Micro-osteoperforations accelerate orthodontic tooth movement by stimulating periodontal ligament cell cycles.

INTRODUCTION: The aim of this study was to investigate the mechanism of how micro-osteoperforations (MOPs) accelerate tooth movement. We focused on inflammation, cell proliferation, and apoptosis of periodontal ligament cells and performed immunostaining of MOPs exposed to tumor necrosis factor-alpha (TNF-α), proliferating cell nuclear antigen (PCNA), and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) during experimental tooth movement. METHODS: Eleven-week-old male Wistar rats were divided into 2 groups: (1) 10 g of orthodontic force applied to the maxillary first molar (TM) and (2) force application plus 3 small perforations of the cortical plate (TM + MOPs). On days 1, 4, 7, 10, and 14 after force application, we investigated tooth movement and alveolar bone microstructure using microcomputed tomography (n = 5). We also determined the expression of TNF-α and PCNA in the pressure sides of periodontal ligaments via an immunohistochemical analysis. The expression of apoptotic cells was also determined by the TUNEL method. RESULTS: The tooth movement in the TM + MOPs group was significantly greater on days 4 to 14 than in the TM group. The TM + MOPs group showed statistically significant decreases in bone volume/tissue volume ratio and bone mineral density compared with the TM group. The ratios of TNF-α positive cells in the TM + MOPs group were increased on days 1, 4. 7, and 10 compared with the TM group. The ratios of PCNA positive cells in the TM + MOPs group were increased on days 1, 4, and 7 compared with the TM group, and the ratios of TUNEL positive cells in the TM + MOPs group were increased on days 1 and 7 compared with the TM group. CONCLUSIONS: These results suggest that MOPs may accelerate tooth movement through activation of cell proliferation and apoptosis of periodontal ligament cells.

Relationship between root resorption and individual variation in the calcium/phosphorous ratio of cementum.

INTRODUCTION: The purpose of this study was to investigate whether individual variation in the hardness and chemical composition of the cementum in the root apex affects the degree of root resorption. METHODS: In a previous study, we evaluated the Vickers hardness scale of 50 extracted teeth. For this study, we classified the 50 extracted teeth into soft, moderate, and hard groups according to the Vickers hardness scale. Then, we randomly selected 7 teeth from each group and measured the resorbed areas of the apical cementum in vitro using human osteoclast precursor cells. We also investigated the calcium/phosphorous (Ca/P) and magnesium/calcium ratios of these 21 extracted teeth using energy-dispersive x-ray microanalysis studies to determine the chemical composition of the cementum in the root apex. RESULTS: In the pit formation assay, the resorbed area in the soft group showed a greater extent than it did in the moderate and hard groups (P < 0.01). A correlation was noted between the Vickers hardness and the resorbed area of the cementum in the root apex (r = -0.714; P < 0.01). The Ca/P ratios in the soft and moderate groups were lower than the ratio in the hard group (P < 0.01 and P < 0.05, respectively). A correlation was noted between the Vickers hardness and the Ca/P ratio of the cementum in the root apex (r = 0.741; P < 0.01). CONCLUSIONS: These results suggest that the hardness and Ca/P ratio of the cementum may be involved in root resorption caused by orthodontic forces.

Interleukin-17 is involved in orthodontically induced inflammatory root resorption in dental pulp cells.

INTRODUCTION: The objectives of this study were (1) to investigate the expressions of interleukin (IL)-17, RANKL (the receptor activator of NF-kappaB ligand), and osteoprotegerin (OPG) in root resorption areas during experimental tooth movement in rats, and (2) to determine the effect of IL-17 on the expressions of RANKL and OPG mRNA from human dental pulp cells. METHODS: Twelve male 6-week-old Wistar rats were subjected to an orthodontic force of 50 g to induce a mesially tipping movement of the maxillary first molars for 7 days. The expression levels of tartrate resistant acid phosphatase (TRAP), interleukin (IL)-17, IL-17 receptor (IL-17R), receptor activator of nuclear factor-kappa B ligand (RANKL), and OPG proteins were determined in dental pulp by immunohistochemical analysis. Furthermore, the effects of IL-17 on the expressions of RANKL and OPG mRNA were investigated using human dental pulp cells in vitro. RESULTS: In the experimental tooth movements in vivo, resorption lacunae with multinucleated cells were observed in the 50-g group. The immunoreactivities for IL-17, IL-17R, and RANKL were detected in dental pulp tissues subjected to the orthodontic force on day 7. Moreover, IL-17 increased the mRNA expression of RANKL from human dental pulp cells in vitro. CONCLUSIONS: The results of this study suggest that IL-17 and RANKL may be involved in the process of orthodontically induced inflammatory root resorption in dental pulp cells.

