PubMed · 11678014
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2001. [Friction].. https://pubmed.ncbi.nlm.nih.gov/11678014/
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Intracellular signals generated by mechanical strain profoundly affect the metabolic function of osteoblast-like periodontal ligament (PDL) cells, which reside between the tooth and alveolar bone. In response to applied mechanical forces, PDL cells synthesize bone-resorptive cytokines to induce bone resorption at sites exposed to compressive forces and deposit bone at sites exposed to tensile forces in an environment primed for catabolic processes. The intracellular mechanisms that regulate this bone remodeling remain unclear. Here, in an in vitro model system, we show that tensile strain is a critical determinant of PDL-cell metabolic functions. Equibiaxial tensile strain (TENS), when applied at low magnitudes, acts as a potent antagonist of interleukin (IL)-1beta actions and suppresses transcriptional regulation of multiple proinflammatory genes. This is evidenced by the fact that TENS at low magnitude: (i) inhibits recombinant human (rh)IL-1beta-dependent induction of cyclooxygenase-2 (COX-2) mRNA expression and production of prostaglandin estradiol (PGE2); (ii) inhibits rhIL-1beta-dependent induction matrix metalloproteinase-1 (MMP-1) and MMP-3 synthesis by suppressing their mRNA expression; (iii) abrogates rhIL-1beta-induced suppression of tissue inhibitor of metalloprotease-II (TIMP-II) expression; and (iv) reverses IL-1beta-dependent suppression of osteocalcin and alkaline phosphatase synthesis. Nevertheless, these actions of TENS were observed only in the presence of IL-1beta, as TENS alone failed to affect any of the aforementioned responses. The present findings are the first to show that intracellular signals generated by low-magnitude mechanical strain interfere with one or more critical step(s) in the signal transduction cascade of rhIL-1beta upstream of mRNA expression, while concurrently promoting the expression of osteogenic proteins in PDL cells.
Resistance to sliding was investigated for 3 self-ligating brackets having passive slides and 3 self-ligating brackets having active clips. Four of these products are currently marketed, and 2 are of historic interest. For all cases, an 0.018 x 0.025-in stainless steel archwire was drawn through each bracket at a rate of 10 mm/min over a distance of 2.5 mm. For each bracket, the resistances to sliding were measured at 14 second-order angulations, which ranged from -9 degrees to +9 degrees. Both the dry and the wet (human saliva) states were evaluated at 34 degrees C. From dimensional measurements, the critical contact angles for binding were determined for all products and ranged from 3 degrees to 5 degrees. Below each characteristic critical angle, brackets with passive slides exhibited negligible friction; brackets with active clips exhibited frictional forces as great as 50 cN (50 g). Above each critical angle, all brackets had elastic binding forces that increased at similar rates as angulation increased and were independent of bracket design. Generally speaking, at second-order angulations that exceeded the critical angle, brackets with active clips that had a low critical angle had more resistance to sliding than did brackets with active clips that had a higher critical angle. Brackets with passive slides that had a high critical angle exhibited the lowest resistance to sliding, but could do so at a cost of some loss of control. Nonetheless, self-ligating brackets represent a compromise between friction and control; ie, self-ligating brackets produce frictional forces that are more reproducible than do conventionally ligated stainless steel brackets but without the potential control problems associated with Begg-style brackets.
The sliding mechanics of multistranded stainless steel (SS) wires were compared with single-stranded leveling wires in the passive and the active regions when dominated by classical friction and elastic binding, respectively. Tests were done under both dry and wet (human saliva) conditions. The round multistranded wires had 3- (triple) and 6-stranded (coax) configurations in nominal sizes of 15.5, 17.5, 19.5, and 21.5 mil; the rectangular wires had 3- (rect3) and 8-stranded (rect8) configurations in nominal sizes of 16 x 16, 16 x 22, 17 x 25, and 19 x 25 mil. While a ligature force of 150 g was applied and the second-order angulation was varied from -12 degrees to 12 degrees, each wire was translated relative to its bracket as the drawing force was digitally recorded. Linear regressions were fitted separately to the passive and the active regions. In the passive region, the kinetic coefficients of friction mu(k-FR) in the wet state were the same as, lower than, and higher than in the dry state for single-stranded SS, single-stranded nickel titanium (NiTi), and multistranded SS wires, respectively. Because the kinetic coefficients of friction were similar for multistranded and single-stranded SS wires, mu(k-FR) is a material property for SS and perhaps also for NiTi. In the active region, the frictional behaviors of multistranded SS wires compared with other leveling archwires are as follows: (1) coax wires had low friction, (2) triple and rect8 wires had midrange friction, and (3) rect3 wires had high friction. The coefficients of binding (mu(BI)) were not affected by saliva and were proportional to the wire stiffnesses. The resistance to sliding depended on wire stiffnesses to the extent that the differences in the mu(k-FR)'s of SS versus NiTi became unimportant shortly after binding occurred.