P. Ngan

Perception of discomfort by patients undergoing orthodontic treatment

The purpose of this study was to determine the perception of discomfort over time by a group of 70 patients undergoing orthodontic treatment. Patients who were selected for comprehensive orthodontic treatment completed questionnaires before insertion of separators and initial arch wires and after placement at 4 hours, 24 hours, and 7 days. The level of discomfort during these time periods was assessed by a visual analogue scale. The results showed a significant increase in the level of discomfort after insertion of either separators or arch wires at 4 hours and 24 hours, but not at 7 days. No significant difference was found in the level of discomfort of patients more than 16 years of age compared with those 16 years and under. No significant difference in discomfort was found between the sexes. These results are useful in relating expectations of discomfort to patients who undergo orthodontic treatment.

Longitudinal evaluation of growth changesin class II division 1 subjects

Longitudinal records from the Ohio State University Growth Study were used to compare the skeletal growth changes between Class II division 1 and Class I female subjects between ages 7 and 14. Tensor analysis was used to determine the yearly growth rate and direction. No significant difference was found in cranial base dimension between the Class I and Class II subjects. In Class II subjects, the maxilla (S-N-A) was found to be normally related to the cranial base. However, mandibular position (S-N-B and S-N-Pog) was found to be significantly more retrusive in Class II when compared with Class I subjects. Mandibular length (Ar-Gn) and corpus length (Go-Gn) were found to be shorter in Class II subjects. The ratio of PFH to AFH was found to be smaller in Class II subjects. This is particularly apparent during the pubertal growth period. The y-axis and mandibular plane angle were more open in Class II subjects which also contributed to the retrusive position of the mandible. Maxillo-mandibular difference (A-N-B) between Class I and II subjects was present at age 7 and persisted through puberty, maintaining a greater angle of convexity (A-N-Pg) in Class II subjects. These results suggest that Class II malocclusion can be detected early. The majority of the Class II cases showed mandibular skeletal retrusion or a combination of horizontal and vertical abnormalities of the mandible rather than maxillary protrusion. These skeletal differences remain through puberty without orthodontic intervention. Individual variations were found within each type of malocclusion.

Involvement of PGE Synthesis in the Effect of Intermittent Pressure and Interleukin-1β on Bone Resorption

Human periodontal ligament (PDL) fibroblasts, cultured from extracted healthy premolars, and a cloned osteogenic cell line (MC3T3-E1) were used in this study to determine the effect of intermittent pressure on bone resorption. Cells (1 x 105) were incubated with BGJb medium in the presence or absence of the following factors: intermittent negative ( - 30 g/cm2) or positive (30 g/cm2) hydrostatic pressure and interleukin-lp (IL-1β, 1 ng/mL), for 24 h. Conditioned media (CM) generated from cultures of either cell types were used for prostaglandin E (PGE) assay, bone resorption assay, and assessment of osteoclast (OC)-like cell formation. Unstimulated PDL fibroblasts or MC3T3-E1 cells produced measurable amounts of PGE and bone-resorbing activity as measured by 45Ca released from mouse calvaria and OC-like cells. IL-1β-treated cells showed significantly elevated levels of PGE, bone resorption, and OC-like cell formation, as compared with unstimulated cells. Intermittent positive pressure (IPP) alone stimulated PGE production, but the resultant CM did not stimulate bone resorption or OC-like cell formation when IPP was applied to either cell type. The application of IPP, together with IL-1β in CM, caused a slight increase in the number of a-like cells, as compared with that of IL-1β-treated CM in both cell types. On the other hand, direct application of IPP on mouse bone-marrow cultures significantly increased the number of OC-like cells. This effect was additive in combination with either CM from unstimulated cells or exogenous addition of PGE2. These results suggest that locally produced autocrines or paracrines can modify the effect of mechanical stress on periodontal and bone cells via PGE synthesis. One of the roles of PGE elaboration in response to mechanical or chemical stimuli is osteoclast recruitment.

Immunohistochemical assessment of the effect of chemical and mechanical stimuli on cAMP and prostaglandin E levels in human gingival fibroblasts in vitro

These were evaluated by: (1) a combined immunohistochemical-microphotometric procedure (IH) and (2) conventional radiometric assays. Human gingival fibroblasts were in the sixth passage, grown and maintained in Dulbecco minimal essential medium (DMEM) supplemented with 10 per cent horse serum. For chemical and hormonal stimuli, cells (2 x 10(4] were seeded on tissue-culture chamber/slides, and incubated with graded doses of either parathyroid hormone (PTH) or prostaglandin E2 (PGE2) for assessment of their adenosine-3,5-monophosphate (cAMP) levels, and with indomethacin or colchicine for their effect on PGE levels. For mechanical stimuli, cells (1 x 10(6] were seeded on culture dishes with a flexible plastic membrane and stretched for 5, 30, 60 or 120 min by placing the membrane over a convex surface and weighting the dish cover. After freeze drying, cells were stained by an immunoperoxidase technique for either cAMP or PGE, using monoclonal antibodies. The staining intensity of fibroblasts was determined at 600 nm wavelength. Per cent light absorbance of 15 cells in each slide was measured and the results tested by analysis of variance. The gingival fibroblasts responded to the drugs and hormones in a dose- and time-related fashion. Stretching significantly increased their synthesis of PGE with concomitant increase in cAMP. The IH results were compared with the radiometric assays to confirm the validity of this technique; both assays were valid for describing the quantitative responses of these cells to the stimuli. In particular, the IH method could localize those intracellular sites which demonstrated chances in relative cAMP and PGE concentrations in response to hormonal stimuli.