Micro-Osteoperforations Accelerate Tooth Movement without Exacerbating the Progression of Root Resorption in Rats.

A recent study reported that micro-osteoperforations (MOPs) accelerated tooth movement by activating alveolar bone remodeling. However, very little is known about the relationship between MOPs and external apical root resorption during orthodontic treatment. In this study, in order to investigate the mechanism through which MOPs accelerate tooth movement without exacerbating the progression of root resorption, we measured the volume of the resorbed root, and performed the terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick-end labeling (TUNEL) method on exposed MOPs during experimental tooth movements in rats. Male Wistar rats (11 weeks old) were divided into three groups: 10 g orthodontic force (optimal force) applied to the maxillary first molar (optimal force: OF group), 50 g orthodontic force application (heavy force: HF group), and 10 g force application plus three small perforations of the cortical plate (OF + MOPs group). On days 1, 4, 7, 10, and 14 after force application, the tooth movement and root volume were investigated by micro-computed tomography. Furthermore, the number of apoptotic cells in the pressured sides of the periodontal ligament (PDL) and surrounding hard tissues were determined by TUNEL staining. The OF + MOPs group exhibited a 1.8-fold increase in tooth movement on days 7, 10, and 14 compared with the OF group. On days 14, the HF group had a higher volume of root loss than the OF and OF + MOPs groups. On the same day, the number of TUNEL-positive cells in the HF group increased at the root (cementum) site whereas that in the OF group increased at the alveolar bone site. Furthermore, the number of TUNEL-positive cells in the OF + MOPs group increased at the alveolar bone site compared with the OF group. These results suggest that MOPs accelerate orthodontic tooth movement without exacerbating the progression of root resorption.

Effects of Improper Mechanical Force on the Production of Sonic Hedgehog, RANKL, and IL-6 in Human Periodontal Ligament Cells In Vitro.

Improper mechanical stress may induce side effects during orthodontic treatment. If the roots and alveolar bones are extensively resorbed following excess mechanical stress, unplanned tooth mobility and inflammation can occur. Although multiple factors are believed to contribute to the development of side effects, the cause is still unknown. Sonic hedgehog (Shh), one of the hedgehog signals significantly associated with cell growth and cancer development, promotes osteoclast formation in the jawbone. Shh may be associated with root and bone resorptions during orthodontic treatment. In this study, we investigated the relationships between Shh, RANKL, and IL-6 in human periodontal ligament (hPDL) cells exposed to improper mechanical force. Weights were placed on hPDL cells and human gingival fibroblasts (HGFs) for an optimal orthodontic force group (1.0 g/cm2) and a heavy orthodontic force group (4.0 g/cm2). A group with no orthodontic force was used as a control group. Real-time PCR, SDS-PAGE, and Western blotting were performed to examine the effects of orthodontic forces on the expression of Shh, RANKL, and IL-6 at 2, 4, 6, 8, 12, and 24 h after the addition of pressure. The protein expression of Shh was not clearly induced by orthodontic forces of 1.0 and 4.0 g/cm2 compared with the control in HGFs and hPDL cells. In contrast, RANKL and IL-6 gene and protein expression was significantly induced by 1.0 and 4.0 g/cm2 in hPDL cells for forces lasting 6~24 h. However, neither protein was expressed in HGFs. RANKL and IL-6 expressions in response to orthodontic forces and in the control were clearly inhibited by Shh inhibitor RU-SKI 43. Shh did not directly link to RANKL and IL-6 for root and bone resorptions by orthodontic force but was associated with cell activities to be finally guided by the production of cytokines in hPDL cells.

Involvement of interleukins-17 and -34 in exacerbated orthodontic root resorption by jiggling force during rat experimental tooth movement.

