Ryoko Ando

Histomorphometric evaluation of alveolar bone turnover between the maxilla and the mandible during experimental tooth movement in dogs

INTRODUCTION The purpose of this study was to quantify the histomorphometric properties of alveolar bone to identify the characteristics of the changes of quantity and quality of alveolar bone between the maxilla and the mandible during orthodontic tooth movement in dogs. METHODS A force of 200 to 250 g was applied from miniature implants to the premolars for either 4 or 12 weeks. Maxillary and mandibular tooth specimens were embedded and sectioned at 100 microm in the sagittal plane for microscopic examination. RESULTS Significantly more orthodontic tooth movement was observed for maxillary than for mandibular teeth. The primary histomorphometric analysis indicated that, after 4 weeks of tooth movement, a marginal increase in resorptive parameters was associated with a decrease of bone volume at both the tension and compression sites. On the other hand, after 12 weeks of tooth movement, secondary histomorphometric analysis indicated an increase in the bone formation rate, resulting in increased woven bone formation, especially at the tension sites. CONCLUSIONS Clinically, maxillary and mandibular bone responds differently to orthodontic force, resulting in a significant difference in the amounts of tooth movement. Significant differences in the primary and secondary histomorphometric indexes between the jaws and at the different time points during orthodontic tooth movement might affect the amount and rate of tooth movement in orthodontic patients. Moreover, orthodontic tooth movement is characterized by a regional acceleratory phenomenon, manifested as increased bone turnover in the alveolar process.

The alteration of a mechanical property of bone cells during the process of changing from osteoblasts to osteocytes

Osteocytes acquire their stellate shape during the process of changing from osteoblasts in bone. Throughout this process, dynamic cytoskeletal changes occur. In general, changes of the cytoskeleton affect cellular mechanical properties. Mechanical properties of living cells are connected with their biological functions and physiological processes. In this study, we for the first time analyzed elastic modulus, a mechanical property of bone cells. Bone cells in embryonic chick calvariae and in isolated culture were identified using fluorescently labeled phalloidin and OB7.3, a chick osteocyte-specific monoclonal antibody, and then observed by confocal laser scanning microscopy. The elastic modulus of living cells was analyzed with atomic force microscopy. To examine the consequences of focal adhesion formation on the elastic modulus, cells were pretreated with GRGDS and GRGES, and then the elastic modulus of the cells was analyzed. Focal adhesions in the cells were visualized by immunofluorescence of vinculin. From fluorescence images, we could distinguish osteoblasts, osteoid osteocytes and mature osteocytes both in vivo and in vitro. The elastic modulus of peripheral regions of cells in all three populations was significantly higher than in their nuclear regions. The elastic modulus of the peripheral region of osteoblasts was 12053+/-934 Pa, that of osteoid osteocytes was 7971+/-422 Pa and that of mature osteocytes was 4471+/-198 Pa. These results suggest that the level of elastic modulus of bone cells was proportional to the stage of changing from osteoblasts to osteocytes. The focal adhesion area of osteoblasts was significantly higher than that of osteocytes. The focal adhesion area of osteoblasts was decreased after treatment with GRGDS, however, that of osteocytes was not. The elastic modulus of osteoblasts and osteoid osteocytes were decreased after treatment with GRGDS. However, that of mature osteocytes was not changed. There were dynamic changes in the mechanical property of elastic modulus and in focal adhesions of bone cells.

A method for observing silver-stained osteocytes in situ in 3-microm sections using ultra-high voltage electron microscopy tomography.

Osteocytes are surrounded by hard bone matrix, and it has not been possible previously to directly observe the in situ architecture of osteocyte morphology in bone. Electron microscope tomography, however, is a technique that has the unique potential to provide three-dimensional (3D) visualization of cellular ultrastructure. This approach is based on reconstruction of 3D volumes from a tilt series of electron micrographs of cells, and resolution at the nanometer level has been achieved. We applied electron microscope tomography to thick sections of silver-stained osteocytes in bone using a Hitachi H-3000 ultra-high voltage electron microscope equipped with a 360 degrees tilt specimen holder, at an accelerating voltage of 2 MeV. Osteocytes with numerous processes and branches were clearly seen in the serial tilt series acquired from 3-microm-thick sections. Reconstruction of young osteocytes showed the 3D topographic morphology of the cell body and processes at high resolution. This morphological data on osteocytes should provide useful information to those who study osteocyte physiology and the several models used to explain their mechanosensory properties.

