SDF-1 involvement in orthodontic tooth movement after tooth extraction.

The stromal cell-derived factor 1 (SDF-1)/chemokine receptor type 4 (CXCR4) axis plays a key role in alveolar bone metabolism during orthodontic tooth movement (OTM). Herein, the effects of the SDF-1/CXCR4 axis on the regional acceleratory phenomenon (RAP) in OTM velocity and on changes in the surrounding periodontium after adjacent tooth extraction in rats were investigated. Six-week-old male Wistar/ST rats underwent left maxillary first molar (M1) extraction and mesial OTM of the left maxillary second molar (M2) with a 10-g force closed-coil spring. Phosphate-buffered saline, immunoglobulin G (IgG) isotype control antibody, or anti-SDF-1 neutralizing monoclonal antibody were injected at the M1 and M2 interproximal areas (10 µg/0.1 mL) for the first three days. Analyses were performed after 1, 3, and 7 days (n = 7). The results demonstrated a significant increase in SDF-1 expression from day 1, which was effectively blocked via anti-SDF-1 neutralizing monoclonal antibody injection. On day 3, the M2 OTM distance and the number of positively stained osteoclasts significantly reduced alongside a reduction in inflammatory markers in the experimental group. Our results demonstrated that serial local injection of the anti-SDF-1 neutralizing monoclonal antibody reduces M2 OTM, osteoclast accumulation, and localized inflammatory responses in an OTM model with tooth extraction-induced RAP.

Periostin splice variants affect craniofacial growth by influencing chondrocyte hypertrophy.

INTRODUCTION: Periostin, an extracellular matrix protein, plays an important role in osteogenesis and is also known to activate several signals that contribute to chondrogenesis. The absence of periostin in periostin knockout mice leads to several disorders such as craniosynostosis and periostitis. There are several splice variants with different roles in heart disease and myocardial infarction. However, little is known about each variant's role in chondrogenesis, followed by bone formation. Therefore, the aim of this study is to investigate the role of several variants in chondrogenesis differentiation and bone formation in the craniofacial region. Periostin splice variants included a full-length variant (Control), a variant lacking exon 17 (ΔEx17), a variant lacking exon 21 (ΔEx21), and another variant lacking both exon 17 and 21 ***(ΔEx17&21). MATERIALS AND METHODS: We used C56BL6/N mice (n = 6) for the wild type (Control)*** and the three variant type mice (n = 6 each) to identify the effect of each variant morphologically and histologically. Micro-computed tomography demonstrated a smaller craniofacial skeleton in ΔEx17s, ΔEx21s, and ΔEx17&21s compared to Controls, especially the mandibular bone. We, thus, focused on the mandibular condyle. RESULTS: The most distinctive histological observation was that each defected mouse appeared to have more hypertrophic chondrocytes than Controls. Real-time PCR demonstrated the differences among the group. Moreover, the lack of exon 17 or exon 21 in periostin leads to inadequate chondrocyte differentiation and presents in a diminutive craniofacial skeleton. DISCUSSION: Therefore, these findings suggested that each variant has a significant role in chondrocyte hypertrophy, leading to suppression of bone formation.

NF-κB Decoy ODN-Loaded Poly(Lactic-co-glycolic Acid) Nanospheres Inhibit Alveolar Ridge Resorption.