BACKGROUND: Orthodontically induced root resorption (OIRR) is considered as an undesirable and unpredictable sequel of orthodontic treatment. Recent reports demonstrated that interleukin (IL)-17/IL-34, and T cells secrete inflammatory/osteoclastogenic cytokines, which might stimulate osteoclastogenesis/bone resorption. However, little is known about the role played by IL-17/IL-34 in OIRR. The present study was aimed at investigating the odontoclastic expression pattern of IL-17 and IL-34 in resorbed cementum during different experimental tooth movements in vivo. METHODS: Twenty-four 8-week-old male Wistar rats were divided into four groups: control group, optimal force group (10 g), heavy force group (50 g), and jiggling force group (compression and tension, repetition; 10 g). After 7, 14, and 21 days, the expression levels of IL-17 and IL-34 protein in the resorbed cementum were analyzed using immunohistochemical methods. RESULTS: On day 21, the immunoreactivity for IL-17 and IL-34 in resorbed roots in the jiggling force group was stronger than that in the heavy force and optimal force groups. Moreover, the number of IL-17-positive and IL-34-positive odontoclasts was significantly increased in the jiggling force group compared with those in the other groups on day 21. CONCLUSIONS: These results suggest that jiggling forces might exacerbate OIRR compared with heavy forces, as evidenced by the increased expression of IL-17 and IL-34 in odontoclasts obtained from resorbed roots.

Effect of caspases and RANKL induced by heavy force in orthodontic root resorption.

OBJECTIVE: Orthodontic root resorption (ORR) due to orthodontic tooth movement is a difficult treatment-related adverse event. Caspases are important effector molecules for apoptosis. At present, little is known about the mechanisms underlying ORR and apoptosis in the cementum. The aim of the present in vivo study was to investigate the expression of tartrate-resistant acid phosphatase (TRAP), caspase 3, caspase 8, and receptor activator of nuclear factor kappa-B ligand (RANKL) in the cementum in response to a heavy or an optimum orthodontic force. METHODS: The maxillary molars of male Wistar rats were subjected to an orthodontic force of 10 g or 50 g using a closed coil spring. The rats were sacrificed each experimental period on days 1, 3, 5, and 7 after orthodontic force application. And the rats were subjected to histopathological and immunohistochemical analyses. RESULTS: On day 7 for the 50-g group, hematoxylin and eosin staining revealed numerous root resorption lacunae with odontoclasts on the root, while immunohistochemistry showed increased TRAP- and RANKL-positive cells. Caspase 3- and caspase 8-positive cells were increased on the cementum surfaces in the 50-g group on days 3 and 5. Moreover, the number of caspase 3- and caspase 8-positive cells and RANKL-positive cells was significantly higher in the 50-g group than in the 10-g group. CONCLUSIONS: In our rat model, ORR occurred after apoptosis was induced in the cementum by a heavy orthodontic force. These findings suggest that apoptosis of cementoblasts is involved in ORR.

Carvedilol blocks cardiac KATP and KG but not IK1 channels by acting at the bundle-crossing regions.

We examined the effects of carvedilol on cardiac inwardly rectifying K(+) (Kir) channels, i.e., ATP-sensitive (K(ATP)), G-protein-activated (K(G)) and background (I(K1)) Kir channels. We found that carvedilol effectively inhibits K(ATP) and K(G), but not I(K1) channels. Carvedilol inhibits K(ATP) channels reconstituted in HEK293 cells with Kir6.2 lacking the C-terminal 26 amino acids (Kir6.2DeltaC26), suggesting that carvedilol acts in the channel pore. A sequence comparison of the three channels revealed that a cysteine residue, C166, in the inner helix of Kir6.2 is conserved in both Kir6.xs (K(ATP)) and Kir3.xs (K(G)), but not in Kir2.xs (I(K1)). The mutation of this residue (C166A) made Kir6.2DeltaC26 resistant to the drug. Homology modeling and docking simulation suggested that interaction between carvedilol and the pore could be located at the cytosolic portion of the inner helix (bundle-crossing region) containing C166. This study shows that carvedilol blocks specific groups of Kir channels by interacting with the bundle-crossing region.

Comparisons of orthodontic root resorption under heavy and jiggling reciprocating forces during experimental tooth movement in a rat model.