The interactive effects of mechanical stress and interleukin-1β on prostaglandin E and cyclic AMP production in human periodontal ligament fibroblasts in vitro: Comparison with cloned osteoblastic cells of mouse (MC3T3-E1)

Human periodontal ligament fibroblasts and a cloned osteogenic cell line (MC3T3-E1) were seeded (4 x 10(5) cells) on 60 mm Petriperm dishes, which have a flexible plastic growth surface. Cells were stretched by placing the dish on top of a spheroidal convex template, equilibrated to 37 degrees C. The amount of stretch was varied by changing the curvature of the template and calculated as percentage stretch. Both types of cell responded to mechanical stress by elevated synthesis of PGE and cAMP; the addition of interleukin-1 beta to mechanically stretched cells produced further elevation. Synergism between mechanical stress and interleukin-1 beta was found at certain lengths of incubation. The production of cAMP was secondary and dependent on the newly synthesized PGE, as shown in the presence of indomethacin. The two cell types were also different in terms of the timing of their response to mechanical stress and interleukin-1 beta. In the absence of stimuli, periodontal fibroblasts tended to produce PGE continually over time, whereas the MC3T3-E1 cells did not. However, both cell types had elevated PGE levels in response to the stimuli used in this experiment. Periodontal fibroblasts responded to mechanical stress and interleukin-1 beta with significant elevations of PGE as early as 15 min, whereas the MC3T3-E1 cells required 2 h to produce significant elevations for mechanical stress and 15 min for interleukin-1 beta. These findings indicate that the chemical and mechanical signals on these cells are mediated by surface receptors. Locally produced autocrine or paracrine factors can modify the effect of mechanical stress on periodontal and bone cells via the cAMP pathway.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of cytokines on prostaglandin E and cAMP levels in human periodontal ligament fibroblasts in vitro

The stimulation of PGE synthesis and cAMP production by cytokines have important physiological effects in many target tissues. The effects of interleukin-1 alpha and -1 beta, tumour necrosis factor-alpha and interferon-gamma on PGE and cAMP production by periodontal ligament fibroblasts were studied. Fibroblasts in the 4th-6th passage, grown and maintained in DMEM supplemented with 10% equine serum, were incubated with graded doses of the various cytokines for 0.25, 0.5, 1.2, 4, 24, 48 or 72 h. At the end of each incubation, PGE in the medium and the cellular content of cAMP were evaluated by a combined immunohistochemical microphotometric procedure, and conventional radiometric assays. The fibroblasts responded to all the cytokines with a dose- and time-related increase in the levels of PGE and cAMP. Such increases were inhibited by the inclusion of indomethacin in the medium. The addition of exogenous PGE reversed that inhibition in respect of cAMP production. Immunohistochemical localization showed PGE predominantly in the cytoplasm and cAMP in the nucleus. These findings indicate that: (1) human periodontal ligament fibroblasts respond to these cytokines by increased synthesis of PGE and the production of cAMP; and (2) the cAMP production is secondary to the PGE synthesis. They suggest that these cytokines may regulate the function of these fibroblasts in physiological remodelling of the periodontium, as well as in inflammatory reactions.

Interactive Effects Between Cytokines on PGE Production by Human Periodontal Ligament Fibroblasts in vitro

Mononuclear cell production of cytokines that stimulate fibroblast production of prostaglandin E (PGE) is an important mechanism by which mononuclear cells regulate fibroblast function. The objective of this investigation was to determine the effects of the cytokines interleukin 1β (IL-1β), interleukin la (IL-1α), tumor necrosis factor a (TNF-a), and interferon γ (IFN--y), alone or in paired combinations, on PGE production by near-confluent human periodontal ligament (PDL) fibroblasts in vitro. Premolars extracted in the course of orthodontic treatment were used for this study. Fibroblast cultures, free of epithelial cells, were obtained after the fourth subculture by the use of accurately-timed trypsin treatment. Cells in the fourth to sixth passage, incubated in DMEM supplemented with 10% equine serum, were used for these experiments. Cells (1 x 105) were seeded in 12- x -75-mm tissue culture tubes and incubated with various doses of IL-1β, IL-la, TNF-a, and IFN-γ, alone or in specific combinations, for 15 min, two, 12, 24, and 72 h. PGE concentrations in the media were measured by radio-immunoassay. The results showed that human PDL fibroblasts responded to the administration of cytokines by an elevation in the synthesis of PGE in a dose- and time-related fashion. The increase in PGE production was inhibited by the addition of indomethacin. The interactions between these cytokines varied in degree, depending on the particular combinations of cytokines. In addition, the administration of cytokine combinations was found to be additive, synergistic, subtractive, or suppressive on the production of PGE by PDL fibroblasts, depending on the duration of incubation. These experiments demonstrate the importance of the consideration of the interplay between cytokines produced by mononuclear cells on the mechanisms that regulate the functions of PDL fibroblasts.

Effects of parathyroid hormone and cytokines on prostaglandin e synthesis and bone resorption by human periodontal ligament fibroblasts

Cultured human periodontal ligament fibroblasts showed synergistic elevations in the synthesis of prostaglandin E and production of cAMP by the administration of parathyroid hormone and cytokines (interleukin 1 alpha, -1 beta, or tumour necrosis factor-alpha). Unstimulated conditioned media derived from these fibroblasts contained bone-resorbing activity. In addition, conditioned media generated by cytokine-or parathyroid hormone-treated fibroblasts showed further increases in bone-resorbing activity. The effects were additive when the hormone was combined with either one of the cytokines in stimulating bone resorption. These findings suggest that the effect of parathyroid hormones and cytokines together on bone resorption can be mediated in part by human periodontal ligament fibroblasts via PGE production and subsequent PGE action on the osteoclasts.