Residual ridge resorption combined with dimensional loss resulting from tooth extraction has a prolonged correlation with early excessive inflammation. Nuclear factor-kappa B (NF-κB) decoy oligodeoxynucleotides (ODNs) are double-stranded DNA sequences capable of downregulating the expression of downstream genes of the NF-κB pathway, which is recognized for regulating prototypical proinflammatory signals, physiological bone metabolism, pathologic bone destruction, and bone regeneration. The aim of this study was to investigate the therapeutic effect of NF-κB decoy ODNs on the extraction sockets of Wistar/ST rats when delivered by poly(lactic-co-glycolic acid) (PLGA) nanospheres. Microcomputed tomography and trabecular bone analysis following treatment with NF-κB decoy ODN-loaded PLGA nanospheres (PLGA-NfDs) demonstrated inhibition of vertical alveolar bone loss with increased bone volume, smoother trabecular bone surface, thicker trabecular bone, larger trabecular number and separation, and fewer bone porosities. Histomorphometric and reverse transcription-quantitative polymerase chain reaction analysis revealed reduced tartrate-resistant acid phosphatase-expressing osteoclasts, interleukin-1ß, tumor necrosis factor-α, receptor activator of NF-κB ligand, turnover rate, and increased transforming growth factor-ß1 immunopositive reactions and relative gene expression. These data demonstrate that local NF-κB decoy ODN transfection via PLGA-NfD can be used to effectively suppress inflammation in a tooth-extraction socket during the healing process, with the potential to accelerate new bone formation.

Effects of local vs systemic administration of CXCR4 inhibitor AMD3100 on orthodontic tooth movement in rats.

INTRODUCTION: Chemokines play pivotal roles in orthodontic tooth movement (OTM) through osteoclast-mediated bone resorption, but the underlying mechanism remains unclear. We aimed to elucidate the effects of serial local vs systemic administration of the chemokine receptor CXCR4 antagonist AMD3100 on OTM. METHODS: The maxillary first molar (M1) of rats was moved mesially using a 10 g of force nickel-titanium coil spring. The injections were performed every other day with phosphate-buffered saline as a control, whereas local and systemic animals were injected with AMD3100 at the buccal palatal mucosa adjacent to M1 and subcutaneously, respectively. OTM distance and alveolar bone were examined by microcomputed tomography and histologic analysis. Osteoclast numbers were quantified using TRAP staining. Cathepsin K and stromal cell-derived factor-1 (SDF-1) were evaluated using immunohistochemistry. Reverse transcriptase polymerase chain reaction for cathepsin K, Runx2, SDF-1, CXCR4, RANKL, and OPG were also examined. RESULTS: OTM and osteoclast numbers were significantly decreased in the local and systemic groups compared with the control group, whereas there was no significant difference among the experimental groups. Local administration inhibited molar but not incisor movement. Trabecular thickness and trabecular spacing of the alveolar bone significantly increased, and trabecular number significantly decreased in the systemic group compared with the control group, whereas local injection also affected bone quality in the same tendency as a systemic injection. AMD3100 significantly downregulated the mRNA expression levels of cathepsin K, Runx2, SDF-1, RANKL, and RANKL/OPG ratio in both experimental groups. CONCLUSIONS: Local administration of AMD3100 can control initial OTM and diminish bone resorption processes during OTM via inhibition of the SDF-1/CXCR4 axis, similar to the systemic administration.

Nuclear factor-kappa B decoy oligodeoxynucleotide-loaded poly lactic-co-glycolic acid nanospheres promote periodontal tissue healing after tooth replantation in rats.

BACKGROUND: Excessive inflammation in the periodontal tissue after tooth replantation can lead to inflammatory root resorption and interrupt periodontal tissue regeneration. We tested the hypothesis that nuclear factor-κB decoy oligodeoxynucleotide-loaded poly lactic-co-glycolic acid nanospheres (NF-PLGA) inhibit excessive inflammation and promote healing of periodontal tissue after replantation in rats. METHODS: The upper right incisors of rats were extracted, immersed in different specific solutions, and replanted. The rats were euthanized at 7, 14, and 28 days after replantation. Morphological evaluation with micro-CT and histological assessment with hematoxylin and eosin and tartrate-resistant acid phosphatase (TRAP) staining was performed. Additionally, we examined the expression of interleukin (IL)-1ß, IL-6, transforming growth factor-ß1 (TGF-ß1), and fibroblast growth factor-2 (FGF-2) in the periodontal ligament (PDL) by performing immunohistological assessment. RESULTS: The NF-PLGA group showed significantly greater dental root thickness than the other experimental groups. Root resorption was not observed after the application of NF-PLGA on day 7. The application of NF-PLGA also resulted in a significantly lower number of TRAP-positive osteoclasts on days 7 and 14 after replantation. Significantly lower expression of IL-1ß and IL-6 and higher expression of TGF-ß1 and FGF-2 were observed under the application of NF-PLGA in the PDL. CONCLUSIONS: NF-PLGA promoted the healing process by inhibiting the initial excessive inflammatory response in the PDL, preventing root resorption, and promoting periodontal tissue regeneration. The findings also suggested that the PLGA nanospheres-mediated transfection of the decoy oligodeoxynucleotides can be useful for the clinical application of replanted tooth root surfaces.