Actin and microtubule cytoskeletons of the processes of 3D-cultured MC3T3-E1 cells and osteocytes

Cell shape is the most critical determinant of cell function and is potentially influenced by the organization of a cells cytoskeletal components. It has been reported that three-dimensionally cultured osteoblasts have a morphology that closely resembles that of osteocytes, most notably including formation of processes. We have previously shown the critical differences between cytoskeletal components in osteoblasts and osteocytes in two-dimensional culture. We have now extended that investigation to the cytoskeletal components of 3D-cultured osteoblasts and osteocytes using 3D cultures of the osteoblast cell line, MC3T3-E1, and primary osteocytes grown in collagen gel. Three-dimensional fluorescent image reconstructions for actin, fimbrin, alpha-actinin, myosin, tropomyosin, and microtubules were made using IMARIS software. Actin, fimbrin, alpha-actinin, myosin, and tropomyosin all appeared in the processes of both cell types, but fimbrin and myosin showed differences in their distribution patterns between cell types. Microtubules were limited in distribution to the proximal region of osteocyte processes but extended the entire length of MC3T3-E1 cell processes. Microtubules were essential for the integrity and formation of MC3T3-E1 cell processes, but osteocyte processes were dependent on actin. These results showed that there are significant differences between the actin and microtubule cytoskeletons in the processes of 3D-cultured MC3T3-E1 cells and in the processes of 3D-cultured primary osteocytes. These differences in the cytoskeleton of the processes of 3D-cultured osteoblasts and of osteocyte dendrites suggest that osteoblast processes may have a different functional role than the osteocyte dendritic network.

Clinical Evaluation of a Low-Friction Attachment Device during Canine Retraction

OBJECTIVE The present study used a split-mouth design to compare the amount of canine movement and the retraction time between brackets with Clear Snap and brackets with stainless steel ligature wires for three different levels of retraction force. MATERIALS AND METHODS A sample of 30 patients was used. After initial leveling, the canine was retracted using a 50-g (n = 10), 100-g (n = 10), or 150-g (n = 10) closed-coil spring. The canine on one side was chosen at random, and Clear Snap was attached to the bracket during the retraction period. The other side was used as a control. The amount of canine retraction was measured with a digital vernier caliper. Statistical analysis was performed by analysis of variance. RESULTS The average canine retraction time was approximately 2 to 3 months less in all experimental groups (50, 100, and 150 g) compared to the control group. In the control group, 150 g resulted in a shorter duration of canine retraction compared to 50 g. There was no significant difference in the duration of canine retraction among the experimental groups. A greater amount of mean total canine movement was observed in all experimental groups compared to the control groups. CONCLUSION A shorter duration of canine retraction time was observed with Clear Snap attached when compared with the control. The authors suggest that with the use of Clear Snap, less than 50 g of force may effectively retract a canine.

Increase of Galanin in Trigeminal Ganglion during Tooth Movement

It is known that nerve fibers containing neuropeptides such as galanin increase in the periodontal ligament during experimental tooth movement. However, the origin of galanin-containing nerve fibers in the periodontal ligament remains unclear. This study was conducted to examine our hypothesis that the increased galanin nerve fibers have a sensory neuronal origin, and that the peptide is associated with pain transmission and/or periodontal ligament remodeling during experimental tooth movement. In control rats, galanin-immunoreactive trigeminal ganglion cells were very rare and were observed predominantly in small ganglion cells. After 3 days of experimental tooth movement, galanin-immunoreactive trigeminal ganglion cells significantly increased, and the most marked increase was observed at 5 days after experimental tooth movement. Furthermore, their cell size spectrum also significantly changed after 3 and 5 days of movement: Medium-sized and large trigeminal ganglion cells began expressing, and continued to express, galanin until 14 days after experimental tooth movement. These findings suggest that the increase of galanin in the periodontal ligament during experimental tooth movement at least partially originates from trigeminal ganglion neurons and may play a role in pain transmission and/or periodontal remodeling.

