bone remodeling during experimental tooth movement, we investigated histomorphometrically the influence of sensory nerve denervation on bone metabolism. Seven days after inferior alveolar nerve (IAN) transection or a sham operation in rats, orthodontic force was applied to the animals by inserting an elastic module interproximally between the lower first molar and second molar. Twenty-four hours after the application of the orthodontic force, osteoclast number, osteoclast surface, and osteoblast surface were measured on the trabecular bone surface in the interradicular septum of the lower second molar. The distribution of sensory nerve fibers immunoreactive to antibody against calcitonin gene-related peptide (CGRP) was also evaluated. In the sham-operated rats, CGRP-immunoreactive nerves were observed to be distributed along the blood vessels in the trabecular alveolar bone. Experimental tooth movement resulted in a fivefold increase in the number of osteoclasts and in increased immunoreactivity of nerves to anti-CGRP in the trabecular bone. However, IAN transection depleted the immunoreactivity to anti-CGRP and reduced the osteoclast number and osteoclast surface significantly. On the other hand, in the rats that were not subjected to experimental tooth movement, there was no significant difference in osteoclast number between sham-operated and IAN-transected rats. Significant changes were not observed in osteoblast surfaces associated with experimental tooth movement or nerve transection. These findings suggest that sensory nerves play an important role in regulating bone resorptive activity during experimental tooth movement.     

Bone Response of Loaded Periodontal Ligament

The tooth-periodontal ligament-alveolar bone complex acts symbiotically to dissipate the mechanical loads incurred during mastication and/or orthodontic tooth movement. The periodontal ligament functions both in the tension and compression. At the molecular and celleular levels, the loads in the periodontal ligament trigger mechanobiological events in the alveolar bone, which leads to bone modeling and remodeling. The current review focuses on the bone response to mechanical loading of the periodontal ligament on the tension and pressure sides. Understanding the bone response has major implications for dentistry, including a better understanding of the different types of orthodontic tooth movement.     

Effects of continuous infusion of PTH on experimental tooth movement in rats.

Development of new methods for accelerating orthodontic tooth movement has been strongly desired for shortening of the treatment period. The rate of orthodontic tooth movement is dependent on the rate of bone resorption occurring in the compressed periodontium in the direction of orthodontic force applied to the tooth. In the present study, we examined the effects of continuous infusion of parathyroid hormone (PTH) on tooth movement. Male rats weighing 350-400 g were treated with subcutaneous of vehicle or hPTH(1-84) at 1-10 micrograms/100 g of body weight/day. When the upper right first molar (M1) was moved mesially for 72 h by the insertion of an elastic band between the first and second molars, M1 movement was accelerated by PTH infusion at 10 micrograms. PTH infusion caused a 2- to 3-fold increase in the number of osteoclasts in the compressed periodontium of M1, indicating that such treatment accelerated tooth movement by enhancing bone resorptive activity induced in the compressed periodontium. When M1 was moved mesially by an orthodontic coil spring ligated between upper incisors and M1 for 12 days, PTH(1-84) infusion at 10 micrograms caused a 2-fold increase in the rate of M1 movement. PTH(1-34) infusion at 4 micrograms had an effect comparable to that of PTH(1-84). However, intermittent injection of PTH(1-34) did not accelerate M1 movement. PTH infusion for 13 days did not affect either bone mineral measurements or the serum calcium level. These findings suggest that continuous administration of PTH is applicable to accelerate orthodontic tooth movement.