PERK-eIF2α-ATF4 pathway mediated by endoplasmic reticulum stress response is involved in osteodifferentiation of human periodontal ligament cells under cyclic mechanical force.

To prevent excess accumulation of unfolded proteins in endoplasmic reticulum (ER), eukaryotic cells have signaling pathways from the ER to the cytosol or nucleus. These processes are known as the endoplasmic reticulum stress (ERS) response. Protein kinase R like endoplasmic reticulum kinase (PERK) is a major transducer of the ERS response and it directly phosphorylate α-subunit of eukaryotic initiation factor 2 (eIF2α), resulting in translational attenuation. Phosphorylated eIF2α specifically promoted the translation of the activating transcription factor 4 (ATF4). ATF4 is a known important transcription factor which plays a pivotal role in osteoblast differentiation and bone formation. Furthermore, ATF4 is a downstream target of PERK. Studies have shown that PERK-eIF2α-ATF4 signal pathway mediated by ERS was involved in osteoblastic differentiation of osteoblasts. We have known that orthodontic tooth movement is a process of periodontal ligament cells (PDLCs) osteodifferentiation and alveolar bone remodeling under mechanical force. However, the involvement of PERK-eIF2α-ATF4 signal pathway mediated by ERS in osteogenic differentiation of PDLCs under mechanical force has not been unclear. In our study, we applied the cyclic mechanical force at 10% elongation with 0.5Hz to mimic occlusal force, and explored whether PERK-eIF2α-ATF4 signaling pathway mediated by ERS involved in osteogenic differentiation of PDLCs under mechanical force. Firstly, cyclic mechanical force will induce ERS and intensify several osteoblast marker genes (ATF4, OCN, and BSP). Next, we found that PERK overexpression increased eIF2α phosphorylation and expression of ATF4, furthermore induced BSP, OCN expression, thus it will promote osteodifferentiation of hPDLCs; mechanical force could promote this effect. However, PERK(-/-) cells showed the opposite changes, which will inhibit osteodifferentiation of hPDLCs. Taken together, our study proved that PERK-eIF2α-ATF4 signaling pathway mediated by ERS involved in osteoblast differentiation of PDLCs under cyclic mechanical force.

Association between mandibular posterior alveolar morphology and growth pattern in a Chinese population with normal occlusion.

OBJECTIVE: To investigate the relationship between growth patterns and mandibular posterior tooth-alveolar bone complex morphology in a Chinese population with normal occlusion. METHODS: Forty-five patients with normal occlusion (23 males, 22 females) were included in this study. Among these patients, 20 displayed the vertical growth pattern, and 20 had the horizontal growth pattern, while the remaining patients displayed the average growth pattern. All of the patients underwent dental cone beam computed tomography (CBCT), which included the region of the mandibular posterior teeth and the alveolar. A linear regression analysis and a correlation analysis between the facial height index (FHI) and the alveolar bone morphology were performed. RESULTS: The inclination of the molars, the thickness of the cortical bone, and the height of the mandibular bone differed significantly between patients with the horizontal growth pattern and those with the vertical growth pattern (P<0.05). Significant positive correlations were found between: the FHI and the inclination of the molars; the FHI and the thickness of the cortical bone; and the FHI and the height of the mandibular bone. CONCLUSIONS: The mandibular posterior tooth-alveolar bone complex morphology may be affected by growth patterns.

[Expression of HIF-1α and VEGF in human dental pulp cells under mechanical stretch].

PURPOSE: To examine the expression of HIF-1α and VEGF after application of mechanical stretch on human dental pulp cells (HDPCs), and to investigate the role of them in maintaining homeostasis of dental pulp during orthodontic movement. METHODS: HDPCs were subjected to 15% elongation by 1.0 Hz stretching frequency for 6, 12, 24, 48 and 72 h. The expression of HIF-1α and VEGF mRNA was measured by real-time polymerase chain reaction (PCR). SPSS12.0 software package was applied for statistical analysis. RESULTS: At the initial time point, HIF-1α mRNA had a weak expression. The mRNA level of HIF-1α increased gradually and then decreased towards its pre-pressure levels. The mRNA level of VEGF was upregulated in a time-dependent manner. CONCLUSIONS: The mRNA expression of HIF-1α and VEGF was enhanced by mechanical stress in HDPCs, which indicates that HIF-1α and VEGF may play an important role in retaining homeostasis of dental pulp during orthodontic movement.