Selective ß2-Adrenoceptor Blockade Rescues Mandibular Growth Retardation in Adolescent Rats Exposed to Chronic Intermittent Hypoxia.

Activation of the sympathoadrenal system is associated with sleep apnea-related symptoms and metabolic dysfunction induced by chronic intermittent hypoxia (IH). IH can induce hormonal imbalances and growth retardation of the craniofacial bones. However, the relationship between IH and ß2-adrenergic receptor signaling in the context of skeletal growth regulation is unclear. This study aimed to investigate the role of ß2-adrenergic receptors in IH-induced mandibular growth retardation and bone metabolic alterations. Male 7-week-old Sprague-Dawley rats were subjected to IH for 3 weeks. IH conditions were established using original customized hypoxic chambers; IH was induced at a rate of 20 cycles per hour (oxygen levels changed from 4 to 21% in one cycle) for 8 h per day during the 12 h "lights on" period. The rats received intraperitoneal administration of a ß2-adrenergic antagonist (butoxamine) or saline. To exclude dietary effects on general growth, the normoxic rats with saline, normoxic rats with butoxamine, and IH rats with butoxamine were subjected to food restriction to match the body weight gains between IH and other three groups. Body weight, heart rate, blood pressure, and plasma concentrations of leptin, serotonin, and growth hormone were measured. Bone growth and metabolism were evaluated using radiography, microcomputed tomography, and immunohistochemical staining. Plasma leptin levels were significantly increased, whereas that of serotonin and growth hormone were significantly decreased following IH exposure. Leptin levels recovered following butoxamine administration. Butoxamine rescued IH-induced mandibular growth retardation, with alterations in bone mineral density at the condylar head of the mandible. Immunohistochemical analysis revealed significantly lower expression levels of receptor activator of nuclear factor-kappa B ligand (RANKL) in the condylar head of IH-exposed rats. Conversely, recovery of RANKL expression was observed in IH-exposed rats administered with butoxamine. Collectively, our findings suggest that the activation of ß2-adrenergic receptors and leptin signaling during growth may be involved in IH-induced skeletal growth retardation of the mandible, which may be mediated by concomitant changes in RANKL expression at the growing condyle.

Intermittent hypoxia retards mandibular growth and alters RANKL expression in adolescent and juvenile rats.

OBJECTIVES: Chronic intermittent hypoxia (IH), a common state experienced in obstructive sleep apnoea (OSA), retards mandibular growth in adolescent rats. The aim of this study was to elucidate the differential effects of IH on mandibular growth in different growth stages. MATERIALS AND METHODS: Three-week-old (juvenile stage) and 7-week-old (adolescent stage) male Sprague-Dawley rats underwent IH for 3 weeks. Age-matched control rats were exposed to room air. Mandibular growth was evaluated by radiograph analysis, micro-computed tomography, real-time polymerase chain reaction and immunohistology. Tibial growth was evaluated as an index of systemic skeletal growth. RESULTS: IH had no significant impact on the general growth of either the juvenile or adolescent rats. However, it significantly decreased the total mandibular length and the posterior corpus length of the mandible in the adolescent rats and the anterior corpus length in the juvenile rats. IH also increased bone mineral density (BMD) of the condylar head in adolescent rats but did not affect the BMD of the tibia. Immunohistological analysis showed that the expression level of receptor activation of nuclear factor-κB ligand significantly decreased (in contrast to its messenger ribonucleicacid level) in the condylar head of adolescent rats with IH, while the number of osteoprotegerin-positive cells was comparable in the mandibles of adolescent IH rats and control rats. LIMITATIONS: The animal model could not simulate the pathological conditions of OSA completely and there were differences in bone growth between humans and rodents. CONCLUSIONS: These results suggest that the susceptibility of mandibular growth retardation to IH depends on the growth stage of the rats.

