This study sought to elucidate the function of NO during the signal transduction wherein fluid shear stress regulates the proliferation and differentiation of osteoblast cells. The isolated rat osteoblast-like cells were exposed to fluid shear stress 12 dyn/cm2 for 5, 10, 15, 30, 60 and 120 min respectively with the use of a flow chamber. The NO release was examined. After the exposure to fluid shear stress, the NO synthesis of rat primary osteoblast-like cells increased significantly (P<0.05) when compared with the control. After 60 minutes of exposure, the release of NO began to increase significantly (P<0.05), but no significant increase as such was seen in the control (P>0.05). NO synthesis may be one of the signal transduction pathways which transduce the fluid shear stress into osteoblast cells. In early stage, it may be induced by cNOS and in late stage by iNOS.
Animals ; Cell Differentiation ; Cell Proliferation ; Cells, Cultured ; Nitric Oxide ; biosynthesis ; Nitric Oxide Synthase ; metabolism ; Osteoblasts ; cytology ; metabolism ; Rats ; Shear Strength ; Signal Transduction ; Stress, Mechanical

OBJECTIVEThe purpose of this study was to evaluate the maximum binding(Bmax) and affinity(Kd value) changes of acetylcholine receptor (n-AchR) in rat lateral pterygoid muscles after functional mandibule advancement.

METHODS40 five-weeks-old male Sprague-Dawley rats were equally divided into experimental and control group. The mimic functional appliances were used in experiment group and the rats were killed after 1, 3, 7, 14 days. Radio-ligand binding assay (RBA) was applied to determine the maximum binding(Bmax) and Kd value of n-AchR of lateral pterygoid muscle.

RESULTSThe Bmax of n-AchR in experimental group was higher than that in control group and the Kd value always kept in high level.

CONCLUSIONThe functional orthopedics can increase the Bmax of n-AchR in rapid growing rat lateral pterygoid muscles.

Animals ; Binding Sites ; Cell Membrane ; metabolism ; Male ; Mandibular Advancement ; Orthodontic Appliances, Functional ; Pterygoid Muscles ; metabolism ; Random Allocation ; Rats ; Rats, Sprague-Dawley ; Receptors, Cholinergic ; metabolism

OBJECTIVEThe purpose of this study was to compare the data of three-dimensional soft tissue obtained by using a three-dimensional digital photogrammetry and the two-dimensional data obtained by using a conventional cephalometry.

METHODSThree-dimensional characters of facial soft tissue were obtained by using four digital cameras. The authors developed necessary hardware and software systems and applied in stereophotogrammetry to obtain the data of three-dimensional facial soft tissues. A total of 40 people with normal occlusion, including 20 males and 20 females, were examined with both three-dimensional soft tissue facial morphometry and cephalometry. Three-dimensional soft tissue facial morphometry was performed, and their relations with facial cephalometry were analyzed.

RESULTSSignificant correlations were found between 6 pairs of linear measurements, 4 pairs of angular measurements and 3 pairs of linear distant ratio measurements. The data obtained by three-dimensional facial soft tissue morphometry and two-dimensional cephalometry was identical.

CONCLUSIONThere was a correlation between the three-dimensional soft tissue facial morphometry and facial cephalometry. The data obtained by the three-dimensional soft tissue facial morphometry can partially represent facial hard tissue.

Adult ; Cephalometry ; Face ; anatomy & histology ; Female ; Humans ; Image Processing, Computer-Assisted ; Imaging, Three-Dimensional ; Male ; Photogrammetry ; methods ; Radiography ; Reference Values ; Skull ; diagnostic imaging

OBJECTIVEThe purpose of this study was to investigate the physiological process of healing after tooth extraction and the biological reaction of tooth movement into extraction sites with the aim of selecting optimal time of tooth movement into extraction sites clinically.

METHODSExtraction of upper first molars were performed on 30 male Sprague-Dawley rats which were divided equally into 5 groups. Orthodontic appliance was placed at different time after tooth extraction in order to move the maxillary second molars mesially into the extraction spaces. The animals were injected continuously with tetracycline and calcein for two days before appliance activation and animal sacrifice. Undecalcified mesio-distal specimans 65-100 microns of thickness were prepared. The quantification of bone remodeling parameters on tooth movement into extraction sites at different time was performed by histomorphometric measurements and computer image analysis.

RESULTS1. The bone turnover had two bone modeling processes: resorption under pressure and formation in tension. 2. The bone resorption was more active on the mesial surface (pressure side) than that on the distal surface (tension side). While bone formation was more active on the distal surface (tension side) than that on the mesial surface (pressure side). 3. Both the resorptive parameters and the formative parameters across time were manifested by a peak at day 7 after tooth extraction.