Three-dimensional evaluation of upper anterior alveolar bone dehiscence after incisor retraction and intrusion in adult patients with bimaxillary protrusion malocclusion.

OBJECTIVE: The purpose of this study was to evaluate three-dimensional (3D) dehiscence of upper anterior alveolar bone during incisor retraction and intrusion in adult patients with maximum anchorage. METHODS: Twenty adult patients with bimaxillary dentoalveolar protrusion had the four first premolars extracted. Miniscrews were placed to provide maximum anchorage for upper incisor retraction and intrusion. A computed tomography (CT) scan was performed after placement of the miniscrews and treatment. The 3D reconstructions of pre- and post-CT data were used to assess the dehiscence of upper anterior alveolar bone. RESULTS: The amounts of upper incisor retraction at the edge and apex were (7.64±1.68) and (3.91±2.10) mm, respectively, and (1.34±0.74) mm of upper central incisor intrusion. Upper alveolar bone height losses at labial alveolar ridge crest (LAC) and palatal alveolar ridge crest (PAC) were 0.543 and 2.612 mm, respectively, and the percentages were (6.49±3.54)% and (27.42±9.77)%, respectively. The shape deformations of LAC-labial cortex bending point (LBP) and PAC-palatal cortex bending point (PBP) were (15.37±5.20)° and (6.43±3.27)°, respectively. CONCLUSIONS: Thus, for adult patients with bimaxillary protrusion, mechanobiological response of anterior alveolus should be taken into account during incisor retraction and intrusion. Pursuit of maximum anchorage might lead to upper anterior alveolar bone loss.

Transcription factor osterix modified bone marrow mesenchymal stem cells enhance callus formation during distraction osteogenesis.

This study was designed to investigate the effects of local delivery of bone marrow mesenchymal stem cells (BMMSCs) with or without osterix (OSX) gene transfected on bone regeneration in the distracted zone using a rabbit model of mandibular lengthening. Fifty-four New Zealand white rabbits underwent osteodistraction of the left mandible and were then randomly divided into group A, group B, and group C (n = 18 for each group). At the end of distraction BMMSCs transfected with OSX, autologous BMMSCs and physiological saline were injected into the distraction gaps in groups A, B, and C, respectively. Nine animals from each group were humanely killed at 2 and 6 weeks after completion of distraction. The distracted mandibles were harvested and processed for radiographic, histological, and immunohistochemical examination. Excellent bone formation in the distracted callus was observed in group A and group B; the former showed better bone formation and highest bone mineral density (BMD), thickness of new trabeculae (TNT, mm) and volumes of the newly formed bone area (NBV) in the distraction zones. Group C animals showed poor bone formation in the distracted callus when compared with groups A and B. Positive immunostaining of bone sialoprotein (BSP) was observed in the distracted callus in all groups; however, BSP expression was much stronger in group A than in groups B and C. The results of this study suggest transplantation of BMMSCs can promote bone formation in DO; OSX-mediated ex vivo gene therapy was more effective during bone deposition and callus formation in distraction osteogenesis.

[Expression of Osterix mRNA and protein levels in cultured human periodontal ligament cells after mechanical stimulation].