Relationship between orthodontic expertise and perception of treatment needs for maxillary protrusion: comparison of dental students, residents, and orthodontists.

INTRODUCTION The aims of this study were to assess the peer assessment rating (PAR) index in relation to perceived treatment needs for maxillary protrusion in Japanese subjects and to investigate how perceived orthodontic treatment needs change with increased experience in dentistry and orthodontics. METHODS The subjects were 155 persons (73 men, 82 women; mean age, 24.2 years; SD, 4.7 years) including dental students, residents, and orthodontists. We showed them casts from 10 patients with untreated maxillary protrusion and gave them a questionnaire with a 100-point visual analog scale (VAS), concerning their perceptions of orthodontic treatment needs. The PAR index was used for cast evaluation. RESULTS The PAR index showed significant correlations with the VAS scores. On the casts evaluated with a PAR index below 17, there was no difference in VAS scores between the 3 groups; however, orthodontists perceived significantly greater treatment needs than did students and residents on casts with a PAR index of 18 or 19. The VAS scores were significantly increased when casts with a PAR index of more than 20 and overjet above 5.0 mm were evaluated. Orthodontists and residents perceived greater treatment needs than students on assessing occlusions with severe maxillary protrusion. CONCLUSIONS The PAR index is clinically useful to evaluate malocclusion, and the perception of treatment needs was significantly greater when the maxillary protrusion cast had a PAR index of more than 20 and overjet above 5.0 mm. Perceived needs for orthodontic treatment for maxillary protrusion changed with increasing experience and skills in dentistry and orthodontics.

Evaluation of catch-up growth from orthodontic treatment and supplemental growth hormone therapy by using Z-scores.

Pituitary dwarfism causes short stature due to partial or complete inhibition of growth hormone (GH) secretion. Supplemental therapy with human GH (rhGH) accelerates the statural growth of patients, but there is limited information about its effects on craniofacial growth. This study describes the orthodontic treatment of 2 patients (a boy and a girl) diagnosed with pituitary dwarfism and treated with rhGH therapy. Growing children have different growth velocities depending on age and sex, and this complicates the assessment of treatment effects; therefore, we used the Z-score to evaluate changes in stature and craniofacial components. Growth in craniofacial structures and stature were both enhanced by rhGH therapy during orthodontic treatment.

Erratum: Actin and microtubule cytoskeletons of the processes of 3D-cultured MC3T3-E1 cells and osteocytes (Journal of Bone and Mineral Metabolism (2007) 25, (151-158) DOI: 10.1007/s00774-006-0745-5)

Cell shape is the most critical determinant of cell function and is potentially influenced by the organization of a cells cytoskeletal components. It has been reported that three-dimensionally cultured osteoblasts have a morphology that closely resembles that of osteocytes, most notably including formation of processes. We have previously shown the critical differences between cytoskeletal components in osteoblasts and osteocytes in two-dimensional culture. We have now extended that investigation to the cytoskeletal components of 3D-cultured osteoblasts and osteocytes using 3D cultures of the osteoblast cell line, MC3T3-E1, and primary osteocytes grown in collagen gel. Three-dimensional fluorescent image reconstructions for actin, fimbrin, alpha-actinin, myosin, tropomyosin, and microtubules were made using IMARIS software. Actin, fimbrin, alpha-actinin, myosin, and tropomyosin all appeared in the processes of both cell types, but fimbrin and myosin showed differences in their distribution patterns between cell types. Microtubules were limited in distribution to the proximal region of osteocyte processes but extended the entire length of MC3T3-E1 cell processes. Microtubules were essential for the integrity and formation of MC3T3-E1 cell processes, but osteocyte processes were dependent on actin. These results showed that there are significant differences between the actin and microtubule cytoskeletons in the processes of 3D-cultured MC3T3-E1 cells and in the processes of 3D-cultured primary osteocytes. These differences in the cytoskeleton of the processes of 3D-cultured osteoblasts and of osteocyte dendrites suggest that osteoblast processes may have a different functional role than the osteocyte dendritic network.