Tadamasa Iwasawa

INHIBITION OF PROSTAGLANDIN E2 AND INTERLEUKIN 1-BETA PRODUCTION BY LOW POWER LASER IRRADIATION IN STRETCHED HUMAN PERIODONTAL LIGAMENT CELLS

It is well-known that orthodontic treatment usually causes some discomfort and pain to the patients. Recently, it has been reported that low-power laser irradiation is effective in reducing the pain accompanying tooth movement. However, the mechanism of such pain relief cannot be elucidated. Since high levels of prostaglandin (PG) E2 and interleukin (IL)-1β are found in the periodontal ligament (PDL) during tooth movement, and both factors are involved in the induction of pain, the effects of low-power laser irradiation on PGE2 and IL-1β production in stretched human PDL cells were studied in vitro. The PDL cells, derived from healthy premolars extracted for orthodontic treatment, were utilized for experiments. Cells were seeded in flexible-bottomed culture plates, and the bottom of each plate was elongated (18% increase) under vacuum at 6 cycles per min for 1, 3, or 5 days. The stretched cells were irradiated with a Ga-Al-As low-power diode laser (60 mW) once a day for 3, 6, or 10 min (from 10.8 to 36.0 J) for 1, 3, or 5 days. PGE2 and IL-1β levels in the medium were measured by radioimmunoassay. In response to mechanical stretching, human PDL cells showed a marked elevation in PGE2 production in a time-dependent manner. IL-1β production was also elevated, but this remained constant. The increase in PGE2 production was significantly inhibited by laser irradiation in a dose-dependent manner. The increase in IL-1β production was also significantly inhibited by laser irradiation, although the inhibition was only partial. Its inhibitory effects on PGE2 and IL-1β production suggest that laser irradiation may have great therapeutic benefits in bringing about relief of the pain that accompanies orthodontic treatment.

Effect of different magnitudes of tension force on prostaglandin E2 production by human periodontal ligament cells

Periodontal ligament (PDL) cells are known to produce prostaglandin E2 (PGE2) in response to mechanical stress. However, the rate of PGE2 production from PDL cells in response to different magnitudes of tension forces has not been examined. This study, therefore, was undertaken to determine the effect of different magnitudes of tension forces on PGE2 production and inositol trisphosphate (IP3) levels in PDL cells in vitro. Human PDL cells were cultured on flexible-bottomed plates and placed on a Flexercell strain unit. Cells were flexed at six cycles (5-s strain, 5-s relaxation) at six steps of tension force (9, 12, 15, 18, 21, 24% increase in surface area) for 5 days. PGE2 production and IP3 levels were determined by radioimmunoassay. There was a 6- and 25-fold increase in the rate of PGE2 production by cells exposed to low (9%) and high (24%) tension forces, respectively, and these increases were tension force-dependent. Tension force also induced increases in the intracellular levels of IP3 that did not seem to be directly related to the production of PGE2. The different rates of PGE2 production by PDL cells in response to different magnitudes of mechanical stress may be of importance in PDL and alveolar bone metabolism.

Stimulatory effects of low-power laser irradiation on bone formation in vitro

The effect of low-power laser irradiation on bone formation in vitro were assessed. Osteoblast-like cells were isolated from rat calvariae of 21d rat fetuses. The cultured calvarial cells were irradiated with a low-power laser (830 nm, 60 mW) one time only or once daily for 21d at various energy doses (10.8-108 J/day). The number and the total area of mineralized bone modules that had developed in the culture dish on day 21 were evaluated. DNA content, alkaline phosphatase (ALP) activity and the amount of extra-cellular collagen were also measured. Calcium and phosphorus in bone nodules were examined with an X-ray microanalyzer. Laser irradiation significantly increased the number and the total area of bone nodules in a dose-dependent manner. Cell proliferation and ALP activity in the irradiation group were higher in the early and middle culture periods, while the collagen content was higher in the middle an late periods compared with the control. Calcium and phosphorus were both higher in the irradiation group. These findings indicate that laser irradiation may play a principal role in stimulating differentiation of osteoblasts during the early stage of the culture, resulting in increased bone formation through acceleration of bone nodule maturation.

Stimulation by interleukin-1 of interleukin-6 production by human periodontal ligament cells

Interleukin-1(IL-1), a cytokine present in the gingiva and crevicular fluid of patients with periodontitis and in the periodontal ligament (PDL) of experimentally moved teeth, has multiple biological activities, including the ability to elicit bone resorption. Interleukin-6, also found in the gingiva of patients with periodontitis, may induce osteoclastic bone resorption through an effect on osteoclastogenesis. Here IL-6 production and its gene expression in response to recombinant IL-1 beta were examined in primary cultures of PDL cells. IL-1 beta stimulated IL-6 production by these cells in a dose- and time-dependent manner; this increase in IL-6 production was much higher than that in human gingival fibroblasts. In situ hybridization, using a synthetic oligonucleotide DNA probe of the IL-6 gene, revealed that most PDL cells expressed IL-6 mRNA in response to IL-1 beta treatment. The finding that IL-6 is produced by PDL cells and is regulated by IL-1 beta has revealed a potentially important mechanism for controlling alveolar bone resorption.