Intermittent hypoxia induces turbinate mucosal hypertrophy via upregulating the gene expression related to inflammation and EMT in rats.

PURPOSE: Chronic intermittent hypoxia (IH) plays a pivotal role in the consequences of obstructive sleep apnea (OSA). It has been demonstrated that IH impairs nasomaxillary complex growth to reduce nasal airway cavity size in rodent models. Although turbinate dysfunction with inflammatory mucosal hypertrophy is related to OSA, the role of IH in turbinate hypertrophy with inflammation-driven fibrosis is unknown. Here, we aimed to clarify the pathogenesis of inflammatory mucosal hypertrophy and epithelial-mesenchymal transition (EMT) in the nasal turbinate under IH. METHODS: Seven-week-old male Sprague-Dawley rats were exposed to IH (4% O2 to 21% O2 with 0% CO2) at a rate of 20 cycles/h. RESULTS: Hypertrophy of the turbinate mucosa occurred after 3 weeks, with the turbinate mucosa of the experimental group becoming significantly thicker than in the control group. Immunostaining showed that IH increased the expression of TGFß and N-cadherin and decreased E-cadherin expression in the turbinate mucosa. Quantitative PCR analysis demonstrated that IH enhanced the expression of not only the inflammatory markers Tnf-a, Il-1b, and Nos2 but also the EMT markers Tgf-b1, Col1a1, and Postn. CONCLUSIONS: Collectively, these results suggest that IH induced turbinate hypertrophy via upregulation of gene expression related to inflammation and EMT in the nasal mucosa.

Differential growth of craniofacial and tibial bones to sympathetic hyperactivity-related hypertension in rats.

OBJECTIVE: To evaluate the effect of sympathetic nervous system hyperactivity on craniofacial skeletal growth in growing spontaneously hypertensive rats (SHRs). DESIGN: Craniofacial skeletal growth was compared between male SHR and Wistar-Kyoto rats (WKR) using linear measurements on lateral and transverse cephalometric radiographs at the age of 12 weeks. Tibia length was measured as an index of whole body growth. Body weight　and blood pressure were measured from 3 to 12 weeks of age. Bone microstructure in the mandibular condyle and tibia between the two groups was compared at the age of 12 weeks using microcomputed tomography. RESULTS: The SHRs had a significantly lower body weight than WKRs from 7 weeks of age, and tibial length was significantly smaller in the SHRs than in the WKR at 12 weeks of age. In all SHRs, blood pressure was significantly higher than in WKRs from 3 to 12 weeks of age. Cephalometric analyses revealed decreased measurements of the neurocranium, viscerocranium, and mandible in SHRs, and mandibular growth was most negatively affected in this group. Lastly, in SHRs, microcomputed tomography analyses revealed decreased bone mineral density and bone volume/tissue volume in the mandibular condyle but not in the tibia. CONCLUSION: In growing SHRs, hypertension related to the hyperactivity of the sympathetic nervous system reduced craniofacial skeletal growth more than the growth of the tibia.

Collaborative treatment for a case of condylar hyperplastic facial asymmetry.

Facial asymmetry can be caused by unilateral condylar hyperplasia. In such cases, it may be difficult to achieve symmetry since there is dentoalveolar compensation on the affected side, and the occlusal cant does not correspond to the frontal mandibular deviation. In the case presented, surgical orthodontic treatment and orthognathic surgery planning was accomplished for a patient with facial asymmetry due to condylar hyperplasia. The surgical plan was devised with particular attention to the severe dentoalveolar compensation. In this case, prior to the two-jaw surgery, the occlusal cant and frontal mandibular plane inclination was corrected through impaction of the left molar region by segmental osteotomy. Facial asymmetry and severe dentoalveolar compensation were successfully corrected after a unilateral segmental osteotomy and two-jaw surgery, resulting in a stable occlusal relationship and facial symmetry as well as good jaw function. Collaboration between the orthodontists and maxillofacial surgeons was essential for the successful treatment of the patient.