CONCLUSION1. Orthodontic retraction into extraction sites should be initiated at an early stage after tooth extraction, so that the advantage of bone remodeling in extraction sites was used. 2. The optimal time of tooth movement into extraction sites clinically was about a week after tooth extraction.

Animals ; Bone Remodeling ; Dental Bonding ; Male ; Molar ; Orthodontic Appliances ; Random Allocation ; Rats ; Rats, Sprague-Dawley ; Root Resorption ; Time Factors ; Tooth Extraction ; Tooth Movement Techniques

OBJECTIVETo investigate the influence of bone remodeling in extraction sites and orthodontic forces on tooth movement with the aim of providing a basis for selecting optimal orthodontic forces, time of tooth movement and reducing the time for tooth moving into extraction sites.

METHODSExtraction of upper first molars were performed on 36 male Sprague-Dawley rats which were divided equally into 3 groups. A method for quantification of orthodontic tooth movement in the rats was presented. Orthodontic appliance was placed at different time after tooth extraction. Different forces were used to move the maxillary second molars mesially into the extraction spaces. X-ray was taken before appliance activation and after 1, 3, 5, 7, 10, 14 days since appliance activation. Tooth movement was measured cephalometrically by Imagine Analysis Technique, adjusting for magnification by using the known digitized length of the broach.

RESULTS1. The tooth on the recent extraction side moved faster than that on the healed side. 2. Tooth movement at all time points on the 0.30 N curve differed from those on the higher force curves (P < 0.01), either moving into recent extraction sites or healing sites. Comparison between 0.60 N and 1.36 N indicated that mesial molar movement did not differ from each other after day 5. 3. The classical tooth movement curve had three parts that represent distinctly different processes: early movement; delay; later movement.

CONCLUSION1. The tooth on the recent extraction side moved faster than that on the healed side. 2. Moderate force maybe was the optimal orthodontic force. It could be overloaded, but resulted in no further enhancement of tooth movement.

Animals ; Bone Remodeling ; Male ; Molar ; physiology ; surgery ; Orthodontic Appliances ; Random Allocation ; Rats ; Rats, Sprague-Dawley ; Tooth Extraction ; Tooth Movement Techniques

OBJECTIVEThe aim of this study was to investigate the effect of short enamel etching time on bonding strength.

METHODS80 healthy premolars were randomly divided into two equal groups, one was etched for 15 seconds, the other for 60 seconds, after normally bonding Edgewise brackets, the tooth specimen was stored in water at room temperature for 24 hours. An MTS NEW810 100KN testing machine was used to examine the shear force.

RESULTSAlthough the bonding strength for 15 seconds etching time was weaker than that for 60 seconds, the means of the bonding strength in 15 seconds group reached 5.8625 MPa.

CONCLUSIONEtching for 15 seconds could provide enough bond strength for orthodontic practice. Furthermore, the adhesive remained on tooth after debonding was less by comparison with 60 seconds etching group, therefore brackets could be removed easily and the work efficiency could be increased in clinic by means of 15 seconds etching time.

Acid Etching, Dental ; methods ; Dental Bonding ; Dental Debonding ; Dental Enamel ; injuries ; ultrastructure ; Humans ; Orthodontic Brackets ; Orthodontics, Corrective ; Stress, Mechanical ; Surface Properties ; Tensile Strength ; Time Factors

OBJECTIVEThe purpose of this study was to investigate effects of static tension-stress and TGF-beta 1 on proliferation of mandibular condylar chondrocytes in vitro.

METHODSThe fourth-passage chondrocytes were harvested from the mandibular condyles of 2-week-old SD rats for this study, and a cellular static tension-stress device was used to apply stress on cells. The effects of continuous static tension-stress and/or transforming growth factor-beta 1 (TGF-beta 1) on the proliferation of mandibular condylar chondrocytes were examined using flow cytometry. The experiment was divided into two parts. The first part consisted of 100 specimens which were divided into 20 groups with different TGF-beta 1 dosage (0 ng/ml, 0.1 ng/ml, 1 ng/ml and 10 ng/ml) for 0, 6, 12, 18 and 24 hours respectively. The second part consisted of 30 specimens which were divided into six groups under continuous static tension-stress (5 kPa) and different TGF-beta 1 dosage (0.1 ng/ml, 1 ng/ml, 10 ng/ml) for 0, 6 and 12 hours. Multivariable analyses were conducted to test for associations between proliferation of mandibular condylar chondrocytes and TGF-beta 1 and/or different stresses.

RESULTSThe results showed that TGF-beta 1 had a mitogenic effect on rat mandibular condyle at the concentrations of 0.1, 1 and 10 ng/ml, and the mitogenic effects of TGF-beta 1 on condylar chondrocytes were demonstrated in 12 to 18 hours after application of stresses, and the peak of mitogenic effects appeared at 18 hour (P < 0.05). The most active mitogenesis happened in the group with continuous static tension-stress (5 kPa) combined with TGF-beta 1.