Relationship Between Attachment of the Superficial Masseter Muscle and Craniofacial Morphology in Dentate and Edentulous Humans

Previous studies have described the importance of the interaction between the masticatory muscles and the craniofacial skeleton in the control of craniofacial growth. This study describes the attachment and orientation of the superficial masseter muscle and its relationship -with craniof acial morphology in dentate and edentulous subjects. Data were obtained from lateral cephalometric radiographs of a total of 31 cadavers in which the superficial masseter muscle had been defined with liquid barium. The results provide evidence that the morphology of the superficial masseter muscle in the gonion region differed significantly between dentate and edentulous subjects, with the masseter being 2.7 mm wider and the gonion-anterior muscle border distance being 4.0 mm greater in dentate subjects. The complex relationship between craniofacial morphology and the dimensions and inclination of the superficial masseter muscle were most clearly evident in dentate subjects where the position of the anterior border was related to ramus dimensions and mandibular and occlusal plane angles. The association is much less clear in edentulous subjects where normal function was disturbed. In general, age was not a significant determinant of variation in superficial masseter muscle dimensions and orientation.

Tweed triangle and soft-tissue consideration of Japanese with normal occlusion and good facial profile

A total of thirty-six Japanese adult subjects (consisting of eighteen men and eighteen women) with normal occlusion and harmonious facial features were subjected to cephalographic examination for the purpose of studying their soft tissues. Out of this group, twenty were selected and compared with twenty Class II, Division 1 and twenty Class III patients for the purpose of establishing an appropriate diagnostic guide for the Tweed triangle. These are our conclusions: 1. The Z angle of the Japanese subjects with normal occlusion was 69.70 degrees for the men and 71.75 degrees for the women. There is no significant difference between the sexes. 2. Although there are no significant differences between the sexes for the integumental and total chins, there is slight sexual difference for the upper lip measurement. 3. As compared to the subjects with normal occlusion, there is a significant difference for the Z angle of Class II, Division 1 and Class III patients. 4. In this study, the measurements of the Tweed triangle were FMA 27.28 degrees, IMPA 95.50 degrees, and FMIA 57.22 degrees. On the basis of this study and the reports of other Japanese investigators, we would like to suggest an FMIA of 57 degrees as being the most suitable basis for the diagnosis of Japanese patients, but this should be modified according to the FMA value.

In vitro Cellular Aging Stimulates Interleukin-1β Production in Stretched Human Periodontal-ligament-derived Cells

Although the severity of periodontal disease is known to be affected by host age, the pathological role of aging in periodontal disease, and especially that attributable to trauma from occlusion, has not been well-characterized. Interleukin (IL)-1β is a key mediator involved in periodontal diseases, a potent stimulator of bone resorption. Furthermore, it is produced by human periodontal ligament (PDL) cells in response to mechanical stress. To investigate the age-related changes in the biosynthetic capacity of IL-1β in PDL cells, we examined the effects of in vitro cellular aging with mechanical stress on IL-1β protein and gene expression by human PDL cells. Human PDL cells (young = 5th or 6th passage; old = 18-20th passage) were cultured on flexible-bottomed culture plates, and the cells were deformed at 6 cycles per min at 2 steps of tension force for 1 to 5 days. We found a two-fold increase in IL-lp production by old PDL cells subjected to mechanical tension compared with that by young PDL cells, although the constitutive levels of IL-1β were similar in both the young and old PDL cells. This increase was tension-dependent. IL-1β mRNA was also detected in both the cell types under basal conditions, and its expression was further enhanced by application of mechanical tension by use of reverse-transcription-polymerase chain-reaction (RT-PCR) and in situ hybridization methods. The increase in signal rate was higher in the old cells than in the young cells. IL-1β-converting enzyme mRNA remained unchanged. It is possible that a large amount of IL-1β produced by PDL cells from an aged host in response to mechanical force may be positively related to the accleration of alveolar bone resorption.

Prospect of relieving pain due to tooth movement during orthodontic treatment utilizing a Ga-Al-As diode laser

The effects of low-power laser irradiation on prostaglandin (PG)E2 and interleukin(IL)-1(beta) production in stretched human periodontal ligament (PDL) cells were assessed in vitro. PDL cells derived from healthy premolars were utilized for these experiments. Cells were seeded in flexible-bottom culture plates and elongated (18% increase) under a vacuum at 6 cycles per minute for 1 to 5 days. The stretched cells were irradiated with a Ga-Al-As low-power diode laser (60 mW) once a day for 3 to 10 minutes for 1 to 5 days. PGE2 and IL-1(beta) levels in the medium were measured by radio immunoassay. Human PDL cells showed a marked elevation in PGE2 and IL-1(beta) production in response to mechanical stretching. The increase in PGE2 production was significantly inhibited by laser irradiation in a dose-dependent manner. The increase in IL-1(beta) production was also inhibited by laser irradiation, although the inhibition was only partial under this irradiation condition. Since high levels of PGE2 and IL-1(beta) are found in the PDL when teeth are moved during orthodontic treatment and since both factors are involved with the induction of pain, the inhibitory effects of laser irradiation on PGE2 and IL-1(beta) production suggest that laser irradiation may have therapeutic benefits in relieving the pain that accompanies orthodontic treatment.