The role of mechanotransduction versus hypoxia during simulated orthodontic compressive strain——an in vitro study of human periodontal ligament fibroblasts

During orthodontic tooth movement(OTM)mechanical forces trigger pseudo-inflammatory,osteoclastogenic and remodelling processes in the periodontal ligament(PDL)that are mediated by PDL fibroblasts via the expression of various signalling molecules.Thus far,it is unknown whether these processes are mainly induced by mechanical cellular deformation(mechanotransduction)or by concomitant hypoxic conditions via the compression of periodontal blood vessels.Human primary PDL fibroblasts were randomly seeded in conventional six-well cell culture plates with O2-impermeable polystyrene membranes and in special plates with gas-permeable membranes(Lumox?,Sarstedt),enabling the experimental separation of mechanotransducive and hypoxic effects that occur concomitantly during OTM.To simulate physiological orthodontic compressive forces,PDL fibroblasts were stimulated mechanically at 2 g·cm?2 for 48 h after 24 h of pre-incubation.We quantified the cell viability by MTT assay,gene expression by quantitative real-time polymerase chain reaction(RT-qPCR)and protein expression by western blot/enzyme-linked immunosorbent assays(ELISA).In addition,PDL-fibroblast-mediated osteoclastogenesis(TRAP+cells)was measured in a 72-h coculture with RAW264.7 cells.The expression of HIF-1α,COX-2,PGE2,VEGF,COL1A2,collagen and ALPL,and the RANKL/OPG ratios at the mRNA/protein levels during PDL-fibroblast-mediated osteoclastogenesis were significantly elevated by mechanical loading irrespective of the oxygen supply,whereas hypoxic conditions had no significant additional effects.The cellular–molecular mediation of OTM by PDL fibroblasts via the expression of various signalling molecules is expected to be predominantly controlled by the application of force(mechanotransduction),whereas hypoxic effects seem to play only a minor role.In the context of OTM,the hypoxic marker HIF-1αdoes not appear to be primarily stabilized by a reduced O2 supply but is rather stabilised mechanically.

Bonding Orthodontic Ceramic Brackets to Ceramic Restorations:Evaluation of Different Surface Conditioning Methods

The purpose of this study was to compare the shear bond strength and Adhesive Remnant Index of four different veneering ceramic materials to ceramic brackets. Additionallly, a further aim of this study was to overcome the etching using hydrofluoric acid which is noxious and could seriously damage the corneas of the eyes. Two surface conditioning methods of four ceramic materials before bonding brackets were examined: in group 1 an air particle abrasion with 25 μm aluminium trioxide (4 seconds at a pressure of 2.5 bars) and subsequently a silane coupling agent (Espe Sil, 3M Unitek, Monrovia, USA) was applicated on one side of each ceramic specimen (10 per group). In group 2 one side of each sample (20 per group) was etched with 37.0 per cent orthophosphoric acid for two minutes and was followed by a silane application (Espe Sil, 3M Unitek, Monrovia, USA). After this procedure the self-ligating ceramic brackets Clarity SL (3M Unitek, Monrovia, USA) brackets were bonded to the ceramic blocks and a thermocycling process started (5°C - 55°C, 6000 cycles). Then, shear bond strength and Adhesive Remnant Index (ARI) were measured. To determine statistical differences Oneway-ANOVA and Tukey Post-hoc test were performed. Hydrofluoric acid seems not to be justifiable anymore for preparing the surface of dental ceramic restorations before bracket bonding. Sandblasting with 25 μm aluminium trioxide and the use of orthophosphoric acid (37.0 per cent) seem to prepare the surface of ceramic restoration sufficiently before ceramic bracket bonding. The found level of shear bond strength values seems to be sufficient for bonding ceramic brackets to ceramic restorations.

Regular nicotine intake increased tooth movement velocity,osteoclastogenesis and orthodontically induced dental root resorptions in a rat model

Orthodontic forces have been reported to significantly increase nicotine-induced periodontal bone loss. At present, however, it is unknown, which further （side） effects can be expected during orthodontic treatment at a nicotine exposure corresponding to that of an average European smoker. 63 male Fischer344 rats were randomized in three consecutive experiments of 21 animals each （A/B/C） to 3 experimental groups （7 rats, 112/3）. （A） cone-beam-computed tomography （CBCT）; （B） histology/serology; （C） reverse- transcription quantitative real-time polymerase chain reaction （RT-qPCR）/cotinine serology--（1） control; （2） orthodontic tooth movement （OTM） of the first and second upper left molar （NiTi closed coil spring, 0.25 N）; （3） OTM with 1.89 mg-kg- 1 per day s.c. of L（- ）-nicotine. After 14 days of OTM, serum cotinine and IL-6 concentration as well as orthodontically induced inflammatory root resorption （OIIRR）, osteoclast activity （histology）, orthodontic tooth movement velocity （CBCT, within 14 and 28 days of OTM） and relative gene expression of known inflammatory and osteoclast markers were quantified in the dental-periodontal tissue （RT-qPCR）. Animals exposed to nicotine showed significantly heightened serum cotinine and IL-6 levels corresponding to those of regular European smokers. Both the extent of root resorption, osteoclast activity, orthodontic tooth movement and gene expression of inflammatory and osteoclast markers were significantly increased compared to controls with and without OTM under the influence of nicotine. We conclude that apart from increased periodontal bone loss, a progression of dental root resorption and accelerated orthodontic tooth movement are to be anticipated during orthodontic therapy, if nicotine consumption is present. Thus patients should be informed about these risks and the necessity of nicotine abstinence during treatment.