The chemokine receptor type 4 antagonist, AMD3100, interrupts experimental tooth movement in rats.

OBJECTIVE: The aim of this study was to clarify the role of the stromal cell-derived factor-1 (SDF-1)/C-X-C chemokine receptor type 4 (CXCR4) axis in osteoclast accumulation, and the influence of orthodontic tooth movement (OTM) under mechanical force application to periodontal tissues, by administration of the CXCR4 antagonist AMD3100. DESIGN: The upper right first molar (M1) of rats was moved mesially with a 10-g force titanium-nickel closed coil spring. Rats were treated with phosphate-buffered saline or AMD3100 (5mg/kg), which is a SDF-1 antagonist. After 0, 1, 3, and 7days, alveolar bones in all groups were examined at each time point by micro-computed tomography and histological analysis. RESULTS: Tooth movement was decreased significantly in the AMD3100-treated group at 1, 3, and 7days after beginning OTM. The numbers of tartrate-resistant acid phosphatase-positive multinucleated cells in the periodontal ligament around the maxillary M1 were decreased significantly in the treated as compared to the control group on Days 1 and 3. CONCLUSION: Administration of AMD3100 decreases OTM and osteoclast accumulation in rat molars under orthodontic force application. These findings suggest that the SDF-1/CXCR4 axis plays an important role in alveolar bone metabolism during OTM.

Ultrasound microbubble-mediated transfection of NF-κB decoy oligodeoxynucleotide into gingival tissues inhibits periodontitis in rats in vivo.

Periodontitis is a chronic infectious disease for which the fundamental treatment is to reduce the load of subgingival pathogenic bacteria by debridement. However, previous investigators attempted to implement a nuclear factor kappa B (NF-κB) decoy oligodeoxynucleotide (ODN) as a suppressor of periodontitis progression. Although we recently reported the effectiveness of the ultrasound-microbubble method as a tool for transfecting the NF-κB decoy ODN into healthy rodent gingival tissue, this technique has not yet been applied to the pathological gingiva of periodontitis animal models. Therefore, the aim of this study was to investigate the effectiveness of the technique in transfecting the NF-κB decoy ODN into rats with ligature-induced periodontitis. Micro computed tomography (micro-CT) analysis demonstrated a significant reduction in alveolar bone loss following treatment with the NF-κB decoy ODN in the experimental group. RT-PCR showed that NF-κB decoy ODN treatment resulted in significantly reduced expression of inflammatory cytokine transcripts within rat gingival tissues. Thus, we established a transcutaneous transfection model of NF-κB decoy ODN treatment of periodontal tissues using the ultrasound-microbubble technique. Our findings suggest that the NF-κB decoy ODN could be used as a significant suppressor of gingival inflammation and periodontal disease progression.

Low-intensity pulsed ultrasound reduces periodontal atrophy in occlusal hypofunctional teeth.

OBJECTIVE: To clarify whether low-intensity pulsed ultrasound (LIPUS) exposure has recovery effects on the hypofunctional periodontal ligament (PDL) and interradicular alveolar bone (IRAB). MATERIALS AND METHODS: Twelve-week-old male Sprague-Dawley rats were divided into three groups (n = 5 each): a normal occlusion (C) group, an occlusal hypofunction (H) group, and an occlusal hypofunction group subjected to LIPUS (HL) treatment. Hypofunctional occlusion of the maxillary first molar (M1) of the H and HL groups was induced by the bite-raising technique. Only the HL group was irradiated with LIPUS for 5 days. The IRAB and PDL of M1 were examined by microcomputed tomography (micro-CT) analysis. To quantify mRNA expression of cytokines involved in PDL proliferation and development, real-time reverse transcription quantitative PCR (qRT-PCR) was performed for twist family bHLH transcription factor 1 (Twist1), periostin, and connective tissue growth factor (CTGF) in the PDL samples. RESULTS: Micro-CT analysis showed that the PDL volume was decreased in the H group compared with that of the C and HL groups. Both bone volume per tissue volume (BV/TV) of IRAB was decreased in the H group compared with that in the C group. LIPUS exposure restored BV/TV in the IRAB of the HL group. qRT-PCR analysis showed that Twist1, periostin, and CTGF mRNA levels were decreased in the H group and increased in the HL group. CONCLUSION: LIPUS exposure reduced the atrophic changes of alveolar bone by inducing the upregulation of periostin and CTGF expression to promote PDL healing after induction of occlusal hypofunction.