CONCLUSIONThese results prove mechanical stimulates and TGF-beta 1 in vitro could influence and regulate the growth of condylar chondrocytes.

Animals ; Cartilage, Articular ; cytology ; Cell Division ; Cells, Cultured ; Chondrocytes ; cytology ; Mandibular Condyle ; cytology ; Orthodontic Appliances, Functional ; Rats ; Rats, Sprague-Dawley ; Stress, Mechanical ; Transforming Growth Factor beta ; pharmacology ; Transforming Growth Factor beta1

OBJECTIVEThe purpose of this study was to investigate the effects of static tension-stress on proliferation of mandibular condylar chondrocytes in rats.

METHODSThe fourth-passage chondrocytes were harvested from the mandibular condyles of 2-week-old SD rats. A continuous static tension-stress was applied on the cells in vitro using a cellular static tension-stress device, and the proliferation of mandibular condylar chondrocytes were examined using a flow cytometry. The other 30 specimens in the control group were divided into six groups to examine the effects of calf serum on cellular static tension-stress without any stress. The experimental group consisted of 70 specimens which were divided into seven groups under continuous static tension-stress (5 kPa, 10 kPa) for 0 to 12 hours. Multivariable analyses were conducted to test the associations between proliferation of condylar chondrocytes and different continuous static tension stresses.

RESULTSThe results showed that the lower calf serum inhibited the proliferation of rat mandibular condylar chondrocytes. There was little effect on the proliferation of chondrocytes under continuous static tension-stress (5 kPa, 10 kPa) for 2 hours. The proliferation of mandibular condylar chondrocytes was promoted as the application time of stress was prolonged (0-10 hours in 5 kPa groups and 0-8 hours in 10 kPa groups). The maximal proliferation appeared, when the condylar chondrocytes were cultured under 5 kPa continuous static tension-stress for 10 hours, and 8 hours under 10 kPa stress (P < 0.05). The proliferation of cells in the 5 kPa group was more obvious than in the 10 kPa group (P < 0.05).

CONCLUSIONThe data prove that mechanical stimulates in vitro can influence and regulate the growth of condylar chondrocytes. It provides experimental evidence for advanced study on cellular mechanical research in functional orthopedics.

Animals ; Animals, Newborn ; Cartilage, Articular ; cytology ; Cell Division ; Cells, Cultured ; Chondrocytes ; cytology ; Mandibular Condyle ; cytology ; Orthodontic Appliances, Functional ; Rats ; Rats, Sprague-Dawley ; Stress, Mechanical

OBJECTIVETo establish an experimental model which was the masticatory myocyte culture and force stimulation in vitro and study the proliferation changes of cultured masticatory myocytes caused by mechanical compression in young rat.

METHODSFlow cytometry (FCM) was used to examine the changes of cellular DNA content and cell cycles of cultured masticatory myocytes.

RESULTSThe DNA content in experimental groups was higher than that in control. After the compressive force was applied for 2 hours, the proliferation index (PI) in experimental group became higher than that in control. Under a continuous pressure for 4 hours, the PI in 2,000 mu strain group reached the maximum (48.9%) but the PI in 4,000 mu strain group reached the minimum (39.0%).

CONCLUSIONThe proliferation of masticatory myocytes from young rat increased under certain force and certain period of time, but decreased if the force applied was overloaded.

Animals ; Cell Division ; Cells, Cultured ; DNA ; analysis ; Dental Stress Analysis ; Flow Cytometry ; Masticatory Muscles ; cytology ; physiology ; Muscle Cells ; cytology ; physiology ; Rats ; Rats, Sprague-Dawley ; Stress, Mechanical

OBJECTIVEThe aim of this study was to establish the average of superfacial masseter muscle of young females with normal occlusion, and further supply a clue for dentists to evaluate the muscle function of patients with malocclusion.

METHODSTotally 31 young females were investigated in this study, whose mean age was 21 years and 4 months old. Ultrasound technique was applied to obtain the ultrasound parameters of images, including area, width, mean thickness, maximal thickness of the cross-section and the length of the vertical-section of the masseter muscle under relaxing, maximal clenching and maximal protruding condition. The data were analyzed using ANOVA analysis.

RESULTSThe mean value and standard deviation of every parameter were figured out and it was found that there was a significant difference between relaxing and maximal clenching as well as maximal protruding.

CONCLUSIONThe result indicates that ultrasonic technique is an effective method for describing superfacial masseter muscle morphology and diagnosing its function.

Adult ; Dental Occlusion ; Female ; Humans ; Mandible ; physiology ; Masseter Muscle ; anatomy & histology ; diagnostic imaging ; Muscle Contraction ; Muscle Relaxation ; Ultrasonography