OBJECTIVE: To examine the expression of Osterix (Osx) mRNA and protein after application of mechanical force on human periodontal ligament cells (HPDLCs), and to investigate the role of Osx in orthodontic alveolar bone remodeling. METHODS: HPDLCs were isolated and cultured in vitro with explant method. Approximately 2.5 x 10(5) cells were seeded onto six-well cell culture plates and then were exposed to centrifugal force for 1, 2, 4, 6, 8 or 12 h at 631 r x min(-1). The expression of Osx mRNA and protein was measured by reverse transcription-polymerase chain raction (RT-PCR) and Western blot respectively. Immunofluorescence assay was used to detect the expression and subcellular At the initial time point, Osx mRNA had a weak exlocalization of Osx protein by green fluorescence. RESULTS: pression and protein was not detected. Under the mechanical stimulation, both mRNA and protein levels of Osx were upregulated in a time-dependent manner. Furthermore, Osx protein was translocated gradually from the cytosol into the cell nuclei. CONCLUSION: The expression and activation of Osx were enhanced by mechanical stress in HPDLCs, which indicates that Osx may play an important role in HPDLCs osteogenic differentiation and periodontal tissue remodeling induced by mechanical stress.

[Effects of non-surgical treatment on temporomandibular joint of adult low-angle subjects with severe skeletal class III deformity].

OBJECTIVE: To investigate effects of non-surgical treatment on temporal mandibular joint(TMJ) of adult low-angle subjects with severe skeletal Class III deformity. METHODS: Thirteen low-angle patients with severe skeletal Class III malocclusion (male 5, female 8) were included in the study. The average age was 21.3 years old. They were treated with OPA-K straight wire technique. Helkimo index evaluation was made before and after treatment. Lateral cephalometric films and corrected TMJ lateral cephalometric radiograghs were taken before and after treatment, and linear and area measurement were observed. All data were analyzed with SPSS 12.0 software. RESULTS: After non-surgical treatment, Helkimo indexes of all patients redistributed. The line distance and area of anterior space in TMJ increased while the posterior space decreased. Linear percent decreased from 20.81% to 8.04%, and area proportion decreased from 1.62 to 1.01. Anterior space was the same as the posterior. Condyles and mandibles were retruded. CONCLUSION: After non-surgical therapy in adult low-angle subjects with severe skeletal Class III malocclusion, condyles remove posteriorly from more anterior position to normal concentric position, and temporo-mandibular disorders symptom is relieved and cured effectively.

[Changes of mRNA and protein levels of activating transcription factor-4 after centrifugal force stimulation in cultured human periodontal ligament cells].

PURPOSE: This study was designed to examine the changes of mRNA and protein levels of activating transcription factor-4 after centrifugal force stimulation in cultured human periodontal ligament (PDL)cells. METHODS: Human PDL cells were cultured by sequential digestio, and then stimulated by centrifugal force (167g) for 10, 30, 60, 90, 120 and 240 minutes. The changes of mRNA and protein levels of ATF4 were analyzed by semi-quantitative RT-PCR and Western blotting. The data was analyzed with SPSS11.5 software package for ANOVA. RESULTS: Unstimulated human PDL cells exhibit an ATF4 mRNA expression, but very low level of protein; Immediately 10 minutes after force application, the mRNA and protein levels of ATF4 increased(P>0.05); at 30-minute,the mRNA level increased significantly to a peak level(P<0.01), at 60-minute, the protein level increased significantly to a peak level(P<0.01); at 90-minute, mRNA and protein levels decreased, but still higher than the control(P<0.01); after 120 minutes, mRNA and protein levels decreased to control levels(P>0.05). CONCLUSION: Centrifugal force stimulates ATF4 gene expression within a narrow time frame: a temporary increase of ATF4 expression and a fast downregulation back to its preloading level. This study demonstrates that ATF4 may play a critical role in orthodontic alveolar bone remodeling.

[Changes of aspartate aminotransferase and alkaline phosphatase activities in gingival crevicular fluid during rapid palatal expansion].