A new approach to transfect NF-κB decoy oligodeoxynucleotides into the periodontal tissue using the ultrasound-microbubble method.

The objective of this study is to investigate the effect of the ultrasound-microbubble technique in nuclear factor kappa B (NF-κB) decoy oligodeoxynucleotide (ODN) transfection in the gingival tissue in mice. The 6-FAM-labeled scrambled decoy ODN with microbubbles was applied to the periodontal tissue in 8-week-old male C57BL/6J mice by ultrasound radiation at low (LUM-Sc) and high (HUM-Sc) intensities to optimize the transfection condition of the ultrasound-microbubble method. Histological inspections were performed two hours after transfection to compare the expression with that in the sham-operated group without ultrasound radiation (A-Sc). Then, an NF-κB decoy was transfected into the periodontal tissue using the high-intensity ultrasound-microbubble (HUM-NF) technique to examine the anti-inflammatory effects of the decoy ODN. Western blot analysis was performed to investigate the expression of interleukin(IL)-1ß, IL-6 and intercellular adhesion molecule-1 (ICAM-1) in the gingival tissues in the HUM-Sc, the HUM-NF and control groups. The fluorescence microscopy results showed that the fluorescent intensity in the periodontal tissues in the LUM-Sc and HUM-Sc groups was significantly higher than that in the A-Sc and the control groups. The fluorescent intensity in the HUM-Sc group, especially in the gingival connective tissue, was the highest of all groups. Western blot analysis indicated that the protein expression levels of IL-1ß, IL-6 and ICAM-1 in the HUM-NF group were significantly lower than those in the HUM-Sc and the control groups. These findings suggest that the high-intensity ultrasound-microbubble technique is an effective tool for decoy transfection into the periodontal tissue.

Intermittent hypoxia causes mandibular growth retardation and macroglossia in growing rats.

INTRODUCTION: In this study, we aimed to examine the role of intermittent hypoxia (IH) in dentofacial morphologic changes in growing rats. METHODS: Seven-week-old male rats were exposed to IH at 20 cycles per hour (nadir of 4% oxygen to peak of 21% oxygen) for 8 hours per day for 6 weeks. Control rats were exposed to normoxia (N). Maxillofacial growth was compared between the 2 groups by linear measurements on cephalometric radiographs. To examine the dental arch morphology, study models and microcomputed tomography images of the jaws were taken. Additionally, tongue size was measured. RESULTS: The gonial angle and the ramus of the mandible were smaller in the IH group than in the N group, whereas the body weights were not different between the 2 groups. Morphometric analysis of the dentition showed a significantly wider mandibular dentition and narrower maxillary dentition in the IH than in the N group. The relative width (+4.2 %) and length (tongue apex to vallate papillae, +3.5 %) of the tongue to the mandible were significantly greater in the IH group than in the N group. CONCLUSIONS: IH induced dentofacial morphologic discrepancies in growing rats.

Intermittent Hypoxia Influences Alveolar Bone Proper Microstructure via Hypoxia-Inducible Factor and VEGF Expression in Periodontal Ligaments of Growing Rats.