OBJECTIVE: Root mobility due to reciprocating movement of the tooth (jiggling) may exacerbate orthodontic root resorption (ORR). "Jiggling" describes mesiodistal or buccolingual movement of the roots of the teeth during orthodontic treatment. In the present study, buccolingual movement is described as "jiggling." We aimed to investigate the relationship between ORR and jiggling and to test for positive cell expression in odontoclasts in resorbed roots during experimental tooth movement (jiggling) in vivo. METHODS: Male Wistar rats were divided into control, heavy force (HF), optimal force (OF), and jiggling force (JF) groups. The expression levels of cathepsin K, matrix metalloproteinase (MMP)-9 protein, interleukin (IL)-6, cytokine-induced neutrophil chemoattractant 1 (CINC-1; an IL-8-related protein in rodents), receptor activator of nuclear factor κB ligand (RANKL), and osteoprotegerin protein in the dental root were determined using immunohistochemistry. RESULTS: On day 21, a greater number of root resorption lacunae, which contained multinucleated odontoclasts, were observed in the palatal roots of rats in the JF group than in rats from other groups. Furthermore, there was a significant increase in the numbers of cathepsin K-positive and MMP-9-positive odontoclasts in the JF group on day 21. Immunoreactivities for IL-6, CINC-1, and RANKL were stronger in resorbed roots exposed to jiggling than in the other groups on day 21. Negative reactivity was observed in the controls. CONCLUSIONS: These results suggest that jiggling may induce ORR via inflammatory cytokine production during orthodontic tooth movement, and that jiggling may be a risk factor for ORR.

Effects of microinjected carbachol on the antinociceptive response to noxious heat stimuli.

Injecting muscarinic receptor agonists into a specific area of the brainstem produces an antinociceptive response. The present study investigates whether direct injections of the cholinergic agonist, carbachol, into the rat nucleus reticularis gigantocellularis (NRGC)/nucleus reticularis gigantocellularis alpha (NRGCalpha) of the rostral ventrolateral medulla evokes antinociception, and then examines the interference action of cholinergic antagonists in rats. Microinjections of carbachol (0.75, 1.5, 3 micro g/site) prolonged hot plate (HP) and tail flick (TF) responses to noxious heat stimuli in a dose-dependent manner. The level of carbachol-induced antinociception during the HP and TF tests reached a maximum at 5-15 min after carbachol administration in all groups. Thereafter, the peak level progressively decreased and reached the baseline by the end of the experiment. Antinociception induced by carbachol at 3 micro g/site was attenuated by the prior administration of the muscarinic receptor antagonist, atropine (200, 500 ng/site). On the other hand, the nicotinic autonomic ganglion blocker, mecamylamine (1, 3 micro g/site), did not affect subsequent carbachol-induced antinociception. These results suggest that the antinociceptive effects induced by a microinjection of carbachol depend on muscarinic, but not nicotinic, mechanisms within the rat NRGC/NRGCalpha.

Alpha 2-adrenoceptor modulates the release of acetylcholine from the rostral ventrolateral medulla in response to morphine.

The present study examined the role of the noradrenergic system in the modulation of acetylcholine (ACh) release in the rostral ventrolateral medulla (RVLM) using in vivo microdialysis of morphine. The basal level of ACh was 325.0 +/- 21.1 fmol/20 microl/15 min in the presence of neostigmine (10 microM). Intraperitoneal (i.p.) administration of 5 and 10 mg/kg morphine significantly increased ACh release by the RVLM. This enhancement was reversed by naloxone (1 mg/kg, i.p.). In addition, pretreatment with yohimbine (0.5 mg/kg, i.p.) or prazosin (0.2 mg/kg, i.p.) attenuated the systemic morphine-induced release of ACh in the RVLM. However, propranolol (0.2 mg/kg, i.p.) did not affect the morphine-induced ACh release. The addition of morphine (10(-4) M) to the perfusion medium increased the ACh release by 72.4% of the predrug values. The increased ACh release induced by local application of morphine was attenuated by pretreatment with yohimbine, but not prazosin. These findings suggest that morphine exerts an indirect stimulatory effect on the release of ACh by the RVLM and that the morphine-induced increase in ACh release is modulated by alpha2-adrenoceptors in freely moving rats.