PURPOSE: This study was designed to examine the changes of aspartate aminotransferase (AST) and alkaline phosphatase(ALP) activities in gingival crevicular fluid (GCF) during rapid palatal expansion, and to explore the relationship between these changes and periodontal tissue remodeling. METHODS: Thirty-eight patients (aged 10.5 to 12.8years) who required opening of the palatal suture as the first stage of their orthodontic treatment were included and studied. The patients were divided into two groups: control group (18 cases) and experimental group (20 cases). GCF samples were collected at 6 observation periods with filter paper strips: before activation, 24 hours and 7 days after activation, 7 days, 14 days, and 28 days in retention. AST and ALP activities were determined by a full automatic biochemical analyzer, and the results were expressed as total AST and ALP activities. The data was analyzed with SAS (r) Proprietary Software Version 9.00 for paired t test and two-sample t test. RESULTS: AST activity was significantly elevated after 24-hour activation in the test group (P<0.05), but after 7-day activation in the control group (P<0.01). Both in the control and experimental group, AST activity remained high until 28-day in retention (P<0.01). AST activity in the test group was significantly greater compared to the control group from 24-hour activation to 28-day in retention (P<0.05). ALP activity increased significantly from 7-day activation to 28-day retention in the control and experimental group (P<0.01), and there was statistically significant difference between the control and the experimental group from 7-day to 28-day in retention (P<0.01). CONCLUSION: Our results suggest that AST and ALP levels in GCF may reflect the tissue remodeling which occurs in the periodontium during rapid palatal expansion to some degree.

[Effects of first premolar extractions on third molar angulations].

OBJECTIVE: To compare the inclinations of third molars of patients treated orthodontically with and without premolar extractions. METHODS: Records of 37 first premolar extraction patients and 32 nonextraction patients were examined. The pretreatment and posttreatment panoramic radiographs were analyzed. The angles were measured between the long axis of the third molar and the occlusal plane and between the long axis of the third molar and the long axis of the second molar. Changes in third molar angulations from pretreatment to posttreatment for two groups were compared by Mann-Whitney U-test. RESULTS: There were statistically significant difference between the extraction and nonextraction groups in the median angle formed by the long axis of third molar angulation relative to the occlusal plane (P<0.05) and the second molar (P<0.05) in mandible but not in maxillary. In the extraction group, at the end of the orthodontic treatment, the mandibular third molars showed more uprighting than did the maxillary third molars. CONCLUSION: Orthodontic treatment involving premolar extractions improves mandibular third molar angulations.

[Study of facial soft tissue profile on angle Class II malocclusion with various vertical growth patterns].

PURPOSE: To investigate the difference of the facial soft tissue profile on Angle Class II malocclusion with various vertical growth pattern. METHODS: The samples (n = 84) were divided into three groups (low-angle, medial-angle, high-angle group) based on their SN-MP angle. Their cephalograms were measured and all data were analyzed by SPSS12.0 software. RESULTS: There were some regular changes in most facial profile variables while the mandibular plane angle increased: the facial profile convexity and the upper- and lower-lip convexity increased significantly; the depth of anterior lower face decreased from too large to small; the radian of upper- and lower- lip curve changed from too winding to upright. CONCLUSION: Vertical growth patterns make significant differences to soft tissue facial profile on Angle Class II malocclusion.

[Study of the incisive alveolar structure in different vertical facial types between osteal Class III malocclusion and normal occlusion].

PURPOSE: To investigate the relationship of the incisive alveolar structure and vertical facial type between osteal Class III malocclusion and normal occlusion. METHODS: Forty-seven lateral cephalometrics of patients with osteal Class III malocclusion and forty-three lateral cephalometrics of controls with normal occlusion were randomly selected before treatment. Then the incisive alveolar structure was measured and analyzed, the results were analyzed with Student's t test. RESULTS: (1) In osteal Class III malocclusion; the UP value in the group of high mandibular angle decreased significantly than that in the groups of middle and low mandibular angle (P<0.05); the LA and MxAD value in the group of high mandibular angle decreased significantly than that in the group of middle mandibular angle (P<0.05). (2) In normal occlusion, the MdAD and LA value in the group of high mandibular angle decreased significantly than that in the groups of middle and low mandibular angle(P<0.05). (3) In patients with the same mandibular angle,the LA and MdAD value in normal occlusion increased significantly than those in osteal Class III malocclusion (P<0.05);the UP value, in normal occlusion increased significantly than osteal Class III malocclusion within the groups of middle and low mandibular angle (P<0.01). CONCLUSIONS: The incisive alveolar structure was different in different vertical facial type and the same vertical facial types between osteal Class III malocclusion and normal occlusion.