Intermittent hypoxia (IH) recapitulates morphological changes in the maxillofacial bones in children with obstructive sleep apnea (OSA). Recently, we found that IH increased bone mineral density (BMD) in the inter-radicular alveolar bone (reflecting enhanced osteogenesis) in the mandibular first molar (M1) region in the growing rats, but the underlying mechanism remains unknown. In this study, we focused on the hypoxia-inducible factor (HIF) pathway to assess the effect of IH by testing the null hypothesis of no significant differences in the mRNA-expression levels of relevant factors associated with the HIF pathway, between control rats and growing rats with IH. To test the null hypothesis, we investigated how IH enhances mandibular osteogenesis in the alveolar bone proper with respect to HIF-1α and vascular endothelial growth factor (VEGF) in periodontal ligament (PDL) tissues. Seven-week-old male Sprague-Dawley rats were exposed to IH for 3 weeks. The microstructure and BMD in the alveolar bone proper of the distal root of the mandibular M1 were evaluated using micro-computed tomography (micro-CT). Expression of HIF-1α and VEGF mRNA in PDL tissues were measured, whereas osteogenesis was evaluated by measuring mRNA levels for alkaline phosphatase (ALP) and bone morphogenetic protein-2 (BMP-2). The null hypothesis was rejected: we found an increase in the expression of all of these markers after IH exposure. The results provided the first indication that IH enhanced osteogenesis of the mandibular M1 region in association with PDL angiogenesis during growth via HIF-1α in an animal model.

Intermittent hypoxia induces disturbances in craniofacial growth and defects in craniofacial morphology.

OBJECTIVES: To investigate intermittent hypoxia (IH) induced changes in craniofacial morphology and bone mineral density (BMD) in the mandible of growing rats. DESIGN: Seven-week-old male Sprague-Dawley rats were exposed to IH for 4 days or 3 weeks. Sham-operated rats simultaneously breathed room air. Lateral and transverse cephalometric radiographs of the craniofacial region were obtained, and the linear distances between cephalometric landmarks were statistically analyzed. BMD and bone microstructure of the mandible were evaluated using micro-computed tomography (micro-CT). RESULTS: Cephalometric analyses demonstrated that exposure to IH only in the two groups for 3 weeks decreased the size of the mandibular and viscerocranial bones, but not that of the neurocranial bones, in early adolescent rats. These findings are consistent with upper airway narrowing and obstructive sleep apnea (OSA). Micro-CT showed that IH increased the BMD in the cancellous bone of the mandibular condyle and the inter-radicular alveolar bone in the mandibular first molar (M1) region. CONCLUSIONS: This study is the first to identify growth retardation of the craniofacial bones in an animal model of sleep apnea. Notably, 3 weeks of IH can induce multiple changes in the bones around the upper airway in pubertal rats, which can enhance upper airway narrowing and the development of OSA. The reproducibility of these results supports the validity and usefulness of this model. These findings also emphasize the critical importance of morphometric evaluation of patients with OSA.

Impairment of nasal airway under intermittent hypoxia during growth period in rats.

OBJECTIVE: To clarify the influences of intermittent hypoxia (IH) on the growth and development of the midfacial area, including the nasal cavity, in growing rats. DESIGN: Seven-week-old male Sprague-Dawley rats were divided into two groups: the experimental group (n=5), which was exposed to IH for 8h during light periods at a rate of 20 cycles/h (nadir, 4% O2 to peak, 21% O2 with 0% CO2), and the control group (n=5), which was exposed to room air. After 3 weeks, the maxillofacial structures in both groups were evaluated with respect to the height, width, length, surface area, cross-sectional area, and volume of the nasal cavity using soft X-ray and micro-CT. RESULTS: The experimental group showed a significantly smaller cross-sectional area and volume than did the control group. The surface area exhibited no significant differences between the two groups, although it tended to be smaller in the experimental group than in the control group. The nasal volume divided by the length of the tibia (for comparison with whole-body growth) was significantly smaller in the experimental group than in the control group. CONCLUSIONS: These data suggest that IH exposure suppresses growth and development of the nasal cavity and may result in nasal breathing disturbance.